Metal Finishing Guide Book

2013

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plating processes, procedures & 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 applications. 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 electronics 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 printed circuit board. Thus, in many printed circuit board and semiconductor fabrication 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 solution of copper sulfate, an acid electrolyte such as sulfuric acid, and various plating additives. Commonly used additives for copper metallization include inhibitors/suppressors, brighteners/accelerators, and/or levelers. The brighteners/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 enhanced by the presence of halogen ions. The concentration of these organic additives must also be closely controlled in order to attain the desired deposition properties and Component Target Range CuSO4 × H2O 75 g/l 65–85 g/l Sulfuric acid 200 g/l 190–220 g/l Chloride 75 ppm 60–90 ppm HT 100 Make-up 8 ml/l 6–10 ml/l HT 100 Wetter HT 100 Brightener Dosing during the plating 0.8 ml/l Temperature Current density 0.6–1 ml/l 22–40°C 2.0–2.5 ASD 1.0–4.0 ASD Table 1: Process Parameters 245

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