Influence of Si on reactive diffusion between Au and Sn at solid-state temperatures

Influence of Si on the kinetics of the reactive diffusion between Au and Sn was experimentally examined at solid-state temperatures. Binary Sn–Si alloys with Si concentrations of 1 and 3 mass% were used to prepare (Sn–Si)/Au/(Sn–Si) diffusion couples by a diffusion bonding technique. The diffusion couples were isothermally annealed at temperatures of T = 433, 453 and 473 K for various times up to 200 h in an oil bath with silicone oil. After annealing, AuSn4, AuSn2 and AuSn layers were observed at the (Sn–Si)/Au interface in the diffusion couple. The total thickness of the Au–Sn compound layers is expressed as a power function of the annealing time. The exponent of the power function takes values between 0.37 and 0.41. The exponent smaller than 0.5 indicates that grain boundary diffusion as well as volume diffusion contributes to the rate-controlling process of the reactive diffusion and grain growth occurs at certain rates in the compound layers. The higher the Si concentration of the Sn–Si alloy is, the slower the overall growth of the compound layers occurs. This indicates that the addition of Si into the Sn-base solder alloy decelerates growth of the Au–Sn compounds at the interconnection between Au/Ni/Cu multilayer conductor and Sn-base solder alloys during energization heating.