Flip-chip mounting technology has been developed using the Stud-Bump Bonding (SBB) method which directly mounts a bare LSI chip on the circuit board. This method uses 2-stage shaped projection electrodes and conductive adhesive, making possible fine connection at less than 100μm pitch. For securing reliability of the mounting, it is important to optimize the conductive adhesive and under-fill material. For this purpose, a high-molecular-weight thermoplastic resin with flexibility over a wide temperature range, and a conductive adhesive using conductive filler have been developed. Also, under-fill material has been developed using a filler with optimized grain-size distribution and a resin material with low-viscosity, high-adhesive-strength and low-moisture-absorption. Thereby the connection between the LSI chip and circuit board is stabilized. Thus. LSI chips can be mounted with high reliability on various kinds of circuit boards, such as glass, ceramic and glass-epoxy, making possible application to MCM, CSP, etc.
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