New flip chip attach technology for fine pitch interconnections using electroplated copper bumps formed on a substrate

We have developed a new FCA (flip chip attach) technology based on a new concept. Bump formation is very important in FCA technology. In conventional FCA technology, bumps are formed on bare chips, and an additional process to LSI manufacturing processes is required for bump formation on the wafer to complete the semiconductor device functional circuits. However, bumps in the new technology are formed on the PWB. Consequently, it is possible to use bare chips supplied by any semiconductor device maker. We have developed two kinds of bump formation technologies based on a newly developed concept. The first is a method using silver paste bumps produced by thick film printing technology (presented at 1996 IMC), and the second is a method using electroplated copper bumps for fine pitch interconnections. In this process, copper bumps are formed on PWB electrode pads by electroplating. Then, underfill resin is dispensed to the bare chip assembly area of the PWB. After bare chip I/O pads are positioned on the bumps, the bare chip is pressed and heated. The underfill resin is then rapidly hardened to retain the bump interconnections between the PWB pads and the bare chip I/O pads. This FCA technology can supply a very simple process and structure. We examined the reliability of this FCA technology by temperature cycling and temperature humidity tests. This FCA technology is very useful for realization of a high density module with fine pitch I/O devices with I/O pitch under 200 /spl mu/m.