IPC-7525 Stencil Design Guidelines is nearing completion and addresses some of these issues.  You can get a review copy (hopefully, if our e-mail feels like working at this particular point in time) by sending a message to:
[log in to unmask] 
and in the SUBJECT line put: request IPC-7525
(ya gotta do it exactly like it's printed above or the computer won't respond.
Msg body can be blank, but good to put in your name/phone number in case we (probably) have an e-mail problem and need to contact you.

We'll join you in rejoicing when all our e-mail is working again!!  jack

>>> "[log in to unmask]" <[log in to unmask]> 01/19/00 10:21PM >>>
Hi Steve,

now that's intersting!

Sure, the stencil opening must be smaller then the pads. But when you make
them triangular isn't there too little paste on the pads? We work with
0.15mm thick steel stencils and the amount of paste is already very low.

What CAD program can generate such shape stencils automatically?

regards

Jens Behrens



><< Ok..so what are the causes of solder beads?? >>
>
>Hi Jan!
>
>Solder beads or "Squeeze balls" as they're sometimes referred to, are caused
>by too much of the gray stuff...solder paste. In a cleaning environment
>they're usually not a problem because they wash off. But in a no-clean
>environment, BIG headache!
>
>They can be eliminated by modifying the apertures in your stencil to reduce
>the volume of paste you're putting down. Instead of square apertures you can
>turn them into triangles or "homeplates" with the pointy ends pointing
>towards each other to the center of the footprint. A lot of  stencil vendors
>will do this automatically...at least mine does. I just tell them I want
>no-clean apertures for all the passives...I think it's an extra $25-50 charge
>for the editing they have to do in the gerber.
>
>Hope this helps...
>
>-Steve Gregory-

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