A Novel Photosensitive Dry-Film Dielectric Material for High Density Package Substrate, Interposer and Wafer Level Package

A new dry-film photosensitive dielectric material (PDM) named PDM-1 with low curing temperature (180°C) has been developed. The lithographic process evolves exposure equipment widely used in solder resist process, which make this PDM-based fine pattern fabrication technique intrinsically high production compared to the laser ablation method. The PDM-1 is able to deliver sufficient resolution for high-density wiring package substrates, interposer and wafer level package (WLP), etal. Through using nano-size fillers, ultra-small vias of 6um in diameter at 10um thickness have been obtained, and meanwhile low CTE and low Df could be kept. Using aqueous Na2CO3 developer (1 wt%) makes the fabrication process environment-friendly and cost-effective. By applying the PDM-1 for semi-additive process with sputtered metal as seed layer, thin copper wires of 6/6 um are fabricated, and superior peeling strength (between PDM-1 and sputtered seed layer) is achieved despite of the smooth surface (roughness 30 nm). PDM-1 demonstrates a superb dielectric reliability attributed to its low halogen impurities. It suggests that the as-developed PDM-1 is a promising dielectric material for high-density wiring applications and the PDM-based fine pattern fabrication technique shows strong potential for commercialization.