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I am attempting to electro-plate vias in a home brew printed circuit board. The medium I am attempting to electroplate is fiberglass bound together with epoxy. This is an intentional insulator.

I drilled a few holes in this medium using a regular electric drill and covered the holes with a graphite based conductive paint by covering the board in the paint and drawing it through the holes using a vacuum. I repeated this in both directions in an attempt to cover the holes evenly. I then cured the paint at about 100C for 20 minutes. In my experiments, this was far sufficient to dry the paint.

I then created a solution of 1000ml distilled water, 250ml of 38% sulfuric acid (battery acid to improve conductivity) 160g of copper sulphate pentahydrate, and 2 ml of polysorbate 20.

I prepared this solution by adding the sulfuric acid to the water slowly (to avoid rapid exothermic reaction between acid and water) then adding the polysorbate and the the copper sulfate pentahydrate. I then mechanically agitated the copper sulfate pentahydrate crystals until the solution was homogenous.

I ran .8A of constant current through the solution with the board as the cathode and an anode consisting of two electrically common (14ish guage) copper wire on either side of the board. After about 90 minutes this was my result...

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I'm wondering why the copper clad had "beads" on it...the entire surface was sanded with 1500 grit sandpaper directly preceding the electroplating.

I'm also wondering why the holes are so "rough". In my testing, every via has come up as 0.0Oohms...or electrically common to the clad. Aesthetically though, this is not pleasing and makes me wonder if my method is truly reliable.

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  • $\begingroup$ Electroplating requires either a very uniform current distribution or very uniform cation distribution (which requires very high current density), otherwise irregularities are to be expected. The process is fragile and should be avoided if possible. $\endgroup$
    – permeakra
    Dec 20, 2017 at 9:26

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There are few things that you can improve.

First, beads are forming because your copper anodes are not pure copper. Beads are forming around impurities. You can try to remove (filter) impurities by firmly wrapping anodes in paper tissue or better with water filtration polypropylene felt filter so only Cu ions can pass into solution. You can after that collect impurities already present in solution by electroplating few hours on some scrap piece of wire.

Second, holes should be drilled cleanly. You should invest into carbide drill bits and good drill stand.

Third, you should also think about adding Cl ions to solution, NaCl or HCl in small quantities. Plated surface will be shinier...

Best regards, Pavle

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  • $\begingroup$ I have some muriatic acid laying around for etching. I'll add some of that and see what changes. I ordered a drill press and I'll look into finding more pure copper. Thanks. $\endgroup$
    – Allenph
    Dec 20, 2017 at 16:16
  • $\begingroup$ Be careful not to add too much muriatic acid. Please check on: thinktink.com/stack/volumes/voliii/consumbl/cplatmix.htm Only 13.3 ml of 35% HCl for 100l of of total solution! $\endgroup$
    – Pavle
    Dec 21, 2017 at 7:01
  • $\begingroup$ @Pavle I wanted to reiterate your point that’s 13.3ml for 100 LITERS! Also, if OP is using tap water and not deionized water they likely already have too many Cl ions in solution which will lead to passivation of the anode and cause more problems. $\endgroup$
    – Jack Spencer
    Jan 10, 2021 at 15:30

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