Advanced module packaging method

An intermediate solution between conventional printed circuit board technology and wafer level packaging, WLP, is to fabricate interconnection circuits and flip chip assembly structures on large glass substrates using LCD manufacturing equipment. Trace widths of 5 microns and a trace pitch of 10 microns are achievable on flexible substrates as large as 1800/spl times/1500 mm. Back planes for displays and keyboards can also utilize thin film transistors, TFTs, as developed for LCDs and enhanced for flexible assemblies (200/spl deg/C processing). A flexible circuit is built on a glass carrier with an intermediate release layer. The carrier is discarded after all processing is complete, including interconnection circuits, IC chip assembly, test and rework. The assembly method uses gold stud bumps on IC chips, and corresponding wells filled with solder on the motherboard 100-micron pad pitch is achievable for IC chips, module cables, and test connections. Avoidance of epoxy under layers contributes to a robust capability for reworking defective IC chips. The methods are applicable to a wide range of products, from cell phones to blade servers.