Improved QFN Reliability Process by John Ganjei. John will talk about the improvements in the reliability process in this webinar. It is free to attend - see www.reliabilitycalendar.org/webinars/ to register for upcoming events.

1. Improved QFN
Reliability Process
Dr. John Ganjei
©2014 ASQ & Presentation Ganjei
http://reliabilitycalendar.org/webina
rs/

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3. ASQ RD Webinar Series
Improved QFN Reliability Process
Thursday January 9, 2014 9-10am PST
Presented by: Dr. John Ganjei
3

4. Outline/Agenda
• Introduction
–Design and criteria
• Discussion Topics
–Industry requirements
• Performance Assessment
–Various solderability tests
• Summary
• Acknowledgements
–MacDermid Southeast Asia Team

5. Introduction
• Move to HDI implied BGAs would replace
QFNs
– difficulties could be avoided but still achieve desired
performance with QFN
• It is expected in 2013, the use of QFNs will
represent 15% of all integrated circuits
• Prismark Partners has stated that the QFN is
the fastest growing package excluding flip-chip
chip scale

6. Design
• A copper foil lead frame is pattern etched or
punched for the package assembly process.
• Singulation can be either punched or sawn.
– copper edges become exposed leaving terminations
susceptible to oxidation
– can degrade solderability during component assembly
to the mating circuit board.

7. Design
• The designer must consider:
– some devices may have oxidized and termination ends
will not ‘wet’ during assembly processing.
JH
JT
JH
G
Solder fillet on bare Cu terminal
end with oxidation build-up
JT
G
Solder fillet on coated or
plated terminal end
Reference:
IPC Webinar June 23, 2011

8. Industry Requirements
• Currently there are no industry (IPC or JEDEC)
requirements for toe fillet wetting
• OEMs are working toward stronger industry
wide specifications to ensure the performance
and reliability of this component style.
• An industry group should decide on the
appropriate preconditioning and fillet height
requirements

9. Toe Fillet Solderability
BOARD LEVEL ASSEMBLY AND RELIABILITY CONSIDERATIONS
FOR QFN TYPE PACKAGES
Ahmer Syed and WonJoon Kang
Amkor Technology, Inc.
Finite element simulations and actual test data generated by
customer have shown that the fillets - if formed - can
improve the board level reliability by as much as 2X for a
package with large die to package size ratio. The fillet extends
the length of solder joint and provides a longer path
for the crack to go through the entire joint, thus improving
the reliability.

Soldered fillet would deliver higher joint reliability
 More

soldered interface
Enable inspectability

10. Process Introduction
• Proposed chemical plating for producing a
solderable sidewall
– Can be applied vertically, horizontally or in barrel
machines
• Will clean the edges and make a more uniform
surface for plating.
• Flank plating can be performed on parts after
singulation
– either mounted on tape or in singulated form.
• No appearance or morphology change is observed
to the original electroplated tin

11. Performance Assessment
• Effect on part integrity and electrolytic tin
plating
• Laboratory solderability testing
– Dip and look
• Assembly simulation at HKUST

12. Performance Assessment
Cu oxides
Sawing burr
Before the process
After the process

13. Performance Assessment
Before the process
1000x
After the process
1000x
• After proposed process, no appearance or morphology
change is observed from the original tin plating of the
DAP and lead terminals by scope or visual

14. Solderability: “Dip and Look” Test Method
Tweezers
JESD22-B102E
•
•
•
•
Solder: Sn96.5 Ag3.0 Cu0.5
Solder temp: 245 C
Flux type:ROL0
Immersion time in flux: 5 -10sec.
– Flux drip time ~ 10 sec. before
dipping into the solder
• Immersion time at solder: 5 sec.
• Use tweezers to grasp two
corner of testing unit and dip the
whole unit at 90 into the solder
Solder pot

15. Solderability: “Dip and Look” Test Method
Pre-condition
QFN 64L “Dip & Look” Solderability Testing
Unit
Fillet qty
< 75% wetting % Solderability
As received
After 8 hrs steam age
After 16 hours bake
4
4
4
256
256
256
For all conditions, Cu does not wet
As received
After 8hr steam age
After 16hr bake @ 155C
0
1
1
100
99.61
99.61

16. Solderability: Assembly Simulation
QFN 64L PCB Mounting Solderability Testing
Pre-condition
Unit
Fillet qty
< 75% wetting
% Solderability
As received
4
256
0
100
After 8 hrs steam age
4
256
10
96.09
After 16 hrs bake
4
256
5
98.05
For all conditions, Cu does not wet
As received
After 8 hr steam age
After 16 hr bake 155oC
Non wetting
Less wetting
• QFN 64L can achieve 100% solder coverage as received
• Some less wetting observed after the steam aging and high
temperature exposures

17. Solderability after Bake Performance
Punched Process
cut edge after plating
Sawn Edge Process
cut edge after plating

18. Solderability after Steam Aging
Punched Process
cut edge after plating
Sawn Edge Process
cut edge after plating

19. Summary: Challenge

No existing or proposed JEDEC standard for the
following requirements
•
Aging environment
–
–
•
Solder toe fillet
–
–
–
•
•
Steam or bake
Dwell time
area coverage and
yield of successful lead coverage
testing protocol
PCB footprint
Long term reliability testing
19

20. Summary: Challenge
• A process that can provide a solderable flank after
component molding and singulation has been described
– should provide significant advantages in inspectability and solder
joint reliability.
• Testing and further evaluations are ongoing with key
OEMs and assembly houses
– we hope to report these results as they progress.
• An industry consensus of required preconditioning to
determine shelf life prior to assembly is needed for
further qualification of this and other potential solutions.

21. Acknowledgements
• I’d like to thank my coauthors
– Mr. Rich Retallick
– Ms Lenora Toscano
– Especially Dr. Gu Hong for his research and
development efforts which made this paper possible
– Also the team at HKUST
Thank You!