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topic 31751

Copper anodes passivating?

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A discussion started in & continuing through 2017


Q. Hi:

I am using a standard acid copper bath
33 oz per gallon copper sulfate
8 oz per gallon sulfuric acid
Proprietary levelers and brighteners.

The bath has been tested and is within good limits for operation. My problems is that as I plate, the voltage stays even but the amperage drops off after about a 1/2 hour of plating. Turn the voltage up to the correct amperage and it continues to drop off.

If I shut the power off and let the bath sit dead for a minute then the amps will go to the appropriate setting that I have the volts on. But, it will start dropping off again. I have swapped out the power supply and the same results. I pulled and cleaned the anodes/bags and it worked great for about 3 weeks. Then the same thing starts happening.

I am using phosphorous copper anodes. I have a mix of bar and basket type copper anode.
Temp is 75 deg F.
Air agitation

It seems to me that the anodes are going passive as I plate?

Is this why people do periodic reverse current? If so, how often should I do this and what do you use to do this with? i.e., what is hanging on the bar at the time you reverse the current. Another copper anode?

Any help would be appreciated.


Tom Haltmeyer
small shop - PHX, Arizona, USA


A. TOM !


1. I would like to check your rectifier ripple. 2. What kind of the bags you use and wash the bag before you use. 3. Look like you lost the conductivity in bath. 4. If your copper sulfate concentration too high and bags plugged up & temp too low- you lost conductivity in bath. 5. Check sulfuric acid concentration more often. 6. Check all electrical connection -rectifier and plating bath.

popat patel
Popat Patel
    Howard Finishing
Roseville, Michigan


A. What is your anode to cathode ratio? What is the chloride level? What current density are you attempting?

Russell Richter
- Danbury, Connecticut, USA


A. Hello. In my opinion, this event is related to rectifier problems. Your bath parameters normal. And we consider your baths contacts good. So there is left any suspicion event. You must maintenance your rectifier, then we can think other reasons.

Emre Tuna
- Turkey




ajay raina
Ajay Raina
Ludhiana, Punjab, India


Q. Thanks for your replies........

I am getting the baths reanalyzed now. I will post the results.

I have found that heating the bath to about 80 °F will cause the amp drop to slow down.

To me is seems the copper anodes go passive and get a non conductive film on their surface. Once I shut the power off and let everything sit for a minute, turn the power back on, the amps are back up to where they should be.I figure this is because the sulfuric in the bath takes the non-conductive film off.Then they start falling off again to about 1/4 of what they should be. I can turn up the volts but it will continue to fall off on the amps. I'm suspicious that I don't have enough sulfuric in the bath to keep it conductive.

Also, I swapped out the power supply and the results are the same. Anode/cathode ratio is at a min of 2:1. I did pull all anodes and clean them in a 1/4 sulfuric to 1 water bath. Everything worked good for about a week and then the problem came back.


Tom Haltmeyer
small shop - PHX, Arizona, USA


A. Tom,

I had a similar problem a few months ago and after going crazy a little by doing a number of things like the ones in these postings. I end up adding more copper bars, and guess what, my problem disappeared. Sometimes the ratio is a very tricky thing. I hope this works for you. Please let us know how do you end up fixing your problem.

Sergio Gonzalez
- Guadalajara, Jalisco, MEXICO


A. If your bath contains Sulphuric Acid more than 50 ml/litre. Then copper sulphate in your bath gets crystallised. It gets crystallised on the anodes as well. So if you increase the temp it gets dissolves & again it gets crystallised after temp comes down and electrolysis starts. I faced similar problem an Year ago, when I decreased sulphuric acid content in my bath the problem got solved. Another reason may be insufficient chloride it should be around 60-80 ppm. Kindly let me know if the problem got solved.

N K Praveen Kumar


thumbs up signAfter analysis it looks like my sulfuric acid was too high.

We diluted the bath by 25 percent and it's working perfect now.

Tom Haltmeyer
small shop - PHX, Arizona, USA

May 20, 2008

Q. We are using Okuno copper plating system. What is the anode to cathode ratio? Why phosphorised copper anodes are used in copper plating?

Vijikumar Abel
pinang,malaysia - Bayanbaru, Pinang, Malaysia

May , 2008

A. Hi, Vijikumar. Sorry, but I'm not quite clear what you mean by 'what is the anode to cathode ratio?'.

If you asking for the meaning of the phrase, it's the surface area of the anode basket compared to the surface area of the workpiece. If you are asking what anode to cathode ratio Okuno recommends for this process, you would have to ask them, but it's usually between 1:1 and 2:1 (it may be on their technical data sheet).

Is this an acid, pyrophosphate, or cyanide bath? Probably the main reasons phosphorized anodes are used is to try to minimize copper buildup by slowing dissolution, and keeping copper particles from breaking off the anodes; such particles could plate out onto the workpiece as roughness. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

sidebar March 18, 2013

Q. What does the anode to cathode ratio mean?

What is the actual positioning of the anodes to the cathodes?

Does it mean that there should be one cathode bar between two anode bars?
e.g., + - +
Are these the ratio?

