Hey Ray-
You can bury an SMT pad in a large trace or plane if need be. Or thermal
relief it like a PTH pad (4 spokes) if space permits. It may or may not
make it a little harder to manufacture. These days, nobody complains when
we have to do it. On the other hand; we're not soliciting input on that
issue. I suspect the CEM plays with the paste stencil aperture if need be.

I think those spec's were written back when a typical soldermask annular
ring was .01 inch rather than .003 or .004...

-Chris (el CID)



                                                                                                         
                       Ray Johnston                                                                      
                       <[log in to unmask]>                   To:   [log in to unmask]                   
                       Sent by: DesignerCouncil          cc:                                             
                       <[log in to unmask]>         Subject:    [DC] trace size vs land             
                                                                                                         
                       09/26/2003 12:15 PM                                                               
                       Please respond to Ray                                                             
                       Johnston                                                                          
                                                                                                         
                                                                                                         
                                                                                                         




I'm looking for any info on how wide a trace can be when it connects to a
smt pad. The IPC-SM-782a says maximum 0.25mm (0.010") neck down trace, so
the trace does not draw the solder away. In a power supply a 0.25mm
(0.010") neck down trace is too small.

Does anyone have a way to figure out the maximum size trace vs. pad size?
Or any info that can give me leads?

Ray Johnston
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