On 05:37 PM 20/02/2002 -0500, Robison Michael R CNIN said:
>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.
>
>let me state that i realize many complex things are
>possible (blind and buried vias come to my mind), but
>somehow i don't think this is the case with this board.
>but i'm not sure.
>
>thanks, miker

Simplest (and most by large majority) smt boards have smt pads only on the 
layer of the component.  Tracks and vias are used to create the layer 
interconnections.  Nothing fancy under the pads at all. They exist only on 
the one copper layer.

More complex boards may have blind and buried vias - but even these will 
*mostly* be separate from the actual smt pads. (Newer micro via techniques 
not withstanding).

Ian Wilson

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