Pete, the traditional solder for electronics ( and wires) has been 60/40 tin lead solder with a rosin core. It's important that you avoid acid core, which is used for plumbing and can cause a lot of long term problems with electronics.
IMO, the best solder is still the old standard but a lot of people/countries don't like the idea of melting lead so there are now "leadless" tin solders available. The types I've tried work ok but they all melt at higher temps which can increase problems with heat transferred control. Personally, I don't think I do enough soldering to worry about using tin/lead solder. I'm careful about NOT breathing fumes when I use it and I have a collection can for any removed solder so it can go to our local hazardous waste collector site.
Rosin core, 60/40, tin/lead solder is available in several different gauges of wire. I keep a coil of very thin solder for small thing and a coil of thicker for heavier, usually wire connection, soldering.
BTW, it's hard to overestimate the value of having a good quality iron or, better yet a soldering station. They are absolutely worth the cost if you intend to do any soldering beyond the occasional wire splice.
My favorite is Ersin Multicore 60/40, but sometimes all you can find is kester. Its good too.
Precisely David. High reliability (Military, Space applications) have prescribed 63/37 for quite a while as the Eutectic nature of the solder produces higher reliability joints as evidenced by extensive testing. You might think that Musical Gear is not exposed to harsh environments (relative to the Army) but sweat, liquids, heat, cold and transport really beats gear up. I used to think that an 18 year old Soldier was my acid test for durability but now I sincerely think that most musicians put them to shame (and most musicians take better care of their gear).
On flux type - amen on Rosin flux. I keep a needle tipped bottle of plain type R flux on my bench to help reflow joints - particularly on potentiometer cases. There are actually 3 types of rosin flux - Type R (plain rosin), Type RMA (Rosin, Mildly Activated - contains a little acid) and RA (Rosin, Activated - contains a little more acid). Try to stick to type R or RMA for the most part. The residual acid from RA can cause premature solder joint failures.
With regard to lead free solder - it can be used and can produce acceptable solder joints, albeit at higher temperatures. Despite decades of soldering, I find it more difficult to work with and the solder joints always look cold when compared to the lead alloys. This makes quality control of your work more difficult. When we switched over in the Military Electronics world, it took a lot of testing and IMHO - is an example of a "good enough" solution. It is simply not as reliable as lead alloys and never will be but it does meet the lifetime requirements.
With all type Rx fluxes - cleanup is simple. Cotton swabs and Isopropyl Alcohol.
One last comment (slightly off topic) is that I find a fiberglass burnishing brush to be an indispensable tool. Light scrubbing on potentiometer cases and other nickel plated surfaces promotes good surface wetting and adhesion.
Thanks for the details on the flux types, JR.
Thanks also for mentioning the substrate prep. It's vital to a successful joint.
Much appreciated input :)
I've been using Kester "44" 63/37 Eutectic solder for .... ever. MultiCore is a SUPERB solder and if it were easily sourced in my location, that's what I'd be using.
The 63/37 solder melts & solidifies within a couple of degrees almost assuring a good joint. For guitar & PCB work, the .031 diameter solder is great. It's wetting and flow properties are ideal.
Lead-free and silver solder have no place in guitar, amp & cabling work. Like Ned advised, acid flux solder is a death sentence for guitar electronics as the acid will corrode & ruin connections and components.
If you visit the websites of Weller, Hakko, Xytronic, Metcal, etc. soldering equipment, you'll discover the MOST important information about soldering: HOW TO DO IT CORRECTLY. You can use a $2,000 soldering station and use Unobtainium solder, but the QUALITY of work completely overshadows the material & equipment used.
Also important is tip selection. For guitar component work, a 1/16"-1/8" chisel tip is nearly imperative. For PCB work, you'll need a fine point conical tip. Of equal importance is the tinning & cleaning of the tip while using the iron and before it's put away at the end of the job. You'll also want to look into a tip cleaning/dressing compound.
A temperature controlled 40-60 watt soldering station is perfect for this work. Any wattage higher or lower and you'll easily damage your work. I've used all kinds of stations form the legendary Weller WCTP station to cheap Rat Shack irons. I currently use a Xytronic LF-389D 60 watt station with vast assortment of Hakko tips. Check out Jameco Electronics for a good selection of gear, good prices and a one stop for your soldering needs. https://www.jameco.com/webapp/wcs/stores/servlet/StoreCatalogDrillD...
One thing to watch out for are counterfeit soldering stations. Most well respected models from trusted manufacturers have been flooding the market. Ex: if you see a genuine Hakko station that normally street's for $125 selling for $39 with 17 extra tips and a 1lb. roll of solder... you can BET it's a fake with performance that matches it's price. Also be aware that iron tips have also been victimized. I pay a bit extra and always buy mine from an AUTHORIZED Distributor.
That's enough info to get you started. Hope it helps & best of luck. It's great to see you expanding your horizons :)
I couldn't agree more on the Hakko FX-888d, David. It's my next acquisition :) It's a sweet looker too, for what that's worth. Very compact.
I'd also like to add that for good clean repair joints, Solder-wick is an absolute necessity bordering upon 'a life saver'.
Also, to Pete..... If you'll private message me your address, I'll send you 20 feet of Kester 44 63/37 .031 dia. so you can audition it. You can e-mail me at: email@example.com :)
If you eventually buy a 1 lb. roll of it and use it for guitar work & light electronics repair, it should be enough to last you SEVERAL years.
You can also take everything David Collins recommends to the bank :)
Iron envy alert :)
Mines bigger, hotter; yeah, know the drill!
Hows your iron hanging pardner,
Mine? Short tip but high wattage & rapid recovery time ;)
You cracked me up, Rusty. THANKS, mate :)