Impact of Current induced Joule heating variation on long-term Low melting temperature solder joint stability

Although the thermo-mechanical reliability performance of low melting temperature solder material shows stable performance levels, it is reported that the solder interconnects under higher level of current can cause Bi segregation and degradation in electrical and mechanical stability. Combined with the lower solidus and liquidus temperature, the Joule heating-induced temperature rise at given current density is important to assure the long-term reliability of the solder interconnect. In this study, the solder interconnect Joule heating and its impact on the temperature rise associated with PCB design configuration are identified. The results show that the test board Cu trace and via structure affects the Joule heating-induced temperature rise of the solder joint per given solder alloy configuration. The test set-up enabled the accurate measurement per solder joint via using the temperature coefficient of resistance (TCR), to accurately and directly measure the Joule heating-induced temperature increase per current density condition. Various PCB structure configurations are used in this study utilizing a test PCB with and without VIPPO configuration, representing various thermal dissipation conditions. 300µm solder joints with SAC305, Sn-Bi system low melting temperature solder hybrid (Hybrid LTS), and near eutectic Sn-Bi system low melting temperature solder joints (Full LTS) are current stressed in a range of 0-5000 A/cm
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in various PCB test structures, which generate different Joule heating-induced temperature increased joint conditions. The results demonstrates that the solder joint with same solder alloy composition and same level of current density show different Joule heating induced temperature increase per PCB configurations. Also, results identifies that the Cu trace at certain current density level needs consideration due to the role of heat sources. The findings presented here indicates that the solder interconnect joule heating needs to be carefully measured to accurately estimate the long-term reliability of the solder joint.