Replace ball attach by developing substrate solder bumping for 0.5mm pitch FBGA

As the solder ball pitch of BGA packages decreases to 0.5mm↓, the conventional solder ball attach process runs into the bottle neck. The capability limit of S/B/A equipment being widely used now is attaching 0.5 mm pitch - 0.3 mm solder ball. It needs to upgrade the equipments and purchase new flux & attach tools to meet the ultra fine pitch process demand, which would require much investment. Thus research on cost-effective solutions is deserved. This paper discusses the substrate solder bumping technology by solder paste screen printing, to offer an economical approach for pitch 0.5mm↓ soldering interconnection. The 0.4mm pitch - 0.2mm pad open FBGA component with 172 I/O count is adopted as the target device. Bumping is conducted on one strip of molded substrate with 96 components. Strip warpage resistant, bump dimension and coplanarity control, bridging issue resolving and yield assurance are all challenges for the solder bumping process development. Finally this process is setup. Good process capability could be assured to get bumps with 200 μm size, 130 μm height and 30 μm cop. Theses bumps could fulfill interconnection demand. And so solder bumping is approved to be a feasible solution to replace solder ball attach for ultra fine pitch usage.