There are several aspects to consider: choosing the right soldering iron, choosing the right solder, and selecting accessories to make the process easier.
First choosing a soldering iron. Consider that the object of soldering is to apply the right amount of heat to the correct spot in a fashion that is easy to do and not tiring. This means an iron with a wattage that generates enough heat for the job, but not too much, that has a tip similar in size to the work you are doing, and is fairly light, maneuverable, and easy to hold. Typical irons for electronic work tend to run in the area of 30 to 60 watts. Tips can vary but would typically be similar in size to anything from a sharp pencil for really fine work to a very dull pencil for typical work to a new crayon size tip for larger work, or work with connecting wires. Most irons have interchangeable replacement tips available, and it is good to consider the availability of these when deciding on an iron.
Why would one want or need a variable temperature soldering iron? Given that there is an optimal yet fairly wide range of temperature in which you can solder, it is good to try to maintain tip temperature in that range. The wattage of the heating element in the iron is constant, just like the burner on an electric stove. It will produce heat at a certain rate. But the size of the tip you are using (fine or corse) and the size of the joint you are trying to solder will remove heat from the iron at different rates. This is just the same as putting a small skillet on the stove with a little butter in the bottom, or a pot with a gallon of water will remove heat from the stove at different rates. It is good to be able to turn down the heat so the iron doesn’t over heat or burn, just like on the burner on an electric stove. A simple soldering iron with a dedicated tip could be fine for soldering one type of joint at a fairly constant rate, but it would need to be matched in size more closely to the job to be done. Since there are many types of things to be soldered in amateur radio, it makes sense to get a variable temperature iron. Heat requirements for tinning #10 stranded wire or soldering coax braid to a connector are quite different from those for soldering a wire to an LED, or soldering a chip to a pc board.
So how is the temperature of a soldering iron tip controlled? The most basic would be that there is no direct control, but that the operator simply uses the iron at a rate which removes the heat at the same rate that it is produced, thus maintaining a fairly constant temperature. But as mentioned, that is difficult given the variety jobs we would do.
A second method is to use a regulating device which plugs into the wall, and has an outlet into which the iron is plugged. The regulator cycles the iron on and off at a rate that is controlled by the setting of a knob. This is very similar to, and may actually use the same component as the control on an electric stove. This has a similar effect to reducing the wattage of the iron. If soldering small things, you might set the dial so that the iron cycles on for 3 seconds and then off for 7 seconds. For larger joints the control can be adjusted to cycle the iron on for 8 seconds and off for 2. Or it may be set to remain on continuously to heat up or for maximum heat output. This works but it’s a bit course and perhaps not the best for fine electrical work.
A third method used in some tips is to employ magnets. As a magnet heats up, its field strength will diminish. So if the right size and strength magnet is built into the soldering iron tip, then the heater can be controlled by a magnetic switch which turns on and off based on the magnetic field from the tip. As the tip reaches a certain temperature, the magnetic field decreases, turning off the switch and allowing the tip to cool. As it cools, the magnetic field builds again, and switches the power back on to the iron. These irons work like magic and the various tip sizes pretty much just stay at the right temperature. While this is great for soldering components on a board, it may not be optimal for switching to a larger job without changing to a higher heat tip.
A fourth method, and the one which is becoming more popular given the decreasing cost of electronics is the digitally controlled irons. These irons are typically 2 parts, a control unit which plugs into the wall, and the iron which plugs into the control unit. The controller has a transformer/ power supply which runs the electronics of the controller, as well as providing power for the iron. Temperature is controlled with a dial on the control unit, and electronic feedback from a thermocouple or other temperature sensor in the iron itself. This system provides almost infinite control of temperature, and a numeric display in C or F of that temperature. Because the heat output is adjustable, even a small tip can be run at max to tackle a slightly larger job such as wicking away solder or tinning a wire. Though not always built in, these stations often provide an iron holder and a spot for a sponge or metallic wool cleaner.
Points to consider- availability of tips, and quality- better tips do last longer than cheap ones. Availability of repair parts. Over the years, parts such as the heating element, handle, cord, or heater cover may need to be replaced. Sometimes it may be easier to replace the whole unit. C or F readout- some Chinese irons only read in C which seems odd, but isn’t terribly relevant, as it is easier to adjust the iron by how it is performing rather than setting it to a specific temperature.
