This message came back undelivered, and I don't have Johannes mail address
so I'll post this to the council. Sorry for the inconvenience if you
are not interested.
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Johannes,
Let me comment a little on your dilemna. These are my recommendations.
> Does anyone know a good site/book/source , commercial/non-commercial for
> SMD footprints library.
#1 SMT Plus Inc. produces a VERY GOOD land pattern book containing most
all of the packages used presently (BGAs,TPFPs,SSOPs,etc.). GET IT!
They can be contacted at: 5403-F Scotts Valley Dr. Scotts Valley,CA
(408)438-6116, (408)438-5450 Fax
www.smtplus.com (Web HomePage)
email [log in to unmask]
I've used this for my land patterns for about 4 years with NO errors!
If you don't find a land pattern (among the nearly 900 patterns!) you
can fax them the mechanical datasheet and they will get back to you
within 24 hours (usually 3-4 hours), guarrenteed!
#2 Use IPC-SM-782A land pattern spec. This gets you alot of land patterns,
but YOU ARE ON YOUR OWN with most patterns. And, if you work with
multiple designers, they all have to know what formulas you're using.
#3 Check the IPC footprint web site: http://www.pcdmag.com/footprints.html
and see what the 782A land patterns would look like in IPC-SM-782. It's
pretty neat, but remember, you'll have to define most of the patterns
you'll be using.
#4 Check the IPC web site www.ipc.org under Design you'll find the IPC
land pattern calculator. You will have to understand their land pattern
naming convention, but it looks neat.
> Does anyone know any mathematical formula to be used to check roughly
> dimensions of a pad ?
See above. (Between IPC-D-275 and IPC-SM-782A you get the formulas, if reqd.
> This problem is coped by reducing the size of stensil apertures. How
> much it can be reduced ?
This is an issue you can take up with your assembly house, AND SHOULD take
up with your assembly house. If you don't have just one, ask what sources
you have and come up with a concensus. I don't think there is a "general"
number.
Good Luck,
Mitch Morey
Opts Mgr/Sr Designer/Librarian
Design Solutions Inc.
Santa Barbara, CA
(888)964-7525 (ext-27)
email: [log in to unmask]
web site: www.designsol.com
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