Soldering, multimeter and test gear for beginners

1. Safety first

2. Choosing an iron and a temperature

• For electronics use a temperature-controlled iron (a station or a good adjustable pen-style iron) with a fine conical or small chisel tip. A cheap unregulated plug-in iron is a frequent cause of lifted pads and bad joints.
• Wattage matters less than heat recovery; a 60 W-class regulated iron suits most work, and USB-C pen irons are good for small jobs.
• A brass-wool tip cleaner is gentler on the tip than a wet sponge.

Use the lowest temperature that makes a joint quickly (about 2 to 3 seconds per joint). Too hot burns flux, lifts pads and damages parts; too cool makes cold joints. Settings are a typical guide, not a standard.

3. Solder, flux, leaded vs lead-free

• Solder wire for electronics usually has flux inside (a "flux core"); common diameters are 0.5 to 0.8 mm. Never use plumbing solder or acid-core solder on electronics: they corrode the parts.
• Leaded (commonly 60/40 or 63/37 tin-lead): melts at a lower temperature (about 183 to 190 degC) and flows easily, so it is easier for beginners. Lead is toxic: wash your hands, do not eat at the bench, and keep it away from children. Rules on selling or using leaded solder differ by country.
• Lead-free (tin-silver-copper or tin-copper; melts around 217 to 230 degC): required for products sold in many places, less toxic to handle, but needs a hotter iron, more flux and gives duller joints. Its fumes still come from the flux, so ventilate either way.
• Do not mix leaded and lead-free on the same joint in anything for sale. For hobby repairs, it is generally fine; you may add a little flux to help.
• Extra flux (a pen, paste or gel; "no-clean" types leave less residue) makes everything easier, especially SMD and desoldering. Clean sticky residue with isopropyl alcohol and a brush if you like a tidy board.

4. Through-hole soldering step by step

1. Fit the part flush to the board. Bend the leads slightly or use tape or a helping hand so it stays put.
2. Tin the tip: touch a little solder to the clean tip so it looks shiny; heat transfer is much better.
3. Touch the tip so it contacts both the pad and the lead for 1 to 2 seconds.
4. Feed solder to the joint (not the tip) until a small cone-shaped fillet forms.
5. Remove the solder, then the iron, and hold still for a few seconds until the joint turns solid.
6. Trim the lead above the joint. Inspect: shiny, smooth, concave fillet wetting both pad and lead.

Order of work: lowest parts first (resistors, diodes), then IC sockets, capacitors, connectors and tall parts last. Check polarity before soldering diodes, LEDs, electrolytic capacitors and ICs.

5. Surface-mount soldering

• Two-pad parts (resistors, capacitors): put a little solder on one pad, hold the part with tweezers, melt that pad to fix it, then solder the other pad.
• Drag soldering (fine-pitch chips): align the chip, tack two diagonal corners, add flux generously to all pins, then drag a loaded tip (with a little solder) along the pins. Bridges between pins are expected: remove with flux and solder wick.
• Hot air: apply solder paste to the pads, place the part, and heat with a hot-air station at a moderate airflow until the paste melts and the part self-centres. Keep the air low enough so small parts do not blow away. Keep the nozzle moving to avoid overheating plastic.
• Hot plate / reflow oven: paste, place all parts, heat the whole board following the paste's temperature profile. A dedicated reflow hot plate or a toaster oven used only for electronics works; never use a kitchen oven used for food, because of the fumes and residue.
• Use magnification (a loupe or a USB microscope) and good light. Start with 0805 or 0603 parts before attempting QFN or BGA.

6. Desoldering

• Solder wick (braid): put the braid on the joint, press the iron on top, and the solder wicks up. Cut off the used part. Add flux to the braid if it does not take up.
• Desoldering pump (solder sucker): melt the joint, then trigger the pump and the solder is sucked in. Practise on a scrap board.
• For multi-pin through-hole parts, remove one pin at a time, or cut the part off and remove each lead. Do not force a part out of a hole that is still solid; you will tear the pad. Add fresh leaded solder to help the old solder melt.

