Environmental factors have a great impact on product reliability, and most of the failure of products is caused by environmental factors1 In nearly 20 environmental factors, the influence of temperature accounts for about 40% of the total proportion of environmental factors. Therefore, it is essential to select the appropriate parameters according to the characteristics of the sample and the test chamber itself, so that the temperature cycle test effect can be optimal. At present, the standards of temperature cycle test are MIL-STD-883G 1010.8, JESD22-A104-B, etc., but there are differences in the parameters in each standard, so the analysis of the key parameters of the temperature cycle test and the selection of appropriate standards are of great significance to improve the reliability of electronic products and monitor the quality of products.
1.Temperature Cycling Test Standard
The temperature cycling test is to place the sample in the test chamber with alternating temperature, so that the sample is under the action of constantly changing high temperature and low temperature, and the different coefficients of thermal expansion of different materials are used to make the specimen deformed due to the action of thermal stress; In the process of continuous stretching and extrusion, the defective places are continuously expanded with the loading of the temperature cycle under the action of stress increase, and eventually develop into failure. Therefore, the potential defects of the product can be efficiently and sufficiently amplified through the temperature cycle test to eliminate the product that is prone to early failure, and the test is mainly used for the electrical properties and mechanical properties of electronic components.
At present, the standards that are more used in temperature cycle tests are MIL-STD-883G 1010.8 and JESD22-A104-B.
MIL-STD-883G is the latest version of the U.S. military standard “Microelectronic Device Test Method Standard”, MIL-STD-883 since its advent in 1968 has developed to today’s G version, after nearly 20 times of improvement, initially mainly for military equipment, its content involves microelectronic device material testing and control, design inspection control, process inspection and control, screening, identification and quality consistency and other fields, the improvement of microelectronic device reliability has an important role, today, MIL-STD-883 has been used as a model for many national standards in the testing of highly reliable microelectronic devices
JESD22 is the environmental stress test part of the JEDEC standard, JEDEC is the leading body standard for the microelectronics industry, it is a standard developed for the global microelectronics industry From this point of view, MIL STD-883 should be more stringent than JEDEC In the process of formulating JEDEC has always taken the principle of fairness, efficiency and economy, and strives to ensure the interoperability of products, shorten the time to market of products, and also reduce its development costs Its main functions include terms, definitions, Description and operation of product characteristics, packaging, test methods, production support functions, product quality and reliability, etc.
For electronic products, the impact of environmental stress caused by periodic temperature changes on the sample will vary according to the test effect, which will lead to great differences in the mechanical properties of the sample (such as coefficient of thermal expansion, coefficient of thermal conductivity, Young’s modulus), etc.
In the temperature cycle test, the main parameters affecting the test effect are: temperature change range, the temperature rate of the test chamber, the exposure time of the test sample at high or low temperature, the conversion time, and the number of cycles of the test are given in MIL-STD-883G 1010.8 and JESD22-A104-B, but there are certain differences
(1) Temperature range
The temperature range refers to the difference between the upper limit temperature T and the lower limit temperature T In principle, the larger the value, the better, because the higher the temperature, the greater the interaction of thermal stress and thermal fatigue added to the specimen at the same time, and the efficiency of culling early failure is also higher, but for some materials, when the temperature reaches a certain value, it can induce a failure mechanism that is generally not seen in the design process, and due to the different coefficients of thermal expansion, when testing under different temperature conditions, it is easy to make the product fail prematurely.
In addition, the test of the heating and cooling process is easy to produce condensation or frost phenomenon in the components or equipment, which will give the sample additional stress, so the choice of temperature range depends on the specific situation of the product, the test temperature can not be too high nor too low, should not harm the normal product under the premise of choosing the maximum temperature range, generally between a 55 ° C ~ +125 ° C.
Due to the different objects of the original application of the standard, the temperature range is not the same MIL-STD-883G was originally mainly for military equipment, so the temperature regulations are more stringent, and JESD22-A104-B is a global electronic products, relatively speaking, it is more relaxed than MIL-STD-883G, MIL-STD-883G3 The high temperature range is almost twice that of JESD22-A104-B. In the selection of temperature, should consider the operating environment and the use of the system, MIL-STD883G 1010.8 in the use of civil electronic products when the temperature is set to 55 ° C ~ +125 ° C. The choice of temperature has an impact on the number of cycles of the test and the choice of model.
(2) Temperature Change Rate
The heating rate and cooling rate of the test chamber are related to the cooling mode in the box, if the air circulation cooling method is directly adopted, then the rate of heating is limited to 5 ~ 10 °C / min; If it is liquid nitrogen for cooling, the value is 25 ~ 40 °C / min domestic temperature cycle.
The test chamber is generally divided into air circulation and liquid nitrogen cooling. The different cooling methods of the test chambers make the standards different when specifying the temperature change rate.
In general, the increase of the temperature change rate is conducive to excitation of potential defect exposure, the higher the temperature change rate, the stronger the test intensity, the easier it is to excite the defect of the sample; However, when the temperature change rate reaches a certain value, the intensity of the temperature cycle test basically reaches a saturated state, the test sample is not very sensitive to the temperature change, and the temperature change of the sample lags significantly behind the temperature change of the test chamber.
Based on the above analysis, it can be seen that the reasons for the difference in the formulation of parameters of the standard are mainly manifested in the following aspects:
The different applicable objects of MIL-STD-883G were originally mainly used in military equipment, and their temperature range is more stringent, while another standard is for civilian products, and the test temperature is relatively weak.
The different cooling methods of the test chamber lead to different temperature change rates, and the air circulation cooling method makes the specified temperature change rate significantly lower than others.
For electronic products, the temperature cycle test is one of the most effective tests, which can not only detect the reliability of the product’s electrical properties, mechanical properties, etc., but also apply a certain stress to the specimen during the test process, so that the potential defects inside it are exposed more quickly. When conducting temperature cycle tests, the appropriate test standards should be selected according to the quality and volume of the test samples, the use of the samples, the operating conditions of the test chamber and other factors, and the parameters should be adjusted on the basis of the standards, so as to appropriately increase the stress intensity and shorten the test time, thereby improving the test strength and ensuring the high quality and reliability of the product.