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March 2012

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From:
"Harp, Ken" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Harp, Ken
Date:
Thu, 1 Mar 2012 20:58:36 +0000
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When begging for the RoHS exemption, I've found that getting down on one knee and weeping really sells it well.  ;-)

Best of luck with your new product!

Ken Harp
Astronics AES

-----Original Message-----
From: Rivera, Raye [mailto:[log in to unmask]] 
Sent: Thursday, March 01, 2012 12:57 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Reverse Backwards Compatibility

Hi Ken,

Thanks for the reply!

It is a high-reliability application and we will build the actual product with SnPb process under RoHS exemption. Believe it or not, the assembly house used SAC solder process on the prototype build by mistake. 

It did make me curious if there is any research on this combination. Probably not. There isn't any good reason to build this way.

Best regards,
Raye Rivera
 
 
QA Manager * Canoga Perkins * 818-678-3872  * [log in to unmask] -----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Harp, Ken
Sent: Thursday, March 01, 2012 12:23 PM
To: [log in to unmask]
Subject: Re: [TN] BGA Reverse Backwards Compatibility

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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