Building a Circuit Dead-Bug Style - dummies

By H. Ward Silver

With dead-bug style circuitbuilding, the integrated circuits (ICs) are all mounted upside down on the printed circuit (PC) board with most of their legs sticking up in the air! They look like a lot of . . . dead bugs! Another name for this type of construction is “air circuits” because the components are attached directly to each other over the underlying PC board. The technique is easy for beginners because it requires no special tools, gadgets, or techniques. Just solder the parts together and to a PC board and go! This is a great method to wire up a simple circuit to see how it really performs.

With dead-bug construction, the PC board surface is usually made to be the circuit’s ground. This is sometimes referred to as a ground plane. Because the ground is literally everywhere, and because it’s such a wide conductor, dead-bug construction works well for sensitive circuits and even at high frequencies. Conversely, this makes routing power supply connections a little more difficult, since everything is exposed.

Dead-bug construction generally becomes impractical once the IC pin count exceeds 20 pins or if there are more than two or three ICs. Complex circuits have so many connections and components that it becomes hard to keep all of the connections straight and separated. Dead-bug style works best with one or two ICs.

If your circuit doesn’t have a lot of components that attach to ground, you can use high-value resistors (1 MΩ or higher) as supports for other components. Solder one lead of the resistor to the PC board and stand it upright. Other components can then use the remaining lead as a tie point for connections with other components. Terminal strips (metal solder lugs mounted on an insulating strip) can also be used.

To make the connections, components are mostly soldered directly together, lead to lead. You will have to bend the leads and orient the components to make the circuit work electrically and for mechanical stability. If jumper wires between connections are needed, bare wire can be used for short distances, but insulated #30 wire-wrap wire or #24 or #26 hookup wire can be used. Solid wire is preferred because it will keep its shape, whereas stranded wire is more flexible.

The drawbacks of dead-bug construction

Dead-bug construction is very straightforward and requires no special tools, but it’s not suitable for all kinds of circuits and applications. In the spirit of helping you choose the appropriate technique for your circuit, the primary weaknesses of dead bugs are listed here:

  • Not mechanically robust. Dead-bug circuits, like their namesake, are easy to squash! They are also not suitable for tough environments like in cars or outside. The technique is a good way to build a prototype or experiment.
  • Hard to make major modifications. While it’s easy to change a component like a resistor or capacitor, it’s quite difficult to change an IC or redesign a large chunk of the circuitry.
  • Solder blobs. Dead-bug technique puts a premium on soldering technique. Messy soldering that drips excess solder will create short circuits, usually in places difficult to access. Use the minimum amount of solder and take your time.
  • Hard to duplicate. When you’re done, you will probably have a one-of-a-kind circuit. If that’s all you need, great! Don’t plan on using this technique on a production line, though.