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"Problems with tin plating over brass"
A discussion continuing through 20212001
Q. I've been trying to tin plate some brass pieces in order to reduce soldering times. However, when the part is heated up in order to receive the solder, the tin layer starts "bubbling", leaving a very bad finish. It is necessary for our process that the surface of the part after soldering remain smooth. We've gone to several platers, and all methods utilized have the same result. One of them suggested silver-plating instead of tin-plating.
I would appreciate any advice on the matter.Arthur F. Allen
- Barcelona, Spain
A. You cannot plate tin directly on brass, you need a barrier like a copper deposit or nickel deposit between the brass and the tin.
chemical process supplier
Q. Sara, thanks for your response. We do use a flash of copper over the brass before tin-plating, and the "bubbling" continues. Because of the electrical properties of nickel (since the part is for RF use, this is very sensitive) we have decided not to use nickel before tinning, although I understand the tin adheres better to nickel than it does to copper.Arthur F. Allen [returning]
- Barcelona, Spain
A. Please can you ask if the suppliers are using acid or alkali tin plating solutions?
surface treatment shop - Stroud, Glos, England
A. Mr. Allen,
Use Tin/Lead to resolve your soldering and appearance issues.
- McAllen, Texas
A. Try asking your supplier about "Dull Tin". We use it and it passes solderability. You still have to have a copper or nickel barrier but it works very well.Kevin Gendron
- Trenton, Ontario, Canada
A. If you already have a copper underlayer, the recommendation for DULL or Matte tin should solve your problem.
chemical process supplier
A. Everyone is giving good advice. Always remember there is more than one correct answer to a question. The more plating experts you get, the more answers. One reason you may be experiencing problems with your present process cycle is that you say you are applying a copper flash. I assume this is from an alkaline bath. You need to plate sufficient thickness to overcome the amount of the copper plate which will be absorbed (not the technically correct phrase but descriptive). Try doubling or tripling the thickness of the copper flash. Also check your copper plating chemistry to insure that you are not depositing excessive organic compounds.
Good Luck,Gene Packman
process supplier - Great Neck, New York
October 8, 2021
A. If you are using bright tin plating and having blistering try adjusting time and temperature in the reflow process and make sure your reflow material is fresh. Use to more then twice.
If that doesn't work, switch bright tin to matte tin plating.
Or try copper flash, nickel, then matte tin plating.
Definitely use matte tin, stay away from bright.
Stamper tool and die guy - New York
Q. We are having exactly the same problem that Mr. Allen has - The tin plating 'bubbles' off during soldering. The substrate is MS58 brass and we have an intermediate layer of copper. Could someone explain why the tin 'bubbles' off and why a matte layer of tin should solve this problem? If the copper layer is not thick enough, what would be the right thickness?
- Zejtun, Malta
June 10, 2008
A. The bubbling could be outgassing from organics in the tin OR the copper plate. Check with the supplier that they are using a pure matte copper and a pure matte tin. Also, the copper should be 100 microinches (2.5 microns) thick. If you are using a nickel barrier, the industry standard for the barrier thickness is 50 microinches (1.25 microns).
This is because the CuTin intermetallic grows at a much faster rate than NiTin intermetallic. The CuTin intermetallic is detrimental to reflow and solderability, whereas the NiSn intermetallic is not.
I worked at MacDermid Inc as a research chemist and tech service engineer for 11 years; my area of expertise was tin and tin lead plating over connectors. If you can switch to nickel, it will improve the lifespan of your parts and minimize whisker growth on connectors.
I hope this info is helpful.
- Devens, Massachusetts
September 9, 2009
Q. I am having a similar issue.
We have: Zinc with Ni underplating, and Sn finish.
The tin has visible "bumps" after reflow (lead-free process, 260 °C max temp). These bumps are solid Sn (cross sections confirmed no air or anything else under them - EDX).
The Sn plating is ~2.3 µm, but the thickness at the 'bump' is ~23 µm (EDX)
What would cause this Sn to want to 'gather' together and from a bump?
- San Jose, California
March 4, 2010
Q. Is it true that Zn in the brass (CuZn) would migrate into Sn layer, when there is no Ni barrier or Ni layer is too thin, say <0.5 micron?John Li
- Melbourne, Vic, Australia
March 16, 2010
Q. I am looking into lead-free soldering processes and I have found visible "bumps" on connector pins after reflow (260 °C max temp).
