Improvement in bonding strength of Ag sinter joining on gold surface finished substrates by increasing the gold grain size

Realizing silver (Ag) sinter joining on gold surface finished substrates has attracted extensive attention because gold surfaces have superior performance and durability. In this work, the bonding strength was improved by increasing the grain size of gold layer, which was accomplished by preheating gold surface finished substrates or changing thickness of gold layer. With the different processes, the bonding strength of Ag sinter joining can be increased in varying degrees, which ranges from 25 % to 100 %. SEM observation and XRD analysis were conducted to calculate the grain size of gold and clarify the mechanism of improvement in bonding strength. The results indicated that gold layer with the large gold grains shows a better bonding strength than the fine gold grains substrates, which because two different Au-Ag diffusion patterns happened on gold surface finished substrates. A possible equation that indicates the relationship between the bonding strength and the gold grain size was also proposed in this work.