Burnishing is critical to success

As stated in a previous post, a printed circuit board is make by depositing a thick, conductive, liquid onto the substrate.

This thick, gooey, mess is of no use at this point. After it is baked for an hour or so it is now a conductive solid. But you can not solder any components or wire to it.

The reason is that there are other chemicals besides conductive metals like silver in there, even after baking. These chemicals prevent soldering. So, we ‘burnish‘ the DPCB. Burnishing can be thought of as polishing or very light sanding. This process removes stuff that prevents soldering, and leaves a shiny surface. In my case, that shiny surface is made of an alloy of tin, bismuth, and silver.

Choice of material is also critical. One desktop PCB printer company supplies a piece of white foam. Not too hard, not to soft. It works very well, but it takes quite a bit of time and the foam wears out quickly.

Proper burnishing is extremely critical. If you do not spend enough time burnishing, every following step will fail.

I recommend that you stick with whatever your machine manufacturer recommends. At least until you have made a few dozen ‘good’ boards. Then you will have a good reference point when you try your own methods.

Things we have tried:

  • #1500 sandpaper – total failure
  • 3M Scotchbrite Heavy Duty – well, it gets the job done, and quickly, but the pcb will look like you ripped it up out of concrete mixer. See an example of this here.)
  • 3M Scotchbrite Non-Scratch – like its name says, it is non-scratch, so your pcb will look great. I do not think this is any faster than using foamed plastic.
  • Pipe insulating foam tubes – this material is much more durable than the foam supplied with our machine – but it is slow… very slow… like burnishing takes 10 minutes compared to 2 minutes with the manufacturer’s foam.
  • #0000 steel wool – wow, this stuff makes your pcb traces look beautiful, and it takes only 10 seconds or so to burnish a 4×5 pcb. The bad news is, something happens between the steel in the steel wool and the conductive ink which makes it impossible to solder tool
  • Copper Wool. Like steel wool, copper wool seemed promising. It is tough to find, but it appears to be reasonably compatible with the conductive ink. Unfortunately, it is also very slow to burnish, much slower than foamed plastic.
  • Stainless steel brush – will quickly burnish the conductor, but even more quickly create deep scratches on the substrate. In addition, like using steel wool, it does something to the conductor that makes it impossible to solder to.

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