Soldering 101 - Bonding

Welcome to Soldering 101. Many of the projects posted at the Build Your Own Arcade Controls FAQ required the use of a soldering iron. Anyone who has never soldered before might be scared away by this prospect. This page is here to help those who have never attempted soldering before. It's really not as hard as it might seem. Good Luck and happy gaming.

Special thanks go out to my buddy Erik for the help with the video tape, AVI & Quicktime movies, and screen captures included in this section. He runs a video production business called Dream World Video Productions, based in the central valley of Northern California . If you have a need for video production and are in the San Francisco Bay or surrounding area, drop him a line. He does great work.

First, what is soldering? The simplest definition of soldering is the bonding of two metals with a third metal. Solder is an alloy comprised of lead and tin.The lead makes it melt at a relatively low tempature and tin is there for good conductivity. There are different combinations but the standard alloy blend is 60% tin and 40% lead or 60/40. Most solders also incorporate something called flux. Flux is a cleaning agent. It melts instantly (a fraction of a second before the solder itself) and flows across the joint to be soldered, cleaning impurities. This helps assure that the chemical reaction of the bonding metals will be most successful. Solder is available in several forms and sizes. It's made in bars for use with solder pots and wave machines but those are for production applications. For small scale electronics applications, solder is typically a thin wire wrapped onto a spool. This wire comes in different diameters for various needs. Spools are made and sold by weight, not length. A typical size spool is 1 pound. More recently, solder manufacturing companies have taken to making smaller convenience packs. This one, made by Kester is called the Pocket Pak. But convenience usually means higher price per pound.

There are some basic rules. More like guidelines, actually. They keep me sane when doing any soldering project.

1st rule - Care must be taken to prevent overheating of the joint being soldered.

2nd rule - Always contact your iron to both the pad and the wire.

3rd rule - Don't burn your fingers.

Rule #1. Don't over heat your joints! A multitude of problems can arise from this one item. If you place the tip of your iron on a piece of wire and leave it there too long, what happens? The insulation melts, right? This is what your components are doing inside if you heat them too long. The metal lead of the component will carry the heat right to the source and blow your part before you ever get a chance to see them work (semi-conductors such as diodes, transistors and IC's are especially prone to damage from overheating). Likewise, the same kind of damage can occur to your wire and PC board. The wire is obvious. The insulation will melt and shrink back making it ugly to say the least and also make it possible to have it short out on other items. The PC or printed circuit board can suffer damage as well. The traces on the board are nothing more than paper thin strips of copper that have been chemically bonded to the fiberglass board. As such, they are very easy to damage, especially the ones that are very thin such as what you might find on a keyboard encoder. Apply too much heat for too long and the copper will lose it's bond to the fiberglass and lift off the board. Though the circuit will still work as long as the solder connection is there, it is best to avoid such problems. A quick "touch, flow, remove" approach to soldering is the best way to be sure you don't damage anything.

Rule #2. Always make sure that your iron tip touches both items to be soldered. One sure way to screw up a circuit is to heat only one side and apply solder. This will result in what's call a "cold joint." A cold joint occurs when the solder does not flow properly over the two metals to be connected. A cold joint can also occur if the wire or component is moved while the solder is cooling, many times creating visible cracks in the joint. A cold joint is usually characterized by a dull gray look to the solder "fillet." If the joint is a good bond, the fillet will typically be shiny. This indicates good "wetting action" (don't ask me where these definitions came from, that's just what it's called) which means that the metals were hot enough and the solder flowed around and filled in the gaps well.

Another important piece to this rule is, when soldering, don't apply solder to the iron tip. Once you have the tip in contact with both parts to be soldered and heating has taken place, apply solder to the parts, not the tip of the iron. A good practice to get into is to clean the tip of the iron with a wet sponge then, just before applying to the joint, apply a little solder to the tip of the iron. This process is called "tinning the iron" and it will help promote the transference of heat from the iron to the parts. As hard as it is to believe, a dry iron even at 700-800 degrees Fahrenheit, does not transfer heat well. If you apply the iron to the parts dry, eventually (we're only talking seconds here) the joint will heat up enough to solder, but because it took so long with the tip in place, now that it is hot enough to melt solder, you are also damaging components or wire. The tinning will cause the transference of heat to occur almost instantly. It is also a good idea to pre-tin your conductors (wires). This will prep them and make them readily accept the solder bond when being soldered into the board. Instructions to follow.

