Automated is the fastest growing area within electronic assembly due to the ever increasing pressure to improve product quality and shorten cycle times in the manufacturing process.
With more complex, double-sided surface mount assemblies, the use of the traditional wave soldering process to solder through-hole components is no longer an option.
The higher density and lower ultimate cost of SMT makes it the preferred assembly technology. However, the mechanical strength of through-hole connections continues to make through-hole the technology of choice in assembling connectors.
As the number of through-hole components on boards has decreased, hand soldering is primarily used as an alternative. Hand soldering is a manual operation and, therefore prone to defects, such as excessive solder, inadequate hole fill, flux residues and thermal stresses at the solder joints. It is not reliable or repeatable and depends entirely on ability and skills of the operator.
Selective soldering is the process whereby specific through-hole devices on a board are selectively soldered using programmable selective soldering machines.
Unlike wave soldering, where a conveyor transports boards through a stationary wave, a selective-soldering procedure uses robotics to individually moves the board over a stationary soldering nozzles and tooling (see Fig:1 )
The robotic PCB support fixture is programmed to move the board in an ‘X’,’Y’ & ‘Z’ direction, precisely positioning the board over the solder fountain. Selective soldering uses two different techniques to drag or dip solder individual sites or components on the board.
About the author:
John Dean, Customer Support Manager, Ultra CEMS. Jdean@ultra.co.uk www.ultra-cems.com
