Monday, January 19, 2015

Microelectronics: Introduction, Evolution Of Microelectronics And vacuum-Tube Equipment.

MICROELECTRONICS

LEARNING OBJECTIVES

Learning objectives are stated at the beginning of each topic. These learning objectives serve as a preview of the information you are expected to learn in the topic. The comprehensive check questions are based on the objectives. By successfully completing the OCC-ECC, you indicate that you have met the objectives and have learned the information. The learning objectives are listed below.

Upon completion of this topic, you will be able to:

1. Outline the progress made in the history of microelectronics.

2. Describe the evolution of microelectronics from point-to-point wiring through high element density state-of-the-art microelectronics.

3. List the advantages and disadvantages of point-to-point wiring and high element density state-of- the-art microelectronics.

4. Identify printed circuit boards, diodes, transistors, and the various types of integrated circuits.

Describe the fabrication techniques of these components.

5. Define the terminology used in microelectronic technology including the following terms used by the Naval Systems Commands:

a. microelectronics

b. microcircuit

c. microcircuit module

d. miniature electronics

e. system packaging

f. levels of packaging (0 to IV)

g. modular assemblies

h. cordwood modules

i. micromodules

6. Describe typical packaging levels presently used for microelectronic systems.

7. Describe typical interconnections used in microelectronic systems.

8. Describe environmental considerations for microelectronics.

INTRODUCTION

In NEETS, Module 6, Introduction to Electronic Emission, Tubes, and Power Supplies, you learned that Thomas Edison's discovery of thermionic emission opened the door to electronic technology. Progress was slow in the beginning, but each year brought new and more amazing discoveries. The development of vacuum tubes soon led to the simple radio. Then came more complex systems of communications. Modern systems now allow us to communicate with other parts of the world via satellite. Data is now collected from space by probes without the presence of man because of microelectronic technology.

Sophisticated control systems allow us to operate equipment by remote control in hazardous situations, such as the handling of radioactive materials. We can remotely pilot aircraft from takeoff to landing. We can make course corrections to spacecraft millions of miles from Earth. Space flight, computers, and even video games would not be possible except for the advances made in microelectronics.

The most significant step in modern electronics was the development of the transistor by Bell Laboratories in 1948. This development was to solid-state electronics what the Edison Effect was to the vacuum tube. The solid-state diode and the transistor opened the door to microelectronics.

MICROELECTRONICS is defined as that area of technology associated with and applied to the realization of electronic systems made of extremely small electronic parts or elements. As discussed in topic 2 of NEETS, Module 7, Introduction to Solid-State Devices and Power Supplies, the term microelectronics is normally associated with integrated circuits (IC). Microelectronics is often thought to include only integrated circuits. However, many other types of circuits also fall into the microelectronics category. These will be discussed in greater detail under solid-state devices later in this topic.

During World War II, the need to reduce the size, weight, and power of military electronic systems became important because of the increased use of these systems. As systems became more complex, their size, weight, and power requirements rapidly increased. The increases finally reached a point that was unacceptable, especially in aircraft and for infantry personnel who carried equipment in combat. These unacceptable factors were the driving force in the development of smaller, lighter, and more efficient electronic circuit components. Such requirements continue to be important factors in the development of new systems, both for military and commercial markets. Military electronic systems, for example, continue to become more highly developed as their capability, reliability, and maintainability is increased. Progress in the development of military systems and steady advances in technology point to an ever- increasing need for increased technical knowledge of microelectronics in your Navy job.

Q1. What problems were evident about military electronic systems during World War II? Q2. What discovery opened the door to solid-state electronics?

Q3. What is microelectronics?

EVOLUTION OF MICROELECTRONICS

The earliest electronic circuits were fairly simple. They were composed of a few tubes, transformers, resistors, capacitors, and wiring. As more was learned by designers, they began to increase both the size and complexity of circuits. Component limitations were soon identified as this technology developed.

VACUUM-TUBE EQUIPMENT

Vacuum tubes were found to have several built-in problems. Although the tubes were lightweight, associated components and chassis were quite heavy. It was not uncommon for such chassis to weigh 40 to 50 pounds. In addition, the tubes generated a lot of heat, required a warm-up time from 1 to 2 minutes, and required hefty power supply voltages of 300 volts dc and more.

No two tubes of the same type were exactly alike in output characteristics. Therefore, designers were required to produce circuits that could work with any tube of a particular type. This meant that additional components were often required to tune the circuit to the output characteristics required for the tube used.

Figure 1-1 shows a typical vacuum-tube chassis. The actual size of the transformer is approximately 4 ´ 4 ´ 3 inches. Capacitors are approximately 1 ´ 3 inches. The components in the figure are very large when compared to modern microelectronics.

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Figure 1-1.—Typical vacuum tube circuit.

A circuit could be designed either as a complete system or as a functional part of a larger system. In complex systems, such as radar, many separate circuits were needed to accomplish the desired tasks. Multiple-function tubes, such as dual diodes, dual triodes, tetrodes, and others helped considerably to reduce the size of circuits. However, weight, heat, and power consumption continued to be problems that plagued designers.

Another major problem with vacuum-tube circuits was the method of wiring components referred to as POINT-TO-POINT WIRING. Figure 1-2 is an excellent example of point-to-point wiring. Not only did this wiring look like a rat's nest, but it often caused unwanted interactions between components. For example, it was not at all unusual to have inductive or capacitive effects between wires. Also, point-to- point wiring posed a safety hazard when troubleshooting was performed on energized circuits because of exposed wiring and test points. Point-to-point wiring was usually repaired with general purpose test equipment and common hand tools.

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Figure 1-2.—Point-to-point wiring.

Vacuum-tube circuits proved to be reliable under many conditions. Still, the drawbacks of large size, heavy weight, and significant power consumption made them undesirable in most situations. For example, computer systems using tubes were extremely large and difficult to maintain. ENIAC, a completely electronic computer built in 1945, contained 18,000 tubes. It often required a full day just to locate and replace faulty tubes.

In some applications, we are still limited to vacuum tubes. Cathode-ray tubes used in radar, television, and oscilloscopes do not, as yet, have solid-state counterparts.

One concept that eased the technician's job was that of MODULAR PACKAGING. Instead of building a system on one large chassis, it was built of MODULES or blocks. Each module performed a necessary function of the system. Modules could easily be removed and replaced during troubleshooting and repair. For instance, a faulty power supply could be exchanged with a good one to keep the system operational. The faulty unit could then be repaired while out of the system. This is an example of how the module concept improved the efficiency of electronic systems. Even with these advantages, vacuum tube modules still had faults. Tubes and point-to-point wiring were still used and excessive size, weight, and power consumption remained as problems to be overcome.

Vacuum tubes were the basis for electronic technology for many years and some are still with us. Still, emphasis in vacuum-tube technology is rapidly becoming a thing of the past. The emphasis of technology is in the field of microelectronics.

Q4. What discovery proved to be the foundation for the development of the vacuum tube? Q5. Name the components which greatly increase the weight of vacuum-tube circuitry. Q6. What are the disadvantages of point-to-point wiring?

Q7. What is a major advantage of modular construction?

Q8. When designing vacuum-tube circuits, what characteristics of tubes must be taken into consideration?