Rule #3. I think this one is pretty basic. This might be peoples deterrence to try soldering. Burnt fingers. I've had my share. When you are soldering, you sometimes are in need of three or four hands. One for the iron. One for the solder. One to hold the PC board. One to hold the wire being soldered in the hole. Since everyone I know was only born with two hands, we sometimes have to get creative. That sometimes leads to burnt fingers or hands. Fingers in wrong place at the wrong time. Or maybe you are holding a wire in place and can't let go until the solder cools. The wire will heat up and burn your fingers right through the insulation before the solder cools and you can let go. A small vise (PanaVise among others; expensive but worth it) can help to hold the PC board. You can also buy little helpers sometimes called "helping hands" (heavy base and two alligator clips on little ball joints). Do whatever it takes to keep you fingers safe.

When you decide that you are going to try soldering for the first time, you will need to get a few things. Here's a quick list and what to look for:

Soldering Iron - get a small iron with a nice pointed tip. No fat tips or big chisel tips. 15-25 watts, no more. I use a soldering station with an output about equal to 60 watts but bigger irons usually mean bigger screw ups for the novice user. I also have a butane powered iron (this one made by Radio Shack) for field work and for small, quick jobs that I don't want to drag the station out for. Never, ever use a soldering gun of any type for electronics.

Iron Stand - this does not need to be fancy. Sometimes even a bent piece of coat hanger wire is all that's needed. Often, an iron will come with a cheesy little stand. Just something to keep the tip from damaging the table you're working on. I need to do my work at the nice kitchen table. The wife would go ballistic if I burned the table.

Solder - there are many types and sizes of solder. Get a small diameter. Make sure that it has a rosin flux. No acid flux for electronics!! The convenience packs are usually a good choice for the novice.

Sponge - you could probably use any sponge but a cellulose sponge is probably the best. Make sure it is wet when you use it. Doesn't need to be soaked, just wet.

Flux - there is flux in most solders that come on spools. I sometimes like to use extra to be sure the joint is clean. Flux is available as a paste and a liquid. I usually prefer paste. I keep paste flux in an interesting container. Yes, that is a case for contact lenses. I found it for a buck at a junk store. It keeps a small amount of two different types of flux handy in my solder kit. There is also a cool item made by Kester. It's called a flux pen. Looks just like an ink marker (although mine is a little beat from heavy usage). You "draw" with the tip where you want the flux. Nice.

Vise - helping hands mentioned above is probably good enough. Although a PanaVise is very nice for this type of thing.

Heat sink - a heat sink is a clip (alligator clip works great, I actually use surgical hemostats because of the long handles and better locking action. Works great!) that attaches to the leg of a component above where it is being soldered. It helps to absorb excess heat before the heat travels up to the actual component and damages it. Not required but nice to have when you need it.



Clean the tip with a wet sponge
Step 1: Plug your iron in and allow it sufficient time to heat. Some take longer than others. Use your sponge to clean the tip. Use only a sponge to clean the tip. If really dirty, DO NOT FILE OR SAND. The tip is coated with nickel so that solder won't stick to it as much. If you file that off, the solder won't flow to the joint. If a sponge does not get the tip clean, Radio Shack sells a small cup they call a tip tinner/cleaner. It works great!

Step 2: When you place a component or wire to be soldered, try to bend the legs so that you don't need to hold it there while soldering. This will allow the component to stay in place without having your hand hold it there (note the PanaVise holding the board).

Bend the leads so the component holds itself in

If using stranded wire, be sure to tin the conductor
Step 3: If you are using stranded wire, you should tin your wire. Strip the wire back with your wire strippers and twist the little strands of wire tightly together. Once twisted, carefully lay the iron down on your work surface (or leave on it it's stand if convenient). Tin the iron and put your wire end on the iron. Quickly apply more solder to the wire as you drag the conductor across the hot iron. This does not apply to the legs of a component (they're not stranded therefore do not need tinning).

See the whole process here:
AVI (711K) or Quicktime (840K)

Right click (Win) or Click and hold (Mac) and select
save target or link as: to save to hard drive.

Step 4: Clean and tin your iron again. Immediately after tinning, place the iron on the joint to be soldered. Be sure to have the iron touching both the pad and the wire to be soldered.

Tin your iron

Apply solder to the joint, NOT THE IRON
Step 5: Apply solder to the joint to be soldered, NOT THE IRON TIP. If all goes well, the solder should melt instantly and flow around the joint. Don't put too much solder. Pull the iron away immediately but be careful not to move the component or the board until the solder has cooled (which takes only a second or two). This could easily cause a "cold joint." You will know if it a good joint by the color of the "fillet." If it is dull or gray, it is a cold joint. If it is bright and shiny, it's perfect.

See the whole process here:
AVI (914K) or Quicktime (929K)

Right click (Win) or Click and hold (Mac) and select
save target or link as: to save to hard drive.

