Homogeneity of joints made of electrically conductive adhesive

Reliability of conductive joints manufactured using electrically conductive adhesives (ECAs) depends mainly on their internal homogeneity. During tests of the reliability of ECAs, a significant incidence of internal inhomogeneities was observed in the joints made by one and two-component adhesives. The reason for the formation of bubbles in the ECAs joints are manufacturer recommended procedures used prior to the preparation of adhesives, processes for deposition of adhesive and the curing process of adhesive. This article presents the results of experiments aimed at research on the causes and consequences of inhomogeneity of ECA joints, and specification of procedures to minimize them. Tested samples were created by one-component (AX 20) and two-component (AX 12 LVT) adhesive, where on the two-component adhesive was studied also the influence of date of the expiration. Homogeneity of the joints was studied both by optical analysis of thin sections and by measuring the shear strength. Test results show that the inhomogeneity is greatest in one-component adhesive. Due to changes in viscosity during the curing process, the one-component adhesive gets under the mounting component. In extreme case this can cause even a short circuit. A similar phenomenon also occurs in two-component adhesives, though on a smaller scale.