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July 2004

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Subject:
From:
"Douglas O. Pauls" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 1 Jul 2004 16:43:14 -0500
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Ken Patel asks:

 I have been given a task of implementing Leadfree change over. We are OEM

 and our CM to build assemblies for us. Part of my responsibility is to

 come

 out with a clear plan for transition from Pb containing to leadfree

 assemblies. Does anyone has created such plan and willing to share with

 me. This plan of attack will help us in moving smoothly to leadfree with

 fewer headaches. I know I have to work with not only CM but also with

 suppliers.








Ken,
I have been meaning to answer this one for a while.  I don't think you can
have a generic plan for transitioning to lead-free, any more than you can
for any other manufacturing process, because it all depends on your
materials of construction and your chosen process parameters, for your
product.  I will have a different approach than you than would our Star
Trek obsessed friend, Dewey.  In essence, you are crafting a new
manufacturing process from the ground up.  You must understand the impact
of reflowing solder at 30-40C higher temperature on your materials of
construction.  Much will depend on what your equipment can or cannot do, so
you have to answer the question not only for your manufacturing processes,
but your CMs as well.

That  being understood, here is a general approach to consider.

   Will your components handle the hotter temperature without loss of life
   Is your equipment capable of providing the 30-40C hotter temperatures
   What is the effect of the hotter temperatures on laminate?  Do you need
   to go to a higher Tg laminate?
   What is the effect on solder mask?  will it degrade at the hotter
   temperatures?  Will it withstand fewer reflow cycles, i.e. rework?
   What are the effects of the flux?  Is is cleanable?  If so, with what
   materials and processes?  If not, will it support dendritic growth
   What is the effect of the hotter temperatures on via or PTH reliability?
   What is the fatigue life of the new solder joints?  What is the life in
   thermal cycle.

Yes, it is a LOT of work since you cannot assume that all the reliability
or quality metrics or guidelines we have used for years are still
applicable.

The best thing that you can do to help develop a test plan for transition
is to participate in the IPC.  The A-610 and J-STD-001 groups meet in
Huntsville, Alabama in August.  It would give you access to all the right
people and most are pretty helpful.  Technet also has many qualified
consultants or technical experts which can contact you off-line to assist
you in the development of your plan.

Doug Pauls

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