The size of the BGA balls is a factor on the decision for yes/no using mix
process.
Small balls and small thermal body mass of SAC BGAs, can be used in mix
process / mix profile.
I have years of experience without failure report from field but still it
is recommended to SAC process for SAC BGAs and Sn/Pb process for Sn/Pb BGAs.
Reuven
On Thu, Mar 1, 2012 at 10:22 PM, Harp, Ken <[log in to unmask]> wrote:
> Is this for a Hi-Rel application? If so, first recommendation would be to
> go for SnPb paste and profile for an SnPb BGA, and beg for a RoHS
> exemption. If you must go SAC, I'd recommend having the BGA balled SAC
> from the factory and make sure they are kept dry throughout the
> manufacturing process.
>
> With respect to the mixed method, I would side with your engineers.
>
> I'm sure opinions will vary...take this with a grain of salt!
>
> Ken Harp
> Principal Mechanical Engineer
> Astronics Advanced Electronic Systems
> 9845 Willows Road NE, Redmond, WA 98052-2540
> Office: 425.376.4423
> [log in to unmask]
>
>
>
> -----Original Message-----
> From: Rivera, Raye [mailto:[log in to unmask]]
> Sent: Thursday, March 01, 2012 12:11 PM
> To: [log in to unmask]
> Subject: [TN] BGA Reverse Backwards Compatibility
>
> Hello TechNet Gurus.
>
> I have seen lots of discussion and studies on the reliability of using
> BGAs with SAC solder balls on an assembly with SnPb paste. Many people are
> interested in this topic because of backwards compatibility issues when
> SnPb BGAs aren't available. At the risk of oversimplifying a complex topic,
> I understand this can be successful using a backward compatibility thermal
> profile such as the one shown on Figure 8-20 of IPC-7095B to ensure
> complete melting of both types of solder. Of course we must take care that
> the profile does not exceed the temperature limitations of the SnPb paste.
>
> Is anyone aware of any study done on the reverse situation? That is, SnPb
> BGAs used with SAC solder paste and a SAC thermal profile? I would think it
> would be at least as reliable as the above situation. We definitely get
> complete melting and the temperature profile is correct for the SAC solder
> paste chemistry so we are not as concerned about holding a narrow process
> window.
>
> This is not just academic curiosity on my part. We have some prototype
> boards built with SnPb BGAs SAC paste, and SAC profile. They are not for
> sale to customers, but some of our engineers are of the opinion that any
> mixed process joint is suspect. I'd like to find some data on the topic.
>
> I hope everyone is enjoying Apex.
>
> Best regards,
> Raye Rivera
>
> QA Manager * Canoga Perkins
> 20600 Prairie Street * Chatsworth * CA 91311-6008
> 818-678-3872 * [log in to unmask]
>
>
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Best Regards,
*Reuven Rokah*
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