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Laser soldering

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Laser Soldering offers the ability to use lead-free solders and to solder complex geometries.

As a consequence of the Removal of Hazardous Substances (RoHS) legislation, several products sold in the EU after July 2006, will need to be lead-free in content. Even products which fall strictly outside of this directive may encounter difficulties with regard to existing recycling legislation, if they persist with using lead in manufacturing. The main area of concern for manufacturers, particularly in the electronics sector is of course the means of eliminating lead from the solders used in printed circuit boards.

A range of lead-free solder substances are already available, but many of them require considerably higher temperatures to melt, and there have been reports that the substances do not flow or bond as well as the traditional lead solders.

Laser soldering has the advantage that the heat is applied only where it is required: at the joint itself; there is negligible heating to the surrounding components, unlike with RF or wave soldering, so the higher temperature requirement can easily be satisfied.

Laser soldering is also fast, much more power can be applied to the joint than using conventional hot iron soldering, and so, each joint can be completed in a fraction of a second.

Laser soldering has the key advantage that less energy is required overall to create the joint with the consequence that the joint also cools quickly; more rapid cooling brings tougher joints with better conduction properties, owing to the fine grain structure and short inter metallic zone.

Today, the laser type that is often preferred is the diode laser; its output wavelengths (808 or 940nm) are well absorbed by metals and can be coupled via fibre optics or standard optical lenses. Such lasers are compact, low maintenance and energy efficient.

Beam delivery may be simply by cartesian CNC motion of either the laser head and optics or the PCB itself, such an arrangement facilitates easy application of solder wire via an automatic feeder.

Alternatively, for the rapid throughput, if solder is pre-applied it may be possible to use a galvo deflection head to send the laser from solder joint to solder joint under computer control, the total move and settle time between consecutive soldering actions can then be measured in milliseconds.

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