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Immersion tin plating issues

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Q. Dear friend
I do it like this but I have these problems
After some days its silver color gets dark and I cannot solder the pad easily.
Can you tell what's the matter?

Majid Ja
- Tabriz, Iran
August 11, 2022


A. Hi. The best solution, when possible, is simply to not wait. Solderability always decreases with age :-)
But Jeffrey Holmes tells us below that when failure comes soon it's due to poor rinsing and drying. And Robert Probert tells us on thread 24114 that plain water rinsing probably won't do it; you need a dip in an alkaline cleaner to clear the tin residues.

Luck & Regards,

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



Q. We are a job shop company looking to put tin on aluminum (6061) by immersion tin solution (base is Potassium Stannate).
Can anybody tell me how to analyze the Tin metal left in the solution after using it? I am looking for a simple analytical procedure to determine the Tin level in the solution.

Jay Nat
- Bangkok Thailand
November 1, 2022




Closely related historical posts, oldest first ...

TUTORIAL FOR NEWBIES:

We think Gordon is asking about depositing tin onto the copper traces on a circuit board. Although he used the term "electroless tin plating", most metal finishing professionals prefer to call that process "immersion tin plating", because they reserve the word "electroless" for something else: processes which include reducing agents, such that the process is sort of "spring loaded", waiting only for the presence of a catalyst to trip the spring and cause the reducing agent to react with the dissolved metallic ions and convert them to metal. "Electroless plating" is therefore sometimes alternately called "catalytic plating" or, if the metal that it deposits can itself serve as a catalyst (which is the usual case), "auto catalytic plating".

One reason for drawing the distinction between "immersion plating" and "electroless plating" is that, in immersion plating, as soon as the object has a thin plating on it, so no substrate metal is exposed, no more can dissolve and be replaced, so the plating stops -- it can't get any thicker. But quite thick plating is possible with "auto catalytic electroless plating" because it can continue long after the substrate has been coated.

Q. Hi, I am looking for the method of electroless tin plating of printed circuit boards. In my country I cannot simply go to a shop and buy some plating crystals, and therefore need to actually make up the stuff to do this. Electronics is my hobby, and so any help will be GREATLY appreciated.

Thanks very much

Gordon [last name deleted for privacy by Editor]
-computers
1996


A. Hello, Gordon,
The Metal Finishing Guidebook lists three formulations for immersion deposits of tin onto copper, only one of which is cyanide-free:
Stannous chloride 3.8 g/L,
Thiourea 49.5 g/L,
Sulfuric acid 12 ml/L,
temperature 80-120 °F.

However, immersion deposits of tin may not be a fully acceptable substitute for tin-lead electroplating. Good luck.

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


Q. Ted,

A little while ago you assisted me by letting me know the mixture for electroless tin plating of copper on PCB. It was stannous chloride 3.8 g/l thiourea 49.5 g/l and sulphuric acid 12 ml/l. But I do not know what strength the sulphuric acid is supposed to be. Please could you assist me with this as I have now found a place to get the thiourea and would like to try the plating as soon as possible.

Thank you for you help.

Gordon [returning]
- computers


A. The source doesn't say, Gordon. I must assume it's based on total weight. But you could probably use 66 degree baumé (96 percent) sulphuric acid without being far off. There are several other formulas for generic immersion tin solutions; you might want to consult some of the standard reference books on this. Good luck.

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


A. Anyone contemplating the use of the above recipe should first read the MSDS on thiourea:

http://physchem.ox.ac.uk/MSDS/T/thiourea

Cor Grooff
- Netherlands
1999

----
Ed. note December 2011: Sorry, that MSDS database is no longer functional.



Q. I am looking for any information on immersion tin or immersion gold processes pertaining to the PCB manufacturing process. Specifically I'm interested in any studies comparing Immersion Tin or Immersion Gold vs. HASL finishes in the application of micro electronics. Thanks, Rick Jackson

Rick Jackson
- Melbourne, Florida, USA
2000


A. You might get this publication: "Implementing Cleaner Printed Wiring Board Technologies: Surface Finishes" (EPA 744-R-00-002); it can be ordered from the Pollution Prevention Information Clearinghouse online through the EPA Website or download from www.epa.gov/dfe. The Design for the Environment EPA project did a good job in their "Making Holes Conductive" project.

