Does flux affect a circuit?

I've heard a couple people say that cleaning the flux off their circuit boards significantly improved the sound. Does flux really affect the sound, and how does it negatively affect a circuit? Capacitance?

I think that mostly applies in very high impedance circuits like the FET amp inside a microphone, where any tiny bit of capacitance drastically alters the noise characteristics, or something

Aha... -classic!

Someone refers to "Flux Capacitance" and not even the slightest hint of a "Doc Brown" Back to the Future reference!!!

In actual fact, you have to clean it all off, in case it causes a time paradox, the consequences of which could be disastrous...

Great Scott!!!

:green:

Okay, "back to the subject" -in high impedance circuits, well, conceivably, but I bet dollars to doughnuts that you can't hear it. A rather more practical reason might be that some fluxes can be corrosive, so it's a decent idea to clean it off anyway. The kind of person who says they can hear the difference in most circuits is probably the kind of person who buys cable-cradles for their speaker wire.

For real.

Keith

[quote author="SSLtech"]Aha... -classic!


Okay, "back to the subject" -in high impedance circuits, well, conceivably, but I bet dollars to doughnuts that you can't hear it. A rather more practical reason might be that some fluxes can be corrosive, so it's a decent idea to clean it off anyway. The kind of person who says they can hear the difference in most circuits is probably the kind of person who buys cable-cradles for their speaker wire.

For real.

Keith[/quote]

The same kind of people who claim to be able to hear the difference of a line level signal running through two different short pieces of wire? Unless flux causes substantialy more capacitance than the pcb material and air it would seem unlikely you could hear a noticable difference?

In very high Z circuits it can cause leakage paths and noise. In microphone it can sometime leak the charge away from the capsule causing low output and/or noise.

Appreciated Gus, but only if it bridges two conductors directly.

If it's just merely present on a trace/joint where the copper meets the Glass Fibre PCB, it can't really do much since a practical capacitor requires two conductors seperated by a dielectric. If the flux bridges two close but exposed conductors, then that's a different story. The impedance has to be staggeringly high (think Condensor mic) in order for the nonlinear conductivity to becoms an issue, I think everyone agrees. -If you have plenty of 'land' between the conductors, there's very little that flux can do, even in mic circuits. If it bridges copper to something non-conductive, it's still an open circuit.

Some folks still might hear an improvement. I need to get in touch with some of these people though. I have a bridge and some C37 to sell to them.

keith

Thing is, sometimes the flux is such a thin film, you can't see it. The first go I had at a mic mod resulted in a noisy mic. I thought "Oh no! I've killed it!" Then it later dawned on me that the board could still be dirty, even though it looked clean. I gave it a good cleaning and it was fine.

I used to work for a company that made radiation analyzers. Scintillation detectors need 700 ? 2K volts to operate so these analyzers had to have high voltage supplies. Just a little bit of flux around the HV area and it was hosed. I can?t tell you how many times I ?repaired? these by just cleaning the boards. Funny thing was, I could never see the flux ? not even with a magnifier.

We had a couple of flux incidents here at work. Somebody ordered the wrong type of solder and hundreads of boards had to be put into a ultrasonic cleaner. Opamp inputs was the area that gave us the heaadache. I do not know if a high impedance leakage path could affect audio, I do not think there are that many high impedance circuits used in audio other than microphones. I would think that you would have to exceed a one or two hundread k-ohm input impedance before you run into trouble.

If you have flux problems, after you clean the board you should probably spray it otherwise moisture might have an efect. The boards we had problems with were 4-20 ma circuits. You could make the 4 ma go up to 6 ma just by breathing on the board.

I think I remember Kev saying he just used a little denatured alcohol to do this. Anyone see any problems with this or do you really need "flux cleaner"
Sleeper

In a pinch, I've seen Vodka used to succesfully clean flux off of boards...

Ian

I've seen a fair amount of vodka spilled on boards, but not intentionally, they generraly still worked ok, unless the tonic and lime ration was too high.. :wink:

I use high-purity isopropyl alcohol to clean flux off circuit boards. Everclear also works like a champ, but resist the temptation to drink it! :shock:

Laquer thinner, Toluene also cleans flux very well; although it isn't too healthy to use this stuff on a regular basis without taking precautions from the fumes. Ethyl alcohol keeps everybody happy.

I have never heard of flux affecting capacitance, however as mentioned by others - high impedance circuits can have leakage if the flux bridges two conductors, although we are talking 10's or 100's of megohms.

[quote author="Sleeper"]Anyone see any problems with this or do you really need "flux cleaner"...[/quote]Depends on what type of flux your solder has in it. I clean with water because I use water soluble flux.

[quote author="BYacey"]although we are talking 10's or 100's of megohms.[/quote]Mic capsules and the FET gates are usually biased with 1Gohm resisters.

I have tried water soluble flux and was less than impressed with the results. It just didn't seem to break through the oxide layer you normally encounter in electronics work. Rosin just seems to work better IMHO.

Flatpicker: you are right, with condenser mics this is an instance where cleaning the flux away is important. leakage around the first stage is critical due to the high input impedance and the high impedance current source. Flux can create noise and reduced polarization voltage. In audio circuits this is one of the few circuits where I think rosin leakage can be a concern.

[quote author="BYacey"]In audio circuits this is one of the few circuits where I think rosin leakage can be a concern.[/quote]I agree. Probably not that big a deal anywhere else.

BTW, what solder did you try? I've been using Kester "331" and it works great. Sometimes you have to squrit some extra flux on the solder joints, but it sure cleans easy. (This flux isn't cheap, either!)

Used Flux is hydroscopic and absorbes moisture which can create a capacitive coupling between traces so even if a dead short is not realized, the soound can be affected.

[quote author="RedHouse"]hydroscopic[/quote]...'hygroscopic', perhaps?

Again, the crucial part of the explanation is "between traces".

Keith

Resin or rosin is an oleo-resin from coniferous trees; sap essentially. Because of the oils and resin mix I haven't found it to be hygroscopic. In fact, I use an ordinary block of cheap violin rosin along side my iron. Works great.

As a hobby I build violins and rosin is an ingredient in instrument varnish in a lot of formulations. I have never been able to get rosin to take on water. In fact, in the process of refining rosin for varnish water is used to leach out impurities from the resin. Alcohol will dissolve rosin as well as other essential oils and essences, but I have never had water do so.