Behavior of electronically conductive filled adhesive joints under cyclic loading. I. Experimental approach

Electronically conductive adhesives have received a great deal of attention in recent years for interconnection applications. Although they have great potential for being a more efficient and less costly alternative to solder joining in electronic components, there are still a number of problems in the areas of durability and design to meet specific needs. Unfortunately, the usefulness of this technique has been limited due to lack of understanding of environmental effects such as exposure to high moisture and/or temperature during mechanical fatigue loading, as faced in the service environment. Furthermore, the environmental effects mentioned may, themselves be acting in cyclic form. The objective of this paper is to add to the fundamental understanding of fatigue degradation in these joints, and to identify the dominant fatigue mechanisms for different service environment regimes, including cyclic mechanical loading under elevated temperature, and humidity. The scope of this study involves in-depth analysis and assessment of fatigue mechanisms and fatigue modes for a wide variety of parameters, i.e. humidity, temperature, pre-conditioning, stress ratio, and frequency. Failure surfaces are examined to identify degradation mechanisms in the adhesive interlayer by optical and SEM techniques. Measurements and observations are related to damage processes, failure modes, and the results are assessed with respect to the relevance of existing failure theories and criteria. It is expected that much improved fatigue life, fail-safe capability, and reduced manufacturing costs will be realized for electronically conductive adhesives.