Hello Gary,
there have been a lot of investigations on that topic done by Thales and
Siemens (may be others as well) in the past. They did tis independently and
both came to the same conclusion: it is possible to solder BGAs having
leadfree balls togeteher with ones having SnPb-balls. As mentioned the
solder temperature is critical, e.g. hot enough to melt SAC solder but not
too hot for the older components. Siemens used vapourphase solder machines
at 230°C. Microscopic analysis showed that a completely mixup of both
solders leadfree as well as leadcontaining was done. At accelerated aging
tests there was no difference visible between leadfree componenents soldered
with a leadfree process and those soldered using a SnPb-process. The results
of Siemens have been published during the SMT meeting at Nuremberg (Germany)
in 2007 resp. 2008. The Thales results on reliability tests have been
published by M.Brizoux/A.Grivon/B.J.Smith/P.Snogovsky titled "Industrial
Backward Solution for Lead-Free Exempted AHP Electronic Products"
Best regards
Wolf-Dieter Schmidt
Industrial Engineering
-----------------------------------------------------------
THALES Defence Deutschland GmbH
Defence Solutions & Services
Ostendstrasse 3
D-75175 Pforzheim - Germany
-----------------------------------------------------------
Phone: +49 7231 15 3386
Fax: +49 7231 15 3390
mailto: [log in to unmask]
http://www.thalesgroup.com
Registered Seat: Berlin
Commercial Register Charlottenburg HRB 93875 B
Managing Directors: Dr. Markus Hellenthal (Chairman), Peter Obermark
Chairman of the Supervisory Board: Bruno Rambaud
> -----Original Message-----
> From: Gary Koven [mailto:[log in to unmask]]
> Sent: Friday, June 26, 2009 6:08 PM
> To: [log in to unmask]
> Subject: [LF] Reflow profiles for mixed Pb status boards
>
>
> For those of you who subscribe to the IPC DesignerCouncil
> email forum, this will be a duplicate topic...
>
> We have a number of PCBAs with both leaded and lead-free
> parts on them.
>
> Looking over the J-STD-020 reflow profiles on one of the
> leaded part datasheets, we saw that its range seemed too
> restrictive for the lead-free profile.
>
> Basically the two parameters that interest us are:
>
> (1) Preheat temperature, 100 oC-150 oC for leaded and 150
> oC-200 oC for lead-free
>
> (2) Liquidous temperature, 183 oC for leaded and 217 oC for lead-free.
>
> On our assembly drawings we call out IPC-A-610 Class 2. I
> understand that J-STD-002 can also be used together with
> IPC-A-610 as a note callout.
>
> Since there is not a RoHS-compliant requirement for these
> boards, we don't call out what type of solder process needs
> to be used.
>
> We're curious about how assembly shops adjust their soldering
> process for boards that have both types of parts on them.
>
> We're also wondering whether we need to begin calling out
> specific solder processes, but we don't want to add cost to
> the assembly.
>
> Give me a solution that doesn't add cost to the assembly, but
> at the same time satisfies the curious, please.
>
> TIA and Best Regards,
>
> Gary M. Koven, C.I.D.
> Dynazign, Inc.
> Charlotte, NC, USA
> Veteran of the Marsh School
>
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