What is a potting compound?

What is a potting compound?

Potting is to pour the liquid basic resin compound into the device with electronic components and circuits mechanically or manually, and then solidify it into a thermosetting polymer insulating material with excellent performance under normal temperature or heating conditions. The liquid base resin compound used in this process is the potting compound.

Electronic thermal potting compound is mainly used for bonding, sealing, potting and coating protection of electronic components. The potting compound is liquid before curing and has fluidity. The viscosity of the glue varies according to the material, performance and production process of the product. The potting compound can realize its use value only after it is completely cured.

There are many types of electronic thermal conductive encapsulants. In terms of material types, the most commonly used three are mainly silicone resin thermal conductive encapsulants, epoxy resin thermal conductive encapsulants, and polyurethane thermal conductive encapsulants. The three material potting compounds can be subdivided into hundreds of different products.

Silicone Thermal Potting Compound

There are many types of silicone potting compounds. Different types of silicone potting compounds have great differences in temperature resistance, waterproof performance, insulation performance, optical performance, adhesion and adhesion to different materials, and softness and hardness. Silicone encapsulants can be added with some functional fillers to give them properties such as electrical conductivity, thermal conductivity, and magnetic conductivity. The mechanical strength of silicone encapsulant is generally poor, and it is precisely this performance that is used to make it “breakable” for easy maintenance, that is, if a component fails, you only need to pry open the encapsulant and replace it with a new one. After the original copy, you can continue to use it.

The color of the silicone potting compound can generally be adjusted arbitrarily according to the needs. or transparent or non-transparent or white color. Silicone potting compound performs very well in shockproof performance, electrical performance, waterproof performance, high and low temperature resistance, and anti-aging performance.
Two-component silicone potting glue (or ab glue) is the most common, and this kind of potting glue includes two types: condensation type and addition type. Generally, the condensation type has poor adhesion to components and potting cavity, and volatile low-molecular-weight substances will be produced during the curing process, and there will be a relatively obvious shrinkage rate after curing. Addition type (also known as silicone gel) has minimal shrinkage and no low-molecular-weight formation during curing. It can be cured quickly by heating.

Advantages: The material of the silicone potting compound is soft after curing. There are two forms of solid silicone rubber products and silicone gels, which can eliminate most of the mechanical stress and have the effect of shock absorption and protection. Physical and chemical properties are stable, with good high and low temperature resistance, and can work for a long time in the range of -50~200 °C. Excellent weather resistance, can still play a good protective role outdoors for more than 20 years, and is not easy to yellow. It has excellent electrical performance and insulating ability. After potting, it can effectively improve the insulation between internal components and lines, and improve the stability of electronic components. With rework capability, sealed components can be taken out for repair and replacement quickly and easily.

Disadvantages: The bonding performance is slightly poor.

Application range: suitable for potting a variety of high-end precision/sensitive electronic devices that work in harsh environments. Such as LEDs, display screens, photovoltaic materials, diodes, semiconductor devices, relays, sensors, automotive ballasts HIV, on-board computer ECUs, etc., mainly play the role of insulation, moisture-proof, dust-proof and shock-absorbing.

Epoxy Thermal Potting Compound

Through the EU ROHS standard, the cured product has high hardness, smooth surface, good gloss, and has the characteristics of fixation, insulation, waterproof, oil-proof, dust-proof, anti-theft, corrosion resistance, aging resistance, and thermal shock resistance. It is used for packaging of electronic transformers, AC capacitors, negative ion generators, aquarium water pumps, ignition coils, electronic modules, LED modules, etc. It is suitable for potting of small and medium-sized electronic components, such as automobile, motorcycle igniter, LED drive power supply, sensor, toroidal transformer, capacitor, trigger, LED waterproof lamp, confidentiality, insulation and moisture-proof (water) of circuit board. Potting.

