A Cold Plate Is a Interface Problem Before It Is a Machining Problem
A vapor chamber cold plate spreads heat by phase change: the working fluid evaporates over the heat source, travels across the cavity, condenses on the cooler surface and returns through the wick. The thermal resistance of that cycle is set by the internal volume, the wick and the fluid charge, all of which are the customer's design. What machining controls is the interface, and on a high power device the interface is where most of the temperature drop happens.
Copper Grade Sets the Ceiling
- C1100 oxygen free copper: oxygen below 10 ppm, the default for sealed vapor chambers because a clean cavity keeps the wick from oxidising during brazing.
- C1020: acceptable for solid cold plates where there is no internal cavity to protect.
- Bimetallic copper and aluminum: used when weight matters, with the braze joint designed to carry the expansion mismatch.
- Nickel plating: applied for coolant compatibility, with thickness recorded so fin gaps do not close.
Machining the Cavity and the Fins
| Feature | Range | Why it matters |
|---|---|---|
| Cavity depth | 2 mm to 12 mm, 0.05 mm tolerance | Sets internal volume and therefore the charge |
| Fin width | From 0.8 mm | Sets wick contact area and flow resistance |
| Sealing land | 3 mm minimum, 0.02 mm flatness | Braze joint integrity across the full perimeter |
| Mounting face flatness | 0.02 mm over die footprint | Contact resistance at the heat source |
Copper is gummy compared with aluminum, so cutters are polished and rake angles are selected for the material. Programs borrowed from aluminum work tend to produce smeared fins and short tool life.
Brazing and Testing as One Operation
A plate that leaks is not a plate with a minor defect, it is a failed part that will destroy the electronics it was meant to protect. Vacuum brazing runs to a recorded thermal profile per batch, and every plate gets a helium leak test with a rejection threshold agreed before the first batch. Liquid cooled versions add a pressure hold at 1.5 times working pressure and a flow test with pressure drop recorded against the drawing value.
Flatness After Brazing
Furnace cycles relax the plate and move the mounting face, which is why the final machining pass and the flatness inspection happen after brazing, not before. Screw counterbores are spot faced so fastener torque does not bow the plate, and the hole pattern is referenced to the die outline rather than to the plate edge so the plate can be flipped without changing the stack.
Our copper vapor chamber cold plate page lists the material, fin and port options together with the documentation supplied per serial number.
