PCB and DCB Stator Windings
A PCB stator is a stator whose windings are etched copper layers in a multilayer printed circuit board rather than wound wire. The conductors are planar, their geometry is fixed by the board artwork, and the board itself forms the structural stator.
A DCB stator — DCB here means direct copper bonded — carries the same planar conductor principle on a ceramic substrate, typically alumina or aluminium nitride, instead of an organic laminate, with thick copper layers bonded directly to the ceramic. The ceramic conducts heat far better than a resin board and tolerates higher temperature, allowing thicker copper and higher continuous current.
Both are the same underlying idea: planar, lithographically defined conductors replacing wound wire. What differs is the substrate, which lands each option in a different place on the trade-off between copper cross-section, thermal capability and cost — PCB is the lower-cost, thinner-copper route, DCB buys current-carrying capability and thermal headroom. Both constructions are also inherently coreless: there are no stator teeth in either one, so everything on the coreless stator page about removing iron applies here too. This page covers how the winding itself is made rather than why the iron is absent.
How a Planar Stator Is Built
A planar stator starts as a stack-up, the sequence of copper and insulating layers that make up the board's cross-section, with each copper layer etched into the coil pattern for one phase or phase group rather than wound as discrete turns. Layers are connected to each other through vias, plated holes that carry current from one copper layer to the next, which is how a planar winding builds up total turns without ever leaving the plane. The phase terminations, where each winding's ends connect to the drive electronics, are pads or connectors on the board edge or a dedicated layer, placed by the same artwork process as the conductors themselves. Because the board is rigid (PCB) or bonded to a rigid ceramic (DCB), it both carries the winding and forms the structural stator disc that the rest of the motor is built around.
Cross-section (simplified):
┌─────────────────────────┐ copper layer (phase A pattern)
│ insulating layer │
├─────────────────────────┤ copper layer (phase B pattern), via-connected to A
│ insulating layer │
├─────────────────────────┤ copper layer (phase C pattern), via-connected to B
└─────────────────────────┘
PCB vs DCB Substrate
| PCB (organic laminate) | DCB (ceramic substrate) | |
|---|---|---|
| Substrate material | Glass-reinforced epoxy laminate (e.g. FR-4) | Alumina (Al₂O₃) or aluminium nitride (AlN) ceramic |
| Thermal conductivity | ≈0.3 W/m·K | Alumina ≈24–28 W/m·K; AlN ≈150–180 W/m·K |
| Achievable copper thickness | Commonly 35–105 µm per layer; heavier copper is possible at added cost and process complexity | Commonly 200–600 µm bonded copper |
| Maximum operating temperature | ≈130–150 °C, limited by the laminate's glass transition temperature | Ceramic substrates are rated to roughly -55 to +300 °C; in a motor the practical ceiling is usually set by the winding insulation and bonding materials rather than the ceramic itself |
| Dielectric strength | ≈20 kV/mm | Alumina ≈20 kV/mm; AlN ≈15 kV/mm |
| Cost profile | Low; a mature, high-volume manufacturing process | Higher; a more specialised, lower-volume process |
| Typical use | Moderate current density, cost-sensitive or lower-power designs | Higher continuous current density, thermally demanding designs |
Sources: Rogers Corporation, "Direct Bond Copper"; Wikipedia, "FR-4".
What Planar Construction Gives You
Every unit comes off the same artwork, so conductor placement, and therefore the air gap it faces, is geometrically repeatable from one stator to the next in a way hand-wound coils are not. There are no end windings, the loops of wire wound coils need outside the active magnetic region just to get from one slot to the next, so a planar stator carries no copper mass that isn't doing useful work in the air gap. Exact, repeatable conductor placement also means very low and consistent torque ripple: cogging and ripple sources that come from winding-to-winding variation in a hand-wound stator are largely designed out at the artwork stage instead of showing up as manufacturing scatter. The construction is inherently thin in the axial direction, since the winding is a flat board rather than a wound coil with radial build. And because the conductor geometry is defined by artwork rather than by what a winding machine or a human hand can physically wind, trace width, spacing and layer count become design variables an engineer can optimise directly, rather than constraints a winding shop imposes on the design.
