Mac's Service Shop: Soldering |
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It is a rare thing when I take exception (i.e., disagree) with anything Mac McGregor has to say, but on the subject of soldering I must object. In this 1956 installment of Mac's Service Shop, Mac and Barney are discussing the plusses and minuses of making a solder joint mechanically sound prior to applying solder. Barney mentions an article he read where the author asserts that the only way to make a quality solder joint is to wrap component leads and wire ends around posts, lugs, eyes, etc. and then flowing the solder. Both Mac and Barney argue that a perfectly sound solder joint can be made simply by laying the lead or wire in place and applying solder. From a servicing perspective that sounds good, because - as I can attest to from much experience - needing to unwrap something from around a post or from passing through a lug or eye of some sort can be a major chore, and the opportunity for inflicting damage is greatly increased. However, part of the motivation for creating a joint that is mechanically sound, independent of the solder, is that doing so helps immobilize the connection during the cooling down phase of the job, thereby reducing the possibility of creating a cold solder joint. Cold solder joints are mechanically and electrically compromised. Also, during construction of the point-to-point assemblies as were prevalent back in the day the practice was to mechanically attach all the component leads and wires to a particular attachment place (lug, post, etc.) - and often to multiple attachment places - and then go back and solder them all (as opposed as doing each one as it is added). That required doing more than simply passing a lead through a hole or holding it next to a post while soldering since not only might a wire get knocked out while doing other work, but adding another wire to the joint would require somehow securing the preexisting wires so they don't come off. Mac's Service Shop: Soldering
It was a beautiful, invigorating, crisp fall day outside; but inside the service shop Barney and his boss, Mac, acted more as if they were suffering from spring fever. In spite of the radios and TV sets that were piled all over the place, they were taking a break. Mac was a great believer in these little "recesses," which he contended kept a fellow from going stale and doing careless and sloppy work from sheer weariness and boredom. At any rate, he and Barney were sitting side by side on the service bench chomping away on a couple of candy bars. "Hey, Mac," Barney mumbled through a mouth full of candy, "I was reading an article in one of my ham magazines the other day written by a guy by the name of J. R. Smith in which he was arguing that the belief you had to make a solder joint mechanically secure before flowing solder around it was just a lot of stuff. What do you think about that?" "With a few reservations, I'm with him," Mac answered promptly. "I'm glad you brought that subject up. Probably no single operation a service technician performs is more important, because it is used so often, than soldering; yet most of us keep right on making solder joints exactly as we did when the solder itself was far inferior to present varieties and when the iron we used was a heavy, clumsy affair with practically no control over the heat. It is just one of those operations that are so common that we never stop to wonder if we could improve our way of doing them; but I'm willing to wager that most of us - including you and me - could do a much better job of soldering than we are if we could just quit thinking we know all that's worth knowing about soldering." "Probably the boys who used solder purely for holding mechanical joints gave us the idea that solder connections had to be mechanically solid," Barney offered. "This fellow Smith said that exhaustive tests of solder joints made in government laboratories showed that merely shoving a wire through a hole in a socket connection, laying it in a slot, or bending it at a right angle around a stud and then flowing solder around the wire would produce a joint that would withstand the most severe shock and vibration under extremes of temperature. The wire or pigtail would give up and break long before the solder joint failed." "That certainly checks with my own experience," Mac remarked. "For a long time now I have made it a practice to install volume controls and other parts in receivers with the thought in mind that one of these days I'm going to have to remove them. You know how exasperating it is to try to unravel one of those soldered connections in which the leads have been twisted securely and the ends tucked in out of sight and reach before the solder was applied. By the time you get all the wires loose, you have probably broken one or two of them and have ruined a component or so with the excessive heat used to keep the knot soft while you sorted out the wires. This sort of thing is especially bad with the connections on small sockets. The sockets themselves will not take too much heat, and the connections break easily under much pulling and twisting. How much easier it is to remove the leads when they have simply been thrust through the holes a sixteenth of an inch or so and solder flowed around them!" "Yeah, and another advantage of that kind of joint is that you can tell if it's good or not simply by pulling on it after the solder has set. If the joint was made mechanically solid before soldering, this pull test will reveal nothing; but when the solder itself is doing the holding, a little tug will break a rosin joint loose at once. As far as I am concerned, still another advantage lies in the fact you can do a much more professional-looking job by this method once you get the knack of it. I know, I tried it on a transmitter kit I was putting together, and I found it was much faster, made neater joints which were easier to inspect, and used much less solder. But I wasn't going to say anything about doing this until I learned if you went along with the idea." "Aren't you the cagey one!" Mac exclaimed with a grin. "But you may have encountered one of the exceptions I had in mind in putting that transmitter together. When the lead being soldered is very