A standard is a set of tests, not a property of a shape. RoHS & REACH is one of the documents aluminium substrate epoxy heaters are built to; the sections below say what it fixes, what it does not, and what has to be named on the enquiry for the approval to be usable.
RoHS & REACH — Scope
Restriction of hazardous substances in the materials and the solder, and declaration of substances of very high concern. Required for anything sold into the EU.
What RoHS & REACH Does Not Cover
A compliance declaration, not a safety approval.
This is the division of labour to carry away from any heating standard: safety standards decide whether the part can hurt somebody, and say nothing about whether it holds a temperature, lasts five years or matches the last batch. Performance is a specification you write; safety is one the standard writes.
How a Made-to-Drawing Heater Is Certified
A construction is built and tested to a standard. The insulation system, the creepage and clearance distances, the earthing, the lead anchorage, the temperature under fault and the marking are what the test covers — and all of those are properties of the construction rather than of the outline it is die-cut to.
So a custom outline does not have a certificate of its own, and no supplier can honestly hand you one. What is available is the construction file: the standard the build is tested to, the materials list with their own ratings, and the test reports. That is what an approvals engineer needs, and it is what the end product's own certification is built on.
The practical consequence: name RoHS & REACH on the enquiry, not after approval. A construction chosen for cost and then asked to pass a standard afterwards usually has to be rebuilt, because the insulation thickness, the creepage distances and the lead anchorage are decided at design time and are not adjustable later.
From the capability table: UL 499, IEC/EN 60335, RoHS, REACH, CE, IATF 16949.
What an Aluminium Substrate Epoxy Heaters Is
The thinnest epoxy construction: a foil element potted onto thin aluminium, for bonding to a curved or awkward assembly that still needs a rigid backing.
A resistance wire or foil element vacuum potted in thermally conductive filled epoxy against an aluminium or steel plate. Rigid, flat, sealed, and thermally bonded to its own plate so the heat leaves the element through metal rather than through air.
The plate is the thermal path: the element is potted against it, so the metal spreads the heat before the load ever sees it. That is what buys uniformity, and it is also what makes the assembly slow — a bolted plate takes minutes to reach steady state where a film takes seconds.
| Element | resistance wire or foil, vacuum potted |
|---|---|
| Insulation system | thermally conductive filled epoxy |
| Total thickness | 2.5 mm to 6 mm |
| Maximum size, one piece | 250 x 400 mm |
| Continuous working temperature | 150 °C |
The continuous limit of 150 °C is set by thermally conductive filled epoxy. The element alloy would run far hotter; it is never the element that decides.
The Other Standards This Construction Is Built To
A heater is rarely governed by one document. This construction is also built and tested to:
Safety, materials, substances and quality system are four separate questions with four separate documents behind them. A part can satisfy all four and still be the wrong heater for the duty, which is what the rest of this page is about.
Control and Protection
This heater has no way of limiting its own temperature. Resistance heating draws roughly the same power whatever the temperature, so with the load removed, the fluid gone, the fan stopped or the sensor open circuit, the element keeps producing watts until something stops it.
The design must therefore contain a control device and, separately, a protective one: a controller with a sensor to hold the set point, and a bimetal thermostat or a one-shot thermal cutoff wired in series with the element to open the circuit if the loop ever fails. The two are not interchangeable — a controller that has lost its sensor cannot protect anything, which is exactly the fault the cutoff exists for.
The limit that matters is the epoxy's, at 150 °C, and it is reached at the element long before the plate face reads anything alarming. Put the limit device in the potting against the element, not on the outside of the plate.
Sensors can be built into the part: NTC thermistor, PT100 or PT1000 RTD, or a K-type thermocouple, fitted under the same insulation and tested with the heater as one assembly. A sensor laminated into the heater reads the heater; a sensor on the load reads the load. Both are legitimate, and the drawing has to say which is wanted.
Watt Density: the Two Figures
Watt density, not wattage, is what the construction is limited by. 0.4 W/cm² unbonded and 2.5 W/cm² bonded to metal are the limits for this build — so if the wattage is fixed by the duty, the area is what has to move.
