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Back to topOverview of Potting Compound Types
Electronic products have become closely integrated with people’s daily lives and are increasingly susceptible to irreversible damage caused by extreme environmental conditions such as moisture, temperature, corrosion aging, vibration, and impact. Therefore, there will be an increasing demand for high reliability and durability in electronic products, which also means that potting compounds must offer higher insulation strength, better thermal conductivity, and lower thermal expansion coefficients. This article introduces common types of potting compounds, analyzes their advantages and disadvantages, and appropriate applications. It also presents common issues encountered in the manufacturing process along with corresponding countermeasures to assist in selecting suitable potting compounds for power converters.
Introduction
Encapsulation processes protects internal electronic components and circuit boards, thereby enhancing their electrical performance, reliability, and durability. Encapsulation of electronic products can prevent moisture in the air from penetrating, protect against mechanical shocks and vibrations, add support and cushioning to delicate or fragile components, improve electrical insulation, aid in heat dissipation, and provide fire protection.
There are numerous types of potting compounds on the market, each with different characteristics. Selecting the appropriate material is therefore a challenging task. During the design phase, it is essential to understand the properties of potting compounds in advance, such as mechanical strength, thermal expansion coefficient, electrical insulation, thermal conductivity, adhesion strength, sealing ability, and corrosion resistance.
Moreover, various issues often arise during the encapsulation process, such as surface roughness and bubble formation, which affect the quality of encapsulation and reduce the reliability of electronic components. Thus, analyzing encapsulation compounds and addressing common problems before designing power converters is crucial.
Types of Potting Compounds
Encapsulation compounds such as epoxy resin, silicone resin, and polyurethane are commonly used in power converters. The following will introduce three common encapsulation compounds, analyze their advantages and disadvantages, and discuss their suitability for different applications.
(1) Epoxy Resin
Epoxy resin, also known as AB glue, is a chemical material commonly used for encapsulating power converters. It is a thermosetting polymer synthesized from Agent A - epoxy resin and Agent B - hardener which have been mixed in proportion. It is known for its excellent adherence, resistance to chemicals and moisture, so it is very suitable for outdoor applications.
When analyzing or troubleshooting power converters, it is often necessary to remove their encapsulation. However, epoxy resin is a challenging material to remove, requiring the use of sharp tools, which may damage electronic components.
The table below outlines the advantages and disadvantages of epoxy resin:
| Epoxy Resin | |
|---|---|
| Advantages |
- High hardness and tensile strength - Resistance to corrosion, moisture and temperature - High insulation - Good adhesion - Low curing shrinkage |
| Disadvantages |
- At room temperature, the curing process continues to generate heat and takes too long - Poor re-restorability |
(2) Silicone Resin
Silicone resin, commonly known as silicone, is a polymer with a three-dimensional branched chain structure. The siloxane bonds (-Si-O-Si-) that form the backbone of silicone compounds delivers properties that are not found in other organic C-C structure polymers and epoxy resin, and its characteristics are also better than those of general organic compounds.
The mechanical stress caused by the heat generated by high-temperature devices can be released through the characteristic of high flexibility. Hence, silicone resin exhibits a wider operating temperature range and excellent electrical insulation properties than other polymers, making it one of the most widely used potting materials on the market.
The table below summarizes the advantages and disadvantages of silicone resin:
| Silicone Resin | |
|---|---|
| Advantages |
- Highly flexible and elastomeric, so that no cracks during process - Wide temperature tolerance, ranging from -55°C to 200°C - Low volume shrinkage, so more resistant to temperature shocks - High insulation |
| Disadvantages |
- Expensive - Low viscosity |
Many applications used silicone resins to be potting consumer electronic components, such as power transistors and voltage regulators in smartphones, computers, and home electronics, and the aim is to increase reliability and extend the life of product. In addition, silicones are also used in automotive systems and communications equipment, including airbags, ignition systems and mobile communications base stations, to protect electronic components from contamination and extreme temperatures. It can be concluded that silicone resin is suitable for electronic components working in harsh environment conditions.
(3) Polyurethane (PU)
Polyurethane, generally abbreviated as PU, is a two-component compound consisting of a base resin with an isocyanate curing agent with high durability and adaptability. The flexibility can help to resist the harsh environment, protect the electronic equipment from humidity and effectively absorb impact collisions and vibrations, and eliminating the risk of damage.
Therefore, polyurethane is an ideal irrigation material for power converter working in indoor. Polyurethane has the advantages of curing at a lower temperature and releasing less heat during the curing process. Compared with epoxy resin, it takes a long time to cure and releases a large amount of heat.
