Perfboard work involves a lot of soldering. Soldering one hole at a time means even a small circuit has dozens of joints, and a single bad one makes the circuit stop intermittently. Fortunately, anyone can get reliable results by following a few principles. This article covers the tools and temperatures you need, the step-by-step order, what a good joint looks like, and common mistakes.
What you need
- Soldering iron: for beginners, an iron whose temperature you can control is best. How to choose one is covered in How to Choose a Soldering Iron.
- Solder wire: a diameter of about 0.6 to 0.8 mm suits perfboard. Use one with flux in the core.
- Iron stand and tip cleaner: wipe the tip often with a wet sponge or a brass wool.
- Side cutters and tweezers: for trimming the leftover leads after soldering and holding small parts.
- Solder wick (desoldering braid): removes solder when you make a mistake. See Desoldering and Rework.
- Protective gear: safety glasses and ventilation are explained in Soldering Safety.
Temperature and choosing solder
The melting temperature differs by type of solder. The iron temperature has to be well above the melting temperature of the solder, but if it is too high the pads lift and the tip oxidizes quickly.
| Solder type | Melting point (approx.) | Recommended working temperature |
|---|---|---|
| Leaded Sn63/Pb37 | 183°C | 300–350°C |
| Lead-free Sn-Cu, SAC305 types | 217–227°C | 340–380°C |
Leaded solder is easier to work with and gives smoother joints, but it contains lead and needs careful handling. Lead-free solder needs a higher temperature, and its surface can look rough yet still be fine. Either way, if the solder does not melt within 3 to 4 seconds because the iron tip is too cool, raise the temperature.
Soldering in 5 steps
- Clean the tip and tin it lightly. A thin coat of solder on the tip surface acts as a bridge that carries heat.
- Touch the tip where the pad and the part lead meet. Heat both at the same time for 1 to 2 seconds. If you touch the solder to the tip first, it just balls up.
- Touch the solder to the heated joint so it melts. Apply the solder between the pad and the lead, not on the tip. Feed just enough that it flows and covers the pad.
- Remove the solder first, then the iron about 1 second later. Do not move the part until the solder sets.
- Wait for it to cool. Leave it for 2 to 3 seconds without blowing on it or touching it.
The whole thing usually takes 3 to 4 seconds. If you need to heat for longer, suspect the temperature or the condition of the tip.
What a good joint looks like
- The surface is smooth and shiny (lead-free may be slightly matte), in a concave volcano shape.
- Both the pad and the part lead are wetted by the solder.
- Too little solder gives a weak connection, and too much, rising like a bead, is a cold joint or easily bridges to the neighboring pad.
The order to attach parts
So that parts do not fall out and the board sits flat when you flip it to solder, attach the shortest parts first.
- Jumper wires, diodes, resistors
- IC sockets
- Ceramic capacitors, transistors, LEDs
- Tall parts such as electrolytic capacitors, pin headers, connectors, and switches
Before soldering, if you push the leads through the holes and bend them slightly outward, the parts will not fall off when you turn the board over. When you finish soldering, cut the leftover leads with side cutters just above the solder.
Tips for holding parts
- Lay resistors down with the body against the board; it looks good and is sturdy.
- We recommend plugging ICs into sockets. There is no risk of heat damaging the IC, and you can fix orientation mistakes. See Reading DIP IC Pin Numbers and Using IC Sockets.
- Inserting the parts of the same row together and then soldering them one after another in one direction goes quickly.
Common mistakes and prevention
| Mistake | Cause | Prevention |
|---|---|---|
| Solder joins the neighboring pad (bridge) | Too much solder, tip too large | Use less solder and a fine tip; remove with solder wick |
| Cold joint | Not enough heat, movement, dirty pad | Raise the temperature, allow time to heat, hold still until it sets |
| Pad lifts | Heated too long or too hot | Finish within 3 to 4 seconds; let it cool and redo |
| Flux residue | Too much flux | Wipe with isopropyl alcohol and a brush |
| Part in backwards | Not enough checking | Recheck polarity and pin numbers before soldering |
How to practice
At first, solder 10 to 20 resistor leads onto a spare or practice board. Check the shape of every joint, and when a bead or bridge appears, think about the cause and redo it. If you draw the layout and wiring in Patterndo first, you decide in advance which holes to solder in what order, and mistakes drop greatly.
Summary
The core of soldering is "heat the pad and the lead at the same time, and touch the solder to the heated joint." Match the temperature to the solder type, finish short and clean, and attach the shortest parts first. Next, learn Reading a Layout Diagram and you can solder straight from a layout.