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Point-to-point construction

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

Point-to-point construction uses terminal strips. A terminal strip is a stamped strip of tin-plated loops of copper. It is mounted in a way that electrically insulates it. Usually it is mounted on a cheap, heat-resistant piece of plastic, usually brown bakelite. The plastic is mounted to a metal standoff with a mounting hole.

The chassis was constructed first, from sheet metal or wood. Insulated terminal strips were then riveted, naileded or screwed to the underside of the chassis. Placing the wiring in the box protects it from mechanical damage when the chassis is mounted in a piece of furniture or an equipment rack. 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. The wires of electronic components were physically looped through the terminals and twisted on them. Small electronic components were mounted by twisting their wires around terminal loops. Finally, the terminals with wires were soldered. The process is error-prone, and nearly impossible to automate. It is quite good for building small numbers of equipment when labor costs are low.

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.

See also: printed circuit board, wire wrap, PCB layout guidelines, veroboard and electronics.