Detailed investigation on the creep damage accumulation of lead-free solder joints under accelerated temperature cycling

Though being accepted and widely employed for decades, there remains no consensus in the industry on the selection of an optimum temperature profile for the accelerated temperature cycling (ATC) test for the evaluation of board level solder joint reliability. It is generally agreed that broader temperature range and higher mean temperature should result in shorter thermal fatigue life. Yet, people have different opinions on the selection of the ramp rate and the dwell time. It was believed that the ramp rate has little influence on the solder joint thermal fatigue life. Emphasis has been put on the design of a suitable dwell time. Therefore, the JEDEC and the IPC standards did not impose strict requirements on the selection of the ramp rate. On the other hand, a certain range of dwell times were recommended. Nevertheless, there were publications showing that the ramp rate may be important and, in some situations, may even overrule the dwell time. This study attempts to investigate in detail the creep damage accumulation inside the solder joint during the ramp time and the dwell time for all practical loading conditions. Based on numerous computational simulation results, the present study reveals that there actually exist two types of creep damage accumulation. One of them corresponds to a ¿mild¿ loading condition where the creep damage is mostly accumulated during the dwell time. Another one corresponds to a ¿severe¿ loading condition in which the ramp time contributes most of the creep damage accumulation.