Point-to-point construction

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Section of a typical Australian late 1930's radio, showing the point to point construction between components.

Point-to-point construction of military radio equipment

Point-to-point construction is the way most electronics circuits were constructed before the 1950s. Point-to-point construction is still used to construct prototype equipment with few or heavy electronic components.

The crucial invention was soldering. In soldering, an alloy of tin and lead, or later bismuth and tin, is melted and adheres to other, nonmolten metals, such as copper or tinned steel. Solder makes a good electrical and mechanical connection.

1 Terminal strip construction
2 'Dead bug' construction
3 See also
4 External links

[edit] Terminal strip construction

Point-to-point construction uses terminal strips (also called 'tag boards'). A terminal strip is a stamped strip of tin-plated loops of copper. It is mounted in a way that electrically insulates it. The metal loops are mounted on a cheap, heat-resistant material, usually synthetic-resin bonded paper (FR-2), or bakelite reinforced with cotton, or sometimes paxolin. The insulator has an integral mounting bracket, sometimes shorted to one or more of the stamped loops to ground them to the chassis.

The chassis was constructed first, from sheet metal or wood. Insulated terminal strips were then riveted, nailed or screwed to the underside or interior of the chassis. Transformers, large capacitors, Tube sockets and other large components were mounted to the top of the chassis. Their wires were led through holes to the underside or interior. The wires of electronic components were physically looped through the terminals and soldered to them. Small electronic components were mounted by twisting their wires around terminal and soldering.

Professional electronic assemblers used to operate from books of photographs, and follow an exact assembly sequence to assure that they did not miss any components. Although this process is error-prone, and nearly impossible to automate, it is quite good for building small numbers of units when labor costs are low.

Placing the completed unit in an enclosure protects it from mechanical damage when the chassis is mounted in a piece of furniture or an equipment rack.

[edit] 'Dead bug' construction

For hobbyist work, free-form construction can be used in cases where a PCB would be too big or too much work for a small number of components. This is sometimes called "dead bug style" as the ICs are flipped upside-down with their pins sticking up into the air. While it is often messy-looking, error-prone, and difficult to repair, this can be used to make more compact circuits than other methods. This is often used in BEAM robotics and in RF circuits where component leads must be kept short.