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42 PCB007 MAGAZINE I JUNE 2018 Feature by Saminda Dharmarathna, Christian Rietmann, William Bowerman, Kesheng Feng and Jim Watkowski MACDERMID ENTHONE ELECTRONICS SOLUTIONS Abstract Copper-filled microvias are a key technolo- gy in high-density interconnect (HDI) designs that have enabled increasing miniaturization and densification of printed circuit boards for the next generation of electronic products. Compared with standard plated through holes (PTHs), copper-filled vias provide greater de- sign flexibility, improved signal performance, and can potentially help reduce layer count, thus reducing cost. Considering these advan- tages, there are strong incentives to optimize the via filling process. This article presents an innovative DC acid copper via fill formulation, for vertical contin- uous plating (VCP) applications which rapid- ly fills vias while minimizing surface plating. For instance, a 125 µm x 75 µm via was filled with just 10 µm copper deposited on the out- er layer surfaces. X-ray diffraction studies were done to obtain information about the grain structure (texture) of the deposit. Based on de- termination of the Lotgering factor, the study shows that the (111) plane has a slight prefer- ence (Lotgering factor ~0.2) over other typical planes (e.g., 200, 220, and 311). X-ray diffrac- tion (XRD), focus ion beam (FIB), and scan- ning electron microscopy (SEM) data show that there is no significant change in the grain structure even after the bath was aged up to 150 Ah/L. This formulation contains no harm- ful formaldehyde, which was classified in 2016 by the European Union as a carcinogen, there- by restricting its use in electroplating formu- lations. These regulations in the future, could expand into other regions as well. Therefore, having no formaldehyde is an added advan- tage for safe operation and waste disposal. Introduction The PCB industry has evolved immensely over the last few decades in response to the need for increased densification and miniatur-

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