"Micro" as applied to
electronics is relative, depending on which decade you reference. In the 1940s,
a micro-size electronic assembly might have included "peanut" vacuum tubes and
even some sort of printed circuit board. That was a huge step down in size from
standard size tubes with point-to-point wiring between tube sockets and solder
lugs on switches, potentiometers, variable capacitors, etc. Fixed value leaded
resistors, capacitors, and inductors, and transformer wires connected to those
lugs as well as to many terminal strips installed specifically for making
connections. See Bob Davis'
Ward Airline 62-437 "Movie Dial" Radio for a look at what a rat's nest those
chassis were. Once transistors came on the scene in the 1950s, a new round of
miniaturization took place based on not just a significantly smaller size of
solid state transistors and diodes, but their lower voltage and current
requirements meant ancillary components could be made smaller as well due to
lower voltage and power handling requirements. By the 1960s, yet another version
of "micro" was defined by integrated circuits that combined functions into a
single package rather than requiring discrete components for each circuit. The
1970s saw a major infusion of microprocessors that replaced analog functions and
added capability. Mixed signal integrated circuits took off in the 1980s,
further reducing circuit board real estate for an equivalent number of features,
which greatly facilitated person computer success. Cell phones
and the Internet drove 1990s technology size reduction, then a host of new
wireless devices and interconnecting interfaces (WiFi, Bluetooth, ZigBee, GPS,
etc.) in the new century. To round out the decades of achievement, the 2010s
birthed the Internet of Things (IoT) and ultra wideband wired and wireless
connectivity via 4G and 5G.
Fig. 1. Evolution of a micro-module in actual size. The basic
wafers are at left. Next, from top to bottom are the following wafers: resistors,
resistors. coil, capacitor, transistor, and diode. The complete micro-module is
at the right.
By T. E. Gootée
Electronic equipment of the future will be Lighter in weight, smaller in size
thanks to this technique.
The electronic and radio-television industries today are at the threshold of
a new and revolutionary change in the design and manufacture of component parts
So great is this change that, ultimately, it will affect the size and weight
of all electronic, radio, television, and other communications equipment - with
possible reductions to one-tenth or more.
The objectives of this revolutionary change are reduced size and bulk and decreased
weight. These objectives are met through micro-miniaturization and the production
Conventional transistors and miniature parts being used in today's radio and
television sets and other electronic and communications equipment are not small
enough for the purpose. There is a need for a further decrease in size, bulk, and
weight-requirements that are responsible for the startling research and design advances
Although ultimately applicable to all kinds of electronic and communications
equipment, the present program of research and design was triggered directly by
the urgent need for compact, lightweight equipment for the Army Signal Corps. This
requirement runs the gamut from small portable radios to complex trunk switching
centrals, from television sets to electronic data processing equipment, and even
to satellite instrumentation. Here, in a military environment, was and is the urgent
need for extreme miniaturization.
After months of theorizing, exploratory tests, and experimental design, in cooperation
with American industry, the Army Signal Corps has now reached the stage where actual
development contracts have been placed - notably one with RCA for five million dollars.
An "industrial preparedness measure," this marks only the start toward refinement
and utilization of multi-function micro-modules.
The key to the future program of micro-miniaturization is the fabrication of
extremely small, solid-state devices, known as micro-modules.
Although micro-modules can be constructed in any physical shape of cover or envelope,
most common will be the standardized type shown at the right in Fig. 1. This is
a complete part composed of a number of sub--assemblies, each constructed in a common
The wafer may be of ferrite, barium titanate, or even metal, as required. Each
wafer measures 3/10 inch by 3/10 inch and is only 1/100 inch thick. Miniature elements
of a sub-assembly are selected and arranged to provide a specific circuit function.
For example, as shown (from top to bottom) in Fig. 1, these sub-assemblies could
be a number of resistors, a coil, capacitor, transistor, or diode. When these particular
sub-assemblies are stacked together, they form a complete micro-module - in this
case the tuning, detecting, or amplifying stage of a five-stage broadcast-band radio
Fig. 2. Two versions of the same homing equipment. Larger unit
uses present-day miniature production, while smaller device (above ruler) uses the
Fig. 3. Enlarged micro-module and multi-unit assembly of several
micro-modules - compared to size of small paper clip.
Fig. 4. Circuitry of earth satellite using conventional present-day
Fig. 5. Satellite circuitry using micro-modular construction.
Compare with Fig. 4.
