GB/T 2424.2-1993 Basic environmental testing procedures for electrical and electronic products - Guidelines for damp heat testing
Some standard content:
National Standard of the People's Republic of China
Basic environmental testing procedures forelectric and electronic productsGuidance for damp heat tests
This standard is equivalent to IEC68-2-28 "Environmental testing Part 2: Test-1 Subject content and scope of application
GB/T2424.2-93
Replaces GB2424.2·81
-Guidelines for damp heat tests" (third edition in 1990)1). This standard introduces the damp heat environment, the method of generating humidity, the physical phenomenon of humidity, the acceleration of physical processes, the comparison between the constant damp heat test and the alternating damp heat test, and the influence of the test environment on the test sample. This standard is used to select appropriate test methods and severity levels when formulating standards for electric and electronic products; it can also be used for product design, manufacturing and testing personnel to understand the physical meaning and mechanism of damp heat tests, so as to ensure the simulation and reproducibility of test results. The damp heat test is mainly used to determine the adaptability of electrical and electronic products to damp heat environments (regardless of whether condensation occurs), especially the changes in the electrical and mechanical properties of the products; it can also be used to check the ability of test samples to withstand certain corrosion. 2 Reference standards
GB2422 Basic environmental test procedures for electric and electronic products Terminology GB2423.3 Basic environmental test procedures for electric and electronic products Test Ca: Steady-state damp heat test method GB2423.4 Basic environmental test procedures for electric and electronic products Test Db: Alternating damp heat test method GB2423.9 Basic environmental test procedures for electric and electronic products Test Cb: Steady-state damp heat test method for equipment GB2423.34 Basic environmental test procedures for electric and electronic products Test Z/AD: Temperature/humidity combination cycle test method GB2424.10 Basic environmental test procedures for electric and electronic products General guide for accelerated atmospheric corrosion tests GB4797.1 Natural environmental conditions for electric and electronic products Temperature GB4798.1~4798.10 Application environmental conditions for electric and electronic products 3 Damp heat environmental conditions
Air temperature and relative humidity are climatic factors. The combination of the two in different values will always have an impact on the product during the storage, transportation and use of the product. www.bzxz.net
Years of meteorological data show that under free air conditions, except for extreme climate zones (such as the Persian Gulf), the relative humidity is not less than 95%, the temperature is not less than 30°C, and the temperature and humidity combination will not appear for a long time. Under natural environmental conditions, the classification of hot and humid areas in my country can be found in GB4797.1\i. In general residences and commercial buildings, the temperature may be as high as 30°C (or more), but in most cases, the relative humidity is lower than that outdoors. For temperature and humidity data under various environmental conditions in different application sites, see GB4798.1~4798.102]. In some humid rooms in chemical, metallurgical, mining and electroplating industries, the environmental conditions are relatively special, the temperature may be as high as 45°C, and the relative humidity may reach 100% for a long time.
Some equipment placed under specific conditions may also withstand a relative humidity of more than 95% under high temperature conditions, especially when these equipment are placed in unventilated closed places such as vehicles, tents or aircraft cabins. The high relative humidity formed by the water vapor released by hygroscopic materials, human breathing and sweating, the evaporation of water in uncovered water containers or other moisture sources may occur simultaneously with the high temperature caused by sunlight. In a room with several heat sources, the temperature and relative humidity may be different in different places. Air pollution exists in almost every place. It may strengthen the effect of humid climate on products. For example, the combined effect of various corrosive gases and moisture will increase the speed of metal corrosion; some dust that easily absorbs moisture will promote condensation on the surface of the test sample or absorb moisture, aggravating the decline of surface insulation performance. Some materials will grow mold after being damp, which will also reduce the surface resistance of the material. Since the air used for damp heat test should not contain pollutants, the effect of pollutants on the tested products and the situation that affects the test results should be paid attention to. If the effect of pollutants on products is to be studied specifically, appropriate test methods such as gas corrosion test or mold growth test should be adopted. 4 Methods of generating humidity conditions
There are many types of damp heat test chambers (rooms) now, equipped with different humidity generation and control systems. The following briefly introduces the principles and advantages and disadvantages of various humidification methods.
