I. Introduction

Encapsulating sealants are used for bonding, sealing, potting, and coating protection of electronic components. Before curing, they are in liquid form and exhibit fluidity. The viscosity of the sealant varies depending on the material, performance requirements, and manufacturing process of the product.

Encapsulation refers to the process of injecting a liquid composite material—either mechanically or manually—into devices containing electronic components and circuitry, where it cures under ambient or heated conditions to form a high-performance thermosetting polymeric insulating material.

Its functions are: to enhance the overall integrity of electronic devices and improve their resistance to external impacts and vibrations; to increase insulation between internal components and circuits, thereby facilitating device miniaturization and weight reduction; and to prevent direct exposure of components and circuits, thus improving the device's water- and moisture-proof performance.

II. Characteristics

1. Low viscosity and excellent fluidity, making it suitable for molding complex electronic components and capable of being poured into even the tiniest details.

2. After curing, it forms a soft, rubber-like material with excellent impact resistance.

3. Excellent heat resistance, moisture resistance, and cold resistance—once applied, it can extend the lifespan of electronic components.

4. Addition-type, which can be cured at room temperature as well as with heating.

5. It offers excellent moisture and water resistance.

6. It boasts excellent electrical insulation performance and resistance to high and low temperatures (-50℃ to 250℃), with a flame-retardant rating reaching UL 94V-0.

7. After mixing the two components, the mixture does not gel rapidly, thus providing a longer working time. Once heated, however, it cures very quickly, and the curing time can be freely controlled.

8. After being cracked by external forces, the gel can automatically heal itself, continuing to provide waterproof and moisture-proof protection without affecting its performance.

9. Safe and environmentally friendly, compliant with the EU RoHS specified standards.

III. Classification

There are many types of electronic potting compounds. Classified by material type, the three most commonly used and widely adopted are epoxy resin potting compounds, silicone resin potting compounds, and polyurethane potting compounds. Each of these three material-based potting compounds can further be subdivided into hundreds of different product varieties.

1. Epoxy resin potting compound

(1) Definition: Epoxy resin potting compound that can be cured at room temperature or with heating. It has passed SGS testing and meets the EU RoHS standards. The cured product exhibits high hardness, a smooth surface, and excellent gloss. It offers features such as fixation, insulation, waterproofing, oil resistance, dustproofing, anti-theft sealing, corrosion resistance, aging resistance, and resistance to thermal and cold shocks.

(2) Classification: Single-component epoxy potting compounds and two-component epoxy potting compounds;

(3) Performance characteristics: After curing, most epoxy resin adhesives are rigid, though a small portion remain flexible. The greatest advantage of epoxy resin adhesives is their excellent bonding strength to rigid materials. Once encapsulated, they cannot be reopened; they exhibit high hardness and outstanding insulating properties. Typically, their temperature resistance is around 100°C. For those cured at elevated temperatures, the temperature resistance can reach approximately 150°C. There are also specialized grades with temperature resistance exceeding 300°C; however, these grades have poor repairability and come with a very high price tag, making large-scale production generally impractical.

(4) Scope of Application: Suitable for potting of small- and medium-sized electronic components, such as automotive and motorcycle igniters, LED driver power supplies, sensors, toroidal transformers, capacitors, triggers, waterproof LED lights, and for the secure sealing, insulation, and moisture (water)-proof encapsulation of circuit boards.

2. Silicone resin potting compound

(1) Definition: Silicone resin potting compounds refer to a class of electronic potting compounds made from silicone rubber. Generally, silicone potting compounds are soft and elastic. There are many different types of silicone potting compounds, and these various types exhibit significant differences in terms of temperature resistance, waterproof performance, insulation properties, optical performance, adhesion to different materials, and hardness/softness.

(2) Classification: Single-component silicone potting compounds and two-component silicone potting compounds (addition-type and condensation-type);

(3) Performance characteristics: After curing, these materials are mostly soft and have poor adhesion. The advantage of silicone resin potting compounds is their excellent resistance to both high and low temperatures— they can be used continuously at temperatures up to 250°C. Heat-curing types exhibit even better temperature resistance. Their insulation performance is superior to that of epoxy resins, withstanding voltages above 10,000 V. They also feature a moderate price and good repairability.

(4) Scope of Application: Used for coating, potting, and encapsulation protection against water, moisture, and gaseous contamination in precision electronic components, solar energy devices, backlight modules, and electrical appliance assemblies.

3. Polyurethane potting compound

(1) Definition: Polyurethane potting compound, also known as PU potting compound, is typically produced through step-growth polymerization by reacting polyols—such as polyesters, polyethers, and polydiene oligomers—with diisocyanates, using diols or diamines as chain extenders.

(2) Classification: Two-component polyurethane potting compound;

(3) Characteristics: low hardness, moderate strength, good elasticity, water resistance, mold resistance, shock resistance, transparency, excellent electrical insulation and flame retardancy, non-corrosive to electronic components, and exhibits good adhesion to metals such as steel, aluminum, copper, and tin, as well as materials like rubber, plastics, and wood. Encapsulating materials can protect installed and properly adjusted electronic components and circuits from the effects of vibration, corrosion, moisture, and dust.

