Friday, July 6, 2018

How to tin your PCB using plumber's paste | Homemade PCB

The last step in making your own printed circuit board (PCB) is tinning. Tinning is important because copper oxidize very fast, leading to an ugly look, hard to solder pads and over longer time, breaks in traces.

When you order PCB's from a manufacturer, the pads look all nice a shiny. I was looking for a way to achieve this at home and I found one. It doesn't involve strong chemicals, it's cheap and it only takes a few minutes.

Example of homemade PCB tinning
Example of homemade PCB tinning

DIY PCB tinning at home using plumber's paste
PCB after tinning

PCB before tinning

PCB tinning at home using plumber's paste

The paste that I use is Cu-Rofix 3 and contains 60% Sn97Cu3 and water soluble flux.

  • First, the board must be scrubbed until it looks shiny, using something not very abrasive like a scouring pad for cleaning dishes and then cleaned with isopropyl alcohol.

  • Next step is to apply a thin layer of paste on the exposed copper. The paste can be spread using a plastic card or popsicle stick until no copper can be seen.

  • Now the paste must be heated. I used an electric hot plate and using some pliers I hold the board over the hot plate at about 1 - 2 mm distance with the paste facing upwards. A hot air gun would be better I think. After a few moments the flux will make the paste liquid. Apply heat until the paste is dry.

  • Remove the heat and wait a few seconds for the board to cool and remove the paste using a paper towel and a popsicle stick.

  • To remove the flux, wash the PCB using a toothbrush and isopropyl alcohol. After that put some paper on top and rub with a brush to absorb the dissolved flux. This must be done 2 or 3 times to make sure all the flux is removed.

  • Some water from the isopropyl alcohol will still remain even if it looks dry. I use a hair dryer for a few seconds.

Heating time

After the paste looks dry, you should be able to wipe it off using a paper towel. If the paste is very solid and requires hard objects to remove then you over heated. If the whole board is a big blob of solder then you really over heated. Keep the propane torch away.

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