ErgoMechKeyboards @lemmy.world Merlin @lemm.ee 6mo ago

Lead free solder on microcontrollers

I’m joining the split keyboard group by building a piantor. I have the pcbs already and they’re lead free coated and I will use lead free solder on the components.

I’m a bit worried though as I used a borrowed split and I noticed I keep touching the soldering in the microcontroller quite a bit and the build I was going for was a bare one where we just put rubber feet directly in the pcb so there’s no case or anything.

I tend to rub my eyes and bite my nails quite a bit during the day. I was wondering if it’s safe enough on lead free solder or if this is something I should completely avoid.

Any suggestions in case I should avoid it entirely. I reckon the worst place would be the top of the pcb maybe I can use some hot glue where the solder is but I have no idea if it’s hard to pull it off later if I need to review/resolder.

This is my first project and I haven’t done anything like this before, so even the flux I’m kind of unaware how to clean, solder comes with it right, do I need to wipe it somehow or use isopropyl alcohol and wipe with maybe a paper towel?

Sorry about being a complete noob. I searched around but most people are concerned about the lead solder not lead free like me.

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12 comments

These are great questions!

I'm going to break down my response into two sections:

Building the machine

Don't breathe flux, if you can do your soldering outside. If you can't, put an extraction fan by your workstation, so the fumes don't get inhaled. If you want to be extra safe, wear a face mask, and gloves will soldering and working with the chemicals. When you're done working on the board wash your hands thoroughly

Using the machine

If you know the entire build process is lead-free, I don't see any issues of touching the board during daily use. If you're not sure if it's entirely lead-free, you can put a chloroformal coating on top of the board, usually used for waterproofing, but that'll prevent you from having direct contact with any of the heavy metals. You can use hot glue as well. Chloroformal codeine can be dissolved later if you need to redo a joint

Advice on solder

Unless you're a large manufacturing laboratory, it kind of sucks to work with lead-free solder, you have to use higher heats, it requires more technical skill. Especially if you're new to soldering, I would recommend using leaded solder anyway. Just don't breathe it, don't touch your face, wash your hands after. The lower temperature will give you a higher chance of success.

In either circumstance, get a practice old circuit board, desolder and solder things until you're comfortable with your heat management. You want to use the least amount of heat will still getting the job done
- Thank you very much for answering.
  
  I believe the pcb is lead free as I got it from jlcpcb and they have it written in the package of each side that they’re lead free. The solder itself is also lead free from a reputable electronic store near where I live so I think it should be safe. I live in an apartment so it will be tricky to do it outside, I may try to solder it where my cooktop is as I can turn on the range hood to suck the bad air up.
  
  Do I need to clean the flux that comes with the solder or it’s not that big of a deal? I’d expect that touching it when dry would be safe as well right?
  
  The problem with flux is that it is corrosive. If you use just the flux in the solder it shouldn't be much of a deal, but if you use more flux I recommend washing it off.
  
  I use 99.9% Isopropanol or an ultrasonic cleaner with water for this. If you use water do not use soap or anything else just water. Also make sure it is completely dry before connecting to power.
  
  Oh. Thanks. I’ll use the flux in the solder only. I’m quite a noob at that so I just got the soldering iron and the solder. I will see about getting the alcohol and use a toothbrush to clean it off after.
  
  Look at your solder spool, and see if it says multi-core? If you're not sure go ahead and show us a photo or write out the type of solder you're using.
  
  You need flux and solder together, flux prevents the board from oxidizing especially when you heat it up, it makes it easier for the metal to flow. A lot of solder has the flux built into the solder itself. When you put a hot soldering iron up to the solder and you see the smoke, the smoke is the flux, the antioxidation element not the metal. The metal does not smoke
  
  If you're using flux in addition to your solder, like a flux paste or a flux gel or a flux liquid you brush on, that's fine too. Just don't breathe the fumes.
  
  If you have a real n95 or n100 mask kicking around, wear that, do your soldering next to an open window or under your vent hood, let it keep venting after you're done for a couple minutes. And wash your hands and you'll be fine
  
  The solder I’m using is this one: https://www.jaycar.com.au/lead-free-solder-1mm-15g-hobby-tube/p/NS3092?pos=1&queryId=f28fc8a65a86eab148b5f9ae9b304dcc
  
  This is the description:
  
  1mm lead free resin core solder. Contains tin and copper 99.3/0.07
  
  Thanks again for the advice. I’ll wear a mask when soldering.
  
  Anytime! It looks good. Have fun making your keyboard!
  
  Lot of good points here. I work in electronics manufacturing so I'll add on a bit. Yes, much of what has been explained about solder and flux is correct. I will caution about trying something like conformal coating a board in this setting. It is hard to work through and can beat up your iron. Lead free is great but sucks for working it into the joints. It just doesn't heatt the same. Even IPC build standards have explicit instructions about visual inspections of non leaded joints looking like shit.
  
  If you are planning to coat the board, I would do outdoors as well. Extraction fans are great for general soldering but we use fume hoods for conformal coat. Just something to keep in mind.

12 comments