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Acid copper plating issue: Passive anodes

adv.: Supplier of Copper Anodes, Nickel Anodes, Bismuth Metal, & Other Metal Products for Industry & The Arts

Quickstart:
     Acid Copper / Copper Sulfate plating solutions are popular with both hobbyists & professionals.
     In a production environment though, a plating shop needs to be concerned not only that the first load of parts plates okay, but that the plating bath can be kept in equilibrium/balance so it will continue to plate okay for the next load and the thousand loads after that.
     One issue the shop must battle is the tendency for the anodes ⇦ huh? to dissolve too readily, causing a build-up of copper concentration in the plating bath which can cause the anodes to go passive ⇦ huh?. One important way to battle this increased copper concentration is for the anodes to be made of "phosphorized copper" rather than pure copper: Read on ...

Q. I read that copper plating solutions should last for years with proper maintenance. In my solution which I used for about a month, I had about a 1/2 inch thick chunk of blue crystals in the bottom of my tank as well as on the sides and anodes. I assume this is copper sulphate. Is there any reason this would grow in there? Thanks, Rob

G. Touch
1995

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Q. I'm doing some experiments with copper plating basically for breadboarding circuits with plated holes and learning the PCB manufacturing process.

I got a fairly functional copper sulphate ⇦ on eBay or Amazon [affil links] / sulfuric acid bath working from chemicals I got at the big orange home center and a constant current power supply. The solution is a basic copper sulphate/ battery acid ⇦ on eBay or Amazon [affil links] / HCl and uses a copper anode made from a piece of copper grounding rod.

I got really bad results until I added citrate ions to the solution, after which I got excellent bonding and an unoxidized (but not smooth and shiny) finish that I can polish fairly easily. Since I was trying to do this without ordering any specialty chemicals, the citrate ions came from calcium citrate tablets that I dissolved in distilled water and decanted into the bath, leaving the sand/talc/whatever behind. The solution should have 0.1% citrate ions by mole count. I figured the small amount of calcium would plate out, and the microcrystaline cellulose doesn't seem to be hurting anything.

But that's not my question, just what I'm working with. I read that for electronics work that I should be using phosphorized copper anodes. In one article at this site someone had trouble with his phosphorised copper anode in that it was turning non-conductive.

So being really cheap I used a copper phosphorus brazing rod as an anode just to see what would happen, and sure enough, it turned black and non-conductive in less than a minute. Probably because it's 7%(!) phosphorus. I'm quite sure that using a copper-phosphorus brazing rod is the wrong material and I may have screwed up the solution, but it led to some questions.

My questions are

1) what is the purpose of a phosphorized anode?
2) what the heck is the black stuff that seems to evaporate when exposed to the air?
3) what is meant by the "polarized anode" and by what physical mechanism does it arise?
4) ignoring the phosphorus fiasco, what is the appropriate level of citric acid ⇦ on eBay or Amazon [affil links] ?

Dennis Schmitz
SCHMITZ ENGINEERING, LLC. - Pinckney, Michigan
2005

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Q. Hello we have a problem with passive anodes in the copper acid bath.

We are copper plating on stainless steel.
Firstly we make Wood's Nickel strike ⇦ huh? , next we put copper layer on in the copper acid bath.
During electroplating of small parts we don't have any problems; but in the case of 3X bigger parts, the current in a few minutes decreases and the copper anodes are covered with a black coating. We tried to solve this problem by using additional anodes and increasing the sulfuric acid H2SO4 but it doesn't work. Anode to cathode ratio is 1:1. The test in the Hull Cell ⇦ huh? goes correctly.
Composition of our copper plating bath:
Copper - Cu 60 g/l
Sulfuric acid - H2SO4 70 g/l
Temp 22 °C
Current at start 2 A/dm2
Mixed by air

Do you have any suggestions to correct this problem?

Waldemar Tomankiewicz
Plating shop employee - Cracow, Poland
2007

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Q. Dear all,
We are also facing the same problem as my friend. While the anodes are not in use, we find that the white paste like formation over phosphorized copper ball anodes is causing decreasing current density in spite of maintaining the required chemical concentration. We have taken out the anodes and washed and put it back into the tank. Now it is okay but we have to check whether the same problem will repeat.

