The name of the circuit board has: ceramic circuit board, alumina ceramic circuit board, aluminum nitride ceramic circuit board, circuit board, PCB board, aluminum substrate board, high frequency board, thick copper board, impedance board, PCB, ultra-thin circuit board, ultra-thin circuit board, printed (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 circuits and the optimization of the layout of electrical appliances. FPC PCB (Flexible Printed Circuit Board) FPC Circuit Board (Flexible Printed Circuit Board) FPC Circuit Board (Flexible Printed Circuit Board) FPC Circuit Board (Flexible Printed Circuit Board) FPC Circuit Board (Flexible Printed Circuit Board) FPC Circuit Board (Flexible Printed Circuit Board) FPC Circuit Board (Flexible Printed Circuit Board) is a highly reliable and excellent Flexible Printed Circuit Board made of polyimide or polyester film as the base material. It has the characteristics of high wiring density, light weight, thin thickness and good bendability. And reechas, Soft and hard combination plate — the birth and development of FPC and PCB gave birth to a new product of Soft and hard combination plate. Therefore, the combination of soft and hard board, is flexible circuit board and hard circuit board, after pressing and other processes, according to the relevant technological requirements combined together, formed with FPC characteristics and PCB characteristics of the circuit board.
Circuit board according to the number of layers divided into single panel, double panel, and multilayer circuit board three large categories.
The first is a single panel. In the most basic PCB, the parts are concentrated on one side and the wires on the other. Since only one side of the wire appears, the PCB is called a single-sided circuit board. A single panel is usually simple to make and low cost, but the disadvantage is that it cannot be applied to too complex products.
Double panels are an extension of a single panel, which is used when single-layer wiring does not meet the needs of electronic products. Both sides are covered with copper wire, and through the hole to conduct the line between the two layers, so as to form the required network connection.
A multilayer board is a printed board that has a conductive pattern layer of more than three layers and an insulating material between which the conductive pattern is interlinked according to the requirements. Multilayer circuit board is the product of electronic information technology developing to high speed, multifunction, large capacity, small volume, thin shape and light weight.
Circuit board according to the characteristics of the word divided into soft board (FPC), hard board (PCB), hard board (FPCB).
FR-1: flame retardant copper foil phenolic paper laminate. IPC4101 detailed specification no. 02; Tg N/A;
FR- 4:1) flame retardant copper-clad epoxy E fiberglass cloth laminate and its bonding sheet materials. IPC4101 detailed specification no. 21; Tg 100 ℃ or higher;
2) flame retardant copper foil modified or unmodified epoxy E fiberglass cloth laminate and its bonding sheet materials. IPC4101 detailed specification no. 24; Tg 150 ℃ ~ 200 ℃;
3) flame-retardant copper-clad epoxy /PPO glass cloth laminate and its bonding sheet materials. IPC4101 detailed specification no. 25; Tg 150 ℃ ~ 200 ℃;
4) flame-retardant copper-foil modified or unmodified epoxy glass cloth laminates and their bonding materials. IPC4101 detailed specification no. 26; Tg 170 ℃ ~ 220 ℃;
5) flame retardant copper foil epoxy E glass cloth laminate (used for catalytic addition method). IPC4101 detailed specification no. 82; Tg N/A;
Detection of repair
A. Chip with program
1. Generally speaking, EPROM chip should not be damaged. Because the chip requires ultraviolet light to erase the program, it won’t damage the program in tests. Because of the materials used to make the chips, they can be damaged over time even if they are not used. So backup as much as possible.
2.EEPROM,SPROM and RAM chip with battery can easily destroy the program. It remains to be seen whether such chips have broken the program by scanning VI curves using the < tester >. Still, colleagues should be careful when confronted with such situations. The author has done a number of tests, the possible cause is: maintenance tools (such as tester, soldering iron, etc.) caused by the shell leakage.
3. Do not remove the battery chip from the board easily.
2. Reset circuit
1. Pay attention to the reset problem when there is lsi on the circuit board to be repaired.
2. Before the test, it is better to put it back on the device, turn it on and off repeatedly and try again. And hit the reset key several times.
3. Function and parameter testing
1.< tester > can only reflect the cut-off region, amplifier region and saturation region for device detection. But can not measure the working frequency and speed of the speed and other specific values.
2. Similarly for TTL digital chip, only high and low level output changes can be known. There is no way to find out how fast it rises and falls.
Four. Crystal oscillator
1. Usually only oscilloscope (crystal oscillator needs to be electrified) or frequency meter can be used to test, multimeter cannot be measured, otherwise only substitution method can be used.
2. Common faults of crystal oscillator include: a. Internal leakage, b. Internal open circuit c. Here leakage phenomenon, with < tester > VI curve should be able to measure.
3. Two judgment methods can be adopted in the whole board test: a. When the crystal oscillator is tested, the relevant chips around do not pass. B. No other fault points were found except crystal oscillator.
4. There are two common crystal vibrators: a. two legs. B. Four legs, of which the second leg is powered, do not accidentally short circuit.
