The latest of several friction based microjoining techniques to emerge from TWI in recent years is now under development in the laboratories at Great Abington.
Known as friction acoustic bonding, the process uses frictional heat generated by a small rotating tool in contact with the parts to be welded. Sufficient heat has to be generated to create plastic deformation across theinterface.
So far the process has been used with great success to lap weld two layers of 0.5mm thick aluminium.
During development of the process it has already been possible to join aluminium sheet, ribbon cable welded to copper on a printed circuit board and copper to copper/polyimide flexi-circuit.
It is possible to produce seam welds in both lap and butt weld configurations and spot welds, so it could be used to join individual wires or ribbon cables without removing the insulation.
The design of the rotating tool is crucial to the success of the process and the shape of the contacting face is thought to have a significant effect on joint quality.
The metallurgical properties of the tool are also known to contribute to the performance of the finished joint.
Trials to date have shown that the process appears best suited to softer materials such as aluminium and copper.
More details of this technique may be obtained from Chris Otter in the Microtechnology and Reliability Centre. E-mail: chris.otter@twi.co.uk
