Thermal stability of self-assembled monolayers for epoxy control in optoelectronic assembly

Given the current trend towards further miniaturization in the optoelectronics assembly, the controllability of epoxy behaviour (i.e. joint fillet) on the substrate to which the epoxy-based adhesives are used to bond the optical component onto the substrate becomes important to allow the reduction of the optoelectronic modules with high packing density. In this paper, the self-assembly monolayer (SAM) with a multi-stage coating method was generated successfully on the hybrid Au/AlN substrate surface. The thermal stability and the epoxy bleed testing of two different SAMs systems, CH3(CH2)17SH + CF3(CF2)16COOH and CF3(CF2)7CH2CH2SH + CF3(CF2)16COOH was measured and compared in order to understand the temperature tolerance of such system and therefore the effectiveness of reducing the bleeding in the subsequent assembly process, e.g. the soldering process. The results suggested that CF3(CF2)7CH2CH2SH + CF3(CF2)16COOH exhibited higher thermal resistance than that of CH3(CH2)17SH + CF3(CF2)16COOH. By analysing the polar and dispersive components of the surface free energy, a quantified guideline was suggested to be used during assembly process to verify the possible bleeding issue.