Preparação de Cross-Section

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DRAFT DOCUMENT FOR INDUSTRY CONSENSUS REVIEW ONLY
IPC-9241: Guidelines for Microsection Preparation
Final Draft for Industry Review – February 2016
1 SCOPE
Microsection preparation is a process. These guidelines discuss the many variables and problems associated with
the process from sample removal to micro-etch. The guidelines do not promote any one vendor’s process, but
discuss the variables common to microsectioning.
The process variables and problems are organized so the reader can research a specific issue or overview the
variables of a process area.
2 APPLICABLE DOCUMENTS
2.1 IPC1
IPC-2221 Generic Standard on Printed Board Design
IPC-2222 Sectional Design Standard for Rigid Organic Printed Boards
IPC-2223 Sectional Design Standard for Flexible Printed Boards
IPC-T-50 Terms and Definitions for Interconnecting and Packaging Electronic Circuits
IPC-TM-650
2.1.1 Microsectioning, Manual and Semi or Automatic
2.2.5 Dimensional Inspections Using Microsections
3 SAMPLE REMOVAL PROCESS
3.1 Sample Location
3.1.1 Coupon Test Strip Companies generally use a ‘‘home grown’’ or military conformance coupon for
microsection inspection. IPC-2221 outlines the attributes a coupon test strip should exhibit based on the product
type being built.
Benefits:
• Production parts are not lost due to microsection testing
• The internal and external features are the same from panel to panel to facilitate SPC data collection.
• The strips may be used to screen product as required
• The customer can correlate to your microsection results easier because you both sample in the same
location on the same test design
Drawbacks:
• Space is lost on the panel that could be used to build parts
• The test strip may not be representative of the associated part
3.1.2 Part The actual production parts are used for microsection inspection.
Benefits:
• Space is not wasted on the panel due to test strips
• There are no paneling constraints that dictate where the test strip must be placed to preserve part
correlation
• There is less of an issue over how representative the test strip is to the associated part
Drawbacks:

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• Microsection inspection of parts may not be cost effective for product with a high unit cost
• For multilayer printed boards, multiple samples are usually microsectioned to inspect all the inner layer
connections for each panel. These multiple samples can significantly increase the sample plan
• The test results may not agree with the customer’s results because microsections were taken on different
locations of the part. This can only be resolved by providing the part sample locations to the customer
3.2 Removal Method Regardless the method chosen, the cutting edge should remain a minimum of 0.25 cm [0.100
in] from the edge of the target plated-through-hole (PTH) pads. This is to prevent cutting deformation causing
damage to the sample which may lead to false failures. The only exception to this guideline is abrasive cut-off
wheels.
3.2.1 Punching This method removes the sample by using a die to punch the sample out of the panel. The die must
be hollow so that it never comes in contact with the target PTHs. The force that pushes the die through the panel
may be pneumatic or manual (kick or leverage) method. This method of sample removal is not recommended for
brittle materials.
All cuts must be made with a fast, smooth, and strong motion. This requires periodic maintenance to keep the die
sharp and the ram properly aligned and well oiled.
Benefits:
• This method quickly removes the sample
• No rout programs or cams are required to remove the sample
• No pin-up holes are required to provide a reference point to remove the sample
Drawbacks:
• The dies can quickly cause a great deal of damage to the test sample when not properly maintained. The
sharpness of the die can be monitored by setting limits on how much crazing the edge of the sample is
permitted. The recommended limits is no more than 0.025 cm [0.010 in] from the sample’s edge at 10X
magnification
• This method is limited by the board thickness. The maximum board thickness this method is recommended
for is [0.125 in] using pneumatic system and 0.25 cm [0.100 in] using the manual method
• Do not punch brittle material (i.e., polyimide). The shock damage will cause false defects to appear in the
sample. The primary concern is laminate defects
3.2.2 Sawing This method removes the sample using a jeweler’s saw or miniature band saw.
3.2.3 Abrasive Cut-Off Wheels The sample is removed by a silicon carbide, aluminum oxide, or diamond rimmed
blade. This method has the lowest opportunity for sample deformation but it also has the longest cycle time. This is
the only method that can cut close (under the 0.25 cm [0.100 in] limitation) to the target PTH pads without damaging
them.
Benefits:
• The method has the lowest sample deformation opportunity of all methods
• There are no limitations on board thickness or material type the sample can be removed from
Drawbacks:
• This method can be slow depending on wheel selecting and dressing
• The saw can only cut in a straight line. This limitation may cut test strips in half causing traceability problems
• and/or require multiple runs to cut the sample to the desired size
• The lubricant used to cool the saw adds an extra operation to the microsection process. The lubricant must
be cleansed from the samples before bake or solder float depending on your microsection methodology.
While there are diamond cut-off wheels that can be used without lubricant, the product may be too hot to
handle with bare hands. This would be a process indicator that thermal damage may have occurred and an
alternative method or process should be considered
3.2.4 Routing This method uses a small milling machine or production routers used by the shop to remove the
samples.
Benefits:
• The board thickness limitations are not as strict as some of the other method

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• The method removes brittle samples while reducing mechanical damage
• When using laboratory milling or routing machines, the set-up time can be shortened, when always routing
the same design of coupon from the panels. Only the alignment of the panel takes some time
Drawbacks:
• The rout operation setup time for each run can be lengthy. The router must be able to rout multiple test
strips (10 or more) within each run to be time efficient. The small milling machine and pin routers usually
only rout one test strip at a time
• Reference zero for the rout cam or program that controls the router bit are defined by pin-up holes. These
pin-up holes are available when the sample is routed in panel form, PTHs within the part, or target PTHs in
the test strip. If the target PTHs are used, care must be taken that no mechanical stresses are transferred to
these holes during the rout sequence
• The rout routine must not dwell in the same location too long. The router bit will generate a great deal of
heat which will cause sample deformation. This becomes more critical as the board thickness is larger. The
patterns that generate the highest amount heat are square corners and tight radius turns
• Beware that the vacuum system cannot swallow the samples. Precautions need to be taken to prevent this
circumstance
3.2.5 Pre-routing The sample is routed leaving a finger tab that holds the sample in the panel. To remove the
sample, the operator pushes or cuts the sample out of the panel by breaking the finger tab.
Benefits:
• The samples are routed and remain with the panel. This resolves panel traceability issues when the actual
sample is not serialized
• The samples, test strip, and parts are routed at one time. This prevents unnecessary use of costly
production routers to only rout the sample
• The coupon can go through processing, and then be removed easily without an additional routing step to
evaluate the process step
Drawbacks:
• The finger tabs width needs to be optimized to keep the sample in the test strip during handling and permit
an operator to push the sample out. The tab width may be different for families of products and/or board
thickness. Thick boards may require needle nose pliers (or equivalent) to break the finger tabs. If the tab is
too small, the coupon may be allowed to fall out unintentionally
• Care must be taken to where the pivot point is located when using a tool to remove the sample to prevent
mechanical stresses
• The location of the tab needs to be as far from the target PTHs, microsection tooling holes, circuit features,
and the production board as possible. This will minimize the likelihood that material stresses will be
transferred to the sample when it is pushed out
• Altering the design of the coupon to allow space for a pre-rout, without routing through copper, may change
the construction attributes (i.e. dielectric thicknesses) so that they are not reflective of the production board
4 MOUNT PROCESS
The samples are mounted in a potting material. The mounts must exhibit certain characteristics for microsection
process to be successful. These characteristics are:
• Holes to be microsectioned (Target Holes) must be in the same axis
• One type of material potted in a mount
• Potting material and sample material are comparable hardness
• No gaps or depressions in the potting material
4.1 Sample Orientation
4.1.1 Same Product Type within A Mount The same product type should be within a mount. Mixing product types
(i.e., MLB and flex) may cause portions of the mount to grind faster than others. When the unequal grinding is
extreme, the mount will not have a flat surface. The portion that is not flat will have scratch problems during the
polish process.
4.1.2 Samples Should Not Touch There should be a minimum spacing between the samples. The recommended
distance is 0.025 to 0.157 cm [0.010 to 0.062 in]. This space allows the mounting material to support all the surface

