Both temperature impact test and temperature cycle test are environmental reliability tests to verify the quality and stability of products in the process of temperature change. For the same test of temperature change, where are the differences between the two?
First. Temperature impact test
The temperature impact test is to accelerate the test sample in a shorter time than in the actual environment to investigate its failure mechanism. At the same time, attention should be paid to avoiding the failure mechanism caused by other stress reasons.
The causes of temperature impact include factors that cause severe temperature changes in manufacturing and repair processes such as reflow, drying, reprocessing and repair.
Typical situations of temperature impact test applied to product testing are as follows:
1) Product conversion between high temperature and low temperature.
2) Quickly lift the product from the high temperature environment on the ground to the low temperature environment at high altitude.
3) Air drop the product from the protective shell of the aircraft under high altitude and low temperature conditions.
So, what are the important factors for conducting temperature impact test?
1. Exposure conditions
The test temperature can be determined according to the geographical location and field data of the product in the actual application process, or according to the most extreme non working temperature requirements.
2. High and low temperature duration
The test duration (impact times) shall be determined according to the conditions encountered in the actual application of the product. Therefore, there are the following impact tests:
1) According to the unidirectional temperature impact of constant extreme temperature, for products exposed to the possibility of unidirectional temperature impact is very small, at least one impact shall be conducted under each corresponding condition;
2) According to the single cycle impact of constant extreme temperature, for equipment exposed to temperature impact environment may only be once;
3) According to the multi cycle impact with constant extreme temperature, when the product is predicted to be exposed to the impact environment more frequently, there is little data available to confirm the specific impact times.
Fig.1 Unidirectional temperature shock with constant extreme temperature
Fig.2 Single-cycle shock with constant extreme temperature
Fig.3 Multi-cycle shock with constant extreme temperature
3. Conversion time
GJB 150 requires that the conversion time between high and low temperature extremes shall not be greater than 5min; In GJB 150A, the conversion time is required to be no more than 1min to achieve the maximum temperature impact effect. When the conversion time exceeds 1min, the rationality of the timeout shall be explained.
4. Temperature change rate
Specifically, the heating/cooling rate shall not be lower than 30 ℃/min. The temperature varies widely, and the test severity also increases with the increase of temperature change rate.
Second. Temperature cycling test
Temperature cycle test is to expose the test sample to the test environment with preset temperature and humidity alternating, and evaluate the functional characteristics change of the sample after temperature and humidity environmental cycling or storage. It is also often referred to as thermal cycle test or high and low temperature cycle test. ESS is a reliability screening test mainly applicable to product development stage and production stage.
To avoid the impact of temperature impact, the temperature change rate during the test must be less than 20 ℃/min. At the same time, in order to achieve the effect of creep and fatigue damage, the recommended test temperature cycle is 25 ℃~100 ℃, or the cycle test of 0 ℃~100 ℃ can be used based on the use of the product, and the exposure time is 15 minutes each.
The technical indicators of temperature cycle include: high temperature, high temperature holding time, falling rate, low temperature, low temperature holding time, rising rate and number of cycles. The severity of the test depends on the high/low temperature, humidity and exposure duration.
Test reference standards include GB/T 2423.34-2012, IEC 60068-2-38:2009, JESD22-A104F: 2020, etc.
Common temperature cycle test curve
Third, the difference between the two
The difference between temperature impact test and temperature cycle test is mainly due to the different stress load mechanism. The temperature impact test mainly investigates the failure caused by creep and fatigue damage, while the temperature cycle mainly investigates the failure caused by shear fatigue.
The temperature impact test allows the use of a two trough type test device, and the temperature cycle test uses a single trough type test device. In the two tank box, the temperature change rate shall be greater than 50 ℃/min.
To sum up, the key to temperature shock is shock, which is the biggest difference from the temperature cycle, not the temperature change rate. The temperature cycle is a gradual change from a certain temperature to a certain temperature, and every temperature point in the middle will experience it.
The temperature impact will suddenly skip some temperature points in the middle to change the temperature, which requires that the temperature impact must change in different temperature zones. From this point of view, the two box type temperature impact box is more in line with the requirements of the temperature impact test.
