Plating Cell Considerations/ Proper Cell Design, Acid copper Bath Study

Tank Design and Tank Materials the tanks must be fully supported to maintail its shape over years of operation. Tank must be clean and free of dirt, oil. Materials unpigmented polypropylene PVC, CPVC, Titanum, EPDM, fluoropolymer. Do not use SUS, rubber,cotton or cellulose etc.

Heating and Cooling +/- 2°C acceptable, +/- 1 °C preferred Heater material : Titanium or Tefron Cooling material: Titanium* * must be shielded and grounded from current and bi-polar plating.

Anode placement, connection, bussing. Copper bussing are normally used, use at least one square inch of copper cross-section(6.5cm2) area per 1000 amperes of current. Check current distribution, especially anode current distribution to each anode regularly with an amp-clamp.

Anode type; anode type must be phosphorized with a uniform phosphorous content of 0.04-0.06% round type is normally recommended use titanium material. Anode baskets need continuous maintenance(bridging in a common problem) damaged baskets should be replaced.

Anode current density(number of anodes on an anode bar); anode quantity used should be calculated to provide an anode surface area of about 15ASF use the front surface area of bars or baskets[ e.g. for a basket, use 1/2(circumference x length{ in solution})]. Anode bags should be napped polypropylene or Dynel. Should be loose fitting and at least a few inches longer than the bar or basket. Bags may contain sizing, the bags must be washed throughly in clean, hot water, and soaked in sulfuric acid before use.

Anode fill and maintenance. Uniform fill of anode baskets and check it frequently. When baskets do not fill fully “bridging”may be the cause.Frequent weighing of the anodes and tamping(dislodging anodes with a stainless rod) or empty or refill when an anode will not fill fully are recommended. The anode baskets should never be spaced farther apart than 1/3 the anode-to-cathode distance(if anode-to-cathode distance is 210mm, then the space between anodes or anodes anode baskets should not exceed 70mm.

Anode- Cathode. Distance; Co-planarity cathode-to-cathode spacing is Min200mm and Max 300mm. Co-planarity anode-to-cathode distance is important, good anode maintenance is needed and requires solid racks with good rack maintenance.

Shielding; for best surface distribution across the plating cell load. anode “window”: to provide anode window anodes should be placed or shielded, which is 100mm smaller than the plated cathode size on all sides(top, bottom, left, right) upper shielding : at the top-inside of each anode bar. Floating shielding : another common shield is an adjustable bottom shield to accommodate different plating rack depths.

Agitation Copper plating depends on agitation to insure uniform solution movement near the plating(cathode area). This solution movement is critical to the proper performance of chemistry used and is necessary to provide a thin and controlled “boundary layer” near the cathode. Boundary layer is diffusion layer in which chemistry concentration in solution is different between inside and outside of diffusion layer.

Mechanical agitation; force solution through the holes of PCB’s. help reduce the differences in solution movement and chemistry between surfaces and holes. Mechanical agitation should be; in a”paddle”motion to push/pull through the holes a large, moderate speed stroke works best(60-80mm total stroke, 8-10 cycles per minute) the cathode rack must be as rigid as possible to work properly.

Air agitation ; air is normally used to create the desired uniformity of solution movement at the surface of a rack. Air should be provided with these features: clean, filtered, oil-free air must be used air sparger must be placed below the cathode, but either travel with the mechanical agitation, or use two pipes so that both sides have air during the full mechanical agitation cycle. Air sparger must be placed and held horizontally. Air sparger should be at least 20mm above the tank floor and at least 150mm below the plated cathode. Total cross-section area of all holes should not exceed 1/2 the cross-section of the pipe.( 1.5mm holes, 45°angle from vertical) air should not be placed under anodes. It is normal not to use air when the cell is not in use.

Filter and Pump Continuous filtration is required. Pump rate should be 3 turn-over/hour. 5-10µm cartridge type is recommended. If cartridge contains sizing, the tubes must be washed thoroughly in clean, hot water and soaked in 5% sulfuric acid before use. Be careful to even minor leak of filter and pump.