Guenter,
I have not seen the specifics of your accelerated test and your test vehicle.
However, your findings seem to agree with familiar trends on the effects of
PWB properties on SMT assembly reliability. 
Can you provide the reference to the paper where you published the solder
joint failure data? I am interested in bouncing your test data against
predictive solder joint reliability models.
Thank you very much.
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: http://members.aol.com/Epsiinc1/index.html

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*
In a message dated 96-12-31 06:41:15 EST, you write:

<< Subj:	Woven Kevlar
 Date:	96-12-31 06:41:15 EST
 From:	[log in to unmask] (Guenter Grossmann)
 Resent-from:	[log in to unmask]
 To:	[log in to unmask]
 
 Hi Bob
 
 I can't give you any advice concerning the scale factors for PCB's with
 woven Kevlar. But we made a lot of investigation about the reliability of
 SMT solder joints on this type of material.
 Be careful !! A PCB with Kevlar can have an anisotropic CTE. The Kevlar is
 not always symmetrically woven ( depends on the distributor ). This means
 there are not the same amount of Kevlar strings in both weaving directions.
 As a result, we observed a stunning crack growth rate in the solder joints
 of ceramic components that are in the direction with just a few strings. on
 the other hand, components with plastic packages show fast growing cracks
 in the solder joints if set in the direction with many strings. I got
 really angry reactions from DuPond when I published this results. The folks
 these explained me that no woven Kevlar is used anymore in PCB's ( due to
 the problems explained in my report ) but a fleece with an irregular
 distribution of the Keflar strings leading to a less pronounced anisotropy
 in the CTE ( hopefully ). However, DuPond never gave us examples of this
 material for testing when I offered them the possibility of performing a
 series of reliability tests. So I can't tell you anything about this
 material. Anyway, it seems as if woven material is still used.
 
 Guenter
 
 Federal Institute of Technology
 Reliability Laboratory
 Zurich
 Switzerland
  >>

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