July, 2016
www.us-
tech.com
IC Temperature Test: Thermal Stream vs. Direct Thermal Head Systems
By Lior Yosef, CTO, Mechanical Devices Ltd. T
emperature forcing systems allow engineers to test ICs and other devices for reliability in different environments under controlled con-
ditions. Thermal stream systems and direct ther- mal head systems can be used to create extreme temperatures that mimic real-world scenarios in order to ensure a device’s functionality. Price, accuracy, portability, electrical require-
ments, and maintenance must be taken into account when deciding between a thermal stream or direct thermal head system. In most cases today, direct thermal head systems have more to offer than thermal stream systems. Unlike temperature test chambers, these
temperature forcing systems induce a small area and are limited to test- ing a single device per test. Also, these units are designed to work only for limited periods of time and not for many days or weeks in con- tinuous operation. These factors should be considered when develop- ing a test strategy as they determine the type of tests the systems can be used for.
Stream vs. Direct Head Both thermal stream and direct
thermal head systems are relatively portable, allowing them to be moved and shared between test stations. They are also versatile and capable of simulating both low and high tem- perature environments. These quali- ties serve product and test engineers at the early stages of design, when characterizing an IC, and also in post-production for failure analysis. A thermal stream system uses
compressed air to provide tempera- ture-controlled airflow to a device. These systems include sensors that monitor the temperature surround- ing the device under test (DUT) and a touchscreen panel for operation. Most thermal stream systems
are fairly large and are not fit for small labs or offices. They can weigh more than 500 lb (200 kg), but can be folded for transport between test sta- tions on a factory floor. Though there are smaller and lighter systems available — some weigh as little as 32 lb (14.5k) and are more suitable for small workspaces — they are gen- erally very loud. The use of com- pressed air can make their noise lev- els reach 70 dB — not very good to use in the office. They also require high power,
200 to 250V (230V nominal), and about 30A to operate. In countries that do not use these as standard voltage levels, including the U.S., Canada and Japan, a special power outlet is needed. It’s also necessary to have an adequate air supply at each test station. Thermal stream systems use air
convection to control the temperature of the DUT. Air is a poor conductor and needs a sufficient flow to move a thermal mass. As a result, it takes time to transfer temperature to the IC case. The thermal head is larger than the DUT itself and might also impact the temperature of surround- ing components, therefore skewing test results. This impact can be mini- mized by using shroud kits or silicon rubber to isolate the DUT. Direct thermal head systems
have similar temperature forcing capabilities, but use a plunger to transfer temperature to a device.
The system’s sensors are in the plunger itself, which allow it to monitor the IC accurately. Weighing around 50 lb (23 kg), they are much more compact than thermal stream systems and can be hand-carried easily from one test station to another. Direct thermal head systems also consume less
Mechanical Devices’ MaxTC direct thermal head system.
power. They are designed to operate at 100/120 or 220/240V and 10 to 15A currents. No special power outlet or air supply is required, which makes them easier to deploy and to transport. Using direct conduction, these systems trans- fer temperature within seconds from the plunger
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