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A basic skill needed in any electronic project or repair is that of soldering. It is both an art form and a skill. It takes some practice to make the perfect joint, but, the practice will pay big dividends. The idea is simple: to join electrical parts together to form an electrical connection, using a molten mixture of lead and tin with a soldering iron. What I expect to do here is give some advice on what equipment you need, as well as explain the techniques you need to apply. Along the way, I will offer tips on what I have found works the best.

But first, a caveat. This tutorial is about general electronic soldering. It will concentrate on the techniques and equipment for through hole PCB components, and wiring. Most notably, it is not about Surface Mount technology, While many of the techniques presented here are applicable to SMT, there are additional considerations that are not within the scope of this article. It is recommended that the hobbyist become proficient with the standard soldering techniques presented here before venturing into the more specialized techniques required of SMT.

There are many different areas in which soldering is used. Our interest is electronics, and the joining of electronic parts and wires together, or to circuit structures such as PC Boards. Jewelry makers also use soldering and brazing. Stained glass artisans solder their creations, And, of course plumbers solder copper pipes together. The applications and tools are different, but the techniques are much the same.

We will start by defining soldering. Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. It is separate from brazing, which uses a higher melting point filler, and welding, in which the base metals are melted and joined.

Selecting a soldering Iron

The first thing you will need is a proper soldering Iron. Most hobbyists will need two to three different irons, small, medium, and large, to match the specific job. A soldering iron can be defined by three things: Tip Temperature, wattage, and the tip size and shape. We will leave the temperature question for much later, and concentrate on the other two first.

The most important defining characteristic of a soldering iron is the wattage. The higher the wattage, of course, the more heat is available. And here is the first important thing to remember! Heat is NOT temperature! It is important to realize that higher wattage does not necessarily mean a hotter soldering iron. Higher wattage irons just have more power available. Whether it is controlled by the physics of the design, or a thermostat in the case of a temperature controlled iron, most all soldering irons produce about the same tip temperature in the range of 750-850 degrees.

My main soldering irons. At top is an 18w Antex. At bottom is a 33w Ungar with a screw in element.

The Wattage reflects the amount of energy available to heat the joint. A low wattage iron may not keep its temperature on a big joint, as it can loose heat faster than it can reheat itself. Conversely, a higher wattage iron may inject so much energy into the joint that the joint cannot dissipate it quickly enough, and will overheat. This point will become very important when we cover De-soldering. Most irons come in wattages starting at about 15 watts, and going up to 60-75 watts. The larger, non electronic irons can have wattages up to 150-200 watts. The smaller irons, below about 16 watts are for specialized work. And, any iron above about 45 watts is too large for general electronics use, with the sole exception of soldering large wires & terminals or RF Shielding.

I have found, for general electronics work, including most through hole PCB work, that an iron with a wattage of 20-35 watts works the best.

Basic Irons - Form Factor

There are a few different ways that soldering irons are constructed. There are irons with replaceable heating elements, most of which screw into the handle, then there are single piece irons, where the Heating element and handle are the integral to each other. The outer end of the heating element then accepts tips that screw on, slide on, or, occasionally, are held by a set screw. Some Irons such as many Wellers use a circular screw on ring to hold the tips. Which design you get is up to you. Other than making sure the tip is replaceable. Some very good irons use the integral heater such as Weller and Antex. One classic design by Ungar and others uses a handle into which a separate heating element or cartridge screws.

A three wire cord, with the tip and element grounded is a good choice. Especially if you are concerned about ESD. There are also Irons and stations made of conductive materials that are advertised as "ESD safe". For the hobbyist, while a grounded tip is appropriate, it is not necessary to invest in an 'ESD safe' Iron. Make sure you observe the usual anti-static precautions when handling the components, and you should be fine.

An 18 watt Antex with 4 replacement tips. The tips slide over the heater core (Above) which is permanently attached to the handle.

Two Ungar irons with modular screw in Heaters. The top one has outside threads for the tip (Shown without the tip), the bottom one has inside tip threads. An 18 watt Antex Iron with a 3 wire cord. The heater is not removable. The tip slides over the heater. Shown with a 1/8" Tip installed. This is a 16 Watt Ersa temperature controlled iron. Made in Europe. The heater is integral, The tip can be replaced the same way as with the Antex.

Make sure the iron you buy has a replaceable tip, a three wire cord, and is the correct wattage

The soldering iron tip - The working end

The soldering iron tip transfers thermal energy from the heater to the solder connection. In most soldering iron tips, the base metal is normally copper or some copper alloy because of its excellent thermal conductivity. A tip's thermal conductivity determines how fast thermal energy can be sent from the heating element to the connection. A bare copper tip is not recommended for any type of electronic soldering. The hot copper is subject to rapid oxidation, and it will react with the tin component in the solder. For this reason most tips are plated. There are various plating processes used in making soldering iron tips. One technique uses a nickel plate over the copper. Then an iron electroplate goes over the nickel. The iron and the nickel create a barrier between the copper base material and the solder alloy. Nickel-chrome plating is often applied to the rear of the tip to prevent solder from adhering to the back portion of the tip and to provide a controlled wetted area on the iron tip. Another plating technique is similar but omits the nickel/chrome plating, leaving the iron to act as the barrier metal.

