Jan,
Your interpretations overlook the true intention. The 0.15mm number is a
diameter of true position tolerance. True position is the theoretical
location of the feature as defined by a grid. The grid has no tolerance
and defines all feature locations with relation to the 0,0 point or
secondary datum. The feature may be located any place within the
specified diameter of true position.
Regards,
Gary
Lamote, Jan wrote:
> Dear,
> I've been looking for the correct interpretation of one section in the
> IPC-2222 (02/1998) norm.
> In section 9.1.5 Conductive Pattern Feature Location Tolerance, there's
> a table 9-1.
> For our boards we're in the >300mm <450mm Level C category. This gives a
> tolerance of 0.15mm.
> According to the text this is:
> "the tolerance to be applied to the nominal dimension chosen for the
> location of the lands connector contacts and conductors in relation to
> the datums."
>
> Now we have 3 different interpretations of this tolerance:
> 1) nominal minus 0.075mm / plus 0.075mm
> 2) nominal minus 0.15mm / plus 0.15mm
> 3) deviation max. 0.15mm meaning on each board individually the max.
> deviation is .15mm, so on one board you can have everything between -0.1
> and +0.05mm, another board can have -0.0, +0.15mm ...
>
> How should I read this 0.15mm tolerance ?
>
> Thanks in advance for your reply.
>
> Regards,
> Jan Lamote
>
>
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