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Abstract

A method is described for attaching circuit chips to a flexible substrate (laminate) using controlled chip collapse connection technology (C-4). The substrate is 'tinned' with an alloy of eutectic composition in its contact region with the solder balls on the base of the chip. The alloy and the solder are chosen such that they are miscible. The system temperature is raised above the alloy melting point thus causing the alloy and the solder to mix, the mixture composition moving away from the eutectic composition with time and thus raising its melting point. Eventually the mixture melting point is higher than the temperature at which the system is maintained and the mixture solidifies to form a contact. In this way contact between the chip and the flexible substrate can be effected at a temperature below the melting point of the pure solder and lower than one which would result in degradation of the laminate adhesive.

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First Claim