As to the shape of the tip. All good soldering irons have some form of replaceable tip which fits into, or over, the heating element. If it does not have a replaceable tip, DO NOT buy the iron! These tips come in all shapes and sizes. They are normally attached directly to the heating element via screw-on threads (Either outside or inside), a set-screw, or by sliding down over the element and clamping onto it. The most general tip shapes are the pointed, and the chisel tip.

A common problem with screw on tips is the tip seizing to the heating element. It is often impossible to get them apart after a couple months use, making the heating element unusable.

This is three modular screw in heaters On the left is an external thread with two 3/16 chisel tips, One is plated (On left), and the other is copper. An internal thread tip is in the center. The right is a heater with a large permanent (Non removable) tip.

To prevent this apply a very small amount of anti-seize compound to the threads, collars, or any other mating parts. You do not need much, and be very careful to not get it on the working surfaces of the tip (or your clothes). When the iron is first heated it will smoke for a while until the oils in the compound burn away. Be careful to not breathe in this smoke! You can avoid some of the smoke by using an anti-seize made for soldering irons. A good source for this is stained glass suppliers. Alternatively, use a High-temperature anti-seize from the car parts store. And again, be very careful not to get it anywhere else on the iron, or you!

For fast and optimal heat transfer to the solder joint the tip mass should be as large as possible. When choosing a soldering tip always select the largest possible diameter and shortest reach. Use fine-point, long reach tips only where access to the work is limited.

For most general use, I use a 1/4" chisel tip, and/or a 1/8" chisel tip. Occasionally you will need a pointed tip for access to a tight space. Use anti-sieze sparingly on the threads.

Soldering iron tip care - Cleanliness

Tinning is an important part of tip care. On the first heating, pre-tin the new tip with fresh rosin core solder. I like to wrap a new tip with a few turns of solder before the first heating. The solder tinning should stick cleanly and evenly to the entire working surface. If the solder balls up, or otherwise does not stick evenly (This is known as un-wetability), you may need to treat it with a mildly activated non water soluble rosin flux made for electronics use. Never, ever, use acid flux (Plumbing flux), on your iron, or anywhere near any electronics. It is highly corrosive! The flux you find in the plumbing department of your home center will most likely be Acid Flux. Do not use it! Use a generous amount of solder when tinning. Wipe or flick off the excess. Keep the tip well tinned at all times. When turning off your iron for the day, do NOT clean off the extra solder. Leave it there as additional protection against oxidation. Any time you wipe or clean the tip, always remember to re-apply a little more solder to it to keep it wetted.

Never file or grind a plated tip! For major cleaning, you can use either a 'suede brush', fine steel wool, or carefully use a fine emory paper. Damp sponges are very popular for routine cleaning. When cleaning a tip with a sponge, be sure to use a synthetic sponge to avoid contamination. It is highly recommended you get tip cleaning sponges made specifically for this purpose. When wetting the sponge, try to use distilled water. Most tap water contains mineral deposits that will cause un-wetability, and further degrade your tip. I also find a small cloth rag can be handy for routine cleaning of the tip, make sure that if you use one it is not a synthetic, or nylon! Pure cotton cloths work well. DO not use a 'treated wipe' such as you find in a paint store. In sum, keep your iron tip very clean, free of any contaminants or chemicals, and well tinned! And never, ever, use the tip for anything except soldering! One more point, while I advocate fine solder for actual use, you may want to keep some thicker rosin core solder handy for tinning, especially on start up. The thinner solder may not contain sufficient flux or tin to properly clean and wet the tip. I also suggest you get a small can of rosin paste flux to help clean oxidation from the tip. Again, do NOT use acid flux. There are also commercial products such as Weller's Tip Tinner & Cleaner that can be useful.

Keep your tip well tinned and contaminant free. Use a damp soldering iron sponge, or a clean, cotton rag, for general cleaning while working. Apply rosin flux, or tip cleaner, to the tip when needed to clean off contaminants, and apply extra solder often to keep it clean and wetted.

Soldering Stands and accessories

There are many kinds of soldering iron rests and stands. I highly suggest you get something to keep from burning your table, contaminating the tip, and to have a safe, dedicated place to put your iron in between uses. An added benefit of a proper stand is it will have some sort of metal heat sink that the tip natural contacts when the iron is in the stand. This serves to dissipate excess heat, and keeps the tip from overheating, and burning the tin coating. A very helpful feature. To the right is a commercial soldering stand made by Idle-Rest (model TL194). It has a large heat sink area in front, and a large well at the back for a tip sponge.

