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Electronics for dummies - McComb G.

McComb G., Boes E. Electronics for dummies - Wiley publishing, 2005. - 433 p.
ISBN: 0-7645-7660-7
Download (direct link): electronicsfordummies2005.pdf
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Before soldering, make sure you have all your tools within easy reach and then follow these steps:
1. Dampen a small sponge or a folded-up paper towel. Squeeze out any excess water.
You want it to be damp, not soaked.
2. Place the soldering pencil securely in its holder and plug it in.
3. If you have the adjustable type of pencil, turn the heat to approximately 675 to 750 degrees Fahrenheit.
4. Wait for the tool to reach proper temperature ó usually within 60 seconds for most 25- to 30-watt soldering pencils.
Many soldering pencils with a temperature sensor let you know when they reach the proper temperature by lighting or blinking an indicator.
If the tip is new, tin it before soldering. Tinning is recommended because it helps prevent solder from sticking to the tip and forming into an ugly globule. If the globule comes off onto your circuit, then you could get a short. You tin the tip by heating up the pencil to full temperature and applying a small amount of solder to the tip. Wipe off any excess solder with a moistened sponge or towel. Periodically use this same technique to keep the tip clean. You can also purchase soldering tip cleaners if dirt becomes caked on and you just canít get it off during regular tip re-tinning.
Successful soldering requires that you follow some simple rules and get a lot of practice. Keep the following in mind as you solder:
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Pencil
168 Part IV: Getting Your Hands Dirty
Figure 8-4:
Hold the soldering pencil at a 30-to 45-degree angle.
The cleaner the metal surface, the better the solder sticks to it. Clean etched circuit boards and wire ends with isopropyl alcohol. Let surfaces dry thoroughly before soldering: You donít want them to catch on fire!
Hold the soldering pencil at a 30- to 45-degree angle to the work surface. (See Figure 8-4.) If youíre using a chiseled tip, the flat of the chisel should rest firmly against the surface of the joint that youíre soldering.
Always apply the heat of the tip to the item that youíre working on,
not to the solder. If youíre soldering a wire into the hole of a circuit board, for example, touch the tip to both the wire and the pad, like the tip in Figure 8-5. Wait a few seconds and then apply solder to the heated area. Immediately remove the heated tip after the solder flows.
Apply just the right amount of solder. Too little, and you form a weak connection; too much, and the solder may form globs that can cause short circuits.
You know you have just the right amount of solder when it forms a raised area (called a fillet) between the wire and the circuit board.
^ Avoid applying more solder to an already-soldered joint. This added solder can cause whatís known as a cold solder joint and the result could be that your circuit simply wonít work. (Check out the following section, ďAvoiding Cold Solder Joints like the Plague,Ē for more on this soldering no-no.)
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Chapter 8: Everything You Need to Know about Soldering 169
Figure 8-5:
Apply heat to the parts youíre soldering, not to the solder! This leads to a better solder joint.
You can damage many electronic components if you expose them to prolonged or excessive heat. Apply the soldering pencil only long enough to heat the work for proper soldering ó no more, no less.
When soldering electronic components that are very heat sensitive, use a clip-on heat sink. These sinks look like miniature aluminum pliers, with a spring-loaded clamp that you attach securely to the component you want to protect. The sink draws off heat and helps prevent the heat from destroying the component. Clip the sink to the wire that youíre soldering, as near to the component itself as you can. Of course, you still have to exercise caution, even when using a heat sink.
Avoiding Cold Solder Joints like the Plague
A cold solder joint happens when solder doesnít properly flow around the metal parts. Cold joints are physically weaker than properly made joints, and they donít conduct electricity as well. You can often (but not always) identify cold joints just by looking at them. A cold joint typically has a dull appearance rather than the shiny, uniform look of a normal joint. And the solder may form jagged peaks rather than having an all-around smooth surface.
Many things can cause a cold solder joint, such as:
You move the work as the solder is cooling. Avoid all movement until the solder cools beyond the plastic phase. (The plastic phase occurs when the solder is still partially liquid and not yet hardened.) If you accidentally jiggle the wire or component, quickly re-apply the tip of the soldering pencil to reheat the solder back to its liquid state.
The joint is dirty or oily. Be sure to keep all metal-to-metal contacts clean.
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170 Part IV: Getting Your Hands Dirty
You donít heat the work to the proper temperature. Be sure that you have the work hot enough to melt the solder to a somewhat runny liquid.
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