4.1 Spray humidification
Deionized water or distilled water is atomized into extremely fine particles, sprayed into the air before entering the working space and evaporated before entering the working space, so as to make the air humid. Avoid spraying water mist directly into the working space. Advantages: simple system, rapid humidification, and low maintenance. Disadvantages: A small amount of aerosol may remain in the working space. Note: 1) Aerosol is a gaseous suspension of ultra-fine liquid or solid particles. 4.2 Steam humidification
Spray hot water vapor into the air before entering the working space of the test chamber (room). Advantages: simple system, rapid humidification, and easy control of water vapor. Disadvantages: Heat is input at the same time as steam, so cooling measures need to be taken but a dehumidification effect is produced; at the same time, condensation may occur on objects with lower temperatures in the test chamber (room). 4.3 Volatile humidification
4.3.1 Bubble evaporation method
The air is turned into bubbles when passing through a water container and is gradually saturated with water vapor. Advantages: simple system; when the airflow remains unchanged, changing the water temperature can easily control the humidity. Disadvantages: Humidification by increasing the water temperature may increase the temperature of the working space; due to Water has a large heat capacity, and a time lag may occur when the humidity is changed; a small amount of aerosol may be generated when the bubbles burst. 4.3.2 Surface evaporation method
The air is humidified by passing it over a large area of water. There are several different methods of surface evaporation humidification, for example, by repeatedly passing the air over the water surface. Notes:
1] In IFEC68-2-28 (1990), see IFC721-1. This standard uses the Chinese standard instead. 2| In IFC68-2-28 (1990), see IEC721-3 series standards. This standard uses the Chinese standard instead. 31 Notes are added to this standard.
GB/T2424.2-—93
Still water surface, or spray water onto a vertical surface to flow countercurrently with the air. Advantages: The aerosol generated Very little; humidity can be easily controlled by changing the water temperature. Disadvantages: Due to the large heat capacity of water, there may be a time lag when changing the humidity. 4.4 Humidification of aqueous solutions
At a constant temperature, a specified relative humidity can be formed above a standard aqueous solution in a small sealed test chamber. Appendix B gives the relative humidity values that can be formed by propylene glycol (glycerol) and various salt solutions. Advantages: The method is simple and the system is reliable.
Disadvantages: Not suitable for heat dissipation test samples and samples with high moisture absorption; cannot be used in alternating damp heat tests. In a poorly designed test chamber, salt particles may be deposited on the surface of the test sample; in some cases, such as when using ammonium salts, ammonium salt particles are harmful to health and cause stress corrosion of copper alloys.
5 Physical phenomena of humidity
5.1 Condensation
The dew point temperature depends on the water vapor content in the air. There is a direct relationship between the dew point temperature, absolute humidity and water vapor pressure. When the test sample is placed in the test chamber (room), if the surface temperature of the test sample is lower than the dew point temperature of the air in the test chamber (room), condensation will appear on the sample surface. Therefore, if condensation is to be avoided, the test sample must be preheated. During the conditional test, if condensation is required on the surface of the test sample, the water content and air temperature in the air must be increased rapidly so that the difference between the dew point temperature of the air and the surface temperature of the test sample reaches a certain value. For example, in the heating stage of the alternating damp heat test, since the test sample has a certain thermal time constant, its surface temperature is often lower than the dew point temperature of the air in the test chamber (room). Therefore, condensation will not appear on the surface of the test sample.
