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?
> 
> Do you have silk screen thats keeping you from getting closer?

Here is a screen capture of pcb with only a single component, the
SOT-428_Transistor in question:

http://kosmosisland.com/island/david/test_428.png

Note the margin arround the device. The board cannot be resized any smaller and
the component is locked in position as it cannot get closer to the edges. The
element in the pcb file is:

Element[0x00000000 "SOT-428" "" "" 32000 40000 -2500 6500 0 100 0x00000000]
(
    Pad[-9000 16500 -9000 20500 6000 1000 7000 "" "1" 0x00004100]
    Pad[0 -9200 0 -9200 27500 2000 31500 "" "2" 0x00000100]
    Pad[9000 16500 9000 20500 6000 1000 7000 "" "3" 0x00004100]
    ElementLine [-15200 24500 -15200 -24500 1000]
    ElementLine [15200 24500 -15200 24500 1000]
    ElementLine [15200 -24500 15200 24500 1000]
    ElementLine [-15200 -24500 15200 -24500 1000]

    )

The same element from the footprint file:

Element(0x00000000 "SOT-428" "" "" 0 0 -25 65 0 100 0x00000000)
(
        Pad(-90 165 -90 205  60  10  70 "" "1" 0x00000100)
        Pad(  0 -92   0 -92 275  20 315 "" "2" 0x00000100)
        Pad( 90 165  90 205  60  10  70 "" "3" 0x00000100)
        ElementLine(-152 -245 152 -245 10)
        ElementLine(152 -245 152 245 10)
        ElementLine(152 245 -152 245 10)
        ElementLine(-152 245 -152 -245 10)
)

The whole pcb file:

http://kosmosisland.com/island/david/test_428.pcb

I should mention that when I reduce the value 315 in the element file for the
Pad Mask parameter I can get it to work. But of course the mask becomes too
small.

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