Today I will present a method for PCB tinning that uses alkaline bath. What does alkaline bath mean? It says that the solution that we're using for tinning has this pH, in opposition acid bathes also exists - one of the example I presented in my previous post about PCB tinning at home.
This method is less expensive that the acid one, the results of both are comparable, but because of how a relatively dangerous alkaline bath is, I don't plan to use it. If you're searching a method to tin your PCBs, I would strongly suggest either using Lichtenberg's alloy (described here) or chemically tin them by using acid bath.
Instead of pure metallic tin, a solder can be used, to increase its reactive surface, it can be melted on a small scrap of a laminate.
Note: NaOH is highly aggressive substance, it can easily permanently damage eyes or skin. Dissolution of an alcaline is strongly exothermic which means that water heats up, it can even start boiling and splashing dissolved NaOH!
Note: protective glasses and appropriate gloves should be used.
Note: don't use any containers, spoons or other small tools that you are also using for cooking, have a separate set for tinning.
PCB and tin (or mentioned above laminate) is placed in a high beaker. 100ml of water is added, then extremely slowly 1/2 teaspoon of NaOH and SnCl2 mixture is added. Mixture is heated (not boiled!) in heated bath similar to presented in this post. Tinning takes 10-20 minutes.
I haven't use polishing paste, so the surface isn't smooth and glossy, but technically it doesn't matter.
Solder wets surface very well, it's visible on below image.
To summarize, despite good results and low proce, I think that it's too dangerous to tin a PCB this way.