Backplane Testers
Backplane testers evaluate and record the integrity of backplanes and passive electronic components such as resistors, capacitors, and diodes. Backplanes are printed circuit boards (PCBs) that contain slots or sockets for expansion boards and other electronic devices. They distribute low-voltage power to each slot and enable high-speed communications. Typically, backplanes contain multiple card cages and are used in large-scale network switching and routing applications. Some backplane testers are continuity analyzers that measure opens and shorts over a large amount of test points. These devices are suitable for traditional PCBs, but do not provide the ability to clamp the compliance voltage or current. Other backplane testers use techniques commonly associated with the in-circuit testing of loaded boards. Manufacturing defect analyzers (MDAs), an alternative to in-circuit testers, are well-suited for the analog testing of backplanes with high pin counts.
Important specifications for backplane testers include test points, test resistance, maximum current and maximum voltage. Test points are the number of wires, tracings, or contact points that a device can test simultaneously. Test resistance is the electrical resistance of the circuit being tested. The maximum current is applied to each test point and the maximum voltage is applied to the entire circuit. In general, the maximum voltage determines whether the spacing between conductors is adequate. For backplanes that include both passive and active components, high voltage testing can cause significant damage. If the application of high voltage does not cause components to fail immediately, problems may appear only after the backplane is deployed in the field. Backplanes that fail due to spacing considerations may generate an arc, leaving a significant amount of debris between the conductors.
Backplane testers are available in a number of configurations and with a variety of features. Handheld devices can be held in one hand and operated with the other. Benchtop instruments are portable and often include handles. Floor-standing units are commonly available. Some backplane testers use computer-controlled switching architectures. Others allow the low voltage testing of backplanes that are interfaced to traditional radial interface cables. Network connections allow users to upload and download test programs on a personal computer (PC) without disrupting backplane testing. These test programs, which are often generated from computer aided design (CAD) software, can test electronic components such as resistors, capacitors, diodes, zener diodes, and light emitting diodes (LEDs). With the advent of switched fabric backplanes, software is available for testing complex designs with higher layer counts.