.int [log in to unmask]

 As I recall, the numbers are.005 for pwas less than 12" and .008 for
 larger pwas per some IPC spec. I did a post on this a few months ago and
 asked how can we do boards with .020 pitch when we allow .008 error to
 the master art. Never did get a good answer. Since the question is asked
 again I assume others are having problems.

 Question to the FAB guys. Without going to glass tooling, how close to
 master can you control feature location on large 16 x 15" boards?
 How good with glass tooling?

 Larry Sternig
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 *** Original Author: [log in to unmask]          04/23/96  161919

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 From: "Yuen, Mike" <[log in to unmask]>
 To: "[log in to unmask]" <[log in to unmask]>
 Subject: RE: dimensional question

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 Q:   How much growth (or shrink) should one expect land-to-land over
        a 16" distance? This has nothing to do with drilling; just master
        pattern to actual board size...

 A:  I believe that's called stretch effect, the  bigger the board gets the
 more severe the growth (or shrinkage) it will have. The stretch also depends
 on the board house and board thickness. The best way to minimize stretch
 effect is to group components which require tight tolorance into the central
 location of the PCB.

 Thanks

 Michael Yuen


  ----------
 From: TechNet-request
 To: technet
 Subject: dimensional question
 Date: Tuesday, April 23, 1996 11:07AM

        The proliferation of sub .5mm peripheral leaded SMD's is causing
        assembly people to look at the overall size relationship
        between the master data and the actual board. When solder paste
        is stenciled on larger boards (say, 12-16"), the stencil image
        many times will not match the land pattern, causing shorts in the
        fine pitch area.
        My question:
         How much growth (or shrink) should one expect land-to-land over
        a 16" distance? This has nothing to do with drilling; just master
        pattern to actual board size...
        Thanks,

            marko