My background is only peripheral to PC board assembly (senior "chemist" at HumiSeal for 12 years). Please excuse me if this is a half baked idea.

Some masking material companies sell gizmos called "rat tails" which look like tapered rubber bands {fattest section is maybe 25 or 30 mils (.025- .03 inches)} for plugging holes in items being coated. The operator inserts the "rat tail" in the hole and pulls it tight, making a tight seal. One side can then be clipped off flush with the flat surface (the side pulled through I think). After coating the "rat tail" can be pulled out from the remaining "tail" or they can be clipped on both sides and left in place forever. These "rat tails" can be used with conformal coating.

While these "rat tails" are too big for the vias being discussed, could pieces of wire be inserted into the vias and clipped flush? Unfortunately no one sells tapered wire but hobbyists use brass wire which is sold in 2-3 mil increments (I use .012" wire all the time). The wire could be deformed (flattened out) so it would get stuck in the hole. Even cutting the wire with a nippers flattens it out a little.

The seal in not complete but instead of having a 13 mil diameter wide path there would be 13 mil diameter hole with a12 mil diameter wire filling most of the space. The surface tension of the liquid might prevent it flowing from one side to the other.

If tapered wires are absolutely necessary jewelers reduce wire by a few mils in diameter by passing it through a tapered die.

The wire in the hole could also be sealed with ACC cement (crazy glue) if it doesn't effect the flux or solder.

The vias are designed to have wires passing through them, right?


Edward Mines BEChE, MEChE
238 Willard Dr.
Hewlett, NY  11557
516 205-6523

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