Transients' effect on the reliability of programmable electronics.

Introduction

It has been said that we are living in the age of microelectronics and computers. They are present in almost every electronic product and system and are also used heavily in products which are not normally classified as electronics. These items range from washing machines to automobiles. All these products and systems have one thing in common. Their electronics are mostly based on microelectronics hardware and their operations are programmed by software. In other words, they are programmable electronics. Programmable electronics' reliability depends not only on the reliability of the constituent hardware and software but also on the ambient physical environment.

Electronic hardware is inherently more reliable than most mechanical equipment due to the lack of wear and tear. From the advent of the transistor in the late 1940s to the latest million-transistor microprocessor chip, the reliability of microelectronics has improved steadily. The device failure rate model follows the Weibull distribution in its early life and is followed by a very long, useful life of constant failure rate. Typically the constant failure rate ranges from a few ppb to a few hundred ppb[1]. Thus, electronic hardware is rarely responsible for failures, even for very complex computer systems[2].

As the processing power of microprocessors (measured in million instructions per second or MIPS) increases, software complexity also increases to harness their power for better performance and to produce more functions. While the control program for a washing machine may be just a few thousand lines of instruction, it is not unusual nowadays to find software with a million lines of instruction, even in personal computers. Software of such complexity also controls the modern telephone exchanges, aeroplanes and non-stop computers for banking and finance. The proliferation of programmable electronics gives rise to concern over the risks of software. To contain the risks of software, structured programming, software quality assurance and fault-tolerance techniques are increasingly being used[1,3]. In a survey of well-debugged programs, MTTF ranging from 1.6 years to 5,000 years was reported[4].

It is well known that temperature and humidity affect the reliability of electronics. The methods to reduce their detrimental effects are also well known. One aspect of the physical environment, however, is not widely known, although it is gaining recognition as one of the most serious elements that affects electronics in general and programmable electronics in particular. This is the susceptibility of electronics to electromagnetic interference (EMI), which is also known as radio frequency interference (RFI). In short, EMI affects programmable electronics' reliability through interaction with the hardware and software.

Transient is one particular form of EMI that is a major cause of failures for programmable electronics. It is represented as a short burst of electromagnetic energy that enters into a victim equipment via conduction on cables and other forms of conductor or via electromagnetic radiation. Strong transients can cause permanent physical damage while weak transients cause only transient faults that involve no physical damage. Nevertheless, transient faults can still cause havoc to programmable electronics' operations. Since there is …