What is Three Proofings?
Electronic equipment is very sensitive to environmental conditions. Especially the environmental factors such as moisture, salt spray and mold are more prominent. The so-called three proofings refers to the moisture-proof, salt-proof, and anti-fungal properties of electronic equipment.
With the increase in the requirements for the three proofings of electronic devices, the problems exposed in electronic devices are also increasing. Some products are difficult to pass the damp heat, salt spray and mold tests smoothly. There are even obvious corrosion of materials, coatings and coatings, as well as a significant drop in electrical performance.This article mainly describes the moisture protection in the three proofings.
Method of Moisture Absorption
The moisture absorption of objects has four forms:
- Diffusion
- Absorption
- Adsorption
- Condensation
The diffusion and absorption cause water molecules to enter the interior of the material, thus reducing the electrical resistivity of the material. The affinity between molecules of some non-metallic materials is less than the affinity for water molecules. When water molecules enter the interior of the material, they will dissolve inside the material, causing the material to change and begin to expand. Adsorption and condensation cause a film of water on the surface of the material, which reduces the surface resistivity of the material.
Four kinds of hygroscopic mechanisms may occur simultaneously, and also be one or two of them. The process of absorbing moisture in this way is called direct wet invasion. This is also the most basic way to absorb moisture.
“breathing” Method
In addition, there is another way to absorb moisture, the “breathing” method. It refers to the process of humid air entering the protective layer, the container, the hose and the defective sealing body under the condition of alternating temperature and a certain air pressure difference. “Breathing” is a slow process that is not easily noticeable in a short period of time. For the more demanding moisture-proof seals, the “breathing” effect cannot be ignored.
When the relative humidity of the air is greater than 80%, the organic and inorganic material components in the electrical product will become heavier, expand and deform due to moisture, and the corrosion of the metal structural member will also accelerate. If the insulation material is selected and the process is improperly handled, the insulation resistance will drop rapidly, so that the insulation is broken down. In order to ensure the reliability of electrical products, moisture-proof design is particularly important.
Wet Hazard
Moisture not only damages mechanical and electrical properties, but also reduces the insulation resistance of the insulating material and the board, increases the tangent of the dielectric loss angle, and reduces the insulation performance. In case of serious, there will be leakage or even short circuit. At the same time, moisture also provides favorable conditions for the growth of mold. The mold is moist and may cause a short circuit when it propagates across the insulating surface. In addition, it will cause corrosion damage to metal materials and electronic components.
Quality Control
The three proofings quality control links mainly include:
- Structural design and process design to avoid corrosion
- Qualified production process
- Strict three proofings acceptance test
The above links are indispensable.
The core of the three proofings quality is to assess the ability of electronic products to resist corrosion under conditions of damp heat, industrial atmosphere and salt spray. In this process, the three proofings acceptance test mainly refers to the environmental simulation test conducted in the environmental test chamber. These tests can verify the effectiveness of the three proofings. In addition, the test cycle can be shortened. Manufacturers generally choose an environmental test chamber that meets their requirements for testing.
Detection Method
Generally, the test methods for detecting the three proofings quality of electronic products mainly include:
- Artificial acceleration test
- Natural atmospheric exposure test
The artificial acceleration test has a short test period, and the test results are quite different from the actual conditions.
The atmospheric exposure test period is long and the test results are closer to the real situation.
The artificial acceleration test is also called the artificial simulation environment test. The most commonly used artificial acceleration tests for electronic products are: temperature humidity test, salt spray test and mold test.In fact, most manufacturers use the temperature humidity test chamber, salt spray test chamberand other equipment to test their products.
Temperature Humidity Test
The temperature humidity test is mainly used to evaluate the reliability of the use and storage of electronic products and materials under the conditions of temperature cycle change and condensation on the surface of the product. It can determine changes in the electrical properties and mechanical properties of electronic products. In addition, it can also be used to check the ability of materials to withstand corrosion.
Because there are many kinds of corrosion that can only occur when the humidity is quite large. Moreover, the higher the temperature and humidity, the faster the corrosion rate. Usually temperature humidity test is not used to determine the corrosion effect. However, impurities such as flux, process residues, dust, fingerprints, and hand sweat attached to the metal surface may induce corrosion or accelerate corrosion in a hot and humid environment. Although there are no contaminants between the different metals or between the metal and the non-metallic materials, corrosion occurs when the relative humidity is high or there is condensation.
Conclusion
Three proofings are not just process protection issues, they involve all aspects of design, process, manufacturing and management. What kind of testing methods and test standards are used in this process is also an important aspect of the three proofings problem of electronic equipment.