James Totter
James Totter, CEF
- Tallahassee, Florida


A. Sir,

Immersion Tin is primarily a three-step process: Cleaning - Microetching - Immersion Tin. But Some suppliers give an option of conditioning the copper surface before Immersion Tin. Please could someone clarify whether I should go for conditioning step before Immersion Tin?

Sonali Kokane
plating shop employee - Mumbai, Maharashtra, India
2006



Q. Dear all,
I have a issue of immersion tin process, we use polyamide coverlay to protect the unwanted plating area, we observe that there's a surface "nick" issue (galvanic effect) found near the coverlay edge where adhesive is squeezed out, this defect appears at same area, and I tried different type of immersion tin chemicals but still can't resolve this problem, please help!

Thanks and Best Regards,

Chen Rong Ming
- Singapore


A. Try an overlay with less adhesive or do not rub it as hard at the edge.

James Watts
- Navarre, Florida
2003



Alternatives to Immersion Tin plating for PCB ?

Q. Hi all,

I make prototype PCB and, after etching the boards, I use Immersion tin to "plate" them and to protect from oxidation of the Copper. I buy the immersion tin solution in three components but I don't know what they are. I only know that one of them is Sulfuric acid. After reading a post by Ted Mooney I think that the three components are Stannous chloride 3.8 g/L, Thiourea 49.5 g/L, Sulfuric acid 12 ml/L since proportions are the same.

When I have to apply the solder (the protective green layer on PCBs) on the boards, before plating, I put the boards, only for a few seconds, in a Ferric Chloride solution to remove oxidation from the copper pads (the boards stay for 60 minutes at 140 °C). Even doing so, some customers (very few considering the total amount) say that it's difficult to solder. Is there another method for depositing, in the same easy way, some other metal that can be better to solder the electronic components on ? Even Gold can be taken in consideration since the effective plated area is usually very small (only the pads on a PCB with the solder).

Sorry for my English !

Thank you,

Francesco Fontana
- Valenza, AL, ITALY
2003



Brightening of Immersion plated Tin surfaces on Printed Circuit Boards

I have successfully immersion plated tin on printed circuit boards -- using Stannous Chloride, Thiourea and HCl-- but the plating is matte in appearance. Can you suggest an additive to the above solution whereby the plating is bright and shiny?

Azhar H. Shah
hobbyist - Karachi, Sind, Pakistan
2004


A. Hi There,

So you found that dreadful formula too ... was that the one with Sodium Metaphosphate as well?

Okay, I gave up on trying to chemically get a bright finish and then buffed the P.C.B's with a fine cutting compound it will just take off that annoying dull/oxide layer and little tin, leaving the sought after highly solderable bright tin.

Have Fun.

Robert Fyfe
Audio Eng. - Wyoming, NSW, Australia


thumbs up sign Mr.Fyfe,

Thanks for your response to my query. I am glad to note that my persistence resulted in the much sought after bright finish. Nothing was changed in the Stannous Chloride, Thiourea and HCl formulation.

No,I did not use Sodium Metaphosphate. Only the method of application was modified. Instead of dunking the PCB in the solution, I briefly swabbed the copper conductors. As soon as the PCB was evenly covered with the plated tin, it was rinsed in water. I immediately got the shiny tin finish. Light buffing with a soft cloth made the plating even more shiny -- though, this is not necessary.

The secret is in not immersing the PCB in the solution for prolonged period but quickly swabbing it with soaked cotton. Immersing the work piece for any length of time -- except very very briefly -- results in the dark gray tin deposit which you claimed to have removed with the polishing compound. I too tried to do just that but by the time the gray deposit is entirely removed, the tin starts to come off too. Perhaps I was not using the right polishing compound. As a matter of fact, I also tried Stannous Chloride, Thiourea, Citric Acid formulation and got a mirror finish on an inch-square copper piece. But in this case you just dip and pull out the PCB a couple of times to get an even coat of tin, or the swabbing has to be real even, otherwise you get dark gray stains in places. Of course, for both the methods to succeed the copper surface has to be meticulously clean. Hand rubbing with a fine polishing compound -- I used a pre-wax auto rubbing compound -- and Acetone [affil. link to info/product on Amazon] wipe will accomplish this. No touching with fingers after that! Regards

Azhar

Azhar H. Shah [returning]
- Karachi, Sind, Pakistan


A. I have used Stannous Chloride for years to prepare Electroless Tin Plating for PCB. You can try the following recipe:

Care must be taken for Sulphuric acid over water.

