Characteristics of low temperature cure type NCP flip chip process

초록

As the miniaturization and high-density packaging is the trend in the next generation mobile devices, the more fine pitch interconnection is needed. The flip chip is the most promising technology satisfying the industrial demand. There are several bonding materials used in flip chip package such as solder, ICA(isotropic conductive adhesive), ACA(anisotropic conductive adhesive), NCA(non-conductive adhesive). Among them NCP is a candidate bonding material replacing capillary underfill process due to its cost effect and accessibility to fine pitch interconnection. In this paper, the process characteristics of low temperature cure type NCP flip chip package were investigated. NCPs were formulated with epoxy resin, hardener, latent catalyst and coupling agent for low temperature snap cure. Following plasma treatment of substrate, flip chip bonding was done by using FCB-3 Flip chip bonder. In NCP bonding process, NCP is pre-applied on PCB and then the chip is placed on it. The subsequent thermocompression on the chip results in the bump-to-pad contact and the curing of NCP. A schematic procedure of NCP flip chip bonding process is shown in Fig. 1. Thermal shock and HAST followed by die shear test and 4-point probe resistance measurement were employed to evaluate the reliability of flip chip packages. Process parameters studied were pre-heating temperature, bonding temperature, bonding time and bonding pressure. The void formation, fillet shape, die shear strength and electrical resistance werw evaluated to characteristics of the flip chip joint.