Elektrisch leitfähige Klebverbindungen in der Mikroelektronik
The use of adhesives often is indispensable, if dissimilar materials have to be joined. This paper presents the findings of a cooperate project with an adhesive manufacturer and an electronics company on the synthesis and application of electrically conductive adhesives. The adhesives comprised a polymer filled with approx. 80 wt.% metal flakes. The polymers were epoxies, silicones, thermoplasts or blends. As for the flakes Ag, Cu, Pd were utilized. Epoxies, possibly blended with thermoplasts, in conjunction with Ag-flakes turned out to be a good compromise between technical performance and economics. Adhesives could be synthesised having much lower shear moduli (lower stress of joint) and higher shear breaking strain (low failure rate during temperature cycling) than soft solders. Ageing the cured adhesives lead to Ag-diffusion. Different modes of diffusion occured depending on adhesive and climate. Ag-Pd-Flakes exhibited the least diffusion. The morphology of the flakes was investiga ted, a mixture of pellets and spheres yielded a low enough viscosity and a good conductivity. Cu-Flakes were covered with oxide. A lasting removal of the oxide could not be achieved which resulted in a poor conductivity. Electronic components were adhesively joined to boards. Soft solder (SnPb) coatings did not cause problems. The formation of an Agsub3Sn interlayer after temperature ageing, out forward by some, did not occur. We found recristallisations of the SnPb, but no Ag-rich interlayer.