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54 SMT Magazine • April 2017 The cleaning process in a vapor degreaser typically requires only minutes to complete. Al- though cycle times vary based on part geome- try and soil difficulty, most cleaning cycles re- quire less than 15 minutes to completely clean and dry a rack of parts. Cleaning a circuit board can take place in either one or multiple immer- sion sumps, depending on the difficulty of the flux residue. For RMA and rosin-based fluxes, cleaning can typically occur in the vapor zone and rinse sump only. Difficult no-clean and high-melt-point fluxes may require immersion in both the boil sump and the rinse sump. The boil sump is very important to the cleaning pro- cess, as the hot solvent can provide better solu- bilizing properties. Additionally, as flux residues begin to accumulate in the boil sump, the dis- solved residues actually help the solubility; in the cleaning industry, it is well known that "like dissolves like." Some electronics manufactur- ers express concerns about immersing circuit- ry into the "dirty" boil sump due to recontam- ination or damage from solid particulate, such as solder balls. However, recontamination is avoided by following the boil sump immersion with a rinse in the rinse sump, and solder balls can be contained by using an auxiliary still or filtering the boil sump fluid, which is common in most vapor degreasing equipment. Once the boards have been cleaned in the boil sump and rinsed in the rinse sump, the vapor zone will re- move any remaining particulate or residue with clean distillate and allow for instant drying as the boards are removed from the equipment. Cost of Ownership Although cleaning is cru- cial to many electronics in- dustries, it is still only one aspect of the total manufac- turing process, and so the cost of cleaning needs to re- main reasonable to the over- all manufacturing cost. For- tunately, the cost-per-clean- ing for the vapor degreas- ing process is considerably low and can be compara- ble or less than that of aque- ous cleaning. When compar- ing solvent vapor degreasing to aqueous clean- ing systems, there are many factors to consider including capital investment, equipment foot- print, power supply, cleaning time, detergent/ solvent supply, and waste disposal. In other words, a vapor degreaser and an aqueous ma- chine capable of cleaning the same number of parts-per cycle will have different overall costs, thus different costs-per-part cleaned. Aque- ous systems typically have larger working foot- prints, power requirements, and longer clean- ing cycles; these are due to the need for several washing and rinsing stations, high temperature inputs, and reliance on mechanical spraying and washing mechanisms 4 . Although vapor degreasers require less time and overall mainte- nance, the cleaning solvents are typically more expensive than aqueous detergents; however, properly maintained equipment should retain solvent, and the distillation process keeps sol- vent pure for continuous use. Table 1 compares cost and maintenance differences of an aqueous system and a vapor degreasing system using the same sized basket and cleaning the same number of parts. Many of the maintenance and operation requirements of the aqueous system are greater than those of the vapor degreasing system. However, the cost of the solvent is three times greater than that of the aqueous detergent. There are certainly oth- er cleaning processes outside of vapor degreas- ing and aqueous cleaning that are less costly, such as manual cleaning with water or solvents, though these processes tend to compromise the Table 1: Operation of Aqueous vs. Vapor Degreasing. VAPOR DEGREASING CHEMISTRIES