Most products sold in the EU after July 2006 will have to be lead-free in content in order to comply with the 'Removal of Hazardous Substances' (RoHS) legislation. Products not covered by this directive may face problems with regard to existing recycling legislation if lead is used in manufacturing. The elimination of lead from the solders used in printed circuit boards is the primary concern for manufacturers, especially in the electronics sector.
Although lead free solder substances are already available, there are disadvantages associated with their use. Unlike traditional lead solders, they do not flow or bond well and need higher temperatures to melt.
The advantage of laser soldering is that heat needs to be applied only wherever it is necessary, at the joint itself. As opposed to RF or wave soldering, only negligible heating of the surrounding components takes place.
Since it is possible for more power to be applied to the joint than in conventional hot iron soldering, Laser soldering is fast. It takes just a fraction of a second to solder each joint. Overall, less energy is utilised to create the joint and consequently, the joint cools quickly. Rapid cooling produces tougher joints with better conduction properties due to the short intermetallic zone and fine grained structure.
Today, there is a preference for the diode laser type. Its output wavelengths (808 or 940nm) are properly absorbed metals and can be coupled via standard optical lenses or fibre optics. Such lasers are low maintenance, energy efficient and compact. Beam delivery may be by cartesian CNC motion of either the PCB itself or the laser head and optics. This arrangement allows easy application of solder wire through an automatic feeder.
For more rapid throughput, a galvo deflection head could be used to send the laser from solder joint to solder joint under computer control if solder is pre-applied. Measurement (in milliseconds) of total move and settle time between consecutive soldering actions can be made.
For lead-free soldering problems, Laser Resources offers a solution with laser technology.