Where the required power will not fit into the available area at the free-air figure, the answer is a better thermal path rather than a thinner margin: bond the whole face down, or add a spreader plate. On 150 cm² the difference is roughly 6 W against 375 W, which is usually the whole argument.
Leads and Terminations
Termination is specified on the drawing: lead length, gauge, insulation and the connector or tag at the end of it.
The lead exit is a thermal discontinuity as well as an electrical one. The joint between a fine element and a stranded lead is the hottest point of many heaters, so it is kept out of the highest watt density zone, strain relieved, and — where the exit sits in a hot area — insulated in PTFE rather than in silicone.
How to Specify One
This is a made-to-drawing part, so there is no catalogue number to quote. A quotation is built from the following, and the more of it that arrives with the enquiry the fewer rounds it takes:
- An outline drawing, or a sketch with dimensions: overall size, holes, cut-outs, radii and the lead exit position.
- The supply voltage, and whether it is AC or DC. The element is wound for one voltage; it is not a switchable range.
- The power required, or — better — the temperature to be reached and the mass or flow it has to be reached in. Given the second, the wattage can be calculated instead of guessed.
- What the heater is attached to, and how. This is what decides which watt density figure applies, and it is the question a quotation cannot proceed without.
- The ambient, and the lowest temperature the assembly must start from. A heater sized for a 20 °C start is undersized for a -30 °C one.
- Duty cycle: continuous, intermittent, or a warm-up to a deadline. Time to temperature is a specification, not a by-product.
- Sensor and protection: which sensor, where it goes, and which limit device is fitted in series with the element.
- The certification the end product is built to, named on the enquiry rather than after approval.
- Quantity and target price, because the construction that is right for fifty pieces is often not the one that is right for fifty thousand.
- The plate material, thickness and mounting hole pattern, and what the plate is bolted to.
Lead time: Samples 7-10 days from approved drawing; production 15-20 days.
Aluminium Substrate Epoxy Heaters — Capability Table
These are process limits for the construction, not the specification of one stocked item. Every line is what the factory can hold; what your part holds is fixed on your drawing.
| Parameter | Specification | Limit / note |
|---|---|---|
| Construction | Resistance wire or foil element potted in thermally conductive filled epoxy on a metal plate | Cured under vacuum so there are no voids in the heat path |
| Plate material | Aluminium 1050 or 3003, 1 mm to 3 mm | Aluminium for spreading, stainless where the chemistry demands it |
| Total thickness | 2.5 mm to 6 mm | Plate plus encapsulation |
| Maximum size, one piece | 250 x 400 mm | Larger plates are built as multiple circuits on one plate |
| Dimensional tolerance | u00b10.5 mm on the plate, u00b11 mm on the encapsulation | |
| Supply voltage | 12 V, 24 V, 110 V, 220 V | Wound to order |
| Resistance tolerance | u00b110% | At 20 u00b0C |
| Watt density | 0.4 W/cmu00b2 typical, 2.5 W/cmu00b2 maximum | Against a load in contact; free-standing operation runs far lower |
| Continuous working temperature | -40 u00b0C to +150 u00b0C | Set by the epoxy, not by the element |
| Dielectric strength | 2500 V AC, 1 minute | Element to plate |
| Insulation resistance | greater than 100 Mu03a9 at 500 V DC | Also after 48 hours humidity conditioning |
| Ingress protection | IP65 as standard, IP67 with a moulded lead entry | The encapsulation is the seal |
| Mounting | Tapped holes, clearance holes, studs or bonded | Machined into the plate before potting |
| Sensor options | NTC, PT100 or thermostat potted into the same plate | Reads the plate, which is what the load actually sees |
| Certifications available | UL 499, IEC/EN 60335, RoHS, REACH, CE, IATF 16949 | Construction level |
Capability figures are for resistance elements encapsulated in thermally conductive filled epoxy on a metal plate. The +150 °C continuous limit is a property of the encapsulant, and it is the lowest limit of any construction in this catalog — the element and the plate would both tolerate far more.
