WHAT IS ENCAPSULATION

ENCAPSULATION

Encapsulation or potting of an electronic component or subassembly is utilized to promote ruggedness, resist harsh environments, provide electrical isolation, and promote improved heat transfer for cooling of the encapsulated components. Encapsulation is also used to seal an assembly to protect proprietary design details from the curious.

A variety of material properties must be considered when selecting an encapsulant. Sometimes the requirements are inconsistent with the range of properties offered by any one material.Of interest are the ability of the material to flow freely and not capture or entrain air bubbles; be lightweight; offer acceptable electrical, thermal, and chemical properties; and resist cutting and abrasion after cure. During cure the material should not produce excessive temperatures or excessive stresses on the encapsulated parts. After cure, the material should not absorb moisture, not produce excessive forces during temperature cycles, be stiff enough to support components and connections, and be able to be removed for purposes of repair.

Some properties of the materials may vary during cure and for some duration following cure. An example would be dielectric strength which may not stabilize until several days after cure.

At least three primary groups of material formulations are used for encapsulation:

Epoxy-Resin-Based Materials.

These materials may be formulated for strength and rigidity. The addition of glass microspheres would reduce density, and addition of metal or other powders will increase thermal and electrical conductivity. Epoxy resins are usually two-part mixtures and require strict control of the mixing, pouring, and curing processes.

Silicon-Based Materials.

These materials are known for having an extended temperature range over which they do not degrade. They tend to remain flexible and are resistant to water. They are either one- or two-part formulations. Some formulations generate acetic acid during cure and may cause corrosion of parts and conductors. Cure time is a function of the thickness and mass of the encapsulant and may require more than one day to achieve full cure.

Polyurethane-Based Materials.

These materials generally consist of a catalyst and resin and require mixing prior to pouring. They tend to remain flexible over a useful temperature range and after cure are of a rubberlike consistency; however, they have less tendency to adhere to components, wires entering the potted volume, and potting box surfaces than an epoxy or silicone encapsulant.

● Epoxy polymers are used to provide low-cost, high-performance reliability without hermeticity to provide environmental protection for bare circuit chips when used in chip-on-board (COB), ball grid array (BGA), multichip module (MCM), and chip scale packaging (CSP) assemblies.

Data describing the properties of encapsulants may be found on manufacturers’ data sheets; however, this information may be incomplete and sometimes does not relate physical properties to the method of cure and the material thickness. It is often necessary to consult with the technical support personnel of the manufacturer and to perform testing to determine suitability for the intended design goals.

_Thank you_

...Fiza Engineer...