Effect of co on the morphology and mechanical properties of the Sn-3.0Ag-0.5Cu/Sn-58Bi composite solder joints on ENEPIG surface

Microelectronic devices have demonstrated advanced capabilities, including multifunctionality and high inputoutput density, rendering them widely used in significant fields such as big data, data centers, and supercomputing. The reliability of microelectronics packages is contingent on the integrity of welded joints under diverse operating conditions for these applications. This research aims to examine the effects of 0.5 wt% Co element on the microstructure and properties of Sn-3.0Ag-0.5Cu/Sn-58Bi composite solder joints fabricated on the ENEPIG pads. The solder joints were exposed to a peak temperature of 220(degrees)C and maintained at this level for different periods of time. The research included conducting a comparative examination on samples with and without additional Co to investigate the influence of Co inside solder joints on their microstructure and mechanical properties. The results show that the IMC changed from needle rod (Cu, Ni, Pd)(6)Sn-5 to granular (Cu, Ni, Co, Pd)(6)Sn-5 with the increase of holding time. The IMC at the solder joint interface added by Co changes from (Cu, Ni, Co, Pd)(6)Sn5 to (Ni, Cu, Co, Pd)(3)Sn-4. The added Co element mainly exists in the form of a solid solution inside the solder joint, resulting in enhanced hardness of the Sn and Bi phases in the solder joint and a reduction in modulus.