If the thermal time constant of the test sample is relatively small, condensation will only occur when the heating rate is extremely fast or the relative humidity is close to 100%. For very small test specimens, condensation may not occur even if the heating rate specified in test Db and test B/AI is met. During the heating period, the relative humidity required to produce condensation on the surface of the test specimen with a thermal time constant of ? is given by the following formula: RH >10 1 0.05t )
Wu Zhong: RH
Relative condensation, %:
Thermal time constant of the test sample,;
Note: The thermal time constant of the test sample is also related to the wind speed in the test box (room). A6
The average rate of change of air temperature in the test box (room), (/s. For example, for the wet heat test with 25C/55C alternation Db.AG— -55 — 25
5~0. 0028℃/s
For small components with t=1min, the relative humidity value that guarantees condensation is 99.2%. After the temperature drops to the ambient temperature, a small amount of condensation may occur on the inner surface of the shell. In the capillary, condensation may occur even if the relative humidity is much lower than 100%.
Instructions for use:
1 The example is added for this standard.
GB/T2424.2--93
Usually, condensation can only be checked by visual observation, but this may not be very effective, especially for small test samples with rough surfaces.
5.2 Adsorption
The amount of water vapor molecules adsorbed on the surface of the test sample depends on the material. The type of material, the surface structure of the material and the amount of water vapor pressure. Since adsorption and absorption occur simultaneously, the absorption effect is usually more obvious. Therefore, it is not easy to evaluate the amount of adsorption alone. 5.3 Absorption
The amount of moisture absorbed by the material depends largely on the moisture content of the surrounding air, and the absorption process proceeds steadily until equilibrium is reached. The rate of water molecule penetration generally increases with increasing temperature. 5.4 Diffusion
An example of diffusion that often occurs in electronic engineering is that water vapor penetrates organic sealing materials into the interior of the housing, such as into capacitors or semiconductor devices.
5.5 Respiration 1
The exchange of air and water vapor inside and outside the cavity of the test sample caused by temperature changes The flow is called breathing. For test samples with poor sealing types that have cavities inside, the inhaled moisture makes the internal structure of the test sample damp, or condenses into aggregated water in the cavity. 6 Acceleration of physical processes
6.1 Overview
The purpose of general tests is to obtain the same characteristic changes that will occur in normal use environments. The purpose of accelerated tests is to greatly shorten the test time to obtain effects similar to normal use conditions. However, it must be emphasized that during accelerated tests, the failure mechanism of the test sample under severe conditions is different from the failure mechanism under normal use conditions. The design use limit conditions and design storage limit conditions of the product should be considered when selecting the test severity level. The absorption and diffusion processes may require relatively When a long time (several thousand hours) is required to reach the equilibrium state, the time required for condensation and adsorption processes is generally quite short.
6.2 Acceleration Factor
It is not possible to give a universal and effective acceleration factor at present. Under the condition of given relative humidity, the acceleration effect of the damp heat test can be achieved by increasing the temperature. The magnitude of the acceleration factor can only be determined after the relationship between the penetration rate, temperature and water vapor pressure is known or an empirical formula between the three is established. For comparative tests, if the failure mechanism of different test samples is the same, it is allowed to use a highly accelerated test. When using a constant damp heat test to simulate the effect under real temperature and humidity conditions, the acceleration effect can be achieved by one of the following methods: a. Use a temperature and humidity higher than the real conditions or one of them. b. If the real environment is characterized by alternating cycles of high temperature and humidity and moderate temperature and humidity conditions, only the high temperature and humidity conditions are considered and the moderate temperature and humidity cycles are ignored. However, in the case of alternating cycles, the sample has a drying period, which is not the case in the constant condition, which may affect the validity of the test. 7 Comparison of steady-state and alternating damp heat tests 7.1 Steady-state damp heat tests Ca and Ch
Tests Ca and Ch should always be used in situations where absorption and adsorption play a major role. Steady-state damp heat tests should also be used when it is required to simulate humid environmental conditions where the temperature and humidity remain essentially constant. 7.1.1 Test Ca
Instructions for use:
1) 1EC68-2-28 (1990) does not have this clause. 53
GB/T 2424.2-93
Test Ca is mainly used to evaluate the ability of components to withstand a humid environment for a long time, but in many cases, it is also used to determine the ability of materials to maintain electrical properties in humid air, to evaluate the ability of packaged components and assemblies to prevent water vapor diffusion, and to detect defects in electrical products. 7.1.2 Test Cb
Test Cb is mainly used to determine the reaction of equipment to high humidity conditions in the absence of condensation. It is particularly suitable for large equipment that cannot be preheated during the installation stage but is required to maintain the specified conditions and equipment with complex connections between the test box (chamber) and the test equipment. When designing the test procedure, except for cooling devices that are running at a temperature lower than the dew point temperature of the test air, no condensation should appear on the test sample. In the test of the heat dissipation test sample, it should be ensured that the free air conditions are well simulated and the effect of the close heating of the test sample on the surrounding environment of the sample is considered.
