In general, residues remain after the soldering process on the substrate when using solder pastes with liquid flux. These residues can be very corrosive. With the encapsulation of acid and salts in the resin of the “no-clean” solder paste, the residues are less aggressive for the PCB and components, but still existing and visible. With a fluxless solder paste no residues occur. Fluxless soldering, i.e. residue-free soldering with the aid of gaseous activation, is known for many years, but only well established in the field of opto- and microwave electronics. In low-cost high-volume applications this technology has not yet become mainstream.
Our research group has developed a fluxless solder on which various tests were applied and different properties of the developed solder were investigated.
For wettability and melting experiments and the demonstration of the functionality of the gaseous activator, fluxless solder paste was printed on a test board for ceramic packaged LEDs. The functioning of the reductive atmosphere can be seen comparing the reflow soldered test board in the figure beside.