Dave's the expert here (I'm just a diligient reader of his stuff and others).  The key question is what's the environment the parts will see.  Vibration?  Temp cycles (mil eq sees incredible shock as fighter planes go from ground to altitude very fast and temp drops like a rock.  Parts can pop off the board.  Why not re-ball?

Polina (Celestica) is on this forum - would love for her to chime in with comments as she's studied this a lot.

(By the way Polina, I've not forgotten your hospitality when Denny Fritz and I visited you for the SMTA meetin - hope later this fall to take a trip up to Toronto to see you all and to have another great Russian dinner with you and your husband and friends from the lab :-).

Bob 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Wednesday, September 26, 2012 8:26 AM
To: [log in to unmask]
Subject: Re: [TN] Leaded Paste and Lead Free BGAs - Do they mix?

Hi Bob - yes, not have collapse would be a very bad idea. Soldering a lead-free BGA in a tin/lead soldering process automatically creates a mixed metallurgy situation which can be a solder joint integrity issue depending on the product use environment.  The degree of solder joint microstructure mixing/uniformity has a direct impact on the solder joint integrity. The customer's suggestion of not having solderball collapse would result in the tin/lead solder paste and the lead-free solderball being very distinct zones in the final solder joint which would be a worst case scenario.

Dave Hillman
Rockwell Collins
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Robert Kondner <[log in to unmask]> Sent by: TechNet <[log in to unmask]>
09/25/2012 07:26 PM
Please respond to
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Subject
[TN] Leaded Paste and Lead Free BGAs - Do they mix?






Hi,

 

I have a customer using leaded paste with lead free BGAs. I think they 
want
to have the balls NOT collapse for better optical inspection.

 

Sounds like a really bad idea to me but I have no explanation where I can
say as why.

 

Can anyone make suggestions either way?

 

Thanks,

Bob K.



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