Solder flux for (dip) soldering small transformers and inductors. - Page 1
Forum section: electronics / projects

author: pope
author_rank: Frequent Contributor
timestamp: November 15, 2022, 04:01:56 pm
content: I just got a solder pot to use when I make small transformers and inductors. Small quantities, around 30-40 at a time.I usually use multi-pin coil formers like this one (or similar) and I'm fed up with soldering each pin separately...So, together with the pot I also got some lead-free (Sn99 3cu0 7) solder with no flux of course.I was wondering whether someone could recommend an appropriate solder flux for this task. Any information like what type of flux, what brand, etc. would be valuable.I realise that I can buy a bunch of different fluxes and mess around but I was wondering whether someone here has experience with this type of job, since it's the first time that I'll be using separate solder flux.I foundthis articlebut quite frankly it wasn't very helpful...FWIW, my pot is 65Watts and has a fixed temperature of 300°C.Many thanks!

author: jonpaul
author_rank: Super Contributor
timestamp: November 15, 2022, 04:21:38 pm
content: use 63/37 leaded eutectic solder barsget regulated adjustable solder pot, we preffered Plato.The Chinese pots are junkuse only rosin fluxuse old iron lam for drossavoid the bobbins like shown, poor plastic temp rating and shaky pins.Jon( winding xformers since 1970)

author: pope
author_rank: Frequent Contributor
timestamp: November 15, 2022, 04:44:42 pm
content: Thank you Jon.I already got a small pot similar to this (but larger) in order to experiment a bit. Do you think it won't work?Also, can you recommend some rosin flux good for this stuff? Is liquid rosin flux better?I asked a couple of solder manufacturers about what solder would work in my case, and they both suggested aSn99 3cu0 7solder.Solder bars are just too big for such a small pot so I went with solid core solder.I do use kester 63/37 for hand soldering but I'd like to avoid leaded solder for the pot.Regarding the bobbins, AFAIK that's the only option for RM cores...

author: Jon_S
author_rank: Contributor
timestamp: November 15, 2022, 06:39:13 pm
content: At a previous place we used to use a little pot of the same stuff that went into the wave solder line, very thin. I believe it was this one:https://bltcircuitservices.co.uk/product/10-95-ws/Dip the wires/pins and then straight into the pot. Must have done tens of thousands of RM cores like that with no complaints from production.I can't remember what the solder pot was back then, but I use a Quick 100-6CA at home and it does exactly what it is supposed to. The advantage of a big pot is that it is very easy to scoop the dross off, the old place used to have a nice titanium spatula...I use an old teaspoon!Hope that helps.

author: pope
author_rank: Frequent Contributor
timestamp: November 16, 2022, 10:01:02 am
content: Thank you Jon,Do you use the same flux and if so, do you clean it after the soldering?Also, may I ask what solder do you use?

author: Jon_S
author_rank: Contributor
timestamp: November 16, 2022, 11:46:28 am
content: I don't, all my home stuff is non-commercial hobby work, so I just made do with what was already on-hand. It's cheap rework spray flux squirted into an old aerosol lid and diluted with IPA until it looks runny enough:https://uk.farnell.com/electrolube/smfl200d/flux-bottle-200ml/dp/298311It seems to be discontinued. I don't think it is anything special, just rosin mildly-activated (RMA) no-clean flux with an IPA base. Kester 186 seems very similar from a quick Google, and it looks like lots of places sell that.The solder came from the same people that sold me the pot, in little nuggets not bars:https://www.somersetsolders.com/lead-free-solder-pellets-for-solder-potsI don't clean parts after dipping, I do clean the finished boards with Electrolube 'Fluxclene' and/or IPA.