LEAD-FREE SOLDER: CHARACTERISTICS AND DIFFERENCES

The Restriction of Hazardous Substances Directive (RoHS), adopted by the European Union in 2003, changed the world of electronics manufacturing forever — especially with regard to solder. The lead-free solder necessary for RoHS compliance presents a set of unique challenges to PCB-manufacturing businesses.

While no one is disputing the fact that lead-free solder is less hazardous to those working in PCB assembly, working with unleaded solder has its complications. Lead-free solder doesn’t flow as easily as traditional leaded solder and, compared to a PCB using leaded solder, the soldered joints on a circuit board using lead-free solder will look noticeably different. You’ll also notice a dearth of top fill on through-plated PCBs (you’ll seldom get more than a seventy-five percent fill). In addition you’ll notice that unleaded solder joints are less shiny than joints using traditional solder because of the differences between the alloys.

It’s important to note that lead-free solder melts at a higher temperature than leaded solder. The exact melting temperature depends on the particular unleaded alloy you choose. A common mixture is ninety-nine percent tin, point seven percent copper, and point three percent silver; this alloy will melt and flow pretty well at two hundred seventy-five degrees.

Replacing and Modifying Equipment

There’s a good chance that the majority of your existing soldering equipment will need modification or replacement for lead-free soldering. You will at least need to replace your soldering irons’ tips — to avoid possible contamination issues — or you may need to replace your soldering irons and soldering stations altogether if they can’t reach the higher temperatures required for melting unleaded solder. Larger soldering equipment (e.g., wave soldering machines) will likely need to have their soldering baths replaced and you should consider replacing your flux as well because the PCBs you’ll be soldering will be lead-free, too.

With regard to solder pots and other types of hand-operated soldering equipment, you can either replace their baths or you could empty the equipment of solder, clean the bath, and coat it with oxide paint, which will save you some money; once the oxide paint has dried you can go ahead and fill your bath with lead-free solder and you’ll be ready to begin soldering again. While transitioning from traditional solder to unleaded solder can seem like a hassle, it’s rather easy and requires minor adaptation.

SOLDERING IRONS: WATTAGE VERSUS TEMPERATURE

A soldering iron has to rapidly heat metal parts above the temperature commonly used in electrical and electronic work — 60/40 or 63/37 tin/lead melts between three hundred sixty and three hundred seventy degrees — in order to make good connections. The solder you apply to the joint will melt and flow smoothly after it has been quickly heated. If your soldering iron heats too slowly the heat will be able to transfer to your components (resistor, capacitor, etc.) which can cause them to overheat and become damaged and, if you’re soldering insulated wire, too-slow heating can cause the insulation to weaken or melt.

Soldering tip temperatures are generally set between seven hundred fifty and eight hundred fifty degrees so that the temperature of the solder will raise above its melting point. Given that most solders have melting points below four hundred degrees you might be wondering why the soldering tip gets so hot. The answer is that using a higher temperature stores heat in the tip, thus speeding up the melting process; this enables you to solder your connections without applying excessive pressure on the joint. In addition, these high temperatures allow the proper formation of intermetallic layering between the components and solder to form, which is crucial for creating reliable electrical and mechanical solder joints.

Since we’ve established that the temperature is perhaps the most important aspect of choosing a soldering iron or soldering station, the next point of confusion is that soldering irons and stations are rated in watts rather than degrees. Most inexpensive soldering irons are actually unregulated, which means that the temperature of the tip isn’t controlled; they don’t advertise a temperature because the tip’s temperature will significantly change during use. The following data on certain unregulated soldering irons (fifteen, twenty-five, and forty watt) will shed some light on why choosing the right wattage is important.

A fifteen watt soldering iron has a resting temperature of roughly five hundred forty degrees Fahrenheit. However the temperature will drop to around four hundred twenty degrees after briefly wiping the tip on a damp sponge and soldering a couple PC board pads. This happens because the iron’s fifteen watt heat-storage capacity can’t maintain its resting temperature during use — it doesn’t have the capacity or the ability to restore temperature so it quickly cools when used. You can work around this limitation by allowing some rest periods between soldering joints, but if you’re doing work that requires more heating power — e.g., tinning a stranded wire — a fifteen watt iron won’t have enough power to get the job done.

A twenty-five watt iron has a resting temperature of around six hundred forty degrees and will retain much of its resting temperature (i.e., over six hundred twenty degrees) after soldering more than ten PC board pads. With regard to tinning wire, a twenty-five watt soldering iron can handle fourteen gauge wire well, but it lacks the power to tin ten or twelve gauge wire. If you tried to tin a ten gauge wire you can get the iron’s tip hot enough to melt solder in around two minutes, but by that time the insulation is hot enough to melt as well. The goal is to heat the surfaces being soldered, so we don’t want to heat the surfaces for more than a couple seconds or we risk damaging components and wires.

