TUESDAY, JUNE 30, 1959







The problem is to compress a room full of digital computation equipment into the size of a suitcase, then a shoe box, and finally small enough to hold in the palm of the hand. This is to be accomplished while increasing the reliability and without sacrificing produceability or maintainability. In addition, the equipment must be capable of functioning in severe mechanical, climatic and nuclear environments.

The objectives of this paper are to demonstrate the techniques and approaches that have resulted in a 95 times size reduction in guidance control computers the past decade and to outline some of the approaches and programs that promise to effect similar further reductions over the next decade.
Significant size and weight reductions were made possible by concerted efforts in the circuits, logical, physical, component and materials engineering areas. All solid state active elements and high density packaging with printed wiring assemblies provided the first big step in size reduction, Reduction of the numbers and size of the components ant higher density volumetric packaging provided a second significant size reduction step.

Future size reduction involves radically different approaches such as microminiaturization of various forms, cryogenics, solid state circuits and molecular and thin film circuits. Each of these will be evaluated and the potential size reduction to be realized are predicted as well as the probable time scale for application.

This paper illustrates the methods of reducing complex electronic systems of tens of thousands of components to sizes compatible with the space limitations of today's aircraft and missiles while maintaining or improving reliability and to predict future methods of size and weight reduction for the complexities of the space age.

In general, the methods discussed are applicable to almost any low power circuitry in which large numbers of components are to be integrated.


Think Small. This is the creed of the engineers working to reduce the size and weight of airborne guidance digital computers, involving many thousands of electronic components in one package.
In an inertial guidance system, acceleration information in the three planes is supplied to the computer by the Inertial Measurement Unit. The computer then continuously computes the optimum steering and engine control signals in accordance with the pre-programmed trajectory information. This is fed to the missile or aircraft control systems for flight control. The guidance system is completely self contained, eliminating the vulnerable ground communication link. Being airborne, the tremendous number of components of the digital computer must be packaged in minimum size and weight. Reliability, maintainability and produceability cannot be sacrificed in the process.

Figure 1 is a simplified block diagram of a typical airborne digital computer. It has all of the elements of a large scale digital computer in simplified and miniaturized form. The operation of the computer is as follows:

Information on the constants of the computation to be performed for the particular mission and pre-flight alignment data are stored in a semi-permanent, instantly available form in the constants memory section. Acceleration data in the three planes is continuously supplied to the computer from the inertial measurement unit.

Figure 1

This data goes into the input section where it is converted into a digital form useable by the machine and preliminary computations such as first integration for velocities and second integration for distances is performed. The information is then stored in a particular slot in the working memory ready for further use. All operations within the computer are controlled in time and synchronism by the program timing unit which generates accurate timing signals. The transfer unit controls the movement of all data from one section of the machine to another.
The computations required are performed in accordance with a predetermined program built into the machine. Data is selected from the constants storage and working storage at the proper sequence time, and inserted into the arithmetic unit where the desired computation is performed. The transfer unit then stores the answer into a particular slot in the memory ready for the next operation. Arma's computers are designed more for reliability than speed, but they can hardly be called slow. Some present machines perform more than 6000 additions per second.
Answers are furnished through the transfer unit to the proper section of the output unit where they are converted from digital data into signale that are compatible with the next piece of equipment such as the autopilot.

A number of size reduction avenues are open to the miniaturization engineer. In order to gain the maximum benefit, it is necessary to exploit all of the approaches to the utmost. In thc case of airborne digital computers the following areas of potential size reduction are of mayor interest:
a.) Improved logical organization. Logical breakthroughs can result in significant reductions in the number of logic circuits required and the total number of electronic components required.

b.) Circuit improvements. Development of new circuit approaches and utilization of the properties of new components can result in power reductions, component size reductions and elimination of many components.

c.) Electronic component characteristics improvements and size reductions. The component industry has been very active in improving the electronic performance of their devices and in reducing the physical size. An example of this is the transistor which has undergone radical size reductions during the past five years. Methods of multiple function semi-conductors in the same size envelope are also in final phases of development.

d.) Physical design or electronic packaging. In order to preserve the size reduction gains indicated above it is essential that the components be mounted, interconnected and protected in the most efficient volumetric and weight approaches available. Material development and new wiring techniques play a large part in the packaging phase. For example, the development of printed wiring permitted significant improvements in the efficiency of mounting and interconnecting large numbers of small electronic components. Utilization of high density volumetric packaging by the use of direct welding promises to affect still further size improvements.

