Journal of SMT Article
Reliability Study and AF Modeling for SnAgCu Solder Joints and SnPb Solder Joints in QFN Packages
Company: Cisco Systems, Inc.
Date Published: 1/31/2010 Volume: 23-1
Solder: SnPb vs. SnAgCu
Body: 10mm vs. 7mm vs. 5mm
Die to package ratio: small (18-28%) vs. large (40-47%)
Board thickness: 8 layer, 93mils vs. 16 layer, 125mils thick
Thermal profiles: 0-100C 30min cycle vs. -40-125C 1hr cycle
Exposed-pad via design: open vs. plugged
Thermal cycling test results showed that the AF between 0-100C and -40-125C thermal profiles is ~3.2 for SnAgCu solder joints and ~1.8 for SnPb solder joints. It was also found that solder joint reliability can be enhanced by making solder joints that have convex-shaped fillets, rather than an increased solder joint standoff. Using the characteristic cycles-to-failure, Coffin-Manson type AF models were developed for SnPb and lead-free SnAgCu solder joints in QFN packages and compared with conventional
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