In a message dated 97-06-09 11:39:36 EDT, you write:
<< Our customer's product is to be used in aeroplane.  It has lot of
 Leadless Chip Carrier (LCC) package IC.  The LCC's solder joint cracked
during the FCC vibration and thermal test.  Could anyone have  experience
with similiar problem share it with me?  We are currently  looking looking
into 2 different solutions:
 1.  PCB finish plating and solder paste.
 2.  Converting LCC to leaded package.
 Other suggestions are deeply appeciated
  >>
Steve,
The problem is solder fatigue and is driven by cyclic stress and strains
caused by thermal expansion mismatch between the board and the component.
This is a common problem with LCCCs on substrates that have a large in-plane
Coefficient of Thermal Expansion (CTE). 
Ways to reduce the incidence of solder joint fatigue include:
a. use a substrate that is better CTE-matched to the LCCC
b. increase the component stand-off height
c. if the LCCC is a castellated device, increase solder volume to increase
the fillet size (larger fillets provide for lower stress, and it takes longer
to propagate fatigue cracks thru a large size fillet).
Upfront reliability modeling should tell you how much gain you can expect in
solder joint life from each of the above.
d. switch to  a leaded package with leads that are compliant enough.
Depending on component size and expected thermal cycles in use, "a, b or c"
may not be enough and switching to a leaded package may be the only way to
go. 

With best regards,
Jean-Paul
________________________________________________________________
 Jean-Paul Clech
 EPSI Inc., P. O. Box 1522, Montclair, NJ 07042 - USA
 tel: +1 (201)746-3796  fax: + 1 (201)655-0815
 Home page: 
<A HREF="http://members.aol.com/Epsiinc1/index.html">http://members.aol.com/Ep
siinc1/index.html</A> 
(last updated on May June 9, 1997).
 - click on the above or copy: http://members.aol.com/Epsiinc1/index.html
 __________________________________________________________________

Note: as of June 1, 1997, our area code will change from 201 to 973.  From
June 1st until December 6th, 1997, both 973 and 201 area codes will work.

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