Abhiraj Naik
- Mumbai, Maharashtra, India

March 19, 2013

Hi Abhiraj. Let me try to bring you up to speed, along with other readers who may be confused, so you can fully benefit from this discussion --


In the electroplating process, the item you wish to plate onto is immersed into a bath of plating solution and attached to the negative pole of a direct current circuit (battery, rectifier, or power supply); for this reason, that workpiece is called the cathode.

Another piece(s) of metal is put into the plating solution and attached to the positive pole, and for this reason it is called the anode.

As the battery pulls electrons from the anode and pumps them over to the workpiece, the workpiece begins to accumulate a negative charge, and attracts the positively charged copper ions, Cu++, that are in the solution. As those ions touch the workpiece, the excess electrons neutralize the Cu++ ions, turning them into Cu0 metal.

Meanwhile, you can choose to either make the anode(s) from an impervious material like platinized titanium, or you can make it from copper. It is usually best to make it from copper because then, ideally, for each Cu++ ion that was in the bath and became plated out onto the workpiece as a copper atom, a new copper atom, Cu0, from the anode will dissolve into solution as a copper ion, Cu++, and keep the bath in balance. When the balance is working properly, the concentration of copper in the bath stays consistent instead of growing or declining and things remain under control.

To keep this balance, i.e., to make sure that the anode will dissolve copper into the solution at exactly the same rate as plating onto the workpiece removes it, requires that we watch several things: First that the surface area of the anode is in good proportion to the surface area of the workpiece, generally that there is about 1 to 2 square feet of anode surface area for each square foot of cathode area. That is the 1:1 or 2:1 anode to cathode ratio we speak of. Secondly, that the composition of the anode be carefully controlled so that it neither 'passivates' (refuses to dissolve) nor dissolves too efficiently (resulting in an ever increasing copper concentration in the plating bath). That is why different anode compositions are used for acid vs. alkali plating baths.

As for the positioning of the anodes, you can see from the above discussion that the plating goes where the current goes. And you already know that electricity takes the path of least resistance. So it is important that the anodes be as close as practical to equidistant from all points on the workpiece; this generally means that your little " + - + " is correct most of the time.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

April 25, 2012

Q. I also have similar problem to this, that is, in our acid copper electroplating bath all the copper anodes gets black.

We are using phosphorized copper anodes in baskets? If the chloride concentration of the bath is high, how it can be brought to normal range?

What should be the pH of acid copper bath?

Your opinions in this regards highly appreciated.

Harsha Rathnayake
- Anuradhapura, Sri Lanka

April 30, 2012

A. Harsha,
It is natural for Phosphorous Cu anodes to build up a black film in acid Cu plating. This presence of black film doesn't mean your anodes are passivating. I am not sure of what exactly you are seeing. Because acid Cu plating baths contain sulfuric acid, the pH is not something that has to be monitored. To answer your question, the pH should be less than 1.0. If your anodes are passivating you should do a complete analysis of the bath, then take measures to bring the bath to operating range. If the bath analysis does reveal a high chloride level, bath dilution with the add back of other key components would be the easiest.

Mark Baker
Engineering - Mesa, Arizona, USA

Researching passivation level of copper anodes

October 25, 2017

Q. I'm working on a project to evaluate the efficiency of copper anodes, and the theme of passivation is getting into my project. I wanted to know a trustable method to measure the passivation level of the copper anode. Also I did some research about copper anodes, and found that increasing the salts concentration (Cl-) I could extend the anode working time before it starts to passivate, any thoughts on this?

Ricardo Escobedo
- Mexico

October 2017

A. Hi Ricardo. I'm a little confused about your project...

First off, exactly what do you mean by efficiency? In electrochemistry of this sort it generally means what percentage of the applied current goes towards the desired electrochemical reaction (in this case, dissolution of copper) vs. undesired reactions (like separating the water of the solution into H+ and OH-). Depending on the electrolyte you are using and some other factors, the efficiency can exceed 100%; in some cases that can be a problem since the buildup of copper can throw things out of balance.

I'm not sure whether 'passivation level' is even a clear and valid concept, let alone measurable, when separated from bath conditions. But you can determine the anode efficiency by weighing the anode before and after the application of a given number of ampere hours of current, and applying Faraday's Law (96,487 ampere-seconds dissolves one gram equivalent weight at 100% efficiency).

High Cl- levels will almost certainly lead to high anode efficiency, but this seems a rather abstract finding unless we understand the application of your work because, for example, high Cl- levels might make for severely stressed and worthless copper electroplates or electroforms. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

October 26, 2017

Q. Thanks for answering so fast, Ted.
I'm using a copper sulfate bath and phosphorous copper anodes, and in our baths the anodes passivate around 3 weeks after the make up (they're used frequently). We want to know a method to evaluate how the passivation evolution (a quantitative method), in order to be sure that we are forced to etch the anodes for a next use. We propose to measure the Resistivity near the anodes, but there are some uncertainties. Any thoughts on this?

Thanks for the help.
PS: Big fan of this website.

Ricardo Escobedo
- Sonora, Mexico

Modern Electroplating

October 2017

A. Hi Ricardo. Topic 848 contains a good discussion on this subject and recommends Modern Electroplating for a better understanding. It seems to me that you may not have enough anode area, as that seems to be the major cause of passivation in sulphate baths.

It would seem to me that you should be able to "track" passivation from the required voltage to maintain current density or from solution analysis for copper content. Good luck and thanks for the kind words.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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