I agree with Vlad and David, but not 100% in all circumstances.....
Here's my 2 cent thoughts
First we have to assume that by lead free you are meaning a SAC alloy.
Second we have to recall that eliminating lead was not just about solder but
board and component finishes.
Lastly structural integrity of components and PCB laminate is a separate
issue, but possibly is not significant (any more). [The components maybe
rated for lead free or lead free capable, whether or not identified as such.
Of course you still have to check.] So I'll leave that out and just think
about the joints.
So continuing with components. As an example: Whether for leaded or
unleaded, ceramic C and R probably do have a tin finish because they always
have had one. So they could be no different. Arguably as a "lead free
device" processed at lead free temps, they have an extra margin of
reliability due to less severe reflow profile. I'm not sure what component
manufacturers do with molded or polymer bodied devices. On BGA, do they run
two lines with different resins or just have one body and different balls?
WRT to PCB: ENIG, immersion silver, OSP, etc are inherently Pb-free and
interchangeable between leaded and lead free, so it makes no difference
whether PCb have PB-free written on the box or not to the joint metallurgy
if you are using those.
HASL finishes are somewhat thicker and have formed solder joints, these
might benefit from further investigation. I leave out immersion tin as I
doubt anyone in high rel would be using it.
So that leaves laminate. Again if you are receiving Pb-free grade material
you could be marginally better off from using in a leaded process.
I imagine the qualifications (and assume these remarks are so qualified)
expressed in articles on this subject are due to the litigation world we now
live in and the fact the authers like me have not run several 1000 hour of
testing on all combinations of finishes, component types, boards and so
forth.
Regards
Mike
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, September 26, 2012 4:36 PM
To: [log in to unmask]
Subject: Re: [TN] Using Tin/Lead balled BGA in a Lead-Free process
Hi Peter - I agree with Vlad, we still have a mixed metallurgy situation
for the solder joint so I would treat it as having the same solder joint
integrity concerns that would need to be reviewed and assessed.
Dave
Peter Barton <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
09/26/2012 09:45 AM
Please respond to
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Peter Barton <[log in to unmask]>
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Subject
[TN] Using Tin/Lead balled BGA in a Lead-Free process
Hi Technetters,
Interesting that this question has arisen for me when there has been a
question posed here on the reverse scenario in the last couple of days.
Firstly, I agree with other posters that full reflow and alloy mixing must
be achieved when using Lead free BGA's in a Tin Lead process. There is
quite a lot of data out there supporting this.
My problem is finding research data on using a Tin/Lead BGA on an
otherwise fully Lead free assembly. This appears to be much more limited.
So far I have only found one paper that refers to this particular scenario
and some of it's conclusions are carefully qualified.
Assuming that all the other the packaging materials for the Tin/Lead BGA
part in question are capable of surviving a suitable reflow process to
successfully solder the lead free parts whilst minimising thermal input,
can anyone out there comment on potential reliability issues. For
information the BGA balls are 63/37 Sn/Pb and the solder paste alloy is
SAC305.
Many thanks in advance,
Peter Barton
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