Figure 2 illustrates the size reductions of typical computers that have been accomplished turing the past decade and predicts the improvements of the next decade. The first mayor breakthrough in size reduction was the development of solid state components such as transistors and diodes. These offered, not only small size and weight, but inherent ruggedness against mechanical conditions and lower power and voltages. Coupled with printed wiring, an all solid state computer has permitted size reductions in the order of 10 between 1952 and 1957 over the best miniature tube computers as shown by B in Figure 2. By a combination of logical, circuit and physical design, the number of components has been further reduced, the power re-quirements and therefore the size of components has been reduced and, by volumetric packaging, the volume has been utilized more efficiently. This has resulted in the further reduction of size by a factor of about 5 as indicated by Unit C representing today's latest missile guidance computer.

Figure 2

Utilizing conventional cased components and normal mounting and interconnection methods, the point of diminishing return of further size reduction has been reached. At best 2-3 times further size reduction could be achieved by concerted efforts. Further significant (10 times or greater) size reductions will require radical approaches. Micro-miniaturization offers this potential for the near future. As the chart in Figure 2 shows, block D, by micro-miniaturization offers a potential size reduction of 5 to 10 times over the best conventional component packaging. The longer range estimates for further size reductions include solid state logical circuit assemblies, cryotronics or low temperature conductivity circuits and molecular film techniques.

Figure 3 is a chart prepared by the Varo Corporation of Garland, Texas, illustrating, by effective component density of equipment per cubic foot against year of accomplishment, the limitations and expectations of various methods of electronic equipment size reduction. Starting with 5000 units per cubic foot for the wired tube aasembly in 1953, we progreas to perhaps 25,000 with etched boarda and high aurface component packaging in 1955 and then to 100,000 or slightly better with the beat combination of miniaturized components and volumetric packaging in 1956 to 1958. The potential for further reduction by this procedure is almost exhausted as shown by the curve flattening off as it begins to approach 800,000 components per cubic foot. This is, perhaps, also somewhat optimistic for cased components.


Micro-miniaturization or micro-circuitry picks up at this point and brings the total number of effective components per cubic foot up to the potential of 10^8 to 10^9 . Cryotronics or low temperature super-conductive circuitry offers greater potential size reduction at the present time but suffers from the limitation that it must operate in liquid helium. Starting in about 1962, materials integration where whole circuits are grown into a single semi-conductor or with etched multiple layer molecular film wafers with lines millionths of an inch wide being the potential up to the 10^9 or one billion components per cubic foot level.

So much for the big picture. Now let us look at some of the details of how size reductions have been effected on typical guidance system computers. Figure 4 is a photograph of three successive guidance computers each performing the same computation, but representing successive generations of size reduction.

The larger or first generation unit is presently in mass production. Significant features of this model are an all magnesium extrusion-welded case of extremely light weight and the use of a laminated, printed circuit, foam sandwich for component mounting. This foam technique provides a light weight, high rigidity unit with good internal damping. The sandwich assembly which is used repeatedly throughout the assembly is shown in Figure 5 on the right.

One of the best ways to reduce size and weight while increasing reliability ia to reduce the number of components. A second is to reduce the size or power requirements of the components. Third, utilize higher volumetric efficiency of packaging these components. A combination of logical, circuit and physical design approaches provided these improvements and produced the second generation unit with significant size and weight reductions, vastly reduced power and improved reliability. This unit is now in pilot production. Component reductions averaged 40% with power reduced to 5% of the previous unit. This has resulted in an overall size reduction of approximately six times.

Figure 4

Micro-miniaturization has been utilized for the next major step in size reduction. An examination of one of today's components reveals that the active element now forms a very small percentage of the total volume. The balance is utilized for mounting protecting and interconnecting the operating element. For example, the widely used J.E.T.E.C. -30 transistor has an operating element in the order of .05 x O x 0.60 x 02.0 or 6 x 10^15 cubic inches. This represents approximately 1/1300th of the total volume.

