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Thermal shock testing is often referred to as temperature shock testing or temperature cycling, high and low temperature thermal shock testing.

The heating/cooling rate is not less than 30℃/minute.

The temperature change range is very large, and the test severity increases with the increase of the temperature change rate.

The difference between the temperature shock test and the temperature cycle test is mainly the different stress load mechanism.

The temperature shock test mainly examines the failure caused by creep and fatigue damage, while the temperature cycle mainly examines the failure caused by shear fatigue.

The temperature shock test allows the use of a two-slot test device; the temperature cycle test uses a single-slot test device. In the two-slot box, the temperature change rate must be greater than 50℃/minute.
Causes of temperature shock: drastic temperature changes during manufacturing and repair processes such as reflow soldering, drying, reprocessing, and repair.

According to GJB 150.5A-2009 3.1, temperature shock is a sharp change in the ambient temperature of the equipment, and the temperature change rate is greater than 10 degrees/min, which is temperature shock. MIL-STD-810F 503.4 (2001) holds a similar view.

There are many reasons for temperature changes, which are mentioned in relevant standards:
GB/T 2423.22-2012 Environmental Testing Part 2 Test N: Temperature Change
Field conditions for temperature changes:
Temperature changes are common in electronic equipment and components. When the equipment is not powered on, its internal parts experience slower temperature changes than the parts on its outer surface.

Rapid temperature changes can be expected in the following situations:
1. When the equipment is transferred from a warm indoor environment to a cold outdoor environment, or vice versa;
2. When the equipment is exposed to rain or immersed in cold water and suddenly cools down;
3. Installed in external airborne equipment;
4. Under certain transportation and storage conditions.

After power is applied, high temperature gradients will be generated in the equipment. Due to temperature changes, components will be stressed. For example, next to a high-power resistor, radiation will cause the surface temperature of adjacent components to rise, while other parts remain cold.
When the cooling system is powered on, artificially cooled components will experience rapid temperature changes. Rapid temperature changes of components can also be caused during the manufacturing process of the equipment. The number and magnitude of temperature changes and the time interval are important.

GJB 150.5A-2009 Military Equipment Laboratory Environmental Test Methods Part 5: Temperature Shock Test：
3.2 Application:
3.2.1 Normal Environment:
This test is applicable to equipment that may be used in places where the air temperature may change rapidly. This test is only used to evaluate the effects of rapid temperature changes on the external surface of the equipment, parts mounted on the external surface, or internal parts installed near the external surface. Typical situations are as follows:
A) The equipment is transferred between hot areas and low temperature environments;
B) It is lifted from the ground high temperature environment to high altitude (just hot to cold) by a high-performance carrier;
C) When testing only external materials (packaging or equipment surface materials), it is dropped from the hot aircraft protective shell under high altitude and low temperature conditions.

3.2.2 Safety and Environmental Stress Screening:
In addition to what is described in 3.3, this test is applicable to indicate safety issues and potential defects that usually occur when the equipment is exposed to a temperature change rate lower than the extreme temperature (as long as the test conditions do not exceed the design limit of the equipment). Although this test is used as an environmental stress screening (ESS), it can also be used as a screening test (using temperature shocks of more extreme temperatures) after appropriate engineering treatment to reveal potential defects that may occur when the equipment is exposed to conditions lower than the extreme temperature.
Effects of temperature shock: GJB 150.5A-2009 Military Equipment Laboratory Environmental Test Method Part 5: Temperature Shock Test:

4.1.2 Environmental Effects:
Temperature shock usually has a more serious effect on the part close to the outer surface of the equipment. The farther away from the outer surface (of course, it is related to the characteristics of the relevant materials), the slower the temperature change and the less obvious the effect. Transport boxes, packaging, etc. will also reduce the impact of temperature shock on enclosed equipment. Rapid temperature changes may temporarily or permanently affect the operation of the equipment. The following are examples of problems that may arise when equipment is exposed to a temperature shock environment. Considering the following typical problems will help determine whether this test is suitable for the equipment under test.

A) Typical physical effects are:
1) Shattering of glass containers and optical instruments;
2) Stuck or loose moving parts;
3) Cracks in solid pellets or columns in explosives;
4) Different shrinkage or expansion rates, or induced strain rates of different materials;
5) Deformation or rupture of parts;
6) Cracking of surface coatings;
7) Leakage in sealed cabins;
8) Failure of insulation protection.

B) Typical chemical effects are:
1) Separation of components;
2) Failure of chemical reagent protection.

C) Typical electrical effects are:
1) Changes in electrical and electronic components;
2) Rapid condensation of water or frost causing electronic or mechanical failures;
3) Excessive static electricity.

Purpose of temperature shock test: It can be used to discover product design and process defects during the engineering development stage; it can be used to verify the adaptability of products to temperature shock environments during product finalization or design identification and mass production stages, and provide a basis for design finalization and mass production acceptance decisions; when used as environmental stress screening, the purpose is to eliminate early product failures.

The types of temperature change tests are divided into three types according to IEC and national standards:
1. Test Na: Rapid temperature change with a specified conversion time; air;
2. Test Nb: Temperature change with a specified change rate; air;
3. Test Nc: Rapid temperature change with two liquid tanks; liquid;

For the above three tests, 1 and 2 use air as the medium, and the third uses liquid (water or other liquids) as the medium. The conversion time of 1 and 2 is longer, and the conversion time of 3 is shorter.