Advantages and Disadvantages of Three Types of Encapsulating Adhesives: Silicone, Epoxy Resin, and PU(2)

What should be considered when selecting encapsulating materials?

1) Requirements for performance after encapsulation: operating temperature, temperature cycling, internal stress tolerance of components, outdoor use or indoor use, load conditions, requirements for flame retardancy and heat conduction, color requirements, etc.

2) Encapsulation Process: Manual or Automatic, Ambient or Heated, Full Cure Time, Pot Life, etc.

3) Cost: The density of encapsulating materials varies greatly, so we must consider the actual cost after encapsulation, rather than simply looking at the material‘s selling price.

The adhesives used for encapsulation can be classified by function as thermal conductive encapsulating adhesives, bonding encapsulating adhesives, and waterproof encapsulating adhesives; by material as polyurethane encapsulating adhesives, silicone encapsulating adhesives, and epoxy resin encapsulating adhesives. Both soft and hard adhesives can be used for encapsulation, waterproofing, and insulation. If high temperature resistance and heat dissipation are required, it is recommended to use silicone soft adhesive. If low temperature resistance is required, it is recommended to use polyurethane soft adhesive. If no specific requirements are required, epoxy hard adhesive is recommended, as it cures faster than silicone.

The application range of epoxy encapsulating adhesive is wide, and the technical requirements are diverse. There are also many varieties of epoxy encapsulating adhesive. It can be divided into two categories according to the curing conditions: room temperature curing and heat curing. According to the type, it can be divided into two categories: two-component and one-component. Generally, the room temperature curing epoxy encapsulating adhesive is a two-component adhesive, which has the advantage of curing without heating after encapsulation, and the equipment requirements are not high. It is convenient to use, but the disadvantage is that the working viscosity of the liquid mixture is large, the penetration is poor, the service life is short, and the heat resistance and electrical properties of the cured material are not high. It is generally used for encapsulation of low-pressure electronic devices or occasions where heat curing is not suitable.

Encapsulation Process

The quality of encapsulated products is mainly related to the product design, component selection, assembly, and the encapsulating material used, and the encapsulating process is also an important factor. There are two types of encapsulating processes: normal state and vacuum.

Epoxy resin-amine curing agent at room temperature, is generally used for low-pressure electrical appliances, and is often used for normal curing.

Epoxy-acid annealed curing encapsulating material is generally used for high-pressure electronic component encapsulation, and the vacuum encapsulation process is often used.

There are currently two common methods of vacuum encapsulation, manual and mechanical, and mechanical vacuum encapsulation can be divided into two cases: A and B component mixture and degassing before encapsulation, and mixture and encapsulation after separate degassing. There are three ways to operate:

The first type is a one-component electronic potting compound that can be used directly and can be applied with a syringe or directly poured.

The second type is a two-component condensation-type electronic potting compound with a curing agent of 2-3% or other ratios. Mix - vacuum degassing - pouring.

The third type is an addition-type electronic potting compound with a curing agent of 1:1 or 10:1.

The process flow is as follows:

1. Hand Vacuum Encapsulation Process

2. Mechanical Vacuum Encapsulation Process

1) Measurement: Accurately measure the A and B components (curing agent).

2) Mixing: Mix the components;

3) Defoaming: Natural defoaming and vacuum defoaming;

4) Pouring: The resin should be poured within the operating time otherwise it will affect the leveling.

5) Curing: Cure at room temperature or heated, the finished product after filling is placed at room temperature for curing, the initial curing can be entered into the next process, the complete curing needs 8-24 hours. In summer, the curing will be faster due to high temperature; in winter, the curing will be slower due to low temperature.

3 Precautions

a. The surface of the sealed product must be cleaned before sealing!

b. Note that before weighing, stir A and B components thoroughly to ensure that the pigments (or fillers) at the bottom of the container are dispersed evenly in the resin.

c. The primer cannot be mixed directly with the adhesive. Use the primer first, and then apply the adhesive after the primer has dried.

d. The curing speed of the adhesive is related to the temperature. The curing process will be slower at lower temperatures.

In contrast, mechanical vacuum encapsulation requires a large investment in equipment and high maintenance costs, but it clearly offers better consistency and reliability in product quality than manual vacuum encapsulation. In any case, the process conditions should be strictly followed to obtain satisfactory products.