Advantages: Most epoxy resin potting glues are hard, and a few modified epoxy resins are slightly soft. The major advantage of this material is that it has better adhesion to the material and better insulation, and the cured product has good acid and alkali resistance. Epoxy resin generally has a temperature resistance of 100 ℃. The material can be used as a transparent material with good light transmittance. The price is relatively cheap.

Disadvantages: weak resistance to cold and heat changes, cracks are prone to occur after being impacted by cold and heat, resulting in water vapor infiltrating into electronic components from cracks, poor moisture resistance; colloid hardness after curing is high and brittle, high mechanical stress is easy Strain electronic components; epoxy resin cannot be opened due to its high hardness after potting and curing, so the product is a “lifetime” product, and components cannot be replaced; transparent epoxy resin materials generally have poor weather resistance and light exposure. Or yellowing is easy to occur under high temperature conditions.

Scope of application: Generally used for potting of non-precision electronic devices such as LEDs, transformers, regulators, industrial electronics, relays, controllers, power modules, etc.

Polyurethane potting compound

Polyurethane encapsulant, also known as PU encapsulant, is usually composed of polyols and diisocyanates of oligomers such as polyester, polyether and polydiene, and diol or diamine as chain extenders. to make. Potting compounds can generally be prepared using the prepolymer method and the one-step process.

Polyurethane potting materials are characterized by low hardness, moderate strength, good elasticity, water resistance, mildew resistance, shock resistance, transparency, excellent electrical insulation and flame retardancy, no corrosion to electrical components, and resistance to steel, aluminum, copper, tin and other metals, as well as rubber, plastic, wood and other materials have good adhesion. Potting materials can make installed and debugged electronic components and circuits immune to vibration, corrosion, moisture and dust.

Advantages: Polyurethane encapsulant has excellent low temperature resistance, the material is slightly soft, and has good adhesion to general encapsulation materials, and the adhesion is between epoxy resin and silicone. It has good waterproof, moisture-proof and insulating properties.

Disadvantages: poor high temperature resistance and easy foaming, vacuum defoaming must be used; after curing, the surface of the colloid is not smooth and has poor toughness, and the anti-aging ability, shock resistance and ultraviolet rays are weak, and the colloid is easy to change color.

Scope of application: Generally used for potting of electronic components with low heat generation. Transformers, choke coils, converters, capacitors, coils, inductors, varistors, linear motors, fixed rotors, circuit boards, LEDs, pumps, etc.

Instructions for use of thermal potting compound

  1. Before mixing: A and B components should be fully stirred by hand or machine respectively to avoid changes in performance due to filler settling.​​
  2. Mixing: Weigh the two components according to a certain ratio (1:1, 10:1) and put them into a clean container and stir evenly. The error should not exceed 3%, otherwise it will affect the performance after curing.
  3. Defoaming: natural defoaming and vacuum defoaming, natural defoaming: let the mixed glue stand for 20-30 minutes. Vacuum defoaming: the degree of vacuum is 0.08-0.1MPa, and the vacuum is evacuated for 5-10 minutes.
  4. Perfusion: The rubber material should be perfused within the operating time, otherwise it will affect the leveling. Keep the substrate surface clean and dry before potting. The mixed rubber compound is poured into the device to be encapsulated. Generally, vacuum degassing is not required. If high thermal conductivity is required, it is recommended to vacuum degassing and then pour. (Vacuum defoaming: vacuum degree is 0.08-0.1MPa, vacuuming for 5-10 minutes)
  5. Curing: It can be cured at room temperature or by heating. The curing speed of the glue has a lot to do with the curing temperature. It takes a long time to cure in winter. It is recommended to use heating to cure. It takes 15-30 minutes to cure at 80 °C, and it generally takes about 6-8 hours to cure at room temperature.

With its excellent performance, thermal potting compound can well meet the needs of the consumer market, ensure effective bonding, sealing, potting and coating protection between electronic devices and products, and better bring high-quality insulation to the electronics industry. materials, so as to effectively improve its product awareness, so that more areas of awareness, effective use.

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