Was KSYN3A mod problem David, you polar comment doesn't make sense to me so let's talk about the real issue: Cleaning PCBs.
Why do we do it? Besides esthetics there are two main reasons. 1} To get rid of flux which may be reactive with RF and reflow where it isn't wanted... like into contacts, mechanical devices, and shaft encoders. 2} To get rid of ionic compounds which may lead to circuit leakage and insulation breakdown. For many years one of the better ways to clean boards involved Freon vapor degreasers. They used a compound known as Freon TE which contained Freon and ethanol. Then, as Wes mentioned, the EPA banded Freon. Without Freon, which acted like the fire extinguisher Halon, ethanol became explosive so degreasers were banded. There are many types of fluxes. Most of the industry switched its machine soldering to water soluble fluxes so only soap and water were needed for board cleanup. Water was in some ways superior to ethanol because ethanol is a non-polar solvent meaning it does not capture ions, the types of atoms that support electron flow (see 2} above). However the most popular cored solders used in hand soldering are still rosin flux based so alcohol is still very viable for hand spot cleaning of PCBs. Ethanol and isopropanol are both good flux cleaners but perhaps are not as good as some other solvents as degreasers and of course they do not remove ions as water does. It should be mentioned that both pure ethanol and isopropanol are flammable meaning they burn with a dull blue flame. They don't burn like gasoline but many gasolines do contain ethanol. I have heard it said here to use only pure alcohol. That's fine if you are drinking the stuff otherwise the reasoning for this proclamation is somewhat nebulous. If you are letting alcohol or any other solvent evaporate on the PCB you are NOT REMOVING FLUX. You are just moving the flux around. After absorbing the flux in alcohol you need to remove it wet (i.e. as a liquid). There are a number of ways for doing this but perhaps the easiest is to blot with a paper towel. The alcohol with flux will be pulled in and trapped in the paper fibers. I like compressed air too. Now back to purity issues. Using a 91/09 or 70/30 isopropanol, commonly referred to as rubbing alcohol, adds water to the process. The water slows the evaporation rate, collects ions, and makes it difficult or impossible to burn. However 50/50 dilutes the alcohol so much that is no longer effective so it is not recommended. So a little water is a good thing; too much you drown. Don't forget your board has seen lots of water during the manufacturing cycle. Don't be afraid of a little more water but of course don't operate anything without thoroughly drying. 73, Fred, AE6QL -----Original Message----- From: Elecraft [mailto:[email protected]] On Behalf Of David Woolley Sent: Thursday, September 10, 2015 4:52 PM To: [email protected] Subject: Re: [Elecraft] KSYN3A mod problem Ethanol and Isopropyl Alcohol are almost as polar as water. That's why they mix so well with water. https://en.wikipedia.org/wiki/Solvent According to its Wikipedia entry, ethanol doesn't even mix well with heavy oils. Isopropanol is better. -- David Woolley Owner K2 06123 On 09/09/15 01:51, Fred Townsend wrote: > Water is not a problem. You want the water to pick up the water > because alcohol is a non-polar solvent meaning it does not pick up the > ionic contamination. The water picks up the ions and alcohol picks up the water. > Conclusion rubbing alcohol containing water works just fine although > the ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
