I have been using SMTPlus for years for footprints
http://www.smtplus.com/  they have the expertise and my customers have
always been pleased with the production results. They will develop a new
footprint quickly and get it back to you the same day. Check it out they
have saved me lots of time and therefore lots of money.
Fran

-----Original Message-----
From: Leo Potjewijd [mailto:[EMAIL PROTECTED] 
Sent: Wednesday, March 10, 2004 5:24 PM
To: Protel EDA Forum
Cc: [EMAIL PROTECTED]
Subject: Re: [PEDA] Common PCB footprint specifications


At 10-03-04 18:36, Ray Mitchell wrote:
>I'm sure this is a repeat, but is there a simple specification readily
>available that gives the "commonly accepted" (if there is such a thing)

>dimensions for 0402, 0603, ..., SIOC-14, etc., and all the other 
>"standard" footprints?  I don't really want to wade through a bunch of 
>technical stuff to derive all of this myself and I certainly don't want
to 
>trust a priori the patterns that come with Protel or any other 
>product.  It's really annoying when part manufacturers don't provide
these 
>footprints, assuming they are common knowledge.

Others have already refrenced the s'standards' (IPC). I'm a little more 
sceptical.....

To my knowledge, there is no such thing as a standard footprint.. Was it
not the CEO of Sun Micro Systems who said at one time "I just LOVE 
standards, because there are so many of them".

In short, even a simple shape such as a 0805 is implemented differently
by 
different manufacturers.
Weird? I'd say so. Surprising? Not really: OUR wheel is MUCH
rounder..... 
New and improved...... New formula......  You know the buzz.

I use a spreadsheet (not ready for the public yet, but I'll post it 
sometime in the not-so-distant future to the Yahoo list) to calculate a 
footprint from the dimensions and tolerances of the component given by
the 
mfgr. The differences are sometimes quite large (as in: HUGE); in fact
so 
large that a component from anoher  mfgr will not fit  on the same 
footprint (we lost a complete production run on that one).....

I'd still say to look up the mfgr datasheets (whenever available) and 
derive your own footprints from that information using a combination of 
guidelines (IPC, JEDEC) and common sense, seasoned with a tuch of 
practicality (you don't want 73 mils distance on 0805 pads when you're 
using a 5 mil grid).
Hey, I even round off pad sizes that were designed in mm to an integer 
number of mils.....and I'm in the metric part of the world ;-) Find
values (IPC, JETEC, your own fab house) for things like placement 
accuracy, heel and toe solder fillets and ask your board stuffer what 
component clearances (and directions) are needed for what processes and 
machines they use.
All of these (and then some) will influence the final optimum
footprint...... Last but not least: small series (50+) can most of the
time get away with 
minor deviations from optimum, big series (500+) usually can not, huge 
series (10k+) never can.

A lot of work, yes, but one only uses so many different components......

I found it worthwile to invest the effort: I have no production failures

yet on my boards (apart from that one that was designed for Philips TSOP

and could not accomodate Fairchild).
BTW, I am designing boards for just 10 years now, so I really don't know

much about the subject yet. In fact, I'm still learning, every single
day.....

To qoute another frequent poster to this list: "I hope this helps".

Regards,

Leo Potjewijd
hardware designer
Integrated Engineering B.V.

[EMAIL PROTECTED]
+31 20 4620700







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