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.
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
01. Environmental test
Some reliability monographs place samples in natural or artificially simulated storage, transportation and working environments, collectively referred to as environmental tests. They are used to assess the performance of products in various environments (vibration, shock, centrifugation, temperature, thermal shock, hot flashes, The ability to adapt to conditions such as salt spray, 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 sample to be tested 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 86 kPa ~ 100 kPa. 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, inner lead breakage, chip cracks, etc.
Test conditions: Conducted in a 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 the 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. The entry of high-energy particles into microcircuits will 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.
02.Life test
Life test is one of the most important and basic items in reliability testing. It puts the product under specific test conditions to examine its failure (damage) changes with time. Through the life test, we can understand the product's life characteristics, failure patterns, failure rates, average lifespan, and various failure modes that may occur during the life test. If combined with failure analysis, the main failure mechanisms leading to product failure can be further clarified, which can serve as the basis for reliability design, reliability prediction, improvement of new product quality, and determination of reasonable screening and routine (batch guarantee) test conditions.
If in order to shorten the test time, the test can be carried out by increasing the stress without changing the failure mechanism, this is an accelerated life test. The reliability level of products can be evaluated through life tests, and the reliability level of new products can be improved through quality feedback.
Purpose of life test: To assess the quality and reliability of the product under specified conditions and during the entire working time. In order to make the test results better representative, the number of samples tested must be sufficient.
Test conditions: The life test of microcircuit is divided into steady state life test, intermittent life test and simulated life test.
The steady-state life test is a test that must be performed on microcircuits. During the test, the sample under test is required to be supplied with appropriate power to keep it in normal working condition. The national military standard steady-state life test environment temperature is 125C and the time is 1000h. Accelerated testing can increase the temperature and shorten the time.
The temperature of the power microcircuit case is generally greater than the ambient temperature. During the test, the ambient temperature can be kept lower than 125°C. The ambient temperature or case temperature of the microcircuit steady-state life test should be based on the microcircuit junction temperature being equal to the rated junction temperature. <Generally between 175°C and 200°C).
The intermittent life test requires cutting off the microcircuit under test at a certain frequency or suddenly applying a bias voltage and signal. Other test conditions are the same as the steady-state life test.
The simulated life test is a combination test that simulates the application environment of the circuit. Its combined stresses include mechanical, humidity and low pressure four stress tests: mechanical, temperature, humidity and electrical four stress tests, etc.
03.Screening test
Screening testing is a non-destructive test that fully inspects the product. The purpose is to select products with certain characteristics or to eliminate products that fail early, so as to improve the reliability of the product. During the manufacturing process of products, due to material defects or out-of-control processes, so-called early defects or failures occur in some products. If these defects or failures can be eliminated early, the reliability level of the product can be guaranteed in actual use.
Characteristics of Reliability Screening Tests:
1. This kind of test is not a sampling, but a 100% test;
2. This test can improve the overall reliability level of qualified products, but it cannot improve the inherent reliability of the product, that is, it cannot increase the life of each product;
3. The screening effect cannot be evaluated simply by the screening elimination rate. The high elimination rate may be due to serious defects in the design, components, processes, etc. of the product itself, but it may also be due to the screening stress intensity being too high.
The low elimination rate may be due to few product defects, but it may also be caused by the intensity of the screening stress and insufficient test time. The quality of the screening method is usually evaluated by the screening elimination rate Q and the screening effect B value: a reasonable screening method should have a large B value and a moderate Q value.
04Field use test
The above various tests were conducted by simulating field conditions. Due to limitations of equipment conditions, simulation tests can often only apply a single stress to the product, and sometimes dual stresses can be applied. This is very different from the actual use environmental conditions, and therefore fails to truthfully and comprehensively expose the quality of the product. Field use testing is different because it is conducted at the site of use, so it can most truly reflect the reliability of the product. The data obtained is of high value for product reliability prediction, design, and guarantee. Field use tests play a greater role in formulating reliability test plans, verifying reliability test methods and evaluating test accuracy.
05 Identification test
Qualification testing is a test performed to evaluate the reliability level of a product. It is a sampling plan developed based on sampling theory. Qualification tests are conducted under conditions that ensure that producers do not cause products that meet the quality standards to be rejected.
