Re: gEDA-user: solder masks, etc.

[David Koski <david@kosmosisland.com>]

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.

Regards,
David Koski
david.nospham@KosmosIsland.com
!.nospham