IMC Growth and Microstructure Evolution of Co13%P/SAC/Co-13%P Solder Joint under Thermal-Electrical Coupling Fields

The high-density integration of electronic devices poses a significant challenge to the miniaturization of solder joints in microelectronic packaging, and the volume ratio of IMC in solder joints gradually increases, especially because the solder joints are subjected to severe current density and Joule heat during service, and it is especially important to study the microstructure changes of IMC by thermoelectric coupling conditions. In this study, we examine the growth behavior of IMCs at the Co-P UBM solder joints interface with mixed nano/amorphous structure. The applied conditions involve a temperature gradient of 1087°C/cm and a current density of 1.5×10
⁴
/cm
²
. Our findings reveal that under an isotropic coupling field, there is a distinct polar effect on the growth of IMC. The average thickness of the cold end (anode) IMC increased from 4.7 μm to 6.5 μm, while the average thickness of the hot-end (cathode) IMC decreased from 5.1 μm to 2.6 μm under the isotropic coupling field, both (Cu,Co)
6
Sn
5
and (Co,Cu)Sn
3
exhibit growth dependence, and the IMC was relatively dense and flat. In contrast, when subjected to a reverse coupling field, Co-Sn-P spalling occurs, and there is little change in IMC thickness due to the reverse thermoelectric stress, which weakens the coupling stress and reduces the migration rate of the atoms.