Effect of Film Construction on Melting Point and Adhesion Strength of Sn-Au-Bi Multilayered Lead-Free Solder

Following lead regulation in recent years, the application of lead-free solder is necessary in the field of multilayered thin-film solder on AlN heat-sink for Laser Diode (LD) mounting. In present study, the melting point of solder and the adhesion strength with LD have been investigated in regarded to the film construction for Sn-10 mass%Au, Ag, and Bi multi-layers. The melting point of multilayered thin-film solder is varied depending on the sequence of the layers. The lowest melting point (453.5 K) was observed, in the case of film construction evaporated Bi layer between Ag layers. The adhesion strength was decreased, as the surface roughness (Ra and Rmax) of the film surface increased. This observation was explained by change of contact state, the contacting area of solder and LD has decreased when the surface roughness increased. We have found that it is necessary to design the film construction that surface roughness of solder could decrease for good LD mounting.