Ultrasonic welding involves the use of high frequency sound energy to soften or melt the thermoplastic at the joint. Parts to be joined are held together under pressure and are then subjected to ultrasonic vibrations usually at a frequency of 20, 30 or 40kHz. The ability to weld a component successfully is governed by the design of the equipment, the mechanical properties of the material to be welded and the design of the components.
The term 'wirebonding' is generally accepted to mean the interconnection (via wire) of components and conducting tracks. The most frequently used method of joining the wires is ultrasonic welding.
The process uses a combination of vibration and force to effectively scrub the interface between wire and substrate, causing a localised temperature rise, promoting the diffusion of molecules across the boundary. In the case of gold wire, substrate heating (100 to 150°C) is usually added to further encourage the migration of materials, this variation of the process being known as thermosonic bonding
TWI's three decades of in-depth experience in all areas of ultrasonic inspection has made it an acknowledged world-leader. Among its notable achievements is the development of novel technology for long-range detection of corrosion under insulation in process pipework. Recent project work has included:
- inspection of critical adhesive bonds in flight simulators
- development of inspection procedures for copper welds in waste nuclear fuel canisters
- monitoring of flaws in pressure vessels operating at high temperature
- optimisation of automated test procedures for welds in stainless steels
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