Think & Tinker, Ltd.
P.O. Box 1606, Palmer Lake, CO 80133
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PREVIOUS NEXTAcid-Copper Electroplating Module Model 1000 Manual
Operation - Overview
Once the through-holes have been activated, your board is ready for acid copper electroplating (short for "electrolytic plating"). Considering the amount of trepidation that seems to surround the entire topic of through-hole connectivity, and the lengths that some people will go to avoid wet chemistry, putting a uniform, reliable sheath of copper on the insides of every hole turns out to be quite straight forward if not downright easy. Thanks to decades of work by the major electrochemical suppliers, the various chemical systems are well understood and readily available in most industrialized nations. Most of the equipment, like acid copper plating tanks, is easy to make and will last for many years if properly maintained. The items that are not easily fabricated in a home shop are available from a variety of sources. A high-performance plating solution can be mixed using readily available materials.
An acid copper electroplating solution is a mixture of water, sulfuric acid, copper sulfate, and a trace of hydrochloric acid. To this is added a number of organic constituents that serve to regulate and distribute the delivery of copper to the surface being plated. The two basic organic additives are commonly referred to as the "brightener/leveler" and the "carrier".
A basic electroplating cell consists of a tank full of the above electrolyte with arrays of copper anode bars arranged along two opposite sides. These bars are referred to as the anodes, and, as you might expect, are connected to the positive terminal of a current source. This supply must be capable of continuous sourcing into a near short circuit load (a typical copper electroplating bath has an effective full load operating "impedance" that ranges between 0.020 Ohms and 0.080 Ohms). Situated halfway between these anode "banks" is the copperclad substrate that is to be plated. It is variously referred to as the cathode or the workpiece.
In the simplest terms, copper deposition occurs when an electrical potential is established between the anodes and the cathode. The resulting electrical field initiates electrophoretic migration of copper ions from the anodes to the electrically conductive surface of the cathode where the ionic charge is neutralized as the metal ions plate out of solution.