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HCl etching of copper for adhesive bonding

Since I'm--obviously--a lay-person with no detailed knowledge of the chemistry and various species interactions, I'd be indebted to anyone that could--and would--succinctly answer my inquiry.

I am "casually" trying to find out why Hydrochloric Acid is not the "pickle" or etchant of choice when preparing a copper surface for adhesive bonding. I've seen many references to etching copper with Nitric Acid; ferric chloride ⇦this on eBay or Amazon [affil links] & Nitric Acid; or Ammonium persulphate, I'm wondering what the advantages and disadvantages of each are. That is, what are the Pros and Cons for each method? Wouldn't HCl be terrific at removing all of the oxides? I've read that HCl won't dissolve or attack the Cu itself.

Perhaps, there are multiple reasons for why HCl isn't used? Is it because the etch rate varies with the amount of Cu dissolved in the acid? Is it because there are Cl gas hazards? Is it because other contaminants greatly affect its process?

If my aim is to achieve good adhesive bonding with a copper surface, would I be better off with another etchant? If I were to use HCl, what "recipe" for concentration and time would be recommended. Or, perhaps, you can steer me to a good resource? Is "bright" dipping just as useful at prepping a surface for bonding as "etching"?

Cheers!

Rob Stix
Development Engineer - Red Bank, New Jersey
2007

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Hydrochloric acid is extremely poor as an etchant for copper. It also has a very corrosive vapor.

Oxidizers are used for etching copper. The etching creates a microscopically roughened surface for bonding. The etch rate by non-oxidizing acids (hydrochloric, sulfuric & hydrofluoric) is ~negligible when the acid is oxygen-free. For equal acid concentrations by weight, the oxidizing nitric acid is ~330 times faster than hydrochloric and 1200 times faster than sulfuric acid. Chemical suppliers such as MacDermid have high-speed etchants for copper which also create greater micro-roughness for enhanced bonding.

ASM Handbook Vol. 5 Surface Engineering, pages 805-808 gives pickling and bright dipping formulas for copper which include hydrochloric acid and/or sulfuric acid. The attack rates of the non-oxidizing acids increase directly with the dissolved oxygen content, as from exposure to air, agitation and dissolution of oxides. Etching is undesirable except as a pre-bonding treatment.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2007