Projection welding of fibre optic receiver

Soft soldering was the joining method used by TWI Industrial Member Hewlett Packard in the fabrication of a fibre optic receiver assembly for telecommunication applications. However, this process presented a number of problems, particularly with the need to remove solder flux to avoid long-term corrosion sensitivity. In addition, product yield was less than optimum and substantial labour content was required for assembly.

TWI was asked to consider alternative techniques to join the optical subassembly to a metal microelectronics package. Requirements were demanding: the joint had to be hermetic with long-term stability, a high accuracy of alignment was needed and a careful eye had to be kept on excessive weld heat which would damage the electronics in the package.

After discussing various possibilities, resistance projection welding was chosen as the most effective solution. Following a feasibility study at Abington, TWI made minor changes to the components to suit the process and designed suitable electrode assemblies. Welding trials established the parameters required to produce welds of acceptable quality and provided samples for evaluation by the customer.

The company was entirely happy with the results and went ahead with the purchase of specified production equipment.

Since this time, production of the component using the new technique has confirmed that objectives were achieved. There has been a reduction in labour content, accompanied by an increase in quality and reliability, less scrap and less downtime.

Total savings have been estimated by Hewlett Packard at more than £20 000 per year, many times the cost of the original study.

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