- Soldering is a process in which two or more metal items are joined together by melting and then flowing a filler metal into the joint—the filler metal having a relatively low melting point.
- Soldering is used to form a permanent connection between electronic components.
- The metal to be soldered is heated with a soldering iron and then solder is melted into the connection.
- Only the solder melts, not the parts that are being soldered.
- Solder is a metallic "glue" that holds the parts together and forms a connection that allows electrical current to flow.
- You can use a solderless breadboard to make test circuits, but if you want your circuit to last for more than a few days, you will want to solder the components together.
Materials and Equipment
- A soldering iron
- A soldering iron is used to heat the connections to be soldered.
- For electronic circuits, you should use a 25- to 40-watt (W) soldering iron.
- Higher wattage soldering irons are not necessarily hotter; they are just able to heat larger components. A 40-W soldering iron makes joints faster than a 25-W soldering iron does.
- A soldering iron can be purchased at hardware stores and at most large department stores.
- Rosin core solder
- Solder has a lower melting point than the metals that are being connected do. The solder melts when it is heated by the soldering iron, but the metals being joined will not melt.
- The rosin core acts as a flux. It prevents oxidation of the metals that are being connected, and enhances the ability of the solder to "wet" the surfaces that are being joined.
- Solder that is used to join copper pipes has an acid core, which is appropriate for pipes, but will corrode electronic connections. Use solder that has a rosin core.
- For most electronics work, a solder with a diameter of 0.75 millimeters (mm) to 1.0 mm is best. Thicker solder might make soldering small joints difficult and also increases the chances of creating solder bridges between copper pads that are not meant to be connected.
- An alloy of 60/40 (60% tin, 40% lead) is used for most electronics work, but lead-free solders are available as well.
- Set the multimeter to read "resistance." Check that the two probes are inserted in the right holes.
- What does the readout say when the probes are not touching anything? When the two probes are separated, there is an infinite resistance separating them, since air does not conduct electricity. Make a mental note of your multimeter's readout for infinite resistance, because it varies with the manufacturer.
- Touch the two probes together. Now what does the readout say? When you touch the two probes together, the resistance is close to zero, since the metal tips are excellent conductors.
- Measure the resistance of some resistors that are not attached to a circuit. For example, test resistors of 100 Ω (ohms), 10,000 Ω, and 1 MΩ (megaohm, or 1 million ohms). You can buy these online at www.radioshack.com. Touch the probes to the wires on either side of the central cylinder. Watch the units: a "k" means kilo-ohms (thousands of ohms), and an "M" means megaohms. Look online for a chart that tells you how to read the value of the resistance based on the colored bands.
- Never measure resistance in a circuit when power is applied. You must also discharge capacitors in a circuit before measuring resistance, because if there is any source of current other than the multimeter itself, you will get erroneous readings. If the circuit you are working with has large capacitors, you should test them to see if they are carrying a charge. Test the capacitor for charge using a voltmeter, set to high DC voltage. If there is a charge on the capacitor, use a high-wattage resistor to discharge it. Carefully touch the two leads of the resistor to the leads of the capacitor. It may take several seconds for the capacitor to discharge. For more details about how to safely discharge capacitors, visit the following website: Capacitor Testing, Safe Discharging, and Other Related Information
