Double Probe or Flying Probe Test Method
The flying probe tester does not rely on the pin pattern installed on the fixture or bracket. In this system, two or more probes are mounted on a small magnetic head that can freely move on the x-y plane, and the test point is generated by CADI Gerber data direct control. The dual probes can move within a 4 mil distance from each other independently, without any real limit to their proximity. The tester with two arms that can move back and forth is based on capacitance measurement. The PCB board is securely pressed on an insulating layer on a metal plate, acting as the other metal plate of a capacitor. If there is a short circuit between the lines, the capacitance will be greater at a certain point, while it will decrease if there is an open circuit.
Test speed is a vital factor in tester selection. The bed of needle tester can efficiently test thousands of test points simultaneously, whereas the flying probe tester can only handle two or four test points at a time. Moreover, the needle bed tester may cost only 20-30% for single-sided testing, depending on the board’s complexity, while the flying probe tester requires much more time to complete the same evaluation. Even though high-volume PCB manufacturers may perceive the mobile flying probe test technique as slow, it remains a suitable choice for manufacturers dealing with complex circuit boards with lower yields, as Shipley (1991) explained.
For bare board testing, specific test instruments are available (Lea, 1990). A cost-effective approach is using a general-purpose instrument, which, though more expensive initially than a dedicated instrument, can offset the high initial cost through reduced individual configuration costs. For standard grids, the standard grid for boards with pin components and surface mount equipment is typically 2.5mm, with the test pad preferably being ≥1.3mm. For Imm grids, the test pad is designed larger than 0.7mm, as a smaller grid leads to smaller, more brittle test needles that are prone to damage. Therefore, selecting a grid larger than 2.5mm is advisable. Crum (1994b) proposed that combining a universal tester (standard grid tester) with a flying probe tester ensures accurate and economical inspection of high-density circuit boards. Another suggested method is employing a conductive rubber tester to detect any deviations from the grid, although varying pad heights leveled by hot air may impede test point connections.
The typical testing levels include: 1) Bare board inspection 2) Online testing 3) Function detection. Utilizing a universal tester allows testing of various styles and types of circuit boards, and it can cater to special applications as well.
The flying probe tester does not rely on the pin pattern installed on the fixture or bracket. In this system, two or more probes are mounted on a small magnetic head that can freely move on the x-y plane, and the test point is generated by CADI Gerber data direct control. The dual probes can move within a 4 mil distance from each other independently, without any real limit to their proximity. The tester with two arms that can move back and forth is based on capacitance measurement. The PCB board is securely pressed on an insulating layer on a metal plate, acting as the other metal plate of a capacitor. If there is a short circuit between the lines, the capacitance will be greater at a certain point, while it will decrease if there is an open circuit.
Test speed is a vital factor in tester selection. The bed of needle tester can efficiently test thousands of test points simultaneously, whereas the flying probe tester can only handle two or four test points at a time. Moreover, the needle bed tester may cost only 20-30% for single-sided testing, depending on the board’s complexity, while the flying probe tester requires much more time to complete the same evaluation. Even though high-volume PCB manufacturers may perceive the mobile flying probe test technique as slow, it remains a suitable choice for manufacturers dealing with complex circuit boards with lower yields, as Shipley (1991) explained.
For bare board testing, specific test instruments are available (Lea, 1990). A cost-effective approach is using a general-purpose instrument, which, though more expensive initially than a dedicated instrument, can offset the high initial cost through reduced individual configuration costs. For standard grids, the standard grid for boards with pin components and surface mount equipment is typically 2.5mm, with the test pad preferably being ≥1.3mm. For Imm grids, the test pad is designed larger than 0.7mm, as a smaller grid leads to smaller, more brittle test needles that are prone to damage. Therefore, selecting a grid larger than 2.5mm is advisable. Crum (1994b) proposed that combining a universal tester (standard grid tester) with a flying probe tester ensures accurate and economical inspection of high-density circuit boards. Another suggested method is employing a conductive rubber tester to detect any deviations from the grid, although varying pad heights leveled by hot air may impede test point connections.
The typical testing levels include: 1) Bare board inspection 2) Online testing 3) Function detection. Utilizing a universal tester allows testing of various styles and types of circuit boards, and it can cater to special applications as well.
