PRÁCTICAS PEDAGÓGICAS

Table 3-2

Capacitor code identification information

This table is designed to provide the value of alphanumeric coded ceramic, mylar and mica capacitors in general. They come in many sizes, shapes, values and ratings; many different manufacturers worldwide produce them and not all play by the same rules. Most capacitors actually have the numeric values stamped on them; however, some are color coded and some have alphanumeric codes. The capacitor’s first and second significant number IDs are the first and second values, followed by the multiplier number code, followed by the percentage tolerance letter code. Usually the first two digits of the code represent the significant part of the value, while the third digit, called the multiplier, corresponds to the number of zeros to be added to the first two digits.

Value Type Code Value Type Code

1.5 pF Ceramic 1,000 pF /.001 µF Ceramic / Mylar 102 3.3 pF Ceramic 1,500 pF /.0015 µF Ceramic / Mylar 152 10 pF Ceramic 2,000 pF /.002 µF Ceramic / Mylar 202 15 pF Ceramic 2,200 pF /.0022 µF Ceramic / Mylar 222 20 pF Ceramic 4,700 pF /.0047 µF Ceramic / Mylar 472 30 pF Ceramic 5,000 pF /.005 µF Ceramic / Mylar 502 33 pF Ceramic 5,600 pF /.0056 µF Ceramic / Mylar 562 47 pF Ceramic 6,800 pF /.0068 µF Ceramic / Mylar 682 56 pF Ceramic .01 Ceramic / Mylar 103 68 pF Ceramic .015 Mylar 75 pF Ceramic .02 Mylar 203 82 pF Ceramic .022 Mylar 223 91 pF Ceramic .033 Mylar 333 100 pF Ceramic 101 .047 Mylar 473 120 pF Ceramic 121 .05 Mylar 503 130 pF Ceramic 131 .056 Mylar 563 150 pF Ceramic 151 .068 Mylar 683 180 pF Ceramic 181 .1 Mylar 104 220 pF Ceramic 221 .2 Mylar 204 330 pF Ceramic 331 .22 Mylar 224 470 pF Ceramic 471 .33 Mylar 334 560 pF Ceramic 561 .47 Mylar 474 680 pF Ceramic 681 .56 Mylar 564 750 pF Ceramic 751 1 Mylar 105 820 pF Ceramic 821 2 Mylar 205 1st Significant Figure 2nd Significant Figure Multiplier Tolerance CSGNetwork.Com 6/4/92 0.1µF 10% 104 k

Chapter Three: Electronic Parts Installation

Figure 3-2 “Dressing” capacitor component leads

(a) Grip outer lead near body and bend out by 45°

(b) Grip about 2 mm down and bend down by 45°, parallel again

(c) Both leads cranked to match 2.5 mm PC board hole spacing

Figure 3-4 “Dressing” TO-92 transistor leads

Soldering joins two pieces of metal, such as electrical wires, by melting them together with another metal to form a strong, chemical bond. Done correctly, it unites the metals so that electrically they act as one piece of metal. Soldering is not just gluing metals together. Soldering is tricky and intimidating in practice, but easy to understand in theory. Basic supplies include a soldering iron, which is a prong of metal that heats to a specific temperature through electricity, like a regular iron. The solder, or soldering wire, often an alloy of aluminum and lead, needs a lower melting point than the metal you’re joining. Finally, you need a cleaning resin called flux that ensures the joining pieces are incredibly clean. Flux removes all the oxides on the surface of the metal that would interfere with the molecular bonding, allowing the solder to flow into the joint smoothly. You also need two things to solder together.

The first step in soldering is cleaning the surfaces, initially with sandpaper or steel wool and then by melting flux onto the parts. Sometimes, flux is part of the alloy of the soldering wire, in an easy-to-use mixture. Then, the pieces are both heated above the

melting point of the solder (but below their own melting point) with the soldering iron. When touched to the joint, this precise heating causes the solder to “flow” to the place of highest temperature and makes a chemical bond. The solder shouldn’t drip or blob, but spread smoothly, coating the entire joint. When the solder cools, you should have a clean, sturdy connection. Many people use soldering in their field, from electrical engineering and plumbing to jewelry and crafts. In a delicate procedure, a special material, called solder, flows over two pre-heated pieces and attaches them through a process similar to welding or brazing. Various metals can be soldered together, such as gold and sterling silver in jewelry, brass in watches and clocks, copper in water pipes, or iron in leaded glass stained windows. All these metals have different melting points, and therefore use different solder. Some “soft” solder, with a low melting point, is perfect for wiring a circuit board. Other “hard” solder, such as for making a bracelet, needs a torch rather than a soldering iron to get a hot enough temperature. Electrical engineers and hobbyists alike can benefit from learning the art and science of soldering.

Chapter Three: Electronic Parts Installation

Solder

The best solder for electronics work is 60/40 rosin-core solder. It is made of 60% tin and 40% lead. This mixture melts at a lower temperature than either lead or tin alone. It makes soldering easy and provides good connections. The rosin keeps the joint clean as it is being soldered. The heat of the iron often causes a tarnish or oxide to form on the surface. The rosin dissolves the tarnish to make the solder cling tightly. Solders have different melting points, depending on the ratio of tin to lead. Tin melts at 450°F and lead at 621°F. Solder made from 63% tin and 37% lead melts at 361°F, the lowest melting point for a tin and lead mixture. Called 63-37 (or eutectic), this type of solder also provides the most rapid solid-to-liquid transition and the best stress resistance. Solders made with different lead/tin ratios have a plastic state at some temperatures. If the solder is deformed while it is in the plastic state, the deformation remains when the solder freezes into the solid state. Any stress or motion applied to “plastic solder” causes a poor solder joint.

The 60-40 solder has the best wetting qualities. Wetting is the ability to spread rapidly and bond materials uniformly; 60-40 solder also has a low melting point. These factors make it the most commonly used solder in electronics.

Some connections that carry high current can’t be made with ordinary tin-lead solder because the heat generated by the current would melt the solder. Automotive starter brushes and transmitter tank circuits are two examples. Silver-bearing solders have higher melting points, and so prevent this problem. High-temperature silver alloys become liquid in the 1100°F to l200°F range, and a silver-manganese (85-15) alloy requires almost 1800°F.

Because silver dissolves easily in tin, tin bearing solders can leach silver plating from components. This problem can greatly reduced by partially saturating the tin in the solder with silver or by eliminating the tin. Tin-silver or tin-lead-silver alloys become liquid at temperatures from 430°F for 96.5-3.5 (tin-silver), to 588°F for 1.0-97.5-1.5 (tin-lead-silver). A 15.080.0-5.0 alloy of lead-indium-silver melts at 314°F.

Never use acid-core solder for electrical work. It should be used only for plumbing or chassis work.

For circuit construction, only use fluxes or solder-flux combinations that are labeled for electronic soldering.

The rosin or the acid is a flux. Flux removes oxide by suspending it in solution and floating it to the top. Flux is not a cleaning agent! Always clean the work before soldering. Flux is not a part of a soldered connection— it merely aids the soldering process. After soldering, remove any remaining flux. Rosin flux can be removed with isopropyl or denatured alcohol. A cotton swab is a good tool for applying the alcohol and scrubbing the excess flux away. Commercial flux-removal sprays are available at most electronic-part distributors.