Comparative Study on the Bonding Property of Laser and Reflow Soldered Sn-37Pb/Ni-P Micro-Joints after Isothermal Aging and Multiple Reflow

Laser soldering is becoming increasingly popular in microbumps joint due to its noncontact and confined heat, rapid joining time, and straightforward mechanization. This study examines the internal structure and fracture features of Sn-37Pb/Ni-P microbumps fabricated by laser soldering and reflow soldering techniques. This study examines the impact of isothermal ageing and periodic reflowing on the microbumps. The experimental results showed that laser soldering of microbumps produced a fine, loose (Cu, Ni)₆Sn₅ intermetallic compound (IMC), whereas reflow soldering of microbumps resulted in the creation of a small plane-like, lumpy (Cu, Ni)₆Sn₅ IMC. The (Cu, Ni)₆Sn₅ particles underwent isothermal ageing at a temperature of 150 °C, resulting in a transformation of their structure into a scallop shape with a notable aspect ratio. These particles were soldered using a laser in microbumps. In contrast, in microbumps that were soldered using reflow soldering, the particles developed into irregular lumps. The thickness of the IMC in microbumps increased in a parabolic manner as the ageing time increased. Nevertheless, the IMC thickness in laser-soldered microbumps was consistently significantly smaller than that in reflow-soldered microbumps. The breaking point of both connected procedures had a significant decline after 100 hours of ageing, and subsequently maintained a similar level as the ageing time increased to 400 hours. Throughout the process involving several reflows, the morphology of (Cu, Ni)₆Sn₅ particles in both laser soldered and reflow soldered microbumps grow into large irregular lumps, and the IMC thick of laser soldered microbumps grows sharply after one time reflowing, then grow over time within both scenarios. The breaking strength of both soldered procedures for microbumps reduced slightly as the reflowing times increased. Hence, laser soldering proves to be efficient in lowering the thickness of IMCs and maintaining the structural strength of microbumps even after undergoing isothermal ageing and numerous reflow operations, comparable to traditional reflow soldering.