KLUTH J. wrote:
 >  A company that I was working for ran into the same situation designing
 > impedence controlled boards.  What we finally ended up doing was contacting
 > our fab vendor.  We worked directly with them specifying engineering needs and
 > they came back to us with a material stack up which we then documented on the
 > drawing.  We developed an open relationship with the fab vendor, which was
 > beneficial as they were more than willing to help us design out fabrication
 > problems, and answer questions as they arose.  I would highly recommend
 > contacting your fab vendor, the open exchange of information is highly
 > educational for both parties.
 
 Thanks, but it sounds like you are happy with a single vendor. I guess our
 biggest problem is that our purchasing department will ALWAYS go with the
 cheapest bid, and I never know where the board is being manufactured. At a
 previous company, we had three EXCELLENT fast-turn prototype houses that
 consistently gave us beautiful boards (vendors that we worked closely with early
 in the design phase). After the designs were released, the production boards
 would be ordered from crummy garage shops, and we would have all kinds of
 problems.
 Kind of ironic isn't it? Didn't it used to be that prototypes were quick and
 dirty, and production boards were higher quality?
 Oh well, I guess our only recourse is to document the "least common denominator"
 as far as desired impedance is concerned, and let whatever vendor that gets it
 call us if there is a problem. What choice is there? Unless I go to purchasing
 and demand to know production vendors in advance! Yeah, everyone jumps when
 designers request things, right?
 
 onward through the fog...                                               Jack

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