Brass pin with Ni underplating, and Sn finish.
Seems the surface tension is gathering the melted Sn into bumps. How to minimise the amount of "free" Sn to limit this? Or would that directly cause fretting issues?
- Gothenburg, Sweden
October 30, 2010
1. if the etching process is with current, you may try to setting the current to 0.
2. set up acid active process with sulfuric acid after Etching process
January 6, 2014
Q. I face high carbon and oxygen content on tin plated surface (with copper underlayer) by SEM-EDX analysis. The black area is unsolderable during reflow.
I used hot air blower and performed manual soldering; I able to re-solder it again.
The tin plating is matte tin.
Any possible cause for the black residue?
- Melaka, Melaka, Malaysia
January 7, 2014
A. Hello Vincent,
The 3 major causes for carbon to be present in the tin deposit is storage conditions, and excessive organic additives in the bath and bath impurities. Because you are using a Matte Tin Bath, you can pretty much rule out the organic brighteners. Are these parts stored at room temperature right after tin plating, up until the point of soldering? What about humidity and the general atmosphere where the tin plated parts are kept?
Here is a test you can run... Plate the parts in tin normally. Be sure you have good rinsing and clean drying techniques. Wrap parts in sulfur free paper, or just a plastic bag and store in a room temperature environment. Wait the usual time before soldering. If you still have the problem, the tin bath should have a full analysis including metallic impurities. It would also benefit you to put a few carbon filters in your filter system for a few hours apiece in case you are dragging in organics during your plating cycle. Good Luck.Mark Baker
Process Engineer - Malone, New York, USA
Tin electroplating on brass problem: oxidationSeptember 23, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. Dear sir,
We have a problem of tin plating on brass part after few days of electroplating (acid solution).
Can you find a solution for this problem? We put tin directly on brass part.
Please see photos.
Best regards,Faouzi Hmaied
- Grombalia, Tunisia
A. Hi Faouzi. I'm not sure if you're saying that the plating solution goes bad after a few days and starts making bad parts, or whether you are saying that parts which looked okay coming out of the plating tank start turning bad in storage a few days later. It would make a big difference in my answer. I'm also not sure of the scale of these photos; a measuring tape would help. But it looks to me like you have a huge "particulates" problem, with loose fines attaching to the parts and getting occluded into the plating as extreme roughness.
Do you have anode bags on the anodes and continuous filtration in the plating bath?
We appended your inquiry to a previous thread which suggests the need for a barrier layer of copper or nickel before the tin plating, but I don't think that's the main problem here :-)
I, too, would like to hear from tin plating experts though because I find this issue very strange! Although, as I say, it looks like particulates to me, they seem to be exclusively in low current density areas. Why? Maybe I'm wrong and it's a reaction between very thin plating and the brass substrate? Those are mighty rough castings.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 24, 2014
It's nothing else but you are stripping Zn and Cu from the brass from which impurities increase daily. You move ahead and it's getting plated in low current density areas. Initially few hours or days you must be getting good results.
As suggested by Mr. Ted, you need barrier layer before entering Acid Tin bath.
- AJMAN UAE
October 24, 2014
A. Hello Faouzi,
The 2 previous responses revealed some good points. In troubleshooting plating problems I have always employed the process of elimination to get to the root of the problem.
1) As Ted mentioned you want to rule out particulate matter. Check the filter tubes to see if they contain insoluble matter. Anode bags must be used, and replaced when they don't drain the solution at at good rate. Pure tin anodes should be used, and they are supplied with a certification of purity.
2) Make sure you have adequate solution agitation to ensure the tin ions are being replenished at the cathode (parts).
3) In addition to a routine bath analysis, have the tin bath checked for metallic impurities such as zinc, copper and lead (if plating leaded brass). If you don't have the means to do this, send a sample out to a lab or supplier of your tin bath.
4) Be sure you are maintaining additions of your bath additives, whatever they may be.
5) Make sure your rinse tanks prior to the tin bath are clean and not loaded with metallics.
This may seem a lot to verify, but if a malfunction in the process is found, you will know how to correct the problem if it re-occurs. Good Luck!
Process Engineer - Phoenix, Arizona USA
August 14, 2017
A. Hi, Faouzi! After long years of experience: Never do tin plating directly on brass ... if you do you will meet such problems after a few days.
You should have copper plating first before tin plating.
I hope your problem will soon meet the answer.
- Bekasi, Indonesia
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