On Mon, 24 Nov 2008 13:53:47 -0800 (PST), "
wrote:



I suppose some would accuse us of hijacking Gunner's post, but some
may learn from our discussion.

Probably any regular epoxy would fail when the voltage is sufficient.
We have a customer that must test his circuit boards at 6kv. His new
design arc'd between leads of through-hole resistors. A quick fix
using corona dope was tried. Didn't work. More layers of corona dope.
Still arced. Had to do a board redesign to reorient the resistors to
give about 3/4 inch spacing between leads. That to cured the problem.

I don't know what is in corona dope, but in the 1950's we used to
repair TV flyback transformers with it. Why it didn't work on the
resistors is unknown.

Paul

Epoxies are routinely used at 50KV and more.

There's an interface between the epoxy, dope or whatever and the
circuit board. Arcs can sneak along this interface. If a slot is
routed thru the board and epoxy fills the slot and covers HV
conductors on both sides of the board, then the "short path" along
the board surface is blocked.