Identification of process variables affecting the quality of fine pitch high performance ASIC substrates

The HyperBGA® semiconductor package is a PTFE based organic flip chip designed to meet the needs of high performance applications. It combines outstanding overall reliability with higher electrical performance to distinguish itself from wirebond applications, build-up technology, and ceramic alternatives. Signal layers are personalized with high wiring density and wire width ranging from 20 to 33 microns. At this time only a liquid photolithographic process can be used to resolve these ultradense fine lines and spaces while also achieving very tight impedance control. Yields thru automated optical test (AOI) test are mostly impacted by non-repairable defects as circuit opens, neckdowns and dishdowns type defects. To improve on existing yield targets, the entire photolithographic process was considered, examined and variables investigated. Higher yielding processes are absolutely critical for next generation design points. In this article, the photo process and operative variables are discussed with regard to their impact on fine line quality, yields and high reliability of the product in the field.