Abstract
Thermal gradient phenomena in SnAg 3.5 solder joints under high current density operating were both acquired from whole device simulation and observed from experiments. A series of structural solder bump models were created and simulated by finite element software under different current density. The thermal gradient and temperature increasing were investigated under current stressing of 10 3 A/cm 2 to 10 4 A/cm 2 at 70°C by infrared microscopy. The magnitude of the thermal gradient is increased by increasing the applied current. The measured temperature increase due to Joule heating is as high as 55.9°C, and the thermal gradient reached 333°C/cm when stressed by 10 4 A/cm 2 , yet only 8.3°C temperature increased and the thermal gradient reached 83°C/cm when stressed by 10 3 A/cm 2 . The temperature increasing in this model is 53.1°C and thermal gradient in the solder is 168°C/cm under 10 4 A/cm 2 current stressing, yet only 10.4°C temperature increased and thermal gradient decreased to 35°C/cm under 10 3 A/cm 2 . After verification, only less than 0.5% error is achieved between simulation results and experiment results. It proves this built model can be used to project thermal characteristic of different module designs. Copyright © 2005 by ASME.