7.2 Cyclic damp heat test Db
Test Db is applicable to various occasions where condensation or water vapor intrusion and formation of liquid water due to respiration are important characteristics. Test Db is applicable to all types of test samples. Variation 1 is applicable to all occasions where absorption or respiration effect is an important feature. Variation 2 is applicable to occasions where absorption and respiration effects are not significant and the test equipment used is relatively simple. "Test Q: Sealing test method" can quickly detect gaps that can cause breathing, but it cannot reproduce the various effects of the damp heat test. 7.3 Test sequence and combination tests
A reliable method for determining the tightness of joints or checking for hairline cracks is to apply one or more temperature cycles to the test sample. In most cases, it is not necessary to combine temperature changes with humid air, that is, it is not necessary to produce two test conditions at the same time. If the temperature change test (test N) is followed by test C or test Db, the expected more severe effect can be obtained: if the damp heat test is followed by a low temperature test (test A), the test effect will be enhanced. This is because the high temperature change rate of the temperature change test combined with the large temperature difference produces much greater thermal stress than the test Db with a relatively small temperature change rate. When the test sample is composed of different materials and has joints, especially when it contains bonded glass, it is recommended to use a combination test method consisting of several damp heat cycles and ... low temperature cycles (see GB2423.34). This combined test method differs from other alternating damp heat test methods in that it has a higher upper temperature limit and reaches sub-zero temperatures multiple times within a given time, thereby obtaining additional effects not found in other mixed heat tests, namely the freezing effect of condensed water in cracks or joints and the accelerated breathing effect. The purpose of adding low temperature cycles between humidity cycles is to freeze the water contained in any defects, and by virtue of the expansion effect of ice, these defects will become failures faster than in the normal life cycle. It should be emphasized that this freezing effect will only occur when the gap is large enough to allow the infiltration of some liquid water, such as the gap between metal components and gaskets or between solder and wire joints. Fine hair-like cracks or porous materials, such as gaps in plastic packaged components, are mainly absorption effects, and constant damp heat tests should be used to consider these effects.
8 Influence of the test environment on the test sample
8.1 Changes in physical properties
A humid atmosphere may change the mechanical and optical properties of the material. Therefore, whether it is a constant humidity test or an alternating humidity test, and whether condensation occurs on the surface, the physical properties of the material will change. For example, the size change caused by expansion, the change of surface properties such as friction coefficient, and the change of strength, etc.
8.2 Changes in electrical properties
8.2.1 Surface dampness
If there is condensation on the surface of the insulating material or a certain amount of moisture is adsorbed, some electrical properties may change, such as a decrease in surface resistance, an increase in loss angle, and even leakage current. Generally speaking, to check the change in electrical properties after the surface is damp, test Db or test Z/AD should be used; if it is known that the use of the material is only related to adsorption, test Ca or Cb should be used. In some cases, the load of the test sample must be connected or measurement must be performed during the conditional test. - Generally speaking. The change in electrical properties caused by moisture on the surface is very rapid and is clearly evident a few minutes after the test begins. 8.2.2 Volume moisture absorption
Volume moisture absorption of insulating materials can change many electrical properties, such as reduced dielectric strength, reduced insulation resistance, increased loss angle, increased capacitance, etc.
