Thermal shock testing determines whether the electronic product under test is capable of withstanding sudden temperature changes.
Thermal cycle testing is conducted to identify the failure mechanisms caused by a mismatch in the coefficient of thermal expansion (CTE) of materials.
The standards MIL-STD 883 Method 1011 and MIL-STD 883 Method 1010 correspond to thermal shock tests and thermal cycling tests, respectively.
Thermal shock tests and thermal cycling tests are used to identify the failure mechanisms caused by temperature
It is a tedious task to collect the life data of an electronic system, component, or product for time-to-failure data analysis. Luckily, the reliability testing of electronic systems or components can be simplified by performing accelerated life tests. In accelerated life tets, life characteristics and failure modes are collected by forcing the electronic system, component, or device to fail faster than it would under normal working conditions. Accelerated life tests are important for guaranteeing the reliability of the device under test.
Thermal shock tests and thermal cycling tests are two types of accelerated life tests that are used to identify the failure mechanisms caused by temperature. When comparing thermal shock tests vs. thermal cycling tests, there are a lot of differences such as the temperature profile, transfer time, dwell (soak) time, and applications. Let’s take a look at thermal shock tests and thermal cycling tests to see how they compare and contrast.
Thermal Shock Tests
The thermal shock test is an accelerated test in which failure modes due to rapid temperature changes are identified. These kinds of rapid temperature variations are observed during self-heating of power semiconductor devices, turn on of optical devices, or during hand or wave soldering. Thermal shock tests determine whether the electronic product under test is capable of withstanding sudden temperature changes. A thermal shock test is associated with a high rate of change of temperature and is the most severe test of all temperature-related tests.
In thermal shock testing, the component or device under test goes from one extreme temperature to another. Temperature stabilization occurs rapidly in this testing. There are two types of thermal shock tests:
- Air-to-air thermal shock test - In the air-to-air thermal shock test, cyclical temperature stress is commonly used, which reduces the time taken to aggravate the failure mechanism in the specimen.
- Liquid-to-liquid thermal shock test - The device under test is transferred from one liquid at extreme temperature to another at the opposite extreme. Heat transfer and absorption are more efficient in the liquid-to-liquid thermal shock test compared to the air-to-air thermal shock test.
Both types of thermal shock tests require a hot and cold chamber for the transition of the specimen temperature from one extreme to the opposite extreme. Both air-to-air and liquid-to-liquid thermal shock testing setups must be capable of varying the hot and cold chamber temperature, dwelling time in the chambers, transition time from one chamber to another, and the number of cycles of the thermal shock testing procedure.
After the final cycle of the thermal shock test, the specimen is thoroughly examined visually for damages in the cases, leads, and seals, and if any damage is present, it is considered a failure. Samples of the specimen undergo electrical testing to detect electrical failure. Typical failure mechanisms accelerated by thermal shock tests are wire breaks, wire bond lifting, flip-chip bumps, die cracking, and package cracking.
Thermal Cycling Tests
The thermal cycling test, otherwise called the temperature cycle test, applies stress to a specimen at extreme temperatures. Thermal cycle tests are conducted to identify failure mechanisms caused by a mismatch in the coefficient of thermal expansion (CTE) of materials. Thermal cycling tests determine the ability of a device under test (or a part of it) to resist extremely high temperatures and extremely low temperatures. It also tests how much the specimen can withstand cyclic exposure to extreme temperatures.
The thermal cycling test is a single chamber test where the transition from hot to cold temperature or vice versa is dependent on the chamber’s ability to shift from one extreme temperature to another and the thermal mass of the specimen. The specimen is held at a stabilized temperature extreme, and the next transition occurs only after this stabilization period—called soak time. The soak time and the number of cycles of thermal cycling testing are varied to exacerbate the various failure modes in the component or device under test. Thermal cycling tests are typically performed to detect solder joint cracking, lead or terminal damages, hermetic seal failures, delaminations in PCBs, or BGA interconnect defects.
Let’s compare thermal shock vs. thermal cycling tests.
Thermal Shock vs. Thermal Cycling Tests
Thermal shock and thermal cycling tests should be conducted on electronic systems, components, or products to validate their reliability as early as possible. Cadence offers tools that help in examining the thermal stress and reliability of electronic designs.
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