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Product Level Design Optimization for Pad Cratering Reliability During
Drop ImpactHuayan Wang1, Jing Wang1, Jiefeng Xu1, Vanlai Pham1, Ke Pan1, Seungbae Park1, Hohyung Lee2, Gamal Refai-Ahmed2
1State University of New York at Binghamton, 2Xilinx Inc
BINGHAMTONU N I V E R S I T YSTATE UNIVERSITY OF NEW YORK
Mechanical
Engineering
Optomechanics & Physical Reliability Lab.
* Professor Seungbae Park
Objectives
Results
Background
Methodology
Conclusion
Drivers of pad cratering
Finer pitchBrittle laminatesStiffer soldersLarge heat sink
Mitigation methods of pad cratering
Solder mask defined
Larger pad
Limitations on board
flexure
Component location
Edge bonding
More compliant solder
To evaluate various factors’ influence to the product level pad cratering
risk
SMD vs. NSMD
Edge bonding effect
Top plate material
Heat sink weight
Case SMD/NSMD Edge BondingTop Plate Material
Heatsink
1(Ref) NSMD No Al 12 SMD \ \ \3 \ Yes \ \4 SMD Yes \ \
5 \ \ Stainless Steel \
6 \ \ Zinc Alloy \7 \ \ \ 1.75
Design of experiments (\: same as reference case)
Max stress on PCB in assembly process
Max PCB stress after reflow
Max PCB stress after top & bottom
plates assembly
Max PCB stress after heat sink
assembly
Max stress on PCB during drop
Free drop method
Input-G method
Input-D method
Direct acceleration
input method 0 5 10
0
500
1000
Accele
ration (
m/s
^2)
Time (ms)
Acceleration
88.23G
Duration: 8.6ms
Schematic of failure site observed during drop test
Finite Element Modeling
Sub modeling to get max stress on PCB
Max PCB stress change in
assembly process
Max PCB stress in
drop test
Max PCB stress in assembly process
1.00
0.86
0.700.62
1.00 1.00 1.00
Ref Case2 Case3 Case4 Case5 Case6 Case70.0
0.5
1.0
Max V
on M
ises
Cases
SMD decreases the stress by 14%
Edge bonding decreases the stress by
30%
Combination of both can decrease the
stress by 38%
Top plate material and heatsink weight
has no influence to the PCB stress
Max PCB stress in drop test
Heat sink weight has the
most significant influence to
the PCB stress during drop
Edge bonding can effectively
decrease the PCB stress
during drop
With the presence of edge
bonding, the SMD’s
mitigation to the PCB stress
is neglectable
Stiffer top plate can reduce
the PCB stress during drop
• Both solder mask define and edge bonding can reduce PCB stress in assembly process
• Heat sink weight is the most inflectional factor to the PCB stress during drop
• With the presence of the edge bonding, SMD and NSMD yield the same max PCB stress
• Rigid reinforce plates can reduce the max PCB stress during drop• Edge bonding, stainless steel plates and light heat sink design gives the
best pad cratering reliability
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