Electronics All-in-One For Dummies. Doug Lowe
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magnifying glass, or a magnifying glass attached to a third-hand tool, or special magnifying goggles.
Desoldering braid and desoldering bulb: These tools are used to undo soldered joints when necessary to correct mistakes. For more information, see the section “Desoldering” later in this chapter.
Preparing to Solder
Before you start soldering, you should first prepare your soldering iron by cleaning and tinning it. Follow these steps:
1 Turn on your soldering iron.It will take about a minute to heat up.
2 When the iron is hot, clean the tip.The best way to clean your soldering iron is to wipe the tip of the iron on a damp sponge. As you work, you should wipe the iron on the sponge frequently to keep the tip clean.
3 Tin the soldering iron.Tinning refers to the process of applying a light coat of solder to the tip of the soldering iron. Tinning the tip of your soldering iron helps the solder flow more freely once it heats up. To tin your soldering iron, melt a small amount of solder on the end of the tip. Then, wipe the tip dry with your sponge.
THE TEN SOLDERING COMMANDMENTS
Have you heard of the Ten Soldering Commandments? In truth, they’re actually more like guidelines than commandments. But if you heed them, it will go well with your solder joints, your children’s solder joints, and your children’s children’s solder joints. So let it be written; so let it be done.
1 Thou shalt wear eye protection whenever thou solderest, lest thy get molten solder in thine eye.
2 Thou shalt not touch the heated end of thy soldering iron, lest thy burn thyself.
3 Thou shalt not fashion molten solder into false globs.
4 Thou shalt wash thy hands after thou solderest, to remove vile lead contamination from upon thy hands before thou eatest.
5 Thou shalt provide bright illumination upon thine objects which thou solderest, that thou might see clearly the way unto which the solder may be applied.
6 Thou shalt not spill thy excess solder upon thy neighbor’s pad lest thy create unintended pathways through which current may flow.
7 Thou shalt not leave thine hot soldering iron unattended.
8 Thou shalt not covet thy neighbor’s professional-grade temperature-controlled soldering station.
9 Thou shalt not apply solder directly upon thine soldering iron, but shalt instead apply solder to the objects which thou solderest, that their heat may melteth thy solder.
10 Thou shalt always place thine hot soldering iron in a suitable holder.
Soldering a Solid Solder Joint
The most common form of soldering when creating electronic projects is soldering component leads to copper pads on the back of a printed circuit board. If you can do that, you’ll have no trouble with other types of soldering, such as soldering two wires together or soldering a wire to a switch terminal.
The following steps outline the procedure for soldering a component lead to a PC board:
1 Inspect the component leads to make sure they’re clean.If the component is really old, you may need to touch it up with an emery board to remove any accumulated gunk.
2 Pass the component leads through the correct holes.Check the circuit diagram carefully to be sure that you have installed the component in the correct location. If the component is polarized (such as a diode or an integrated circuit), verify that the component is oriented correctly. You don’t want to solder it in backward.
3 Secure the component to the circuit board.If the component is near the edge of the board, the easiest way to secure it is with an alligator clip. You can also secure the component with a bit of tape.
4 Clamp the circuit board in place with your third-hand tool or vise.Orient the board so that the copper-plated side is up. If you’re using a magnifying glass, position the board under the glass.
5 Make sure you have adequate light.If you have a desktop lamp, adjust it now so that it shines directly on the connection to be soldered.
6 Touch the tip of the soldering iron to both the pad and the lead at the same time.It’s important that you touch the tip of the soldering iron to both the copper pad and the wire lead. The idea is to heat them both so that solder will flow and adhere to both.The easiest way to achieve the correct contact is to use the tip of the soldering iron to press the lead against the edge of the hole, as shown in Figure 7-2.
7 Let the lead and the pad heat up for a moment.It should take only a few seconds for the lead and the pad to heat up sufficiently.
8 Apply the solder.Apply the solder to the lead on the opposite side of the tip of the soldering iron, just above the copper pad. The solder should begin to melt almost immediately.Figure 7-3 shows the correct way to apply the solder.FIGURE 7-2: Positioning the soldering iron. Do not touch the solder directly to the soldering iron. If you do, the solder will melt immediately, and you may end up with an unstable connection, often called a cold joint, where the solder doesn’t properly fuse itself to the copper pad or the wire lead.FIGURE 7-3: Applying the solder.
9 When the solder begins to melt, feed just enough solder to cover the pad.As the solder melts, it will flow down the lead and then spread out onto the pad. You want to feed just enough solder to completely cover the pad, but not enough to create a big glob on top of the pad. Be stingy when applying solder. It’s more common to have too much solder than too little, and it’s a lot easier to add a little solder later if you didn’t get quite enough coverage than it is to remove solder if you applied too much.
10 Remove the solder and soldering iron and let the solder cool.Be patient — it will take a few seconds for the solder to cool. Don’t move anything while the joint is cooling. If you inadvertently move the lead, you’ll create an unstable cold joint that will have to be resoldered.
11 Trim the excess lead by snipping it with wire cutters just above the top of the solder joint.Use a small pair of wire cutters so you can trim it close to the joint.
Checking Your Work
After you’ve completed a solder joint, you should inspect it to make sure the joint is good. Look at it under a magnifying glass, and gently wiggle the component to see if the joint is stable. A good solder joint should be shiny, and it should fill but not overflow the pad, as shown in Figure 7-4.
Nearly all bad solder joints are caused by one of three things: not allowing the wire and pad to heat sufficiently, applying too much solder, or melting the solder with the soldering iron instead of with the wire lead. Here are some indications of a bad solder joint:
The pad and lead aren’t completely covered with solder, enabling you to see through one side of the hole through which the lead passes.