Cruciform Packaging—A General Synthesis for Airborne Electronics

Summary

Accelerated development schedules, combined with a tremendous increase in number and complexity of design factors, have pointed out the need for a general package design adaptable to a wide variety of environmental conditions.

Cruciform packaging has been developed in order to optimize reliability, maintainability, size, and weight, with capabilities of meeting any specified environment of temperature, humidity, shock, vibration, and radio noise. Starting with an internal structural skeleton, in lieu of an outer casing, the synthesis proceeds structurally to diagonally braced plug-in module assemblies of selected cross section and continuously variable length. Reliability target of duplex connections is achieved by mechanical and electrical connections at each component and dual lead support in fixture boards and encapsulation. Maintainability at any level is assured by plug-in structure, plug-in modules, and chemically dissolved encapsulation. Size is kept minimal through high-density cordwood arrangements of components between parallel fixtured boards; as component parts of smaller size become available, they can be immediately accommodated without extensive design modification. Solid circuits and thin-circuit subassemblies are likewise acceptable component parts of cruciform modules.

Weight can be minimized consistent with environmental requirements by straightforward machining operations in the metalwork and substitution of foamed urethane for loaded epoxy encapsulants.

Heat transfer by free or forced convection, radiation, conduction, or any combination thereof, can be readily employed to suit customer requirements.

The over-all result of a generalized design with extreme versatility in size and weight with positive environmental margin has been the transferring of the design engineer’s packaging effort from synthesis of a required package to analysis of the generalized package in light of specific requirements. This analysis, based on actual test data obtained from the generalized design, results in simple straightforward adaptations to meet specific needs. In two years’ utilization at the General Electric Company’s Armament and Control Section, Johnson City, N.Y., the cruciform has appeared in actual delivery, or in proposals for airborne, shipborne, and jeep-borne equipment, and for primary and ground-support equipment, for all Armed Services. In each case, the configuration and customer requirements dictated the design specifics, but the general concept has remained essentially intact throughout.