heavy and stiff, as you sometimes find in tank coil and band-switching circuits, making the joint mechanically secure before soldering is just taking out insurance against the severe strain and prying the joint may have to endure because the leads are so heavy. This is far in excess of any pressure that could be exerted through ordinary connecting wire used in radio or TV sets or through the pigtail leads of capacitors or resistors." "I'm away ahead of you," Barney exclaimed. "I did make those joints solid before soldering. Awhile ago you said something about solder being better now than it used to be. How about that?" "It most certainly is," Mac answered. "To appreciate just how much soldering has improved, you should have had to heat a big old heavy iron in a gas flame and then gouge solder off a big bar the way I did when I started in this "wacky" radio repairing business. The flux used in present day solder is also far superior to the rosin-core solder that first came on the market. In those days, it was not at all unusual to find great lengths of the stuff with no flux in it at all. But I still think there is a lot of difference between present brands of solder intended for radio and TV repairing. The other day the salesman was out of the brand I have been using for years, mostly through sheer habit; so I let him sell me another kind he recommended. I was astonished to discover it melted easier and flowed much more smoothly around a joint than the kind I had been using. Solder is not all alike." "I'm sure some of the present solders are deliberately designed to work with the solder guns that practically all of us use today," Barney observed. "With them, you want a solder that melts easily, sets fast, and has a good flux evenly distributed." "You have to keep in mind, though, that no matter how you prepare the joint mechanically, you still have to observe the rules for good soldering. I mean the metal parts to be jointed have to be clean and bright; they must all be raised to a temperature well above the melting point of the solder; and they must all be held perfectly rigid while the solder is setting. Carelessness in any of these particulars means a bad joint, no matter what other preparations you make." "Check!" Barney agreed. "And I was just thinking that the advent of printed circuits has made it necessary for us to learn some new soldering habits. I learned them in a hurry when I was putting together that scope kit that used two printed circuit boards. Too much heat there will cause the metallic conducting foil to separate from the board itself; so you have to be very careful not to use too much heat. What's more, in some places the conducting lines are quite close together, and an excess of solder means a short-circuit. The manufacturer suggests that you use one of the very small and light soldering irons of the solder-pencil variety on the circuit boards; so I tried this and found it worked reasonably well, but I also found you had to hold that light iron against some of the joints, especially the 'ground' ones that were surrounded by large areas of foil, for a long time to make a good joint. Finally I went back to my trusty old solder gun." "How did you keep from overheating the printed circuit boards ?" "I held the solder gun against the wires protruding through the hole in the printed circuit board until they were hot. Then I dabbed the solder against these leads just opposite the solder gun tip. Almost instantly a little solder would melt and run down the short length of the wires to the foil, where it would instantly fuse to this foil that had been preheated through contact with the hot wires. This system was far faster for me than using the light iron; and anyway I just don't feel like I'm soldering unless I can hear the trigger of that gun click." "Sounds all right to me," Mac commented; "and incidentally, it always worries me to see a fellow holding the tip of a solder gun against a joint while the tip heats, especially when that joint carries leads to units easily damaged by heat. The way to do it is to hold the tip off the joint for a second or so until it is hot and then dab it to the joint with the solder being applied almost simultaneously." "Well," Barney said as he slipped off the bench and stretched luxuriously. "I guess we have reviewed the soldering situation pretty completely. As I get it, you are all in favor of making easy-to-remove joints in which the solder is depended upon to hold them solid, rather than making the joints mechanically' solid." "That's right. And don't forget to make neat-looking joints without too much solder. But don't go all out on this business of using a small amount of solder as one fellow did who brought a receiver he had put together for my inspection. He had barely tacked the connections together with a tiny speck of solder on each one, and you could break any of them loose with very little effort. The joint should be completely surrounded by a thin smooth layer of solder. It should be shiny and bright. If it looks dull and the solder looks grainy, the joint is a poor one and must be done over. With a little practice you can usually tell a good joint from a bad one by just looking at it; but never forget that you can get a fooling. Now and then a rosin joint will look fine on the outside. The layer of insulating rosin is all on the inside where you cannot see it; so never hesitate to lay the iron to what seems to be a perfect joint when you are hunting trouble."
Posted December 10, 2020 Mac's Radio Service Shop Episodes on RF Cafe This series of instructive technodrama™ stories was the brainchild of none other than John T. Frye, creator of the Carl and Jerry series that ran in Popular Electronics for many years. "Mac's Radio Service Shop" began life in April 1948 in Radio News magazine (which later became Radio & Television News, then Electronics World), and changed its name to simply "Mac's Service Shop" until the final episode was published in a 1977 Popular Electronics magazine. "Mac" is electronics repair shop owner Mac McGregor, and Barney Jameson his his eager, if not somewhat naive, technician assistant. "Lessons" are taught in story format with dialogs between Mac and Barney.
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