EV Battery Cooling Plates: Design and Manufacturing
Short answer: An EV battery cooling plate is a sealed aluminum cold plate, typically 3003, 3005 or 6063 alloy, with internal channels sized for 2-8 L/min of coolant flow and a flatness tolerance of 0.05-0.2 mm across the cell contact face. Manufacturing routes are extruded-and-welded, stamped-and-bonded, or CNC-machined from plate. BQUQ produces these in one ISO9001 Dongguan factory across four production lines, holding ±0.005 mm on CNC features, quoting in 12 working hours, with flexible MOQ for prototype and pilot builds.
Battery packs live or die by temperature uniformity. A cell running 5 °C hotter than its neighbour ages measurably faster, and a pack that drifts 15 °C across its length will hit its end-of-life capacity warranty years early. The cooling plate is the component that decides whether that happens. It is also one of the hardest parts in the pack to manufacture well, because it must be simultaneously thin, flat, leak-tight, electrically isolated, and cheap enough to build in volumes of tens of thousands.
This article covers the design decisions that matter and how each one maps to a manufacturing process.
What does an EV battery cooling plate actually do?
A cooling plate sits under, between, or wrapped around prismatic, pouch, or cylindrical cells and removes heat through a flowing coolant — usually a 50/50 water-glycol mix, sometimes a dielectric fluid for immersion systems. Three functions must be satisfied at once:
Heat removal rate
Peak cell heat generation in a fast-charging pack is roughly 5-30 W per cell depending on chemistry and C-rate. A cooling plate must pull that away without letting the cell surface exceed about 45-55 °C. That sets the required coolant flow, channel cross-section, and wall thickness.
Temperature uniformity
This is usually the tighter constraint. A well-designed plate holds cell-to-cell delta-T under 3-5 °C. Poor channel routing creates hot spots at the inlet end and cold zones at the outlet, so serpentine or parallel-channel layouts must be balanced hydraulically.
Structural and sealing integrity
The plate is a pressure vessel, albeit a low-pressure one. It must survive burst testing, thermal cycling from -40 °C to +85 °C, vibration, and the mechanical load of the cells pressing down on it for a decade.
Which material should you specify?
Aluminium dominates for one reason: specific heat removal per kilogram. Copper performs better thermally but costs roughly three to four times more and weighs 3.3× as much, which matters in a vehicle where every kilogram costs range.
| Material | Typical use | Thermal conductivity (W/m·K) | Notes |
|---|---|---|---|
| 3003 / 3005 aluminium | Stamped + brazed or bonded plates | ~150-160 | Best formability, lowest cost, most common |
| 6063 aluminium | Extruded channel plates | ~200 | Good extrusion, weldable, moderate strength |
| 6061-T6 aluminium | CNC-machined plates | ~167 | High strength, machinable, higher cost |
| 1100 aluminium | Thin stamped plates | ~220 | Very formable, low strength |
| Copper C11000 | High-flux modules, busbar cooling | ~390 | Used selectively, not for full packs |
| 316L stainless | Specialised or high-corrosion loops | ~16 | Rare; corrosion resistance only |
For most passenger EV packs, 3003 or 3005 stamped plates with a brazed or epoxy-bonded closure plate is the cost-optimal answer. For extruded micro-channel plates, 6063 is standard. Copper appears in high-heat-flux sub-modules such as inverter or busbar interfaces — see our copper and aluminium heat sink material comparison for the trade-off maths.
How are the internal channels formed?
This is the core manufacturing decision, and it determines tooling cost, lead time, and achievable channel density.
Extruded multi-port profiles
A 6063 profile is extruded with 8-30 parallel micro-channels, then cut to length and fitted with end manifolds. Channel hydraulic diameter is typically 1-3 mm. Advantages: excellent channel uniformity, low per-unit cost at volume, no welding along the channel length. Disadvantages: extrusion die cost (indicative USD 1,500-6,000), fixed cross-section, and manifolds must be welded or brazed on.
Stamped and bonded / brazed
Two thin sheets (0.5-1.2 mm) are stamped with matching channel patterns and joined by vacuum brazing, controlled-atmosphere brazing, or epoxy bonding. This gives complete freedom in channel routing — serpentine, parallel, pin-fin, or variable-width — and is the dominant route for large pouch-cell plates. Tooling is cheaper than extrusion but per-part joining cost is higher.
CNC-machined from plate
A solid 6061 or 6063 billet is machined with the channel geometry, then a cover plate is friction-stir welded or laser welded on. This route suits prototypes, low volumes, and complex 3D channel geometries. BQUQ holds ±0.005 mm on machined features, which matters for sealing grooves and port locations. It is the most expensive per part but has the shortest path from CAD to a working sample.
