Failures of flip chip assemblies under thermal shock

Flip chip on board (FCOB) solder joint reliability under thermal shock stress was investigated. With underfill materials, the solder joint lifetime was increased from 37 to 1,300/2,480 cycles depending on the particular underfill material used. Through the use of CSAM, SEM, dye penetration tests and cross sectioning, the reliability of a FCOB assembly under thermal shock stress was evaluated. Both dye penetration and SEM fracture analysis can be used to measure quantitatively the extent of crack propagation for assemblies without underfill. A new failure mechanism, PCB cracking was also observed and discussed.