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features of the samples and prevent false failures (i.e., lifted lands).
4.1.3 Sample Orientation The samples should be orientated in the mount so the first sample is easily
distinguishable. This will enable the operator to use the chosen traceability system to report results. The samples
also may be orientated so that layer one is in the same direction.
4.1.4 Traceability A system needs to be developed to trace each sample back to its associated panel and/or part.
This requires traceability not only within the mount but also from mount to mount. Marking methods for the mount
are external labels, embedded labels, mechanical scribing, and permanent ink markers. The type of label chosen
must be compatible with lubricants, solvents, abrasive, and etchants the mount is exposed to during processing.
The use of a ‘standard’ coupon pinning scheme, computer processing, or bar code labeling can be used as
alternatives to the standard marking methods. A tremendous amount of time can be saved by using a well-
documented and integrated traceability system.
4.2 Tooling System The tooling holes, tooling pins, and molds are the heart of the high volume microsection
system. The tooling pins are placed in the tooling holes to align the target PTHs in the same axis. This alignment
increases the likelihood the grinding process stops at the centerline of all the target PTHs at the same instance.
4.2.1 Holes Drilled at Drill Process
4.2.1.1 Misdrills Audit the location of the tooling holes with a template or X-Y coordinate machine. The audit should
only be done when problems are suspected.
4.2.1.2 Sample Removal Damage There should be a minimum of 0.127 cm [0.050 in] of material between the
tooling hole edge and edge of the sample. This will prevent tooling hole damage that will allow the sample to move
during the cure of the potting material.
4.2.1.3 Plugged Holes Inspect the tooling holes to ensure no solder or debris is plugging them. If the holes are
plugged, remove the obstruction with a hand held drill bit. Do not use a tool that will enlarge or ‘egg-shape’ the
tooling hole.
4.2.2 Tooling Pins
4.2.2.1 Pins Fit Tight The tooling pins must fit tight in the tooling holes. Any play in the holes will translate to the
distance the grind process will miss the centerline of the target PTHs. Also a loose fit can cause the samples to
hang at an angle (planar distortion) instead of straight down. ‘‘Planar distortion will cause an overestimation of the
plating thickness which will be significantly increased when combined with the center of the hole tolerance.’’ See
Figure 4-1 and Figure 4-2.
Figure 4-1 Planar distortion

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Figure 4-2 Center line integrity – to be accompanied by supportive line drawing
4.2.2.2 Pin Positioning The pins should be equal length on each side of the first sample and last sample. This
helps to ensure the samples are mounted in the center of the mold. The samples should not be skewed to the side
of the mount.
4.2.2.3 Flush to Mount Tooling Edge The tooling pins are placed on the mount mold edge or on pads attached to
the grind mount holder (see Figure 4-3). The mount edge dimensions the distance from the centerline of the tooling
holes to the target PTHs. A system must be developed to assure the pins remain in contact with the edge during the
mounting process. Some current methods are weights, metal clips, and physical stops that hold the pins in place.
Figure 4-3 Reference Zero relationship between target holes and tooling edge
4.2.3 Mounting Molds
4.2.3.1 Sample Positioning The samples should not be skewed to one side of the mount. The minimum distance

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the sample should be from the mount edge is 0.078 cm [0.031 in]. Samples at or near the mount edge tend to
grind/polish unevenly. Also the sample external features are not supported to prevent false failures due to
microsection damage.
4.2.3.2 Construction Permits Exothermal Reaction The potting material cures by an exothermal reaction. The
mount must be constructed of material that efficiently transfers heat from the curing potting material to the
atmosphere. Recommended mold construction materials are stainless steel, aluminum, and plastics. If the mold
insulates the exothermal reaction, the cure will take longer which may have an adverse effect on the mount
material’s hardness and increase the likelihood of false failures.
4.2.3.3 Mount Tooling Edge The mount will have an edge or pad that specifies the distance from the centerline of
the tooling holes to the target PTHs. This is the critical dimension that determines the amount of material that must
be removed by the microsection process. This edge must be kept clean from buildup and free of surface damage
(i.e., dents, scratches, nicks).
4.3 Mounting The encapsulation of the test samples in potting material is necessary to ensure edge retention of the
surface features and prevent mechanical forces of grinding to be transferred to the sample’s PTH barrel.
4.3.1 Methods
4.3.1.1 Room Temperature Cure The potting material cures due to an exothermic reaction of the material. The rate
of cure is dependent on the ratio of the resin and hardener, and the ability of the mold to transfer the heat away from
the potting material.
4.3.1.2 Compression Molding This technique cures the potting material using high temperatures and pressure.
The method is not recommended because the opportunity for creating false failures is too great.
4.3.1.3 Vacuum Assist Vacuum assist is a specialized method to help room temperature cure resins to flow more
easily into small diameter plated-through-holes.
4.3.1.4 Oven Cure Some of the epoxies and polyesters have long cure times. These longer cure times are caused
by a low exothermal reaction during curing. The oven cure method was developed to artificially add heat to
accelerate the cure reaction thus shortening the cure time.
Caution: Be sensitive to the cure temperature of the resin (See 4.3.2.1.5).
4.3.1.5 Low Pressure Potting This technique cures the potting material at room temperature under low pressure
(less than 7 kg per sq. cm). Samples are cured in a pressure vessel using the same potting material as room
temperature cure (see 4.3.1.1). The technique improves flow of material into small holes and will provide a cleaner
polymer to aid in microsection inspection.
4.3.2 Mounting Material
4.3.2.1 Characteristics These are the various potting material characteristics required to support the needs of high
volume microsection. Some of these traits are common to microsectioning and others are unique to the high volume
method. Often one mounting material will not meet every requirement. Selection of a potting material depends on
each lab’s unique needs. Mounting material characteristics are provided in Table 4-1.
Table 4-1 Mounting Material Characteristics
Acrylics Epoxies Polyesters
High Shrinkage Low Shrinkage Low Shrinkage
Variable Exotherm Variable Exotherm Variable Exotherm
Rapid Cure Slow Cure Slow Cure
Translucent Semi-Transparent Transparent
Moderate Hardness Moderate Hardness Fair Hardness
Solvent Sensitive Solvent Resistant
(dependent on mix ratios)
Solvent Sensitive

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4.3.2.1.1 Sample Surface Cleanliness The surface must be free of all contaminants that may act as a release
agent to the mounting material. Common sources of contamination are flux, abrasive cut-off wheel lubricant, water,
plating solutions, oils, hand lotions, and grease. The cleaning process needs to be tailored to the contaminant that
must be removed.
4.3.2.1.2 Hardness The cured hardness needs to closely match or exceed the hardness of the embedded samples.
When the potting material is softer, there is a tendency for this material to be removed faster than the samples
feeling like ridges higher than the mount material after polish (speed bumps). See Figure 4-4 and Figure 4-5. This
problem inhibits the accurate reading of surface dimensions and causes inaccurate inspection results of surface
features (i.e., lifted lands).
Figure 4-4 Samples above potting material Figure 4-5 Samples above potting material
4.3.2.1.3 Low Shrinkage Shrinkage is the amount the material contracts due to curing. High shrink rates
(contraction forces) can be severe enough to bend tooling pins, move the samples within the mount, reduce the
diameter of the mount, and change the location of the reference edge on the mount. Any sample movement during
the potting material cure can be disastrous to the grind process capability to stop at the centerline of all the target
PTHs.
4.3.2.1.4 Low Viscosity The material must have a low viscosity after mixing to allow the liquid to flow freely around
the samples. The low viscosity is especially important when it must fill small diameter PTHs [0.015 in] diameter or
less). When a low viscosity is not practical, the flow of the mounting material can be facilitated by placing the mount
in a vacuum environment.
4.3.2.1.5 Cure Temperature The cure temperature should not exceed 93 °C [200 °F] unless the material has a cure
time of 1 hour or more. Temperatures above 93 °C [200 °F] may cause laminate failures that would not normally be
present. The recommended cure temperature is 60 to 71 °C [140 to 160 °F].
4.3.2.1.6 Chemical Resistant The mount material must be able to withstand the lubricants, etchants, and polish
media without softening, voiding, or cracking.
4.3.2.1.7 Easy to Mix Many of the above characteristics are based on how the material is mixed from batch to
batch. A system for measuring component volume is recommended to ensure reproducible curing characteristics.
This can be accomplished using a pneumatic dispensing system, pipette, or scale. Whatever method chosen should
be audited regularly and monitored by SPC. This single process along with thermal stress can cause more false
failures than any other step of the microsection process.
4.3.2.2 Material Problems Most material problems are related to poor mounting material quality, improper
exotherm of the curing reaction, or improper mixing ratios of the mounting material. Cure temperature testing prior to
use can eliminate the introduction of inferior material into the microsectioning process. Mixing problems can be
prevented by technician training and the use of proper measuring equipment (scale, pipette, graduated container,
etc.).
If acrylic mounting material has problems with poor edge retention and severe rounding, add 1 micron alumina to