Temperature Control and Soldering Stations

The simplest and most affordable types of irons do not have any form of temperature regulation. Thermal regulation is "designed in" (by physics). These may be described as 'thermally balanced' in that they have some degree of temperature balancing built in, but their output will otherwise not be controlled. Unregulated irons form an ideal general purpose iron for most users, and they generally work very well with through hole printed circuit board soldering and general wiring.

A temperature-controlled iron will be more expensive, and will have some form of built-in thermostatic control, to ensure that the temperature of the tip is maintained. Some irons have a bimetallic strip thermostat built into the handle, other types use electronic controllers, and some may be adjustable using a screwdriver. Many temperature controlled irons have a sprat controller built into a stand along with an iron holder, and have some form of knob to adjust temperature, as well as, often, a temperature readout. These "soldering stations" are simply not necessary for the average hobbyist. An over awareness of the temperature can actually be a hindrance, especially in de-soldering, as many times they are adjusted for an inadequate amount of heat, on the premise that too much is bad. As well, many of the cheaper (and sometimes not so cheap) stations do not actually measure or control temperature, but only control the wattage, based on the predicated behavior of the iron. If you are buying one specifically for the temperature control, be aware of how it is controlled! While a simple station with only adjustable wattage is still a useful tool, it is not necessary for most applications. One final note here. A true temperature controlled iron, with a thermistor in the tip, and sufficient wattage will enhance soldering speed and efficiency by 'turning up the heat' when touched to a cold joint. This allows the joint to heat up much faster. This is one reason why they are used in production environments. It will also help avoid overheating smaller components by 'turning down the heat'. But, you can do the same thing with proper technique, and for a lot less money.

This is a Mid-Priced Temperature controlled station made by Tenma. (Distributed by MCM Electronics).
It has a thermistor in the heating element, which is not removable.
I have removed the tip to show how
it slides down inside the heater.

Fancier Soldering stations can consist of a complete bench-top control unit into which a special low-voltage soldering iron is plugged. Some versions might have a built-in digital temperature readout, and will have a control knob to enable you to vary the setting. These are designed for continuous production line and professional use. The best stations have irons which are well balanced, with comfort-grip handles which remain cool all day. A thermocouple will be built into the tip or shaft, to monitor the temperature. Most often the heater in these units is not replaceable, and the tip will slide inside the 'barrel' of the heater. Additionally, there are Re-work, or desoldering stations, which incorporate a vacuum system and a hollow tip to remove excess solder. While these can be extremely useful for desoldering, their cost is often prohibitive for the hobbyist. Finally, if you are considering purchasing one of these, note that many with access to these units will still turn to the tried and true basic iron for much of their normal soldering work.

Larger Irons

Finally, there will be a few times when you may need a larger soldering iron. These can range from just a higher wattage version of the above types, all the way to a 'soldering copper' that is meant to be heated in a flame. The heaters range from 60 watts on up to the hundreds of watts. The classic large soldering iron is commonly known as an "American Beauty' (or, sometimes a Black Beauty) after the name of one of the original manufacturers.

I am not going to dwell on these in this article, but here is a picture of my Vulcan Model 30 - It is a 60 watt model. I don't use it very much, and it is totally unsuitable for most electronic soldering.

Soldering Guns

A soldering gun is a handy addition. While not at all applicable to soldering PCBs or small components, they can come in very handy for soldering larger connections, putting terminal lugs on wires, soldering grounds and large areas such as shields. The instant on feature can also be very useful. Although there are a number of different models available, I would recommend one model that has become the 'standard bearer'. The Weller Model 8200N (Seen at right). This is a 100/140 watt, two heat model with a trigger switch. These can often be found in surplus stores, and garage sales, as well as on Ebay. Hold out, and get one that is rather new, and in the original case. They are fairly available.

The tips on these are basically a piece of large copper wire. They are held in place by two nuts. As can be seen in the photo, the ends need to be bent under the nuts to fit into the tongs on the gun. At the top of the picture is a new tip before being bent. The gun heats the tip by passing a large current through it. These connections can very easily corrode, and degrade the performance. The secret to using these guns is to make it a practice to often loosen and retighten the tip nuts to restore the connection - especially if the gun does not seem to be heating properly. It is highly suggested you read and follow the manufacturers instructions on how to attach and replace the tips as this is the key to success with these units.

There are also a number of special purpose tips available for these, and you can even make your own out of a large piece of copper wire in an emergency, although It will not work nearly as well. Be careful of the case on these guns. They break easily. It used to be common to find one completely wrapped in electrical tape to hold it together after it broke! Keep it in the original case it came in along with the accessories (Tips, tip wrench, etc).

On the left, you can see the Weller gun in it's original carrying case with accessories. This is an excellent way to store these. Above is a larger gun. This one is a Millers Falls
Catalog # 642. Dual Heat 240/325 watt.

Shown also are a couple accessory tips. These are for cutting and smoothing plastics. And one final note. These guns have a duty cycle. Be careful of overheating them. After a period of use, make sure to let them cool off!

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