I’ll confess: I really enjoy making a well-crafted solder join between two wires or soldering a component onto a PC board. There’s something very satisfying about the smell of the rosin (we won’t talk about the lead fumes, of course) and the crisp eutectic transition of the solder between its solid and liquid states at 183 oC (for tin 63% /lead 37% solder), Figure 1, and the shiny end-product of the well-formed connection.
A eutectic material goes from solid to liquid phase and reverse without an intermediate “plastic” state; for solder, the eutectic formula is a composition of 63% tin and 37% lead. (Image source: FCT Solder)
Being able to solder in various situations has saved me in tough spots many times, such as when doing a smart-thermostat installation (see Simple Schematic, Challenging Installation) or replacing a $3 failed capacitor in a $50 TV-converter box. Way back in the day, soldering even let me build all sorts of experimental circuits with discrete transistors, passive components, switches, and more, and these circuits were both reliable (if soldered well) and low cost (no prototyping board needed).
But I am also a realist: that was then, while this is now. I don’t see much need or opportunity for basic soldering for students, advanced hobbyists, or even project engineers. Let’s face it: most components are too small to solder (yes, I know it can be done in some cases with a fine-tipped iron, good eyes, steady eyes, and a magnifier, but still…) and many ICs simply can’t be hand-soldered due to connection bumps that are under their packages. It is possible to convert a toaster oven into a home wave-solder machine – lots of web sites show how – but that’s another soldering story altogether. Even analog sensors and specialty components now often come complete with miniature connectors thus eliminating the need to solder leads, and have you ever tried to solder those hair-thin wires used in earbuds when trying to replace a bad connector?
That’s why I was truly surprised, pleased, and slightly mystified to see the sign of Figure 2 outside our local library. I’m not sure if soldering is a skill for 10-year-olds, but maybe it’s at least OK to get them started. Unfortunately, I was not able to drop in and see what the class was actually like, how it was taught, and if the basics were being presented properly.
This library sign advertising a soldering class for 10-year-olds was definitely not expected. (Image source: author)
Coincidentally, a few weeks after I saw that sign, there was a very brief one-column piece “How to Use a Soldering Iron” in the April 2019 issue of Popular Mechanics (scanned as Figure 3).
This column from Popular Mechanics is mistitled; it should be “How NOT to Solder.” (Image source: Hearst Corp./Popular Mechanics)
Hey, I thought, perhaps the “maker” movement is helping basic wire and board soldering make a comeback. But when I read the column, I was shocked. It would have been better if it were placed in the “what’s wrong with this picture?” item which was on the back page of that same issue. Look at the column and review the oversights and outright mistakes:
- no mention of use of rosin flux (yes) versus acid flux (a big no-no);
- no mention of use of rosin-core solder which applies just the right amount of flux, rather than brushed-on paste. Most beginners who use paste flux use too much, which then interferes with the soldering process and also becomes a mess to clean off;
- never use sandpaper to clean and prep the iron’s tip; most tips are plated to improve “wetting” of the solder with the tip. It’s like cleaning tarnished silver-plate utensils with sandpaper;
- no mention of the need for cleaning any residue, oil, varnish, or other substances from the wires being soldered (very important!);
- perhaps most worrisome: while it is unclearly written, it implies that you heat the solder until melts, and let it drip onto the wires. That’s the classic recipe for a cold-solder joint which is both mechanically and electrically unsound. (Best is to heat the bare joint you are making, apply the solder to the other side, and let the heated joint melt the solder);
Pretty much the only point that is right in this column is the warning to be careful, as the iron will be hot.
What puzzles me is that even if the anonymous author commissioned to do the article didn’t know anything about soldering, he or she could do a web search on “How to Solder Wires” and tens of credible sites would pop up with detailed text and hands-on videos. It’s almost as if the author just imagined soldering as an abstract construct.
Do you still see a need for hand-soldering skills? To what extent? Has your ability to properly solder wires and PC-board components (assuming you can) ever been a real plus, either personally or professionally?
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