ABSTRACT

A die bonding interface consisting of a plated gold surface and conductive silver paste was investigated using two approaches: One was a computational method for the ideal interaction, while the other was an experimental technique to get some ideas about the actual bonding. A density functional theory (DFT) calculation was employed to clarify the adhesive interface between the Au (1 1 1) surface and bisphenol-A type epoxy resin which included dicyandiamide as a curing agent. The computational results showed that the cyano group involved in the hardener strongly binds to a gold atom on the ideal surface. This interaction is likely to be assigned to σ-donation and π-back donation. The predicted adhesive strength was 1.15 GPa. To evaluate the real adhesion strength, small-sized single lap-shear joints were fabricated and tensile shear tests were performed. The measured adhesive stress was about 27 MPa. The results of surface analytical methods indicated that the actual die pad surface was not smooth. Furthermore, an altered layer terminated with Au(CN)_x was found on the top of the die pad. It was inferred that the mechanism of the actual die bonding interaction would be changed to the formation of hydrogen bonds. This could be a reason why reduced adhesive strength was observed.

摘要

使用两种方法研究了由镀金表面和导电银浆组成的芯片键合界面：一种是理想相互作用的计算方法，另一种是获得有关实际键合的一些想法的实验技术。采用密度泛函理论 (DFT) 计算来阐明 Au (1 1 1) 表面与双酚 A 型环氧树脂之间的粘合界面，其中双氰胺作为固化剂。计算结果表明，硬化剂中的氰基与理想表面上的金原子强烈结合。这种相互作用很可能被分配给 σ 捐赠和 π 回捐赠。预计粘合强度为 1.15 GPa。为了评估真实的粘合强度，制造了小型单搭接剪切接头并进行了拉伸剪切试验。测得的粘合应力约为 27 MPa。表面分析方法的结果表明，实际的芯片焊盘表面并不光滑。此外，以 Au(CN) 终止的改变层_x位于芯片焊盘的顶部。推测实际芯片键合相互作用的机制将转变为氢键的形成。这可能是观察到粘合强度降低的原因。