Thermal stress of PWB coupons is different than what I'm referring to. The
thermal shock I'm talking about is typically performed in an environmental
chamber (or chambers). Basically, you have two chambers, one ant a low
temperature, the other at a high temperature. After a predetermined time in
one chamber, the test sample is removed and placed into the other. The
temperature change rate (ramp) is quite high (fast). Thermal cycling, on
the other hand, usually takes place in a programmable chamber with
pre-programmed high and low temperature extremes and a controlled ramp rate
like 5 degrees C per minute.
Hope this clarifies things.
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879
-----Original Message-----
From: Paulus, Jim [SMTP:[log in to unmask]]
Sent: Wednesday, June 23, 2004 9:37 AM
To: [log in to unmask]
Subject: Re: [TN] Antw: [TN] Shock vs. Cycling
What is the difference between "thermal shock" and "thermal stress",
which is generally a coupon that is floated or dipped into solder
for 10
or 20 secs at 500 or 550F?
Thanks,
Jim Paulus
at Itron: 507-837-4326
at office: 608-787-0817
-----Original Message-----
From: Guenter Grossmann [mailto:[log in to unmask]]
Sent: Wednesday, June 23, 2004 2:28 AM
To: [log in to unmask]
Subject: [TN] Antw: [TN] Shock vs. Cycling
James
The results you will achieve will be totally different and specific
to
the test.
In thermal shock deformation and degradation mechanisms will be
activated that are irrelevant in thermal cycling and vice versa.
- Degradation in solder joints depends on the strain rate
- The degradation path in solder joints can be influenced by the
stress
applied. And, the higher the strain rate the higher the stress.
- Thermal shock can lead to the destruction of the components
something
that will not occur in thermal cycling
- Due to thermal shock the substrate will bend or warp and bring in
additional stress into the component and the joints not occurring in
thermal cycling
If your application includes thermal shock you must test the
specimen
accordingly if the stress is thermal cycling, thermal cycling is the
test you have to do otherwise it is impossible to make any
connection
between the test results and the real application. I do have even
doubts
about the validity of comparative tests done with thermal shock if
no
thermal shock occurs in the application (see above).
Best regards
Guenter
EMPA
Swiss Federal Laboratories for Materials Testing and Research
Centre for Reliability
Guenter Grossmann, Senior Engineer
8600 Duebendorf
Switzerland
Phone: xx41 1 823 4279
Fax : xx41 1 823 4054
mail: [log in to unmask]
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