(4) Scope of Application: Suitable for sealing various electronic components and microcomputer control boards, such as fuzzy controllers for washing machines, pulse igniters for gas water heaters, induction sanitary appliance controllers, and electric bicycle drive controllers, among others.

4. Hot-melt potting compound

(1) Definition: Hot glue (English name: Hot Glue) is a plastic adhesive whose physical state changes with temperature within a certain range, while its chemical properties remain unchanged. It is non-toxic and odorless, making it an environmentally friendly chemical product. Due to its solid nature, which facilitates packaging, transportation, and storage; its solvent-free, pollution-free, and non-toxic characteristics; as well as its simple production process, high added value, strong bonding strength, and fast curing speed, hot glue has gained widespread popularity.

(2) Classification: EVA hot melt adhesive;

(3) Characteristics: Features rapid adhesion, high strength, excellent aging resistance, non-toxicity, good thermal stability, and tough adhesive film.

(4) Scope of application: Primarily used in the production of garments, shoes, and hats.

5. UV encapsulating adhesive

Also known as light-curing potting compounds, these materials feature rapid curing compared to traditional potting compounds, significantly boosting production efficiency. However, due to the relatively high cost of light-curing resins and certain performance limitations—such as inferior adhesion, yellowing resistance, and high-temperature durability—UV potting compounds have not yet achieved large-scale production, and their application fields remain relatively narrow. Nevertheless, overall, from the perspective of the UV industry, the potting compound segment represents a promising next growth target for the UV sector.

4. Instructions for Use

Electronic potting compounds are divided into manual pouring and machine pouring. The 1:1 addition-type ones are poured by machines.

There are three operating methods.

Type 1: Single-component electronic potting compound—ready to use, applicable either by dispensing with a gun or by direct pouring.

The second type: two-component condensation-type electronic potting compound, with a curing agent content of 2%-3%. Mix → vacuum degassing → potting.

Third type: Addition-curing electronic potting compound, with a curing agent ratio of 1:1 or 10:1.

Operating steps:

1. Measurement: Accurately weigh Component A and Component B (the curing agent).

2. Mixing: Add Component B to the container containing Component A and mix thoroughly.

3. Pouring: Quickly pour the thoroughly mixed adhesive into the product that needs to be encapsulated.

4. Curing: After potting, the molded parts should be allowed to cure at room temperature. Once initial curing is complete, they can proceed to the next process step; full curing takes 8 to 24 hours. In summer, when temperatures are higher, curing will be faster; in winter, when temperatures are lower, curing will be slower.

V. Precautions

1. The products to be encapsulated must be kept dry and clean.

2. Before use, first check Agent A for any sedimentation and thoroughly stir it until evenly mixed.

3. Take the ingredients according to the specified ratio and ensure accurate weighing. Please remember that the ratio refers to weight rather than volume. After mixing agents A and B, stir thoroughly until completely homogeneous to prevent incomplete curing.

4. After thorough mixing, please proceed with dispensing the adhesive promptly and try to use up the mixed adhesive within its usable time limit.

5. After injection, the adhesive will gradually seep into the gaps of the product; if necessary, please perform a second injection of adhesive.

6. During the curing process, please keep the environment clean to prevent impurities or dust from falling onto the surface of the uncured adhesive.

7. After mixing, this product will gradually begin to cure, its viscosity will steadily increase, and it will release some heat in the process.

8. The more adhesive is mixed together, the faster the reaction will be, and the faster the curing process will proceed—potentially accompanied by the release of significant heat. Please pay attention to controlling the amount of adhesive you mix at one time, as the accelerated reaction will also shorten the usable time. It’s best to use the mixed adhesive as quickly as possible.

Working time refers to the duration, under conditions of 25℃, during which the viscosity of a 100g mixed adhesive increases by a factor of two. This is not the same as the open time—after the open time has elapsed, the adhesive must no longer be used under any circumstances.

9. A very small number of people may experience mild skin allergies and slight itching or pain after prolonged contact with the adhesive liquid. It is recommended to wear protective gloves when using the product. If it gets on your skin, remove it promptly with acetone or alcohol, then thoroughly clean the area with a detergent.

10. Before using a large quantity, please first test a small amount to familiarize yourself with the product’s usage techniques and avoid mistakes.

It is classified as a non-hazardous material and can be transported as a general chemical.

VI. How to Choose

1. Performance requirements after potting: operating temperature, conditions of alternating hot and cold cycles, stress levels endured by components, whether the application is indoors or outdoors, load-bearing conditions, whether flame retardancy and thermal conductivity are required, color requirements, etc.;

2. Potting process: manual or automatic, at room temperature or heated; total curing time, gelation time of the adhesive after mixing, etc.;

3. Cost: The specific gravities of potting materials vary significantly. We must consider the actual cost after potting, rather than simply looking at the material’s listed price.