Introduction to Common Welding Technologies in the Thermal Management Industry

Welding technologies in the thermal management industry (e.g., for heat sinks, heat exchangers, power device packaging, liquid cold plates) are critical manufacturing processes that ensure product sealing, thermal conductivity, and structural strength. The following introduction combines industry applications and the latest trends.

Thermal management systems (e.g., battery cooling plates, heat exchangers, electronic heat sinks) typically involve joining lightweight, high-thermal-conductivity materials such as aluminum alloys and copper. Welding technologies in this field are primarily used for:

• Sealing Requirements: For example, welding of liquid cold plates for battery packs must prevent leakage. Laser welding or TIG welding is often employed to achieve high-precision sealing.
• Thermal Performance: Welded joints must maintain the thermal continuity of the materials, avoiding increased thermal resistance due to defects like pores or slag inclusions.
• Lightweight Structures: Solid-state welding techniques, such as friction stir welding, minimize distortion in the heat-affected zone and are suitable for aluminum alloy components.

Brazing is the most widely used and fundamental welding technology in thermal management, suitable for conductive materials like aluminum and copper.

Principle: A filler metal (brazing material, e.g., aluminum-silicon alloy, copper-phosphorus alloy) with a melting point lower than the base metal is used. The assembly is heated until the filler metal melts, flows by capillary action into the joint gap, and diffuses with the base metal to form the bond.

Common Types:

• Vacuum Brazing: Conducted in a vacuum furnace. It is oxidation-free and fluxless, producing clean, corrosion-resistant joints. It is the preferred method for manufacturing high-end aluminum heat sinks, cold plates, and complex flow channel heat exchangers.
• Atmosphere Brazing: Performed in an inert atmosphere like nitrogen, offering lower cost than vacuum brazing.
• Flame Brazing / Induction Brazing: Suitable for localized welding or simple components.

Advantages: Capable of welding complex structures and large areas; good sealing; suitable for mass production.

Disadvantages: High requirement for part fit-up gaps; requires specialized fixtures; significant investment for vacuum furnace equipment.

Typical Applications: CPU/GPU heat sinks, liquid cold plates, battery cold plates, parallel flow heat exchangers.

A solid-state joining technology, particularly suitable for aluminum alloys, experiencing rapid growth in thermal management.

Principle: A non-consumable, rotating tool (pin) is plunged into the abutting edges of the workpieces. Frictional heat softens the material without melting it, and the material is plasticized and joined under the tool's forging pressure and stirring action.

Advantages:

• High Joint Strength: Can reach 70%-90% or more of the base metal strength.
• Low Thermal Distortion: Low-temperature process minimizes distortion.
• No Porosity/Cracks: Solid-state welding avoids defects common in fusion welding.
• Environmentally Friendly: No fumes, arc light, or spatter.

Disadvantages: Relatively slower welding speed; workpieces require rigid clamping; tool wear.

Typical Applications: Large aluminum liquid cold plates, heat spreader substrates, enclosures, bonding heat pipes to bases, welding of battery trays and housings.

Abbreviated as TIG or GTAW, it is a non-consumable electrode gas-shielded arc welding process.

Principle: It uses a refractory tungsten electrode to create an arc shielded by an inert gas (typically argon), melting the base metal and a filler wire (if used) to form a high-quality weld.

Advantages: High weld strength, relatively low equipment investment, no spatter, aesthetically pleasing, applicable to a wide range of materials.

Disadvantages: Significant distortion.

Typical Applications: Plate-fin heat sinks, housings for high-power cooling modules.

4. Laser Welding

A high-energy density beam welding technology widely used in precision thermal management components.

Principle: Utilizes a high-energy-density laser beam as a heat source to locally melt the base metal, forming a weld seam. It can be subdivided into conduction mode welding (shallow melting) and keyhole welding (forming a vapor capillary).

Advantages:

• Concentrated Energy, Small HAZ: Minimal distortion, suitable for precision welding.
• Non-contact, High Automation: Fast speed, easily integrated into automated production lines.
• Weldable Refractory Materials: Such as copper, aluminum (high reflectivity materials requiring specific wavelengths/techniques).

Disadvantages: Expensive equipment; extremely high requirement for workpiece fit-up accuracy; challenging for high-reflectivity materials like pure copper.

Typical Applications: Copper-aluminum composite fins, heat pipe sealing, IGBT water-cooled substrate (DBC/AMB) packaging, microchannel heat sink cover sealing.

5. Vacuum Diffusion Bonding

A solid-state precision joining technology achieved in a high-vacuum environment, used for manufacturing high-performance, high-reliability thermal management components.

Principle: Under high temperature and pressure, atoms at the contact surfaces interdiffuse, achieving a monolithic bond. An interlayer material is often required.

Advantages:

• Excellent Joint Properties: Composition and structure close to base metal; no brittle phases; high thermal conductivity and strength.
• Joining of Dissimilar Materials: Such as copper-aluminum, copper-ceramic (e.g., aluminum nitride).
• Extremely Low Distortion, High Dimensional Accuracy.

Disadvantages: Long cycle time, extremely high cost, stringent surface quality requirements.

Typical Applications: Aerospace-grade compact heat exchangers, ceramic substrate-to-metal packaging, manufacturing of high-performance vapor chambers (VC).

6. Soldering (Soft Soldering)

Primarily used for lower-temperature connections, common in electronic cooling and packaging.

Principle: Uses low-melting-point solders (e.g., tin-based, indium-based alloys), heated via soldering irons, reflow ovens, etc., to form a connection.

Advantages: Low temperature, friendly to heat-sensitive components, simple process.

Disadvantages: Relatively lower joint strength, temperature resistance, and long-term reliability.

Typical Applications: Bonding fins to bases (replacing thermal adhesive), connecting small heat pipes to copper bases, mounting certain power devices.

7. Ultrasonic Metal Welding

A solid-state welding technology that uses high-frequency vibrational energy for joining.

Principle: High-frequency vibrations generated by an ultrasonic transducer, under pressure, cause plastic deformation and friction at the contact surfaces, breaking up oxide films and enabling atomic bonding.

Advantages: No external heating required, especially suitable for high-conductivity materials (copper, aluminum) and dissimilar material joining; energy-efficient, fast.

Disadvantages: Typically suitable for welding thin sheets, wires, and points; not suitable for thick sections or complex structures.

Typical Applications: Connecting heat pipes to fins (replacing mechanical fit methods like zipper fin or folded fin), welding heat spreaders for lithium batteries, copper-aluminum transition joints.

3. Development Trends of Welding Technologies in the Thermal Management Industry

Hybrid Processes: Such as "laser + friction stir welding" hybrid technologies, combining the advantages of both.

High-Power Orientation: Developing welding technologies with lower thermal resistance and higher reliability (e.g., low-temperature silver sintering) for wide-bandgap semiconductor devices like SiC and GaN.

Intelligentization and Online Monitoring: Integrating vision sensing and process control to improve welding consistency and quality.

Material Innovation: Developing new brazing alloys and interlayer materials to improve the weldability of dissimilar materials.

The selection of a welding technology requires comprehensive consideration of material combinations, product structure, performance requirements (thermal conductivity, strength, sealing), production volume, and cost. Currently, brazing, friction stir welding, and laser welding are the three mainstream technologies widely applied in the thermal management industry.