Need advice on electroplating
The company I work for makes Roto Graver cylinders for the printing industry. I work in the electroplating department. Along with other plating processes, I plate copper onto the cylinders. The copper plating tanks used in this process contain a copper sulfate bath. After plating and polishing the copper, a diamond stylus is used to engrave an image on the plated copper layer. In order to engrave the image, the diamond stylus must make a clean cut through the copper. To accomplish this, the crystalline structure of the copper must be carefully controlled. If the structure of the copper is not right, the stylus will tear the copper, which ruins the engraved image.
The way we control the structure of the copper is to add some type of "hardener" additive to the bath, which hardens the copper. It seems no one really knows what the active ingredient in this additive is, or how it works. In addition to the hardener additive, a minute quantity of chloride, (a few ppm's), is required in the bath in order to achieve the desired results. I am at a loss to understand how the chloride and the hardener additive work in conjunction to control the crystalline structure of the plated copper. If some one could tell me what is in the additive and explain to me how it works with the chloride ion to control the crystalline properties of the plated copper, I would be forever grateful.Scott Ksobiech
- Milwaukee Wisconsin
As a copper plater I feel your pain too. What's in the purple stuff? Must be simple chemistry but a well guarded secret . I do know that it is organic in nature, and the end result is improved grain structure. Chlorides ,play small part are needed but easily overdone.ppms.Harry England
- Benton Harbor Michigan
Come on, doesn't any body have the balls to lay it on the line? I an not asking you the give me your first born. Just explain to me in a general way: is it organic or is it inorganic? Does it become a part of the crystalline structure of the plated copper or not? How dose Cr- play a role in it? Thank you very much!Scott Ksobiech
- Milwaukee Wisconsin
Mr. England already told you that "I do know that it is organic", Scott.
The supplier knows exactly "what the active ingredient in this additive is" but won't tell you because they paid for man-years of research to figure out what works best. Rather than charge you hundreds of thousands of dollars for their research, they charge you by the gallon for the product. That's the way the plating industry works, and it has worked pretty well.
The basic principal is, however, described in the plating textbooks: without additives, there will be a small number of crystals which will grow quite large. Because they are relatively large and with few dislocations, the plating is soft. And because these large crystals will run into each other at random, leaving large gaps, the plating is porous.
The organic additives "shield" the surface of the crystals, causing a greater number of small crystal adatoms to form in place of a small number of large crystals. Because they are smaller, there is less porosity. And because there are more breaks, more dislocations, the grain is tighter and harder.
Yes, the organics also become incorporated into the crystal structure and for very high temperature applications organic additives can be a problem.
Tens of thousands of research projects are documented in the electroplating industry journals, and if you conduct a thorough literature search you will no doubt develop some very good leads as to what the additives probably are.
The chloride is a catalyst that discourages streaky deposits, but I don't know exactly how it does that. I am not aware of chrome being a beneficial component in a copper plating bath, but I would not rule out the possibility that it could be in very low concentration. Some findings in the plating field are still empirical -- experimentation sometimes reveals that an additive is beneficial long before we fully understand exactly why.
Ted Mooney, P.E.
Pine Beach, New Jersey
Scott, I have to admit your last response made me smile. For the majority of us it makes no difference at all what each component of the brightener does. Most hands on platers know how much of each component to put in and what each does to the deposit when they do. If we want to know any more details our supplier usually gives us general information on cause and effect of the additives. The 10 years I have been plating with acid copper has been with McGean Rohco products. Their lab has always been open for me to visit and they have never tried to evade my questions. I also did not feel the need to ask them for the recipe to their products. If your supplier isn't at least this cooperative.....switch suppliers.
Anoplex - Dallas, Texas USA
To all of you who took the time and effort to reply to my inquiries, I thank you very much.Scott Ksobiech
- Mil, WI
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