What flux and when to use it

[81F]

I have just written a long post with my reasons for this question but it seems to have got lost so my appologies for repeating it. However, in brief, I remember being told at school that there were two types of flux, Active and Passive and that Active fluxes should be best avoided for electrical work. The reason being was that if any residue was left the joint joint coulds act like a microscopic battery and corode.

 

My queries are therefore:

 

1. is the above true.

 

2. could any micro-current this might cause effect the operation of DCC chips.

 

Finally I understand that the flux in multicore solder is passive and therefore only keeps the surfaces being soldered together clean rather than the active fluc (bought as a liquid separately) cleans the joint of any oxide on soldering.

[Flashbang]

For Electrical soldering there is no need for any additional flux at all.  The flux (Rosen) in a multicore style solder is all that's needed. I've never use anything else in over 50 years of electrical soldering!  Try whenever possible to use a Lead content solder of the 60/40 type.  Lead Free can be used but needs a higher iron tip temperature to get a good joint!

The main things to ensure are .... The two items to be soldered are spotlessly clean (There should be no signs of any Oxidation - Use a fibre pencil to clean the area if necessary) Next that the iron has reached its full working temperature (wait a full 5 minutes for a normal iron to full heat the tip).  Ensure the tip itself is in first class condition and have a damp sponge available to wipe the tip on frequently. The iron is of a suitable wattage for the job.  Never use a to small a wattage as this will cause the joint to fail.

 

Acid based fluxes need washing off which can't normally be done on electrical joints.  There are special fluxes sold for electrical work such as Carrs Orange label or Reflow flux, but I've never found these necessary.

[morairamike]

Agreed for 99%of soldering on model railway the flux in  60/40 solder is sufficient.

However when soldering droppers to rails I use a flux pen as the need the time needed to get a good joint us us refrefd and thus the heat transfer down the rail is less. These flux pens are of the non rinse type of flux so no need to wash it off afterwards.

[96RAF]

Got a ref for that flux pen Mike.

 

My 40+ year old ex-RAF stores roll of multicore is nearing the end of days and lately I have found the flux to be ineffective, so a little external help would probably work.

 

I have some high silver content solder paste/flux for SMD circuit work but it has to be kept in the fridge and brought up to room temp before use, but it is good when used with a hot air iron system, although it is expensive - from memory about £15 for a toothpaste sized dispenser - presumably the silver content.

[morairamike]

Here you go picture and a place to buy ref.

Part number is CW8100.

/media/tinymce_upload/2b598de94bb82e77c82af531f9e08d2e.jpg

https://www.ebay.co.uk/itm/Chemtronics-9g-Pen-Solder-Flux-Water-Soluble/114164549597?epid=1504442652&hash=item1a94bcc7dd:g:LmQAAOSwFhxeg5Us

[96RAF]

Thanks Mike.

[Yelrow]

I always dip my wires in flux, prior to soldering. Cant tell you the make, as 20 plus years old, in green pot. Never had a problem.