From thin cores to outer layers: Filling through holes and blind micro vias with copper by reverse pulse plating

This paper presents new advancements in copper electroplating technology for both blind micro vias and through holes. Processes and manufacturing technology are described as well as current limitations and requirements. As a highlight the complete filling of through holes with electroplated copper by reversed pulse plating, RPP, is described. Both blind micro via and through hole filling using this technology are already targeted for production at HDI and also at the packaging level. The basis of the latest advancements has been the development of the so called SuperFillingtrade process. SuperFillingtrade combines the electrolytic reverse pulse deposition of copper into specific structures together with the simultaneous etching of copper from the substrate bulk surface in a continuous panel plating step. This combination reduces the amount of overplated Cu by up to 50% compared to conventional copper deposition processes for HDI fine line applications. The SuperFillingtrade mechanism as well as manufacturing requirements and production supervision tools such as online analysis are described in detail. The latest development, through hole filling by RPP, offers a viable alternative to the standard paste plugging for core processing in substrate manufacturing. Current core manufacturing requires a paste plugging process for through holes so that subsequent build up layers can be produced by sequential lamination, the flat core surface is essential for stacked via and also via in pad technology. This paste plugging process requires additional process steps, each of which has its own limitations and contributes to the overall cost. Filling the core through vias by electroplating can eliminate the plugging process and significantly reduces the number of overall process steps which will also reduce costs. Moreover, it offers certain advantages such as potentially higher reliability in accelerated aging tests and an improved thermal management as the thermal conductivity of a completely copper filled through via is significantly higher than a paste plugged through via. First manufacturing experiences with the Through Hole filling technology are presented along with a discussion of its manufacturing prerequisites and limitations.