What do I use? My soldering station is a Weller EC2002A. It hails from the 1980’s and has a digital readout in F and a knob for adjusting the temperature. A spring style iron holder is on one side, and an area to hold a sardine tin with a sponge is in the front. This was an industry standard back in the day, and can be found at hamfests or on eBay. All replacement parts are still available and readily obtained.
Now on to solder selection. We all should know, as it is a question on the exam, that for electronics work we use Rosin core solder. Never use acid core solder. But all rosin core solder is not created equal. There are different alloys and different rosin formulations, and different diameters of the solder to consider. As to lead alloy vs lead free, I use lead based solder, so can’t address lead free, except to say that it seems to melt at a higher temperature, and is more of a pain to deal with when making repairs.
I have used many varieties of solder, but have the preference to use Kester “44” Rosin Core solder. Kester is the name brand. “44” is their trademark name for whatever the specific rosin core is. Looking at mine, the alloy is 60-40 or 60 parts tin or Sn to 40 parts lead or Pb. There are other alloys such as 50-50 or 63-37 which may also be used, the difference being the melting and solidifying temperatures of those alloys.
Solder comes in different diameters, and while they all work the same, it is convenient to use a diameter which will match in size to the work you are doing. A diameter of .062 is a pretty good all around size. It is a little thinner than some,but still thick enough for large joints or wire tinning. .031 is good for finer joints or larger surface mount components. The thinner solders may aid in not using too much solder in a joint, but jobs like tinning a large stranded wire may use 4 or 5 inches of solder.
What accessories are good to have while soldering? There are many tools that can help in the process, but the most important would be a soldering iron holder and a cleaner if these are not already a part of a soldering station. The holder could be a simple metal gadget that sits on a table and the iron is laid on it. It keeps the hot iron from contacting the table or from rolling away. A better solution would be the spring type holders which are mounted to a soldering station or to a heavy metal base. The iron is inserted into the coil of the spring and is held at a good angle for grabbing it again. Ideally, the actual tip of the iron won’t contact the metal of the coil.
Part of soldering is keeping the tip of your iron clean and tinned. Personally, I just use a wet cellulose kitchen sponge in an aluminum sardine tin to clean my iron. The sponge wipes the tip, the tin collects the excess solder, and the aluminum doesn’t rust when wet. Some people prefer the little brass wool type cleaners, but I’ve never used those so can’t speak to their efficacy.
Other accessories like wire probes or solder spool holders may help but are not things I use. Similarly, the “helping hand” devices with clips and perhaps a magnifying glass may come in handy for some, but I’ve never found them useful. In theory, the helping hand could be good, but I find that I sometimes need to apply more pressure than it can support and end up moving the board around. I find a small vice to be useful when holding a small board is absolutely necessary.
Solder bulbs, plunger solder suckers and solder braid could all play a part. Solder bulbs are like mini turkey basters that can be used to remove molten solder from a pc board. The plunger solder suckers use an internal spring which moves a plunger rapidly when a button is pressed. This sucks solder off a pc board. The plunger must then be pressed down again to reset it for the next sucking operation. A disadvantage I’ve found with these is that the slight recoil can tend to lift delicate traces on the board. Solder braid or solder wick has become my go to method for the finer electronics of today. It is basically a a fine copper braid, similar to a shoelace, that is coated with flux. When placed on top of the solder to be removed and heated with an iron, it wicks up the solder, removing it from the joint. This braid comes in different widths to match the job, and is as effective as its flux- ie if it is cheap flux, it won’t wick as well. I normally use the Solder-wick brand, or Chemtronics brand. Size #2 works well for me. It comes in varying lengths, and I’ve used a bit over 50 feet in the past year, but that’s likely more than a casual user would consume. As a side note, this braid can be tinned and used as conductors or connections similar to un-insulated wire.
In summary, the object is to apply the right amount of heat to a clean joint to flow a good rosin core solder. A better quality iron will help do this and make the process easier and more enjoyable. Quality solder will improve the joint. Keeping your tip at the right temperature and keeping it clean and tinned will not only add to the life of the tip, but will also make the soldering process easier. Through use and familiarity with your iron, your soldering skills will naturally improve.
Chaz
KC3ZPB