Point-to-point construction
From Wikipedia, the free encyclopedia
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 strong electrical and mechanical connection.
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[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 each loop from the others. 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 terminals and soldering.
Professional electronics 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.
Point to point construction continued to be used after the invention of printed circuit boards for many tube based electronics. The heat of the tubes would degrade the circuit boards and cause them to become brittle and break. This is often seen on inexpensive tube radios produced in the 1960s with the tubes mounted on printed circuit boards; especially around the output and rectifier tubes, which ran the hottest. The American manufacturer Zenith continued to use point to point wiring in its tube based television sets until the early 1970s.
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, prevents foreign objects which may alter the electrical characteristics of the circuits and interfere with proper operation (such as by causing short circuits or altering electromagnetic fields), and protects humans and animals from contact with potentially dangerous voltages which may cause an electric shock while the machine is operating and from sharp edges and points on the assembly which could cause physical injury such as cuts.
[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, evoking the image of the upturned body of an expired insect. 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.
[edit] See also
[edit] External links
- A picture of free-form construction
- A picture of "dead bug style"
- Progressive Wiring Techniques shows an example of point-to-point construction applied to surface-mount components.