Regards,

S G SUNDARRAJAN
- Chennai, TamilNadu, India
2007

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Q. We are using acid copper plating bath for our printed wiring board copper plating process.

We are unable to maintain the copper sulphate concentration in plating bath and the concentration drops daily.
Control range :
CuSO4 = 9-12 oz/gal
H2SO4 = 24-26 oz/gal

After adjusting the CuSO4 concentration, it seems to drop to 8 oz/gal overnight.

There isn't any dilution on my bath.
There isn't leakage from the machine.

Ideally, the concentration should not drop as the process goes on daily.

Is this due to poor activation/anodizing of my copper anodes?
We've checked the copper anodes and they have a dark black film on the copper balls.

Jake Ng
- Los Angeles, California
January 16, 2013

Q. Hi David,

Thank you for your response.

My bath contains 80 ppm chloride.
And we are using copper balls with 0.04-0.06 wt%.

Meanwhile, when you mentioned the voltage to be high, what would be the normal operating voltage for the anodes?

What would be considered as high voltage?

Thank you.

Jake Ng [returning]
- Los Angeles, California

A. Hi Jake, Rectifier voltage depends on total resistance and current setting. We usually observe ~3V for 100-200 ampere setting. Imagine if anode basket is not tightened to contact bar well may result in poor contact and high resistance to cause abnormal high voltage under same current setting and poor dissolution of copper anode. Therefore, you should compare existing voltage (which you encounter low copper concentration issue) to last time voltage (e.g., during plating line setup time which you don't face such problem) to see if any abnormal voltage surge. Also, you should always do proper maintenance to ensure all contacts (e.g. wire cable to contact bar, contact bar to anode basket, etc) are in good condition. Regards, David David Shiu - Singapore A. First, a black film on the anodes in your bath is normal. Second, acid copper baths I've run pretty much stayed below 3V. Finally, have you checked the ratio of the anode surface area to the cathode surface area? James Totter, CEF - Tallahassee, Florida

Q. Hi David,

The voltage on my rectifiers are above 4V.
Is this considered high?

Meanwhile, there's only one contact point on my cathode bar to the rectifiers.
Will it be better to have both ends on the bar connected to the rectifier?

My plating current is only between 3 - 6 Amperes.
This is rather low compared to 100 A that you are doing right now.

Appreciate your comments and input.

Q. Hi James,

What do you suggest for the plating surface ratio between anode:cathode?
Is 1.5:1.0 good enough?
What will be the maximum ratio?

Thanks!

Jake NG [returning]
- Los Angeles, California

A. Hi Jake, 4V is abnormal high (especially at such low current setting) which could cause poor anode dissolution. You should have both ends of contact bar connect to rectifier and ensure all contact points are properly cleaned and tightened. For anode to cathode ratio, please try to increase to 2:1 to 4:1. Regards, David David Shiu - Singapore A. Try increasing the ratio to 2:1 anode to cathode, and the anodes should extend below the bottom of the cathode to some extent. 4V seems a little high, but increasing the anode area should bring that down some. James Totter, CEF - Tallahassee, Florida

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Q. Hello Sir/Madam,

bright acid copper anodes get gray instead of black and plating becoming very very slow. Rectifier voltage goes up while plating in ON ... normally it goes down (e.g., 1 volt goes 1.2 or 1.4). Before it was set to 1 V goes 0.9 or 0.8V

In my area no hull cell testing no lab for electroplating test. I did clean it was working fine mirror finish, but after few hours same problem.

Check attacked pictures. We use bags; they where normal from outside inside it was some black & gray. Using Phosphorized copper 0.04 to 0.08% anodes. Cu anodes are then put in Ti basket and then wear bags.

2nd picture was taken about 72 hours -- second time cleaning seems darker color than 1st picture.

