Development of Anhydride-based NCFs for Cu/Sn-Ag Eutectic Bonding and Process Optimization for Fine Pitch TSV Chip Stacking

Methyl tetrahydrophthalic anhydride (MeTHPA), and Methyl hexahydrophthalic anhydride (MeHHPA) were added as curing agent for bisphenol A/phenoxy resin-based non-conductive film (NCF). Only NCF with MeTHPA showed thermal stability and void-less interface at 250 degrees C, and addition of 0.5 wt% of latent curing accelerator showed minimum NCF cure at pre-bonding stage (120 degrees C) and full NCF cure after main-bonding stage (250 degrees C). The formulated NCF were applied to TSV chip on substrate bonding with Cu/Sn-Ag double bump to Cu pad joint structure. Film thickness and bonding pressure were optimized at 15 mu m and 2.4 MPa to form state-of-art joint structure with optimal fillet shape. The joint structures were observed to be stable even after three reliability tests: high temperature storage test (HTST) of 200 hours, pressure cooker test (PCT) of 24 hours, and thermal cycle (T/C) of 200 cycles. Anhydride-based NCF showed stable joints due to flux-ability of anhydride; however, conventional dicyan diamide (DICY) based NCF showed broken joints after T/C due to lack of flux-ability.