On Sun, 7 May 2006, Jesse Lackey wrote:

> Hi - for this, I have a filled rectangle of silkscreen, and I write the 
> number there with a Sharpie after the board has been tested.  After a few 
> years of (indoor) use it hasn't worn away at all.
>
> However, it washes off pretty easily with solder flux cleaner, sometimes this 
> is a good thing, I normally just write it on after any board fixes are done.

You can use an engraving tool instead (the electric kind).

Peter
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