Epoxy/silane pre-synthesis improving thermal properties and adhesion strength of silica-filled non-conductive adhesive for fine-pitch thermocompression bonding

Abstract

We modified an epoxy with silane to improve the bondability and thermal properties of a non-conductive adhesive (NCA) for fine-pitch thermocompression (TC) bonding. The main objectives of this modification were to improve the silica dispersion in the NCA and its wettability to achieve a low coefficient of thermal expansion (CTE) without any filler entrapment and a robust bonding joint. A commercial diglycidyl ether of a bisphenol A and F mixture resin and 3-glycidyloxypropyl trimethoxysilane were synthesized at 250 degrees C for 2 h. An anhydride (hardener) and an imidazole (catalyst) were used as the NCA curing system. The CTE of the silane-modified NCA was 29.1 ppm/ degrees C, which was lower than that of a neat epoxy NCA (42.6 ppm/ degrees C), and was the result of uniform silica dispersion in the NCA matrix. The shear strength of the TC bonded joint was also improved from 31.8 MPa to 46.5 MPa (1.45 times higher) after the epoxy silane modification due to the improved wettability of the epoxy resin. Void formation in the cured NCA layer and silica filler entrapment at the Cu/Sn interface were also suppressed. Thus, this epoxy silane modification produced a robust and thermally reliable NCA material for fine-pitch interconnections.