Author: Yasuhisa Kaga Company: The Furukawa Electric Co. Date Published: 8/23/1998
Surface Mount International
Abstract: In responding to demands for smaller and more powerful electronic devices, flip chip on board (FCOB) surface mount technology is developed and gradually entered the micro interconnect market.[ l] To successfully apply FCOB, choosing adequate wafer bumping methods, including flip chip (FC) under bump metal (UBM) formation and solder bumping, are critical. Conventionally, wafer bumping were implemented through sputtering, vapor deposition or electroplating, resulting in complex processes and high bump formation cost. In this study, authors are presenting an alternative wafer bumping technology: SuperSolder bumping using electroless plated Ni/Au UBM. This development is based on following concepts: simplified manufacturing processes - maskless bumping, low cost and providing reliable FCOB assemblies. To assure sufficient yield and solder bump height, the Solder Surrounded Stud (S3) bump has been developed based on specifications of Ni/Au UBM. This new wafer bumping method combines low cost with very high productivity, and the resulting S3 bumps offer excellent adhesion to Ni/Au UBM, assuring a high-quality solder composition.