"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 for equipment.
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 of micro-modules.
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 in micro-miniaturization.
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 wafer shape.
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
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
Fig. 2. Two versions of the same homing equipment. Larger
unit uses present-day miniature production, while smaller device (above ruler)
uses the micro-modules.
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
Fig. 5. Satellite circuitry using micro-modular construction.
Compare with Fig. 4.
Fig. 6. Same radio navigating gear made with present and
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 of today.
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
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
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 million dollars.
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
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
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