Using water-cleanup flux core solder with rosin RMA flux? - Page 1
Forum section: electronics / beginners

author: grix812
author_rank: Newbie
timestamp: March 10, 2017, 05:37:44 am
content: I recently got some fine .38mm 63/37 multicore solder off ebay and it has hydro-x flux cores. Can I use this solder with RMA flux where I need to add additional flux? Or would there be some kind of bad interaction between the two?I'm wondering if I must buy water based flux to go along with this solder.

author: Rick Law
author_rank: Super Contributor
timestamp: March 10, 2017, 07:25:58 am
content: I'd stay away from buying more water-based flux. Wait till you see how the solder works.I just replaced a few connectors on speaker wires - soldered with rosin flux that was mixed with 70% alcohol. That to me implies probably 30% water in that alcohol.Speaker wire was actually used for 5V power on 5.1mm connectors. It was breaking often. Since speaker wires jacket happens to be clear, I can see the copper wires inside. I can see the wires closer to the solder was black-ish green --- copper oxide was destroy the wire in about a couple month or so, and in another couple of month or so, the soldered part broke clean off like a rusted wire! So, my reasoning of what happen was: the little water in my flux was probably steamed (or just flow) into the wire jacket caught inside the clear isolation. The copper and any thing that could oxidize did.

author: wraper
author_rank: Unknown
timestamp: March 10, 2017, 08:52:18 am
content: You will need to wash your boards with cleaning fluid in ultrasonic bath or PCB cleaning machine. Otherwise they will corrode over time if water based flux is used. Throw away that solder, it is suitable only at factories.Quote

author: james_s
author_rank: Super Contributor
timestamp: March 12, 2017, 05:39:47 am
content: I use solder with water based flux on some things without issues. I wash the boards in my little ultrasonic cleaner and it comes right off. Also works to just scrub it in the sink with warm soapy water.

author: wraper
author_rank: Unknown
timestamp: March 13, 2017, 07:24:13 pm
content: Quote from: james_s on March 12, 2017, 05:39:47 amYes but parts must survive that without damage. If using any switches or most of the relays, it's a no go. Also you cannot solder wires as it will get between the strands and under insulation,QuoteNo it does not. You still need to get it out from under the SMD parts, and every trough hole.

author: james_s
author_rank: Super Contributor
timestamp: March 13, 2017, 07:35:06 pm
content: I don't use it for SMD parts, only through-hole where I can scrub the bottom of the board with a toothbrush. It has advantages, but as with anything you have to understand the limitations.

author: alank2
author_rank: Super Contributor
timestamp: March 14, 2017, 02:35:58 am
content: I use water soluble for everything as long as it gets a hot watch rinse / air compressor dry. Never had any problem with it.If I don't plan on cleaning a pcb then it gets rosin.

author: Cubdriver
author_rank: Unknown
timestamp: March 14, 2017, 07:56:45 am
content: I have a spool of water soluble solder, and frequently use it when assembling through hole boards as long as they can be washed in hot water and blown dry with the compressor. If they have a mix that includes components that would be damaged by water, I'll put everything but those components on and rinse, then install the remaining parts with rosin flux that's then cleaned off with alcohol. I actually prefer the water soluble for things that can be properly rinsed as it comes off quickly and easily with warm water and a scrub brush, as opposed to rosin that must be removed either by chipping it away or with alcohol or some other solvent that is more expensive and difficult to handle compared to hot water from the faucet in the kitchen sink, and unless thoroughly cleaned with alcohol rosin tends to leave streaks and residue behind. (In its defense, I've had no issue with NOT cleaning rosin flux from boards. Aside from looking messy, I haven't seen it cause any problems over the years.)As others have previously stated, the water soluble flux MUST be washed off, as it is hygroscopic and, with time, WILL corrode and trash your board if not removed. To help with drying, the board may be dipped in alcohol after rinsing; the alcohol will displace much of the residual water and then quickly evaporate when blown off.I have both rosin and water soluble kicking around for use as supplemental flux; I try to match the type used to that in the solder being used, but have on occasion used supplemental rosin with water soluble cored solder with no ill effect other than needing both water and alcohol to clean the reside off the board. In those cases I've followed the alcohol cleaning with another run through the hot water as a belt-and-suspenders means to ensure that there's no residual water soluble remaining that was underneath and protected by the rosin during the first water cleaning.I DO NOT use the water soluble on wire (it will wick under the insulation where it can't be properly cleaned out and do its corrosion thing), or on anything I can't give a bath to (for instance, a point to point wired chassis).I don't currently mess with SMD stuff as a hobby, but lacking an ultrasonic cleaner, if I did do any, it would be with rosin rather than water soluble.-Pat