Think & Tinker, Ltd.
P.O. Box 1606, Palmer Lake, CO 80133
Tel: (719) 488-9640, Fax: (866) 453-8473
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Acid Copper Electroplating
Cu Plating Baths and Consumables


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Questions about:
  1. Can I use copper sulfate that is in powder form? I'm not so sure how to mix it, since the guide I have only deals with liquid copper sulfate.

    Copper sulfate "powder" is actually made up of very fine crystals. The recipes on the web contain instructions for mixing acid copper plating solutions using both liquid copper sulfate (CuSO4) and crystalline copper sulfate pentahydrate (CuSO4•5H2O). Go to: Acid Copper Plating Solution .

    Specifically, you want 10 to 12 oz of copper sulfate crystals per gallon of plating solution. To make up a single gallon of acid copper electrolyte, add:

    • 25 oz (weight) or 1.6 cups (volume) 98% sulfuric acid to 3 quarts (12 cups) of COLD deionized. The solution will heat up VERY rapidly as you add the acid so be VERY CAREFUL!!!
    • Heat the solution to 60C (140F) and slowly stir in 10 oz. of copper sulfate flakes. Stir until ALL of the crystals are dissolved.
    • Add 0.63 cc of 35% HCl (hydrochloric acid) and 19 cc of Copper Gleam PCM+.
    • You have added a little less copper sulfate than you actually need but the anodes, when they activate, will quickly make up the difference.

    If you are planning to use the crystalline form, be sure that you specify "snowflake crystal", "plating grade" or "high purity" copper sulfate pentahydrate. The industrial or agricultural grades may contain impurities (e.g. iron and chloride) that will be detrimental to the proper functioning of your bath.
  2. When I am going to pattern plate my circuit anyway, why do I first have to panel plate the board just after holewall activation?

    To insure that all of the through-holes in your finished board are completely covered with a uniform layer of copper, it is essential that the conductive ink layer deposited during activation be as conductive as possible to optimize deposition and adhesion. Exposing the conductive ink to the developing solution can result in a "surface poisoning" of the exposed conductive particles, making it very difficult to plate.
  3. How do I determine the total surface area of exposed copper when I am pattern plating?

    Hopefully, your CAM software will give you the total combined surface area of all your circuit elements (on both sides of the board). All you will have to do is add in any surrounding copper that is not covered with plating resist. If your CAM software does not provide this critical datum, throw it away and pick up a package that does. Stop by the vendor's web site to thoroughly flame them on your way to the dumpster.
  4. How do I account for the area of the holewalls when I am pattern plating?

    When determining the area that you are pattern plating, only use the area that is exposed on the SURFACE of the board (e.g. traces and pads). This is a very good first order approximation since the contribution of the walls of the through-holes to the total surface area is somewhat masked by "electrostatic" effects at the rim of each hole.
  5. What will the effect be if I reduce or increase the plating current to a value other than that calculated using your formula?

    Generally speaking, reducing the plating current to about 10 ASF increases the "throwing power" of the plating bath making it easier to plate inside of the through-holes. A good practice is to plate a freshly activated board at reduced current for 10 to 15 minutes. During this time all of the hole walls should become completely covered with a shiny layer of electrolytic copper. After all of the holes are covered, you can boost the current up to 20 ASF to continue building up the bulk copper on your board.

    The effect of increasing the current above the calculated value is somewhat less predictable. The electrolyte recipe in the web site has been tested at current densities up to 40 ASF with acceptable plating up to 30 ASF. At plating current densities above 20 ASF, there was an accelerated consumption of the organic additives as well as an increase in the production of organic contaminants.
  6. Why are some of the through-holes in my board not plating? Some are partially covered with copper while others do not seem to have been plated at all.

    1. Before assuming that the problem is with your system, please review: Holewall Activation

      Pay close attention to the section that describes holding your board up to the light to make sure that ALL of the holes are filled after you spread out the ink.
    2. Also read: Acid Copper Plating

      Remember to swish the board back and forth a few times to remove any air bubbles that might be trapped in the holes.
    3. Other problems that result in poor throwing power:

      High copper - low acid - Other than poor conductive inking technique and trapped air bubbles, this is the primary cause of poor or inconsistent plating of activated through-holes. You need to check your bath to insure that the ingredients have been mixed in the correct proportions. A high acid level can dramatically improve throwing power. Generally speaking, it is safe to operate a bath with an excess of acid (max. 15% by volume) so adding more is often a quick fix. Brightener stability is not affected by increasing the sulfuric acid content. Exceeding 15%, however, might cause dissolved copper to begin to precipitated out of solution in the form of tiny suspended crystals that can roughen the board during plating.