Skived and folded constructions
For air-cooled auxiliary plates and some hybrid designs, skived fin or folded-fin geometries are used. These are covered in our skiving process overview.
| Route | Tooling cost (indicative) | Channel freedom | Best volume | Leak risk |
|---|---|---|---|---|
| Extruded + welded manifold | Medium-high | Low (fixed profile) | >10,000/yr | Medium (manifold joints) |
| Stamped + brazed | Medium | High | >5,000/yr | Low |
| Stamped + epoxy bonded | Low-medium | High | 500-20,000/yr | Low-medium |
| CNC machined + welded lid | Very low | Very high | 1-2,000/yr | Medium (lid weld) |
| Friction stir welded | Low | High | 100-5,000/yr | Very low |
Why does flatness matter more than most engineers expect?
A cooling plate that is not flat does not make proper contact, and poor contact means the thermal interface material has to bridge a gap. Typical thermal gap pads run 1-3 W/m·K; aluminium runs 150-200 W/m·K. A 0.3 mm gap bridged by pad material adds thermal resistance equivalent to roughly 100 mm of aluminium.
Practical flatness targets:
- Cell contact face: 0.05-0.15 mm total flatness for pouch cells with gap pad; 0.02-0.05 mm for direct-contact designs.
- Mounting interface: 0.2-0.5 mm.
- Surface roughness on the contact face: Ra 0.8-1.6 µm is usually sufficient; finer is wasted unless you are using a thin, low-modulus interface.
Flatness is achieved differently by each route. Stamped plates need stress-relief and a flattening station after brazing. Extruded plates need controlled cooling and often a machining pass. CNC plates are flat by nature if the fixture is right — but residual stress in the billet will move the part after machining, so rough-machine, stress-relieve, then finish-machine.
How do you size the channels and flow rate?
Start from the heat load, not the geometry.
1. Total heat to reject. Sum peak cell heat generation. A 75 kWh pack at 3C fast charge can generate 15-40 kW momentarily.
2. Allowed coolant temperature rise. Typically 3-8 °C across the pack. Higher delta-T means lower flow but worse uniformity.
3. Flow rate. For water-glycol at 50/50 (cp ≈ 3.4 kJ/kg·K, ρ ≈ 1,070 kg/m³), rejecting 20 kW with a 5 °C rise needs about 1.1 L/s, or 66 L/min for the whole pack — split across parallel plates.
4. Channel velocity. Keep between 0.3 and 1.5 m/s. Below 0.3 m/s you get poor convection and risk of sedimentation; above 1.5 m/s pressure drop and erosion become problems.
5. Pressure drop budget. Most packs allow 20-60 kPa total. Parallel channel arrays reduce pressure drop but must be balanced, or flow will short-circuit through the path of least resistance.
A useful sanity check: for a 1 mm hydraulic diameter channel with water-glycol at 0.5 m/s, the convective heat transfer coefficient is typically in the 3,000-6,000 W/m²·K range. That is the number that drives your wall-to-coolant resistance.
Coolant chemistry: the compatibility question
Aluminium cooling plates are not inert. Water-glycol with incorrect inhibitor packages will corrode aluminium, and mixed metals in the loop (aluminium plate, copper busbar cooler, stainless fittings) create galvanic couples.
Design rules that prevent most field failures:
- Specify coolant to a recognised specification (e.g. ASTM D3306-type or an OEM-approved EV coolant) and validate with the actual supplier.
- Avoid direct aluminium-to-copper contact in the loop without an insulating barrier.
- Keep chloride content below 25 ppm in the coolant.
- Specify an internal surface finish and cleaning process — brazing flux residue is a corrosion accelerant. Post-braze flushing is not optional.
- Test to ASTM D2570 or an equivalent cyclic corrosion protocol before release.
Our coolant compatibility guide covers the galvanic series and inhibitor chemistry in more detail.
Leak testing: what actually catches defects
A cooling plate that passes a pressure test at the factory and leaks at 30,000 km is a warranty disaster. Use a layered test strategy.
| Test | Method | Typical sensitivity | When |
|---|---|---|---|
| Burst | Hydrostatic until failure | Pass/fail at 2-3× working pressure | Design validation |
| Pressure decay | Air or helium, pressurised | 1×10⁻³ to 1×10⁻⁵ mbar·L/s (He) | 100% production |
| Helium mass spec | Vacuum chamber, tracer gas | 1×10⁻⁷ mbar·L/s | High-reliability / safety-critical |
| Flow and pressure drop | Flow bench | Functional | 100% or AQL sampling |
| Thermal cycling | -40 to +85 °C, 500-1,000 cycles | Detects fatigue cracks | Qualification |
| Vibration | Random profile per pack spec | Detects weld fatigue | Qualification |
Pressure decay with dry air is the workhorse for production. Helium is reserved for the joints most likely to leak — manifold welds, port fittings, and the perimeter seal of bonded plates.
What tolerances and finishes should be on the drawing?
