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Solder Diameter Question

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I plan to buy 1lb rolls of 63/37 solder and actually never bought solder before. The rolls I have were given to me years ago and the diameter size is okay. Sometimes I feel the diameter may be too large for 0402 components because one quick jab of solder and I have a bubble of solder that makes a mound on the component end.

Anyway, after using the filters on DigiKey for 63/37 and selecting a 'roll', I narrowed down the 'diameter' sizes for 63/37 and 'flux type'. I found the following sizes (see below) along with the flux type (no clean, no-clean water soluble, rosin activated, rosin mildly activated, and water soluble).

I've always assumed all solder was the same, so I'll use the term 'standard' and believe my 'standard' roll is rosin activated. Should I go with rosin activated or use another type of flux?

As for solder diameter sizes, most likely I just two (or maybe three) sizes to cover most of my soldering jobs. Usually I solder anything from 0402 to through-hole.

My question: which solder diameter sizes are best for covering all the jobs I work on?

Solder diameter sizes I found on DigiKey (in mm):


i use no-clean 0.56mm with 2% flux - but i don't solder 0402

stay away from any "water soluble" fluxes.
Rosin Activated (RA) will probably have the strongest flux so would work best with slightly old components, oxidized pads etc the flux will attack surfaces better,  but downside is SOME solders will require you clean the board after soldering (with isopropyl alcohol or flux removers) otherwise the flux may continue to corrode the pads and leads over time. You'll have to read the datasheets, they say if cleaning is required or recommended
RMA is rosin, mildy active, it's less strong flux.
No-clean is usually weaker flux but still perfectly fine if the components are relatively new - some no-clean fluxes may be a bit worse for your health, if you inhale the fumes .. but with all soldering it's recommended to have some fan or something move the smoke away from you as it's not good for your lungs.

Note lead free solders usually have quite stronger fluxes due to the higher melting temperature, so no-clean fluxes in them can be particularly hard on your lungs.

In your situation, I'd probably order a smaller spool (250g/500g) of 0.38 for small smd work (with 1-2% flux, and  0.51-0.61 with 2-3% flux for the bigger stuff - you can always cut a piece of solder wire and bend it in two to feed more solder if you have bigger soldering jobs.
I wouldn't get anything bigger than 0.7mm - that's already quite thick.

0.032" regular 0.062" think, we use USA made Kester 63/37 with 44 type flux.

Unsure EU/mm equiv


When soldering SMT parts I often put the solder on the iron tip and flux on the part rather than feeding solder in the way I do with through hole.

Water soluble flux is great but only for applications where you can easily wash the assembly when you're done assembling. I keep both water soluble and rosin flux as well as solder with each on my bench and choose based on what I'm doing.

For electronics, I use only two sizes: 0.81mm(0.032") and 0.38mm (0.015").  Both Kester 63/37 with #44 flux.  I have heavier gauges for other stuff.   The 0.38mm is used primarily for SMD.


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