FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1962
1962 - 2394.PDF
FLIGHT International, 18 October 1962 AVIATION ELECTRONICS... tion of the transistor into extensive use in relatively high-frequency circuitry, and its application to power supplies, which produced the really attractive miniaturization, that is, a combination of greatly reduced size, with far lower power requirement, much smaller heat dissipation and, last but by no means least, greatly improved reliability. It is from this last quality that the real benefits of micro miniaturization are to be expected. Small size is implicit in the new solid-state electronics as much as being its purpose. With the introduction of the solid-state device in place of the thermionic tube the whole picture changed. The transistor itself was much smaller than the tube and could normally be mounted directly on a board without a mechanical socket. It afforded real opportunities for exploiting entirely new forms of wiring and inter connection and, indeed, of rearranging conventional circuitry quite extensively. The printed-circuit board, the plug-in-card module, quite different power supplies and new forms of interconnection between components and circuits all provided opportunities for a new approach to equipment design. From the technical back ground of the man who designs equipment to the space and power requirements for its installation, transistorization has introduced a new look in electronics. But while miniaturization was in itself a most attractive prospect, it was the increased reliability of the fully developed transistor which became its main attraction. Space reduction was spectacular mainly where a great many transistors replaced an equal number of valves —for example, in large digital computers and complex information- handling systems. The present range of transistorized airborne equipment is a good deal smaller than its valved predecessor, but at least one manufacturer has decided to concentrate on reliability and maintainability rather than out-and-out size reduction in designing his equipment for the nineteen-sixties. And the transistor is being exploited on an almost equal scale to replace mechanical components, which are as unreliable as large groups of valves used to be. As equipment becomes smaller, its application tends to change. Smaller aircraft can carry the lighter units and generate sufficient power to run them. In the USA, the numerical majority of potential customers are the business-aircraft owners, and it is their require ments for all-in-one-case equipment in a single aircraft, as opposed to a fleet, which probably dictated the latest Arinc specification for all VHF navigation equipment to be packaged in one case. The air lines themselves may not be so happy about this arrangement, because a failure (for example, in the glide-slope receiver) makes it necessary to remove the whole nav package for servicing. A larger and much more expensive spares holding is required to allow for this scale of replacement. Packing of three separate types of unit in one common case inevitably makes it rather more difficult to service the equipment and trace faults. In closely packed equip ment, random human factors in servicing become very important. The screwdriver which slips can do much more damage. Small modules which are difficult to handle can equally be damaged, often without visible trace—the failure occurs later, in the air. The top of a standard nine-wire transistor header, less than 0.5in in diameter, showing planar transistors and resistances connected with gold filament wiring. The larger posts are header wires seen end-on and bent over Marconi planar components etched into silicon substrates. Top, small logic transistors, each 0.007in square, made in batches of several hundred on a single wafer; centre, 2W lOOMc/s medium-power transistors with power gain of 4dB, each measuring O.OlOin x 0.011 in; bottom, chains of four resistors in strips 0.001 in and 0.002m wide For the airlines, the point of diminishing returns is not far ahead, if it has not already been passed in some equipment. Miniaturization for its own sake is, beyond this point, sought under the stimulus of military requirements, and here one of the great problems is mass production in emergency. A good deal can be done with printed circuits to assemble components automatically by feeding them off paper strips, like machine-gun bullets, into a machine which bends and trims the terminal wires, inserts them in the appropriate holes on the board and then dip-solders all the terminals at once on the reverse side of the board. But still further automation was attempted when R.C.A. began in America a few years ago to develop micromodules, the first stage in microminia turization. On ceramic substrates, or wafers 0.36in square, R.C.A. mounted groups of specially developed miniature components and printed wiring. In some cases, such items as capacitances were produced by plating both sides of part of a wafer; and transistors were made "in the open" on the surface of the wafers. Contacts were taken to notches cut round the edges of the wafers. A small number of components was mounted on each wafer and a module was then built up by stacking four wafers on pillars formed by the edge- mounted contact wires. The whole module was then potted and became a small, solid block which would be attached to other modules. A considerable amount of soldering was involved, but the modules could be automatically mass-produced by machines. Maximum dissipation per plate was about 0.5W. The US Army started a similar project, called Tinker Toy, and Lear offered Millimin packaging. Collins produced an experimental version of their flight director instrumentation in which the com puter, normally separately packaged, was built into the instrument cases themselves. The US Army has specified a microminiature walkie-talkie radio. R.C.A. are still offering various micromodules as off-the-shelf items, but the system has largely been superseded by what might be termed true microminiaturization—the more radical forms of solid-state physics and electronics. What the transistor clearly showed was that active electronic elements can be produced by precisely controlled deposition and diffusion processes applied to various materials, without the con ventional forms of filament and mechanical components associated with valves. The process by which the equivalent of one valve was made in a tiny block of solid material could logically be extended to form groups of components in one tiny block. Elements which could not yet be made by these processes could be replaced by existing components applied in" a different way. It was the physicist
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
