Cold plates

Definition (what it is)

A cold plate is a liquid-cooled heat exchanger: a thermally conductive metal plate with internal flow passages (channels, fins, or embedded tubes) through which a coolant circulates to remove heat from components mounted to its surface. Heat flows by conduction from the device into the plate and by convection from the plate into the coolant, which carries the heat to a remote heat rejection element (radiator, chiller, or heat pump).

Function and purpose (how it works)

Provides high heat removal in compact spaces where air cooling is insufficient, maintaining component temperatures within specified limits.
Spreads and equalizes heat under the mounting surface for temperature uniformity and hotspot control.
Operates in a closed-loop thermal circuit with pump, reservoir, valves, sensors, and a downstream heat exchanger.
Enables higher power density, improved reliability, and reduced acoustic noise compared with large forced-air heatsinks.

Key technical characteristics

Thermal path: Smooth, flat mounting faces; use of high-conductivity substrates (aluminum, copper); optimized channel-to-surface proximity; appropriate thermal interface materials (TIMs) and clamping pressure to minimize contact resistance.
Internal flow design: Serpentine, parallel, manifolded, pin-fin, plate-fin, or microchannel passages tailored to balance heat transfer coefficient, pressure drop, and flow maldistribution. Features may be added to mitigate hotspots and facilitate air removal.
Heat-flux capability: Standard designs commonly support several to tens of W/cm²; engineered pin-fin or microchannel plates can exceed 100 W/cm², with specialized designs reaching roughly 50–300 W/cm² depending on coolant, materials, and allowable pressure drop.
Structural integrity: Leak-tight construction with brazed, welded, or diffusion-bonded joints; designed for pressure cycles, vibration, and thermal expansion. May include ports, seals, bleed screws, and, in some applications, pressure relief features.
Electrical isolation: Options include anodized surfaces, dielectric coatings or films, polymer housings, or ceramic inserts to provide creepage/clearance and isolation for high-voltage components while maintaining thermal performance.
Cleanliness and filtration: Fine passages (especially microchannels) require low particulate levels and compatible coolants to prevent fouling or blockage.

Coolants and compatibility

Common coolants: Water-glycol mixtures, deionized water, dielectric oils (PAO, silicone), and engineered fluorinated dielectrics. Selection depends on electrical safety, temperature range, materials compatibility, and environmental constraints.
Chemistry control: Corrosion inhibitors, biocides, and pH control are used to protect mixed-metal systems. Designs consider galvanic coupling (e.g., copper in aluminum plates), elastomer seal compatibility, and long-term stability.
Operating range: Freeze/boil protection, cavitation avoidance, venting/degassing provisions, and allowance for coolant property changes over temperature.

Common cold plate architectures

Machined plate with a sealed cover (vacuum-brazed, laser/TIG welded, or diffusion bonded).
Extruded profiles with integrated channels and sealed end caps.
Tube-in-plate designs with embedded copper or stainless tubes.
Plate-fin or pin-fin cores (brazed) to increase surface area and turbulence.
Stacked/etched plates joined by diffusion bonding for microchannel and manifolded flow.
Additive manufactured plates with conformal, topology-optimized channels and localized high-flux features.
Single- or double-sided cooling surfaces for modules requiring two-sided heat removal.

Materials and manufacturing

Materials: Aluminum alloys (lightweight, cost-effective, good conductivity), copper (higher conductivity for hotspots, heavier), stainless steel or nickel-plated substrates (chemical compatibility, lower conductivity), and carbon/graphite layers for heat spreading. Dielectric coatings or plastics may be used for isolation.
Processes: CNC machining, extrusion, vacuum brazing, diffusion bonding, friction stir welding, laser welding, tube swaging/bonding, stamping and bonding for high volume, and additive manufacturing for complex geometries.

Integration, monitoring, and control

Mechanical integration: Mounting bosses and patterns matched to device footprints; manifolds for series/parallel distribution in multi-plate assemblies; quick-disconnects for service.
Sensing and diagnostics: Embedded temperature sensors, flow/pressure sensors, and bleed/vent features to aid filling and purge air.
System interfaces: Designed to integrate with pumps, valves, radiators/chillers, heat pumps, and controls for setpoint management and fault detection.

Performance metrics (typical)

Thermal resistance from device to coolant (K/W) or heat flux capacity (W/cm²).
Coolant flow rate and pressure drop across the plate (kPa).
Surface flatness/planarity and temperature uniformity (ΔT) across the mounting area.
Approach temperature to the coolant and allowable junction/case temperature limits.

Applications and relevance

Power electronics: Inverters, rectifiers, DC/DC converters, RF amplifiers, and high-density power supplies.
Computing and data centers: CPUs, GPUs, accelerators, and high-performance servers (direct-to-chip liquid cooling).
Batteries and energy systems: EV battery modules and packs (cold plates/rails), stationary storage, fuel cell stacks.
Motors and drives: Traction e-axles, industrial drives, and servo systems.
Photonics and medical: Laser diode stacks, imaging systems, MRI gradient amplifiers.
Aerospace, defense, test, and industrial equipment requiring compact, quiet, and reliable high heat-flux cooling.
In modern EVs, cold plates are central to battery thermal management (uniform temperature, fast charging, safety) and cooling of inverters, onboard chargers, and e-motors, improving efficiency, range, and durability, and enabling higher power density (especially with SiC electronics).

Synonyms and related terms

Synonyms: Liquid cold plate, cooling plate, liquid-cooled plate, chill plate, cold rail (battery cooling), baseplate cooler, cold block.
Related: Direct liquid cooling (DLC), microchannel heat sink, heat spreader, heatsink, heat pipe, vapor chamber, immersion cooling.

Design considerations and limitations

Trade-offs: Higher heat transfer often increases pressure drop and pump power; microchannels improve coefficients but are more clogging-prone and harder to clean.
Reliability: Ensure leak integrity, joint quality, and resistance to thermal cycling and vibration; specify cleanliness and filtration to protect fine passages.
Interfaces: TIM selection (grease, pads, gap fillers) and controlled clamping torque to minimize contact resistance without warping devices; manage TIM pump-out and aging.
Compatibility and safety: Corrosion control for mixed metals, elastomer/coolant compatibility, proper electrical isolation and creepage/clearance for high voltage, and mitigation of freezing/boiling and cavitation.
Environmental and regulatory: Coolant selection considering toxicity, flammability, and potential restrictions on certain dielectric fluids; provision for end-of-life handling and serviceability.