Abstract
The impact of design and material choices on solder joint fatigue life for fine pitch BGA packages is characterized. Package variables included die size, package size, ball count, pitch, mold compound, and substrate material. Test board variables included thickness, pad configuration, and pad size. Three thermal cycle conditions were used. Fatigue life increased by up to 6× as die size was reduced. For a given die size, fatigue life was up to 2× longer for larger packages with more solder balls. Mold compounds with higher filler content reduced fatigue life by up to 2× due to a higher stiffness and lower thermal expansion coefficient. Upilex S tape with punched holes gave 1.15× life improvement over Kapton E tape with etched holes. Once optimized, tape-based packages have equal board level reliability to laminate-based packages. Solder joint fatigue life was 1.2× longer for 0.9 mm thick test boards compared to 1.6 mm thick boards due to a lower assembly stiffness. The optimum PCB pad design depends on failure location. For CSP applications, NSMD test board pads give up to 3.1× life improvement over SMD pads. For a completely fan-out design, there was a 1.6× acceleration factor between −40⇔125°C, 15 min ramps, 15 min dwells and 0⇔100°C, 10 min ramps, 5 min dwells.
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