Ken,
1) True position is to the drill tape specified position.  Best way to get
a handle on this number is to look at your process capability by measuring
position on a large number of your small holes on the bottom panel of the
stack and perform the statistics.

2) Front to back is a layer to layer registration specification.  Features
on different layers that are supposed to line up exactly should not be more
than 0.005" out.

        Jeff Perkins

-----Original Message-----
From:   Ken Patel [SMTP:[log in to unmask]]
Sent:   Wednesday, November 18, 1998 8:03 PM
To:     [log in to unmask]
Subject:        [TN] True Position and Registration on Fab

Fab Gurus,
We are designing board with a 40 mil BGAs first time and the fab will be
having 10 mil plated finished holes on it. I opened up an old existing
drawing of different non-BGA board and now I have couple of questions after
reading my fab drawing notes.

(1) Fab note: All holes to be within .006" true position on the diameter
with respect to original data.
Question: What is true position and why .006"? How to decide this number?

(2) Registration: Front to back to be within  +/-.005". Can anyone explain
what is registration and why .005"? Who can decide this #, is it fab
house's
processing capability?

re,
Ken Patel
______________________________________________________
Ken Patel                       Phone:  (408) 490-6804
1708 McCarthy Blvd.             Fax:    (408) 490-6859
Milpitas, CA 95035              Beeper: (888) 769-1808

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