Optimizing of PCBA cleaning process through process calibration tools

The paper explores complex interactions between chemistry, mechanics and thermodynamic parameters involved in the water based PCBA cleaning process. Current complexity of PCB assemblies, together with the needs to clean flux residues with the high grade of polymerization, due to higher soldering temperatures, requires a new approach in design of cleaning systems. A very detailed study of individual process parameters influence is necessary. Commonly used methods of the PCBA cleanliness testing-ionic contamination, chromatography, SIR and other are either unable to detect not dissolved residues under components, or are expensive in term of cost and time. A simple and fast method for determination of cleaning efficiency is introduced. It targets the first, most difficult and least monitored process phase - dissolving of flux residues - the cleaning step. It is based on optical evaluation of visible rest residues under low stand-off components on the precise standard test substrate with dedicated pattern of components. Evaluation can be done by visual checking, for more precise studies by means of modified AOI system. The special pattern was designed and made on a glass substrate with ceramic models of chips. Different possibilities of application of this test method are presented. This includes comparing of different fluxes- to cleaner matching, comparing different mechanical agitation efficiency in Spray-in-air and Spray- under-immersion processes, studying of influence of different process parameters on the cleaning result. Other application includes cleaning machine calibration and cleaning process capability studies. This method was already used in optimizing and diagnostics of cleaning equipment as well as in the design of new cleaning equipment.