Circuit board name: ceramic circuit board, alumina ceramic circuit board, aluminum nitride ceramic circuit board, circuit board, PCB board, aluminum substrate, high frequency board, thick copper board, impedance board, PCB, ultra-thin circuit board, ultra-thin circuit board, printing (copper etching technology) circuit board. The circuit board makes the circuit mini and intuitive, which plays an important role in the mass production of fixed circuit and the optimization of the layout of electrical appliances.
Circuit boards are divided into three major categories according to the number of layers: single panel, double panel, and multi-layer circuit boards.
The first is a single panel. On a basic PCB, parts are concentrated on one side and wires on the other. Because the wire only appears on one side, the PCB is called a single-sided circuit board. Single panels are usually simple to make and cheap to build, but the disadvantage is that they cannot be used in too complex products.
Double panel is the extension of single panel, when single layer wiring can not meet the needs of electronic products, the use of double panel. Both sides are clad and wired, and the wiring between the two layers can be conducted through holes to form the required network connection.
A multilayer board is a printed board having three or more layers of conductive graphics laminated with insulating materials between them and interconnecting conductive graphics as required. Multilayer circuit board is the product of electronic information technology developing towards high speed, multifunction, large capacity, small volume, thin type and light weight.
The circuit board is divided into soft board (FPC), hard board (PCB) and hard board (FPCB) according to the characteristics.
Fr-1: flame retardant copper-clad phenolic paper laminate. IPC4101 detailed specification no. 02; Tg N/A;
Fr-4:1) flame-retardant copper-clad epoxy glass fiber cloth laminate and its adhesive sheet material. IPC4101 detailed specification no. 21; Tg 100 ℃ or higher;
2) flame-retardant copper-foil modified or unmodified epoxy E fiberglass cloth laminate and its adhesive sheet material. IPC4101 detailed specification no. 24; Tg 150 ℃ ~ 200 ℃;
3) flame-retardant copper-clad epoxy /PPO glass cloth laminate and its binder. IPC4101 detailed specification no. 25; Tg 150 ℃ ~ 200 ℃;
4) flame retardant copper-foil modified or unmodified epoxy glass cloth laminate and its adhesive sheet material. IPC4101 detailed specification no. 26; Tg 170 ℃ ~ 220 ℃;
5) flame retardant copper clad epoxy E glass cloth laminate (used for catalytic addition). IPC4101 detailed specification no. 82; Tg N/A;
Detection of repair
one A chip with a program
1. Generally, EPROM chip should not be damaged. Because the chip requires ultraviolet light to erase the program, it did not damage the program during the test. But material introduction: because the material that makes chip is caused, with the passage of time (year grows), even if do not need, also may break (basically point to program). So back up as much as possible.
2.EEPROM,SPROM, etc., as well as RAM chip with battery, can easily break programs. Whether such chips break the program after using < tester > to scan the VI curve remains to be determined. Still, colleagues should be wary of such situations. The author has done a number of tests, may be a major reason: maintenance tools (such as tester, electric soldering, etc.) caused by leakage of electricity in the shell.
3. For the chip with battery on the circuit board, do not take it off the board easily.
two Reset circuit
1. When there is lsi on the circuit board to be repaired, please pay attention to the reset problem.
2. Before the test, it is better to put it back on the equipment and turn it on and off repeatedly. And press reset several times.
3. Function and parameter testing
1. The test of < tester > on the device can only reflect the cut-off region, amplifier region and saturation region. But can not measure the frequency of the high and low and the speed of the speed and other specific values.
2. Similarly, for TTL digital chip, only the output changes with high and low levels can be known. And there’s no way to find out how fast it’s going up and down.
Four. Crystal oscillator
1. Generally, only oscilloscope (the crystal oscillator needs to be electrified) or frequency meter can be used for testing, otherwise, substitution method can be used.
2. Common faults of crystal oscillator include: a. internal leakage, b. internal open circuit c. Metamorphic frequency deviation d. Here leakage phenomenon, using < tester > VI curve should be able to measure.
