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topic 9676 p.2

Problems with tin plating over brass

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A discussion started in 2001 but continuing through 2020

June 14, 2016

Q. Hi,
In FPCB, Tin plated on Cu.
Customer found dewetting issue & cross-section shows a kind of a corrosion in Tin layer.
Almost 50% of Tin thickness from outside has turned to black (not shiny) and rest is intact with Cu layer.

tin plating on copper is corroding

Please advise what could be that black layer which is causing dewetting during soldering.

Manju Penang
- Penang, Malaysia

July 19, 2016

Q. I want to set up a small and not very expansive electroplating unit to plate brass strips of 20 to 26 gauge with dimension 10 mm x 50 mm, approximate number 30,000 to 50,000 per month. I want a plating that will use less soldering material and will not tarnish and will keep looking good with time. Right now I am getting it done from out side source, who does copper plating and then tin plating, but results are not very good and quality is not consistent. Can some one suggest me as to what I should do.

Matman Plastics, Making Junction Boxes for Solar Panel - New Delhi, India

September 20, 2016

Q. I'm facing Cu frame exposed on the bending lead after Trim and Form process.
How can I solve this?
Lead frame type: Cu-Ni-Cu
Plate : Sn 100% plate (solder thickness ~11um)
Process : Mold -> Sn plate -> Trim n Form

Sarul Afzan
Semiconductor Industry - Melaka, Malaysia

June 17, 2017

Q. Tin plating over terminal brass is not being successfully done; some places we find still unplated surface especially inside feed terminal mainly of small terminals like multi lock ones.


June 2017

A. Hi Suresh. Unfortunately I don't think you've actually provided any info yet from which people can use to help you try to troubleshoot. You are the plater? Send a picture of the part if you can; tell us what the tin plating process is; barrel plating vs. rack plating, etc. and we can perhaps get started. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

July 5, 2017

Q. We are observing bubbles and surface blackening after soldering for copper, barrier nickel, flash tin plating. Can anyone guide us to resolve the issue?

Narayan Chavan
- Bangalore, karnataka, India

July 2017

A. Hi Narayan. Well, you can break some of the blisters and look at the underside of the blister and the surface they detached from, and tell us whether the nickel detached from copper, nickel delaminated from itself, or tin detached from the nickel -- and we can proceed from there. You can also send pictures of the blackening to , because cosmetic/aesthetic issues are difficult to cover with words alone. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

July 24, 2017

Q. Hello Everyone,

We are continuously facing an issue of soldering in a terminal. We are having brass terminal & undercoat of copper which have 2 microns thickness is done over brass & after that tin plating of 7 to 9 microns is done over copper. At the time of soldering dry soldering issue is faced by us. We have checked everything. Cleaning & plating thickness all are as per specification. Can anybody advice me on this issue??

Jaikishan Dayma
- gurgaon, Haryana, India

May 12, 2018

Q. Hi, we do tin plating on brass components, but in bend test some parts get flaking off, plating gets flaking off. Supplier does flash of copper before tin plating but problems not solved yet.

Sandip Rajput
Service in private sector - Jamnagar, Gujarat, india

May 2018

A. Hi Sandip. You can review this page and maybe get some ideas regarding what your supplier might be doing wrong, but the chances of solving your supplier's problem for him this way are low. Usually your only realistic alternative is to try a different plating shop. But best of luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

May 19, 2018

A. Find out whether the brass is leaded. If so, dip in 30%/vol commercial fluoboric acid, then copper strike in copper fluoborate. This is because lead is insoluble in other mineral acids and cyanide copper will not stick to lead salts. The plumbing industry knows all about this.

robert probert

Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Plating solder over brass

August 17, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

affil. link
Tin and Tin-alloy Plating
from Abe Books


affil. link
Tin and Solder Plating
from Abe Books


Q. I would like to know if plating solder on brass is possible?
If yes, I'd like to know how I can do it.
Thank you.

rana fz
- tabriz, Iran

August 2018

A. Hi Rana. Yes, you can do tin-lead plating on brass. It's best and may be necessary to copper plate it first, before doing the tin-lead plating.

… but please introduce yourself! We don't know if you are a highly experienced tin-lead plater who just hasn't happened to try plating onto brass yet, or a young student wanting to do a science project for school. There are entire books on solder plating, so it is very hard to tell someone how to do it in a paragraph or two until they tell us their situation so we understand what they actually want to know. Thanks!


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

May 21, 2019

Q. Hi to all.

I work over 15 years with same tinning bath. Now I have a problem when I changed the bath -- putting in some new components.
I have a problem with tinning brass terminals. It seems that after 5 days tin is not shining on terminal and after one month terminals are all black.
The bath is good; tin is shiny on tester but when I go to tin the terminals I have a problem. About 8 min terminals is in bath and I think that is okay time to tin on brass terminals. And terminals are shiny maybe too shiny --maybe that is a problem? Someone have any idea what to do?

Thank you

Marko Petrovic
private - Uzice Serbia

May 22, 2019

A. Hello Marko, when you say you changed the bath, adding new components, I would assume it's a brand new tin bath, not a slide conversion attempt? Have you measured the thickness of the tin deposit? If you have had success in the past with plating directly on brass. The bath should undergo a full chemical analysis, and deposit thickness verified. Your tin bath supplier should become involved as well.

