Re: gEDA-user: solder masks, etc.

[David Koski <david@kosmosisland.com>]

On Wed, 12 May 2004 21:14:58 -0400
Dan McMahill <dan@mcmahill.net> wrote:

> On Wed, May 12, 2004 at 11:40:43AM -0700, David Koski wrote:
> > On Tue, 11 May 2004 20:28:40 -0400
> > Dan McMahill <dan@mcmahill.net> wrote:
> > 
> > > On Tue, May 11, 2004 at 12:42:17PM -0700, David Koski wrote:
> > > > Hello,
> > > > 
> > > > In the following file:
> > > > 
> > > > http://kosmosisland.com/island/david/test_1.pcb
> > > > 
> > > > I have a SOT-428_Transistor (Q1) footprint that I made. With a solder mask as
> > > > shown in the file, I cannot get the large pad closer than about 170 mils from
> > > > the edge of the board. It is as close as it can get in the above referenced
> > > > board. If I make the solder mask parameter small, the pad can be placed next to
> > > > the edge of the board. What am I missing?
> > > 
> > > I think PCB is preventing the soldermask relief from extending beyond the
> > > edge of the board.
> > 
> > That is what I thought. But it doesn't seem to add up. Using the following example:
> > 
> > Pad(0 -92 0 -92 275 20 315 "" "2" 0x00000100)
> > 
> > Thickness: 275
> > Clearance: 20
> > Mask:      315
> > 
> > I expect a 10 mil clearance between the pad and any polygon (Clearance
> > parameter/2). [Land Pattern Creation for Thomas Nau's and Harry Eaton's PCB,
> > Stephen Meier, May 2, 2003, {Example 2}]
> > 
> > I expect a margin between the pad and solder mask to be 20 mils ((Mask
> > parameter/2)-(Thickness parameter/2)). [Land Pattern Creation for Thomas Nau's
> > and Harry Eaton's PCB, Stephen Meier, May 2, 2003, {Example 3}]
> > 
> > But given a Mask parameter of 315, I cannot get closer than about 170 mils from
> > the edge of the board. I'm still missing something.
> > 
> 
> Did you try selecting Screen->Show Soldermask in PCB to show the soldermask relief?

Yes. There was only a few mils of white arround the pad as expected (maybe 5-10?)
 
> Do you have silk screen thats keeping you from getting closer?

Of course the silk screen outline is bigger than the pad but not much. It was
not close.  I will do a test and capture to image and post it.

I should mention that when I reduce parameter that is 315 (Mask) to 0 the
problem goes away. But of course the silk screen covers the pad then.

David Koski
david.nospham@Kosmosisland.com
!.nospham