The rising heat loads of high power electronics and the drive towards more compact packaging has changed the mind-set of designers. Liquid cooling is no longer regarded as a risk but rather a necessity. When compared with more traditional air cooled solutions Liquid cold plates offer significant performance advantages particularly in high power and high heat flux applications.
Columbia-Staver are the go to experts in liquid cooling and offer a comprehensive range of cold plate technologies such as, serpentine (tube in plate) designs, gun drilled, and multi-piece designs that can have enhanced surface areas included in the liquid path. Columbia-Staver can select the joining method of a multi-piece design to suit the design and volume required. Columbia-Staver can offer FSW (friction stir welded) cold plates, vacuum brazed and dip brazed.
Each manufacturing technique has advantages depending on the liquid cold plate design, the manufacturing volume required, the choice of cooling liquid, pressure drop requirements and the financial budget of the customer.
Typical Applications for Liquid cold plates
Liquid cold plate solutions are currently deployed in: Renewable Energy Systems, Traction Systems, Medical Equipment, IGBT and Power Semi-Conductor Systems, Lasers, Data Centres, Industrial Power Applications, Defence Systems, Avionics, Fuel Cells, Battery Cooling and many more High Power and High Heat Flux Applications.
Tube in Plate (Liquid cold plate)
Possibly the simplest form of cold plate where a joint free tube is embedded into a copper or aluminium carrier.
Dependent on the required thermal performance and the cooling fluid to be used, the tube can be copper or stainless steel and can be a simple mechanical (dry) press fit, press fit with a thermal epoxy boundary to eliminate micro voids, or soldered in place for maximum thermal performance.
Gun Drilled (Liquid cold plate)
A gun-drilled cold plate is manufactured by drilling a series of holes through the length of an aluminium plate to form multiple flow paths.
For the inlet and outlet fluid path, holes are drilled perpendicular to the main fluid path and then partially plugged to create a continuous coolant path.
These cold plates have the advantage that there are no thermal boundaries and the aluminium plate has had no thermal stress during the manufacturing process so flatness is easier to achieve.
FSW Friction Stir Welded (Liquid Cold Plate)
This is a two-piece construction. The liquid flow path is CNC machined into the base. This flow path can be complex and can even incorporate fins to enhance the heat transfer surface.
A profiled lid is then placed into a recess above the flow path and is FSW (friction stir welded) into place. Finally, the welded surface is fly-cut flat, inlet/outlet holes and component mounting holes are added.
Die Cast (Liquid cold plate)
This is a two-piece construction suitable for complex high volume liquid cold plates.
Multiple internal and external features can be incorporated into the two die cast tools. After casting the two halves can be bonded together by welding or by the use of an epoxy.
Brazed (Liquid Cold Plate)
These cold plates are generally used for high-performance designs that require low thermal resistance, and superior leak-free reliability. They enable designers the greatest flexibility in specifying such criteria as thermal resistance, thermal flow, pressure drop, fluid path, size, shape, material hardness, surface geometry, and the ability to mount components on both sides of the plate. The internal features can be created by machining flow guides and fins from the base metal or by introducing high-performance corrugated aluminium fin.
This multi-part assembly is then brazed together:
Dip Brazing
The assembly is then preheated in an air furnace to 1,025°F to insure uniform temperature of dissimilar masses in the assembly. The part is then immersed in a molten salt bath, the molten flux comes in contact with all internal and external surfaces simultaneously. This liquid heat is extremely fast and uniform. Since the bath is a flux, complete bonding on oxide-free surfaces assures unusually high quality joints. The time of immersion is determined by the mass to be heated but is seldom over two minutes in duration.
Controlled Atmosphere Brazing
The next step beyond an open-air environment is to use a controlled atmosphere under normal or close-to-normal atmospheric pressure. In this type of environment, a high degree of control over the overall process can be achieved and open-air issues of oxidation, scaling and carbon buildup can be virtually eliminated.
Vaccuum Brazing
Brazing in a high vacuum environment provides the most process control and produces the cleanest parts, free of any oxidation or scaling. It is the preferred brazing environment for brazing aerospace components, hardening medical devices and other applications that require the absolute highest part quality.
Multi-Layer Cold Plate
Columbia-Staver have developed the epoxy bonded multilayer cold plate.
This technology is ideal for prototypes and small production runs as no tooling investment is required.
The middle layer forms the flow path and can be customised so that the cold plate can mimic:
• Bubble plates
• Friction stir welded plates
• Serpentine plates
• Parallel flow extruded plates
Finished Cold plate with the three layers Epoxy bonded together and connector blocks fitted with “O” ring sealing
Image of Cold Plate with the upper layer made transparent. This shows the flow path, in this case designed to perform like a Bubble Plate
Exploded image showing the three individual layers, connector blocks and fixing screws
Three plane Cold Plate
