The Lichtenberg's alloy is an interesting way of home PCB tinning - it's inexpensive and there is no need to polish cooper or use specialized tools and chemicals. The negative side is that the alloy is hard to obtain, fortunately it's not expensive. For some countries, it might not be possible at all to buy it.
The alloy contains 50% of bismuth, 30% of lead and 20% of tin, but what makes it interesting is that its melting point is 95-100°C. It means that it melts in boiling water - that's the idea if this technique.
Below you may see drops of The Lichtenberg's alloy.
We will need a couple of grams of the alloy, pan with lid, a tablespoon of citric acid, silicon spoon and old tweezers or similar tool.
- Fill pan with tap water to 1/2 - 1/3 of volume, put inside the alloy and your PCB, cover the pan with lid to speed up heating.
- When the water boils, use tweezers to immobilize the PCB - squeeze it to the pan. Dispatch alloy on whole copper surface by using a spoon. Put the lid again.
- After a couple of minutes, immobilize the PCB again and by using a spoon, remove alloy excess from the PCB.
- Clean the PCB in water, dry it by using a rag.
Citric acid is used here in two ways: as a flux and to decrease boiling temperature.
Note: don't use pans or spoons that you are also using for cooking, have a separate set for tinning. Please keep in mind that Lichtenberg's alloy contains lead, the method involves citric acid, a product of those (lead citrate) is (at least) unhealthy if digested.
Note: several similar alloys exists (e.g. Lipowitz's alloy), probably they could be also used, but always check theirs recipe. Especially make sure you don't use something that contains cadmium!
Note: don't spoil on your body any boiling water during above procedure.
Below is an example of a PCB tinned by using this method, it's a USB Li-Ion battery charger
If you liked this idea, you may also check the article about inexpensive chemical PCB tinning.