In my experience the IPC guidelines (SM-782) usually are wide enough to
contain the set of supplier suggested designs for a given component. In some
cases the component supplier specifies a pattern outside the guidelines,
usually, optimised for component population density, these frequently create
problems in manufacturing (placement, moving components and insufficient
solder fillets).

The best solution, IMHO, is a custom library based a combination of supplier
provided patterns compared to IPC guidelines (which are optimised for
manufacturing yields and robust solder fillets), followed by lessons
learned. Which, as I read your message, is exactly what you do.



> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
> Sent: Monday, April 15, 2002 6:20 AM
> To: [log in to unmask]
> Subject: Re: [TN] IPC SMT FOOTPRINT DESIGN GUIDLINES VS SUPPLIERS
>
>
> Thanks Wolfgang and others who have replied on and offline so
> far. I always
> think I have the right answers but really know better.
>
> I have several reasons for asking this question. The first
> relates to who is
> doing what out there just out of curiousity. Next, IPC has developed
> relatively new reliability and design requirements for surface
> mount solder
> joints as 9701, 785, and 279 as examples in addition to 7095 and,
> of course,
> 782. Also, IPC, according to Jack, has had its great 610 adopted
> by the DoD.
> Finally, while realizing 782 is a set of guidelines, as most all IPC
> documents have been for years up until recently, I wonder how many folks
> have the resources, or dedication like Wolfgang, to whittle, cut,
> scrape, or
> otherwise come up with better, lesser, or more pad sizes.
>
> I have worked with comanies as HP, Nortel, NG, and Celestica who
> used their
> vast resources to come up with very different land patterns and pad sizes
> for some parts. I recognize the component manufacturers also have the
> wherewithall to do the same. Additionally, like the round pad
> string earlier
> in this month's forum presented some interesting and, to me, realistic
> possibilities for non BGA pads and the ability to minimize, mitigate, or
> otherwise prevent small chip devices from tombstoning let alone
> moving - period.
>
> What I'm really after, if we accept all our solder joints to IPC
> STANDARDS,
> not guidelines, how can we not design to the guidelines without having to
> spend so much extra effort refining them to be STANDARDS, or rules.
>
> A very small company I am continuing my contract with, has reached a
> critical point where they/I must decide what direction in which
> to proceed.
> With but two designers, we are faced with decisions concerning a starting
> and staying point and path. We can go all IPC, go with the "big
> boys proven"
> land requirements, or go with component supplier recommendations.
>
> Sure, I can use my stuff gathered and continually evolving over
> the years or
> have a library created using available guidelines and hope to refine them
> over the years. Furthermore, if all my suppliers are accepting in strict
> accordance with IPC 610, as an example, surely I must design to them
> especially in light of my first paragraph's important issues. These
> reliability requirements are based on considerable research using IPC
> guidelines, aren't they Werner and associates?
>
> Earl Moon
>
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