The impact of design and material choices on solder joint fatigue life for
fine pitch EGA packages is characterized. Package variables included die si
ze, 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 6x as die size was reduced. For a given die
size, fatigue life was up to 2x longer for larger packages with more solde
r balls. Mold compounds with higher filler content reduced fatigue life by
up to 2x 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 boar
d level reliability to laminate-based packages.
Solder joint fatigue life was 1.2x longer for 0.9 mm thick test boards comp
ared 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 3.1x life improvement over SMD pads. For a completel
y fan-out design, there was a 1.6x acceleration factor between -40 <----> 1
25 degrees C, 15 min ramps, 15 min dwells and 0 <----> 100 degrees C, iO mi
n ramps, 5 min dwells. (C) 2000 Elsevier Science Ltd. All rights reserved.