Re: [PROTEL EDA USERS]: Special Solder Paste

[Ian Wilson <considered@ozemail.com.au>]

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On 06:26 AM 19/10/2000 -0500, blmarshall2@mmm.com said:


>I need to offset and make the solder paste pads smaller on chip components.
>
>Can anyone please make suggestions?
>
>Thanks in advance.

I do this by making complex pads out of multiple primitives in the PCB 
Library editor.

So I might have a "complex-pad" made up with a normal pad along with a 
track or a fill on the top layer.  Add tracks and/or fills (a little over 
sized to your added entity(ies) on the top solder mask layer and this will 
expose your complex pad.

The top mask entities will flip correctly to the bottom mask layer if you 
flip the component to the bottom layer.

You can even make complex paste mask details using additional entities on 
the top paste layer.

The first gotcha is that the auto-router will rip up additional copper 
portions of the complex pad in some circumstances - this is a bug and I 
would like it fixed soon!  You can see this on the Protel SOT-89 footprint. 
By adding layer specific keepouts to the footprint you may be able to 
prevent the router from placing tracks and vias in the newly freed location 
- under you component pad - but I haven't tried a great deal.  After 
auto-routing you need to go back and refresh the butchered footprints and 
then manually clear the inevitable DRC errors - a pain.  There are other 
aids that help - such as using temporary keepouts etc to prevent the router 
using the space you know is needed for the "extra" parts of the pad, that 
you will reinstate after routing.  Note that the pad part of the complex 
pad is not ripped up.

The other gotcha is problems associated with putting the correct net name 
onto the extra copper - again there are a number of solutions to this 
including a helpful checkbox in the synchroniser (that slows it waaaay 
down) and the magical recently dredged up from right-click-land Upadate 
primitives from connected copper command.

Ian Wilson
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