In a message dated 6/11/98 3:58:52 PM Pacific Daylight Time, [log in to unmask]
writes:

> IPC support,
>
>      I would like the exact formula used for generating the chip resistor
>  land pattern values for IPC-SM-782 manual. If the formula does not reside
in
>  the SM-782 spec, please E-mail it, Fax it, or explain how I could get ahold
>  of it.
>
>      FYI - From looking through IPC-SM-782 manual (published in 1996) I
don't
>  find a straight forward formula for a chip resistor. In your IPC-D-275
>  publication (dated September 1991) I find a formula for chip resistors
>  within section 5.3.4.3 that's very clear. Upon using this formula, when I
>  plug in values from SM-782 subsection 8.1, heading 4.0, for the 1206 chip
>  resistor, results doesn't match the land pattern dimensions supplied on the
>  following page.
>
>  If you have any questions.. please E-mail, or call me.
>
>  - Thanks for your help....   Al Arellano
>
>  E-mail = [log in to unmask]
>  Phone = (303) 581 2407
>  FAX = (303) 581 9973
>

Hello there Al,

     There really isn't any "formula" for determining your pad dimensions...I
think you're reading too much into it and confusing yourself. What 4.0 of
subsection 8.1 actually is, are just the component dimensions...that's all. It
just illustrates what the part basically looks like and gives you a min and a
max dimension for each axis of the part. For instance with axis "L" for a
1206, that dimension needs to be within 3.05mm to 3.35mm in order to use
RLP103A (RLP means recommended land pattern) for a 1206. Just look at 4.0 as a
part of the document to determine for sure what the component should be
identified as.

     Trust me, the 782 is a very good reference for pad geometry and
footprints...if only EVERYBODY followed the 782 I might not have the gray hair
that I do now...(GRIN)

                                          -Steve Gregory-

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