LIQUID COLD PLATES & FSW

Thermal management

What is a liquid cold plate?

A liquid cold plate is a device that is designed to cool down electronic equipment. It consists of a housing in which a channel has been machined to allow coolant to pass through (for example water), and a cover over the channel. This cover is welded to the housing using the FSW.

Most often these liquid cold plates are made of aluminium, but they can also be made of copper. The advantage of these two materials is their high thermal conductivity.

Cold plate housing

Cold plate cover

Cold plate housing & cover

Cold plate welded by FSW

Types of liquid cold plates

Large liquid cold plate

Size: 400 x 400 x 20 mm

Aluminium alloy: 6061 T6

Complex water-cooling channel

Thin liquid cold plate

Total thickness: 3mm

Welding process: lap welding of 3 1-mm aluminium sheets in one step.

Pressure resistance: 9 bars

Standard liquid cold plate

From aluminium block, we obtain a ready to use waterproof thermal management part.

Copper liquid cold plate

FSW can weld aluminium or copper (Al with Cu is also possible).

Liquid cold plate & thermal management

Liquid cold plates are required for customised solutions in industries where small batches are predominant and where perfect thermal management of equipment is essential: rail, wind energy, solar energy, space, aeronautics, data centres, military.

The challenges of thermal management

Cost reduction and mass reduction

Better integration of components, increased heat flux density (W/m²) and the use of lightweight materials (such as aluminium) are required.

Thermomechanical constraints

The cold plate flatness has to be optimized to guarantee a perfect contact with the electronic equipment.

Low coolant pressure drop

The pressure drop has a direct impact on the energy efficiency of systems (pumps consumption).

Coolant quality, safety, and storage

High compatibility between materials and coolant is essential.

FSW liquid cold plate: the answer to the challenges of thermal management

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A welding technique with many benefits for welding of liquid cold plates

Machined cold plate friction stir welded

Lower cost

Replacement of vacuum brazing or EBW (electron beam welding).

Higher pressure resistance

Up to 300 bars.

Perfectly waterproof

No porosity.

Excellent thermal conductivity

Metallurgical junction.

Ease of use

Compared to vacuum brazing or EBW.

Comparison of welding techniques for a liquid cold plate

FSW advantages vs. other existing techniques of cold plate manufacturing

FSW VS. COPPER TUBE

The welding between the tube and the end connectors is not required using FSW. The end connectors are directly machined into the housing.

dipped liquid cold plate vs. fsw liquid cold plate

copper tuber liquid cold plate vs. fsw liquid cold plate

Epoxy coating + pressing operation for epoxy drying are not required using FSW.

FSW VS. GUN DRILLING

Not allow much design freedom in terms of the cooling surface: the liquid paths are only straight lines.

For cold plates longer than 500mm, gun drilling becomes very difficult.

Seams are very sensitive areas for leakage.

Do you want to know more about the comparison of manufacturing methods?

Read article

FSW welded cold plate cost

Friction stir welding is the most economical technique in terms of operational cost (machine investment and cover supply) compared to EBW or vacuum brazing.

With the Stirweld FSW head, the investment cost is drastically reduced, and the cover design does not need to be extremely accurate. As a result, the cover can be manufactured by laser cutting which significantly reduces the cost compared to machined covers, which are required for Electron Beam Welding.

Another cost reduction using FSW is the cost of quality control. In the case of friction stir welding, this cost is minimal because:

There is no risk of sticking or channel collapse (main defects of vacuum brazing),
It is a solid-state welding process: no porosity (main defects of electron beam welding),
There is no risk of coolant leaks in service due to a potential crack propagation by cycled fatigue pressure.

2 essentials reasons led us to choose Friction Stir Welding. First, it’s a good opportunity for us to secure the assembly operations between the sole and the cover, which make up the heat sink. Then, we wanted to use a technology which is simpler and to make the operation more reliable.

FSW technology not only permits to simplify the industrial process, but i’ts also safer and it can lead to significant cost reductions.

X.A - Supplier Development

French electronics group specializing in aerospace, defence, security and land transport.

Video testimonial:

Design of friction stir welded liquid cold plate

Design of liquid cold plate cover

The cover dimensions of the liquid cold plate are one of the parameters that influences the welding operation but also the mechanical strength of the welded cold plate. There are two ways to increase the burst pressure strength of the part: to increase cover thickness or to decrease its width.

Friction stir welding parameters

For an efficient and quality FSW welding of your liquid cold plate, several elements must be considered:

The thickness and width of the cover,
The definition of the tool path,
The definition of the dead zone (area of FSW tool exit).

Quality control of the welded liquid cold plate

BURST PRESSURE TEST

Introduction of water under pressure into the channel of the liquid cold plate to mesure the resistance to cracking of the cover.

LEAK TEST

This is the most important test for checking the quality of the welded liquid cold plate.

THERMAL MANAGEMENT

Experimental characterisation of the thermal resistance and pressure drop of the cold plate.

test visuel VISUAL TEST

To identify the presence of excessive flash (very common FSW defect), to check if the force applied by the shoulder on the part surface was high enough.

FSW of machined cold plate – thermal management :

Video on the welding of a thermal management part

Technical differences between FSW & Vacuum Brazing

PROS & CONS OF FRICTION STIR WELDING: IMPACT ON DESIGN & MANUFACTURING PROCESS OF A LIQUID COLD PLATE

COMPARISON BETWEEN FSW & VACUUM BRAZING: IMPACT ON COST & SAFETY

comparing vacuum brazing with FSW technology

Stirweld FSW expertise

With a team of experts in friction stir welding, Stirweld supports you throughout your process for welding of liquid cold plate. Indeed, you can count on Striweld’s design office for:

Codesign of your liquid cold plate,
Design & manufacturing of your clampig jig,
Definition of your welding parameters & quality control,
Manufacturing of first batches.

Stirweld refers to ISO 25239 – Friction Stir Welding standard throughout the industrial process: weld joint design, welding operator qualification, specification and qualification of welding procedures, inspection & quality requirements.