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the mixture ratio to reduce the effect. The 1 micron alumina should not exceed 10% of the mix ratio. Do not reduce
the other components of the mix ratio when adding alumina.
4.4 Mount Process Quality
4.4.1 Target PTHs in the Same Axis The target holes are the plated-through-holes that are to be microsectioned
for evaluation. The centerline of the holes must be in the same axis from sample to sample as shown in Figure 4-6.
This assures the target PTHs are ground and polish to the same depth in the holes. The grind/polish process will not
correct any axis problems in the mount. As the old saying goes ‘‘Junk in, junk out.’’
Figure 4-6 Target holes in same axis
4.4.2 No Gaps on the Mount or Sample Any gaps on the surface acts like a debris trap. These debris traps make
the cleanliness requirements between polish steps tougher to accomplish. Cleanliness is required to ensure the
cloths are not contaminated with debris that will cause unwanted scratches. Common gaps are:
• ‘Target Holes’ are not 100% filled. They must have mounting material, bonding material, copper, solder, etc.
in the hole (See Figure 4-7)
• Gap between the mounting material and samples. These gaps trap debris that will ooze out on the finished
sample. This gap will cause the most problems (See Figure 4-7)
• Depressions in the mounting material. These are evident after the grind sequence. These gaps make the
cleanliness in the polish sequences troublesome (See Figure 4-8)
Figure 4-7 Gaps between mounting material and samples Figure 4-8 Depression in mounting material
5 GRIND PROCESS
Grind variables can be generalized into the following categories: equipment, tooling system, and the consumables.
The grind operation removes material to a location short of the center of the target PTH. This leaves room for the

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polish process to remove the scratches and deformation from the grind process. The minimum distance
recommended is 0.025 mm [0.001 in]. The maximum is dependent upon the size of the PTH and abrasive paper grit
size of the final grind step (see Figure 5-1).
Figure 5-1 Abrasive paper grit size (American vs. European)
Gunter Petzow in Metallographic Etching states ‘‘scratches, sample deformation, and smearing are characteristic
consequences of mechanical grinding and polishing.’’ Sample deformation and scratches are prevalent during
coarse grinding. The effects of these consequences on the sample surface are shown in Figure 5-2.
Figure 5-2 Effects of mechanical grinding and polishing
5.1 Equipment The materials microsectioned will dictate the type of equipment needed. All the systems have
advantages and disadvantages. Special items to be considered when purchasing a system are:
• Hardmount Tooling System
• Potting Material Type
• Throughput volume (# sample/day)
• Consumable Costs

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• Ease of Use – Consumables
• Ease of Use – Tooling System
• Ease of Use – Variables Control
• Repeatability of process to stop at the center of the PTH
• Labor Needs
• Technical Support (printed board industry specific)
• Calibrations
• The equipment must tolerate adjustments on four major variables: pressure, coolant flow, RPM of the
grinding wheel, and time.
5.1.1 Controls
5.1.1.1 Pressure A person has to weigh the benefits versus the drawbacks for using a particular pressure setting.
Benefits of High Pressure (0.246 + kg/cm2 3.5+ psi):
• Fast grind times
• Low consumable usage
Drawbacks of High Pressure (0.246 + kg/cm2 3.5+ psi):
• Scratch depth is usually deeper
• The sample has greater sample deformation
• The next grind and polish times are increased (the longer grind times equate to an increase in labor and
consumables, and loss in cycle time).
Note: The polish sequence is very sensitive to the scratch characteristics on the sample. The ability of the grind
process to produce consistent scratch pattern and depth is dependent on the hardness of the material and the
amount of pressure.
Benefits of Low Pressure (0.035 – 0.246 kg/cm2 0.5–3.5 psi):
• Less scratch depth and sample deformation
• The scratch characteristics on the sample are more consistent (regardless of the hardness of the material)
Drawbacks of Low Pressure (0.035 – 0.246 kg/cm2 0.5–3.5 psi):
• Higher consumable usage
• Longer grind times
5.1.1.2 Volume of Water /Coolant The water serves two purposes: (1) to prevent heat generation due to friction in
the samples, and (2) to retard the abrasive paper from filling with grinding debris causing it to lose its ability to cut
material efficiently. Use a generous amount of water/coolant.
Note: Filter the incoming water. This prevents rust, calcium deposits, and debris carried in the water from
contaminating the grind process. Calcium deposits sprayed on the grind wheel during the fine grind sequence will
cause deep scratches to be formed that the fine grit abrasive paper is unable to remove.
5.1.1.3 Abrasive Paper RPM The rotation speed of the abrasive paper controls the material removal rate and the
amount of heat generation. Start at 300 RPM and tailor the process to the material being ground.
5.1.2 Calibrations
5.1.2.1 Grind Pressure The pressure gage measures the direct force required for the mount holder to touch the
abrasive paper. To determine the pressure on each mount divide the pressure setting by the surface area of the
mount being processed. The recommended pressure setting is approximately 0.35 kg/cm2 [5 psi].
For Example:
(6) 3.8 cm [1.5 in] diameter mounts Grind Pressure is 20.5 kg [45 lbs-force]
Area of Mount = 22.58 cm2 [3.5 square in]
[2*pi*(radius) squared] Area of (6) Mounts = 21.2 square in
Grind Pressure (psi) = 45 lbs-force/21.2 square in
= 2.12 psi

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If the grinding wheel is reworked or a new one is installed, the pressure must be audited and adjusted accordingly.
This audit is not required when abrasive paper is used to rework the grinding wheel surface.
5.1.2.2 Motor Shaft Angle The motor shaft turns the mount holder which affects the flatness on the mounts. The
motor shaft must be perpendicular (90 degrees) to the grinding wheel surface as shown in Figure 5-3. The tolerance
for the 90 degrees requirement is determined by knowing the distance from the grinding wheel to the mounting bolts
on the motor shaft. The longer the distance the tighter the tolerance. This relationship should be checked on a
regular (6-12 months) basis.
Figure 5-3 Perpendicularity of motor to sandpaper disc assembly
5.1.2.3 Location of Mount Holder on the Grinding Wheel The abrasive paper removes more material towards
the outside edge of the grinding wheel. The mount holder should be positioned near the outside edge to take
advantage of the removal rates as shown in Figure 5-4. This is one method to maximize material removal without
high pressure or large grit abrasive paper.
Note: If positioning the mount holder requires moving the motor shaft, ensure the motor shaft remains perpendicular
to the grinding wheel.
Figure 5-4 Position of mount holder on sandpaper disc
5.1.3 Maintenance
5.1.3.1 Surface Damage on Grinding Wheel The abrasive paper is held in place by a metal disc. The disc surface
is easily damaged when the tool stops rip the abrasive paper. The damage must be removed from the surface
because it will cause the abrasive paper to rip and/or cause unwanted scratches on the mount.
Minor damage can be removed by abrasive paper. All other damage must be removed by a lapping process in a
machine shop. When lapping the surface, take care the dimension between the edge the abrasive paper ring sits on
the lapped surface does not change significantly. If this occurs, the abrasive paper holding ring will not work and
allow the abrasive paper to rip.
5.1.3.2 Grinding Wheel Base Is Free of Corrosion / Debris Buildup Corrosion or trash buildup can cause the
grinding wheel to be tilted which will affect the motor shaft perpendicularity.

