On Sat, 2 Jun 2007 00:32:01 -0400, "Tom Del Rosso"
wrote:

"John Larkin" wrote in
message

Layers are connected by
holes that are drilled through the board and metal-plated inside.
Those are called "vias" and 2000 of them wouldn't be unusual.

In the mid-80s there was a new PCB technology without vias. Traces just
came to an end and disappeared into the board, with maximum density. What
happened? There should be more demand for it than ever, and good yield
should be possible by now if it was done 20 years ago.

I saw some boards that looked like that, but they were just plated
vias without annular rings. I think there were cracking problems where
the trace dived into the hole.

John