In the non-contact viscous medium dispensing technology called jetting, which has been developed in the course of the recent years, a central issue is how to generate droplets of a predetermined size at a predetermined pace. In many respects this technology is superior to other available dispensing technologies. However, at an early stage, when jetting viscous medium containing a substantial amount of particles, such as solder paste, a problem encountered was an unexpected interference and unintentional interruption of the series of consecutive solder paste droplets jetted from the device.
Since the solder paste is a most special type of medium consisting of a solder powder, i.e. small metal grains, solved in a viscous flux, and since the jetting technology is rather an extreme variety of dispensing, it was initially presumed that the problem could be overcome by improving the mechanical parts of the jetting device. Indeed some mechanical causes were found, such as smearing of the solder powder at narrow passages. These deficiencies have been corrected, and yet occasionally similar problems occur. The reasons therefore are still to be found.