Good Joint
Bad Joint
Good Joint
Notice the shine on the fillet and that the fillet is not blobby with too much solder.
Bad or Cold Joint
This is what will happen if the component or wire moves while solder is cooling. Note the dull color and the crack that surrounds the fillet.

Soldering 102 - Separation

Often, when we talk about soldering as it relates to arcade controller or cabinet building, there is also talk of desoldering. Desoldering is the action of removing the solder from a joint or joints for the purposes of removing a component. This most often would be connectors from a keyboard encoder for a keyboard hack or wires and micro switches from a game pad or joystick controller. It is just as important to be careful when desoldering as when soldering. You are desoldering for a reason. To reuse the item being desoldered for another purpose. We would not want to destroy the item in the process, right?

Most of the same tips apply to desoldering as to soldering. The only other items that you might need to know is what tools can be used. There are a couple of items that will not only make desoldering possible (without them, trust me, it's near impossible), but will make it down right easy. One of the items is kinda expensive and will usually provide mixed results for the novice user. I have one but I don't even use it much due to it's difficulty in use. The other is a simpler technology that is not only cheaper but really works better. Both are covered below.

Vacuum Tool (avoid) - This is a great tool if you are at a rework desk and you use it about 1000 times a day. If not, it's really difficult to learn how to use effectivly. Affectionely nick named the solder sucker by most people who use them, this device does just that, sucks solder. The principal is simple and seems like it would work great but there is definitely a technique to using such a device. The unit uses a spring that is loaded to a release button. When released, a plunger flies up the shaft creating a vacuum at the tip that will suck up liquid items such as hot solder. You typically need three hands and even that is sometimes not enough. The trick is that you have the have the solder molten hot when you discharge the spring. This takes a little skill to master as you need to have the iron in one hand and have the sucker in the other, then you need to move quickly to get to the solder while still hot and discharge. The unit also has a recoil action that is similar, although not as intense, to firing a gun. This can throw the unit away from the joint being sucked. Basically a pain in the ass that is included here for completeness. Not recommended.

Solder Braid (preferred) - This is a great product for the novice user as there is little skill or practice required to use it. While I called it a tool above, it is actually an expendable item that you use up as you go along. The wick or braid is made of pure (or nearly pure) copper. When used with your iron, the braid will suck up the solder that is holding a component in the PC board. Simply pull it out, lay it over the joint you want desoledered and apply your hot iron.



Step 1: Find a joint or a component you would like to remove.

Find a component or joint you want removed

Get yer wick ready
Step 2: Take your solder braid out and find the end on the little plastic spool it comes on. Spread the braid out a little. It tends to work a little better this way.

Step3: Lay the expanded braid over the joint in question.

Lay the braid over the joint to be removed

Apply your iron to the joint with the wick in between
Step4: Apply your hot iron to the joint through the braid. You may have to press a little harder than you feel like you should be pressing on this. Be careful not to damage anything. You may have to stay on the joint for a little while but use caution to not overheat the joint. You can still damage the PC board and lift the trace doing this. You will likely need to repeat this operation 2-5 times per joint, each time using a fresh area of the braid. You might want to let the joint cool for at least 30 seconds between attempts to be sure you will not damage the PC board.

Step5: When you are finished, if all has gone well, the connector/component, may just fall out in your hand. If not, you might need to wiggle it a little. If it does not pop out with minor pulling, inspect closely for solder that may still be holding it in the PC board. Repeat the above steps until the connector/component comes out easily.

See the whole process here:
AVI (885K) or Quicktime (957K)

Right click (Win) or Click and hold (Mac) and select
save target or link as: to save to hard drive.

And behold, the solder is gone


Soldering 103 - Practice,Practice, Practice!

The best advice I can give is to take the above and practice. You might want to try a few times on something you can afford to destroy. If you have an old radio that is ready for the scrap bin, tear it apart and practice soldering and desoldering some of the components. If you do not have such a unit in your possession, you could check at a local thrift store or Goodwill second hand store. They often have great deals on items that would fit the need. If that is not your style, electronics stores such as Radio Shack have little PC boards called experimenters boards (we used one in the examples above). It's a pre punched PC board that has dozens of solder pads that you can use to practice soldering wires and components into and out of. These boards will run you a buck or two. Well worth the cost for the practice.

Another bit of advice I can give you is try and have steady hands when doing any soldering. Having a shaky hand can lead to problems (and burnt fingers). You might want to avoid that Triple Latte at Starbuck's before attempting soldering!

Good luck and happy soldering.

Updated October 17, 2003

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