On Tue, 22 Dec 2009 09:47:20 -0800, you wrote:

>Happy Holidays Ya'll,
>
>I'm about to order my first stencil directly (rather than thru CEM),  
>but have a few Q's, which I've not been able to get properly answered  
>from a couple stencil companies.
>
>(1) Since a copper layer specifies pads and traces on that layer, how  
>do they determine what is a pad, vs. what is a trace?  Is there  
>something in the specification of the gerber that tells them that  
>(I've found some basic gerber-format explanations so far, but nothing  
>yet that tells me how a trace is specified different from a pad)?  Or  
>is it that pads are copper without soldermask?  Or???

You output a paste -specific gerber layer from your PCB sofwtare, as it knows which pads are for SMD
parts
 

>(2) Are the stencil holes always the exact size as the pads, or is  
>there some border that's left, making the stencil holes a bit smaller?

Typically  a bit smaller

>(3) I need to add four 0.125" holes on the stencil to match holes on  
>my PCB.  I'll use these to easily align the stencil, by using four  
>0.125" dowels.  How can I best specify this on the PCB.  If I create a  
>library part that is a 0.125" circle and add these to the appropriate  
>locations on the PCB, will I get these as 0.125" holes on the PCB, or  
>will they be a bit smaller, or...?

Depends how the pad stack is defined for the hole - should be doable though.

>(4) Is there a simple way to temporarily block holes on a stencil (for  
>various configurations etc of a PCB)?

Why would you need to do this ? Doesn't matter if there is paste on unused pads.

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