[PCB_FORUM] Re: Strange solder paste mask creation... how to??

We do this and I have found that the best way is to add a shape on to the top paste layer in the symbol. It seems to work out the best in most if not all situations. It allows you to modify it if necessary in the design and to put in really crazy shapes as necessary. I use a shape for the pad also. If you add a teeny, tiny pin in the shape it attaches the net to the shape.
The only issue I have seen is when one of these needs to be mirrored to the bottom. It usually does not happen as these components are usually large. But when it does the soldermask needs to be manually mirrored. Or it used to anyway. I am not sure about the latest version as it hasn't come up yet.
Good luck,
Kevin McCowan
Sr. PCB Designer
TSI Telsys

MAILER-DAEMON@xxxxxxxxxxxxx wrote:
OK here is one for the group...

We work with some rather strange shaped parts in the RF world...
things that are built the way they are built, due to physics, not
some IPC or JEDEC suggested "standard" footprint. (you digital folks are lucky... )

These footprints often have large odd shaped center "slugs" in
the middle of the package that needs to be soldered for RF ground
and heatsink reasons. Rather than put an equal amount of solderpaste
on the slug (in other words a 1:1 solderpaste "pad" equal to the component
"pad") we have found that smaller solder paste shapes work better... the
part will then not "float" on the huge center pad, which can cause the
outer, smaller pads to not solder correctly. Making smaller solder
dots and stripes on the center "slugs" roughly the same size as the
other connection pads works best.

Well, the problem with this is defining what ends up as several "pads"
for pastemask verses one (odd shaped) "pad" for the slug.

It looks as though the best solution, at this point, is to put the
paste mask on a new subgroup layer: package geometry pastemask_top
and pastemask_bottom... this permits us to add any unusual hourglass
shapes, dots or stripes, or whatever as recommended by the manufacture as needed.

I am just wondering, are there any other better solutions?

Gene Carman
gcarman@xxxxxxxxxxxxxxx -----------------------------------------------------------
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