The Fill-Factor Constraint
The honest limitation of a planar stator is fill factor, the fraction of the available winding cross-section that is actually occupied by conductor rather than by insulation, clearance and manufacturing margin. Well-packed round or rectangular wound wire achieves a higher fill factor than an etched or bonded planar conductor typically can, because a wound coil can pack conductors against each other far more tightly than a lithographic process's design rules allow. Lower fill factor means fewer ampere-turns per unit area for a given current, which is the direct consequence of that lower copper density.
The practical result is that planar stators favour higher electrical frequency and speed over low-speed, high-current duty: a design that needs a large ampere-turn total from a fixed area is fighting the fill factor directly, while a design that reaches its power target through speed rather than sheer current is not. This is a large part of why DCB exists: pushing to thicker bonded copper is the direct way to claw back some of the ampere-turn budget that a thinner PCB layer gives up to fill factor, without abandoning the planar construction's other advantages.
AC Losses in Planar Conductors
Skin and proximity effect, the tendency of AC current to concentrate near a conductor's surface and to be pushed around further by the field of neighbouring conductors, apply to a planar trace exactly as they do to a round wire. A wide, thin trace in a changing magnetic field develops eddy currents across its width just as a wide wire strand would, and at the electrical frequencies a planar stator's speed range often reaches, this can become a significant fraction of total copper loss.
The usual mitigations are conductor segmentation, splitting a wide trace into several narrower parallel traces to reduce the eddy-current path each one supports, layer interleaving, arranging phase layers so opposing fields partially cancel, and trace width and spacing chosen deliberately as loss-reduction levers rather than left to whatever an autorouter or a simple sizing rule produces. Getting these right is a job for simulation rather than hand calculation, since the loss depends on the actual field distribution around each conductor in its real position within the stack-up, a level of geometric detail a closed-form formula doesn't capture.
Thermal Path
With no iron core and no end windings to conduct heat toward a housing, a planar stator's thermal path runs through the substrate itself, and from there into whatever the board is bonded or clamped to. An organic laminate is a thermal bottleneck in this path, since its low thermal conductivity means heat generated in the copper has a long, resistive route out. A ceramic substrate removes that bottleneck directly, which is the main reason DCB exists at all. In practice, the substrate choice usually decides a planar stator's continuous current rating well before the magnetics do — the winding could often carry more current electromagnetically than the thermal path can remove, which is the same thermal design question a sealed motor's encapsulated stator construction faces from the opposite direction: a potted or encapsulated planar stator adds another layer to that same heat-removal path, so the substrate and the encapsulation have to be chosen together.
Where Planar Stators Fit
Planar construction fits high-speed, axially compact drives well: robotics joints, aerospace and drone propulsion, and any application where unit-to-unit repeatability matters as much as raw output. It's a poor fit where the fill-factor constraint bites hardest: low-speed, high continuous-current duty on a tight budget, where a well-packed wound-wire stator still reaches a higher ampere-turn density for the same cross-section, at lower manufacturing cost, than a planar equivalent can match.
Related Terms
- Coreless axial flux motor: the ironless stator — planar stators are coreless; that article covers why the iron is gone, and its discussion of AC copper losses applies directly to planar traces too.
- Torque and power density — removing end windings removes non-active copper mass, a density argument the fill-factor constraint above directly counterweighs.
- Canned motor vs sealed motor — a planar stator suits both constructions, and the substrate choice interacts directly with the sealing and thermal path.
- Direct-drive motor — torque ripple matters most where there is no gearbox to attenuate it, which makes a planar stator's low, repeatable ripple particularly valuable in a direct-drive design.
- Configurator Guide: Stator properties — how turns, layers, copper thickness and trace width are actually set for a PCB stator design.