      Brightener shortage - Assuming that your bath is new and that you followed the mixing procedures accurately, this is not your problem. In an older bath, however (or a new one that has seen lots of use) brightener level can fall if the bath is not properly maintained. See: Hull Cell for a concise treatment on how to determine the level of brightener function in your bath.
  7. Why are my plated boards coming out rough, like copper plated sandpaper?

    Deposit roughness can result from a number of sources. To wit:

    1. Anode type - Phosphorized copper (0.04 - 0.08% phosphorous by assay) sheathed with polypropylene or Dynel bags or packaged in machined Porex® tubes is ideal. OFHC copper, copper plumbing pipe, or copper wire is not sufficiently pure to avoid the presence of copper particles in the plating solution.
    2. Anode bags or tubes - check for holes or breaks in the bottom seal by filling with water and allowing to drain. Watch closely to see of water pours out of any one area.
    3. Solution clarity - It is always a good idea to continuously filter a plating bath at the 1 to 5 micron level. If you use your bath infrequently, and are very careful to maintain the chemistry and not allow foreign materials to enter the solution, you can often get by for a while without filtering. Sooner or later, however, you are going to have to provide some means of removing the particulate contamination that inevitably begins to accumulate.
    4. High chloride - Above 125 ppm chloride ion content, there is a tendency to produce roughness and duller deposits. Letting the bath stay idle with the sparger running overnight is usually enough to drop the chloride content significantly. Hull cell testing or chemical analysis should always be used to determine when the proper chloride level is attained.
    5. Low brightener - In extreme cases, low brightener can contribute to surface roughness. Hull cell testing should always be used to determine the amount of brightener to be added.
  8. Why is my plated copper coming out dull? Does it matter?

    From a practical point of view, dull copper will conduct heat and electricity just as well as bright, shiny copper. The problem is that, a change from bright to dull plating can indicate that some form of contamination has entered your solution. Some types of contamination will not materially affect the performance of the plating solution. Others will lead to severe deterioration of both the operation of the bath as well as the quality of the deposited copper. Some common causes include:
    1. Brightener shortage - Use a Hull Cell to determine whether your bath is low on brightener. Excess brightener (up to 3 normal strength) is not harmful and can be beneficial in the presence of organic contaminants in holding stress levels at a minimum.
    2. Low chloride - Less than 20 ppm chloride can result in dull deposits. Analyze the bath and restore the chloride content to its optimum level.
    3. Organic contamination - Dull deposits, possibly accompanied by step plating around the through-holes, are occasionally the result of the build up of organic contaminants in the electrolyte. For best results the entire volume of the bath should be oxidized with stabilized hydrogen peroxide followed by carbon treatment using an approved activated carbon filter.
  9. Why should I add copper electroplating capability to my PCB shop?

    The short answer to this question is that you would add copper electroplating if you wanted to fabricate printed circuits with plated through-holes. Electroplating is cheaper, faster, and far more reliable than using mechanical rivets (a.k.a. eyelets) to achieve front to back connectivity. If you are thinking about adding multilayer capability later on, copper electroplating will be essential.

    Copper plating is also very handy if you do not have a way to create negative artwork. Using positive artwork and pattern plating with copper (for surface build and through-hole plating) and tin/lead (as an etch resist), you can actually make boards superior to those made using conventional "print and etch".
  10. How many boards can I plate with a standard charge of anode material?

    Assuming that you will be starting with "half ounce" copper clad (0.00065", 17 micron foil on both sides of the substrate), and plating up the thickness to "1 ounce" (0.0013", 35 micron foil) you can expect to plate about 290 square feet of double- sided copperclad in the 11 gallon system (12 lb of nuggets) and about 750 square feet in the 22 gallon system (32 lb of nuggets).

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