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Incoming Water Quality



Incoming Water Quality | 11 June, 2001

Are there incoming rinse water quality standards - specifically maximum concentrations of magnesium and chloride - for an aqueous or semi-aqueous cleaning process? If there aren't standards, does anyone have experience with what the max can be before problems occur? Thanks for the help.

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Incoming Water Quality | 11 June, 2001

The issue is not the cleanliness of your in-bound water. The issue is the cleanliness of the board your customer receives. Look at J-STD-001C, Para 8, "Cleanliness Requirements".

The end product cleanliness is the end result of your: * In-bound components and boards * Flux res from reflow, wave, and hand soldering operations. * Handling of these materials. * Cleaning operations.

All of the minerals [and other stuff] in water affect its resistivity [megohm-cm], er conductivity {1/[resistivity]} in microsiemens-cm, either of which can be measured. Our tap water is ~50k ohm. Public water authorities have varied resitivities. Ours varies through the year.

Our wash plan is: * DI Wash (conductivity = 10 uS [100k ohm] max) * DI Rinse (conductivity = 5 uS [200k ohm] max) * DI Rinse (conductivity = 2 uS [500k ohm] max) * Air- knife dry

Other places, other times; we controlled a 0.5 uS [2M ohm] final rinse and just cascaded to the front of the washer.

Consider starting at your board cleanliness requirement and then working backwards to determine the requirements of your wash water.

3 Water soluble fluxes leave ionic residue detectable by: 3a ROSE testing (Omega meter, Ionograph, etc.). This test is useful to determine whether the cleaner is in control. Commonly used throughout the industry. 3b Ion chromotagraphy. This test measures specific residues that can causes failure. Generally, only large shops can maintain the equipment. 3c Surface Insulation Resistance. This test actually has a correlation with field failures. [No failures relating to residue, if resistivity is above a certain level. Guaranteed failures, if its below a certain level.] The level depends upon environment, panel design and circuit design (voltage, current, impedance, spacing, indoors vs. under the hood...). This test should be done on test coupons in an environmental test lab. It is rarely done as a process control, since the test takes a week, and is not usually done on production panels.

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