Amol,
Let me take a stab at MY set of answers.

1. "Since our products are not subject to RoHS and our customer is not
requiring lead mitigation, is there a vendor preferred process of Pb based
or Pb-free processing."
By vendor, I am presuming they are referring to an EMS they are wanting to
hire to build the product.  First answer: it depends!(C)
Second answers:
- Are they supplying you a bill of materials of leaded or unleaded parts?
- Have they checked temperature limits and MSL levels for the parts?
- Is your shop, Amol, a lead only, lead free or mixed shop?  (What do you do
best?)
- The product may not be subject to the RoHS directive, but what does the
ultimate customer want?  For instance, RoHS does not apply in the US as a
country, but it sure does if you want to sell to AT&T!

1.a. "Describe your history/experience and process for adding ~3% Pb to
Pb-free paste and utilizing Pb-free processes."
Are they kidding?!! What are they smoking?!  Never mind the mixed metals,
imagine the mess this would make of your metal loading to flux ratio!  And
who wants to buy and deal with fine lead powder? Your EHS people will go
squirrelly and/or apoplexic.  At least in Ontario lead is a Designated
Substance.  You need detailed control plans on how you deal with it, dispose
of it, etc. And then there are the problems of mixing it properly, and
printing and print characteristics. I could go on and on and on....

1.b. "Any quality or reliability concerns adding ~3% Pb to Pb-free
soldering."
Well we haven't covered SAC305+3%Pb, but we sure have covered SAC305 solder
paste + SnPb solder balls in this forum.  It can be done. We did it when we
went from fully SnPb to SnPb solder paste with some SAC387 solder balls to
SAC387 solder paste + some SnPb solder balls and then fully SAC. Can't
remember exactly when we changed from SAC387 to 305. BUT we made and make a
thin, low mass product.  My hat is off to IBM and others with half inch
thick boards going to lead free! But SAC solder with added 3% Pb? It hasn't
been done and without a multi-year, multi-million dollar project my
prediction would be product made with a dog's breakfast of solder paste
would be no better than fecal material for reliability.  Considering some
huts, maybe worse. 

1.c. "Describe your history/experience and processes used in transitioning a
product from Pb to Pb-free (or reduced Pb)."
Finally! A sane question.  But why start now?  :)

2. "Do you know of any issues with RoHS and reliability at -65C?"
Heck, I don't know of any studies going to that low of temperature, although
I am sure that some NASA people do.  I shudder to think these people may be
designing a satellite! In which case, God help us all and I do not mean that
flippantly.

Regards,
Bev
RIM

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Amol Kane
Sent: Tuesday, November 13, 2012 11:19 AM
To: [log in to unmask]
Subject: [TN] SnPb and Pb-free paste mixture -- Resend

Hi all,
Resending the original e-mail as plain text because I don't think the
original went thru. Please disregard and my apologies if you receive a
duplicate.


We have this unusual (at least for me) request from a potential new
customer. This is taken verbatim from their request for process information.
Before I go and tell them this cannot be done, I want to ask the experts out
on technet if they have seen/done something like this. My thinking is that
this would be very hard to do on the floor unless there is a custom
formulation available. I am not aware of their reasoning for asking this
other than for a very unusual (and ineffective) way of mitigating tin
whiskers. Leaving the potential flux incompatibilities aside, is this
something that is being done/can be done? I could use some expertise or
references/studies on # 2 as well.

1.      "Since our products are not subject to RoHS and our customer is not
requiring lead mitigation, is there a vendor preferred process of Pb based
or Pb-free processing.
a.      Describe your history/experience and process for adding ~3% Pb to
Pb-free paste and utilizing Pb-free processes.
b.      Any quality or reliability concerns adding ~3% Pb to Pb-free
soldering.
c.      Describe your history/experience and processes used in transitioning
a product from Pb to Pb-free (or reduced Pb).
2.      Do you know of any issues with RoHS and reliability at -65C?"

Thanks,
Amol



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