"John Larkin" wrote in message
news
On Sat, 02 Jun 2007 16:53:34 -0500, Spehro Pefhany
wrote:

On Sat, 02 Jun 2007 07:48:51 -0700, the renowned John Larkin
wrote:

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

Ah, I've seen those maybe once... (ummm intentionally, that is).

They can do cool stuff like blind 5 thou microvias but the cost might
be too much for many applications.



Best regards,
Spehro Pefhany


What's standard these days? We're running 6 mil traces and 10 mil
microvias, but "normal" keeps creeping down.

One of our board houses does 4/4 mil lines spaces without extra charge and
will go down to 3/3 mil (thou) lines spaces. They can do some really small
micro vias with drill, and even much smaller with laser (as in via in fine
pitch pad without problems). The boards are a little more expensive but the
quality is generally top notch (we usually go to them with anything with
more then 4 layers, fine traces, microvias, BGA's, generally anything more
complex then usual PCBs. The boards don't sag badly during reflow, are very
accurate, and the machines generally have very little problems building
stacks of PCBs from them.) They have a location that may be close to you in
California which is capable of true IPC level 3 boards, although we
generally use a location that is more local to us. Email me if you want
contact info.

If I were you I would stick with the 6 mil traces, since plating and etching
is not completely even over a large area, such as the boards you do, which
could lower the yield of boards. If you need to go smaller, do it only in
localized areas.



John