David I would not necessarily agree about the severity comparison :
Seen joints to live through shock test and die on parallel cycling .
The joint mass ; and ghost of applications specifics can be designed to
perform to both terms .
Both are different, in each term , with in-between "interpolations" quite
often misleading without knowing the specific design
(components/pads/solders/etc.) interplays .

I think in IPC-SM-785 Werner wrote anything slower than 30'C/m ramp is cycle
;
faster is shock .

It always very much depends on the actual life of the task character .
To give you extreme example :
Implanted pacemaker needed only some 50 cycles for validations ; no need for
shock tests .
as it spends most of it's life in constant 37'C (forget the surgeon's
storage in Alaska);
The same board working in field would need 5000 cycles just to get on
shortlist .
The same in space 10 to 100 times more again .

Very simplified ; the shock is looking at strength ;
the cycle at endurance .
Solder, being relatively strong joint type to start with gives sufficient
initial strength base,
making thus the endurance part of reliability much more in effort focus .

That goes to such peculiarities as experienced on some railway cards ,
when certain componentry resonating to certain frequencies had to be
soldered to different designs because of very specific conditions .
First is the task ; THAN you look for the standards and tests (or make your
own) .

See you

Paul Klasek
http://www.resmed.com



-----Original Message-----
From: David yeh [mailto:[log in to unmask]]
Sent: Tuesday, 3 August 1999 0:25
To: [log in to unmask]
Subject: [TN] Reliability test


Could anyone enlighten me on the difference between Thermal shock and
Temperature cycling test. I know the former is more severe but what is each
test looking at?

Thanks.

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