Corrosion effects and reliability improvement of silver wire bonded contacts in automotive application

Silver (Ag) bonding wires are mainly used in consumer products as a reliable low-cost alternative to gold (Au) bonding wires. In automotive applications, the materials are exposed to particularly harsh environmental conditions. In order to understand the influence of these conditions in the electronic package on the silver-aluminum material system, we carried out extensive studies. 4N Ag wire, Pd alloyed Ag wire and a new Ag wire with innovative additives (GX2s) were encapsulated after wire bonding on Al chip metallization in a package with a chloride and sulfur-containing molding compound and subjected to corresponding reliability tests. Then, the material behavior of the different silver wires was compared to Au wire bonds after high temperature storage life test (HTSL) and unbiased highly accelerated stress test (uHAST). After broad ion beam cross sectioning the samples were investigated subsequently by Scanning Electron Microscopy (SEM). Additionally, high resolution transmission electron microscopy (TEM) investigations with nano-spot element analyses (EDS) and electron beam diffraction were done to characterize the intermetallic compounds formed and to specify the running corrosion mechanism in correlation to the alloying elements/additives used. The results show that similar degradation mechanisms take place in the Ag-Al system compared to the Au-Al system. Both material combinations show corrosion effects after testing. However, the reliability behavior of the Ag wires can be significantly optimized by adding alloying elements such as palladium or other innovative additives. Thus, the reliability behavior of electronic assemblies can be optimized even under low-cost conditions.