Thermal shock testing, also known as temperature shock testing or temperature cycling, refers to a rapid change in the ambient temperature of a device. According to GJB 150.5A-2009, thermal shock is defined as a temperature change rate greater than 10°C per minute. Similarly, MIL-STD-810F 503.4 (2001) supports this definition. This test is commonly used to evaluate how well a product can withstand sudden and extreme temperature variations, which can occur during transportation, storage, or operation.
The primary purpose of a temperature impact test varies depending on the stage of product development. During the engineering development phase, it helps identify design or manufacturing flaws. In the production or certification stage, it verifies the product’s ability to perform under temperature shock conditions and provides data for acceptance decisions. Additionally, as an environmental stress screening method, it helps eliminate early failures and improve product reliability.
Temperature shocks are common in electronic devices and components. When a device is not powered, internal parts tend to respond more slowly to temperature changes compared to the outer surfaces. Rapid temperature shifts can occur in various scenarios, such as when equipment moves between indoor and outdoor environments, is exposed to rain or cold water, or is installed in external locations. These conditions can cause significant stress on materials and components.
When a device is powered on, high voltage gradients can create additional stress. For example, a high-power resistor may generate heat that affects nearby components, while others remain cool. Cooling systems can also cause sudden temperature changes, and these effects are particularly pronounced during manufacturing processes. The frequency, magnitude, and duration of temperature changes all play a critical role in determining their impact.
Thermal shock primarily affects the outer surface of a device. The deeper the component is from the surface, the slower the temperature change, and the less severe the effect. Packaging and transport boxes can help reduce the impact of temperature shocks on enclosed equipment. However, even temporary exposure to extreme temperatures can lead to performance issues, including mechanical, chemical, or electrical failures.
Common physical effects include glass cracking, loosening of moving parts, material deformation, coating damage, and seal leakage. Chemical effects might involve component separation or failure of protective coatings. Electrical effects could include component failure, condensation, or static buildup.
There are three main types of thermal shock tests based on IEC and national standards: Test Na (temperature change with specified conversion time using air), Test Nb (temperature change at a specified rate using air), and Test Nc (two-tank method using liquid). The first two use air as a medium and have longer conversion times, while the third uses liquid (such as water) and has a shorter conversion time.
| Serial Number | International Standard | Domestic Corresponding Standard | Applicable To | Medium | Conversion Time |
|---------------|------------------------|----------------------------------|----------------|--------|------------------|
| 1 | IEC 60068-2-14:2009 | GB/T 2423.22-2012 | Components, assemblies, equipment | Air | Within 3 minutes or longer |
| 2 | MIL-STD-810F Method 503.4 | GJB 150.5A-2009 | Equipment | Air | 1 minute |
| 3 | MIL-STD-202G Method 107G | GJB 360B-2009 | Components | Liquid | Short |
Understanding these tests helps engineers ensure that products can endure real-world conditions and maintain reliability over time.
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