Tin Platting Experiments

OK, I am in a little over my head, -- I need a Chemist.

To improve my HomeBrew projects I have been playing with Tin Platting materials and methods for my Homebrew PCB's.

For the last few week I have been dissolving Tin Sinkers in a small amount of Hydrochloric Acid (34% by vol), thinking that I want to create Tin(II) Chloride (stannous chloride).

There are several video on YouTube showing how to create stannous chloride with diluted acid and a current flow. Because it is stinky/messy and I am not ready to try that, I thought I would just try to dissolve the Tin in concentrated acid and then dilute as needed later.

So far I have dissolved 1 and 1/2 sinkers to nothing (the acid is still a clear liquid), the next sinker was added tonight.

The questions for a Chemist is:

• How much Tin will a milliliter of HCL 34% acid absorb?
• Does it become Stannous Chloride?
• What are the other by products?
• Please verify, the weight of the results should be the weight of the acid, plus the Tin, minus evaporation?
• Does any of the Tin or Tin compound leave in the form of vapor?

My current plan is to continue adding Tin until it is no longer is absorb, and then the plating experiments begin.

Some of the web information suggests Tin Sulfate should be used to plate copper, but I think I read somewhere that Tin Chloride with Polyethylene Glycol will make a nice electric-less plating solution.

Note: Here is a interesting REAL TIME YouTube video, showing growing Tin Crystals in Stannous Chloride with 16 volts at 4 amps.

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Impressive HB in Russian

Bruce Baxter, provided links via one of his notes on the "Homebrew_PCBs" list server that was very impressive, video narrative is Russian but, Homebrew is a universal language.

With permission, a copy of Baxter's original note/email text is provided here (normally, I would just link to the original note, but it contains many links that I want to capture here for future reference)

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> See this --à http://radiokot.ru/lab/hardwork/34/ Russian site, but with

> google translate is you will know everything.

Chris,

While Looking at your reference, I noticed the statement" "There is still everyone's favorite FGK-120".

I couldn't find any availability of the product in the US. However, from the photos of the Chinese marketers, I recognized it as a Tamerica LP-120 which is sold in the US for about $51. This is the laminator I use and it does a great job with toner transfer.

During my search for the FGK-120, I came across this URL,

http://easyelectronics.ru/izgotovlenie-pechatnyx-plat-videourok-nomer-dva.html

Although this is a bit off topic, The second video discusses a PCB tinning method using citric acid, boiling water and some metallic particles called alloy Rose. The process seems quite simple without any bad chemicals. A bit of searching identified alloy Rose as a low temperature solder (203-212 deg F) called Rose's metal or Rose's alloy composed of bismuth, tin and lead,

http://en.wikipedia.org/wiki/Rose%27s_metal

You can make your own,

http://www.angelfire.com/planet/skerjastrond/casting.html

or buy it,

http://www.mcmaster.com/#bismuth-alloys/=97u0jk

The McMaster-Carr product seems to have the lowest melting point (203 deg F) with

Bismuth = 52.5%

Tin = 15.5%

Lead = 32.0%

wikipedia-Solder has this to say about Bismuth alloys,

"Bismuth significantly lowers the melting point and improves wettability. In presence of sufficient lead and tin, bismuth forms crystals of Sn16Pb32Bi52 with melting point of only 95 °C, which diffuses along the grain boundaries and may cause a joint failure at relatively low temperatures. A high-power part pre-tinned with an alloy of lead can therefore desolder under load when soldered with a bismuth-containing solder. Such joints are also prone to cracking. Alloys with more than 47% Bi expand upon cooling, which may be used to offset thermal expansion mismatch stresses. Retards growth of tin whiskers. Relatively expensive, limited availability."

Based upon this, Rose's alloy may of limited utility for DIY PCB tinning. However, With the low melting temperature, it seems almost as useful as polymorph (friendly) plastic for prototyping parts .

Baxter

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UPDATE:

I have tried to obtain Bismuth from locations around Seattle, so far I have NOT located a source - Green (no-lead) Sinkers and Green Shotgun Shot has not sold well enough to stock it locally. Because of it's weight, an Internet purchase may be prohibitive for medium (e.g., 10lbs) quantities.

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UPDATE:


I now, have some Bismuth on order from Rotometals in San Francisco.

• http://www.rotometals.com/Bismuth-s/4.htm

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