What is the need of "FLUX" when soldering on PCB?

[hermin]

how to clean flux off pcb

it helps the melted metal to bind to the copper plate, without the flux even if you heat the soldering lead hot enough, it wont stick to the copper, with the help of the soldering flux, the melted soldering lead will bind to the copper and its shiny white telling you its a good solder

 

[pisoiu]

buy interflux if-8300

I've made some tests, as promised. The test fixture was 2 SMA PCB connectors soldered back to back, with a wire between center connection. The hot wire was bended paralled to metal case on a 5 mm length, the distance between the wire and the gnd was approx. 0.5mm. I've normalized both traces (amplitude and phase), then I've poured some flux between the hot wire and gnd. The only noticeable effect was a phase shift of approx. 0,1deg. between 100 and 200 MHz, slightly increased towards 200 MHz. The ohmmeter showed nothing on 200Mohm scale. The tests were performed with HP3577A and Interflux IF8300 flux. This kind of flux is evaporating if the hot air is kept a little longer over it.

/pisoiu

 

[JohnJ]

flux pcb can

I assume you are all talking about rosin flux?

All fluxes do the same thing, clean the surface as they boil away, allowing the solder to bond to unoxidized copper.

Unfortunately the effects of residual flux is hard to quantify. The type of flux, the impedance of the circuit, and the amount of moisture it has been exposed to all will have an effect. Both the aircraft part industry and military suppliers are required to test for residual flux to very low levels in a lab before shipping boards. This should indicate that there is a problem with flux conducting.


When I started, activated rosin flux was about all that was used (basically pine sap with some chemicals added). That flux tended to become corrosive if left on circuits and if exposed to high humidity it could become conductive for a long time even if moved to a low humidity environment. Couple that with extreamly high impedance tube (valve) circuits and it was a real problem. Lucky for us we had vapor degreasers and gallons of FREON TF to clean it with! I still think this is the best flux. Only problem is without FREON TF it's very difficult to clean.

Next (from what I know) was water soluble flux. It works fairly well (nowhere near as good as rosin) and the idea was to use a machine that was basically a dish washer to clean the boards after soldering. It gave off very irritating fumes and the we were never able to get it all off the boards!

In manufacturing, we are now using "No Clean" flux. I don't know a whole lot about it besides it is supposed to be non-corrosive, but I've still fixed operating problems by cleaning the flux off!

NOT ALL FLUX IS COMPATABLE WITH ELECTRONICS! Plumbers use acid flux (ever wondered why those throwaway lab brushes are called "acid brushes")? If that is used on a circuit board...give up now and throw out the circuit board. It will actually get under the circuit traces and eat the trace eventually. It is also VERY conductive when mixed with water (humidity) and I've actually seen it eat the fiberglass of the board. You can buy flux at the hardware store that will allow solder to work on both brass and stainless steel!

Oh BTW, I've tried all three types of flux on lead-free solder with no problems (higher heat, but that's the solder).

 

[mmike]

need to flux?

how do I clean the FLUX from pcb after soldering?


By Water

 

[ahmad_abdulghany]

pcb which flux should i use

how do I clean the FLUX from pcb after soldering?


By Water

No, Water may not clean it well, you can use Acetone

 

[JohnJ]

pcb cleaner stainless steel dishwasher

No-Clean (most common today) is like it says. If you want to clean it, we use isopropal alcohol in the lab.

Water Soluble Like it says, but a SMALL amount of dish soap can be used IF you rinse thoughly! Believe it or not, most places I have worked use a home automatic dishwasher for small batches, the big professional machines just do bigger batches, not better. WARNING :!: do not solder on the board after getting it wet until really, really dried. For aircraft parts, we had to bake the boards for ~8 - 12 hours at around 120°F before soldering. Turns out that most lifted pads and traces come from moisture in the board below the copper. That gets expensive with 28 layer PCBaords.

Rosin (best flux, hardest to clean) Now that they took away our freonTF . Try Isopropanol, Methanol, mineral spirits, and acetone (watch that one, it desolves some plastics) individually or a mixture of them. Also, sometimes you will leave a white film that these solvents don't work on; That is usually a water soluble component you can remove with a wet q-tip. HINT: if you can get 90+% isopropl alcohol it's better than the 70% that is normally sold. Look around for it; it's used as a prep for medical shots. That extra 30% is water, which causes the white film I mentioned above.

 

[mmike]

water soluble flux oscillator

By the by I would mlike to know what are the different types of solder available