Hot air solder levelling (HASL) process parameters optimization for SN100CL

Abstract

Reliability of electronic packaging has now become the most critical factor in electronic industries. The prediction of solder joint failure and its shelf life becomes more challenging as the increasing demand for superior performance of electronic devices. In electronic packaging, surface finish plays an important role for soldering and assemblies process. This study was made to determine the solderability of SN100CL coating surface and optimized the Hot Air Solder Levelling (HASL) process parameters. This research work was divided into two phases. The first phase is to study the relationship between solderability and the total coating thickness, free solder thickness and interfacial intermetallic compound (IMC). The second phase was the investigation of different composition of Germanium (Ge) in SN100CL solder. Five different composition of Ge used are 0 wt%, 0.002 wt%, 0.006 wt%, 0.010 wt% and 0.020 wt% in Sn-0.7Cu-0.05Ni solder alloy. This research reveals the effect on solderability of SN100CL coating with different Ge compositions. Gen3 wetting balance test method was used to evaluate the solderability. The quality of wetting was evaluated by relative comparison on the wetting time and maximum wetting force exerted on the coated copper surface. It was found that the wetting time was longer and the maximum wetting force was lower with decreasing of free solder thickness layer due to growth of interfacial IMC layer and produced less wettable surface of solder coating. Apart from that, 0.006 wt% of Ge was observed to have the best composition of Ge in SN100CL solder. The results was determined with SN100CL coated surface when introduced to reflowed and aged conditions. The IMC and free solder thickness of 0w wt% and 0.006 wt% was observed under Scanning Electron Microscope (SEM) and the results shows that IMC of 0 wt% Ge growth higher compared to 0.006 wt% of Ge. Sn-0.7Cu-0.05Ni+0.006Ge solder alloy was then deployed in HASL process. The parameter optimization was performed and the good HASL coating was observed under SEM. Overall, the solderability are found to be affected by free solder thickness and 0.006 wt% of Ge shows the best composition in HASL process with 2 seconds and 5 seconds of dwell time and level time respectively.