I do not discount low temperature ranges--what I discount is the combination
of low and high temperatures in the same test cycles. This confounds a number
of different damage mechanisms.
Sure, cycling assemblies from -55 (or -65) to +125 (or +150) C will give you
failures fast, but so does dropping them from the Empire State building.
 What do these cycles mean for your product that never sees any cycles even
remotely close to the test cycles? It is NOT accelerated reliability testing,
because you do NOT accelerate a damage mechanism that is dominant for your
product, but create a different dominant damage mechanism(s) and their
interactions.  This has clearly been shown by Roger Wild, IBM, many years ago
and that is the reason that most new military contracts no longer put those
cycle extremes as requirements.

Just because something is popular (actually a hold-over from the old military
hay-days and people do not like change) does not make it technically correct.
 If the customer requires these cycles you are stuck.  You had better design
your electronics to meet these requirements, which in most cases means that
these assemblies are less reliable in the field than they could be if the
requirement were more closely associated with actual use conditions. Managers
sure like these tests, because they take much less time than properly
designed accelerated reliability tests. But they are like 'security
blankets,' they sooth the mind but are no real protection. It is my opinion,
that if you can not do proper accelerated testing, you are better of not to
do any testing at all--saves more money too.

PS: What is "Engelmaier's Curve"? I don't know of any other Engelmaier in
this industry, but I sure have never heard of "Engelmaier's Curve"

Werner Engelmaier
Engelmaier Associates, Inc.
Electronic Packaging, Interconnection and Reliability Consulting
23 Gunther Street
Mendham, NJ  07945  USA
Phone & Fax: 201-543-2747
E-mail: [log in to unmask]

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************