The flux medium is designed to perform two tasks: Firstly, the flux medium must provide the correct rheological properties that will allow the application of the solder paste. This will be discussed in greater detail when reviewing the printing process. The next function of the flux system is to clean the surfaces that are to be soldered. Only when all contaminants, coatings, and oxides have been removed can the necessary metal interactions take place to form a reliable joint. There are two types of flux systems available in the market place today. The most common is the no-clean technology, which means that the residues left after soldering can be left on the board without adversely impacting reliability, please understand that this does not mean that there will be no residues. Within the no-clean class of fluxes, there a number of subclasses, with the most important of these being halide and halogen free. When No Clean flux systems are not an option, Water Wash fluxing systems may be the next appropriate choice. Water Wash fluxes do in fact require cleaning and can be cleaned off using standard de-ionized water. Since the Water Soluble flux systems can be of the most aggressive systems available, the residues must be removed in order to keep from causing corrosion. While the IPC does not specify flux composition in the way it does alloy, there is a system for classifying them. All of Henkel’s no-clean fluxes are classified as ROL0. The RO because they are based on modified rosins, the L because the flux has a low tendency for corrosion and 0 because it has no detectable halides.