A reliability study of adhesion mechanism between liquid crystal polymer and silicone adhesive

Abstract

Liquid crystal polymer (LCP) and silicone adhesives are widely used in electronics manufacturing. The integrity of the adhesion between the two materials is crucial to the reliability of electronic products, however, the adhesion mechanism and associated reliability has not been thoroughly understood. In this paper, the adhesion mechanism between a commonly used LCP and a silicone adhesive is evaluated by employing the 85°C/85% RH temperature humidity test, autoclave test, boiling water test (BWT), and dry air reflow aging test. The effects of different plasma treatments of the LCP surface are evaluated by the surface analysis methods, namely XPS and FTIR–ATR spectroscopy, as well as the surface roughness and energy measurements. Moreover, the adhesion strength between the LCP and silicone adhesive is measured by a shear strength tester. The shear strength testing process is simulated by the finite element method for a better understanding of the failure mechanism. The experimental results indicate that the adhesion between the LCP and silicone adhesive is based solely on the hydrogen bonds. It is found that the humidity significantly weakens the adhesion strength between the LCP and silicone adhesive. This is related to the breakdown of hydrogen bonds when water molecules are introduced to the system. Furthermore, the reflow test shows that the weakened adhesion strength can be recovered by removing the moisture from the interface.