some do, but not many.  in any case, the package info is the place to
start.  i have found some manufacturers that do provide suggested
layouts, but not all of them do (i'll try and check tomorrow the places
i've found them recently).  another reasonable source is: <
http://landpatterns.ipc.org/default.asp> which has many layouts from
many manufacturers and their own generics for common packages as well as
a calculator for designing your own, though i haven't used the
calculator and it requires knowledge of what you want the solder joint
to look like.  many of the discrete manufacturers like rohm, philips,
cde, epson, etc. do provide them for discretes at least.

it is somewhat frustrating as everyone has a different recommendation
however the ipc site does explain some of the criteria and why.  for
instance most government specs call for a nice large solder fillet
that's easy to inspect, but this is actually bad, it's best for soic's
and j-lead devices to have less solder than you would normally think to
reduce stress and bridging problems.  on my last design, i looked around
and finally used what came with the board layout package i used (Osmond,
free for the mac though lacking in connectivity awareness but other wise
excellent and it handles metric and english measures at the same time
very nicely).

i know those layouts weren't optimal, but i'll be hand soldering most
likely and there aren't many parts on the board so it's less critical
(if i make money i'll get a heat gun, i've found that works well with
solder paste on small boards, now i'll be using paste and a metcal iron
with some of the wide tips, i shouldn't mention it but you can get a
very good deal on metcal gear on ebay and after using it where i worked
before i've always wanted it, it's just too slick!).  by the way, i've
also managed to fix one of my metcal power supplies i got on ebay (which
made it cheaper of course!) and it's certainly the only place to look
for most tips at a hobbyist friendly price (it spoiled me the first time
i used them for soldering, and for desoldering they are even better!).
sorry, i just love, love, love metcal, at least their better system, i
haven't tried the "low cost" system but it probably still beats most irons.

Liam O'Hagan wrote:
--------
> On Monday, Jun 14, 2004, at 19:59 US/Pacific, Philip Stortz wrote:
>
> > the best bet is always to download the datasheet from the part
> > manufacturer (they may have a separate file/link for the package info)
>
> I haven't found many vendors that suggest PCB layouts.  Lots of detailed
> specs on the package itself, usually, but no suggestions for the pads...
>
> (If anyone DOES know of a vendor that provides these, please let us
> know!)
--------

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