John Larkin wrote:
On Tue, 02 Oct 2007 06:32:55 -0400, Chuck Harris
wrote:

Tom Del Rosso wrote:
"Chuck Harris" wrote in message

Then the boards get clamped firmly to a copper cathode bar, and
get inserted into the copper plating tank. Because the metal doesn't
like to plate into holes, you need to use an excessively high current
density, and high agitation. The tank looks like it is at a roiling
boil. The plating "rectifiers" are 0 to 6V, 300A power supplies.
In the 80's I once popped out the contents of some holes and they were like
spring coils that fit tightly in the holes. There must have been other
variations.
There were some companies that were incapable of doing plated through
construction that did that, mostly TV and appliance makers. It was
grossly unreliable.

Plated through holes on multilayer holes can look funny because the hole
drilled in the board isn't always perfectly smooth... the boards are
fiberglass laminates, after all and the plating will be an exact image
of all the nooks and crannies in the hole.

-Chuck Harris


How about these PTH's?


John

Those are real beauties!

The plating is always at its thinnest half way through the hole. That is
because the electric currents are lower there than anywhere else on the board,
and the copper needs current to plate out of solution.

I would guess that there was a combination of two problems that caused that PTH
failure. One is not enough plating thickness, and two, a delamination of the
board that caused a gap that the plating had to bridge (unsuccessfully).

Plating being too thin can be caused by 1) too little time, 2) too little current,
3) spent copper anodes, or 4) insufficient agitation.

Chuck