Although the number of Through Hole (THT) connections the electronics assemblies is decreasing due to miniaturization, selective soldering is still a growing market. More and more Surface Mount Devices (SMD) technology is being used and reflow soldering is becoming the main stream solder method. Nevertheless there will remain components that require through hole connections for strength or because they simply can’t withstand the high temperatures of a lead-free reflow process.
Selective soldering is very effective method to solder the THT components. There are two mainstream selective solder applications:
• Drag soldering (point to point)
• Dip soldering (stamp)
Both applications have a dropjet flux device to apply very small amounts of flux on the areas that are soldered. Despite these small amounts the remaining flux residues might cause electro-migration if not de-activated completely during the assembly process. This drives engineers to implement different flux formulations to avoid claims. Special in the automotive applications there are examples in the field that bridges and corrosion are caused by the growth of dendrites due to flux residues in combination with temperature, humidity and a current. The solder joints can be much more reliable when an inert flux is used in combination with a controlled soldering process.