[Elecraft] OT Why Clean Boards?, Was KSYN3A mod problem

[Wes (N7WS)]

Great post.

A fellow employee at Hughes Aircraft, albeit a different division and someone I 
didn't know, developed the water soluble flux ("lemon juice") that became a 
standard.  Hughes held the patent but sold the manufacturing rights so that 
anyone could purchase the flux.



On 9/11/2015 12:23 AM, Fred Townsend wrote:
> 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
>
>     
>