Thermal Chambers Boost Electronic Device Reliability

Electronic devices are affected in different ways by operating temperatures. Some devices are designed for narrow temperature ranges, typically around room temperature,  while other devices can handle wide operating temperature ranges without key deviations in performance. Some electronic devices, for example, are built for mission-critical applications, such as avionics, military, and space missions, and they deliver consistent performance over wide temperature ranges. But determining such capability usually requires evaluating performance across the temperature range over which an electronic device under test (DUT) is designed to operate, often also at various levels of relative humidity (RH). Such environmental testing is usually performed within a thermal test chamber in which temperatures can be set to match the temperatures under which the DUT is expected to be used.

Thermal test chambers come in many shapes and sizes and with many different measurement capabilities. Some are large floor-standing units, even as large as walk-in units, capable of containing large DUTs over wide operating temperature ranges. Others are more compact thermal chambers such as benchtop units, designed to provide thermal and/or humidity control for smaller DUTs, where operating volume is limited and at a premium.

Regardless of size, thermal test chambers may not be part of a company’s everyday test requirements and may represent a significant investment of a company’s test capabilities. Fortunately, thermal chambers can be rented when needed, to be used as part of a practical environmental test strategy when designing electronic devices and products for use over wide operating temperature ranges.

Finding a suitable thermal test chamber for a particular DUT is a matter of matching the capabilities of a thermal test chamber to those test requirements. Thermal chambers are typically compared in terms of test volume, temperature range, the rates over which temperatures can change, how tightly the temperature is controlled once stabilized, and the power requirements of the facility in which the thermal chamber will be used. How uniform the temperature is maintained throughout the test chamber is another important consideration. The size of the temperature chamber and its temperature range are usually two good starting points in the search for a thermal test chamber.

Depending upon their capabilities, thermal chambers can perform as many as three types of temperature-based testing: thermal cycling, thermal shock, and burn-in testing. Thermal cycling changes the temperature of the test chamber between upper and higher limits, at a well-controlled rate of change. In contrast, thermal shock testing subjects a DUT to rapid transitions between temperatures, either by changing the temperature of a single test chamber or physically moving a DUT between two test chambers at different temperatures. Burn-in testing is performed at an elevated temperature for an extended period. Testing is often performed according to well-established standards, such as from the American Society for Testing and Materials (ASTM), or military standards such as MIL-STD-810 which includes thermal shock and humidity testing.

Taking Temperatures

For many DUTs, thermal testing with a temperature cycling chamber such as the ESPEC BTZ-4200, provides the temperature range and control needed in a system occupying little more floor space than a standard rack-mount test system. It has a temperature range of -70 to +180°C (-100 to +354°F) with control within ±0.5°C. The BTZ-4200 is unique in that it has a very fast temperature transition cycle rate of up to 15°C/minute without requiring cooling water or liquid nitrogen. When even faster temperature cycling rates are required, the chamber can be ordered from the factory with an optional liquid nitrogen (LN₂) injection feature for the fastest cool-down speeds. The chamber has a test volume of 19.6 × 15.0 × 23.6 in. (498 × 381 × 600 mm) or about four cubic feet. It runs on 208/230 VAC. A color touch-screen controller facilitates temperature control and adjustments.

To fit different test spaces, the Test Equity 115A thermal test chamber is available in two configurations, as the benchtop model 115A-B and the floor-standing model 115A-F. The benchtop unit measures  24 × 44 × 26 in. (610 × 1118 × 660 mm) while the floor model is 24 × 61 × 26 in. (610 × 1549 × 660 mm); both offer a test volume of 16 × 12 × 14 in. (406 x 305 x 353 mm). These thermal test chambers have a temperature range of -73 to +175°C with ±0.5°C temperature stability and ±1.0°C uniformity across the test volume. Typical heat-up rate is 5°C/minute while typical cool-down rate is 2.8°C/minute cool-down rate from +85 to -40°C in standard models. Both thermal chamber configurations are designed for 120 or 230 VAC power supplies.

When thermal shock testing is needed, the ESPEC TSE-12-A thermal shock chamber has a test volume of 12.6 × 5.8 × 9.0 in. (320 × 148 × 230 mm) divided into two temperature zones. A DUT weighing as much as 2 kg is held within a specimen basket and can be transferred from hot to cold temperature zones in 10 s or less. Temperatures for the hot zone can be controlled from +60 to +200°C (+140 to +392°F) with cold-zone thermal control from -65 to 0°C (-85 to +32°F), with both zones providing temperature stability within ±0.5°C. The compact thermal shock chamber is powered by 200, 220, 380, or 400 VAC supply.

When testing involves both temperature and humidity control, both compact and larger chambers are available. The Espec SH-242 makes a great choice for a compact chamber (with outside dimensions of 17.4"W x 27"D x 25"H). With a test volume of 12”W x 10”D x 12”H in. (0.8 cubic feet), the model SH-242 chamber has a temperature control range of -40 to +150°C. It adds a humidity control range of 30 to 95% RH at temperatures.

Or if more interior space and a wider temperature and humidity range is required, consider the Test Equity 1007H Temperature & Humidity Chamber. With a test volume of 24”W x 24”D x 21”H in. (7 cubic feet), the model 1007H chamber has a temperature control range of -73 to +175°C. It adds a humidity control range of 10 to 95% RH at temperatures

For innovation, the MPI Thermal Air TA-5000A temperature conditioning system is unlike the traditional thermal test chambers in that it is designed for semiconductor and PCB (printed circuit board) temperature applications. It is truly portable and capable of extremely fast temperature ramp rates. With a total temperature range of -80 to +225°C, adjustable with 0.1°C resolution and ±1.0°C temperature accuracy, the thermal test system can shift temperatures from -55 to +125°C and from +125 to -55°C in less than 10 s. Operating without LN₂, it is powered by 220 VAC and can move easily around a test laboratory on four swivel-caster wheels. It features and industry-leading airflow output of up to 20 SCFM (Standard Cubic Feet per Minute).

When workspace is at a premium and test requirements are not as stringent, consider the Intest ATS-605 (formerly Temptronic TPO4100A. It covers a range of -20 to +225°C with 0.1°C resolution, and ±1°C accuracy. It is powered by 115 or 230 VAC and will easily fit on your test bench.

This is a sampling of thermal test chambers to help enhance electronic product reliability through temperature and reliability testing. All these thermal test solutions can be found on the Axiom Test Equipment website, along with downloadable data sheets for more information on all models.