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Tin plating solution for PCBs - RESULTS

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Proud Mary

Mon Jan 10 2011, 12:08PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Dr. H. wrote ...

Good day Proud Mary - do you think that it will work OK for PCBs ? Those chemicals are easy to find here so if I can find an accurate "recipe" (how much of eache chemical) I would give it a try.

Hiya Dr H!

I must point out that I have not tried out these electroless tin plating recipes, though I see from my stock list that I could if I wanted to.

Both recipes below claim to be suitable for PCB use:

The first one comes from an electrofinishing site, where there is some additional discussion:

Stannous Chloride 5 grams/liter
Sulphuric Acid (66 Be) 10 ml/liter
Thiourea 50 grams/liter
Use only distilled water or demineralized water.

And here is another recipe, in which sulphamic acid/H3NSO3 is substituted for sulphuric acid:

In the September 1971 issue of "Ham Radio Magazine" Larry Hutchinson had an article "Practical Photofabrication of Printed-circuit boards". In that article he had an electroless tin-plating bath.

Formula

* 0.5g Stannous Chloride
* 2.0g Thiourea
* 3.0g Sulfamic Acid
* 100.0 mL Distilled water

To 100ml distilled water add 500 milligrams Stannous Chloride, 2 grams Thiourea, and 3 grams of Sulfamic acid. The chemicals are all powders so they keep but the bath is unstable, so only mix enough for one days job. All you need is enough to cover the board. Action takes 10 to 20 minutes. The article suggests a few mg of Alizarin or Alizarin Red S can be added as a brightner.

As sulphamic acid is a powder, I'd guess that these two recipes are behind the ones used in the commercially available liquid and dry powder electroless tin plating kits mentioned by Anders.

Conundrum

Mon Jan 10 2011, 02:15PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

hm..
reckon the thiourea containing silver cleaner i have would be suitable?
it doesen't say what percentage but its a straw yellow coloured solution.
regards, -A

Dr. H.

Tue Jan 11 2011, 08:34AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Thank you SOO MUCH Proud Mary

That is what I needed - I will start accuiring the chemicals.
Will post as soon as I have results ... or problems

Cheers

1294734861 931 FT105517 Thank You Smiles

Dr. H.

Wed Jan 12 2011, 11:47AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day

after a fast trip to the chemistry store it was time to test the recipe. I didn't have any way to measure the chemicals so I watched the video carefully and used aproximatelly the same quantity (well ... apparently I didn't as when I added the water it turned into white solution). I decided to try it anyway and placed a piece of PCB clad in it .... 15 mins later I had a verry well coated board. There are no traces of tin on the insulation materrial. The plating is really strong. We used some sandpaper to test it (that is why it looks like that on the pic). Also soldering is very easy

Once again thanks Proud Mary

Cheers

Proud Mary

Wed Jan 12 2011, 01:06PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Oh I am very pleased for you, Dr H.

Did you know that tin plate is prone to whisker formation, which can cause shorts? It's not a subject I know much about, but there is a useful-looking summary of this potential problem here:

Dr. H.

Thu Jan 13 2011, 07:38AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day Proud Mary

I've heard about that amazing phenomenon but I didn't know much about it. That is a nice article. Most of the info I've found in the net is about tin whiskers formed by electroplated tin, couldnâ€™t find much about chemical plating. I hope it won't be a problem, but I might do the experiment of placing a board under some of the conditions stated to cause intense growth of whiskers and leave it for few months.

Cheers

Conundrum

Sat Jan 15 2011, 03:46PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059

tin nanotubes?!
heh.. these can cause major problems in space where they can short out relays etc.

-A

Proud Mary

Sat Jan 15 2011, 04:51PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

[quote]
Good day Proud Mary

I've heard about that amazing phenomenon but I didn't know much about it. That is a nice article. Most of the info I've found in the net is about tin whiskers formed by electroplated tin, couldnâ€™t find much about chemical plating. I hope it won't be a problem, but I might do the experiment of placing a board under some of the conditions stated to cause intense growth of whiskers and leave it for few months.
quote1295110266]

I don't think it's anything to worry about, but it's always good to know that little bit extra.

Martin King

Thu Feb 10 2011, 10:15PM

Registered Member #3040 Joined: Tue Jul 27 2010, 03:15PM
Location: South of London. UK
Posts: 237

A bit late to the party I know but some years ago I bought a jar of this :-

Note the price! I'm now getting low on it. I suspect the formulae is the same (or at least similar to) the second one in Proud Mary's post. I already have the Sulfamic Acid (industrial de-scaler) and looks like the Stannous Chloride and Thiourea are easily and cheaply available on EBay

This thread has probably saved me a lot of money!

Thanks.

IntraWinding

Sat Feb 12 2011, 11:14AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Good post - thanks very much

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