Automatic Detection Technology of Printed Circuit Board: Double probe or Flying Probe Test Method

Double probe or Flying Probe Test Method

The flying probe tester does not depend on the pin pattern installed on the fixture or bracket. Based on this system, two or more probes are mounted on a tiny magnetic head that can move freely on the x-y plane, and the test point is made by CADI.

Gerber data direct control. The dual probes can move within a distance of 4 mils from each other. The probes can move independently, and there is no real limit to how close they are to each other. The tester with two arms that can move back and forth is based on the measurement of capacitance. The PCB board is pressed tightly on the insulating layer on a metal plate as the other metal plate of the capacitor. If there is a short circuit between the lines, the capacitance will be larger than at a certain point. If there is an open circuit, the capacitance will become smaller.

Gerber data direct control. The dual probes can move within a distance of 4 mils from each other. The probes can move independently, and there is no real limit to how close they are to each other. The tester with two arms that can move back and forth is based on the measurement of capacitance. The circuit board is pressed tightly on the insulating layer on a metal plate as the other metal plate of the capacitor. If there is a short circuit between the lines, the capacitance will be larger than at a certain point. If there is an open circuit, the capacitance will become smaller.

Test speed is an important criterion for selecting a tester. The bed of needle tester can accurately test thousands of test points at a time, while the flying probe tester can only test two or four test points at a time. In addition, the needle bed tester may only cost 20-305 for single-sided testing, depending on the complexity of the board, while the flying probe tester requires Ih or more time to complete the same evaluation. Shipley (1991) explained that even if manufacturers of high-volume printed circuit boards consider the mobile flying probe test technique to be slow, this method is still a good choice for manufacturers of complex circuit boards with lower yields.

For bare board testing, there are special test instruments (Lea, 1990). A more cost-optimized method is to use a general-purpose instrument. Although this type of instrument is initially more expensive than a dedicated instrument, its initial high cost will be offset by the reduction in individual configuration costs. For general grids, the standard grid for boards with pin components and surface mount equipment is 2.5mm. At this time, the test pad should be greater than or equal to 1.3mm. For Imm grids, the test pad is designed to be larger than 0.7mm. If the grid is small, the test needle is small, brittle, and easily damaged. Therefore, it is best to choose a grid larger than 2.5mm. Crum (1994b) stated that the combination of a universal tester (standard grid tester) and a flying probe tester can make the inspection of high-density circuit boards both accurate and economical. Another method he suggested is to use a conductive rubber tester, which can be used to detect points that deviate from the grid. However, the height of the pads that are leveled by hot air is different, which will hinder the connection of the test points.

The following three levels of testing are usually carried out:
1) Bare board inspection
2) Online testing
3) Function detection

Using a universal type of tester, it can test a class of styles and types of circuit boards, and can also be used for special applications.