Dear Raye,

We are in the process of completing the "C" revision of IPC-7095. The topic in which you expressed an interest will be in the new document. 

I've attached the minutes of the telephone call last year in which this topic was reviewed and we agreed to add the explanations to the table as shown in the minutes. That information should give you some good advice and characterize the reflow profile that is recommended for the situation.

I've just returned from the APEX meeting in San Diego and although we are in the Balloting process we have a few additional Technical comments that were resolved at the meeting. These comments were about adding some more information on the causes of voids in the solder joint. We have to go for another short circulation to get the committee approval before we publish. There were no additional comments on the section that references table 7-3.

I hope this helps.

Best regards,

Dieter 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rivera, Raye
Sent: Thursday, March 01, 2012 2:11 PM
To: Technet
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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