Linden,
Well the IPC land patterns are in fact a very good
place to start. However you are right there is a later
version coming out which does in fact address the needs
of most situations. The version you have gave a broad
range in tolerenaces and yes if you go towards the
can be assembled any where range the patterns are
somewhat big. The new data provides 3 categories
of build it anywhere, to the middle of the road, to
the high end leaving the designer with an easy choice
pending the technology of the type of designs being done.
Rather than try to figure out what tolerances equate to
what technology.
What I have found though is when it comes to the run of the mill parts ie
chip type res's, caps etc and SO parts
the IPC has been very acceptable but when it comes to
any fine pitch parts you really need to look at the MFG
for tolerances of their part. Even if two MFG's call it
a TQFP100 the basic dimension could very well be the
same but each could have vastly different tolerances,
which could sway which way to go ultimately for a
land pattern. The MFG have been getting better with
respect to this but not quite there yet. I have also strayed
from the IPC as far as a maximum material design strategy for land patterns
on the basic stuff too as I needed to design much tighter designs moving
towards the minimums
on these packages.
Hope this helped
Bob Wolfe


----- Original Message -----
From: "Linden Doyle" <[EMAIL PROTECTED]>
To: "PEDA" <[EMAIL PROTECTED]>
Sent: Monday, August 12, 2002 1:36 AM
Subject: [PEDA] IPC Footprint Standards


> Greetings all,
>
> I have a copy of IPC-SM-782. In it are described various recommended
> footprints for resistors, capacitors, discrete semis and ICs.
>
> I also have some documentation from Philips Semiconductors describing the
> same items.
>
> The problem is that the sizes represented in each publication are vastly
> different.
>
> What dangers are there in straying from the path prescribed by the IPC? If
I
> work from the Philips documents I have smaller footprints for things like
> generic 0603 and 0805 thus allowing for tighter layouts. My copy of
> IPC-SM-782 is date 1993 - is it likely that the footprint recommendations
> would have changed in later revisions of the standard?
>
> My previous surface mount boards have not been overly tight but this is
not
> the case with the latest job - I need all the space I can get.
>
> Any comments would be greatly appreciated.
>
>
> Thanks and Best Regards,
>
> Linden Doyle
> Product Development Engineer
> Zener Electric Pty Ltd.
>
> Ph: +61 2 9795 3600
> Fax: +61 2 9795 3611
> [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
>
>
>
> ************************************************************************
> * Tracking #: 7AE998780E1AD14BA518CF969F9E79261307E4BB
> *
> ************************************************************************
>
>


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