Interface Stress-Induced Degradation of the Performance of Electrically Conductive Adhesives

Electrically conductive adhesives are of increasing importance as a powerful alternative to eutectic bonding. In the use of electrically conductive adhesives in soldering applications, a lack of conductivity of the adhesive bond between surface mounted devices (SMD) and the printed circuit board was frequently observed. This lack of conductivity caused failure of the unit because of an unacceptable series resistivity in the circuit. A failure analysis proved that the resistance of the contact between the adhesive and device depends on the stress situation in the bonded interface induced by the shrinkage of the adhesive during curing. Under stress, the formation of a resin segregation layer of low conductivity results. The outer shape of the electrical component as well as the SMD assembly process has strong influence on the electrical performance.