It should be noted that polyurethane is only suitable for low working temperature. When the working temperature is higher than 120 ° C, the electrical performance decreases, and the chemical structure changes to decompose.
The table below outlines the advantages and disadvantages of polyurethane:
| Polyurethane | |
|---|---|
| Advantages |
- High elasticity in low -temperature environment - Excellent impact and vibration resistance - Better electrical insulation and combustion resistance |
| Disadvantages |
- Lower maximum allowable temperature - Lower resistance to corrosive liquids - Moisture sensitive before curing - Prone to air bubbles, requiring vacuum potting |
Relative comparison table of common properties of three potting compounds
Each of these three common potting compounds has different properties. The following table is a relative comparison of common properties of three potting compounds.
| Epoxy | Silicon | Polyurethane | |
|---|---|---|---|
| Flexible | Low | Medium | High |
| Viscosity | High | Low | Medium |
| Adhesion | High | Medium | Low |
| Temperature range | Medium | High | Low |
| Anti-thermal shock | Low | High | Medium |
| Electrical insulation | High | Medium | Low |
| Price | Low | High | Medium |
| Hardness | High | Low | Medium |
| Repairability | Low | High | Medium |
| Moisture resistance | Low | High | Medium |
| Thermal conductivity | Medium | High | Low |
| Heat resistance | Medium | High | Low |
Common Issues
Encapsulation is a crucial step in ensuring the performance and reliability of electronic components. If improper conditions occur during the encapsulation process, such as incomplete penetration of the encapsulating compound into coil turns, resulting in voids between the coil turns, it may lead to local arcing or breakdown phenomena during operation, thereby reducing the reliability of electronic components. The following describes common problems and their solutions:
(1) Surface Roughness
In a ventilated environment, all potting materials will not only continue to release heat during the curing process from liquid to solid, but also take a long time to complete, and the surface will even appear uneven after curing. This problem is related to the operating temperature. If the operating temperature is too high and the potting material has not been naturally flattened in the shell, and some areas will solidify, resulting in an uneven colloid surface. For blocks with thinner colloids, it has poor moisture resistance and insulation, and other electrical properties are also reduced; For blocks with thicker colloids areas, which are difficult to use probes or thermocouple wires to measure components.
To prevent the problem from recurring, it knows that keeping the laboratory environment temperature to be constant, and maintaining equipment regularly, and removing dust inside the converter.
(2) Bubbles
During the encapsulation process, all bubbles must be removed during the potting process because the gas molecules are not tightly packed, which leading lower thermal conductivity. So, the bubbles reduce heat transfer. The causes of air bubbles formation include:
a. Water Vapor Pollution
Moisture can come from many sources, such as the curing agent or the Interior surface of shell. The water vapor reacts chemically with the potting material, and then produces gas. This gas will form bubbles in the sealant.
The solution is to use a small jet to blow into the shell for a period of time in advance, which ensure that no moisture exists, and then potting in lower humidity.
b. Non-uniform Mixing
When many kinds of potting compound are mixed, air will be driven into them during the stirring process. Potting with small bubbles is injected into the inner shell of power converter. When the sealant expands due to heat, the gases will gradually gather together and eventually form bubbles of different sizes, which will affect the electrical characteristics.
The solution is to vacuum the mixed potting compound, which can fully extract the gas from the potting compound.
c. Impact of Holes
When the material has high viscosity and slow flow speed, bubbles and other undesirable phenomena may occur where it flows through holes or slits. The solution is to preheat the potting sealant, so that the viscosity will be reduced, and which can fill every hole to exhaust the air. Another solution is to slow down the filling speed of potting sealant and make it even. This allows it to flow slowly to every corner and then reduces bubbles.
Summary
When choosing epoxy resin, silicone resin, and polyurethane as encapsulation compounds for power converters, priority should be given to good insulation performance, high-temperature resistance, good sealing, and environmental corrosion resistance. This paper briefly summarizes these three encapsulation compounds:
- Epoxy resin has excellent adhesion and chemical resistance, making it suitable for outdoor applications.
- Silicone has the features of high flexibility and wide continuous operating temperature range, which is ideal for potting in high-power applications
- Polyurethane have better flexibility, good low temperature performance and strong impact resistance, which makes it popular for consumer electronic products.
Potting helps to solve numerous problems within the manufacturing and assembly of electronics products. Using the right resin materials for each application is crucial to the cost-effective and timely production of quality.
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