Fine pitch copper wire bonding on copper bond pad process optimization

In power and automotive IC assembly, non-fine pitch copper wire bonding on aluminum bond pads using 1.5 mil and 2 mil wire diameter process for mass production mode was demonstrated decades ago. In recent months, a great deal of interest from various new package research an development groups from the semiconductor industry have included in their future roadmaps the development of a new copper wire bonding process for fine pitch applications. The advantages of copper wire over gold wire: 1. Higher electrical and thermal conductivity. Higher clock rates and improved thermal management of high-end ICs are possible. 2. Monometallic nature of copper wire to copper wafer metallization offers increased lifespan at higher ambient temperatures. 3. Higher Young's modulus reduces wire sagging and mold sweep. 4. Lower material costs. The bond pad cleanliness and oxidation levels are important for the ball bond (first bond). By applying an organic coating layer it is possible to protect the copper bond pad from-oxidation. Copper wire in an unopened sealed spool already has a thin layer of copper oxide on the surface and does not readily weld (stitch bond) to silver spot plated lead frames and BGA substrates with Au metallization. The intent of this study is to establish the effects of the process parameters for a wire bond process with copper wire with an initial bond pad of 70 mum. The copper ball bond on copper bond pad and copper wire stitch bond on silver spot plated lead frame and BGA substrate as well the materials were studied.