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The grinding wheel is rotated by a drive plate. This design allows a person to quickly swap out discs. The drive plate
has a tendency to trap material and corrode. If a buildup occurs on the drive plate, the grinding wheel will not lay
flat.
5.2 Tooling
5.2.1 Mount Holder Construction The mount holder is a platform that acts as reference zero between the tool
stops and the reference edge of the mounts (See Figure 4-3). The tool stops are extended a predetermined
dimension from the mount holder to ensure the microsection process stops at the centerline of the target PTHs. The
dimension for the tool stops is a sum of the distance from the centerline of the target PTH to the centerline of the
tooling holes plus the radius of the tooling pin.
5.2.1.1 Samples Are Held Tight The orientation of the samples in the mount holder will dictate how efficient
material is removed during grinding. If the mounts in the holder are loose, the orientation will quickly be lost as they
turn to the path of least resistance. This turning will reduce the abrasive paper’s efficiency to remove material
quickly.
There are various methods of securing mounts in the holder. Some of the common methods are: tooling edges on a
mount or pins embedded in the mount. The method of holding the mounts is to each one’s liking as long as
orientation is maintained.
5.2.1.2 Deflection of Mount Holder The mount holder attaches to the motor shaft via a collar as shown in Figure 5-
4. A ball mechanism in the mount holder to deflect slightly when the mounts first come into contact with the surface.
If the following problems are experienced, the mount holder must be repaired or replaced.
Too Tight The ball mechanism is too stiff and doesn’t deflect. This is apparent because the abrasive paper quickly
rips regardless of pressure settings and hardness of material. This can be tested by attempting to grind mounting
material with no samples in it. This suggestion assumes there is no problem with the tool stops or grinding wheel
surface.
Too Loose The ball mechanism can wear out where the deflection is too much. This problem is not as obvious. Too
much deflection is indicated by mounts that won’t grind flat or a circular scratch pattern (‘crescent moon’ in shape)
on the outer edge of the mount. (See Figure 5-6)
Figure 5-5 Mount Holder Collar: Effects of Deflection
Figure 5-6 Crescent moon scratch pattern

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5.2.1.3 Weight of the Mount Holder Don’t use mount holder with material of construction (i.e., aluminum and
stainless steel) in the same process. The process settings will vary based on the weight of the holder. The best
results have been experienced with a light material.
5.2.1.4 Base of Mount Holder Is Flat Over time the mounts wear a depression in the surface of the mount holder
as shown in Figure 5-7. As this depression becomes more significant, the grind process will start to undergrind. The
surface should be checked for depressions several times a year.
Figure 5-7 Effect of wear depression on mount holders
5.2.2 Mount Holder Process Guidelines
5.2.2.1 Orientation of Mounts in Mount Holder As discussed earlier, the material removal rate is greater near the
outer edge of the grinding wheel. Mounts should be oriented in the holder to take advantage of this as shown in
Figure 5-8.
The portion of the mount with the highest sample surface area should be oriented to the outer edge.
Note: The location in the mount holder (see Figure 5-8) does not need to be the same for grind and polish
sequences.
This will permit repeatable grind and polish results from run to run permitting a process to be developed and
maintained. Being random in the orientation of the mounts make troubleshooting of the process nearly impossible.
The key to success is consistency so one can predict how the process will perform.
Figure 5-8 Balanced Mount Holder
5.2.2.2 Load All Holder Positions with Common Material The mount holder develops flatness in all the mounts.
This process is complicated when mounts with soft (kapton, adhesive) and hard material (epoxy, glass) are loaded
in the same mount holder. Softer material reaches the tooling stops sooner than harder material. This creates
scratch removal problems by the surface not being flat (i.e., crescent-moon scratches). (see Figure 5-6)

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5.2.2.3 Use Lower Pressure for Uneven Surfaces Some labs mount samples with a portion of the sample sticking
out of the mount material. Whenever this condition exists, start with a lower pressure for approximately 20 seconds
to prevent the uneven surface from ripping the abrasive paper.
5.2.2.4 Balanced Mount Holder The mount holder must be balanced from side to side (see Figure 5-8) to ensure
the mount grinds flat (i.e., prevent crescent-moon scratches). If there are not enough production mounts to balance
the holder, make some ‘dummy’ mounts and insert them in the holder. The overall height of the ‘dummy’ mount
must be approximately the same as the production mounts. Height is measured from the mount reference edge to
the sample or hardmount surface (whichever is longer).
5.2.2.5 Debris Between Mount and Holder A hidden source of scratches is debris getting between the grinding
wheel and the abrasive paper. A good habit to develop is to clean the grinding wheel whenever the abrasive paper
is replaced.
5.3 Tool Stops In the past, technicians learned the skill for how far to grind (distance) with each grit of abrasive
paper. This skill was developed through OJT and experience. The high volume microsection system controls this
variable numerically using tool stops on the mount holder.
The tool stops work with mount holder to develop flat mounts and to define the end point for each grind sequence.
To attain a scratch free surface the tool stops are set a specific distance (and tolerance) from the bottom of the
mount holder as shown in Figure 5-9. The user is thus able to set the removal distance for each grit size of abrasive
paper to assure the scratches from the previous grit size are removed. This type of scratch management requires a
thorough knowledge of the abrasive papers being used.
Figure 5-9 Carbide pad flatness and height
5.3.1 Calibration Proper setting of the tool stops involves an understanding of abrasive paper grit sizes, scratch
depth, and deformation created by the grind process. The abrasive paper vendor can supply abrasive paper grit
information. The tooling stops need to be set so the fine grind step has ample room to remove the rough grind
scratch deformation.
Example: Managing Scratches Via Tool stops
Target Hole Distance from Mount Tooling Edge to Target PTHs = .584 cm [0.230 in]
Abrasive Paper Data
Grit Size Scratch Depth
180 0.018 cm [0.007 in]
1000 0.0018 cm [0.0007 in]
Calculate Tool Stop Height for 1000 grit sandpaper Target Hole
Distance –2* (sandpaper scratch depth)
0.584 cm –2* (0.0018 cm) 0.5804 cm [0.228 in]

15
*The sandpaper scratch depth is doubled to provide process tolerance for the removal of the 1000 grit abrasive
paper scratches. The extra tolerance permits the removal of any sample deformation caused by 1000 grit scratches.
Calculate the Tool Stop Height for 180 grit sandpaper 1000 grit sandpaper
Tool Stop Height –2* (sandpaper scratch depth)
0.5804 cm –2* (0.018 cm) = 0.544 cm [0.214 in]
5.3.2 Maintenance Stops need regular care and adjustment. If the tool stop height is set wrong, the grind process
will miss the centerline of the target PTH (see Figure 5-9).
Maintenance required are adjusting the tool stop height, testing for flatness of the stop, noting wear trends, and
checking condition of tool stop’s material.
Tool stop wear varies due to the exposure time and grit size of the abrasive paper. The need for accuracy is
explained in the prior section.
The flatness of the tool stops should be monitored. The variation on the stops can alert the user to deflection
problems in the mount holder collar, problems in the perpendicularity in the motor shaft to the grinding wheel, and
corrosion buildup on the base of the grinding wheel. The recommended variation on the tool stop is 0.013 cm [0.005
in] from side to side. Any larger variation allows minimal point contact of the tool stop on the grinding wheel.
Consequently, the stop wears out of tolerance faster.
Inspect the surface of the tool stops for cracks or other degradation. The tolerance level for defects is determined by
the user’s discretion.
5.3.3 Purchasing The primary characteristic considered when purchasing tool stops is the Hardness of Material.
The hardness affects the wear characteristics of the stops. This should be monitored in case the vendor switches
material.
5.3.4 Location of Stops On Mount Holder The tool stops must be positioned so the inside edge of the tool stop is
on the arc from the outside edge of the mount as shown in Figure 5-10. This location is critical to ensure flat mounts.
If the tool stops are further in, the first rough grind will damage the outside of 2-3 samples (of 6) in the holder. The
damage is in the form of deep scratches that cannot be removed and ‘crescent moon’ effect (see Figure 5-6). These
problems will become evident early in the polish process.
Figure 5-10 Carbide pad should be center on arc
5.3.5 Tool Stop Audits
5.3.5.1 Stops Are Touching Some common methods for auditing when the tool stops touch the abrasive paper are:
• Grease Pencil – Mark the surface of all the stops. As the stops touch, the abrasive paper will remove the
grease on the surface. When all stops are clean, the grind step is complete and the desired flatness is
developed.
• Flat Surface – Lay the mount holder on a flat surface and see that all the tool stops are touching. A
disadvantage with this method is the mounts may be scratched when doing the check. The flat surface must
be clean.
• If the rough grind step is stopped prematurely, a long period of fine grind will result. If the rough grind is

