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they have arrived!F e at u r e — n e W a d Va n c e d p c b m at e r i a l s                                              ...
materials contriBUte only one Part of a comBination                “of systems that dictate the reliaBility of a ProdUct. ...
MATERIALS FOR HIGH-RELIABILITY APPLICATIONS continuestH e Y HaV e arri Ve d — ne W adVanced pcb materials                 ...
MATERIALS FOR HIGH-RELIABILITY APPLICATIONS continuestH e Y HaV e arri Ve d — ne W adVanced pcb materials                 ...
MATERIALS FOR HIGH-RELIABILITY APPLICATIONS continuesFailure analysis                                    IPC- 4101 listing...
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High Reliability PCB Materials: All IPC-4101-Grouped Materials are not Created Equal

When discussing high-reliability materials for printed circuit board applications, the conversation typically gears towards opinions of reliability: is one material system versus another better? Other times, it's materials' properties that are stressed to imply reliability. Written by Yash Sutariya Saturn Electronics Corporation, Rigid PCB Fabrication / Saturn Flex Systems, Flexible PCB Fabrication. From June 2011 issue of The PCB Magazine.

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High Reliability PCB Materials: All IPC-4101-Grouped Materials are not Created Equal

  1. 1. they have arrived!F e at u r e — n e W a d Va n c e d p c b m at e r i a l s Materials for High-Reliability Applications: All IPC-4101-Grouped Materials are not Created Equal By Yash Sutariya A summary table of three commonly called saturn electronics corporation/ out standards is provided in Figure 1 for saturn Flex sYstems, inc. reference. Once stacked next to each other, it’s easy to see why one could infer reliability via summarY higher-level IPC categories and/or underlying materials properties such as Tg or Td. We argue, When discussing high-reliability materials however, that these characteristics are almost for printed circuit board applications, the meaningless when taken in a vacuum. They conversation typically gears towards opinions are merely indicators of the raw material, of reliability: is one material system versus not the finished product, when it comes to another better? other times, it’s materials’ reliability. Materials contribute only one part properties that are stressed to imply reliability. of a combination of systems that dictate the reliability of a product. In order to test the system, we have to undergo reliability testing. Materials Callouts Test Methods One commonly cited document is the Thanks to our industrious friends on IPC-4101C Specification for Base Materials the other side of the Great Wall, we’ve been for Rigid and Multilayer Printed Boards. This pushed to diversify our customer base over standard creates slash sheets, or “silos,” to the past decade away from our historical combine like materials based on meeting automotive supply base. This allowed us to product or performance characteristics such experience a broad array of what people like as resin type or a minimum Glass Transition to rely on for reliability testing. Industries (Tg) rating. In recent years, new slash sheets we serve as a significant part of our business have been created to address materials capable include Automotive, Military/Aerospace, for lead-free assembly that incorporates Glass Industrial Controls and Telecommunications. Decomposition Temperature (Td). Typically, the most intensive tests focus on For purposes of this discussion, we will via hole wall reliability. We’ll review a few of focus on these lead-free capable materials. the common ones below. 22 The PCB Magazine • June 2011
  2. 2. materials contriBUte only one Part of a comBination “of systems that dictate the reliaBility of a ProdUct. ”Figure 1: ipc-4101 summary table.Delphi C7000 approximately 1/6 to 1/7 the time required for Delphi’s testing attempts to simulate real the C7000 testing. However, there are schoolsoperating conditions of the PCB by applying of thought that believe this method is not astemperature cycling to Daisy Chain coupons. aggressive as the full thermal cycling requiredEach coupon contains a series of vias linked by Delphi’s testing.to each other through plated vias and innerlayer connections. The test qualifies the Interconnect Stress Test (“IST”)vendor based on layer count and min via IST is another accelerated method ofdiameter. Testing is performed using two air- testing. Rather than use an air-to-air method toto-air test chambers. Standard parameters are bring the test vehicles to temperature, this testfive minutes transition time between peak method relies on an electrical charge to heattemperatures, and 25 to 30 minutes at peak the coupon and stress the vias. To date, we aretemperatures. Measurements are performed not aware of a direct correlation between thisfive times during the process, which terminates method and the previous air-to-air methods.at 1000 cycles. Needless to say, this is not a The main difference between these tests isquick test. how they attempt to stress the test vehicles. The main commonality is that they measureHighly Accelerated Thermal Shock reliability based on resistance measurements of(“HATS”) the daisy-chained vias. The HATS test simulates the C7000 testingrequirements by using an air-to-air thermal Materials Comparison Testingcycling procedure that rapidly heats and Before we discuss the reliability of onecools the test vehicles to the min and max material over another, it’s critical to establishtemperatures by using a single chamber why a particular material may display betterand introducing heated and cooled air. The reliability testing results. Notice that thebenefit of this method is that it requires reliability test results are not of a particular June 2011 • The PCB Magazine 23
