Single point ILB at narrow pitch

The size of VLSI components is increasing every year, following the improvements made by the silicon technology. The gang bonding TAB technology, usually applied at ILB (Inner Lead Bonding) assembly step, shows limitations when integrated circuits size becomes larger than 10-12 mm. The problem comes from the difficulty of obtaining coplanarity between bonding tool and the set of bumps and leads at the bonding temperature. This requirement is mandatory, in order to obtain at each bonding site, an equal amount of pressure and temperature necessary to obtain a reliable joint. During the last ten years, wire bonding equipments have been improved dramatically and have been in the mean time adapted to TAB bonding (sequential). With single point bonding, the bonding time increases compared to gang bonding, but this is partially compensated by the ease of controlling local bonding conditions. Single point ILB also allows a reduction in the constraint on bump thickness tolerance, since each pad is treated separately; it even allows the nominal thickness, which is 20-25 μm for normal gang bonding operation, to be reduced down to a couple of micrometers. Constraints on copper and gold hardnesses are different in single point bonding compared to gang bonding and are described in this paper. Single point ILB has been demonstrated down to 75 μm pitch, and reliability data show an excellent stability of joint integrity. This technology is already applied industrially and may become an alternative technology for gang bonding when dealing with large size components