"Potting adhesives are a wide range of names, originally mainly used for bonding, sealing, potting and coating protection of electronic components, currently we mention them, mainly because potting adhesives, especially silicone, are more and more in the application of power battery systems."

Potting adhesive materials can be divided into:

Epoxy resin potting adhesive: one-component epoxy resin potting adhesive, two-component epoxy resin potting adhesive;

Silicone rubber potting adhesive: room temperature vulcanized silicone rubber, two-component plus formed silicone rubber potting adhesive, two-component condensed silicone rubber potting adhesive;

Polyurethane potting adhesive: two-component polyurethane potting adhesive.

 

 

01 Epoxy resin

Advantages: Epoxy resin sealant is mostly hard, and there are few modified epoxy resins that are slightly soft. The main advantages of this material are good adhesion to the material, good insulation, and the cured material has good acid and alkali resistance. Epoxy resin generally has a temperature resistance of 100 ℃. This material can be used as a transparent material with good transparency. The price is relatively cheap.

Disadvantages: Weak resistance to cold and hot changes, prone to cracking after cold and hot impacts, causing water vapor to seep into electronic components through cracks and poor moisture resistance; After solidification, the colloid has higher hardness and brittleness, and higher mechanical stress can easily strain electronic components. Epoxy resin cannot be opened due to its high hardness after sealing and curing, so this product is a "lifetime" product and cannot achieve component replacement. The weather resistance of transparent epoxy resin materials is generally poor, and they are prone to yellowing under light or high temperature conditions.

Application: Generally used for LED, transformer, regulator, industrial electronics, relays, controllers, power modules and other non-precision electronic devices.

02 Polyurethane

Polyurethane potting material is an ideal potting material with high insulation resistance and bonding strength. Polyurethane potting material is used for the preparation of sealing castings, for electronic products such as circuit boards, electronic components, plug sockets potting, can also be used as adhesives and coatings.

Advantages: polyurethane potting adhesive has excellent low temperature resistance, the material is slightly soft, and the general potting material has good adhesion, and the bond strength is between epoxy resin and silicone. With good waterproof, moisture-proof, insulation.

Disadvantages: poor high temperature resistance and easy to bubble, must use vacuum defoaming; After curing, the surface of the colloid is not smooth and the toughness is poor, the anti-aging ability, seismic resistance and ultraviolet light are weak, and the colloid is easy to change color.

Application: It is generally used in the potting of electronic components with low calorific value. Transformers, choke coils, converters, capacitors, coils, inductors, rheostat, linear engines, fixed rotors, circuit boards, leds, pumps, etc.

03 Organic silicone rubber

Silicone rubber can maintain elasticity in a wide temperature range for a long time, no heat absorption, no heat release when vulcanized, and has excellent electrical properties and chemical stability, is the first choice for electronic and electrical assembly parts.

Room temperature vulcanization (RTV) silicone rubber is divided into condensation type and addition molding according to the vulcanization mechanism, and is divided into one component type and two component type according to the packaging form. Condensed silicone rubber usually emits low molecular matter when vulcanized. Therefore, it should be placed for a period of time after potting, and can be used until the low molecular matter is volatilized as much as possible. RTV silicone rubber has excellent electrical strength and chemical stability, weatherproof, waterproof, moisture-proof, shock-proof, non-corrosion, non-toxic, tasteless, easy to perfusion, deep vulcanization, low shrinkage, simple operation, can be used at -65 ~ 200 ℃ for a long time; However, in the process of use, care should be taken not to contact with N, P and metal organic salts, otherwise the rubber can not be vulcanized.

Advantages: silicone potting adhesive is soft after curing, there are two forms of solid rubber and silicon gel, which can eliminate most of the mechanical stress and play a damping protection effect. The physical and chemical properties are stable, with good high and low temperature resistance, and can work in the range of -50~200℃ for a long time. Excellent weather resistance, outdoor for more than 20 years can still play a better protective effect, and not easy to yellow. It has excellent electrical performance and insulation ability, and effectively improves the insulation between internal components and lines after potting, and improves the use stability of electronic components. With the ability to repair, it can quickly and easily take out the sealed components for repair and replacement.

Disadvantages: slightly poor bonding properties.

Application: Suitable for filling a variety of harsh environment and high-end precision/sensitive electronic devices. Such as LED, display, photovoltaic materials, diodes, semiconductor devices, relays, sensors, automotive stabilizer HIV, car computer ECU, etc., mainly plays the role of insulation, moisture, dust and shock absorption.

With the development of electronic technology, because of its many excellent properties, silicone rubber will undoubtedly become the best potting material for sensitive circuits and electronic devices.

 

Longitudinal performance comparison

 

	Epoxy resin	Polyurethane	Organosilicon
Uncured characteristic
Price of materials	Intermediate	Low to medium	High
How easy it is to handle	Easy	Easy	As easy as pie
Sensitivity to moisture when not cured	Low to medium	High	Low
Curing rate	Slow to fast	Slow to fast	Slow to fast
Temperature rise	Small to high	Intermediate	Small
Contractility	Small to high	Small to medium	Small
Properties after curing
Hardness (rigidity)	Medium to hard	Soft to medium	Soft
Stickiness	Superb	As good as gold	Good
Chemical resistant substance	Superb	Normal	Poor
Moisture resistance	Superb	Fine	fine
Expansion rate	Small to medium	Medium to large	Big
Tensile strength	Medium to high	Intermediate	Low
Shear strength	Medium to high	Intermediate	Low
Ductility	Low	Medium to high	High
Element stress	The least desirable	Fine	Superb
Thermal shock, thermal cycling performance	Good enough to be good	Fine	Fine
High temperature performance	Fine	Poor	Superb
Electrical insulation property	Superb	Good	Superb

 

Cost

Silicone Resin > Epoxy Resin > Polyurethane

The cost of the condensed type in the silicone resin is close to that of the epoxy resin, and the modified epoxy resin is also close to PU.

Manufacturability

Epoxy Resin > Silicone Resin > Polyurethane

PU because of its hydrophilicity, there must be vacuum drying to get a better curing material, such as the cost of vacuum and drying is too high, so although the hot sol is heated to dissolve and cast, but overall its operability is much simpler than PU.

Electrical performance

Epoxy resin > Silicone Resin > Polyurethane

The addition of silicone or paraffin wax and other types of hot sol, some electrical properties are even higher than epoxy, such as surface resistivity.

Heat resistance

Silicone Resin > Epoxy Resin > Polyurethane

The heat resistance of cheap PU is not much better than that of hot sol.

Cold tolerance

Silicone Resin > Polyurethane > Epoxy resin

The low temperature characteristics of many hot sols are actually very good, so in many cases, epoxy is to be ranked last.