First, the introduction of common potting glue
Electronic potting adhesives are mainly used for bonding, sealing, potting and coating protection of electronic components. The potting compound is liquid before uncured and has fluidity. The viscosity of the glue differs depending on the material, performance and production process of the product. It can be used after it is fully cured. After curing, it can be waterproof, moisture-proof, dust-proof, insulated, heat-conductive, confidential, anti-corrosive, temperature-resistant and shock-proof. There are many kinds of electronic potting glues. Here we mainly introduce epoxy resin potting glue, polyurethane potting glue, silicone potting glue, etc.
Epoxy resin potting
Through the EU ROHS specified standards, the cured product has high hardness, smooth surface and good gloss. It has the characteristics of fixed, insulated, waterproof, oil-proof, dust-proof, anti-theft, corrosion-resistant, aging-resistant, and resistant to thermal shock. It is used in the packaging of electronic transformers, AC capacitors, negative ion generators, aquarium pumps, ignition coils, electronic modules, LED modules, etc. 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 light, circuit board for confidentiality, insulation, moisture (water) Potting.
Advantages: Epoxy potting is mostly hard, and there are very few modified epoxy resins. The material has the great advantage of good adhesion to the material and good insulation, and the cured product has good acid and alkali resistance. Epoxy resin is generally resistant to temperature of 100 ° C. The material can be used as a transparent material and has good light transmittance. The price is relatively cheap.
Disadvantages: weak resistance to cold and heat, cracks easily occur after thermal shock, resulting in water vapor infiltrating into the electronic components from the cracks, poor moisture resistance; high hardness and brittleness after solidification, high mechanical stress Easy to pull electronic components; epoxy resin can not be opened due to high hardness after potting and curing, so the product is a "lifetime" product, the replacement of components can not be achieved; transparent epoxy resin materials generally have poor weatherability, It is prone to yellowing under light or high temperature conditions.
Applications: Generally used for potting of non-precision electronic devices such as LEDs, transformers, regulators, industrial electronics, relays, controllers, power modules, etc.
2. Polyurethane potting compound
The polyurethane potting compound is further formed into a PU potting compound, usually consisting of a polyol of polyacetate, a polyether and a polydiene, and a diisocyanate, a glycol or a diamine as a chain extender, and is gradually polymerized. to make. Potting compounds can usually be prepared by a prepolymer process and a one-step process.
Polyurethane potting materials are characterized by low hardness, moderate strength, good elasticity, water resistance, mold resistance, shock resistance, transparency, excellent electrical insulation and flame retardancy, no corrosion to electrical components, steel, aluminum, copper, tin Other metals, as well as rubber, plastic, wood and other materials have good adhesion. The potting material protects the installed and commissioned electronic components and circuits from vibration, corrosion, moisture and dust.
Advantages: Polyurethane potting compound has excellent low temperature resistance, the material is slightly soft, and has good adhesion to general potting materials. The bonding force is between epoxy resin and silicone. It has good water and moisture resistance and insulation.
Disadvantages: Poor heat resistance and easy foaming, vacuum defoaming must be used; after curing, the surface of the colloid is not smooth and the toughness is poor, anti-aging ability, anti-shock and ultraviolet rays are weak, and the colloid is easily discolored.
Application range: Generally used for potting of electronic components with low heat generation. Transformers, chokes, converters, capacitors, coils, inductors, varistors, linear engines, stationary rotors, circuit boards, LEDs, pumps, etc.
3. Silicone potting compound
There are many types of silicone potting compounds. Different types of silicone potting compounds have great differences in temperature resistance, water resistance, insulation properties, optical properties, adhesion to different materials, and hardness. Silicone potting compounds can be added with some functional fillers to impart properties such as conductive, thermal, and magnetic properties. The mechanical strength of silicone potting glue is generally poor, which is to borrow this performance, so that it can be "opened" for maintenance, that is, if a component fails, it only needs to open the potting glue and replace it with new ones. After the original, you can continue to use it.
The color of the silicone potting compound can generally be adjusted as needed. Or transparent or opaque or colored. Silicone potting compounds perform very well in shock resistance, electrical properties, water resistance, high and low temperature resistance, and anti-aging properties.
Two groups of silicone potting compounds are the most common, and such glues include both condensed and additive types. Generally, the condensation type has poor adhesion to the components and the potting cavity, and volatile non-molecular substances are generated during the curing process, and the shrinkage rate is more obvious after curing. Additive (also known as silicone gel) has very low shrinkage and no low molecular weight during curing. Can be heated quickly to cure.
Advantages: The silicone potting compound has a soft material after curing. It has two forms of solid silicone rubber products and silicone gel, which can eliminate most mechanical stress and provide shock absorption protection. It has stable physicochemical properties, good resistance to high and low temperature, and can work in the range of -50~200 °C for a long time. Excellent weather resistance, it can still play a good protection role for more than 20 years outdoors, and it is not easy to yellow. It has excellent electrical and insulating properties, effectively improves the insulation between internal components and lines after potting, and improves the stability of the use of electronic components. With the ability to repair, the sealed components can be quickly and easily removed for repair and replacement.
Disadvantages: The bonding performance is slightly worse.
Applications: Suitable for potting all kinds of work in harsh environments as well as high-end precision/sensitive electronic devices. Such as LED, display, photovoltaic materials, diodes, semiconductor devices, relays, sensors, automotive stabilizers, automotive ECUs, etc., mainly for insulation, moisture, dust, shock absorption.