Thermocompression

Thermocompression is a solid-state bonding process in which two surfaces are joined by applying heat and mechanical pressure, often with an interfacial alloy or diffusion-assisted mechanism. The technique generally operates at temperatures below the bulk melting point of the adherends, and the bond forms through diffusion, plastic deformation, and interfacial reactions rather than bulk melting.

The bonding mechanism relies on elevating the materials to a temperature that enhances atomic mobility while applying sustained pressure to promote intimate contact and displacement of surface oxides or contaminants. Process parameters typically include a controlled temperature (a fraction of the melting points of the involved materials), chosen pressure, and bonding time. An inert or controlled atmosphere is often used to minimize oxidation. Some implementations use interlayers or diffusion barriers to tailor joint characteristics and prevent undesirable reactions.

Materials commonly involved include metals such as gold, copper, aluminum, and nickel, and the method is widely used in electronic and microfabrication contexts. One well-known application is thermocompression wire bonding, where gold wires are bonded to metal pads using heat and pressure without ultrasonic energy. The approach is also used for certain metal-to-metal or metal-to-die bonds in semiconductor packaging and MEMS devices, sometimes in combination with polymer interlayers or solder-like intermetallic formation.

Advantages of thermocompression bonding include the absence of flux and reduced risk of thermal damage associated with bulk melting, as well as strong, hermetic joints for suitable materials. Limitations include sensitivity to surface contamination and oxidation, control of intermetallic formation, and the need for precise temperature and pressure control and compatible material systems.