Potting means filling a housing around an assembled circuit board with a liquid resin that cures into a solid mass. Encapsulation is the same idea with the resin forming the outer body itself. Either way the board disappears into a block: water cannot reach it, vibration cannot flex it, and nobody — including you — can service it again.
That last clause is the entire decision. Potting solves environmental problems permanently and forecloses repair permanently, and teams that adopt it because a competitor did have usually not priced the second half of the trade.
What Potting Buys You
- Moisture and chemical ingress. Sealed at the component level, not just the enclosure seam — it survives immersion, condensation cycling, and washdown in ways a gasketed box does not.
- Vibration and shock. Leads, electrolytics, and connectors stop moving relative to the board, removing the dominant fatigue failure mode in vehicle and industrial equipment.
- Dielectric isolation. Filling air gaps raises breakdown voltage and shrinks creepage and clearance distances, a real space saving under the constraints in mains-powered product design.
- Tamper resistance. Reaching a potted board without destroying it is genuinely hard, a meaningful layer alongside secure boot and firmware encryption.
Choosing Between Epoxy, Urethane, and Silicone
Epoxy
The hardest and most chemically resistant of the three, typically 80 to 90 Shore D, with excellent adhesion and the best tamper resistance. It is also the least forgiving thermally: cured epoxy expands at 40 to 70 ppm per degree Celsius against roughly 17 for copper and 3 for silicon, and is stiff enough to push that mismatch into solder joints. Over repeated cycles it cracks ceramic capacitors and fractures at sharp corners. Epoxy suits rigid, chemically aggressive, or security-critical work over a narrow temperature range.
Polyurethane
The general-purpose default, from roughly 30 Shore A to 70 Shore D. Soft enough to absorb the expansion mismatch, so thermal cycling is far better than epoxy, and easier to remove for rework. Drawbacks: it reacts with water and foams if the board or compound is damp, and its upper limit is around 260°F. Most consumer and light industrial potting is urethane.
Silicone
The widest service range, roughly −65°F to 400°F, the lowest cure stress, and the softest options available, down to gels you can push a probe through. Right for wide-temperature outdoor equipment, LED drivers, and fragile assemblies. It costs two to four times urethane, adheres poorly without primer, and contaminates painting lines elsewhere in the building.
Thermal Expansion Is the Failure Mode That Catches People
Most potting failures are not moisture failures. They are stress failures that appear after a few hundred thermal cycles, and they are predictable from the data sheet.
Three numbers matter together: thermal expansion, glass transition temperature, and modulus. Below glass transition the compound is stiff and expands modestly; above it, expansion jumps two or three times while modulus collapses. If your operating range straddles that point, the assembly sees large cyclic strain. Pick a compound whose transition sits outside the window, or one soft enough that the mismatch does not matter.
Practical mitigations:
- Conformal coat the board first; the thin flexible layer decouples components from the rigid mass, as covered in conformal coating.
- Use a lower-modulus compound than the environment strictly demands.
- Keep resin thickness uniform — thick pockets cure hotter and shrink more.
- Radius internal corners, because cracks initiate at sharp geometry.
- Avoid potting tall electrolytics and crystals in rigid compounds.
Heat: Potting Can Help or Hurt
Unfilled resins conduct heat at about 0.2 W/m·K — better than air at 0.026, far worse than metal. Loading with alumina or boron nitride raises that to 0.8 to 3.0 W/m·K at the cost of density, viscosity, and abrasive wear on dispensing equipment.
The catch is that potting removes convection entirely. If a device relied on air movement over a hot regulator, encasing it may raise junction temperature rather than lower it, unless there is a conductive path into a metal wall or baseplate. Model that path first, using the framework in thermal management in electronic products — which overlaps with how the board is held in the first place, discussed in mounting a PCB in an enclosure.
The Process and What It Costs
Two-part compounds have a pot life of four minutes to several hours. Cure is ambient over 12 to 24 hours or oven-accelerated, typically 30 to 90 minutes at 175°F to 250°F. Deep pours generate an exotherm — fast epoxy can self-heat past 300°F and damage the board it is protecting — so thick sections go in stages. Trapped air is the other enemy: bubbles create voids that defeat the dielectric and thermal purpose, so compound is vacuum-degassed or dispensed by equipment that degasses inline.
Budget realistically:
- Compound: roughly $30 to $70 per gallon for urethane, $45 to $110 for epoxy, $120 to $400 for silicone and thermally filled grades — $0.40 to $4.00 of resin in a typical small assembly.
- Hand potting with cartridges and static mixers: under $3,000 of equipment, but 90 to 240 seconds of labor per unit and inconsistent results.
- Benchtop meter-mix dispense system: $18,000 to $45,000.
- Automated dispensing cell with vacuum and cure oven: $70,000 to $250,000.
- Potting fixtures and dams: $500 to $4,000 per variant.
The Repairability You Are Giving Up
A potted unit has no repair path. Some urethanes and silicones can be dug out with heat or solvent to recover an expensive component, but it takes an hour per unit and damages neighbors; epoxy is effectively permanent. Assume a field failure means replacing the whole assembly.
Warranty reserve must therefore cover full unit replacement rather than component repair, and the factory cannot rework a potted unit that fails final test — so anything potted before its last test becomes scrap. Test fully before the pour.
Before committing, ask whether the requirement is really this severe. A sealed enclosure with a proper gasket and a vent membrane reaches the ratings explained in IP ratings explained at far lower cost and keeps the unit serviceable, using the techniques in waterproof electronics design. Potting is the answer when the environment is brutal, vibration is constant, dielectric spacing has run out, or tamper resistance is a requirement.
Decide Before the Enclosure Is Tooled
Pour geometry, dam features, fill and vent ports, and the thermal path all have to be designed into the housing, and none can be added later. Projects House specifies encapsulation strategies and qualifies them with suppliers for US clients through a global engineering and manufacturing network. Send your board and environmental requirements through our contact form.