Manufacturing ultra fine line PBGA substrates in a PWB factory

The IBM interconnect Products printed wiring board factory in Endicott, NY has produced high quality, multi-layer circuit boards for over two decades. In recent years this same factory has also produced PBGA substrates using essentially the same tools and processes that were developed for PWBs. Because of our experience with ceramic substrates and the availability of a manufacturing facility that is capable of circuitizing truly fine features, we decided to launch a development effort to define how to build ultra fine line PBGA substrates for the new market needs. In this paper we describe the changes in tooling and the changes in processes that were necessary to move between a conventional PWB facility, which is designed to process 20"×24" panels, and a ceramic substrate factory, which is designed to process 3"×5" cards. We also describe the processing changes that need to be implemented to circuitize fine line features in foil copper, typical of the PWB facility, rather than thin, sputtered copper which was used in the ceramic substrate factory. In addition we offer bond and assembly results and reliability stressing results that demonstrate that the PBGA substrates that we built in this hybrid factory are both functional and reliable