Laser soldering control using optical imaging

The use of lasers to selectively solder joints in electronic assemblies has a number of advantages over methods which involve heating of the whole assembly. However, the localised energy delivery means that the heating and melting behaviour of the solder is particularly dependent on external and process influences. This paper aims to propose a new approach to monitoring and feedback control of the melting process through image acquisition and processing.

In order to evaluate the proposed feedback strategy, a series of experiments have been performed using a semiconductor diode laser controlled by a PC, which also performs image acquisition and processing operations. Two main processing techniques, based on edge detection and Fourier analysis, have been evaluated.

It has been shown that the proposed technique is capable of controlling laser pulse duration to correct for variations in joint geometry, material parameters and laser energy delivery and results in more consistent solder joint formation than is achieved using fixed pulse durations.

The results demonstrate that image processing is a viable technique for the control of laser soldering processes. This could significantly increase the range of applications of laser soldering techniques where determination and control of pulse parameters have been one of the major challenges.

Although some work has been conducted on the use of pyrometer feedback to control laser processing, it appears that no work has been published on the use of image processing. While the processing algorithms themselves are not novel, this is a new application of these algorithms.