16
stopped too late, the fine grind will not remove the rough grind and stop at the centerline of the target PTHs.
5.3.5.2 Stops Touch Too Long The abrasive paper will preferentially grind the inside edge of the mounts when the
process is allowed to run while all the tooling stops are touching as shown in Figure 5-11. This will cause the mount
to not be flat and cause the same problem as crescent-moon scratches (see Figure 5-6). This can be avoided by
doing frequent audits of the tool stops touching the abrasive paper.
Figure 5-11 Leaf cut effect
5.4 Consumables Consumables must be of uniform quality. The process will be set assuming the abrasive paper’s
grit size, life span, and resistance to water. If any of these qualities vary, the consistency of the overall process is in
jeopardy.
5.4.1 Abrasive Paper The user should be familiar with characteristics of the abrasive paper used. The key
characteristics are the grit size and life of the abrasive paper.
The life of the abrasive paper is determined by grinding time and material removal. No appreciable amount of
material will be removed after a set amount of time because the paper is filled up with grinding debris and worn out.
Grind time is dependent on the hardness of the material. To determine the grind time run a test on the material that
will be ground 80 - 85% of the time.
There are many variables to consider when choosing grit size. Some of the major ones are sample material
hardness, useful life span of abrasive paper, and scratch size.
5.5 Grind Process Quality The mounts must exhibit certain characteristics (quality) for the polish process to be
successful. The polish process cannot overcome problems created during grinding. The reason is the polish
process removes a small amount of material (0.002 to 0.0036 cm typical [0.0008 to 0.0014 in]).
5.5.1 Flat Mounts Flatness is defined as the even removal of material across the face of the mount such that all the
target PTHs are within the specification for center of the hole tolerance (typically 10%). (see Figure 4-2) Flatness is
not to measure the surface to a metallurgical value (number of flatness rings).
The quality of flatness is driven by the hole diameter. Flatness is more critical on smaller hole diameters which
requires greater accuracy from the tooling system.
Care must be taken to guarantee no foreign material is trapped between the tooling edge of the hardmount and
mount holder (see Figure 5-12). Overgrinding will occur on the mount at the trash location.

17
Figure 5-12 Effect of trash trapped between mount holder and tooling edge
5.5.2 Scratch Removal The polisher should not be expected to remove scratches larger than those typical of the
fine grind step. If wider scratches are seen (as viewed in bright light on metallograph at 100X magnification) the
samples need more grinding on the fine grind.
5.5.3 Cleanliness Samples should be washed off using a mild hand soap and water to remove any abrasive paper
grit from previous grind steps. Dry with air to remove moisture from samples. This will reduce the possibility of
depositing contaminates from water (especially hard water) onto polish cloths.
5.5.4 Gaps Hardmounts should not have any gaps between samples (see Figure 4-7) or surface depressions
(see Figure 4-8) in the mounting material. These imperfections can trap grit from previous steps that may
contaminate the cloth and scratch samples processed later. Any samples with gaps or surface depressions should
be processed manually or restarted.
6 POLISH PROCESS
The variables can be generalized into the following categories: equipment, tooling system, and consumables.
The polish process removes material gradually until reaching the center of the hole. The gradual material removal is
required so the scratch damage and sample deformation is reduced to negligible levels.
There are many dangers to avoid during the polish process. The major dangers are uneven material removal, grind
process scratches, and sample deformation (metal smear and rounding).
Uneven Material Removal (see Figure 4-4 and Figure 4-5) This is the removal of one material faster than another.
The materials that are removed the fastest is the potting material and the laminate material. The materials that are
left exhibit severe rounding as the uneven condition increases.
Grind Process Scratches (see Figure 6-1) The scratches will obscure surface defects on the metals (i.e., inner layer
separation, crack plating, and crack internal layers). The scratches can also contribute to false failures by appearing
as one of the above listed defects.
Metal Smear (see Figure 6-2) Smear is metals being pushed on the surface of the sample instead of being
removed. The smear will create a layer of metal over surface defects making them undetectable.
Metal Rounding Metal rounding is a leading indicator to uneven material removal. Rounding causes an edge
definition loss at dissimilar material interfaces (copper and tin-lead interface or laminate and potting material edge),
or the edge loss can occur for voids or cracks. The edge definition loss can affect the accuracy of dimensional
measurements or make a crack or void appear as a ‘ghost defect.’ A ‘ghost defect’ is an anomaly that is only
apparent at the edge of the microscope view and invisible at the center of the view.
Figures 4-4, 4-5 and 6-1 through 6-4 are pictorials of the above dangers.

18
Figure 6-1 Scratch deformation Figure 6-2 Smeared metal
6.1 Equipment
6.1.1 Controls Equipment considerations are the same for the grind and polish process with the following
exceptions.
6.1.1.1 Pressure Pressure settings are usually lower at polish than at grind so as to remove material gradually to
avoid rounding and smearing of the metals.
The polish process tends to smear the metal because the contact surface area is much higher and amount of
coolant is lower than the abrasive paper steps. Care must be taken to balance amount of coolant added to the
polish with the abrasive to minimize heat generation (recommended limit is -12 to -9 °C [10 to 15 °F] above ambient
room temperature).
6.1.1.2 Volume of Coolant The volume of coolant used during polish process must be controlled closely. The
equipment must have the capacity to numerically control coolant application to assure a consistent and repeatable
process. The coolant application will probably differ for each polish step, numerical control is recommended to
permit the technician to supply the correct coolant rate for each step on a repeatable basis.
Too much coolant will lower the polish step efficiency to remove scratches from the previous step. The polish
abrasive is usually an additive to cloth instead of being affixed. An oversupply of coolant will wash the polish
abrasives off the cloth.
Too little coolant has the same effect as the pressure being too high. Also the increased friction will significantly
reduce the life of the polish cloth.
6.1.1.3 Polish RPM The polish disc is operated at a lower speed than in the grind process. Removal rates are more
gradual at the lower speed setting, and this avoids heat generation.
If a higher speed is used, more coolant must be applied to reduce heat build-up. The higher speed will throw
abrasive and coolant off the cloth quicker requiring increased usage.
6.1.1.4 Time The length of time on the polish cloths is more critical than the grind process. When the time is too
long, there tends to be uneven material removal between the softer materials (i.e., tin/lead, laminate, mounting
material) and the harder material (i.e., copper, glass bundles).
6.1.2 Calibration and Maintenance These considerations are the same as those for the grind process.
6.2 Tooling The tooling system is not as critical during the polish process. The reasons are:

