Process challenges and solutions for embedding Chip-On-Board into mainstream SMT assembly

The fundamentals of the Chip-On-Board (COB) process imply attaching the chip (die) in place and wire bonding it directly to the substrate metalization alongside other surface mount devices attached by standard SMT processes. In essence, the packaging and testing task transfers from the IC backend process to the SMT board assembly shop. The process significantly improves footprint efficiency, cutting cost and lead-time. COB technology includes variants such as Chip-On-Flex or on other substrates. COB technology is at work in many routine day to day products but process information has remained somewhat limited in the mainstream Surface Mount world possibly because wire bonding has more in common with IC backend processes than traditional surface mount assembly. Merging COB into mainstream surface mount processes has usually entailed acquiring the specialized know-how through considerable ´hands-on´ experimentation. This paper provides the required information on all aspects of the COB process from applications, positioning, costs, die selection, layout, process options, equipment and rework for implementing COB processes into existing SMT lines and manage COB yields. Based on real life examples, the paper covers the key considerations, major critical factors and the challenges for a successful COB-SMT merge.