Rick,

We have been using a hole location within .009"TP of the center of the
hole location based on a datum established on the PWB.

We locate 2 tooling holes which create a X-Y datum and a 0,0 point, and
then all holes are to be within their designated X-Y dimension from the
0,0 point within .009"TP. So, unlike you, where your referencing the
hole to the pad center, we are using a 0,0 point on a datum to reference
all locations, pads as well as holes. This eliminates the buildup of
tolerances. We have been requiring this for about the last 10 years with
no problems. At first we had a problem with the PWB vendor, but that
turned out to be the method of creating the drill files (bomb sighting).
Once we gave them electronic drill files, we have been 'fat, dumb, and
happy" | :)

Hope this helps.

Richard Hamilton
Clemar Mfg. / Rain Bird
[log in to unmask]

> -----Original Message-----
> From: Richard G Smith [SMTP:[log in to unmask]]
> Sent: Friday, March 13, 1998 5:26 AM
> To:   [log in to unmask]
> Subject:      [TN] PTH Positional Hole Tolerance
>
>      Hi All,
>
>      Here's the issue:
>
>      We specify in our fab spec that all holes are to be within .003"
> of
>      their corresponding pad center (true position of .006"). We are
> being
>      told by our fab house that this tolerance is unreasonably tight.
>
>      Any comments???
>
>      Thanks,
>      Rick
>
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