We calculate the spacing between through-hole and surface mount pads as
follows:

-----------------------         |            |         /---
         Cu           |         |            |        /   Cu
                      |  0.003" |   0.006"   | 0.003" | through
         SMD          |         |   solder-  |        | -hole
                      |         |   resist   |        \
-----------------------         |            |         \---


                      |<------------0.012"----------->|

The reasoning behind this is that the manufacturing tolerance for the
solder-resist mask is less than 0.004" and its minimal structure width is about
0.006". That way we make sure, that there is hardly any solder-resist on the
copper and the solder-resist structures have a good adhesion to the board
surface.


         Volkmar




     Mike Wedlock wrote:
     Hello all,
     Can anyone tell me if there is an IPC standard for spacing between a
surface
     mount pad and a feedthru?
     Thanks,
     Mike W

--
  Volkmar Huß                              Dräger ProTech GmbH
  Engineering Electronic Circuit Boards    Elektronikbaugruppen
  Phone +49 451 882-3998                   Moislinger Allee 53/55
  FAX              -4365
                                           23542 Lübeck / Germany
  mailto:[log in to unmask]