The flying needle tester does not depend on the pin pattern mounted on the fixture or bracket.Based on this system, two or more probes are mounted on tiny, free-moving heads in the x-y plane, and the test points are directly controlled by CADI Gerber data.The dual probes can move within 4 mil of each other.The probes can move automaticaly, and there is no real limit to how close they can get to each other.The tester with two movable arms is based on capacitance measurements.The circuit board is placed tightly on an insulating layer on a metal plate that ACTS as another metal plate for the capacitor.If there is a short circuit between the lines, the capacitance will be larger than at a certain point.If there is a break, the capacitance will be smaller.
Test speed is an important criterion for choosing a tester.While the needle bed tester can accurately test thousands of test points at a time, the flying needle tester can only test two or four test points at a time.In addition, a single test with a needle bed tester may cost only 20-305, depending on the complexity of the board, whereas a flying needle tester requires Ih or more to complete the same evaluation. Shipley (1991) explained that this method is a good choice for manufacturers of complex circuit boards with lower yields, even if manufacturers of high-volume printed circuit boards consider the moving flying pin test technique to be slow.
For bare plate testing, there are dedicated test instruments (Lea,1990).A more cost-effective approach would be to use a universal instrument, although initially more expensive than a dedicated instrument, its initial high cost would be offset by a reduction in the cost of individual configurations.For general purpose grids, the standard grid for boards and surface mount equipment with pin elements is 2.5 mm.At this point the test pad should be greater than or equal to 1.3mm.
For the Imm grid, the test pad is designed to be greater than 0.7mm.If the grid is small, the test pin is small, brittle, and prone to damage.Therefore, it is best to use grids larger than 2.5mm.Crum (1994b) stated that the combination of universal tester (standard grid tester) and flying needle tester can make the detection of high density circuit board accurate and economical.Another approach he suggests is to use a conductive rubber tester, which can be used to detect points that deviate from the grid.However, different heights of pads treated with hot air leveling will hinder the connection of test points.
The following three levels of detection are usually carried out:
1) naked plate detection;
2) online detection;
3) functional detection.
The general type tester can be used to detect a kind of style and type of circuit board as well as for special applications.
Common metal coatings are:
Copper
Tin
The thickness is usually between 5 and 15 cm
Lead-tin alloy (or tin-copper alloy)
That is, solder, usually 5 to 25 m thick, with a tin content of about 63%
gold： Generally will only be plated on the interface
silver：Generally will only be plated on the interface, or the whole is also an alloy of silver