  3. 3. MATERIALS FOR HIGH-RELIABILITY APPLICATIONS continuestH e Y HaV e arri Ve d — ne W adVanced pcb materials characteristic or measurement of the laminate maTeRialS: Finally, there are the itself, but rather a measurement of a feature physical properties of the material itself. These created in the material—the via itself. include Tg, Td, CTE, among others. IPC-4101C The fact that we are testing the vias for uses these and other materials’ properties to reliability means that we are not testing the create classifications that are often used for material, but rather the effect of the material on product selection for particular applications. various manufacturing processes, and vice versa. In order to establish a difference in The process/material combinations that reliability between two resin systems, the have the most impact on these reliability tests proper method would require us to hold as are as follows: many things constant between the two test procedures, such as: DRilling: Drilling parameters (feed, speed, retract, max hit count) must be Material Choice: We chose two materials optimized by resin system. Some systems are that are qualified to the IPC-4101/126 slash more abrasive against drill tools, while others sheet. Both have similar Tg and Td values are more brittle. Incorrect or non-optimum that are the most commonly called out parameters can result in rough holes walls, characteristics in customer fabrication notes gouges, incomplete de-smear and inter- that we see as part of the normal course of connect defects, among others. business. DeSmeaR: Regardless of whether the Test Vehicle: Eight-layer daisy chain fabricator uses plasma or permanganate coupon with finished hole sizes (in mils): 6, 8, methods, the process must be modified based 10, 12 and 14. on the resistance of each resin system. Cycles times may have to be increased if inefficient drill parameters result in excess smear across inner layer interconnects. CoPPeR PlaTing: Cycles to failure is often correlated directly with copper plating thickness. Rough holes can create turbulence during copper electroplating that has a negative effect on average plating thickness in the hole. Of course, plating a fine grain structure copper with high tensile strength and elongation properties is critical to increased life in a thermal cycling environment. Figure 2: Failures recorded at test intermission points. 24 The PCB Magazine • June 2011
  4. 4. MATERIALS FOR HIGH-RELIABILITY APPLICATIONS continuestH e Y HaV e arri Ve d — ne W adVanced pcb materials Quantity: 11 coupons per resin system. Preconditioning: All coupons were passed six times through a lead-free reflow cycle. Test parameters: -40°C to 120°C temperature range. Five minutes transition between extremes. Twenty-five minutes at temperature. Test requirements: Endpoints of each daisy chain (one per hole size) are measured throughout the test at hours 0, 336, 504, 750 and 1,000. Hole size fails for qualification if any of the coupons show a change in resistance of more than 10%. Coupons that pass are cross-sectioned to validate no potential for latent failures exist, such as cracks in the copper plating. Figure 3: Barrel cracks due to Z-axis expansion. Test results As the charts display (Figure 2), there is a the material type, but holding all other inputs significant change in performance by changing constant (i.e., manufacturing process). Figure 4: stress crack in copper plating. Figure 5: stress cracks in copper plating. 26 The PCB Magazine • June 2011
  5. 5. MATERIALS FOR HIGH-RELIABILITY APPLICATIONS continuesFailure analysis IPC- 4101 listing. The benefits of those Failures in this test can include blistering properties can be easily diminished if theand delamination, but are predominantly hole material diminishes the performance of otherwall cracks or interconnect separations (Figures processes such as drilling or plating.3, 4 and 5). If true reliability is of utmost concern, The thermal cycling causes the material the PCB user must qualify not only the resinto expand and contract in the Z-axis. As seen system, but also the entire system used toin the photos at left, this can cause hole wall produce the PCB to ensure that the fabricatorfailures if the expansion is too great compared and laminate system are compatible. PCBto the ability of the copper plating in the holewall to adjust accordingly. Yash sutariya is Vice presidentConclusion of corporate strategy at saturn When it comes to materials reliability, our electronics corporation (sec) and owner/president of saturn Flexfirst stop is typically and IPC-4101 category, or systems, inc. (sFs). since joining thea specific material property, such as CTE, Tg or team, sec has successfully navigatedTd. We have found that materials categorized from a low-mix, high volume, automotiveinto the same IPC slash sheet are not all equal. supplier to a high-mix, medium-to-high-volume Unfortunately, laminators trying to meet diversified supplier to a broad range of industries.a particular value of a higher performance sutariya received his bba from the university ofproperty can overlook other properties that michigan, school of business administration.sometimes are not found on a datasheet or Rogers’ New High-Frequency Laminate Video interVieW by Real Time with...IPC APEX EXPO 2011 Greg bull of rogers corporation discusses rt/duroid 6035Htc High Frequency laminate, their new material that’s getting plenty of attention from designers, for its ability to manage heat. bull also explains more about his company and their new factory in www.realtimewith.com china. June 2011 • The PCB Magazine 27