Similarly, the thin resistive film of the deposited resistor and plates of the capacitor represent a very small percentage of the total volume used up by conventional cased components. The next obvious step is to remove this superfluous support and protective material and to utilize the active elements directly integrated into the support and interconnecting medium. This operation is one form of micro-miniaturization called "strip tease".

Recognizing the tremendous potential of micro- miniaturization for all low power electronics, but particularly for airborne and missile digital computers because of their tremendous numbers of components, Arma has sponsored a company funded program to investigate the various methods and techniques of micro-miniaturization and to establish methods of application to airborne digital computers. The first results of this program are shown in Figure 4 where the upper left unit illustrates a micro-miniaturized version of the missile guidance computer discussed previously. This is the third generation. The micro-miniaturized unit performs the same mathematical computations as the first generation unit in 1/27th the volume and 1/17th of the weight of the first generation. Reliability has been increased by reducing the number of interconnections and wires required and improving the mechanical resistance to shock and vibration because of the small size and greater inherent stiffness. In addition, the small size permits the utilization of increased redundancy or duplicate circuits to provide insurance against failure without tremendous size penalties.

Figure 5 illustrates successive building block steps that have led to micro-miniaturization. The right unit is representative of high efficiency conventional component printed wiring single plane mounting. Significant improvements in size have been effected by the central unit which represent volumetrically or three dimensional packaging of miniaturized cased electronic components. On the left is a series of micro-miniaturized wafers surface mounted on a flat interconnecting plate. Each of these performs the same electronic operation, but the size difference is obvious.

Figures 5 & 6

Figure 6 shows in the left section a close-up of a multi-component wafer. Much of the basic development on the multi-component wafer approach was pioneered by the Diamond Ordnance Fuze Laboratory in Washington, D. C. This form of micro-miniaturization is particularly well suited to the repeatable, small logic block functions of digital computers.

In this case, the basic support and interconnecting plate is a thin ceramic wafer with metallic conducting lines. The resistors are deposited on the surface in thin films between the proper conducting lines. Capacitors may be integrated into the ceramic or surface mounted on the conducting lines as very small thin wafers. The semi-conductors are mounted into holes provided in the plate. Following electrical tests, the entire wafer may be encapsulated to provide protection against the atmosphere. The center unit indicates a further potentiality of a number of diodes or transistors being grown on a single silicon wafer for further size reduction. The unit on the right in Figure 6 is a presently available micro-miniaturized silicon diode manufactured by the Pacific Semi-Conductor Company, Inc. It has most of the necessary properties of conventional diodes in 1/20 the volume and is completely hermetically sealed for applications where the smallest, cased unit is desirable.

Figure 7 illustrates the steps in assembly of a micro-miniaturized logical computor block. On the right is the wafer representing a computer logical function such as a "flip-flop", multiple "and" gates, dual "pre-amp" or similar function. Groups of twelve of these wafers are mounted and interconnected on the larger plate in the center to form a functional section of the computer such as an "adder". Groups of the plates are then mounted together in a thin walled hermetically sealed plug in package to form an operating section of the computer as illustrated by the left unit in Figure 7. This may typically be an "arithmetic" unit, an "input", an "output" section or a aimilar aized section of the computer.

Figure 8 illustrates a concept of the integration of the various functional sections of the computer into a complete operating unit. The various blocks are plugged into and fastened to the case and the miniaturized welded matrix interconnecting plate.

Figures 7 & 8

This represents but one of the many approaches being studied to provide the best techniques for mounting, protecting and interconnecting micro-miniaturized components. The component as such is slowly losing its identity and is becoming an integral part of the larger (in number of components, but not in size) assemblies of a number of components performing a specific function.

Forming on the horizon is solid state circuits or the growing of the whole circuit on a single small solid state wafer and molecular film techniques where films millionths of an inch thick and equally narrow conductors are built up layer over layer to form whole sections or perhaps complete computers in fractions of cubic inches.

To you, the military engineers, this means that in spite of the increasing complexity of airborne electronics, research is producing methods of making them smaller, lighter, and more reliable.

*** ON ONE PAGE: FIGURE 7 and FIGURE 8 ***


The author wishes to acknowledge the contributions of W. Birnbaum, E. Harmon, E. Keonjian, J. Maguire, and H. Wolff of Arma Division, American Bosch Arma Corporation, to the developments discussed in this paper.