Challenges and Limitations of Subtractive Processing in PWB and Substrate Fabrication

This paper examines the limitations of subtractive processes. Conventional process sequences such as pint & etch, pattern plating, panel plate/tent & etch, and semi-additive processing (SAP) are briefly reviewed to emphasize the commonality of resolution limitation due to lateral etching. While semi-additive processing is still the technology of choice for fine line substrates, it too may find its limit in the inherent limitations of isotropic etching. Process improvements are reviewed which address etching problems. Several damascene-like processes are reviewed that show promise to provide finer lines and spaces than the semi-additive process can achieve.