Electronic Design

Microminiature Guidance Computer

A prototype microminiature guidance computer, using a combination of ceramic wafer-mounted microcomponents and deposited elements in its logic, is scheduled for completion before the end of this year. A nondestructive multiaperture-type memory, using either ferrite sheets or strips, is planned for the experimental unit. The techniques, being used by American Bosch Arma Corp., Garden City, L.I., N.Y., are derived from the 2-D packaging approach developed by Diamond Ordnance Fuze Laboratories, Washington. Although the basic approach to the Arma Computer has been decided, according to James P. Maguire, supervisor of the company's microminiaturization group, some design details are not yet settled.

This is the third generation of guidance computer designed by Arma (see photo). The first-generation computer, shown at the left, is the present Atlas ICBM inertial guidance computer. The second-generation computer, center, which is not yet assigned to a specific project, uses circuitry embedded in foamed polyurethane. The third-generation computer, right, is the microminiature unit now in development. The new computer weighs just 15 lb, occupies 0.3 cu ft, and dissipates 50 W, a large decrease from the first generation's 200 lb, 8 cu ft, and 1000-W dissipation.

Six basic circuit types, mounted on about a thousand 1-in.-sq. alumina wafers, will be used in the computer. Arma plans to join the wafers to printed-circuit boards with a flow-solder process. Present test boards contain six wafers each, but a shift to nine wafers on a board is being considered, according to Mr. Maguire.

Conduction paths on the wafers are silk-screened, and resistors are added by injection printing. Silk-screening of resistors was evaluated, Mr. Maguire said, but the injection method was chosen because of better thickness control.

Microcomponents—transistors, diodes, and capacitors—are then soldered in place. A fixture for holding these components in place while the wafer is dipped into a solder pot is now being designed by Arma for computer production. (Electronic Design, April 26, 1961, p. 8)

Miniaturization was the key word in the electronics industry of the early '60s. Even without the ready availability of integrated circuits, aerospace computer makers were able to achieve significant size reductions by using discrete transistors and thick- and thin-film hybrid circuits based on alumina substrates.

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