Modern electronic equipment is being used in a very large number of different areas that range from simple applications, such as automobile keys and temperature control devices, to very complex applications, such as airplanes, space exploration vehicles, and optical scanning medical devices. It is probably safe to say that virtually all electronic systems will be exposed to some form of vibration or shock during their lifetime.
The vibration and shock exposure may be due to the operating environment experienced by an airplane or an automobile. The vibration and shock exposure may also be due to shipping the product across the country by truck or train. Electronic systems that are required to operate in a harsh shock or vibration environment will often fail. If a failure occurs in an automobile temperature-sensing device or a fuel gage, it may be inconvenient for the owner, but the chances of someone being injured or killed are small. If the electronic failure happens to occur in the flight control system or navigation control system of an airplane or a missile, several hundred people could be injured or killed.
Many different types of materials, for example, metals, ceramics, plastics, glass, and adhesives, are being used today to fabricate and assemble a wide variety of electronic systems for commercial, industrial, and military applications. Many types of sophisticated electronic component parts are now available from a large number of manufacturers for specific applications and functions that did not exist only a decade ago. These components are often soldered to multilayer printed circuit boards (PCBs). PCBs may have from 6 to 12 internal layers of thin copper ground planes and voltage planes to remove heat and to provide electrical interconnections. The PCBs make it easy to assemble, remove, and maintain complex sophisticated electronic equipment at reduced costs. The PCBs must also protect the electronic components in storage, shipping, and operation in severe vibration, shock, thermal, and high-humidity environments. A wide variety of special plastics and metals are available to fabricate cost-effective and reliable electronic systems for special conditions.
The soldering process must be carefully controlled because solder is often the major source of early failures in the field. Good solder joints usually require the use of paste and flux to obtain a reliable connection. The paste and flux must be carefully removed from the PCB to prevent electrical malfunctions in sensitive systems after several months of operation