MANAGING WASH LINES AND CONTROLLING WHITE RESIDUE BY STATISTICAL PROCESS CONTROL

摘要

A statistical-based method was developed for thernmanagement and control of conveyorized wash lines whichrnemploy aqueous cleaning chemistry for removing rosinrnfluxes. The method tracks reagent concentration, work load,rnand soils loading to determine replenishment rates, andrnwhen to dump process baths to minimize consumption ofrnchemical reagents while maintaining effective cleaning.rnWhile automatic process control systems monitor cleaningrnchemistry level in the bath and add concentrate as needed tornmaintain a set concentration and level, this equipment doesrnnot monitor soils loading. Wash solutions that contain thernspecified level of cleaning agents are rendered ineffectivernwhen saturated with flux residues and other soils. Therntesting procedure and statistical control methods developedrnhere allow for forecasting the point of soils saturation. Bathrndumps can be planned to avoid white residue defects whilernminimizing consumption of costly aqueous cleaningrnchemistry.rnCase studies of equipment illustrate the differences inrnefficiency and variability between two makes of wash line.rnThe data also show why there is a difference, and what canrnbe done about it.rnFMEA disciplines are employed to develop troubleshootingrnguides and standard rework procedures which allows morernrapid diagnoses and correction of wash problems. Some fluxrnresidues that have been left on assemblies for extendedrntimes and those residues formed by soldering/pre-heating atrntoo high a temperature and/or for too long do not alwaysrnwash off with the standard bath. Residues caused byrnoperating the wash line off-spec (insufficient rinse,rntemperature wrong, concentration wrong, etc) do not alwaysrnwash off in the line. The troubleshooting guide will helprnwith determining what kind of residue is present, then leadrnline personnel to the appropriate rework method to removernit.rnThe data will show a before-and-after picture of chemicalrnconsumption for conveyorized wash lines and will quantifyrnthe cost savings.