19
• The process removes a negligible amount of material
• The flatness of the mounts is developed during the grind process. The overall flatness will not be changed
significantly by the polish process
• The tooling considerations unique to the polish process are discussed below
6.2.1 Mount Holder Construction
6.2.1.1 Deflection of Mount Holder The mount holder collar prevents polish cloth damage using the same
principles as the grind process. The collar can malfunction and cause the following problems:
Collar Too Tight – The polish cloth may gradually develop wrinkles and/or fibers will be shaved off the cloth. Both of
these problems reduce the life of the cloth.
The wrinkle problem can be tested for by running a new polish cloth on the wheel for 10 minutes. Assuming the
coolant addition system is operating properly, wrinkles indicate the mount holder collar is too tight.
Collar Too Loose – Too much deflection will allow the mount edge along the outside edge of the polish cloth to
round and occasionally miss the center of the hole.
6.2.1.2 Tool Stops The mount holders should not have tool stops for the following reasons:
• The material removal rate is small (less than 0.0025 cm [0.001 in]).
• The flatness established by the grind process is not changed significantly in the polish step.
• If diamond abrasive is used, the tool stops are worn out of tolerance quicker. Diamond abrasive cuts
carbide more efficiently than abrasive paper.
6.2.2 Mount Holder Process
6.2.2.1 Orientation of Mounts in Mount Holder A standard orientation should be chosen. This practice allows the
repeatability of the polish process to be monitored (see Figure 5-8).
Note: The location of the mounts in the mount holder does not need to be the same for the grind and polish
process.
6.2.2.2 Loading the Mount Holder Load the holder with the same group of mounts that were ground together. This
ensures the polish process will produce repeatable results on the group.
Each run has unique scratch and sample deformation qualities due to variability in the process and consumables.
Do not mix mounts from different runs in the holder because the polish quality and center of hole accuracy will be
affected.
6.3 Consumables
Initial Polish The initial polish sequence removes previous grind scratches. This can be accomplished in one or
more steps depending upon the hardness of the material, distance to the center of the hole, and the scratch size on
samples. Equipment settings such as pressure used, type of cloth, type of abrasive, and type of coolant will control
polish results.
The pressure setting is much lower than grind (approximately 0.07–0.14 kg/cm2 [1–2 psi]).
Low nap cloths are generally used because they allow more abrasive to come in contact with the mount. The harder
cloths (thin cushion layer) will remove material faster and maintain good edge retention qualities. The softer cloths
(thick cushion layer) will remove material at a slower rate and lose good edge retention qualities.
The coolant must work well with the type of cloth and abrasive used. The coolant must minimize heat generation
without removing the abrasive from the cloth. The initial polish steps usually require less coolant using low nap
cloths.
Final Polish The final polish step produces a scratch free sample by buffing the surface. This sequence cannot
remove large scratches or fix any sample deformation problems from the previous steps (grind or polish).

20
Final polish is very dependent on the scratch size on samples, process pressure used, type of cloth, type of
abrasive, and type of coolant. The process time is usually very short (45 seconds maximum). If the initial polish is
successful, the buffing of the surface can be done quickly. Long run times will create metal smear (see Figure 6-2)
and uneven removal of material (see Figure 6-3 and Figure 6-4).
Figure 6-3 Rounding at copper plate and solder interface Figure 6-4 Rounding at copper plate and solder
interface on the surface
The pressure setting is usually the same as the preliminary polish steps.
The polish cloth type generally used is high nap. High nap will remove minor scratches but may cause metal smear
(see Figure 6-2) and uneven material removal (rounding) (see Figure 6-3 and Figure 6-4). Metal smear is when the
cloth pushes the metal instead of cutting it. Edge retention qualities can be lost quickly with this type of cloth.
The coolant considerations are the same as preliminary polish with the following exceptions. The final polish steps
usually require more coolant because the high nap cloths are harder to keep moist. Dry cloths will generate heat
quickly.
6.3.1 Cloth Construction The cloth has several roles. It acts as a carrier for the polish abrasive, retains the
coolants to minimize heat generation, and defines edge retention qualities of the mount. To a lesser degree the
cloths also supply a cutting action. The cloths must be chosen with these variables in mind.
A cloth’s ability to exhibit the above characteristics is directly dependent upon the amount of nap:
Low nap cloth
• Faster cutting action because more abrasive in contact with the mount. Usually these cloths have a higher
abrasive use. The reason is the abrasive is more exposed to being removed by the mount and/or coolant
• The amount of coolant required is lower. The reason is the heat generation is lower and the cloth does not
absorb as much of the coolant
• The edge retention qualities are better. The reason is there is very little cushion to the base of the cloth
which maintains a flat surface during this polish step. Polish run times 2–5 minutes is no problem. If a polish
cloth is used with cushion, the run time must be reduced significantly to prevent metal smear (see Figure 6-
2) and rounding (see Figure 6-3 and Figure 6-4)
High nap cloth
• Slower cutting action because the abrasive is buried in the nap. Usually these cloths have lower abrasive
use. The nap retards the removal of the abrasive from the cloth by the process.
• The amount of coolant required is higher because the high nap causes more heat generation. Usually this
nap requires 3-5 times more coolant than low nap.
• The edge retention is marginal. A run time over 1 minute will cause serious problems with copper smear
and rounding. Beware of these cloths.
6.3.2 Cloth Maintenance

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6.3.2.1 Storage The cloths must be stored in an area protected from dust. Airborne dust particles such as dirt,
copper (from drill area), and glass (from rout and drill areas) can cause unwanted scratches in the samples.
6.3.2.2 Prevent Wear The nap surface can be shaved off by sharp edges on the mount. This shaving problem
might be caused by the mount holder collar being too tight or the amount of coolant too low.
6.3.2.3 Charging the Cloth Charging is stabilizing the cloth with coolant and abrasive before use. Proper charging
allows the cloth to polish efficiently on the initial runs as well as later runs. This procedure applies to both old and
new cloths.
The old cloths must be charged with coolant after they have been idle for 4 hours or longer. This is especially true
for high nap cloths that require large volumes of coolant to perform correctly.
Periodic charging is required while the process is running. This replenishes the cloth with coolant and abrasive. The
application rate must be optimized to permit the removal of scratches, account for ambient room temperature on the
stability of the coolant, and lower the risk of metal smear and rounding. If the cutting action for the cloth is
unsatisfactory, verify the coolant and abrasive application is correct.
In general, the effects of charging the cloths are as follows:
• Low Coolant Volume – unwanted heat generation will occur
• High Coolant Volume – reduces the abrasive cutting action
• Low Abrasive Content – increased polish step run times.
• High Abrasive Content – Alumina will smear and round the sample; Diamond will scratch the sample
6.3.2.4 Abrasive Buildup The buildup of diamond abrasive on the cloths is good. Do not clean the buildup off. The
thicker the buildup the less diamond charging is required. When the buildup becomes impermeable to the coolant,
metal rounding will start to be apparent. To solve this problem replace the cloth.
6.3.2.5 Cleaning Whenever alumina is used on a polishing cloth, a stringent cleaning discipline is required. The
problem is the alumina has a tendency to coagulate when drying and form large granules which create large
scratches and increased wear of the cloth.
6.3.3 Polish Abrasives
6.3.3.1 Alumina Alumina is widely used in powder or paste form. The powder is usually mixed with water to make a
slurry. The advantages of this system is as the abrasive is applied the water acts as a coolant and the granules do
not tend to coagulate into larger grains. The disadvantage is there is no system available to consistently
(numerically) apply the slurry. Consistency is operator dependent which is not desirable.
The paste usually comes premixed in a carrier providing a consistent concentration of alumina. The disadvantage is
the paste tends to coagulate causing scratches and consistent application problems over the entire surface of the
cloth. Also, the periodic charging of the cloth while the process is running can be difficult.
Alumina grains wear faster making the cutting action less efficient. The charging frequency is dependent on the
number of mounts being polished in the run and the grain size of the alumina. A potential process problem when
using alumina is smear (see Figure 6-2) and rounding (see Figure 6-3 and Figure 6-4). Therefore run times on
alumina should be kept as short as possible.
6.3.3.2 Diamond Diamonds can be bought in aerosol, suspension, or paste form. The aerosol and suspension form
is easier to apply and the application rate can be controlled consistently (numerically). The disadvantage for the
aerosol carrier is that it is extremely flammable and easy to waste (may be a major cost problem). The use of a
diamond suspension will reduce but not eliminate the flammability problem.
The paste form has the advantage that it’s easier not to waste. The disadvantage is the difficulty to evenly distribute
over the cloth and the inability to do periodic charging while the polish process is running.
The diamonds have the best cutting efficiency. This efficiency is dependent on the coolant and polish cloth used.
6.3.3.3 Colloidal Silica Colloidal silica is available as solvent or water-based suspension. It is usually applied on a
neoprene cloth.

