After doing a lot of research about this subject, there appears to be a lot of opinions about the proper way to clean a PCB and when or if even necessary to use an Ultrasonic Cleaner. Which manufacturers make descent ones etc. After building up a board I normally clean it with an acid brush and copious amounts of Isopropyl Alcohol. The board was failing with a digital input to a CPLD having 3K of resistance to an adjacent pin that was an output pin. I had to literally spray at high pressure Isopropyl alcohol between the pins to get under the CPLD (A TQFP package) to get at flux residue under the part. This fixed the problem. Question is, can a Ultrasonic cleaner do the same? And if so what type of cleaning agent should be used and how to go about it?