With the development of science and technology, the reliability of electrical appliances is becoming higher and higher. Especially in aircraft, aerospace and other applications. In general, in order to achieve the reliability of the project, an environmental assessment process is carried out to evaluate the reliability of the equipment over time from production to delivery.
Among these environmental tests, the most important and effective test is the thermal cycle test. According to the US IES magazine, among the various environmental research pressures that are commonly used, the value of climate research is the highest, reaching 77%. Therefore, effective thermal cycle testing is critical to improve the reliability of electronic equipment.
Thermal cycle test method
Principles of thermal cycle testing
Thermal cycle tests usually use different factors and the coefficient of thermal expansion of the different materials to be tested. The main purpose is to reduce the thermal stress caused by rapid temperature changes and damage to the sample. When an electronic component goes through a thermal cycle, the internals expand and contract again. And make it produce heat stress and deformations. If the coefficient of thermal expansion of the adjacent material in the assembly does not match. Fire stress and these problems are getting worse. Possible defects will cause the pressure to increase, continuing with the installation of the heat system. Bones develop and eventually become spots (like cracks) and are visible. This is called heat exhaustion.
Rise and fall principle of the temperature cycle test
Thermal cycling test the rise and fall of temperature is done by heating or cooling by circulating cold or hot air in a thermal cycling chamber. The performance of the thermal cycling room used in the test has a significant impact on the accuracy of the test results. The method of temperature control through room temperature cycling is to use a temperature sensor to measure the temperature of the air or sample in the room. After the signal is generated, the controller compares the input value to the controller. The result of the comparison determines whether the heating system or the cooling system is working and adjusts it to the desired temperature. There is usually a fan in the room that circulates the heat to force convection to make the temperature everywhere in the room as uniform as possible.
There are two administrative methods for the order:
One is controlled by the temperature response of the species
The other is controlled by ventilation and temperature cycling.
In any case, the sample on the wall of the house will change the temperature of the water and the air of the house.
Thermal cycle test key analysis
For battery products, since different materials make test pieces, the materials used are also very different. Among them, the material properties include Young’s coefficient, yield strength, coefficient of thermal conductivity, coefficient of thermal expansion, etc. Therefore, when the temperature of the sample changes, due to different temperature values, geometrical dimensions, material number, structural composition, etc., the stress and pressure they experience will also be different.
For thermal cycling tests, the factors that affect the test results are the most:
The temperature is different
Round number
Time holding
The rate of temperature change
Wind speed
These key parameters are analyzed separately below.
The temperature is different
Extreme temperatures are the difference between high and low temperatures. In principle, the higher the temperature, the better. However, the actual situation depends on the temperature of the electronic product. Through the analysis of heat transfer characteristics, we can understand the distribution and evolution of the temperature inside the product under different temperature conditions. The analysis of heat transfer characteristics can be evaluated by theoretical models or measured directly from existing conditions.
In real work, it is better to use the measuring system. However, pay attention if the product is supposed to work when you are considering. Because when the light is turned on, the temperature of the product will change, especially for high-quality electrical products. When you understand the internal temperature distribution and the change of the product under different temperature cycle conditions, you can choose the maximum temperature without damaging the normal product.
Round number
As temperature changes cause mechanical stress on the sample, the internal pressure of the sample increases with the increase in temperature. In theory, more cycles, more acceleration. But of course, many times can affect the working life of the product. That increases the cost. Therefore, it is important to refer to past experience or related details to select the appropriate number of cycles. The optimum cycle time was determined by test analysis.
Time Holding
The time holding depends on the thermal equilibrium time when the test piece reaches air temperature. The retention time of the sample must be chosen according to the temperature of the sample. For large products, the internal and external temperature factors can be different, and the internal temperature or weak parts should be chosen for the determination.
The rate of temperature change
Generally speaking, the higher the temperature change rate, the better the test effect. However, due to the effect of the air flow in the thermal cycling chamber on the heat capacity of the sample, the temperature response of the sample is not consistent with the heat capacity of the heat cycling chamber. The results show that the thermal cycle test strength does not always increase with the increase of temperature change. When the rate of temperature change reaches a certain value, the increase in temperature change has little effect on the environmental stress test. Here, the sample is insensitive to temperature changes. The temperature change of the sample is clearly less than that of the laboratory.
Wind speed
Wind speed is closely related to the parameters of the heat cycle test. It is also very sensitive to temperature rise and fall at room temperature. In addition, high wind speeds can lead to temperature changes. In addition, the temperature uniformity of the sample can be improved.
Summary
Among the various environmental testing pressures that are commonly used, the testing cycle temperature is the most effective. Our company’s laboratory meets the following standards:
IEC62133
UL1642
UN38.3