22
The advantage is an easy application and no safety issues as the suspension is water based and the lubricant and
coolant to be added throughout the polishing process is DI water.
The disadvantage is the danger of coagulation. Drying of the silica suspension must be avoided under all
circumstances, and the cloth must be cleaned thoroughly from all silica residues after use - otherwise the
microsection is scratched and not polished.
Usually colloidal silica is applied for a final finish after diamond polishing to obtain a completely scratch-free and
very smooth surface, e.g. of the copper. For several applications colloidal silica polishing can be a fast and cheap
alternative to ion beam polishing. It is possible to observe the copper crystal structure in a scanning electron
microscope (SEM) using backscattered electron (BSE) detection. A perfect finish with colloidal silica polishing can
make possible structural analysis with electron backscatter diffraction (EBSD). Furthermore, colloidal silica has
different material removal rates for materials of different hardness, and thus forms reliefs e.g. between copper, tin,
and the intermetallic phases which form in between them, so that they can be distinguished better in the SEM than
just from their material contrast in the BSE image alone.
6.3.4 Coolants
6.3.4.1 Water Water is used both as a coolant and abrasive carrier. The most frequent application is an alumina
slurry.
The disadvantage of water is it washes the abrasive off the cloth. High volumes of water are required to prevent
heat generation unless additives are used to lower its evaporation point.
The application rates are dependent upon the polish step and the type of polish cloth being used at that particular
step.
6.3.4.2 Oil Based Coolant mixtures based on oil prevent heat generation by lowering the friction between the mount
and cloth.
A disadvantage of the oil based coolant is it tends to thicken. The abrasive cutting action will be reduced as the oil
thickens into a film. Also the coolant can leave a residue on the samples if not properly cleaned. This residue will
affect the etching quality of the samples.
Verify the coolant does not attack (i.e pit, soften) the potting material. Oil based coolants usually won’t attack potting
material.
The application rate depends on the polish step and the type of cloth used.
6.3.4.3 Alcohol Based Coolant mixtures of alcohol and ethylene glycol prevent heat generation by evaporation.
The advantage is evaporation helps retard the abrasive from being washed off the cloths. The disadvantage of this
coolant is that long exposure (3+ minutes) can prematurely etch the samples in the mount and attack (i.e., pit,
soften) the potting material. An ethanol and ethylene glycol mixture will soften an acrylic potting material, and
contribute to the problem of samples being higher than the surrounding potting material (see Figure 4-4 and Figure
4-5).
The application rate depends on the polish steps and type of cloth used.
Warning: Ethylene glycol is a desiccant for water. Water on the samples, mount holder, or in the polish step will
significantly degrade the efficiency of this coolant.
6.4 Cleanliness Cleanliness is important throughout the polish process. As the grit sizes get smaller, the need for a
clean mount surface becomes more imperative.
Cleaning considerations are:
• dust control
• clean mounts between polish steps
• coolants may affect etch quality on the samples

23
• When cleaning the mount, use a mild hand soap to remove polish materials from the step just completed.
Use a soft scrubber that won’t scratch the surface of the samples (sponge, cotton balls, tissue).
• Alternate cleaning methods are using your fingers with a mild soap or an ultrasonic cleaner with a mild soap
or alcohol solution. If you decide to use your fingers to clean the samples, they must be free of human oils
and dirt. The contamination on the fingers can etch or scratch a sample easily.
• To complete the process, air dry samples to remove any water debris. Low air pressure is best to prevent
water streaks. Blot drying the samples is an alternate but beware of scratches.
Note: If your samples were polished having gaps between the samples and mounting material extreme care must
be taken to clean and dry the samples because the water and air will lift the polish debris out of the gaps and dirty
your samples.
6.5 Polish Process Quality The completed high volume microsection process must have certain polish qualities so
as not to induce or hide defects.
Recommended sample polish qualities are:
• microsectioned to the center of the hole +10%
• no scratches on copper surface (using bright field at 100X magnification) – see Figure 6-1
• no metal smear – see Figure 6-2
• no rounding of surfaces – see Figure 6-3 and Figure 6-4
• fractured or gouged glass bundles in the laminate
• samples are not higher than mount material – see Figure 4-4 and Figure 4-5
• Figure 17 is an example of acceptable polish quality
Figure 6-5 Acceptable polish quality Figure 6-6 Acceptable polish quality
6.5.1 Heat Generation The surface area in contact with the polish cloth is much greater than in the grind process as
shown in Figure 6-7. Consequently, an imbalance in the coolant variables will permit friction which causes high
temperatures within the mount (93+ °C = 200+ °F). These temperatures for long periods may cause thermal related
defects on the samples. Using an IR thermometer (non-contact), the polish cloth surface temperature should never
exceed -9 °C [15 °F] above ambient temperature of the room.

24
Figure 6-7 Contact area comparison – sandpaper vs. polish cloth
6.5.2 Material Removal Uneven The polish process is very sensitive to material of different hardness (i.e., potting
material, laminate, copper, tin/lead, constraining material). The polish process has a tendency to remove the softer
materials faster. This is apparent on several areas of the mount.
• Potting Material – the potting material is removed faster than the samples (apparent as ridges – see Figure
4-4 and Figure 4-5). The issue is the sample edges were not supported. The samples are susceptible to
microsection damage.
• Tin/Lead – the tin/lead is removed faster than surrounding copper (apparent as rounding) which prevents
accurate copper measurements (see Figure 6-3 and Figure 6-4).
• Laminate Butter Coat – potting material is removed faster than the buttercoat (apparent as rounding) which
prevents an accurate evaluation measurement of surface defects (i.e., lifted lands).
6.5.3 Sample Deformation The scratches from the grind process are not removed, or new scratches were caused
due to contamination in the polish process (see Figure 6-1).
6.5.4 Smeared Metal The metal can be smeared instead of being removed by cutting action (see Figure 6-2).
Usually smeared metal is in association with heat generation. The smear is caused by an imbalance between the
coolant and abrasive. Smear is apparent as small saw-toothed edges along the copper-tin/lead interface. Smear will
mask fine defects (i.e., separations and cracks).
7 MICRO-ETCHING
Micro-etching is an important portion of the microsection process. Poor micro-etching techniques can hide defects
as readily as poor polishing quality. Regardless of the method of application, it is tough to get repeatable micro-
etching quality from mount to mount.
Micro-etching is the preferential attack of a metal surface with an acidic or basic chemical solution. Three
techniques can be used: swabbing, immersion, or electrolytic.
The requirement for when to micro-etch and what to evaluate before and after micro-etch is specified in the
procurement documentation and IPC performance specifications.
7.1 Application Methods
7.1.1 Safety Etchants should not routinely be in contact with the operator’s skin. These etchants can cause skin
problems including dermatitis. Impermeable gloves are highly recommended for both these methods. Table 7-1
provides examples of etchant types.

