Surface Mount International Conference Proceedings


Author: Hahn Jong Hsiung
Company: Gintic Inst. of Mnfctr Tech.
Date Published: 8/23/1998   Conference: Surface Mount International

Abstract: Chip-on-board (COB) is a direct chip attach technology which combines first and second level packaging. Most of the COB modules manufactured today contain only one chip, which is attached on the substrate and covered by an encapsulant. Two outstanding issues for this type of structure are heat dissipation for high power chips and how to make high density multi-chip COB with a limited footprint. This study addresses these two issues to broaden the applications of COB. Multi-chip COB modules with metal heat sink attachment were made. Silicon chips were attached on a metal heat sink and the assembly was attached to a PWB substrate which had an opening over the die attachment area. Wire bonds were used to connect bond pads on the dice and substrate. Interconnections among chips in the same module were made by die-to-die wire bonding. In each COB module, one thermal die was included for thermal resistance measurement. A daisy-chained loop consisting of wire bonds which connects bond pads on the dice and substrate is for reliability evaluation of the module. COB modules with different sizes of metal heat sink plates were assembled. Junction to ambient thermal resistance (RJA) data were measured to optimize the heat sink size requirement. Key words : chip on board, thermal resistance, heat sink, die-to-die wire bonding

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