Oftentimes when people think of soldering, they immediately conjure up thoughts of dangerous fumes, searing irons, and lead exposure. And while these are accurate descriptions of the soldering process, there’s nothing to fear when handled properly. In fact, it’s very similar to working in a kitchen.
Yes, a hot stove will burn you if you’re not careful but always use your oven mitts and there’s nothing to worry about. You must be careful to avoid touching the hot iron and any heated surfaces. You could wear heat-resistant gloves but it isn’t so common because it can affect your dexterity, making it more difficult to solder. Instead you can use hand tools like pliers and just stay cognizant of where the heat is. If you’re unsure if something is safe to touch, a handheld infrared thermometer works great.
You’ll also find that sometimes molten solder can splatter like grease on a frying pan. Fast movements of the iron, slipping on a component, or an accidental flick of molten solder are all ways this could happen. So wearing eye protection is crucial for your safety along with gloves to help avoid any possible injuries or burns. This also prevents flying component leads, trimmed zip ties, and wire insulation from causing any harm. Soldering and electronics work in general should not be taken lightly. You always want to be aware of what’s happening. You should NEVER solder when you’re tired, sleepy, under the influence, or otherwise impaired.
Alright great but I thought this was supposed to be about lead solder? Don't worry, I was just getting to that. When using lead solder, think of it like handling raw meat. It’s perfectly safe as long as you don’t ingest it and be sure to wash your hands and work surface when you’re done. I personally like to wear a glove on just the hand I’m using to handle the solder wire. This makes me feel safe. Do your best not to contaminate everything and never eat or drink where you work and you’ll be safe. It’s really that easy! Oh and don’t leave the soldering iron on when you leave the house. It can cause a fire or at the very least wear down your iron and tip!
So what about the fumes? That’s what I’m most worried about. The good news is that soldering fumes do NOT contain lead. The melting point of both lead and tin are much higher than temperatures used for regular soft soldering. So what are these fumes composed of if not lead?
Well inside your solder wire, there is a core running throughout with a chemical called flux. This is what allows the solder to actually adhere to the workpiece and make a strong connection. When heated on your iron tip, the flux starts to smoke, and that’s the fumes you’re seeing.
Rosin-core flux is the most organic type and actually doesn’t smell too bad. But make no mistake, you really don’t want to be breathing these fumes in whether or not you like the scent. It is important to solder in a well-ventilated area and we recommend using a fume extractor to direct any fumes away from your face. When you’re looking over the workpiece and you breathe in, the fumes will naturally run directly into your nostrils. The fume extractor solves this by creating a stronger suction to pull them in the opposite direction. This way the exposure is minimized and makes for a much safer environment to solder.
The reason that soldering is so synonymous with lead is because it has been used in the formulation of solder since the beginning of time. When searching for the best solution, chemists discovered that the alloy of tin mixed with lead resulted in a much lower melting temp than the metals alone.
In other words, tin melts at 450F/232C and lead melts at 621F/327C but when they are combined into an alloy of 63% Tin and 37% Lead, the melting point drops way down to 361F/183C. Which is a temperature low enough for a soldering iron to handle, where higher temperatures would require a torch.
So now you may be asking, if lead solder is so functionally superior and not really a health risk under ideal conditions...
Well as we have come to realize, there are definite dangers of ingesting lead whether it’s lead paint, leaded gasoline or leaded solder. The main concern in pioneering these alloys though was not what happens while using it, but what happens after. We were causing a lot of environmental damage by allowing our landfills to be contaminated with lead-filled products.
If you think about how quickly new electronic devices are being released today, you can begin to imagine how many old devices are being thrown away or recycled every day. It’s staggering when compared to decades past when devices were made to be easily serviceable and last forever. So with all of this equipment contaminating our landfills, it only made sense to seek alternative alloys.
The first lead-free alloys were actually developed in the 1990s by a man named Iver Anderson and following his efforts came the lead-free initiatives we know today such as ROHS (Restriction of Hazardous Substances Directive) which seeks to limit environmental exposure of lead. When you see devices listed as ROHS compliant, this means they were produced with lead-free solder. Some regions such as the European Union, China, and California have banned the sale of leaded alloys to non-commercial consumers or maybe even entirely. The majority of consumer electronic devices produced today are now constructed with lead-free solders. Especially those made for mass consumption.
So we now have alternatives to lead solder that don’t pose any sort of risk, so why use leaded solder at all?
There are four valid reasons I can think of to still use leaded solder.
As mentioned earlier, leaded solder has the advantage of a lower melting point than lead-free alloys. The same job with lead-free would require more power from your soldering iron and the higher heat needed poses a greater risk of damaging your workpiece and shortening the life of your tip.
In addition to this temperature advantage, Lead possesses excellent wetting abilities. Meaning it is very easy to make a proper looking cone-shaped solder joint with. It also makes a nice shiny finish when cooled. For these two reasons, it is still preferred by many and provides a smaller learning curve for beginners.
It is a general rule of soldering to match the solder and flux chemistries to the project. For example, hobbyists and repair shops reworking older equipment should not be using lead-free alloys because the devices were not built with it originally.
Finally, it is an inexpensive solution compared to lead-free alloys.
With all that being said, lead-free is the future of soldering and these alloys have come a long way since their inception. The most popular lead-free alloys in our experience are SAC305 (96.5% Tin / 3% Silver / 0.5% Copper) and 96/4 (96.5% tin / 3.5% Silver).
For most general electronics soldering, we recommend SAC305 for lead-free and 63/37 for lead. These seem to be the easiest to work with in our experience and have excellent wetting. The 63/37 alloy is Eutectic meaning it melts and solidifies at the same temperature. This drastically reduces the likelihood of a cold solder joint since the range between solid and liquid is virtually non-existent. A cold solder joint is when the solder doesn’t get hot enough to melt entirely, resulting in a compromised connection.
In the end, the lead versus lead-free decision is up to the user but remember to avoid mixing alloys and flux chemistries for the best results. And to stay safe the number one safety precaution to take when soldering is doing so in a well-ventilated space such as next to an open window where air can circulate. Again we recommend incorporating a stand-alone fume extractor or one integrated into the iron to redirect fumes. Whether it be burning flux, plastic, or other chemicals the fan will pull the fumes through its carbon filter and get them away from your face. Also wear gloves and eye protection to cover all your bases.