Abstract
Flip chip technology has been adopted for high-density packaging due to its excellent electrical performance and better heat dissipation ability. As the required performance in microelectronic density becomes higher, the current that each bump needs to carry has reached 0.2A or higher ones in the future. Moreover, electromigration, thermalmigration, and diffusion effect be formed on the solder joint in packaging when under high current stressing. These effects will cause electronic devices to occur reliable problems. At present, almost researches focus on electromigration effect influence on aluminum, copper trace and solder joints in packaging, especially in current crowding and crack formation in solder joint. Because of temperature measuring limitation, only few researches focus on thermal characteristic in solder joint in Flip-Chip during current stressing. For this study, thermal infrared microscopy (Infrascope) was especially used to measure the temperature distribution inside the solder bump and aluminum trace at various stressing conditions. It also can help us to find some of thermal characteristics in the solder joint, such as temperature increasing and temperature gradient. Based on the experimental data, we also constructed a electric-thermal finite element model (FEA) to simulate the temperature distribution inside the solder bump during current stressing. After verification, only less than 1 % error is achieved between simulation data and experiment results. Then, many kinds of models were built up, which were used to predict different parameters influence on thermal characteristic in Flip-Chip packaging under high current stressing. Moreover, FEA model also helps us solve measuring limitation and save much time. Results of this study show that temperature increase and temperature gradient inside the solder bump were increased by the raised applied current in destructiveness model in temperature measuring. Besides, in the 85% remaining solder bump, temperature increase inside the solder bump was as high as 55.9°C and the temperature gradient reached to 333°C/cm under stressed by 0.43A. In another kind of non- destructiveness device, the measuring results showed that aluminum trace was the main heat generator in packaging. The measuring temperature around the corner of aluminum trace was as high as 134°C and the aluminum pad above the solder bump was only 105°C when it was stressed by 0.59A. Besides, it also showed that temperature gradient between the extending aluminum trace and pad reached to 1,960°C/cm. So, it means that temperature around this joint changed greatly and it could form a hot spot here. Another topic of this study, the FEA model was used to simulate and analyze different UBM resistivity and trace material influence on thermal characteristics in packaging. Although it showed that average temperature of solder bump was increased when UBM resistivity was enlarged, the temperature gradient of trace was decreased and the vertical temperature gradient of far away trace was raised. Therefore, it means that heat spread inside the solder bump and the hot spot effect could improve. When aluminum trace was replaced by copper trace in the packaging, the simulation results showed temperature increase and temperature gradient in the solder bump were decreased greatly, besides their maximum drop were 10°C and 651.4°C/cm, respectively. As a result, this phenomenon was caused by the copper trace, which was lower resistivity and higher thermal conductivity. Hence, it is a good way to slow down packaging to occur reliable problem. Finally, these ways of temperature measuring and simulation models will play an important role in packaging industry in the future.