LGA VS. CSP: A COMPARISON IN VARIOUS LEAD FREE APPLICATIONS
Authors: Heather McCormick, et al. Company: Celestica Inc. Date Published: 5/16/2008
ICSR (Soldering and Reliability)
Abstract: In this study accelerated thermal cycling at 0°C -100°C and -55°C to +125°C has been performed on a test vehicle including LGAs and CSPs among other components. Both CSP64 and LGA64 were assembled on identical pad geometries. The LGA package is a standard Ball Grid array component shipped with no spheres. The LGA solder interconnects are formed solely by the solder paste applied at board assembly. They were assembled on HT OSP, Immersion Ag, Immersion Sn, ENIG, and Electrolytic Ni/Au finished boards using both the most popular Sn-Ag-Cu alloy, 3% Ag - SAC 305, and the alloy with higher Ag content, SAC 405 solder. CSPs had SAC 305 and SAC 405 balls; therefore pure SAC 305 and SAC 405 solder joints were formed. The test matrix included two board thicknesses - 0.093” and 0.125”. Thermal cycling using a 0°C -100°C profile was conducted on assembled test boards for 6000 cycles and cycling using a -55°C to 125°C profile was terminated at 3000 cycles. As-assembled and thermal cycled solder joints were examined using optical and scanning electron microscopy. This paper compares the fatigue life of LGA64 and CSP64 in different conditions including different solder alloys, surface finishes, board thicknesses, and thermal cycling profiles.
Key words: LGA, CSP, Lead Free Assembly, Reliability