Making liquid tin/tin plating - DIY Recipe

[Kevin Mitchell]

I recently came across a youtube video for making liquid tin at home. I've never used liquid tin because I'm a cheap bastard but I'm totally down to try to make some. You'll find info on the chemistry side of things in the video.

Here are some notes I've gathered to make this stuff;

Materials (check out the safety data sheet for information):
-1 gram solid core tin solder (lead free) - at least 95% tin
-10mL 30% hydrochloric acid
-100mL thiourea based metal cleaner - I'll use Tarn-X
-A couple of glass containers - I'll be using glass jars
-A stirring rod - plastic spoon?

-Pour the acid in a glass container with the solder and let dissolve. This could take quite a few hours.
-Once it's dissolved the remainder of the non-tin material should be sitting on the bottom. Pour off the solution into another glass container and dispose of the unwanted material.
-Mix in the thiourea based substance until dissolved.

Store in glass container with a plastic lid. No info on shelf life at the moment.

Use;
Place etched PCB in solution for a few minutes. Once it's completely coated the reaction should stop so no worries overdoing it.

I'll post my results tomorrow night.

-KM

[davent]

The commercial version of Liquid Tin in my experience, oxidizes anyways if you let the pcb sit for any length of time, no better then bare copper in the long run.

Far far better for me is a quick light spray of lacquer, no time limit on preventing oxidation, no hindrance to soldering, vaporizes with the touch of the hot iron.
dave

[Kevin Mitchell]

Far far better for me is a quick light spray of lacquer

I already do that I mostly wanted to use the tinning as added protection for the edge connection of my cards.


I can't say that I've seen my solder oxidize. We'll see how the home-brew liquid tin holds up.

-KM

[Govmnt_Lacky]

I got into using Liquid Tin for a while. It does work however, the biggest problem that I ran into was product impurity. When I say that, I mean that you REALLY need to keep the liquid tin CLEAN. If ANYTHING gets into it (dust, water molecules, etc.) then it will reflect in the final product in the form of spots in the tin. Problem with this is that by the time you notice the faux pas, it is too late to fix it 

[Kevin Mitchell]

I'll take your warning!

-Be cautious not to contaminate the mixture.
-The container should always be sealed unless pouring into the tinning container.
-Never mix used substance with the fresh stuff. In fact it might not be worth the gamble using it more than once - as some people have done.

Would you say the solder takes/flows easier on tinned pads? Just wondering. I always use 60/40 when soldering onto bare copper. I wonder if tinning would make lead free solder easier to work with.

-KM

[Kevin Mitchell]

A quick followup;

It turns out the muriatic acid did not dissolve the tin. I looked into it and found "generally any solution with a concentration of more than 31.5% HCl by mass qualifies as hydrochloric acid, and anything less is muriatic acid."

The SDS ingredients lists for the muriatic acid notes "Hydrochloric acid {Hydrogen chloride} <30.0 %" and the additive "Specific percentage of composition is being withheld as a trade secret." The muriatic acid is likely not strong enough and also contains other ingredients that I do not want. It's strange that the recipe calls for 30% since it's technically not considered hydrochloric acid. So I have to source a bottle of "hydrochloric acid" that only has distilled water as an additive.

I'll be back next week after I get my hands one the real stuff.

-KM

[deadastronaut]

+1 on the quick spray of clearcoat on a pcb.....

[Kevin Mitchell]

I'd say it was a success! I'll report back on how it holds up over time.

[deadastronaut]

looks great, came out nice man. 

[Govmnt_Lacky]

If you look closely at the picture above, you can see a shaded area between the tinned and copper areas. THAT is what I would typically see in some of my tinning attempts that frustrated me. It would show up looking more like 'water spots' however, it was shaded and looked just like that area. The only thing I could say is that it was due to contamination

[Kevin Mitchell]

The only thing I could say is that it was due to contamination

Sounds like the mixture needed more thiourea to lower the redox potential. This would allow a more even layer of tin to take onto the copper and also help prevent oxidizing. Perhaps it was just a weak/old bottle?


Or contaminants. I barely know what I'm talking about 

-KM

[amptramp]

These guys:

http://www.hunterproducts.com/index.html

have plating pens for tin as well as many other metals.  A bit pricey but you could probably make your own.

[Kevin Mitchell]

plating pens for tin as well as many other metals.  A bit pricey but you could probably make your own.

I'd likely only use a pen like that for repairs but it's not often something is bad enough to need new traces or pads - though it happens.

I'm thinking about solder masks now. I use clear or tinted spray paint to protect the copper on most of my boards. Imagine if there was a UV curable spray paint - like those liquid solder mask tubes but in a spray can. That way you can spray on a thick even layer and place your images of the pads on a transparency sheet and put it under a UV light to cure. Seems like a more friendly approach to the paste like stuff that you have to spread or the dry film stuff that requires appropriate equipment like a laminator.

I'm looking for UV curable heat resistance spray paint. Or perhaps I'll see about making some 

-KM

[davent]

Maybe  these guys have something that fits the bill...

https://www.solarez.com/
dave