I have a PCB with no solder mask with a very dense layout and a very fine trace spacing.

I didn't get a solder mask because it's still in the prototyping phase, and it's way cheaper.

I keep having to stop, find the new shorts that keep popping up, and remove metal fibers that are barely visible.

From what I can tell the fibers are aluminum from the pcb so a magnet is no help.

Is there a trick to remove them faster or a way to stop this from happening?

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    \$\begingroup\$ Aluminum? That would be rare as aluminum is pretty much only used for the heat sink layer of a metal core pcb. More likely you're learning about Tin whiskers and would benefit from reading more about them. I don't know the answer to this question the way you've phrased it other than "better tools, use solder mask" \$\endgroup\$ – K H Mar 3 '19 at 23:35
  • \$\begingroup\$ compressed air? \$\endgroup\$ – Wesley Lee Mar 3 '19 at 23:43
  • \$\begingroup\$ Compressed air didn't help. Your right it is Tin... I looked at "whiskering" on wikipedia, that seems to be whats happening. Tomorrow I'll get some solder on the problem traces and see if that fixes it. \$\endgroup\$ – Tony Mar 4 '19 at 0:03
  • \$\begingroup\$ Who did the soldering? \$\endgroup\$ – Ale..chenski Mar 4 '19 at 0:13
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    \$\begingroup\$ Yes, there is one proven way: USE MORE FLUX. \$\endgroup\$ – Ale..chenski Mar 4 '19 at 0:14

The trick to stop this from happening is to order your PCB with solder mask. Do consider the cost of your time when deciding that it is cheaper to order boards without.

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  • \$\begingroup\$ I got this board w/ 1 day turn around time with overnight shipping for $250 vs paying over $2000 and 5 day turn around when including a solder mask for a design that hasn't been proven. \$\endgroup\$ – Tony Mar 4 '19 at 0:11
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    \$\begingroup\$ You might also want to consider using leaded solder, as lead inhibits the formation of whiskers, if that is your problem. As long as you dispose of it properly, there's nothing wrong with using lead in your prototypes, just try to keep it out of any final products. \$\endgroup\$ – Hearth Mar 4 '19 at 0:13
  • \$\begingroup\$ Yep, that's all we use. All of our designs are just for internal use. \$\endgroup\$ – Tony Mar 4 '19 at 0:27
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    \$\begingroup\$ Did you end up using more or less than $1750 worth of your time finding and fixing shorts, though? \$\endgroup\$ – The Photon Mar 4 '19 at 2:03
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    \$\begingroup\$ You can run an x-acto knife backward between all the traces (backward meaning to scrape, rather than to cut). That seems to clear the whiskers. \$\endgroup\$ – TimWescott Mar 4 '19 at 3:22

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