Laser Ablation of Thin Films on Low Temperature Cofired Ceramic

Abstract

Direct digital manufacturing techniques such as laser ablation are proposed for the fabrication of lower cost, miniaturized, and lightweight integrated assemblies with high performance requirements. This paper investigates the laser ablation of a Ti/Cu/Pt/Au thin-film metal stack on fired low temperature cofired ceramic (LTCC) surfaces using a 355-nm Nd:YAG diode-pumped laser ablation system. It further investigates laser ablation applications using unfired, or “green,” LTCC materials in the following ways: (1) through one layer of a laminated stack of unfired LTCC tape to a buried thick-film-conductor ground plane, and (2) in unfired Au thick films. The UV-laser power profile and part fixturing were optimized to address defects such as LTCC microcracking, thin-film adhesion failures, and redeposition of Cu and Pt. An alternate design approach to minimize ablation time was tested for efficiency in manufacture. Multichip modules were tested for solderability, solder leach resistance, and wire bondability. Scanning electron microscopy, as well as cross sections and microanalytical techniques, were used in this study.