7. Common joint faults

8. Electrostatic discharge (ESD)

Static electricity can damage chips (MOSFETs, CMOS ICs, microcontrollers) without any sign. Keep boards in anti-static bags until needed, work on a hard surface rather than carpet, touch a grounded metal object first, and consider an ESD mat and wrist strap with a built-in resistor. Do not use a wrist strap near mains-powered or high-voltage equipment. Humidity helps: dry winter air with wool clothes is the worst case.

9. Using a multimeter

The red lead goes in the socket marked for voltage and resistance (V, ohm), black in COM. Use the 10 A socket only for a high-current measurement, and put the lead back afterwards.

• DC voltage (V with a straight line): probes in parallel with the part. Black to ground, red to the point. The meter reads a small current only, so it does not disturb the circuit.
• Continuity (the beeper): with the circuit unpowered, touch two points; a beep means a low-resistance connection. Use it to check joints, cables and shorts (power to ground should NOT beep).
• Resistance (ohm): with power off and the part out of the circuit (or at least one leg lifted), as other paths give wrong readings. Never measure resistance on a powered circuit.
• Diode test (diode symbol): shows the forward voltage of a diode or the base-emitter junction of a transistor, about 0.5 to 0.7 V for silicon diodes (roughly 1.8 to 3 V for LEDs, which may glow faintly) in one direction and "OL" (over limit) in the other.
• Current (A): the meter goes in series: break the circuit and connect the meter in the gap, with the red lead in the A or mA socket, and the right range. Measure the unknown at the highest range first.

An auto-range meter picks the range for you; a manual one needs you to choose. A "true RMS" meter is more accurate for AC that is not a pure sine. Accuracy is limited; do not trust the last digit.

10. What an oscilloscope and a logic analyser do

A multimeter shows a number; a scope shows a voltage drawn against time, so you can see a signal's shape.

• Timebase (time/div): how much time each horizontal grid square represents. Faster (smaller time/div) zooms in on shorter events.
• Volts/div: how many volts each vertical square represents. Set it so the signal fills a good part of the screen.
• Trigger: tells the scope when to start drawing so a repeating signal stays still: set the level near the middle of the edge and choose rising or falling edge. Without a trigger the trace jumps around.
• Probe: a 10x probe loads the circuit less; set the scope channel to 10x to match. The probe's ground clip goes to circuit ground; clipping it to the wrong point can short something. Use a floating (battery) scope or isolation for anything connected to mains: never connect the ground clip to a mains-live point.
• Bandwidth: the scope should be several times faster than the signal you want to see.
• A logic analyser records many digital lines (1 or 0) over time and decodes protocols such as I2C, SPI and UART into readable bytes. It is the right tool when "the sensor does not answer" and you want to see who spoke and when. Low-cost USB analysers work with free software.

11. Bench power supply and current limiting

A bench supply lets you set both voltage and a current limit. For a new or repaired board: set the voltage to the rated value, set the current limit low (for example 50 to 100 mA, or whatever the board should draw), turn the output on, and watch the current. If it jumps to the limit and the voltage collapses (constant-current mode), there is a short or a wrong part: switch off and look. Raise the limit once things behave. This turns a likely smoke into a harmless indicator. Never connect a supply with reversed polarity; add a reverse-protection diode in your own designs.

12. First-fault troubleshooting flowchart

• Change one thing at a time and write down what you tried.
• If a part is hot to the touch (touch gently, quickly, with the supply current-limited), switch off: a wrongly oriented chip or capacitor is the usual cause.
• Compare against a known-good board or the reference design if you have one.
• Wiring checks: for a breadboard, remember the power rails can be split in the middle on long boards, and loose jumper wires are a very common failure.

Related: Design and order your first PCB, Your first microcontroller project, Electronics calculators, Circuit cookbook and the Electronics cheat sheet.

Temperatures and safety advice are general guidance for hobbyists; follow your solder and equipment manuals, and ask a qualified person for anything involving mains.