3. During the whole plate test, two judgment methods can be adopted: a. during the test, the relevant chip around the crystal oscillator fails to pass. B. No other fault point was found except crystal oscillator.
4. There are two common crystal oscillators: a. bipod. B. Four legs, the second leg is the power supply, pay attention to do not random short circuit.
Five. Distribution of fault phenomena
1. Incomplete statistics of circuit board fault parts: 1) 30% chip damage, 2) 30% discrete components damage,
3) the wiring (copper coated PCB board) is broken by 30%; 4) the program is broken or lost by 10% (with an upward trend).
2. It can be seen from the above that, when the circuit board to be repaired has problems with wiring and procedures, there is no good board, neither familiar with its wiring, can not find the original program. The possibility of repairing this board is not very big.
Compatible with the design
Electromagnetic compatibility (emc) refers to the ability of electronic equipment to coordinate and work effectively in various electromagnetic environments. The aim is to make the electronic equipment can not only suppress all kinds of external interference, so that the electronic equipment can work normally in the specific electromagnetic environment, but also to reduce the electronic equipment itself to other electronic equipment electromagnetic interference.
1, choose a reasonable wire width because the transient current on the PCB printed line produced by the impact of interference is mainly caused by the printed wire inductance component, so it should try to reduce the printed wire inductance.
2, USES the correct wiring strategy USES the equal linear conductor inductance can be reduced, but the mutual inductance between conductor and distributed capacitance increases, the layout of permitting, had better use well glyph structure network cabling, specific side lateral approach is printed circuit board wiring, the other side vertical wiring, then at the cross hole is connected with metallized hole.
3. In order to suppress the crosstalk between the leads of PCB circuit board, it is necessary to avoid the long distance equal wiring when designing and wiring, to pull the distance between the wires as far as possible, and not to cross the signal line with the ground line and the power line as far as possible. In some signal lines which are very sensitive to interference, a ground printed line can be set up to suppress crosstalk effectively.
Circuit board is mainly composed of solder pad, throughhole, mounting hole, conductor, components, connector, filling, electrical boundary, etc. The main functions of each component are as follows:
Welding pad: used for welding metal hole of component pin.
Through hole: metal through hole and non-metal through hole, in which metal through hole is used for connecting components and pins between layers.
Mounting hole: used for fixing circuit board.
Lead: copper film of electrical network used for connecting pins of components.
Connectors: components used for connecting circuit boards.
Filling: used for copper coating of ground wire network, which can effectively reduce impedance.
Electrical boundary: used to determine the size of the circuit board, all components on the circuit board must not exceed the boundary.
The main classification
Circuit board systems are classified into the following three categories:
Single – Sided Boards
We just mentioned that, so we call this PCB single-sided. Because single panels have many strict restrictions on the design of circuits (because there is only one side, the wiring can not cross * but must go around a separate path), only early circuits used such boards.
Double – Sided Boards
The circuit board has wiring on both sides. But to use the two sides of the wire, there must be a proper electrical connection between the two sides. The “bridge” between these circuits is called a guide hole (via). A guide hole is a small, metal-filled hole in a PCB that can be connected to a wire on both sides. Because the double panel is twice as large as the single panel, and because the wiring can be interlaced (it can go around the other side), it is better suited for more complex circuits than the single panel.
[multilayer board] in more complex application requirements, the circuit can be arranged into a multi-layer structure and pressed together, and the through hole circuit is laid between the layers to connect the circuit of each layer.