Mark Baker
Electronic Plating - Winston Salem, North Carolina USA

May 23, 2019

A. It is common to take the finished tin deposit back thru a mild soak cleaner to remove the tin solution. Otherwise the deposit turns gray/black in a few days.

robert probert

Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

June 8, 2019

Dear All, I have to solder brass-zinc plated contacts & copper-tin plated contacts together. Is it possible or not? Kindly give your comments.

Yuvaraj Jayavel
- chennai, tamilnadu, India

June 2019

A. Hi Yuvaraj. Your question is too abbreviated for me :-(

Are you saying that you have brass contacts that have been zinc plated, and copper contacts that have been tin plated? And these 'contacts' are for conduction of electricity? ... because I've personally never even heard of a zinc plated electrical contact, and even googling for that topic comes up empty. Maybe you have a zinc plated brass chassis and you trying to solder a grounding lug to it?

Please follow up with the full details of your situation, rather than an abstract proposition :-)

Thanks & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

June 10, 2019

Q. Yes, we want to solder a diode which is tin plated to the zinc plated screw.
Kindly give a suggestion is this possible to get a perfect soldering?

Yuvaraj Jayavel [returning]
- chennai, tamilnadu, india

June 2019

A. Hi Yuvaraj. Please just get a tin plated screw.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

Nickel and Tin Plating Fails Humidity Test

July 3, 2019

Terminal material BS36 was underplated with Nickel and top plated with Tin. Terminals were exposed to humidity during tests and it resulted in ugliness -- platings seemed removed and terminal base material exposed. Can anybody tell me, does humidity affect plating? Or what could be the best way to pass humidity test after plating?

Sukhram Mandal
Gentherm inc - NORTHVILLE TW Michigan USA
  ^- Privately contact this inquirer -^

July 2019

A. Hi Sukhram. Sorry, I don't recognize "BS36" -- can you be a bit more explicit please? The plating should withstand the test, of course, and the fact that the base material was exposed tells us that the problem started early in the process -- the parts either not being clean, not being properly activated, or the nickel plating too thin or too poorly done.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

Solderability of tin plate containing intermetallic compounds

October 8, 2020

Q. We are having solderability issues with the following:
(Ground rule: the design cannot change.)

Item: Circa 1980 machined 2024-T854 aluminum chassis, approximately 0.08" at the solder point.

Finish: Copper Plate 0.00010/0.00025 thick per MIL-C-14550 Class 2 followed by tin plate 0.0003/0.0005 thick per MIL-T-10727 Type I Matte finish (alkaline type electro-deposited tin only)

Solder: Sn63Pb37

We need to solder a grounding tab of a component to the inside of the chassis but the solder will not wet to the tin plate of the chassis. (The component is new; the chassis is 40+ years old.)

1. Since we are trying to solder to an efficient heat sink, we are working to verify that we are getting the solder point to the correct temperature. We have used up to 300W soldering irons with heat gun support. An oxyacetylene torch was also tried for brute force but the solder balled up. We have used several fluxes with varying activity levels, but no success.

2. We are wondering if the copper has diffused into the tin creating IMCs which are impacting solderability. Does it seem plausible that after 40 years a majority of the tin layer could be consumed by Cu-Sn IMCs? Some internet research indicates it may be.

2.a. Is it possible to spot re-plate the tin onto the IMCs to "refresh" the tin at the solder point? We would prefer to not have to strip and re-plate the entire chassis.

The minimum solder point is approximately 1" x 1/4".

Many Thanks!

Tim Winkler
- Heath Ohio

November 19, 2020

A. Tim, You raise some interesting points here. Firstly, since the substrate is old, it will be heavily oxidised, so I presume you are using a good flux before applying the solder - the oxide surface will be resistent to wetting by the solder, so it needs to be thoroughly and carefully prepared to make it wettable. Secondly, you are correct in that copper and tin readily forms intermetallics - under low temperatures only two are formed (Cu3Sn and Cu6Sn5), but at over about 400 °C other ones are formed (Cu10Sn3 and Cu41Sn11). Maybe heating the surface to over 400 °C is resulting in a tenacious oxide film that is preventing the solder wetting the surface. My first guess would be that you need to make sure your surface is clean and free of oxidation, because I would not expect IMCs to inhibit the surface wettability by the solder.
I am not sure if the following is relevant to you, but many years ago I worked on another tin based IMC - iron-tin intermetallics and these are commonly seen in tinplate. There is a range of them (FeSn2, FeSn, Fe3Sn2 and Fe2Sn3), but the only one found under normal conditions is FeSn2 - the others are thermodynamically unstable and will break down to FeSn2 and Fe. Furthermore, under conditions up to about 450 °C, the only initial IMC formed is FeSn2, but once the tin source is exhausted, the other compounds start to form as the tin diffuses deeper into the iron. It is hence possible to get all 4 Fe-Sn IMCs, but if they are left alone, they will all break down to FeSn2 and Fe.

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

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