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Leaded and Lead Free BGA's on hte same board

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#54539

Leaded and Lead Free BGA's on hte same board | 30 April, 2008

There must be discussions about this on SMTnet but I have yet to find them. I would like to hear from all you smart people about running LF and PB BGA�s on the same board using 63/37 solder. If you run your profile up to peak at around 225C +/- (nitrogen atmosphere) and the PB BGA�s are speced to handle the temperature what issues would I expect to have, if any. Does anyone have case studies. Thanks in advance.

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#54540

Leaded and Lead Free BGA's on hte same board | 30 April, 2008

Doug, yes sir there are some excellent stuff out there in the fine SMTNet archives. Here's one example:

http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=9822&#Message39512

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#54558

Leaded and Lead Free BGA's on hte same board | 1 May, 2008

Thanks for the link Samir. Although this thread does have some good info in it I don't think it is hitting the exact point I am trying to resolve. This seems to talk to a one profile fits all for running lead and lead free paste. I want to know about putting lead free and leaded BGA's on the same board using Lead free solder. So If I were to run a profile that peaks at about 225C and the time above 183 is about 90 seconds +/- will I get a good solder joint on the BGA without Lead and assuming the parts can handle 225C will the leaded parts be acceptable as well? Thanks again all

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#54560

Leaded and Lead Free BGA's on hte same board | 1 May, 2008

In our house we have had some of our BGA's reballed because it was a lead-free part and wanted to place on a leaded assembly. Hope this helps.

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#54561

Leaded and Lead Free BGA's on hte same board | 1 May, 2008

Most white papers, like this one http://members.ipc.org/ipclogin/ipcmembers/IPC/Route/0706/0706techpaper.pdf, have written that lead contamination in a lead-free solder joint leads to all sorts of reliability problems. Consensus is that, if the contamination is minimal (< 10%) you should be okay.

Keep in mind, the bulk of your BGA solder joint IS that Sn63Pb37 solder ball.

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#54562

Leaded and Lead Free BGA's on hte same board | 1 May, 2008

CK So as I see it batch B represents a leaded process with leaded components and D is a leaded process with lead free components. Batch Components Paste B SnPb Sn62 D Lead-free Sn62

If so it is BETTER to run a lead free BGA with Sn62 (leaded) solder! Not so great to run leaded parts in a leaded process! WOW!

BGA Electrical Testing � Only Batch D survived 2000 thermal cycles with no electrical test failures � Electrical failures occurred only in the following: Batch A, 19 failures in the C-rings between 1000 and 2000 cycles Batch B, 3 failures in A-rings between 1500 and 2000 cycles 7 failures in B-rings at 2000 cycles 22 failures in C-rings between 1000 and 2000 cycles 7 failures in D-rings between 1500 and 2000 cycles

With all that said I think this study still does not answer the question posed above. This is more great information though! Thank you!

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#54563

Leaded and Lead Free BGA's on hte same board | 1 May, 2008

Yes, the authors do give the caveat that small amount of lead contamination in a SAC/Lead-Free system is tolerated provided the Pb-BGA has sufficiently reflowed.

This verbiage is on the bottom of Figure 10.

For my own peace-of-mind, I would send your PCB out to a lab capabable of cross-sectioning, tensile testing, and picture taking of a collapsed BGA solder joint.

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#54573

Leaded and Lead Free BGA's on hte same board | 1 May, 2008

The concern about lead contamination of lead-free solder has to with zone refining. For more, look here: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=30315

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#54574

Leaded and Lead Free BGA's on hte same board | 1 May, 2008

Took a couple of jumps to other threads but it was there http://www.mot.co.jp/about/ehs/green/ENV_PBFREEOV.pdf

This document was exactly what I needed to send to my paranoid customer!

Thanks again!

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