Collective screen printing for carrier bump and SMT pads

Bare chip attach on organic carriers is one of the solutions of high density assembly. IBM developed SLC/FCA (Surface Laminar Circuit/Flip Chip Attach) technology with solder bump joints. This technology has been applied to PCMCIA cards and a graphic acceleration card. This report describes the development of a collective solder apply method to carrier bump and SMT pads using solder paste. In this study, the viscosity and the powder distribution of the solder paste were optimized for higher printability against 254 μm pitch pattern. Controlling the solder amount, the thickness and the aperture size of a stencil were studied, and their relation was introduced. The tolerable displacement of the printed pattern against bump pads was also evaluated. Based on these studies, the collective screen printing method was applied to the double sided cards which had bare chips and SMT components