Hi Al! The short answer to your question is "yes" - if you are able to
completely reflow the Pbfree solderball on the BGA then the likelihood of
having solder joint integrity problems becomes low. There have been a
number of published papers on the topic and the majority show that allowing
the Pbfree solderball to completely reflow results in a uniform
microstructure. If you only achieve partial melting of the solderball or
just diffusion of the solderpaste into the solderball then you have a
nonuniform microstructure that doesn't play well with your use environment.
Some folks have suggested to just increase the Sn/Pb reflow temperatures if
there is a Pbfree BGA component present on an assembly but the temperature
increase impact on the other components can cause other problems! Rockwell
Collins is presenting a paper on a case study of Pbfree solderballs in a
Sn/Pb reflow process at the Toronto Pbfree conference in May 24-26.  I
think Steve G. also has a picture of a Pbfree solderball microstructure
after going thru a Sn/Pb reflow process. Good Luck.

Dave Hillman
Rockwell Collins
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             ADYNE.COM
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             01/25/2005 07:41                                      Subject
             AM                        [TN] Lead-free BGA using Lead Paste


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Technetters:

What happens when using a lead-free BGA with SN63 paste profile (ie above
liquidus approx 60 seconds and peak temperature approx. 210)?  I do not
know the alloy of the ball at this time.

Will the paste wet to the ball and form a reliable solder connection?  Is
it similar to using non-eutectic balls or column-grid-arrays?

Do I need the ball to reflow?


Thanks in advance,

Al Kreplick
Sr. Mfg. Eng.
Teradyne, Inc.
500 Riverpark Drive
Mail Stop NR500 1-1
North Reading, MA 01864
Tel: 978-370-1726

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