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March 2012

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Subject:
From:
Karen Tellefsen <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Karen Tellefsen <[log in to unmask]>
Date:
Thu, 1 Mar 2012 16:37:57 -0500
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I just heard a very good paper at APEX about this very subject a few hours
ago:

The Relationship Between Backward Compatible Assembly, Microstructure, and
Component Warpage on the Thermal Fatigue Reliability of an Extremely Large
Ball Grid Array
Richard Coyle, Alcatel-Lucent


Karen Tellefsen - Electrical Testing
[log in to unmask]
908-791-3069



                                                                            
                                                                            
                                                                            
   [TN] BGA Reverse Backwards Compatibility                                 
                                                                            
                                                                            
   Rivera, Raye                                                             
                to:                                                         
                  TechNet                                                   
                                                        03/01/2012 03:09 PM 
                                                                            
                                                                            
                                                                            
                                                                            
   Sent by:                                                                 
          TechNet <[log in to unmask]>                                         
   Please respond to TechNet E-Mail Forum, "Rivera, Raye"                 
                                                                            
                                                                            
                                                                            






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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