Juan Oyarce
PCB-CNC - Santiago, Chile
2005



"Build your own Printed Circuit"
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Q. In the recipe you mention Stannous Chloride 3.8 g/L.
Is this SnCl2 [anhydrous] or SnCl2.2H2O [dihydrate] or will both do equally well?

Thanks for your reply,

Hans Schaaper
hobbyist - Alkmaar, NH, The Netherlands
2006


A. Hi Hans. That sourcebook did not say. However, the usual meaning of concentrations like this is on a final weight basis -- i.e., you need 3.8 g/L of the chemical stannous chloride. Whether you got it from anhydrous or hydrated doesn't matter; you need to end up with 3.8 g/L of SnCl2, stannous chloride.

Regards,

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



Q. We are making PCB The tin plating we need should be Electroless. But how the mentioned processes are possible for the exploitation on Manufacturing Level? Which parameters are critical for maintaining?
I had tried but we got Black slurry & minor tin plating, How to reduce this problem? The Sn was released in Black Granules form I suppose. Then the process will be expensive. How to control Thickness, whatever it may be.

Chetan Choudhari
Owner, associate unit - Nasik, Maharashtra , INDIA
July 10, 2008



Q. Hello dear,
I've tried to do electroless plating of tin on copper PCB and has worked and I've used the formula Stannous chloride 3.8 g/l, Thiourea 49.5 g/l, Sulfuric acid 12 ml/L.
But the surface wasn't bright, so how can I make the surface bright.

thanks

Hanibal Najjar
university teacher - Gaza
April 24, 2011


A. You can get a bright finish with Barkeepers Friend [affil. link to info/product on Amazon] - it probably goes by another name in Gaza... It is a cleaner used by restaurants for polishing brass, copper and such. The active ingredient is 5% oxalic acid - which shouldn't be any problem - mixed with a mild abrasive and a bit of detergent.

Nicholas O. Lindan
- Cleveland, Ohio, USA



Q. My mixing is:

Stannous chloride 3.8 g/l, Thiourea 49.5 g/l, Sulfuric acid 12 ml/L.

It is changing to silver colour, then after some time it turns to black not suitable for soldering. Can you tell me what I should do to make it good to solder?

puvan vijayakumar
- karur, tamilnadu, India
April 9, 2016


A. The plating formulations listed, with thiourea, are actually immersion plating and not electroless plating. It should be noted that thiourea is a suspected carcinogen.

Lyle Kirman
Consultant - Cleveland, Ohio USA


A. Hi, Puvan.

The immersion tin coating is very thin.

If it turns black in a few hours or days, then it was not carefully rinsed and dried.

If it turns dark after weeks or months, then it is due to alloying of copper with the thin tin layer.

So ... either rinse and dry it better, or use it sooner.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina


A. ... or plate it thicker.

Hi, Puvan. Some suppliers claim that a proper conditioning step before the immersion plating process will increase the thickness to 1 µ (.65 µm of pure tin) which they say will remain solderable for a year.

Regards,

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



Q. Thiourea-free immersion tin plating over brass?
Sir,
we plate brass zip roll. It is electroless process.
We use tin chloride and thiourea to plate brass color in white.
Maybe the process known as immersion process.

Now thiourea is not available. Please guide us substitute for Thiourea which we can use.

mukand garg
July 3, 2018
- delhi, India



Tin plating pcb boards

Q. Hi everybody, I hope someone can help me. I'm an electronics hobbyist and I'm always looking for methods to upgrades my pcbs. The copper board gets rusted with time and I'm looking to cover the traces with tin.

I studied and read lots of information on the internet until I came across this site, and have many doubts.

