Bob
You are right, about what the cold numbers say.
But....
When the innerlayers are produced and laminated in a ML, you are having
misregistrations due to all cycles of exposing, drilling, laminating, etc.
The external layers suffer less from these problems, as you can "see" the
registration and improve it when you are exposing them.
So, giving a larger inner pad, you are expected to have less scrap.
You can easy see that in your coupons, look for misregistration in inner and
outer.
So, at my opinion, if you can "pay" larger pads in the inner layers, what is
usually the case - do it


At 07:26 AM 4/8/97 -0400, you wrote:
>  John..
>         I'm still surprised! We have been designing 12-14 layer (standard)
>   smt designs for about a zillion years, maybe not quite a zillion, but
>   a looonnng time and no vendor has ever requested that the inner layer
>   pads be larger. In fact, unless I am looking at the formula/chart in
>  the Mil and IPC specs incorrectly, the minimum annular ring requirement
>  for internal is .001/.002 mils vs .002/.004 mils for external layers.
>  Therefore, by definition, your external pads should be larger. What
>  am I missing???
>                                       Regards,
>                                                  Bob
>
>
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Roberto Tulman
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