Re: What is the Best PCB Layout software ? (Money no object)

From: Ralph Malph (noone_at_yahoo.com)
Date: 01/13/04 

Date: Tue, 13 Jan 2004 00:02:06 -0500

Ralph Malph wrote:
>
> Ian McBride wrote:
> >
> > "Ralph Malph" <noone@yahoo.com> wrote in message
> > news:40036859.F8EA05E7@yahoo.com...
> >
> > > One thing it can't do (without screwing up the DRC) is holes in a PAD.
> > > I am using a small regulator that requires heat spreaders on the top and
> > > bottom of the board connected by vias directly under the thermal pad on
> > > the bottom of the package. I know this is not normal, but TI recommends
> > > it. I was never able to get rid of the DRC errors this produced.
> >
> > If this is the package I remember, you can make the thermal pad a small pad
> > with THERMAL=OFF inside a rectangle on the top layer. A pain, but no DRC
> > complaints.
>
> I am not trying to make a thermal. I am trying to make a fairly large
> rectangular pad with six holes (vias) in it. The entire rectangle needs
> to have the solder mask removed from it. I guess I could have split the
> pad up into six equal, rectangular areas as pads. But they should be
> touching and I don't think I can get this past the DRC either unless I
> allow everything to touch. I believe I have object spacing set for 10
> mil at the moment.
>
> Or could I use a polygon to open up an area in the solder mask? I did
> not try much in that area.

By George! That did it! I can draw a rectangle on the tStop layer to
open up some copper around the six pads. I already found somewhere that
you can put the same name on multiple pads by adding a $ or # or
something similar to the name. So I could use six pads inside a solder
mask rectangle to add these to the part.

However, there are still four more vias that are outside this pad area
that need a surface plane which is under solder mask. I believe adding
a rectangle to the copper layer of a part causes problems because it
does not have the signal name. Or maybe a rectangle does not need a
name? But will that cause other problems such as a copper pour leaving
a gap around it?

The part according to TI should be like this...

  +---------------------+
  | +-----------+ |
  | O | o o o | O |
  | | | |
  | | | |
  | O | o o o | O |
  | +-----------+ |
  +---------------------+

The inner rectangle has no solder mask and six 0.013" vias. The outer
rectangle has solder mask and 0.018" vias. I don't see how to do the
outer ones.

Relevant Pages

  • Re: What is the Best PCB Layout software ? (Money no object)
    ... The problem is with the vias that need to be ... > the signal name is the same for different polygones or Vias, ... > PAD. ... I can draw a rectangle on the tStop layer to ...
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  • Re: What is the Best PCB Layout software ? (Money no object)
    ... >> pad up into six equal, ... >> Or could I use a polygon to open up an area in the solder mask? ... I can draw a rectangle on the tStop layer to ... there are still four more vias that are outside this pad area ...
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    ... >> the bottom of the package. ... I was never able to get rid of the DRC errors this produced. ... > If this is the package I remember, you can make the thermal pad a small pad ... > with THERMAL=OFF inside a rectangle on the top layer. ...
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