Dee,

You hit a sensitive point with me on my last day.

If your process is under control, and either you increase the time above
reflow or the temperature above reflow, you may get a "good" solder
joint. There is data that indicates that mixing technologies may be
acceptable for low reliability "commercial" applications. I found the
data scientifically acceptable, but the thermal cycle range was very low
(0 - 80C) when compared to aerospace requirements (i.e. -55C to 125C).

The JG-PP / JCAA Program and NASA / DoD Lead Free Program shows that
mixing technologies for high reliability applications results in solder
joints failing prematurely. Dave Hillman presented papers indicating
that the resulting solder joint is a "funky" solder joint, with lead
(Pb) congregating at the solder ball / PWB Pad area. 

My recommendation is to not to mix technologies (eutectic SnPb solder
paste with Lead Free Solder balls) unless you absolutely have to. For
additional information, I suggest you get a copy of the Manhattan
Project Phase I report, the JG-PP / JCAA Program report, or the NASA /
DoD Lead Free Program report. Dave's paper should be on the net
somewhere.

Hope this helps. Good Luck. Now back to packing-up :)

Lee Whiteman, PMP
Senior Member Engineering Staff
L-3 Communications East
Telephone: (856) 338-3508
FAX: (856) 338-2906
E-Mail: [log in to unmask]
 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dee Stover
Sent: Thursday, June 10, 2010 10:13 AM
To: [log in to unmask]
Subject: [TN] rohs, BGAs & assembly

Hi all,

I need to find some written data on the long term reliability of rohs 
assemblies.  We don't have comply with rohs but can only get the 
parts in rohs, with BGA's being the main drive for rohs compliant
solder.

Just had an assembly vendor say that a rohs bga can be assembled with 
eutectic solder paste with good results.  2 other assembly shops say 
that is not recommended.  Is there any real studies or data available 
that provides the real answer?  Also studies and data for the 
reliability of rohs?  We need our boxes to work for 10 years or more.

Thank you for your time.   What a great network for people to share 
knowledge.  I will also be going through PCD&F and google to 
(hopelessly behind on my reading)

:-) Dee Stover  [log in to unmask]   520-318-8489
Tech Associate II
National Optical Astronomy Observatories
www.noao.edu 



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