Dave, you'll probably get a lot of learned comments from technetters about solder and temperature cycling.  My generic suggestion would be to look at 3-axis random vibration as a screen for other types of connections.  For a while I was hearing about environmental stress screening, which involved 3 axis random vibe with thermal cycling.  Getting and analyzing data are important.  I don't know if anything better has come along over the past few years, but you might want to look at a couple of books by Wayne Nelson - Applied Life Data Analysis and Handbook of Accelerated Testing.

Lou Hart  412-858-6184 

----------
From:   David Fish[SMTP:[log in to unmask]]
Sent:   Friday, March 10, 2000 12:41 PM
To:     [log in to unmask]
Subject:        [TN] Estimating Reliability

Good morning all:

Classic reliability models define categories of failures:
*  Infant mortality:  occurring within weeks of assembly; measured in
Defects Per Million Opportunities (DPMO); caused by failure of:
components, wire/harness connections, board solder connections, and
board vias.
*  Random failure:  occurring over the operating life of a product;
measured in Failure In Time (FIT).
*  End-of-life failure:  measured in time or thermal cycles; caused by
temperature cycling, mechanical wear, degradation of materials, and
fatigue.

What would you specify for rates of:
*  Infant mortality for circuit board solder connections?  Board vias?
Wire harness connections?
*  Random failure mortality of circuit board solder connections?  Board
vias?  Wire harness connections?
*  End-of-life wear-out mortality for circuit board solder connections?
Board vias?  Wire harness connections?

How do you measure these rates?

Do you have base data of failure rate information of components?

How would you suggest to screen boards and wire harness for infant
mortality?  What Delta T can use use for accelerating stress?  How many
temperature cycles do you suggest for such screening?

What needs to be considered in figuring the cost (production and NRE) of
such screening?

What needs to be considered in figuring the production lead time issues
relating to such screening?

Thanks

Dave Fish

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