25
Table 7-1 Etchant Types
Use Etchant Composition Application Method Notes
Copper and Copper Alloys with Sn/Pb
Solder
Ammonium Hydroxide 3%
Hydrogen Peroxide
50 ml
50 ml
2-3 seconds with swab 1,2
Copper and Copper Alloys with Sn/Ag
Solder
Phosphoric Acid Acetic
Acid Nitric Acid
Hydrochloric Acid
10 ml
10 ml
20 ml
20 ml
2-3 minutes at 85°C
Copper and Copper Alloys with Solder Sodium Dichromate
Sodium Chloride Sulfuric
Acid
RO Water
24 g
4 g
24 ml
0.3 ml
2-3 seconds with swab or
immerse
3
Nickel Acetic Acid Nitric Acid 50 ml
50 ml
1-2 seconds immerse 1
Gold Silver Palladium Platinum Hydrochloric Acid Nitric
Acid
60 ml
40 ml
2-3 seconds immerse 1
Note 1. 50 ml of water may be added to buffer etchant severity.
Note 2. The swabbing necessary for effective etching may scratch the surface.
Note 3. The etchant will discolor the solder preventing analysis of the surface.
7.1.2 Swab This method applies the etchant with a cotton swab. A swab may be used several times or only once
depending on the chemical activity of the etchant solution. Immerse the swab in the solution for 2-10 seconds and
apply the etchant on the samples. Lightly spread the solution over the surface by moving the swab only in one
direction. Do not scrub the surface with the swab to prevent scratching of the surface. Hold the mount at a slight
angle when swabbing so the excess drains off. Rinse the surface with water, apply alcohol (if desired), and blow
dry.
7.1.3 Immersion This method applies the etchant by dipping the mount in a bath of etchant. Immerse the mount in
the etchant solution and rinse the sample with water, apply alcohol (if desired), and blow dry.
7.2 Types All reagents are analytical grades and acids are concentrated.
8 TROUBLESHOOT GUIDE
Table 8-1 provides some common causes and solutions to microsection problems.
Table 8-1 Cause and Solution for Common Microsection Problems
Problem Possible Cause Solution
OVERGRIND (beyond the
centerline of the target
holes)
Trash between the mount holder and the
mount.
Tool stop height.
a) Check for trash between the mount
edge and the mount holder.
a) Adjust tool stop height
UNDERGRIND (before the
centerline of the target
holes)
Tool stop height out of tolerance.
Excessive wear on the mount holder
surface (depression).
Pin up problems at the hardmount
process.
a) See OVERGRIND #2
a) Rework holder at a machine shop or
replace.
a) Check the hardmount process
variables.
UNEVEN GRIND (side to
side on the mount)
Scratches from the previous step.
Grind step too long (on the tool stops).
Mount not secure on holder (Reference
0).
Trash between the mount holder and the
mount.
a) Adjust the stop height to prevent
scratches.
a) Decrease grind time
a) Change ‘O’ rings or adjust holder.
a) See OVERGRIND #1.
UNEVEN GRIND (Location
to location on the mount
1. Mount holder collar too tight. a) Adjust or replace collar.
OVER/UNDER GRIND
(within the same run)
Materials being ground together do not
have similar hardness (i.e., POM and
flex).
Mount holder collar too tight.
a) Keep common product types in a run.
a) See UNEVEN GRIND.

26
ABRASIVE PAPER RIPS Pressure setting too high.
Gouge in grinding disc.
Abrasive paper slipping.
a) Adjust the pressure.
a) Resurface the disc.
Assure water is under the abrasive paper
when loading.
Abrasive paper holding rind is bent.
Grinding wheel was refinished and
outside tolerance for holding ring to
secure the abrasive paper.
EXCESSIVE Tool stop
WEAR
Stops on abrasive paper too long.
Carbide tip construction has changed.
Reduce grind time.
Adjust tool stop height.
a) Replace tool stops.
GRIND TIME INCREASING Change in pressure.
Machine parts worn.
a) Audit the pressure gage.
a) Service the machine.
UNEVEN POLISH 1. Mount not ground flat. a) Rework mount.
SCRATCHES (after polish) Mount not flat.
Rough grind scratches not removed.
Gaps or depressions in the potting
material.
Contaminated cloth.
Too little abrasive.
Too much coolant.
a) See UNEVEN GRIND.
a) Increase fine grind run time.
a) Clean mounts and check the cloth for
contamination.
a) Clean or replace the cloth.
a) Increase abrasive application.
a) Reduce coolant application.
COPPER SMEAR Too little coolant.
Too much pressure or heat generation.
Dulled abrasive.
a) Increase coolant application.
a) Reduce pressure.
a) Increase abrasive application.
ROUNDING Alumina
High nap cloth.
a) Adjust process settings.
a) Same as 1a.
EXCESSIVE ROUNDING
(Samples are ridges above
the hardmount)
Potting material is soft.
Too little coolant.
Too much pressure.
a) Adjust mix ratio.
a) See COPPER SMEAR.
a) Same as 2a.
CLOTH FIBERS ON THE
SAMPLES
Cloth is worn.
Mounts are shaving the cloth.
a) Replace cloth.
Remove sharp edges from mount.
Mount holder too tight.
BLACK RESIDUE ON THE
SAMPLE
Film from an oil based coolant.
Diamond spray residue.
a) Reclean the sample with isopropyl
alcohol.
9 GLOSSARY
9.1 Abrasion The process of grinding or wearing away a surface using an abrasive (abrasive paper and/or polish
media).
9.2 Charging Application of a small amount of polishing media and lubricant to a polishing cloth.
9.3 Coupon Test Strip A portion of the printed board panel containing a complete set of test patterns used to
determine acceptability of the board(s) on the panel.
9.4 Crescent Moon Scratch A portion of the polished mount that has an area scratched the shape of a crescent
moon. The pattern usually appears on the portion of the mount closest to the outer edge of the mount holder. The
cause of the scratch pattern is the potting material ground selectively deeper than the rest of the mount. The polish
process cannot remove these scratches. See Figure 5-6.
9.5 Grind Removing material from a sample by abrasion. Abrasive paper or lapping discs are the most common
abrasive materials used.
9.6 Grinding Wheel The metallic wheel that supports the abrasive paper during the grinding process.
9.7 Grit Size Nominal size of the abrasive particles in the abrasive paper corresponding to a set granular size. The
granular size defines the depth of scratch damage that will be done to the sample.

27
9.8 Grind Mount Holder The high volume microsection hardware that consists of the mount holder and tooling
stops.
9.9 Micro Etchant A chemical solution used to etch the metal to reveal the metallic structural details for
examination.
9.10 Mounting The embedding of the sample in a plastic prior to the grind/polish operation. The material protects
the plated-through-hole from structural damage during grind/polish.
9.11 Polish Mount Holder The high volume microsection hardware that consists of the mount holder with the
tooling stops withdrawn.
9.12 Polish A mechanical, chemical, or electrolytic process or combination thereof used to prepare a smooth,
reflective surface suitable for microstructural examination. The surface finish of the polished sample must meet
minimum guidelines to ensure accurate inspection of the sample.
9.13 Sample Removal The removal of a sample from the product or test pattern.
9.14 Scratch A groove produced in a surface by an abrasive.
9.15 Scratch Trace A line of micro-etchant markings produced on a surface at the site of a metal deformation from
a preexisting scratch. The etchant is preferentially attacking the metal deformation.
9.16 Speed Bump A polish characteristic when the softer materials (i.e., tin/lead, laminate, mounting material) is
removed faster than neighboring harder materials (i.e., copper, glass bundles). This usually appears as the target
being higher than the surrounding mounting material. The ‘bump’ can be seen by light reflecting on the surface or
rubbing a finger over the edge of the sample. CAUTION: Do not rub your finger over the PTHs so as not to scratch
the polish finish.
9.17 Stops, Tooling These stops are used on the grind mount holder to define the end point for material removal
from the mounted sample. The end-point setting is a specified distance from the tooling reference edge. The stops
are used to ensure that each subsequent step of grinding will remove the scratches of the prior grinding step.
9.18 Target PTH The PTHs on the sample that will be inspected after the grind/polish operation.
9.19 Tooling Edge, Mount The mount mold has a tooling edge which sets a predetermined distance from this edge
to the centerline of the target plated-through-holes. The tooling pins are placed on this edge. This distance is critical
to proper use of the microsection tooling stops.
9.20 Tooling Holes, Microsection Non-plated through holes which are utilized for alignment of the target plated-
through-holes on multiple samples in the same plane. This alignment is critical to ensure the center of ALL the
plated- through-holes is reached simultaneously during the grind/ polish operation.
9.21 Tooling Pins, Microsection Pins which are inserted into the microsection tooling holes. These pins may be
reusable or dedicated.
10 REFERENCES
(1) Gunter Petzow, ‘‘Metallographic Etching,’’ American Society for Metals, 1978, pg. 9.
11 RECOMMENDED READING
Samuels, LE, ‘‘Metallographic Polishing by Mechanical Methods,’’ 3rd Edition; American Society for Metals; 1982;
ISBN: 0-8717-135-9.
Vander Voort, George F., ‘‘Metallography Principles and Practices,’’ McGraw-Hill Book Co; 1984; ISBN: 0-07-
66970-8.
Petzow, Gunter, ‘‘Metallographic Etching,’’ American Society for Metals; 1976; ISBN: 0-87170-002-6.

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