Effect of autoclave test on anisotropic conductive joints

Abstract

This paper reports that the stress-corrosion cracking induced by autoclave test condition reduces the mechanical strength of anisotropic conductive joints and also increases the contact resistance by allowing more moisture to reach the aluminium metallization. The use of anisotropic conductive joints with bumpless chips allows a reduction in the costs of the flip chip bonding process. The epoxy-based anisotropic conductive adhesive film (ACF) absorbs moisture and experiences hygroscopic swelling, hence degrading adhesion strength and elasticity in hazardous environments, e.g. if moisture at high vapour pressure, and test temperature near to its glassy temperature ( T g) are applied. Contact resistances also show an increasing trend that is similar to that typical of a corrosion process. It is most probably due to the formation of an oxidation layer on top of the aluminium metallization and to the hygroscopic swelling of the ACF. The elastic properties of ACF joints reduce by about 50% after 384 h test time. In this study, 336 h of autoclave test is the critical test duration to affect the electrical and mechanical properties of an ACF joint.