Robison Michael R CNIN wrote:
> 
> hello,
> 
> well, thats a pretty dumb question, isn't it?  hahaha.
> but i'm serious.  i'm trying to reproduce a board which
> has smt top and bottom, and it appears that some of the
> smt pads overlap from top to bottom.
> 
> so how do smt pads work?  on a thru-hole, they obviously
> go thru the entire board.  how far does a pad go thru as
> an smt?  obviously it has to at least burrow thru to any
> layer it runs on, but do top and bottom overlapping smt
> pads necessarily net together?  i'm confused.

Surface mount pads are only on the surface - it is generally considered
a Bad Thing to have holes in surface mount pads.

If you want to connect a surface mount pad to another layer, you run a
short track on the same layer as the pad, place a via, then run a track
as needed on the other layer.

There is no problem with SM pads on opposite sides of the board
overlapping, nor with bottom side tracks running under top side pads
(other than possible concern with crosstalk between the signals
involved.)

-- 
Peter Bennett
TRIUMF
4004 Wesbrook Mall, Vancouver, BC, Canada      
GPS and NMEA info and programs: 
http://vancouver-webpages.com/peter/index.html

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