1. Field of the Invention
This invention relates to testing an electrical net of an electrical or electronic circuit and, more particularly, to a method of and apparatus for quickly detecting fault conditions in individual wiring nets in a multi-layer device carrier, for example. It also relates to a unique method and means for counting the number of pulses received from any source in a fixed period of time and to an interface which permits coupling to any general purpose computer for software manipulation of the collected test data.
2. Description of the Prior Art
In the electrical arts, the testing of electrical "nets" of an electrical or electronic circuit for fault conditions is universally recognized to be of high importance. Among other things, circuit manufacturers and purchasers want to test nets for "opens," "shorts," and other faulty characteristics, such as circuits having incorrect resistance, inductance, and capacitance characteristics ("RLC" characteristics). The term "net" is known in the art and generally refers to the electrical characteristics of a circuit as they appear from a given circuit node. These electrical characteristics are measured with reference to a predetermined reference point, e.g., ground. A circuit typically includes several nets of interest.
The prior art includes methods that subject the net under test to a sinusoidal input stimulus and then measure both the magnitude and phase of the net's response to the input stimulus. The magnitude and phase may then be analyzed to detect faults in the net. In addition, the prior art includes methods that directly measure the various RLC characteristics of a net to be tested.
Though the prior art methods are generally perceived as capable of detecting many types of faults, they have undesirable shortcomings. Among other things, certain nets, particularly those having large capacitances, require unduly long testing times. This is so, because the prior art methods must use a low frequency stimulus to ensure accurate measurement of a high capacitance. The low frequency results in longer testing times, and the longer testing times, in turn, increase the testing cost. This becomes particularly acute when high volume testing is required.
In addition, many prior art methods require a priori knowledge of the net configuration being tested, including knowledge of the arrangement of various components and their RLC characteristics. This complicates the testing, increases the cost, and in certain instances is entirely impracticable.
Further, many prior art methods are particularly configured to test nets having a relatively limited range of possible RLC characteristics. Consequently, manufacturers and purchasers are required to buy additional testing equipment, if they desire to test nets outside the limited range of their existing testers.
In addition, test equipment is typically designed for control by and operation with a specific computer for acquisition and evaluation of test data.
Accordingly, there is a need in the art for an improved method and apparatus for testing nets quickly.
It is an object of the invention to provide a method and apparatus to detect faults in a net quickly.
It is a further object of the invention to provide a method and apparatus to detect faults in a net without requiring a priori knowledge of the net to be tested.
It is yet a further object of the invention to provide a method and apparatus that can test a variety of nets having a wide range of RLC characteristics.
It is a further object of the invention to provide a method and apparatus which can utilize any general purpose computer and its software for controlling the testing and fault detecting procedures thereof.