Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 168 of 707

electroplating solutions HIGH-TEMPERATURE ACID COPPER PROCESS FOR PLATING THROUGH- HOLES BY MARIA NIKOLOVA, JIM WATKOWSKI, DON DESALVO, AND RON BLAKE, MACDERMID, INC., ELECTRONICS SOLUTIONS, WATERBURY, CONN. Electrolytic copper plating solutions are employed for many industrial applica- tions. They are used in the automotive industry to deposit base layers for subsequently applied decorative and corrosion protection coatings. They are also used in the elec- tronics industry, especially during fabrication of printed circuit boards (PWB). During circuit fabrication, copper is electroplated over selected portions of the surface of the printed circuit board and onto the walls of through-holes passing between the surfaces of the circuit board base material. The walls of the through- holes are metallized to provide conductivity between the circuit layers of the print- ed circuit board. Thus, in many printed circuit board and semiconductor fabri- cation processes, electroplating has been adopted by industry as the primary deposition means for copper metallization.1–3 The most widely used copper plating electrolyte is based on an aqueous solu- tion of copper sulfate, an acid electrolyte such as sulfuric acid, and various plat- ing additives. Commonly used additives for copper metallization include inhibitors/suppressors, brighteners/accelerators, and/or levelers. The brighten- ers/accelerators change the nucleation process, enhancing the formation of new deposit nuclei as opposed to the growth of existing nuclei. The suppressors/inhibitors adsorb at the cathode surface uniformly, increasing the deposition over-potential. The levelers are selectively adsorbed on the protruding features or at the flat surface, and the leveling effect is a result of the diffusion control of the leveling species. The adsorption and inhibition may be further Component CuSO4 × H2 O Sulfuric acid Chloride HT 100 Make-up HT 100 Wetter HT 100 Brightener Temperature Current density Table 1: Process Parameters 167 Target 75 g/l 200 g/l 75 ppm 8 ml/l 0.8 ml/l 2.0–2.5 ASD Range 65–85 g/l 190–220 g/l 60–90 ppm 6–10 ml/l Dosing during the plating 0.6–1 ml/l 22–40°C 1.0–4.0 ASD

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