Hi Peter,

Theoretically, a BGA package designed to withstand Sn/Pb reflow temperature,
could not withstand the Lead Free (like SAc 305) Reflow higher temperature. 

Only the Tech Data Sheet of BGA can tell you how much could be the max
temperature inside/outside of package that can withstand ( review the
thermal profile is must), according also with IPC/J-STD-20 D, table of max
reflow temperature for Pb and Pb free packages.

At the, the solder joint can show a good shape, but who knows exactly what
happened inside the BGA (Substrat Laminate - IC - Molding Compound - Single
o Multi Chip ? etc), not so easy to predict the real reliability of such BGA
once "over cooked " .... just a guess ? 

Gabriele


-----Messaggio originale-----
Da: TechNet [mailto:[log in to unmask]] Per conto di Peter Barton
Inviato: mercoledì 26 settembre 2012 16.45
A: [log in to unmask]
Oggetto: [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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