Since the absorption and diffusion process takes a long time, it takes hundreds or even several hours to reach an equilibrium state, so a longer test time should be selected. Only by knowing the dependence relationship between moisture penetration and time can the test results be inferred. For example, after a 56-day constant humidity test, a plastic package seems to be good, but after 6 months, due to absorption and diffusion, a large amount of water vapor penetrates into the material, and the performance of the plastic package deteriorates. After the main parts of the package are treated with moisture-proof treatment, such as passivation of semiconductors, encapsulation of desiccant, etc., it may become difficult to evaluate the impact of moisture absorption on electrical performance.
8.3 Corrosion
There are many types of corrosion that can only occur when the humidity is quite high. The higher the temperature and humidity, the faster the corrosion rate. Generally speaking, corrosion is most serious when there is repeated evaporation and multiple condensation. For information on this, see GB2424.10. Wet heat tests are not usually used to determine the effects of corrosion, but when there are impurities on the metal surface, such as residual flux, residues from other processing processes, dust, fingerprints, etc., a humid environment may induce corrosion or accelerate the corrosion process. The joints between different metals or metals and non-metallic materials may also be a source of corrosion when the relative humidity is high or condensation exists, even if there are no contaminants.
A1 Overview
GB/T 2424.2—93
Appendix A
Wet heat effect diagram
(Supplement)
Figure A1 shows the basic physical processes of wet heat tests and the relationship between these processes, and explains the influence and effect of wet heat tests on test samples and material properties.
The following lists the various test parameters and their codes for the damp heat test. These codes have been written in the various boxes at the appropriate places in Figure A1 or where the existing data can prove their correctness: Time (sum of the duration of the condition test) Temperature
Rate of temperature change
Relative humidity
Absolute humidity
Degree of pollution of the test atmosphere
A2 Notes
A2.1 Water penetration
The mechanism of water penetration into the interior of solid materials is different from that of water penetration into closed cavities through gaps. The difference is as follows: a. Water penetration into solid materials is the result of "volume diffusion", which is the movement of individual water molecules through the molecular gaps of solid materials. This mechanism leads to the phenomenon of "absorption". Volume diffusion allows water molecules to reach the sensitive parts inside the plastic package device, such as the resistive film in the thin film resistor of the encapsulated plastic shell. According to the same process, water molecules can also reach the internal cavity of the enclosure. In this case, desorption is the end of the process of moisture entering the cavity. b. Penetration through cracks is the result of the movement of water vapour in leaks or enclosures filled with air. This can be divided into three mechanisms of action;
Diffusion: The movement of water molecules along the concentration gradient of the gas in the crack. Diffusion is independent of the macroscopic flow of air. Flow: Water molecules are drawn into the air flow through the crack. Breathing: The difference between the air pressure and the water vapour partial pressure varies with the depth of the crack, causing water vapour to flow along the crack, i.e., due to temperature changes.
Note: There is a certain arbitrariness in the identification of the penetration mechanism of cracks. In fact, diffusion and flow are a continuous process of transformation. Flow may also be the result of breathing.
A2.2 Physical processes
See Chapter 6.
A2.3 Effects
See Chapter 8.
