Cleaning after rework, no clean flux| 26 February, 2003
No-Clean paste + IPA = White Residue!
#1: Stop using IPA
#2: Switch to either a solvent-based de-fluxing chemical or an aqueous-based de-fluxing chemical.
If you are using an ultrasonic cleaner for your boards as stated, do not use saponifiers (an aqueous chemical that chemically converts flux to soap). Although saponifiers are the most common aqueous-based solutions, they require a lot of mechanical energy (more common in spray-in-air systems).
De-fluxing chemicals that are effective in an ultrasonic cleaner are:
As a general rule, consider most aqueous-based de-fluxers non flammable and (in most cases) able to be sent to drain (after filtration).
As a general rule, consider most solvent-based de-fluxers flammable (if you�re use to IPA then no big deal) and (in most cases) not able to be sent to the drain.
As far as a better method is concerned, not many people are using ultrasonic cleaning equipment for post reflow cleaning applications. Although ultrasonic technology works very well for wash (placing flux into solution), most ultrasonic cleaners do not adequately rinse. If you are considering another de-fluxing chemical (aqueous or solvent) consider the following. The only thing worse than leaving flux on a board is leaving de-fluxing chemistry on a board. Many modern de-fluxing chemicals are high pH. Although they are highly effective and environmentally safe, they must be thoroughly removed. Rinsing is the most important feature of any de-fluxing system. The most common technology used for de-fluxing are spray-in-air systems. Available in batch or inline format, they come in all sizes and capabilities from a number of manufacturers.