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topic 48396

Fuzzy Copper Electroforming


A discussion started in 2008 but continuing through 2019

April 2, 2008

I'm a grad student at the Missouri University, I'm using an acid copper electroplating bath in an attempt to electro-form micro channels. I've been using my bath for about 3 weeks now and it had a very sudden unexplainable change in performance.
I've been using it for about 250 hours thus far and it was working well, not perfectly;

48396-1

but that, I think, has more to do with the fact that I'm trying to electro-form without using a pulse power supply. I'm getting what appears to be dendritic growth (roundish lumps about 2 mm or smaller in diameter, after plating parts at about 20 ASF for ~15-20 hrs. Is that due to the long plating times? any other suggestion on how to get a thick layer (at least 250 um) that is smooth and uniform?

48396-2

This figure shows the dendritic growth, and the channel structure that I
later coated with conductive ink one to which the fuzzy copper formed.

Anyways, on to my bigger question. I'll just explain what happened and see if anyone has any ideas.

System Description
The bath that I've been using is 10% sulfuric acid, 50ppm HCl, with 0.56% Copper Gleam CLX Start-Up (recommended amount) the bath is about 30 liters. It is a 12" square x 14" deep with 6 anode tubes 3 on one side 3 on the other filled with phosphorized copper nuggets ~18 lbs, nuggets are roughly 1" diameter. The anode tubes are PVC pipe with 1/3 cut out and replace with a screen. The opening of the anode tubes faces away from the cathode.

The cathodes that I have been plating are ~1.5" x 3" 1/8" copper sheet attached by drilling a hole in the top center of the plate, inserting a piece of wire and twisting to secure, the wire is then held in the cathode holder, making sure that the workpiece is under at least 1" of fluid. I generally use jewelry casting wax as a masking material (melts and adheres very well to the copper, and allow one to use a tool to selectively remove wax to control deposition location. I also use 'conductive ink' - basically a solution of silver, carbon and graphite powders in a resin base, it is commonly used for though hole plating of circuit boards.

Attached to this I have a heating and filtering system. The heater is a stainless steel heater (in a PCV housing, I'm going to remove the heater as I don't use it).

Next in the pump line is a 1 micron filter, and a pump (designed for highly corrosive environments). The pump returns the fluid to the tank via a pair of nozzles that are positioned to encourage flow across the work piece (providing agitation with out the hassle of pumping filtered air that will then cause further aerosolization of the working fluids.

Modification Description
As I said earlier, the system seemed to be working mostly fine, until...
I wanted to reposition the fluid return nozzles so that they were aimed to the center of the tank rather than about 1/4 down the tank in an attempt to even out the plating results that I was getting. So I put on my face mask, liquid repellent lab coat and gloves, stuck my fingers of one hand into the bath and adjusted the nozzle spray direction. Then next plate that I plated was drastically different that what I expected!


The Change
So right before I adjusted the nozzle, I had just removed the workpiece from the plater, it looked like all the others, plated but a bit dendriticy (as seen in the first two figures). I rinsed that and put it aside,, adjusted the nozzle and place my work piece into the bath, following the same basic procedure that I have for all the previous pieces.

When I returned to examine the work piece it was covered with a very fine but sharp 'copper fuzz'. The fuzz was completely uniform and very attached to the work piece
48396-3
This figure show the 'fuzzy copper' growth after 18 hours in the bath.

Next I plated a flat piece of copper to see if it too would turn fuzzy, the following pictures show, the results
48396-4
This figure shows the two plates side by side, TCV-2.0 was done first TCV-2.1 was done second. The lines on TCV-2.0 are due to the underlying channel structure. TCV-2.1 is 'flat' as it was simply a flat plate


48396-5
Figure showing the initial flat plate for TCV-2.1.

48396-6 48396-7
As seen in the above figure, TCV-2.1 grew a long 'tail' spontaneously after ~24 hours in the plating bath.

So my questions are:
1. Is this common? has it been seen before?

2. If it is common what is causing it, and how can I purposefully make a bath chemistry that will produce similar results?

3. Also if anyone has time if you could comment on how to prevent the dendritic growth, describe in the first section and as seen in the first figure.

I would be VERY grateful of any help that anyone can provide.

Christopher Vincent
Student / Research Engineer - Columbia, Missouri, USA


sidebar2 April 11, 2008

Christopher, you may be better off shortening your submission - this is too long to take in at one go and not made any easier by having to go outside the website to see the pictures. I know I always ask for process and material details, so perhaps I have met my come-uppance!

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK


April 16, 2008

thumbs up signHi, Thanks for the hint, Trevor! We've now reduced the font size, added thumbnail pictures, and presented it in two columns, to try to make it more digestible.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


April 16, 2008

A. Have you analyzed the bath to be certain copper and sulfuric concentration have not changed? Have you added additional addition agent to replace what has been consumed?

Sounds like low addition agent to me.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina


April 23, 2008

A. I will have to agree with Jeffrey Holmes. If you are going to plate for 18 - 24 hours at a time addition agents have to be added per so many ampere hours. See if the addition rate is being met. You are experiencing severe burning. Other possibilities to examine after the first recommendation is satisfied is as follows:
You will want to make sure the anode to cathode spacing is at least 4-6 inches consistently, and have ample solution agitation.
I don't quite understand your anode system, I assume you are maintaining electrical contact throughout the anode(s). I also don't know why the opening of the anode is facing away from the part. Is this some type of shielding technique? Cu Electroformers I have worked with keep the H2SO4 on the high end and the CuSO4 on the low end, drop the current density accordingly (otherwise known as the low and slow approach). It sounds like you are using a proprietary system (equipment and chemistry). You will want to contact your supplier to see if they agree with my suggestions. Other than low brightener concentration, here are some other causes of burning.
Current density too high
Metal concentration too low
Inadequate agitation
Bath temperature too high
Anode polarization
Low chloride concentration
Let us know how you make out!

Mark Baker
Process Engineer - Syracuse, New York USA


June 7, 2008

Q. Hello everyone. My name is Mike Campbell and I am taking over Chris's electroforming project here at Mizzou since he has moved on to greener pastures (lucky guy got a job).

The project's aim shifted a bit after Chris's little "fuzzy copper" incident. Instead of trying to PREVENT the dendritic structure, we now want to ENCOURAGE it.

Here's the interesting part. Chris left two weeks ago, and since then, I've run several tests using the same bath that he had. Unfortunately for me, the bath now plates very smooth. In any other situation, this would be very nice, but for this particular project, it is very bad.

This may be a strange request, but is there a tweak to the system that might ENCOURAGE this dendritic (fuzzy) growth?

Thanks in advance,

Mike

Michael Campbell
- Missouri, United States


November 13, 2019

Q. Hello, I'm fabricating some pieces for an artist by electroplating copper growths onto a plastic part with copper spots. (The attached image shows one such spot under magnification.) I'm using a bright acid solution with high sulfuric acid content, low copper ion content, and no levelers. The artist wants branching dendrites, and operating the solution without agitation has yielded decently course growths but little branching. I want to maximize branching. I understand that the common additives attach to high current density sites and block deposition. Are there any additives that attach to low current density sites?
Thanks!

Conrad Volle
Printmaker - New York, New York

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