Ray,
How good of a relationship do you have with your supplier? Are you
purchasing from the "low bidder"?
There are AOI systems out there which can check for minimum trace widths on
innerlayers. If your supplier has this capability, then can you trust your
supplier to a) use the machine, and b) to NOT use the bad material it finds?
When I worked for GE I learned that "you get the performance you measure."
If you are willing to measure the 4 mil traces, and reject boards below a
set criteria, then you will either a) get good results, or b) get another
PWB house.
If a criteria is not important enough for you to check, then it implies that
the criteria is not important enough for the supplier to meet.
For your case, innerlayer trace widths, I would be talking cross section.
X-rays might be usable, but I have never used them. Working with your
supplier to build the trust that he is doing what he says is the most
important thing.
As to the "special instructions", start off asking for acceptance cross
sections from each panel which demonstrate that the supplier meets the trace
width requirement. The blood will drain from the suppliers face, and he
counter with another option. Negotiate until you hit a good
cost/verification trade-off. If you accept the minimal offer, "I will
accept the lot based on one coupon", then... well, do you really trust them?
Is the 4 mil requirement that important? And I know a great little board
shop in just over the Rio Grande...... Hey! I gots some property in Florida
also... ;-)
Ray, I have worked in Board houses, and now buy boards. Finding a board
house you can trust is a hard, but rewarding job. The more critical your
PWB, the more critical the level of trust. Putting the requirements down on
the drawing is only the first part of the job.
In general, we design with 8 mil traces. Much thinner traces are allowed
for impedance, or other critical routing needs. Traces are verified
mechanically, or electrically if they are at all critical.
Thank you for this oppurtunity to get on my soapbox.
George Franck
Raytheon E-Systems
Falls Church Va
"The opinions expressed from this soapbox are mine, and not those of my
company"
----------
> From: "Raymond Klein" <[log in to unmask]>
> To: "Technet" <[log in to unmask]>
> Subject: RE: Standard PCB/PWB Trace Withd's
> Date: Fri, 18 Jul 1997 15:57:17 -0700
>
>I am very interested in the replies to this query. I using 4 mil traces in
>somplaces on a new board. What special instructions must I give to the fab
>house to get reliable results?
>
>Ray Klein
>
>PCPI [log in to unmask]
>
>
>
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