Automatic detection circuit board

With the introduction of surface mount technology, the circuit board packaging densities increase rapidly. Therefore, even if the density is not high, the general number of circuit boards, circuit board auto-detection is not only essential, but also economical. In a complex circuit board test, the two common methods is to test and double needle bed or flying probe testing method.

A bed of nails test method

This approach by the spring-loaded probe connected to a circuit board test points each. Spring so that each probe has 100 - 200g of pressure to ensure good contact of each test point, with this probe arrangement is known as "bed of nails." Under the control of the detection software can detect the signal of the detection point and the program, there is a typical bed of nails tester structure, testing all the test points can learn the information. Only those who actually need to test the test point of the probe is installed. Although the use of the needle bed in the test method may also be detected on both sides of the circuit board when designing the circuit board, or should all test points in the circuit board solder surface. Needle bed tester equipment is expensive and difficult to repair. Needles selected based on their specific application different arrangement of the probes. A basic general-purpose processor grid board constituted by a borehole, the distance between the center pin on the 100, 75 or 50mil. Play the role of the probe pin, and the use of the circuit board electrical connectors or direct mechanical connection node. If the circuit board pads to match with the test grid, then in accordance with standard perforated polyester film will be placed on the grid and the circuit board so that the design-specific probe. Continuity test is accessed through the end of the grid point (has been defined as the xy pad) to achieve. Since the board of each network are for continuity testing. In this way, an independent testing is complete. However, the proximity of the probe test method limits the effectiveness of needle bed. Two pairs of probes or flying probe test method

Flying Probe Tester does not depend on the fixture or bracket mounted on the pins on the designs. Based on this system, two or more probes installed in the xy-plane can be moved freely on the tiny head, and test point data from the direct control of CAD and Gerber. Double probe in the range of each other move away from 4mil. Probe can move independently, and there is no real limit the extent of their close to each other. With two arms can be moved back and forth tilting of the tester is based on capacitance measurement. Pressed the board on a metal plate with the insulating layer, another metal plate as a capacitor. If there is a short circuit between the line capacitance than a certain point in the large. If there is - of the circuit, the capacitor will be smaller. Test speed is an important selection criteria tester. A bed of nails tester can accurately test thousands of test points, and a flying probe testers can test only two or four test points. In addition, the needle bed tester for single test may only take 20--305, depending on the complexity of the board, and flying probe testers require Ih or more time to complete the same assessment. Shipley (1991) explained that even high-volume printed circuit board manufacturer that slow moving flying probe test technology, but this method is low yield for the complex circuit board manufacturers, but still a good choice.

For bare board testing, there are special test equipment (Lea, 1990). A cost-optimization approach is to use more a generic instrument, although such instruments initially more expensive than a dedicated instrument, but it is the high cost of initial deployment costs will be reduced to offset the individual. For general grid, with pin board and surface mount components of the standard equipment grid is 2.5mm. At this point the test pads should be greater than or equal to 1.3mm. For 1mm grid, designed to test the pad is greater than 0.7mm. If the grid is small, the test needle is small and brittle and easily damaged. Therefore, the best selection of more than 2.5mm of the grid. Crum (1994b) stated that the universal tester (standard grid tester) and flying probe tester in combination, can detect high-density circuit board that is accurate and economical. He suggested that another method is to use conductive rubber tester, this technique can be used to detect deviation from the grid point. However, the use of hot air leveling process of the pad height, could affect the test point connections.

Usually the following three levels of testing:

1) bare board testing;

2) On-line detection;

3) function tests.

Adopt a common type of tester, can a class style and type of circuit board testing can also be used for the detection of special applications.