The inner line
Copper foil substrate first cut into suitable for processing the size of production. Before the substrate pressure film usually need to use brush grinding, micro-corrosion and other methods will be the surface of copper foil do appropriate coasting treatment, and then with appropriate temperature and pressure will dry film photoresist close paste on its. The substrate coated with dry film photoresist is exposed in the uv exposure machine. The photoresist will polymerize when exposed to ultraviolet light in the transparent area of the plate (the dry film in this area will be retained as the etching resist in the later development and copper etching steps), and the line image on the plate is transferred to the dry film photoresist. After tearing off the protective film on the film surface, firstly remove the unilluminated area on the film surface with sodium carbonate solution, and then remove the exposed copper foil corrosion with hydrochloric acid and hydrogen peroxide mixture solution to form a circuit. Finally, the photoresist was removed by sodium hydroxide solution. For the inner circuit board with more than six layers (including), the automatic positioning punch is used to rush out of the riveting datum hole of line alignment between layers. Multi – Layer Boards
In order to increase the area that can be wired, multilayer board used more single or double-sided wiring board. Multilayer boards use several double panels and are glued (pressed) by placing an insulating layer between each layer.
The number of layers on the board represents the number of independent wiring layers, usually even, and contains the outermost two layers. Most motherboards have 4 to 8 layers, but it is technically possible to have nearly 100 layers of PCB. Most large supercomputers use fairly multi-layered mainframe boards, but because such computers can be replaced by clusters of many ordinary computers, the use of super-multilayered boards has become obsolete. Because the layers in the PCB are tightly integrated, it’s not always easy to see the actual number, but if you look closely at the motherboard, you might.
With the introduction of surface mount technology, the automatic detection technology of PCB has been applied, and the packaging density of PCB has increased rapidly. Thus, even for a low density, average number of boards, automatic detection of boards is not only basic, but also economical. In the complex circuit board test, two common methods are needle – bed test and double – probe or fly – needle test.
According to the characteristics of the board material and the wide application of the field, in order to save more effective volume and achieve a certain degree of accuracy, make the characteristics of three-dimensional space and thin thickness better applied to digital products, mobile phones and laptops. Recommended instruments suitable for board of circuit (FPC) testing include MUMA200 all-aluminum alloy optical image measuring instrument, three-axis automatic optical image measuring instrument VMC250S, VMC four-axis automatic optical image measuring instrument, VMS series optical image measuring instrument and so on.
The test method
The needle bed process
This method consists of a spring probe connected to each inspection point on the circuit board. The spring gives each probe a pressure of 100-200g to ensure good contact at each inspection point. Such a combination of probes is called a “needle bed”. Under the control of the detection software, the detection points and detection signals can be programmed. Figure 14-3 is a typical needle-bed tester structure, and the tester can learn the information of all test points. Only the probes for the test points that need to be tested are actually installed. Although it is possible to test both sides of the board using the needle bed test method, when designing the board, all test points should be on the welded side of the board. Needle bed tester equipment is expensive and difficult to maintain. Different arrays of probes were selected based on the specific application of the needle.
A basic general purpose grid processor consists of a board drilled with pins spaced 100, 75, or 50mil from center to center. The pin ACTS as a probe and USES electrical connectors or nodes on the circuit board for direct mechanical connections. If the pad on the circuit board matches the test grid, the film of polyvinyl acetate punched according to the specification is placed between the grid and the circuit board to facilitate the design of specific probes. Continuity detection is achieved by accessing the end points of the grid (defined as the x-y coordinates of the pad). Since every network on the circuit board is continuity tested. In this way, an independent test is completed. However, the proximity of the probe limits the effectiveness of the needle-bed test.
The circuit board is small in size and complex in structure, so it is necessary to use professional observation instruments to observe the circuit board. Generally, we use a portable video microscope to observe the structure of the circuit board. Through the microscopic camera of video, the microscopic structure of the circuit board can be clearly seen from the microscope. Through this way, we are easier to carry out the circuit board design and test. The portable video microscope, the portable video microscope MSA200, VT101, because it can achieve “at any time observation, at any time detection, many people discuss” more convenient than the traditional microscope!
Flying probe test
The flying pin 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 on the x-y plane, and the test points are directly controlled by CADI Gerber data. The dual 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. The 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 on a metal plate to act as another metal plate for the capacitor. If there is a short circuit between the lines, the capacitance will be greater 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. 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, the needlebed tester may only cost 20-305 for a single surface test, depending on the complexity of the board, while the flying needle tester may require Ih or more time to complete the same evaluation. Shipley