Bob,
Here at NASA/JPL, we have done an extensive evaluation of different surface
mount components' solder joint failures including LCCs. For LCCs, an attempt
was made to correlate quality of solder joints to reliability. Single LCCs of
20, 28, and 68 terminations with .050" on FR4 were used for thermal cycling
evaluation. Our thermal cycle was between -55 and +100 for 4.2 hour duration.
Your results when adjusted for the maximum temperature differences should come
close to what we found.
Please refer to few of my publication in this area:
1) "SMT Solder Joint Reliability/Workmanship Environmental Test Results
Correlation for LCC Assemblies" The 20th Annual Electronics Manufacturing
Seminar Proceeding., supported by Naval Air Warfare Center, Feb. 21-23, 1996,
Ridgecrest, CA..
2) "The Interplay of Surface Mount Solder Joint Quality and Reliability of Low
Volume SMAs", NEPCON WEST Proceeding, Feb. 25-29, 1996, Anaheim, CA.
3) "Solder-Joint Quality with Low-Volume PCB Processintg," SMT Magazine, July
1996
Reza Ghaffarian, Ph.D.
JPL
4800 Oak Grove Drive
Ms 125-161
______________________________ Reply Separator _________________________________
Subject: ASSY:FAB:Des: Joint Cracking LCCCC
Author: [log in to unmask] at Internet
Date: 9/10/96 12:05 PM
I have been looking at some 20 pin Leadless Ceramic Chip Carriers which have
exhibited cracks. They are mounted on standard FR4 and thermal cycled between
-55 +80 for 1000 hours.
Cracking is a problem with this device as we know but not at these low lead
counts. Many uses in their design rules make 28 pin devices the limit and then
incorporate the use of matched substrate to reduce differential expansion.
I would appreciate any feed back on failure that people have seen on testing of
low lead count devices or even feed back on where people see the limit on pin
count and the need for special substrates.
Bob Willis
Process Engineering Consultant
Electronic Presentation Services
2 Fourth Avenue, Chelmsford, Essex CM1 4HA. England.
Tel: (44) 01245 351502
Fax: (44) 01245 496123
Home Page: http://ourworld.compuserve.com/homepages/Bwillis
Email: [log in to unmask]
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