Environmentally sound CSP using wire separation technology

This paper describes the study result concerning the influence of heating after wire bonding on the separability of wires for introducing the wire separation technology into the process. This paper also introduces a new CSP (Chip Size Package) manufactured by way of trial by using the separation technology. We examined the separability of gold wires bonded to silver plating on a thin plate of copper alloy. As a result, we found that the bonding temperature should be kept as low as possible to separate wires in close proximity to the contact interface, that the heat processing after mire bonding increased the adhesion and acted to impede separation, and that the silver concentration on the exposed wire surface was lower in this separation method than in the separation method in which the substrate is dissolved by etching. The conclusion from the above results is that the best procedure in CSP assembly is to peel the substrate immediately after molding and to perform post-cure after that. The trial model of the CSP introduced in this paper contains no interposer in its package and has an environmentally sound structure consisting of very small amount of materials. Gold ball bumps are arranged in narrow pitches and they are connected to the wires directly. The bump pitch can be reduced to the level of the wire bonding pitch.