Manufacturing ultra fine line PBGA substrates in a PWB factory

The industry trends for PBGA substrates are smaller and smaller features to support more input/output (I/O) in less space. Packaging technologies such as fine pitch wire bonding and flip chip attach are driving the circuit features to tighter dimensions, both narrower lines and smaller spaces. Many PWB factories are now producing laminate substrates and have exercised more stringent process controls to build finer circuit patterns. Even with the improved process controls, however, the conventional PWB processes and materials cannot achieve the 1 mil lines and 1 mil spaces that are required. Changes in processing and or materials and design are required to make the jump from 3 mil circuit features which are characteristic of leading edge PWB technology to the 1 mil circuit features needed for the newer laminate substrates. 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. In this paper we describe the changes in tooling and in processes that were necessary to move between a conventional PWB facility, which is designed to process 20 in×24 in panels, and a ceramic substrate factory, which is designed to process 3 in×5 in cards. We will 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 will 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