Generally speaking, tests conducted to evaluate and analyze the reliability of electronic products are called reliability tests. In order to predict the quality of the product from the time it leaves the factory to the end of its service life, after selecting an environmental stress that is highly similar to the market environment, The main purpose of setting the environmental stress level and application time is to correctly evaluate product reliability in the shortest possible time. Corresponding to this are various test chambers, such as: constant temperature and humidity test chamber, UV aging test chamber, salt spray test chamber, xenon lamp aging test chamber, etc.
The reliability test is to determine whether the products that have passed the reliability qualification test and are transferred to mass production meet the specified reliability requirements under specified conditions, and to verify whether the reliability of the product changes with the process, tooling, work flow, and parts during mass production. Decreased due to changes in quality and other factors. Only through this can product performance be trusted and product quality be excellent.
Electronic product reliability test classification
Environmental testing
Some reliability monographs place samples in natural or artificial simulated storage, transportation and working environments. Tests are collectively called environmental tests. They are used to assess the performance of products in various environments (vibration, shock, centrifugation, temperature, thermal shock, hot flashes, salt). The ability to adapt to conditions such as fog, low air pressure, etc. is one of the important test methods to evaluate product reliability. Generally, there are mainly the following types:
(1) Stability baking, that is, high temperature storage test
Test purpose: To evaluate the impact of high-temperature storage on products without applying electrical stress. Products with serious defects are in a non-equilibrium state, which is an unstable state. The transition process from non-equilibrium state to equilibrium state is not only a process that induces the failure of products with serious defects, but also a transition process that promotes products from an unstable state to a stable state. .
This transition is generally a physical and chemical change, and its rate follows the Arrhenius formula and increases exponentially with temperature. The purpose of high temperature stress is to shorten the time of this change. Therefore, this experiment can be regarded as a process to stabilize product performance.
Test conditions: Generally, a constant temperature stress and holding time are selected. The temperature stress range of the microcircuit is 75°C to 400°C, and the test time is more than 24 hours. Before and after the test, the tested sample must be placed for a certain period of time in a standard test environment, with a temperature of 25±10°C and an air pressure of 86kPa~100kPa. In most cases, the endpoint test is required to be completed within a specified time after the test.
(2) Temperature cycle test
Test purpose: To assess the product's ability to withstand a certain temperature change rate and its ability to withstand extreme high temperature and extreme low temperature environments. It is set based on the thermomechanical properties of the product. When the materials that make up the components of the product have poor thermal matching, or the internal stress of the component is large, the temperature cycle test can cause product failure caused by the deterioration of mechanical structural defects. Such as air leakage, internal lead breakage, chip cracks, etc.
Test conditions: Conducted in gas environment. It mainly controls the temperature and time when the product is at high and low temperatures and the rate of high and low temperature state conversion. The circulation of gas in the test chamber, the position of the temperature sensor, and the heat capacity of the fixture are all important factors to ensure test conditions.
The control principle is that the temperature, time and conversion rate required by the test refer to the product being tested, not the local environment of the test. The switching time of the microcircuit is required to be no more than 1 minute, and the holding time at high or low temperature is no less than 10 minutes; the low temperature is -55°C or -65-10°C, and the high temperature ranges from 85+10°C to 300+10°C.
(3) Thermal shock test
Test purpose: To assess the product's ability to withstand drastic temperature changes, that is, to withstand large temperature change rates. The test can cause product failure caused by mechanical structural defects and deterioration. The purpose of the thermal shock test and the temperature cycle test are basically the same, but the conditions of the thermal shock test are much more severe than the temperature cycle test.
(4) Low pressure test
Test purpose: To assess the product's adaptability to low-pressure working environments (such as high-altitude working environments). When the air pressure decreases, the insulation strength of the air or insulating materials will weaken; corona discharge, increased dielectric loss, and ionization will easily occur; the decrease in air pressure will worsen the heat dissipation conditions and increase the temperature of the components. These factors will cause the test sample to lose its specified functions under low pressure conditions, and sometimes cause permanent damage.