Fig. 6. Same radio navigating gear made with present and micro-modular
After stacking, the sub-assemblies are encased in a mold or envelope of standard
size to form a solid body. Appropriate connectors are provided for plugging into
another micro-module or a socket of another part of the complete equipment. In final
form, a micro-module is three dimensional and approximately cubic in shape for most
effective space utilization.
A greatly enlarged view of a typical micro-module is shown in Fig. 3, with identification
of the signal circuit and power terminations. A number of different solid-state
micro-modules may be connected together, by means of connecting bars and supporting
braces, o achieve the desired circuitry. Note the size of the micro-module when
compared to a small paper clip, both of which have been enlarged the same number
of times in Fig. 3.
The mechanical structure of micro-modules makes them ideally suited for automatic
manufacturing - automation - with completely controlled production processes. This
will mean greater reliability at less cost than the conventional parts and components
Use of micro-modules will mean greatly simplified servicing and maintenance.
An entire module assembly, consisting of 30 to 40 electronic elements, can be replaced
easily without the necessity for testing the individual elements of a stage or unit
separately. If trouble develops, the entire module can be removed and replaced.
For a comparison of the functional and mechanical advantages of micro-modules,
see Fig. 2 which represents the electronic homing assembly of one kind of Army missile.
In the larger device, present-day miniature tubes, components, and transistors are
used with economy of space, with bulk and weight held to an absolute minimum. But
even this is no match for the assembly of micro-modules shown below it (and just
above the ruler), which represents a reduction of more than ten to one in size,
bulk, and weight. Through the use of the micro-module technique more than 50 separate
electronic parts and components of the larger homing assembly are replaced by a
single multi-unit micro-module.
High-thrust rockets and earth satellites also require elaborate electronic controls,
data recording, storage, and transmitting equipment. Since bulk and weight are luxuries
which cannot be indulged in rockets and satellites, the use of micro-modules is
of extreme significance.
Some of the present-day components of a typical earth satellite are shown in
Fig. 4. All parts are miniature, printed circuits abound, and every effort has been
made to conserve space and weight. Yet when the identical circuit equivalent is
in micro-modular form (Fig. 5) there is a reduction in weight and bulk to less than
one-tenth of the original. Since satellite instrumentation requires a number of
such electronic circuits - for surveillance, memory storage, telemetering, and other
functions - the immediate application of micro-miniaturization could not be more
appropriate than in this field of inter-space exploration and operation.
In another operational instance, large commercial airliners presently require
literally thousands of pounds of gear for communication, navigation, traffic control,
and other electronic functions. As a typical example of only one type of radio navigation
equipment for aircraft, there is the bulky apparatus shown in Fig. 6, and its electronic
equivalent using micro-modules. With this kind of reduction in weight and size,
considerable space can be released for profitable payloads - passengers or freight.
If military requirements can be met through the present ambitious program of
micro-miniaturization, later application to the commercial products of industry
will follow easily since, in general, operational requirements for military electronic
equipment are much more rigorous than for industry.
Army environment includes rough handling of equipment under extremes of temperature
and humidity plus the heavy shock imparted when used in projectiles, rockets, missiles,
and space satellites. Electronic equipment in . Army missiles and projectiles must
work through more than 10,000 g's and spins greater than 10,000 rpm. Equipment in
earth satellites must operate in an almost-perfect vacuum.
After the value of micro-modular construction has been proven in military applications,
commercial or industrial use will follow automatically. Such acceptance will progress
more rapidly after the manufacturing concepts of automation have been perfected.
To achieve present military goals of micro-miniaturization, the combined military-industry
program will take from four to five years at a minimum development cost of fifteen
In addition to savings in space and weight, whole new concepts of manufacture
and supply, repair and maintenance will develop with universal acceptance of micro-modular
construction. There will be a substantial increase in the dependability of electronic
equipment since automatic machine control of the micro-module production process
will eliminate human error and reduce the quality variations which crop up on even
the most efficient of present-day production lines. Automatic production will ultimately
lower the cost price of micro-modular assemblies far below that of present-day single-function
components used in electronic equipment.
Even though some electronic systems - such as automatic data gathering and processing
equipment - become increasingly more complex, with the continued development of
micro-modules, their repair and maintenance will become progressively simpler.
Micro-miniaturization - and its end product, the micro-module - is a revolutionary
concept of vast proportions and major consequences. As development progresses, more
and more electronic circuit designs will be approached from the standpoint of solid-state
physics of basic materials.
Micro-miniaturization indeed heralds a new era of electronics and communication.
Posted February 10, 2020