Interfacial reaction on different solder composition after laser soldering Grenzflächenreaktion auf unterschiedliche Lotzusammensetzungen nach dem Laserstrahllöten

Abstract

This study used electroless nickel-immersion gold surface finish. The lead free solder used are tin-silver-copper 305 and tin-silver-copper 307 solder alloys. The difference in copper composition will affect the intermetallic compound′s microstructure after the laser soldering process. The intermetallic compound formation analysis reveals that only (Cu, Ni)₆Sn₅ was observed at the solder joint interface for both solders after laser soldering. The grain microstructure of tin-silver-copper 305 formed is rounded-shaped and bar-shaped, while tin-silver-copper 307 shapes are oval-shaped and flake-like. However, for cross-sectioned analysis, the intermetallic compound grain microstructure formed at the solder joint formation was (Ni, Cu)₃Sn₄ and (Cu, Ni)₆Sn₅ presented in dendrite-like and scale-like shapes. This result shows that copper content in solder composition is directly affected the intermetallic compound grain microstructure. When exposed to the ageing process, the intermetallic compound thickness will increase directly with ageing time. The intermetallic compound thickness for tin-silver-copper 305 was increased from 0.98 μm to 8.34 μm while tin-silver-copper 307 was increased from 1.54 μm to 8.76 μm. The result also shows that nano-sized of Ag₃Sn grain particle was formed on the intermetallic compound surface after an ageing process for both samples, tin-silver-copper 305 and tin-silver-copper 307.