Improve thermal cycling time
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 6/1/2008 2:00:00 AM
Thermal cycling tests can help you improve the reliability of electronic components, subsystems, and systems, but ensuring all areas of a product get tested at the correct temperature can be tricky. Electronic products consist of numerous materials, and each material has unique thermal characteristics. To ensure that you achieve the desired temperature at a given location, you should attach a thermocouple or other probe and monitor the temperature at the point of interest.
 Product temperature (red trace) rises exponentially in response to step changes in thermal-chamber temperature (blue trace). |
During your tests, keep in mind that chamber temperatures change nonlinearly and temperatures of materials used in products change exponentially. The figure shows material temperature (red trace) and chamber temperature (blue trace) as a function of time. Changes start out fairly linear but then roll off as the material temperature approaches the chamber temperature. After three thermal time constants of a material, it will have reached 95% of the chamber's temperature. It will reach 99% after five thermal time constants.
Because of the roll-off in temperature change, getting a product to reach the desired temperature at a location inside the product can take some time. To reduce cycle time, you can set a chamber's temperature above or below the desired product temperature. Doing so will keep thermal changes in the more linear portion of the cycle.
To learn more about thermal cycling and how to set chamber temperatures, you can download “Thermal cycling: Keep it linear,” a paper by Mark Woolley, Jessica Greco, Wes Brown, and Dr. Jae Choi of Avaya Product Technology and Reliability Laboratory.
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