Electronic device performance is sensitive to temperature, with most electronic devices and components specified according to operating and storage temperature ranges. Those ranges differ according to the type of component and application, with electronic products for industrial and military applications usually characterized over wider temperature ranges than commercial electronic products. Thermal test systems provide convenient ways to reproduce the temperature ranges that a device might encounter under actual operating conditions, but they also help bring temperature control to a device under test (DUT) as the means of performing thermal shock testing and accelerated lifetime testing. Selecting the best thermal test system for the job is simply a matter of understanding the thermal test requirements for an application and how to best deliver them.
Many electronic device failures are related to thermal issues, such as solder joints and other electronic junctions that exceed maximum safe operating temperatures. Printed circuit boards (PCBs) and other electronic materials have different coefficients of thermal expansion (CTEs) which describe how they expand and contract with rising and falling temperatures, respectively. For example, PCB assemblies consist of layers of dielectric substrate materials and metal conductors, such as copper, with surface-mount-technology (SMT) and other types of miniature packaged components attached to conductive circuit patterns. Each material has unique thermal characteristics and expands and contracts in different ways as a function of temperature, resulting in stress points at the interfaces of different materials. Thermal testing is often used to check the reliability of plated through holes (PTHs) and solder joint connections in PCBs to determine reliability.
Thermal cycling through a temperature range at a prescribed rate of change in temperature is also used to perform accelerated life testing of electronic devices and components, speeding failure mechanisms in a DUT to better understand how to improve and/or optimize reliability. Temperature cycling is also a key part of semiconductor design and manufacturing processes, to ensure that devices can perform as expected over an industry-accepted operating temperature range. The capability to control a wide range of ambient temperatures in a DUT’s environment also makes it possible to determine the storage temperature range for an electronic device or component. The storage temperature range is typically larger than the operating temperature range and provides details about the safe non-operating temperature range for a DUT, such as the temperatures which it must endure when shipped to a customer.
A temperature cycling profile for a DUT is specified by temperature range, dwell time (the time spent at a final or maximum temperature), heating and cooling rates, and the number of temperature cycles. Industry-accepted thermal test procedures and standards, including for thermal shock testing, are generally spelled out in military test standards, such as MIL-STD-810 and MIL-STD-883, and by different standards organizations, such as ASTM International (www.astm.org) standards for measuring changes in circuit material characteristics as a result of temperature, IPC (www.ipc.org) test standards for thermal analysis of PCBs and PCB assemblies, Joint Electron Device Engineering Council (JEDEC, www.jedec.org) thermal test standards for thermal analysis of semiconductor packages, and even government organizations such as NASA (www.nasa.gov) for thermal evaluation of electronic devices for use in space.
For a thermal test system to offer the environment needed for a DUT such as a PCB or packaged semiconductor device, it must first provide a test chamber large enough to house the DUT. Temperature forcing systems work with an outside source of compressed air to create a temperature-controlled stream of hot or cold air to change the temperature of a test chamber and the temperature around a DUT. Some of these systems are portable, for example built onto casters, to allow movement of the system and its temperature-controlled test chamber around a facility, such as where needed near a test bench. In addition to ensuring that a thermal test system provides the temperature control needed for thermal testing, a suitable system should feature high efficiency to a facility’s energy resources.
For example, the ThermalAir TA-5000A thermal test system from MPI Thermal (www.mpi-thermal.com) is a unique localized temperature-forcing system with an energy-efficient architecture for temperature control at a user’s test bench, on the production floor, or almost anywhere it is needed. It is a two-part system with a control unit and thermal test unit. Each subsystem has its own touch-screen display, with the color touch screen on the thermal head providing monitoring and control of temperature cycling parameters, such as temperature range, ramp rate, and dwell time. The thermal unit features high-temperature glass-cap enclosures with inside diameters of 7.0, 5.7, or 5.5 in. for temperature control of DUTs.
The system requires an external source of compressed clean dry air (CDA). It produces a thermally controlled air stream to achieve a temperature range of -80°C to +225°C with stable DC temperature control providing accuracy within ±1°C. The temperature can be set with ±0.1°C resolution. Capable of temperature ramping speeds of 10 s or less from -55°C to +125°C or from +125°C to -55°C, it is well suited for high-speed programmable temperature cycling. The system achieves frost-free subzero temperatures and has a built-in air dryer for control of humidity at elevated temperatures. It operates on either 50 Hz and 60 Hz power from 200 to 250 VAC, with full extension between units of almost 5 ft. for thermal testing in those hard-to-reach places.
Similarly, the TPO4300A THERMOSTREAM® Thermal Airstream System from Temptronic Corp. (www.inTESTtherma.com) also has a maximum temperature range of -80°C to +225°C, but only when operating with 60-Hz AC power (from 200 to 250 VAC). When running from 50-Hz AC sources (also from 200 to 250 VAC), the temperature range is -75°C to +228°C. Still, by using thermally controlled air, this system is also capable of typical temperature transition rates of 10 s or less from -55°C to +125°C or from +125°C to -55°C. The temperature accuracy is within ±1°C and the temperature set and display resolution is ±0.1°C. The thermal test system includes a choice of two glass-cap thermal enclosures with 4.5 or 5.5 in. inside diameter. When a larger thermal chamber is needed, such as for thermal cycling of PCBs or PCB assemblies, an optional MOBILETEMP® thermal chamber is available in three configurations. The InTest-Temptonic ATS-810-M THERMOSTREAM® system is a high-performance temperature source with much the same performance as the TPO4300A, although it is only for 60-Hz operation.
For thermal shock testing, the ESPEC TSE-12-A from ESPEC (www.espec.com) is a two-zone thermal chamber designed to meet the requirements of many test standards for commercial, industrial, and military thermal shock testing. It moves test specimens vertically between hot and cold zones, with a hot temperature range of +60°C to +205°C and a cold temperature range of -77°C to 0°C. Both chambers reach their maximum cold and hot temperatures, respectively, within 90 minutes of being at ambient temperature.
The temperature-cycling thermal solutions mentioned above are all based on the use of temperature-controlled airflow into environmental chambers. They offer different-sized test chambers and facility requirements in terms of compressed air, power supplies, and ambient temperature, but all the systems provide effective high-speed temperature cycling over wide temperature ranges, and all achieve subzero temperatures without liquid nitrogen or liquid carbon dioxide. To rent or purchase these or other test instruments, please visit Axiom Test Equipment’s website at www.axiomtest.com to view our inventory. If you would like help selecting the right equipment for your project, contact Axiom Test Equipment’s sales department at email@example.com, or by calling an Axiom sales representative at 760-806-6600.