Mike,

Allow me to respond to a couple issues relating to your mail.  I'm a little
confused by the way the specs interrelate and could confuse the designer.
> 
> IPC-SM-782A does contain the land pattern formulas. Look on pages 10-14 
> of the document. 
> 
I don't think IPC could have possible made their calculations more complicated.
I use and will continue to use the calculations from IPC-D-275 for my land
dimensioning, which is totally understandable. At least until I encounter a
special case where I might need empirical guidance. Don't get me wrong, I'm not
against "new" calculations, but do make them as understandable as the past.

> The Surface Mount Land Patterns Subcommittee, which is responsible for 
> IPC-SM-782 and its updates, has acknowledged that there are some typos in 
> the document, which may explain the "inconsistencies." Nevertheless, one 
> must also consider three factors when comparing IPC-SM-782 to 
> its successor:
> 
Has IPC decided how they can and will communicate these inconsistancies with
the designer community which has spent good money for what we hoped was
solid information? I would like to see, possibly, quarterly updates sent to
those of us who have "BOUGHT" into this Rev A spec.
 
> 1. Land patterns in the "A" rev. were developed which the goal of the best 
> possible solder joint per J-STD-001, which was released in April 1992 
> (well after the 1987 release of IPC-SM-782).
> 
> 2. Manufacturing tolerances change as improved equipment reaches the 
> marketplace. These, too, will impact the land patterns.
> 
> 3. The land patterns in the second half of the document reflect the 
> industry consensus based on empirical knowledge. Given the variety of 
> manufacturing methods in use, some tinkering of the land patterns will 
> probably be necessary from time to time.
>
Where might one get this "empirical" data? Is IPC going to get on the internet
and have it published? Or do I have to BUY this from them?

> An amendment to IPC-SM-782A is underway. IPC awaits the final draft from 
> the aforementioned volunteer committee. Per ANSI rules, we will then 
> circulate (30 days) the proposed amendment to our full membership for 
> approval. If all votes are affirmative, IPC will publish the amendment.
> Unfortunately, it is difficult at this time to predict when it will be ready.
> 
I'm not looking for this document any time soon, based on the past history of
amendments and final drafts, and I also would hesitate, as I am now, to use
another specification which I have to tinker with to make sensible.

THIS IS NOT A FLAME!
Thank you for your time, Mike.
> 
> > Mitch Morey
> > Sr. PCB Designer
> > TRW, Inc.
> > Redondo Beach, CA
> > (310) 814-5765
> > Fax: (310) 812-4949
> > ([log in to unmask])