I have wondered about using chemicals to restore older paste to usefulness. When I commented about using the ultrasonic to extend the shelf life of solder paste...I should have stated that I stored the paste in an airtight container in the refrigerator. When I opened the container each time, I could smell the strong odor of alcohol, I thought it was isopropanol but was never sure and never checked the MSDS. Perhaps the sealed container prevented or minimized the loss of some of the chemicals in the flux. I've also heard ultrasonics can damage or weaken the bonding wires in ic's and transistors. But, I've never had a failure in anything I've built-as far as I can tell, there is no damage to the bonding wires. I built a keyer for the shack years ago, it was one of the first projects I used the ultrasonic for cleaning flux with. I have ultrasonic'd that board for 10 hours (intentionally) just as a test, and it has worked fine (for years)-in fact, I use the keyer almost daily and take it to contests too. Enjoy. Art >From: Matthew Bajor >Date: 2008/06/12 Thu AM 11:52:51 CDT >To: "Microcontroller discussion list - Public." >Subject: Re: Re: [BUY] Solder paste in a syringe >I worked a few summers ago at an aerospace contractor doing alot of SMT >work. If I needed to touch something up, I used 3-Propanol to thin out the >flux and sometimes the paste. For really fine work, I would thin the flux >with the propanol, but mix it in with a little solder paste. The heating >action is imparted better on the solder balls of the paste, almost negating >what would be a sort of surface tension. I've never heard of the ultra-sonic >method but I'm guessing it could work in the short term. > >Matt Bajor > >On Thu, Jun 12, 2008 at 4:11 AM, Alan B. Pearce wrote: > >> >I throw my completed and tested new boards straight into the >> >ultrasonic bath, with plain water. I usually leave then there for 30 >> >seconds. >> > >> >It removes any and all flux, even the flux left residue underneath the >> >chips (on smt packages). It works great to remove the flus, even if >> >the flux is not the water soluble type. >> > >> >It sure beats the heck out of drowning the board with toxic and >> >expensive flux remover::> >> >> However ultrasonic baths are also a known destroyer of chips. What appears >> to happen is that the ultrasonic vibration seems to shake bond wires off >> chips. >> >> I know that ultrasonic cleaning is banned for anything we fly in space >> because of known problems induced by ultrasonic cleaning. >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >-- >http://www.piclist.com PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist