Dave

We had a similar discussion lately. I cut and paste the question and
the answer I gave.


On 16.5.2003 Wee Mai wrote

 understand the topic of Pb-free is very hot especially with the
annoucement if its ban within the European markets with effect from
2006. Having much talks about Pb-free and its many concerns and
uncertainties, I would like to add one question :

IPC-SM-782 has been around for many years and if I may put it would be
in conjunction with the current SnPb process so the pad goemtory so
used
at design will not cause any reliability from fabrication to assembly.
Will implementation of Pb-free process require changes to be made to
the
current pad geometry? Someone asked me this question because some
sources say so.

1. A Practical Guide to Achieving LEad-Free Electronics Assembly by
Karl
Seeling and Davide Suraski of AIM
    - mentioned in this paper that established PCB designs rules may
need to change during the tranisition to lead-free soldering to ensure
amnufacturability and reliability.

2. IPC Roadmap : A Guide for Assembly of Lead-Free Electronics 4th
draft
date Jun 2000
    - mentioned a list of standards that will be affected and one of
them is the design standards from IPC-2221 - 2225. Although IPC-SM-782
is not mentioned, IPC-2221 - 2225 uses it.

I would appreciate some of you can give me some lights to brighten my
dark path :8)

Thanks and regards,
Wee Mei

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The question of design rules came up by the fact that the wetting
behaviour of led free solder in the possible process window is somewhat
different from the one of SnPb. However, our trials in LEADFREE and some
pilot production in the companies associated in the project with
standard design rules showed no problems in the soldering process due to
the design. It can be, in wave soldering, if space is very restricted
and thus no solder thieves can be used when soldering fine pitch
components and components are set close together, you see more bridges .
But it has to be emphasised that, if the IPC design rules are
consequently applied, lead free soldering is not a big deal.


Best regards


Guenter


EMPA
Swiss Federal Laboratories  for Materials Testing and Research
Centre for Reliability
Guenter Grossmann,  Senior Engineer

8600 Duebendorf
Switzerland

Phone: xx41 1 823 4279
Fax :     xx41 1 823 4054
mail:     [log in to unmask]

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