Effect of thermal cycling and vibration on cracking in Sn-3.0Ag-0.5Cu solder bump

Abstract

In present study, the effects of thermal cycling and vibration on cracking in Sn-3.0Ag-0.5Cu (SAC305) solder bump (interconnection between flip chip and printed circuit board) were studied. The thermal cycling test was set in 2 conditions as “TC180C” and “TC140C” that differed in temperature cycle i.e. 15 °C to 180 °C and 15 °C to 140 °C, respectively. While, the vibration test was also set in 2 conditions as “VB20G”and “VB05G” that differed in vibration acceleration ranges i.e. 20G and 5G respectively. Crack initiation and propagation in SAC305 solder bump were investigated by interrupted tests using scanning electron microscope. Results of the thermal cycling tests indicated that cracks initially developed at the edge of solder bump and subsequently propagated along solder/intermetallic compounds layer interface for TC180C condition. While crack propagated to bulk solder for TC140C. And crack initiation cycle differed between test conditions that were 40 cycles and 60 cycles for TC180C and TC140C, respectively. Crack initiation and propagation were accelerated by temperature range. The lower number of crack initiation cycle for TC180C condition, which was operated under a large temperature range, would be induced by higher thermal strain that could accelerate crack initiation in SAC305 solder bump. Results of the vibration tests showed that crack initiation and propagation were found only under VB20G condition, the number of crack initiation cycle was 12 cycles at X vibration axis. While any crack was not found for VB05G condition. The crack initiation and propagation in the SAC305 solder bump under VB20G condition would be induced by higher mechanical vibration acceleration. Whereas, damage accumulation in the SAC305 solder bump would not be induced by lower mechanical vibration acceleration under VB05G condition.