September, 2019 Continued from previous page
149°F (65°C) on a controlled hot plate and continuously stirred for 12 days. Solutions were covered with a watch glass to prevent major evapo- rative losses. Each solution was re- plenished with deionized water as needed to remain at the original liq- uid level. After 12 days, a control part with aluminum pads and an aluminum panel were submerged in solution for 60 minutes, then rinsed with deionized water as before.
Experimental Results All four parts underwent vari-
ous tests to determine cleanliness levels. The pH of each solution at the conclusion of testing was 7.67 for the balanced alkaline cleaner and 5.77 for the neutral cleaner. The pH levels of both solutions shifted, but the pH neutral cleaner moved into an acidic range, whereas the alkaline cleaner remained closer to neutral. The sample with the aluminum
pad was inspected using a scanning electron microscope with a backscat- ter electron detector, as well as an energy dispersive X-ray spectroscopy detector. Two pads on each part were analyzed using SEM-EDS. The per- cent change of aluminum and carbon were recorded for the parts cleaned with a fresh bath and the aged flux- loaded bath. The neutral cleaner caused a 630 percent rise in detected carbon residues and a 35 percent drop in aluminum residues detected. The part that was cleaned in
the flux-loaded bath had extensive visual residues and was tacky to the touch. The appearance along with the spectroscopy results indicates that the loaded bath deposited flux from the cleaner to the originally clean test vehicle. The balanced alka- line cleaner caused a 29 percent drop in detected carbon residues and a 16 percent increase in aluminum detect- ed. The part was visually clean and free of any tacky residues. The alu- minum pad was intact after testing in both the balanced alkaline cleaner and the neutral cleaner. The cleaning agent’s ability to
be rinsed was tested using aluminum panels cleaned before testing with IPA and a lint free cloth. After rins- ing and drying, the surface tension of each solution was measured using a dynes solution. A dynes reading of 72 or greater typically indicates a sur- face free of contamination, which is the starting value for the panels. The balanced alkaline cleaner panels gave a reading of greater than 72 dynes after a fresh bath and a flux- loaded and aged bath. The neutral cleaner panels were tested at greater than 72 dynes after a fresh bath and 35 to 40 dynes after a flux loaded and aged bath. The aged neutral cleaner bath negatively affected the ability of the chemistry and flux to be removed from the panel. The preliminary testing per-
formed suggests that the neutral cleaner does not hold flux in solution as well as the balanced alkaline cleaner. This is likely due to the flux being weak acids that are more like- ly to react with alkalinity than sol- vents alone. Improperly solubilized flux residues can and do cause many issues during production. These flux residues can remain
in the interior of the wash chamber, along the walls of the wash tank, and redispose during the cleaning process. Residues remaining in the
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interior of the machine can also shorten the bath life of a fresh bath. This study demonstrates that
artificially flux-loading a bath, while keeping it at operating temperature can provide insights into problems
Page 51 Cleaning Chemicals: Qualification Versus Production
that may arise in a new production cleaning process. Adding a simulated wash bath to a qualification process provides the opportunity to observe changes in pH, rinsing properties and flux loading over an extended pe- riod, without the cost of charging up a machine. While the neutral clean- ing agent had similar initial results, with added time and flux, the data raises concerns for both consistency and long bath life in a real-world pro- duction process. Contact: KYZEN, 430 Harding
Balanced alkaline cleaner bath with 3 percent flux (left). Neutral cleaner bath with 3 percent flux (right). Note flux residues easily visible in the top layer of the neutral cleaner.
Industrial Drive, Nashville, TN 37211 % 615-831-0888 E-mail:
tom_forsythe@kyzen.com Web:
www.kyzen.com r
See at SMTAI, Booth 207
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