Guenter,
Thanks for the data. My interpretation is that, since 160 I/O QFPs have very
compliant leads, global CTE mismatch between the package and the board has
little effect on attachment reliability. 
Local CTE mismatch is probably dominant, with Alloy 42  and the board
material working together against the solder joints (as seen with other
Alloy42 packages). In that sense, your particular "Kevlar" situation is worse
than FR-4, which your data shows well. I'd like to know the x-y CTEs of your
CEM1, Aramid 1 and 2 to better understand and differentiate the crack data
for the last three test vehicles.
Still interested in your paper, it will be an opportunity to brush up on my
German.
Danke schoen,
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/Epsiinc1/index.html</A>
_________________________________________________________________

In a message dated 97-01-06 05:17:56 EST, you write:
<< Subj:	Re : Re: Woven Kevlar
 Date:	97-01-06 05:17:56 EST
 From:	[log in to unmask] (Guenter Grossmann)
 Resent-from:	[log in to unmask]
 To:	[log in to unmask]
 
 Jean Paul
 
 I published these data in a seminar about the reliability of solder joints
 in Germany at the CEM Neumuenster. The paper is in German so it doesn't
 help you too much. The test I did was passive thermal cycling:-20/100°C;
 2°C/min; dwell time 30min. I'll fax you a graph where the average crack
 length in percent of the wetted solder length in the solder joints of a QFP
 160 leads of alloy 42 after 2000 cycles is shown for some PCB materials. To
 avoid more E-mail send in order to fax the graph to various people I
 include the data in this mail.
 In the example, the cracks perpendicular to the main direction of the
 fibres where longer than those in the main direction despite the fact that
 the components body is made of plastic.
 
 Aramide 1 = Kevlar reinforced Epoxy, leads in the main direction of the
fibres
 Aramide 2 = Kevlar reinforced Epoxy, leads perpendicular to the main
 direction of the fibres
 
                    PCB Material I FR 4 I CEM 1 I Aramide 1 I Aramide 2 I
 Average crack length in percent I 8    I  20   I    41     I    100    I
 
 Best regards
 
 Guenter Grossmann >>

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