Characterisation of Anisotropic Conductive Adhesive Compression During the Assembly Process

Models of the anisotropic conductive adhesive assembly process have previously been developed. Such models may be used to predict the time for adhesive resin flow out and whether this can be successfully achieved before resin cure. Modelling has also been used to provide significant insights into the effects of component and substrate bond pad geometry on the resin flow distribution and hence on the resulting conductive particle distribution. These models have however only been experimentally validated to a very limited extent. This paper will describe a new experimental technique, which has been developed to allow continuous monitoring of the adhesive thickness throughout the compression process. This technique applies a controlled assembly force through a linear “voice coil” type actuator and the resulting changes in capacitance of the adhesive material can be used to monitor its thickness. The data from tests using this technique show, for example, the effect of the conductor particle stiffness on the rate of adhesive compression during the later stages of the compression process. Such data will be used to further improve more sophisticated models of the ACA assembly process, which will both lead to a better understanding of the process and also facilitate establishment of design rules for different applications.