Reliability qualification tests are divided into two categories: one is product reliability qualification tests, and the other is process (including material) reliability qualification tests.
Product reliability qualification tests are generally conducted when new product design and production are finalized. The purpose is to assess whether the product indicators fully meet the design requirements and to assess whether the product meets the predetermined reliability requirements. The content of the test is generally consistent with the quality consistency inspection. All four groups of tests A, B, C, and D are performed, and products with radiation resistance intensity requirements are also required to undergo group E tests. Reliability qualification tests are also required when there are significant changes in the design, structure, materials or processes of the product.
The reliability qualification test of process (including materials) is used to assess whether the production line's selection and control capabilities of materials and processes can ensure the quality and reliability of the manufactured products, and whether it can meet the requirements of a certain quality assurance level.
06.Others
(1)Constant acceleration test
The purpose of this test is to evaluate the ability of the circuit to withstand constant acceleration. It can expose failures caused by low microcircuit structural strength and mechanical defects. Such as chip falling off, inner lead open circuit, tube shell deformation, air leakage, etc.
Test conditions: A constant acceleration greater than 1mm is applied in the direction of microcircuit chip removal, compression direction and the direction perpendicular to this direction. The acceleration value range is generally between 49000m/s:-1225000m/sV5 000~125000z). During the test, the housing of the microcircuit should be rigidly fixed on the constant accelerator.
(2) Mechanical impact test
The purpose of this test is to assess the microcircuit's ability to withstand mechanical shock. That is, the ability of microcircuit to withstand sudden force is assessed. Microcircuits may be suddenly stressed during loading, unloading, transportation, and on-site work. For example, microcircuits will be subject to sudden mechanical stress when dropped or collided. These stresses may cause microcircuit chips to fall off, inner leads to open, tube shells to deform, air leaks and other failures.
Test conditions: During the test, the microcircuit shell should be rigidly fixed on the test bench base, and the outer leads should be protected. Five half-sine wave mechanical shock pulses are applied to each of the microcircuit's chip ejection direction, pressing direction, and direction perpendicular to this direction. The peak acceleration value range of the impact pulse is generally 4900m/s2~294 000m/s2 (500g~30000g). The pulse duration is 0.1ms-1.0ms, and the allowed distortion is not greater than 20% of the peak acceleration.
(3) Mechanical vibration test
There are four main types of vibration tests, namely sweep frequency vibration test, vibration fatigue test, vibration noise test and random vibration test. The purpose is to assess the structural solidity and electrical characteristics stability of microcircuits under different vibration conditions.
The frequency sweep vibration test causes the microcircuit to vibrate with constant amplitude, and its acceleration peak value is generally divided into three levels: 196 m/s: (20e), 490m/s2 (50g) and 686m/s2 (70g). The vibration frequency changes with time in the range of 20Hz to 2000Hz. The time required for the vibration frequency to go from 20Hz to 2 000HZ and back to 20Hz is not less than 4mm, and it must be done five times in three mutually perpendicular directions (one of which is perpendicular to the chip).
The vibration fatigue test also requires the microcircuit to vibrate with constant amplitude, but its vibration frequency is fixed, generally tens to hundreds of Hz, and its acceleration peaks are generally divided into 196ms2 (20g), 490m/s2 (50g) and 686ms2 (70g) Third gear. Perform this once in each of three directions that are perpendicular to each other (one direction is perpendicular to the chip), and the time for each time is approximately 32 hours.
The test conditions of the random vibration test are to simulate the vibrations that may occur in various modern field environments. The amplitude of random vibrations has a Gaussian distribution. The relationship between acceleration spectral density and frequency is specific. The frequency range is from tens to 2000HZ.
The test conditions of the vibration and noise test are basically the same as those of the sweeping vibration test. When the microcircuit is made to vibrate with constant amplitude, its acceleration peak value is generally not less than 196m/s2 (20g). The vibration frequency changes logarithmically with time in the range of 20HZ to 2000Hz. The time required for the vibration frequency to go from 20HZ to 2000Hz and back to 20HZ is not less than 4 minutes, and it should be done once in three mutually perpendicular directions (one of which is perpendicular to the chip).
But the microcircuit must apply specified voltage and current. Measure whether the maximum noise output voltage at the specified load resistance exceeds the specified value during the test.