[SI-LIST] [OFF TOPIC] SMD Land patterns

Going beyond raw specifications I'm trying to understand some of the choices
made when designing land patterns for various types of SMT devices.  The
thinking was inspired by looking at different footprints for the same
devices.  It seemed to me that there are various schools of thought:  

1) This is the way we've been doing it, I don't really know why.
2) We bought a library and this is what's in it.
3) I fit everything into nice round 0.005 or 0.010 increment pads.
4) 0.025 in front and 0.025 in back and about 0.005 on the sides
5) If it looks good it will work
n) Etc., etc.

Virtually none of these are acceptable to me.  Number (2) might have some
merit, so long as the library is proven reliable.

So, rather than actual footprints I am looking for any kind of study/paper
that looks into the consequences of varying the geometry of the patterns.
In other words: How does pattern geometry affect such areas as soldering,
rework, reliability, testing, manufacturing, etc.?

Does anyone know of such a resource?

IPC-782's table of contents seems to hint that some of this is covered in
there.  Is it?

Thanks,

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Martin Euredjian
eCinema Systems, Inc.
voice: 661-305-9320
fax: 661-775-4876
martin@xxxxxxxxxxxxxx
www.ecinemasys.com
 
 


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