A2.4 Examples of effects
The last row of Figure A1 lists typical examples of hygrothermal effects, but it must be noted that these examples are not necessarily the only examples caused by these physical processes. At the same time, since there may be interactions between the various effects, each box in this row cannot be considered to be completely independent. For example, chemical reactions between moisture and materials may cause changes in volume resistance and loss angle, etc. This is indicated in the fourth box from the left. Of course, there are undoubtedly many other examples of interactions. 556
Environmental factors
Water attached to the outer surface of the test sample
|Water entering the material
or the test
! Consequences of water intrusion into the sample Example of effects Ao.de/dt.RH Diffusion through the material to the volume 8. (RH).t Absorption of the material 6. RH, t Changes in mechanical properties of the test sample 8. AH, t Dimensional effects 8. AH, t Sealing failure Non-dimensional effects of materials e Hardness changes GB/T 2424. 2--93
Diffusion through tiny bells
Color
8. A(RH).t
Changes in the non-mechanical properties of the test sample
D. AH, t
Electrical properties influence
B. AH, t
Diffusion through larger gaps
Glandular
Air flow
Respiration
Air flow, 48
The microenvironment in the closed cavity
Water may accumulate
|Deposited on or (and)
penetrated into the sealing material
Test sample's non-
mechanical properties change
B, RH, Pu.t
Non-electrical properties influence
6, AH, t
Volume
6, AH, t
[Volume conductivity change
material and moisture
change, loss angle increase, chemical reaction
dielectric constant change,
breakdown voltage change
may cause
Influence of electrical properties
, RH, Pu
Interface
B, AH, t
Corrosion adhesion reduction
Influence of non-electrical properties
o., t, RH, Pu
Single material
, RH, t, Pu.e
Multiple materials
o.RH, t, Pu
Chemical brain etching of capsule surface resistance (contact
magnetic core, solder)
Rate change,
Surface coating Layer peeling, flashover, light transmittance and color change of printed marks, electrolytic corrosion (between different metal materials) GB/T2424.2-93 Appendix B! Relative humidity of air above glycerol and various salt solutions (reference) B1 Relative humidity of air generated by glycerol-water solution The different concentrations of glycerol listed in Table B1 [% (m/m) can provide the corresponding relative humidity in the temperature range of 15~~60℃. The error of relative humidity is about ±1%. When linear interpolation is used to obtain values not given in the table, the additional error is less than 1%. Table B1
Relative humidity
%(m/m)
Density at 25℃
Refractive index at 25℃
The relative humidity generated by glycerol-water solution varies with its concentration, so its concentration should be checked and adjusted frequently. In addition, the high viscosity of glycerol will also cause the concentration inside the solution and the surface concentration to be inconsistent. The refractive index should be measured with a refractometer with a measurement range of 1.33~1.47n and an error of ±0.001n. Relative humidity of air generated by saturated salt solution B2
Saturated salt solution has a strong ability to absorb and release moisture. At a constant temperature, saturated salt solution can maintain the relative humidity in a closed space at a certain value, see Table B2.
Adoption instructions:
1) is supplemented by this standard and is cited from IEC260 (1968). 538
Saturated salt solution
1. Potassium sulfate
2. Potassium dihydrogen phosphate
3. Potassium nitrate
4. Potassium chloride
5. Ammonium sulfate
6. Sodium chloride
7. Sodium nitrite
8. Ammonium nitrate
9. Sodium dichromate
10. Magnesium nitrate
11. Potassium carbonate
12. Magnesium fluoride
13. Potassium acetate
14. Lithium chloride
KH,POA
(NH.),SO4
NH,NO3
NazCr2O,·2H.0
Mg(NO3), - 2H20
K,CO3· 2H20
MgClz· 6H,O
CH,COOK
LiCI ? XH.O
GB/T 2424.2—93
When preparing saturated salt solution, there should be excess solid salt in the solution to ensure its saturation. 40
When using saturated salt solution for testing, any salt that can produce corrosive gases that are harmful to the test sample shall not be used. For example, ammonium salts are not suitable for test samples containing copper or copper alloys. In addition, crystallization of salt in solution or "precipitation" from the salt solution should be avoided. Additional remarks:
This standard is proposed by the Ministry of Machinery Industry of the People's Republic of China. This standard is under the jurisdiction of the National Technical Committee for Environmental Conditions and Environmental Testing of Electrical and Electronic Products. This standard was drafted by the Guangzhou Electric Science Research Institute of the Ministry of Machinery Industry. The main drafters of this standard are Xie Jianhua, Xu Fu, Zhong Kaihua, Jia Xuemao and Xia Yuemei.
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