Test conditions: The sample to be tested is placed in a sealed chamber, the specified voltage is applied, and the sample temperature is required to be maintained in the range of 25+-1.0°C from 20 minutes before the pressure is reduced in the sealed chamber until the end of the test. The sealed chamber is reduced from normal pressure to the specified air pressure and then returned to normal pressure, and during this process it is monitored whether the test sample can work normally. The frequency of the voltage applied to the microcircuit test sample is in the range from DC to 20MHz. The occurrence of corona discharge at the voltage terminal is considered a failure. The low pressure value of the test corresponds to the altitude and is divided into several levels. For example, the A-level air pressure value of the microcircuit low-pressure test is 58kPa, and the corresponding height is 4572m. The E-level air pressure value is 1.1kPa, and the corresponding height is 30480m, etc.
(5) Humidity resistance test
Test purpose: To evaluate the ability of microcircuits to resist decay under humid and hot conditions by applying accelerated stress. It is designed for typical tropical climate environments. The main mechanisms of microcircuit decay under humid and hot conditions are corrosion caused by chemical processes and physical processes caused by the immersion, condensation, and freezing of water vapor that cause the growth of microcracks. The test also examines the possibility of electrolysis occurring or exacerbating electrolysis in the materials constituting the microcircuit under humid and hot conditions. Electrolysis will change the resistance of the insulating material and weaken its ability to resist dielectric breakdown.
Test conditions: There are two types of hot flash tests, namely variable hot flash test and constant hot flash test. The hot flash test requires the sample to be tested to be in a relative humidity range of 90% to 100%. It takes a certain period of time (usually 2.5h) to raise the temperature from 25℃ to 65℃ and maintain it for more than 3h; and then again Within the relative humidity range of 80% to 100%, use a certain period of time (generally 2.5 hours) to drop the temperature from 6s°C to 25°C. After another such cycle, lower the temperature at any humidity. to -10°C, and keep it for more than 3 hours before returning to a state where the temperature is 25°C and the relative humidity is equal to or greater than 80%. This completes a cycle of blood changes to hot flashes, which takes about 24 hours.
Generally, for a humidity resistance test, the above-mentioned large cycle of alternating hot flashes needs to be carried out 10 times. During the test, a certain voltage is applied to the sample being tested. The air exchange volume per minute in the test chamber is required to be greater than 5 times the volume of the test chamber. The sample to be tested should be one that has undergone non-destructive lead tightness testing.
(6) Salt spray test
Test purpose: Use an accelerated method to evaluate the corrosion resistance of exposed parts of components under salt spray, humidity and hot conditions. It is designed for tropical seaside or offshore climate environments. Components with poor surface structure will corrode exposed parts under salt spray, humid and hot conditions.
Test conditions: The salt spray test requires that the exposed parts of the test sample in different directions must be under the same specified conditions in terms of temperature, humidity, and received salt deposition rate. This requirement is met by the minimum distance between the samples placed in the test chamber and the angle at which the samples are placed.
Test temperature: The general requirement is (35+-3)'C, and the salt deposition rate within 24 hours is 2X104mg/m2~5X104mg/m2. The salt deposition rate and humidity are determined by the temperature and concentration of the salt solution that generates salt spray and the air flow flowing through it. The proportion of oxygen and nitrogen in the air flow should be the same as that of air.
Test time: generally divided into 24h, 48h, 96h and 240h.
(7) Irradiation test
Test purpose: To assess the working ability of microcircuit in high-energy particle irradiation environment. High-energy particles entering microcircuits can cause changes in the microstructure to produce defects or generate additional charges or currents. This results in microcircuit parameter degradation, locking, circuit flipping, or surge current causing burnout and failure. Irradiation beyond a certain limit can cause permanent damage to microcircuits.
Test conditions: Microcircuit irradiation tests mainly include neutron irradiation and gamma ray irradiation. It is further divided into total dose irradiation test and dose rate irradiation test. Dose rate irradiation tests all irradiate test microcircuits in the form of pulses. In the test, the dose string and total dose of irradiation must be strictly controlled based on different microcircuits and different test purposes. Otherwise, the sample will be damaged due to irradiation exceeding the limit or the sought threshold value will not be obtained. Radiation tests must have safety measures to prevent human injury.
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