A forty watt soldering iron’s resting temperature is roughly seven hundred forty degrees and will keep a tip temperature of over seven hundred degrees through repeated PC pad solders. While a forty watt iron has enough power to easily tin twelve and fourteen gauge wire, ten gauge wire will still be on the slower side. Lower wattage soldering irons and soldering stations can really slow down your work and may not be suited to the electrical or electronic work that you’ll be doing.

HOW TO REPLACE ELECTRIC GUITAR PICKUPS

Swapping the pickups in your guitar can dramatically affect its tone; you can transform a student model guitar into tone machine that nails your favorite sound simply by installing the right combination of pickups and tone/volume potentiometers, and it’s surprisingly easy to do.

(Note: It’s best if you already have experience with a soldering iron.)

First things first: you’ll need wire cutters (preferably needlenose), new strings, a Phillips head screwdriver, solder, and a soldering station or iron. Every electric guitarist should invest in a good soldering iron, because almost all the electronic repairs you’ll ever need to do require one.

Remove your guitar strings to make things easier on yourself. On a rear-routed guitar you’ll remove the plastic plate on the back of the guitar or, if you have a Fender-style guitar, you’ll remove the entire pickguard to which the pickups are attached. Be sure to keep the screws organized according to where they came from, i.e., keep pickups screws, screws from the pickguard or backplate, etc. in separate piles.

Next you should orient yourself by identifying where the jack is, which potentiometer is which, where the selector is at, and how the wires connect the various parts. Use your needlenose pliers to pull out and separate the wires to make things easier, but don’t pull any wires out completely, as this will damage both the wires and components.

Take your new pickup and pull each colored wire out. Strip an inch or so of the black wire coming out of the pickup. After that pull each of your new pickup’s wires out and apart from each other. On rear-mounted guitars you’ll then feed the new pickup’s wires into the cavity making sure there is enough space in the cavity for the new pickup’s wiring.

Let your soldering iron warm up for five to ten minutes. Examine where the guitar’s current pickup’s wires solder to the jack, pots, etc. while you wait. Desolder one by putting the soldering iron’s tip to the solder point. Be sure that you’re desoldering the wires for the pickup you’re replacing, which can be accomplished by pulling on that pickup’s wire.

Break out the needlenose pliers again and pull the wire from the liquified solder. If you have a desoldering bulb you can suck up the excess solder — otherwise take the correspondingly colored wire from your new pickup and solder it where the old one was. If the point where you’re soldering has a hole, loop the wire through first. Hold your solder to this point and touch it with the soldering iron to get just enough solder to secure the wire. Do this for each wire and solder point.

Take the old pickup out, plug your guitar into your amp, and turn it up. Touch the new pickup’s screws and magnets with a screwdriver and, if you hear a popping noise each time you tap the screws or pole pieces, you’ve successfully soldered your new pickup in place.

Screw the pickup in position — with the wire facing down, i.e., toward the bridge — replace the backplate or pickguard, and restring your guitar. That’s all there is to it.

Building a Distortion Pedal with a Kit

Distortion pedals — which compress the peaks of your electric guitar’s sound wave and add overtones, resulting in a warmer, dirtier, and fuzzier guitar tone popular in rock, blues, punk, and metal music — are the most popular effects pedals around and you can easily build your own distortion pedal with a kit. Let’s have a look at the process of distortion pedal assembly. You’ll need a distortion pedal kit, wire strippers, a screwdriver, and a soldering iron.

Build Process

First off, you’ll need your distortion pedal kit, which you can buy from a number of online retailers. There are a variety of different types of distortion pedals so you’ll need to make a decision on what type of distortion suits the music you play. A Tube Screamer-type pedal sounds much different than pedals based on Big Muff or Turbo Rat circuits. If you play grunge or punk music you’ll want a fuzzier distortion pedal with lots of overdrive and, if you play the blues, you’ll want a pedal with good compression and more midrange.

Take the components from your kit and attach them in the appropriate places on the perfboard. The components will plug straight into the board and should fit securely in their respective slots. These components consist of capacitors, transistors, and diodes. Every kit is different, so be sure to consult your kit’s schematic to find out what goes where.

Strip the kit’s wires’ ends with your wire strippers and wrap the stripped ends around the terminals of each of the components. The wires are likely all one color, meaning that you don’t have specific wires for specific components. Although all kits are different, you can expect to connect five to ten wires to the terminals.

After allowing your soldering iron or soldering station to warm up, solder the wire connections. A mildly active rosin-core solder is best for these kinds of circuits.

Attach the perfboard to the bottom of the pedal’s chassis. Use your screwdriver and the included screws to secure the perfboard in place.

Then secure the top part of the pedal’s chassis to the bottom half. Plug your distortion pedal into the wall and test it out. If you plug the pedal in and the LCD doesn’t light up when you turn the pedal on then you’ll need to check your connections. If the light does come on and no sound comes out of your amp or the sound cuts in and out with you guitar plugged into the pedal you’ll need to take the pedal apart and ensure that everything is correctly connected.

So long as you have experience with a soldering iron, building a distortion pedal from a kit is a rather straightforward process that will give you the experience and confidence you’ll need to start building more complex circuits.