Circuit board is small in size and complex in structure, so the observation of circuit board must use professional observation instruments. Generally, portable video microscopes are used to observe the structure of the circuit board. Through video microcameras, the microscopic structure of the circuit board can be clearly seen from the microscope. In this way, it is easier for us to design and test the circuit board. The portable video microscope is used in the factory site, the portable video microscope MSA200, VT101, because it can realize "observation at any time, at any time to detect, many people discuss" more convenient than the traditional microscope!
Flying needle test
The flying needle tester does not rely on a pin pattern mounted on the fixture or bracket. Based on this system, two or more probes are mounted on tiny freely moving magnetic heads in the x-y plane, and the test points are directly controlled by CADI Gerber data. The two probes can move within 4mil of each other. The probes can move independently, and there is no real limit to how close they are to each other. A tester with two arms that move back and forth is based on the measurement of capacitance. The circuit board is pressed against an insulating layer placed on a sheet of metal to act as another sheet of metal 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 standard for choosing a tester. The needle-bed tester can accurately test thousands of test points at a time, while the flying needle tester can only test two or four test points at a time. In addition, a single-side test with a needle-bed tester may only cost 20-305, depending on the complexity of the board, while a fly needle tester may require Ih or more to complete the same evaluation. Shipley (1991) explained that even though manufacturers of high volume printed circuit boards find moving fly pin testing techniques slow, this method is a good choice for manufacturers of complex circuit boards in lower volumes.
For bare board testing, there are special testing instruments (Lea,1990). A more cost-effective approach would be to use a generic instrument, which, although initially more expensive than a dedicated instrument, would be offset by a reduction in the cost of individual configurations. For general purpose grids, the standard grids for boards and surface mount devices with pin components are 2.5mm. At this time the test pad should be greater than or equal to 1.3mm. For Imm grids, test pads are 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) states that the combination of a universal tester (a standard grid tester) and a flying needle tester can make the detection of high-density circuit boards both accurate and economical. Another method he suggests is to use a conductive rubber tester, a technique that can be used to detect points that deviate from the grid. However, the different height of the pad with hot air leveling will hinder the connection of the test point.
The following three levels of detection are usually performed:
1) Bare plate detection;
2) Online detection;
3) Function detection.
The universal tester can be used to detect a type of circuit board, and it can also be used to detect special applications.
Circuit board repair is a new repair industry. The degree of automation of industrial equipment is getting higher and higher, so the number of industrial control board in various industries is also increasing. After the industrial control board is damaged, the high cost required to replace the circuit board (at least thousands of yuan, more than tens of thousands or hundreds of thousands of yuan) has become a very headache for the enterprises. In fact, the vast majority of these damaged circuit boards can be repaired in China, and the cost is only 20%-30% of the purchase of a new board, the time used is much shorter than the foreign fixed board. The following introduces the basic knowledge of circuit board maintenance.
Almost all circuit board maintenance without drawing materials, so many people are skeptical about circuit board maintenance, although various circuit boards vary, but the same is that each circuit board is composed of a variety of integrated blocks, resistors, capacitors and other devices, so the circuit board damage must be caused by one or some of the device damage, The idea of circuit board maintenance is established based on the above factors. Circuit board maintenance is divided into two parts: inspection and maintenance, among which inspection occupies a very important position. The basic knowledge of each device on the circuit board is repaired and tested until the bad parts are found and replaced, so a circuit board is repaired.
Circuit board detection is the process of finding, determining and correcting the fault of each electronic component on the circuit board. In fact, the whole detection process is the thinking process and the testing process of providing logical reasoning clues, so the detection engineer must gradually accumulate experience in the maintenance, testing and overhaul of the circuit board, and constantly improve the level. General electronic equipment is composed of tens of thousands of components, in the maintenance, overhaul, if by direct test and check each component in the circuit board to find the problem will be very time-consuming, implementation is also very difficult. So from the fault phenomenon to the fault cause of the type of check, is an important maintenance method. As long as the circuit board has detected the problem, then maintenance is easy. The above is the basic knowledge of circuit board maintenance.