High Throw Electroless Copper - Enabling new Opportunities for IC Substrates and HDI Manufacturing
Two new electroless copper baths have been developed to cope with upcoming miniaturization challenges in the high-end IC substrate segment as well as in the evolving HDI board market. The main challenge to be overcome is the reduction of the differential etch in the pattern plating process by decreased electroless copper thickness on the surface of the build-up layer. To this end,several requirements need to be fulfilled to ensure a safe and high yield production. First of all,the throwing power performance of E’less Copper IC and E’less Copper HDI especially in the wedges respectively at the bottom of the BMVs is crucial for the via-filling performance due to conductivity requirements. Two reliable throwing power measurement methods have been introduced and throwing power results presented in this paper show that the new electroless copper baths constantly achieve significantly better throwing power performance compared to the reference systems that are industry standards in the respective markets. A minimum target thickness of the electroless copper layer in the BMV (wedges) is therefore ensured while the thickness on the surface can be reduced for improved L/S resolution. Secondly,the adhesion of the copper layer on the bare laminate is a basic requirement for the high-end IC substrates manufacturing process. Favorable internal stress characteristics of the copper layer of the E’less Copper IC bath combined with excellent peel strength results ensure a reliable and strong adhesion of the copper layer on the resin surface. Thirdly,dry film adhesion and differential etching are key process steps for high yield manufacturing. The surface morphology of the E’less Copper IC layer enables improved mechanical anchoring of the dry film compared to the reference system and dry film adhesion data for E’less Copper HDI is under evaluation. Both electroless copper baths were thoroughly tested for industry standard reliability requirements and achieved excellent results.