Degradation of flip-chip-on-glass interconnection with ACF under high humidity and thermal aging

摘要

In the LCD industry, anisotropic conductive adhesive film (ACF) has been widely used as a medium for fine pitch interconnection. The electrical and mechanical properties of adhesives play an important role in the reliability of the assembly. This paper presents a reliability assessment of adhesive joints using chip-on-glass (COG) technology which was conducted by testing such samples at various aging temperatures and at high humidity. The range of aging temperatures took into account the glass transition temperature (Tg) of the adhesive films. The effects of high temperature and high humidity on the bond strength of flip-chip-on-glass joints were evaluated by shear testing as well as by microstructural examination. It was found that aging generally caused a decrease in shear strength while the aging temperature was below the glass transition temperature of ACF. This might well be due to thermal degradation of the cross-links. When the aging temperature was slightly above the Tg of the ACF, a significant decrease in shear strength was observed. In particular, the high aging temperature might have caused the formation of covalent crosslinks between adjacent molecular chains, leading to lower strength in the ACF. Moreover, results from scanning electronic microscopy revealed the presence of some voids near the component bumps which are possibly due to the thermal expansion mismatch between materials, resulting in high stresses at the high aging temperature. DSC results showed that the ACF was not fully cured. As a result, the ACF underwent moisture absorption more seriously than a fully cured ACF, leading to its joint degradation.