In selective soldering, only through-hole components are soldered. A key goal is to minimally affect the surface-mount components and other adjacent materials on the board. Because every PCB has its own specific layout and materials, the selective soldering machine is designed for different configuration, using software.
The fluxing process in selective soldering is very critical. The soldering requires a sufficient amount of flux on the solder areas, but non activated flux can cause electro migration and damage of products. The high frequency dropjets can apply flux in an accurate way at high speed. The number of droplets per second, the droplet size and robot speed are optimized for every single component. Due to the dropjet technology the amount of flux that is used is minimal and overspray is limited. The flux can be sprayed very accurate at high speeds enabling to penetrate in the barrels of the through hole components. The high frequency dropjets are able to spray high solid content fluxes. The flux flow can be monitored with accurate flowmeters that define the amount of flux sprayed for every single PCB.
After the flux is applied on the PCB to clean the oxidized surfaces and support the solderability the solvents have to be dried out. All solvents need to be evaporated before soldering starts to avoid splattering. Two methods of preheating are available. The IR lamps system is able to respond fast and heat up the PCB in an efficient way. Forced convection uses hot air to heat up the assembly minimizing the temperature differences. Depending on the application IR lamps, forced convection or even a combination of both can be used. The ZEVAm point to point soldering machine has one preheat unit where the high volume ZEVAv application can have two or three units to increase through put. The IR lamps unit can be equipped with pyrometer to make it a closed loop controlled system. The lamps are programmed to have the target temperature at the moment the robot picks up the assembly for soldering.
Today's selective soldering technology is capable of soldering with lead-free solders and tin-lead combinations. The process offers flexibility, advanced control and automation. Its robustness and wide process window make it ideal for lead-free soldering, where solderability and thermal vulnerability of certain components may be issues. Selective soldering delivers quality, repeatability and increased product reliability.