The cure reaction is exothermic: it releases heat as it proceeds. In a thin film that heat escapes to the surroundings as fast as it appears, but in a deep pour the centre is insulated by the resin around it, so temperature climbs. Higher temperature then accelerates the reaction, which releases heat faster still.

In a large mass that feedback can run away, reaching temperatures that scorch or crack the resin, damage components, distort the housing and in extreme cases smoke.

The controls are pour depth limits, casting in layers with time to cool between them, low-exotherm grades formulated for mass casting, and heavily filled compounds where mineral filler both dilutes the reactive mass and conducts heat away.

When the encapsulated parts and the resin expand at different rates. A cured epoxy is stiff, and it grips everything it surrounds; if the assembly is then heated or cooled, differing coefficients of thermal expansion generate real force at every interface.

That force is carried into fine wires, solder joints, component leads and ceramic bodies, and thermal cycling can fatigue them until something cracks.

Toughened and semi-flexible epoxy grades exist to soften this, and filler selection is used to bring the expansion coefficient closer to that of the components. Where the parts are genuinely delicate or the cycling severe, a softer chemistry is often the better answer than a modified epoxy.

Very precisely, because epoxy cures by stoichiometric reaction rather than by drying. Resin and hardener react in fixed molecular proportions, and material in excess of that ratio has nothing to react with.

An off-ratio mix does not simply cure a bit softer. It leaves unreacted material in the matrix, which lowers glass transition temperature, reduces chemical and moisture resistance, and can leave a permanently tacky or soft region.

Weighing rather than eyeballing, mixing the full quantity supplied in pre-measured kits, and scraping the sides and base of the mixing vessel all matter. Unmixed material clinging to a container wall is a frequent cause of a soft patch in an otherwise sound casting.

Mineral fillers such as alumina, boron nitride or silica are loaded into the resin at high volume, forming conductive paths through what is otherwise an insulating polymer, so heat from a component can reach the housing instead of accumulating.

The costs are viscosity and abrasion. Heavily filled compounds are thick and flow reluctantly into fine gaps, often needing vacuum assistance, and the filler is abrasive to dispensing equipment.

Filler also settles. A drum standing for a period will stratify, so thorough remixing before use is essential; drawing from the top of a settled container gives a resin-rich mix with much of the conductivity left at the bottom.

Rarely, and strong adhesion without primer is one of its main advantages. Epoxy bonds well to metals, most engineering plastics, glass, ceramics and circuit board laminates as it cures, which is why it seals so effectively against moisture ingress at the housing wall.

The exceptions are the usual low-surface-energy plastics, where an adhesion promoter is needed as it would be for any adhesive.

Cleanliness governs the result more than chemistry does. Mould release on a plastic enclosure, flux residue on a board or oil on a metal can all leave the resin bonded to a film rather than the part, and that shows up later as moisture tracking along the interface.

Realistically, no. Cured epoxy is chemically resistant and mechanically hard, and it is bonded firmly to everything inside, which is exactly what it was chosen to do.

Removal methods are destructive: mechanical breaking out, prolonged soaking in aggressive strippers, or thermal decomposition, all of which risk the components far more than the resin.

This has to be a design decision rather than a discovery. Where field repair or component recovery is required, either a softer removable chemistry is specified, or serviceable parts are kept outside the potted volume. Choosing epoxy is choosing a sealed unit.

Pot life is how long the mixed material stays workable in the container; cure time is how long the poured material takes to reach its properties. They are not proportional, and confusing them causes real problems on the bench.

Pot life shortens dramatically with the mass mixed, because a larger batch retains its own reaction heat. The same compound that gives twenty minutes in a small cup may thicken in five in a large one.

Ambient temperature moves both, and the practical response is to mix quantities matched to what can be poured comfortably, in a shallow vessel rather than a deep one, and to allow the manufacturer’s full cure schedule before the unit is handled or tested.