Mr./Ms. dhickey asks:

>     What is currently the tightest line width and spacing which
>     can be done in high volume?

0.005"/0.005", at suppliers with the better process controls and equipment.
For others I'd say 6/6.

>     What is the cost impact, if any, of going from 5/5 to 4/4 or
>     4/3 on a 4 layer, .020-.025 board in selected areas?

SWAG on my part is that you would incur a 10-15% cost increase by going
below 5/5. I have info from one big supplier which lists 3/3 on the
"technology roadmap" for '96. Since you asked for "volume production",
remember:
these roadmap things are ususally TOLLroads.

>     What board processing steps are most affected?

Photoimaging and etch.

>     Are there ways of minimizing the impact?

Several possible, but predominantly specifying thinner copper. Go to 1/2
ounce and they might talk to you nicer. You'd certainly want to permit
teardrops and make sure your routing is clean. Note that a 4 mil trace on
1/2 ounce copper is only about 3 square mils, about a third the copper of a
more conventional 6 mil 1 ounce trace. If you are routing power traces,
better take a look at what that does to power distribution and for that
matter characteristic signal impedances.

IMO, you should tell the layout people that the 4/4 should only be used
where it must be rather than plugging it into the DRC's and going to it for
everything. It is bound to affect yield and price in the end.


Good luck, and the usual disclaimers apply.


Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com


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