Photothermal effects on low-temperature hybrid solder joints and its superior drop reliability

Abstract

Hybrid solder joints incorporating the Sn-3.0Ag-0.5Cu/Sn–58Bi structure have been studied to tackle challenges such as warpage, thermal degradation, and excessive intermetallic compound (IMC) growth in heterogeneous integrated packages. However, the presence of Bi diminishes drop impact reliability, and conventional reflow processes aimed at increasing the Bi mixing ratio exacerbate IMC growth. This study investigates the feasibility of intense pulsed light (IPL) soldering for hybrid solder joints on electroless nickel immersion gold (ENIG) and (electroless nickel electroless palladium immersion gold (ENEPIG) PCB substrates, with the goal of advancing reliable and sustainable electronic packaging technology. Microstructural evolution and drop impact reliability of IPL-soldered joints were compared with those of conventionally reflow-soldered joints. Specifically, IPL soldering exhibited approximately sixfold higher drop impact reliability in ENIG and threefold in ENEPIG compared to reflow soldering under the lowest temperature conditions. This underscores IPL's effectiveness in suppressing interfacial reactions, thereby promoting crack propagation in the SnBi phases. Furthermore, under optimized IPL conditions on the ENEPIG substrate, drop reliability was approximately threefold higher than that achieved under the lowest temperature conditions, despite lower power consumption of 13.36 kWh. These findings demonstrate the potential feasibility of IPL soldering as a reliable and sustainable technology for electronic packages.