Although amounts spent by manufacturers on production testing are increasing rapidly, a rising percentage of faulty equipment is being delivered to customers. Every step in the manufacture of an electronic product, for example, produces defects of which a certain number inevitably remain undetected. There is a direct relationship between the percentage of undiscovered defects and the cost of the final product, since some defects must be accepted if costs are to be kept down. Such difficulties are likely to get worse rather than better with the introduction of more sophisticated techniques, such as integrated circuit technology, and with the increasing complexity of equipment which such techniques make possible.
Electronic equipment failure most often occurs in complicated radio-electronic equipment, such as computers and automatic control devices. The principle causes are imperfect soldering, poor contact in plug and socket connectors and internal defects in the elements.
A transistor protected by a fast-acting fuse will protect the fuse by blowing first (Klipstein's fifth law of production).