On Mon, 4 Jun 2007 10:23:04 -0400, "tempus fugit"
wrote:

No, it means that there are eight layers of etched copper foil. The
board is a sandwich, thin (like 1 mil) copper layers separated by
insulating layers (8 mils maybe) of epoxy-glass. The two outer copper
layers, "top" and "bottom" are on the surface, so you can solder parts
to them. Sometimes you need all those layers to distribute all the
power supplies and make all the connections. 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.

Parts are usually all on the top side of the board, but if things get
really dense sometimes people put parts on the bottom, too.



Thanks John. I've been wondering about that for a while...



Here's a cross-section sample from a lot of 8-layer boards we did.

John