Investigation of adhesive bonding on non-noble metal in Electronic Packaging

Electrical conductive bonding for certain application is more and more an interesting alternative to soldering in Electronic Packaging. Noble surfaces like gold, silver, palladium and silver-filled polymer-based adhesives are state of the art in such bonding. The usage of electrical conductive adhesives on non-noble metals such as tin is problematical. Even though the usage is given by physical principles such as laws of electro-chemical potential series, a number of studies in the literature describe issues related to electrical conductive bonding on non-noble metal surfaces. Electrical conductive adhesive bonding show a degradation in terms of mechanical strength and electrical conductivity after aging processes. There doesn´t exist a complete understanding of the mechanisms behind this phenomenon until now. Different theories and a lot of investigations in practice are presented in the literature. At first this document presents a literature review regarding conductive adhesive and connecting surfaces on non-noble metal. At second the own investigations are presented. In this work electrical conductive adhesives are applied by dispensing on structured metal surfaces, tin compared to gold in this case. It is used to be silver filled conductive adhesives based on acrylic and epoxy resin. The test boards are hardened and then subjected to various types of accelerated aging. Subsequently, the samples will be tested on the electrical properties and shear strength. The XPS-analysis (x-ray photoelectron spectroscopy) and EDX-analysis (energy dispersive X-ray spectroscopy and SEM-images are carried out on metallographic cross sections. The focus of this study is to analyze the interface and the underlying degradation mechanisms in the interface by accelerated aging.