Today I decided to work on my list of home maintenance tasks. The first one I tackled was to find and repair a leak in our 110 year old iron yard-irrigation pipes. The leak had been going for a while, and had not caused a convenient surface pool, so I spent a few hours slipping around in gooey mud (clay soil) and scraping mud off of my shovel blade. I found it, but the condition of the pipes was such that I decided we didn’t really need to irrigate the yard until April, so I shut off the yard water, and turned to fixing a nice old lamp that had belonged to my wife’s grandparents.
The lamp’s wires led to the sockets through sharply bent tubes and various channels through the structure. I found that wires and sockets alike were either broken or worrisomely used, so I changed all of them. making many connections as I went through it. But although the connection locations inside the lamp structure were accessible through removable plates and such things, there was not enough room to use wire nuts. So I twisted them together, soldered them, wrapped them with tape, and bingo—new lamp. Much better than making ditches in the mud.
But I realized how much I like to solder. If the joints are clean and they are at the right temperature, the solder happily flows to cover all surfaces, bridges all gaps, and turns an ugly bunch of twisted wire into a shiny and beautifully conducting electrical joint. And you can do this without spending large amounts of money on equipment and learning esoteric theory. The photo at the left shows the content of my soldering equipment box, and as can be seen, it is old and dirty, but performs very well indeed.
I was one time involved in the quality of soldered joints while at the Jet Propulsion Lab, and became interested in the history of soldering. I learned to solder from my grandfather, (clean everything and then clean it again— heat the joint, not the solder). He was a part time blacksmith and sheet-metal worker, did larger scale jobs (tanks, funnels, buckets, ducts, etc.) and heated his irons with blowtorches. I was restricted to tin cans a single iron, and a tin snips, but that was enough to start. In fact I scored in the second grade because we were studying dairies and had to build a model one. I made my part out of soldered together tin can metal.
As far as history, I figured that soldering had been around at least as long as my grandfather. But I found out that the Romans had used solder to join the pipes in their empire, and that the solder had approximately the same mixture of lead and tin that was being used at JPL. This was interesting. Tin helps solder wet the surfaces it will join, which is good. But beyond that, a mixture of 63% lead and 37% tin is called a eutectic mixture. It has the lowest melting point of any mixture of lead and tin, and will go from molten to solid without going through a stage when one solidifies while the other remains liquid —excellent characteristics for solder. But I don’t think the Romans had metallurgy books that told them that, and through practice they figured it out. And the most commonly used solder these days for manual work is probably 60% lead, 40% tin—shades of the Romans.
Going backwards, the Sumerians used solder to assemble their swords, the Egyptians for their metal work, and so on. Soldering has always been used heavily in jewelry. Apparently soldering has been around for at least 7000 years—even before my grandfather’s time. As you might expect, Wikipedia contains a large amount of information on solder and soldering. It is here.
Of course there are many types of solder, since the label includes any metal or combination of metal that can be molten and when solidified will hold other metals together. There are soft solders (what I used on the lamp), hard solders (silver solder, etc.) and brazing metals (copper based). Increasingly, due to health and environmental concerns, solders used in electronics and for other purposes are no longer containing lead.
Solder is produced in many forms —wire with or without a flux core, bars (plumbers), and sheets (jewelers). It is also applied in many ways, ranging from manually (me) to mechanically. Components with leads that penetrate circuit boards are commercially soldered to the circuitry with what is called wave soldering. A wave soldering machine contains a pool of molten solder in which a wave is formed, and the bottom of the boards pulled through the wave. Surface mounted components are attached by a different process called reflow, in which components are attached by a mixture of powdered solder and an adhesive flux, the solder then being melted by heat.
But all of them produce the same magic—a quick attractive joint that is both electrical and mechanically sound. Not as strong as a welded joint, in which the parts of the joint themselves are melted, but good enough for many applications. And it can be produced quickly and at low cost—good for me, good for the electronic industry.