Regards,

Dipen Pattni
jeweler/goldsmith - Dar-Es-Salaam, Tanzania
November 12, 2013

A. Hello Dipen, You didn't mention that you dummy plated after cleaning the anodes. This is very important before you start production plating cycles. I like to start at 2 ASF for 1 hr, increase to 4 ASF for another hour and then 10 ASF for the final hour. I have found this method builds a nice thin protective film (cupric oxide) on the anodes. Other possible causes are high chloride level in the bath, poor quality anodes, high anode current density, high CuSO4 or H2SO4 in the bath. Anode current density should not exceed 2.5 A/dm2. Anode to cathode ratio should be 1:1 - 2:1. Mark Baker Process Engineer - Mesa, Arizona, USA A. Hi Dipen, Have you added ~50ppm Cl in form of HCl or NaCl? Chloride is necessary to facilitate copper anode dissolution in acid copper plating. Regards, David David Shiu - Singapore

Dear Sir,
I did not reply until now because I had given Cu solution for test but seems they did mistake. Attached is analysis report.

I'm planning to do zinc dust ⇦ on eBay or Amazon [affil links] , carbon treatment and then add 1st brightener and start working.



Thanks,

Dipen Pattni
jeweler/goldsmith - Dar-Es-Salaam, Tanzania

Ed. note: We cropped out the name of the test lab because they understandably wouldn''t want their name on copies they do not have control over or which could be altered.

Q. Hi,

Got new report from India for same Acid copper solution says:-

copper sulphate/229.59 (gm/lt)
sulfuric Acid/ 79.35 (ml/lt)
Chloride / (49.63 ppm)
Copper metal 58.42 (gm/lt)

Advised to make 30% dilution ... add 3 ml/lt hydrochloric acid (32 ml/lt), carbon treatment ... add 1st & 2nd brightener.

Regards,

Dipen Pattni
jeweler/goldsmith - Dar-Es-Salaam, Tanzania

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Current problem with acid copper

Q. Lately I have been having a problem with my acid copper. After I put in the pieces to copper plate, the amps go down to zero. It is like it loses contact. It resists for about five minutes then slowly lowers until zero. All contacts are clean but I noticed that the anodes blacken quickly.

John Perilli
Employee - Italy
October 25, 2018

Q. Sorry to ask another question, but I would like to know how to check chloride content and what it is. I have little experience in acid copper plating.

John Perilli [returning]
- Rome, Italy

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Q. Dear all experts,

I am performing copper plating on stainless steel wire with usual acid based copper plating solution with copper anodes in the basket. What I have observed yesterday that the copper anodes, part which are immersed in the electrolyte solution, is turning into black. It seems that it is a black film of something, unknown, is being deposited. That film can be removed by water rinsing or by rubbing on the surface. Does anybody has any idea what is that film and why it is being built? The concentration of H2SO4 is fine. Chlorine content is not measured yet.

Kind Regards,
Ridwaan

Ridwaan Ali
- Karachi, Pakistan
July 2, 2020

Ed. note: As you will read on this page, that blackness on the anodes is normal and desirable and the result of the phosphorous in the anode.

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Q. My copper sulphate content is continuously decreasing in acid copper bath. I have also monitored the drain valve, there is no leakage or wastage of the solution. Kindly suggest me a solution to overcome this issue.

Annie Tahir
- Lahore, Pakistan
July 6, 2020

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Hello there,

We have the same problem with black film on the copper anodes. I just got the chemical analysis result which says that:
Cu = 53 g/L
H2SO4 = 128 g/L
Chloride = 48 mg/L.

It seems that the sulfuric acid amount is more than double of the suggested amount (60 g/L). I am going to take out some amount the copper bath and will dilute the rest with water to reduce the sulfuric acid value.
I will let you know guys.
Thanks for the wonderful thread on this issue.

Kind Regards
Ridwaan

Ridwaan Ali [returning]
- Karachi, Pakistan

Ed. note -- Readers: As you have read on this page, blackness on the anodes is normal and desirable and the result of the phosphorous in the anode.

adv.: Supplier of Copper Anodes, Nickel Anodes, Bismuth Metal, & Other Metal Products for Industry & The Arts