Laser soldering addresses lead-free legislation
As a consequence of the Removal of Hazardous Substances (RoHS) legislation, most products sold in the European Union (EU) after July 2006 will need to be lead-free in content.
Daventry, Northants, UK - As a consequence of the Removal of Hazardous Substances (RoHS) legislation, most products sold in the European Union (EU) after July 2006 will need to be lead-free in content. Even products that 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 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 they do not flow or bond as well as the traditional lead solders.
Laser soldering has the advantage that the head 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.
Also, laser soldering is 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. This has the key advantage that less energy is required overall to create the joint with the consequence that the joint also cools very 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 940 nm) are well absorbed by metals and can be coupled via fiberoptics 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 application of solder wire via an automatic feeder.
Alternatively, for the most 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