On 07:52 AM 6/04/2001 -0500, [EMAIL PROTECTED] said:
>I've got a question for the group.
>
>I need to place thieving pads on some bottom side pads.
>
>My question is how do I remove the solder paste from these pads?
>
>Thanks.


Hang-on... I assume you want the thieves to reduce bridging on the last two 
pads of an IC during wave solder (the usual use).  Why then are you worried 
about a paste mask layer?  Is it so you can support either reflow or wave 
soldering on this layer?

Ben Uytenhaak answered you question about how to do it (though in his point 
4) it should be a negative expansion of half the maximum pad dimension.

If all your solder thieves have the same designator (say THIEVE) and size 
you can use a paste mask expansion rule to close them off using Pad Scope 
with Free-THIEVE as the pad.  Add the negative expansion to the rule as 
required.

You do *not* want to close off the solder mask on these pads otherwise they 
will not function correctly, of course.

For wave solder I usually just make the last pad of any IC twice as wide 
and increase the distance from the other pads to keep the same pad 
separation.  This has always worked well.  (But, I would not be able to 
close of the thieve if a paste mask was being produced.)

Suggestion(s):
1) On this subject of wave solder thieves - I think Protel could automate 
the process.  We would have design rules hat set the direction and layer(s) 
of wave solder and then a command would say Add Thieves.  If the component 
was rotated then it would be really nice if the thieves automatically 
changed ends.  This could hook into the component rotation rule to ensure 
that orientations not appropriate for wave soldering could be caught by 
DRC. (Though I get the feeling that the majority of designers do not make 
the distinction between wave and reflow and hence do not use thieves.  Am I 
right?)

2) I would also like the library system to support wave and reflow 
footprints - as for optimum performance and density they are slightly 
different.  So one footprint can contain one or more variants and a drop 
list selects which one is used.  Much like the Schematic multi-part symbol 
feature. Even better if the different parts in the library could be 
user-named and the names inserted into the variant selection drop list.  So 
I could have reflow and wave but you could have, say, Manufacturer1 and 
Manufacturer2 footprints. The variants should be available to the rules 
system as well to allow restrictions on what variant of any component can 
be placed on what layer and what orientation can be used for the different 
variants.

If I had to choose one of these suggestions over the other I would prefer 
option 2 - as I can always produce more than one wave footprint with 
thieving at different ends and place angle restrictions on their use by 
sensible library design, variant naming and rules set.  Option 2 has many 
more applications than just solder/reflow fp selection.

Ian Wilson 


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