A Study of Adhesion Interface about Die Bonding Structure with Conductive Silver Paste

In the electronic packages, gold surfaces are useful for stable connections. In this paper, adhesion interface for die bonding structure with conductive silver paste is investigated. The adhesive interface between gold surface and epoxy resin is investigated in two approaches. The first-principles calculations are employed to optimize the structure and calculate the theoretical bonding strength. The fragment model is constructed for bisphenol-A type epoxy resin and a curing agent which includes dicyandiamide. The results show that a cyano group included in the hardener greatly interacts with ideal gold surface, whereas a hydroxyl group seems not to interact with them regardless of high polarity. This interaction is likely to come from the $\pi$-back donation. The predicted bonding strength is as high as 1.15GPa. Next, the actual die pad surfaces prepared with plating gold are characterized to presume the substantial bonding structure by analytical method. Besides, measurements of adhesive strength have been performed by using small size lap shear tests under various temperatures. These results show that there are altered layers at the top of plating gold, which seems to affect the interaction mechanisms to hydrogen bond and make the adhesive strength lower.