A practical specification block for a stamped-and-brazed aluminium cooling plate:
- Material: 3003-H14 or 3005, 0.8 mm nominal
- Overall flatness (cell face): 0.10 mm
- Channel depth tolerance: ±0.05 mm
- Port position: ±0.15 mm
- Surface finish (contact face): Ra ≤ 1.6 µm
- Internal cleanliness: no free flux residue, particulate ≤ 100 µm
- Working pressure: 200 kPa; burst ≥ 600 kPa
- Leak rate: ≤ 1×10⁻⁴ mbar·L/s helium equivalent
- Coolant compatibility: validated per supplier specification
For CNC-machined plates, BQUQ routinely holds ±0.005 mm on critical features such as O-ring grooves and port bores, with flatness controlled by a rough/stress-relieve/finish sequence. The thermal specification sheet template is a useful checklist for making sure nothing is omitted.
Where does manufacturing go wrong?
Five failure modes account for most production problems:
1. Weld porosity at manifolds. Caused by inadequate surface preparation or contaminated filler. Fix with pre-weld cleaning and inert gas coverage verification.
2. Distortion after brazing. Caused by asymmetric thermal mass. Fix with fixture design and a controlled cooling ramp.
3. Flux residue blocking micro-channels. Fix with post-braze flushing and a particulate cleanliness spec.
4. Flatness drift after machining. Fix with stress relief between rough and finish operations.
5. Galvanic corrosion at mixed-metal joints. Fix with isolation washers, compatible plating, or eliminating the mixed-metal joint entirely.
When should you talk to a factory rather than finish the design?
The honest answer is earlier than most teams do. Channel geometry, alloy choice, and joining method are interdependent, and a design that is elegant in CAD can be unmanufacturable at the target cost. A short review with a manufacturing partner before tooling is committed typically saves more than it costs.
BQUQ runs CNC machining, metal stamping, custom springs, and heat sink production across four lines in one Dongguan factory under ISO9001. That combination matters here: a cooling plate often needs stamped channel sheets, CNC-machined ports and sealing grooves, and a spring or clip for cell compression — all from one supplier, one quality system, one shipment. Quotes are returned in 12 working hours, and MOQ is flexible enough for prototype and pilot volumes. Send drawings to sc@bquq.com.
Frequently Asked Questions
Q: What is the best material for an EV battery cooling plate?
A: Aluminium 3003 or 3005 for stamped and brazed plates, and 6063 for extruded micro-channel profiles. Both offer roughly 150-200 W/m·K thermal conductivity at low weight and cost. Copper conducts better at around 390 W/m·K but is far heavier and more expensive, so it is normally reserved for high-flux sub-modules rather than full pack plates.
Q: How flat does a battery cooling plate need to be?
A: For pouch cells using a gap pad, 0.05-0.15 mm total flatness across the cell contact face is typical. For direct-contact designs, tighten to 0.02-0.05 mm. The reason is that a 0.3 mm gap filled with 2 W/m·K pad material adds thermal resistance equivalent to roughly 100 mm of aluminium, which destroys the plate's effectiveness.
Q: What coolant flow rate does a cooling plate need?
A: Size from the heat load. Rejecting 20 kW with a 5 °C coolant rise requires about 1.1 L/s of 50/50 water-glycol across the pack. Keep channel velocity between 0.3 and 1.5 m/s, and budget 20-60 kPa total pressure drop. Below 0.3 m/s convection drops sharply; above 1.5 m/s pressure drop and erosion risk rise.
Q: How do you leak test an EV battery cooling plate?
A: Use pressure decay with dry air for 100% production testing, typically at 1.5-2× working pressure, and reserve helium mass spectrometry for manifold welds and bonded perimeters where sensitivity of 1×10⁻⁷ mbar·L/s is needed. Add burst testing and 500-1,000 thermal cycles for design qualification, plus vibration testing per the pack specification.
Q: Can a cooling plate be CNC machined instead of stamped?
A: Yes, and it is often the fastest route to a working prototype. A 6061 or 6063 billet is machined with the channel geometry, then a lid is friction-stir or laser welded on. It costs more per part than stamping but needs almost no tooling and allows complex 3D channel routing. BQUQ holds ±0.005 mm on machined features for sealing grooves and ports.
Related Resources
- About BQUQ and our Dongguan manufacturing footprint: /about/
- Heat sink product range, including liquid cooling plates: /heat-sinks/
- CNC-machined heat sinks and cold plates: /cnc-machined-heat-sinks/
- Extruded aluminium heat sink profiles: /extruded-heat-sinks/
- Industry trends in EV thermal management: /industry-dynamics/
- Full technical article library: /bquq-blog/
- Frequently asked questions: /faq/
- Case studies and build examples: /case/
- Contact the engineering team: /contact/
Authored by the BQUQ Engineering Team. BQUQ (Dongguan) runs CNC machining (±0.005 mm), metal stamping, custom springs, and heat sink production in one ISO9001 factory. Source-direct from Dongguan, China — quote in 12 hours: sc@bquq.com | WhatsApp +86 13713157787 | www.bquq.com