I want to cover the copper of a pcb board with tin. The tin I have available is the solder (60/40) or soldering bars with a tin content of 50%.

I prepared an electrolyte solution I found with White vinegar and 60/40 tin. I think it should be tin acetate...

For the plating and according to Faraday's Law and taking into account a valence of +2 for the tin, I should have a current density of about 7.8 A/ft^2.

When trying to regulate the current, changing the output voltage of the power supply I see bubbling over the copper board (as a test I use a board 5 cm x 3 cm). I see the board gets plated but a black cover forms over the Surface and even precipitates. And the plating is very thin (if I scratch it slightly with sandpaper the cover is removed).

I know that the bubbling is because of electrolysis of the solution so I performed a new test but regulating the current to avoid the bubbling. According to my calculations for tinning the area that I use is 120 mA. In this new case I performed the plating with 10 mA.

I don't know if what I'm doing is correct. wWhat do I have to do to obtain a greater thickness of tin over the board? More time?

The board has to be cleaned from time to time because of the black layer deposited?

The electrolyte solution I prepared is right, or what do you recommend to use for the plating I want to perform?

I've never done this before and I'm learning.

Thanks in advance

Carlos Martin
- Argentina
November 13, 2018


A. I am not a tin plating expert, but I doubt you are going to have much luck getting quality plating with a solution of vinegar and tin solder.

I'd recommend buying a proper tin plating solution from a supplier as a first step; if you really can't do that, at the very least find a better source of tin.

Brendan McNamara
- Rochester, New York, USA


A. Hi Carlos.
There are many reasons why your idea is unlikely to work.
Unmodified acetate solution will not produce an acceptable deposit and with both tin and lead in solution you are trying to deposit an alloy; even more unlikely.
Printed circuits are commonly plated with both tin and tin/lead but using far more complex solutions.
It is common practice to plate the circuit pattern through a resist and use the deposit as the etch resist. Once the pattern is formed you have a major problem achieving electrical continuity.
There are two simple ways of coating the conductors.
Boards are dipped in a molten solder bath - Quick and effective but needs a large heated pot of solder.
Or, for you the easiest way is to use an immersion tin bath (sometimes wrongly called electroless tin.)
You can make your own (see above discussion) but the chemicals are available cheaply and ready mixed on the internet.
Just search "Immersion Tin"

geoff smith
Geoff Smith
Hampshire, England



Q. Hi there! I'm reading this thread, quite interesting. I'm trying to prepare a solution for electroless tin plating. I have all the chemicals (SnCl2.2H20, H2SO4, Thiourea) and according what is mentioned here you need to have some proportions.

Please, can you tell me in detail how to prepare the bath? I tried in many ways but I can't get it done correctly.

Thanks in advance!

Carlos Martin [returning]
- Argentina
June 26, 2022


A. Hi Carlos. As Geoff Smith noted, it's better to call the process 'immersion' or 'displacement' plating because to most platers 'electroless' implies an autocatalytic process, as in the electroless copper and electroless nickel baths which can be used on plastic & other non-conductive substrates.

This page already lists formulations at least 4 times -- one by me, one by Juan_Oyarce, one by puvan_vijayakumar, one by Hanibal_Najjar (plus notes about where to find many others), and you say you've tried many times. This leaves an obvious question:

Are you sure the substrate isn't the problem, rather than your many formulation attempts? What substrate are you trying to immersion plate onto?

Luck & Regards,

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


June 28, 2022

Q. Hi everyone! I'm trying to make a bath for tin plating pcb's.

When mixing all the components I got a white sediment. I saw in this post the components and the proportions per liter.

Please can you help to prepare the bath correctly and the way of doing it?

Thanks in advance!

Carlos Martin [returning]
- Mendoza, Argentina


A. Hi Carlos. I've never prepared it myself, so I can't advise exactly what is going wrong. However, tin is well known for its stannous (white precipitate) form, so I suspect that something went wrong with the pH or the lack of thiourea. Are you using stainless steel instead of glassware?

Are you sure you can't just buy an immersion tin process as Geoff Smith suggests? -- thiourea is carcinogenic, so somewhat random experiments with it are probably not a good idea.

Luck & Regards,

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

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