Five. Distribution of fault phenomena
1. Incomplete statistics of fault positions of circuit boards: 1) 30% damage to chips; 2) 30% damage to discrete components;
3) the connection (PCB copper coated wire) is broken by 30%, 4) the program is damaged or lost by 10% (with rising trend).
2. From the above, when the circuit board to be repaired and the program problems, and no good board, neither familiar with its wiring, can not find the original program. There is not much chance of repairing this board.
Compatible with the design
Electromagnetic compatibility refers to the ability of electronic equipment to work harmoniously and effectively in various electromagnetic environments. The purpose is to make the electronic equipment not only can restrain various external interference, make the electronic equipment can work normally in the specific electromagnetic environment, but also can reduce the electronic equipment itself to other electronic equipment electromagnetic interference.
1, choose a reasonable wire width since the impact interference caused by transient current on printed PCB circuit board lines is mainly caused by the inductance of printed wires, so the inductance of printed wires should be reduced as far as possible.
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 crosstalk between PCB circuit board wires, long distance equal wiring should be avoided as far as possible in the design of wiring, and the distance between wires should be pulled as far as possible, and the signal wire and ground wire and power line should not cross as far as possible. Crosstalk can be effectively suppressed by setting a ground printed line between some signal lines which are very sensitive to interference.
The circuit board is mainly composed of welding pads, through holes, mounting holes, wires, components, connectors, filling, electrical boundaries, etc. The main functions of each component are as follows:
Pad: metal hole used to weld the pins of components.
Through hole: there are metal through hole and non-metal through hole, among which metal through hole is used to connect the pins of components between layers.
Mounting hole: used to fix circuit board.
Conductor: electrical network copper film used to connect pins of components.
Connector: an element used to connect circuit boards.
Fill: copper coating for ground 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 this boundary.
The main classification
Circuit board systems are classified into the following three types:
Single – Sided Boards
We’ve just mentioned it, so we’ll call this PCB single-sided. Because of the strict limitations of a single panel on the design circuit (since there is only one side, the wiring cannot intersect and must take a separate path), only early circuits used such boards.
Double – Sided Boards
The circuit board is wired on both sides. But to use two-sided wires, you need to have proper electrical connections between the two sides. The “bridge” between these circuits is called the guide hole (via). A guide hole is a small hole in a PCB, filled with or coated with metal, that can be connected to two wires. Because the double panels are twice as large as the single panel, and because the wiring can be interlaced (it can be wound to the other side), they are more suitable for more complex circuits than single panels.
[multi-layer 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 built between the layers to connect the circuits of each layer.
The inner line
Copper foil substrate first cut into suitable size for processing production. Before pressing the substrate, it is usually necessary to use brush grinding, micro erosion and other methods to do the appropriate coarsening of copper foil on the plate, and then at the appropriate temperature and pressure, the dry film light resistance is tightly attached to it. The substrate attached to the dry film photoresist is sent to the uv exposure machine for exposure. The photoresist will generate polymerization reaction after being exposed to ultraviolet light in the light-transmitting area of the film (the dry film in this area will be retained as etching inhibitor in the later development and copper etching steps), and the image of the circuit on the film will be transferred to the dry film photoresist on the plate surface. After tearing off the protective film on the film surface, the unilluminated area on the film surface was firstly developed and removed with sodium carbonate solution, and then the exposed copper foil was corroded and removed with hydrochloric acid and hydrogen peroxide solution to form a circuit. Finally, the photoresist of dry film was washed away by sodium hydroxide solution. For the inner circuit board with more than six layers (including), use automatic positioning punching machine to rush out the riveting reference hole of inter-layer circuit alignment. Multi – Layer Boards
In order to increase the area that can be wired, multilayer boards use more single or double wiring boards. Multiple laminates use a number of double panels, and place an insulating layer between each layer of laminates to secure (press).
The number of layers on the board means that there are several independent wiring layers, usually with an even number of layers and containing the outermost two layers. Most mainboards are 4 to 8 layers, but it is technically possible to have nearly 100 layers of PCB boards. Most large supercomputers use fairly multi-tier motherboards, but because such computers can be replaced by clusters of many regular computers, superlamination is becoming obsolete. Because the layers in the PCB are tightly integrated, it is not always easy to see the actual number, but if you look closely at the motherboard, you may be able to see it.
With the introduction of surface mount technology, the automatic detection technology of circuit board is applied, and the package density of circuit board increases rapidly. Therefore, even for the low density, general number of circuit boards, the automatic detection of circuit boards is not only basic, but also economical. In the complex circuit board inspection, two common methods are needle bed test and double probe or flying needle test.
According to the characteristics of circuit board material and its wide application fields, in order to save the volume and achieve a certain degree of accuracy, the three-dimensional characteristics and thin thickness can be better applied to digital products, mobile phones and laptops. The recommended instruments for circuit board (FPC) detection are MUMA200 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-loaded probe connected to each test point on the circuit board. The spring provides a pressure of 100-200g for each probe to ensure good contact at each test point. The arrangement of such probes is called “needle bed”. Under the control of the detection software, the detection points and detection signals can be programmed. FIG. 14-3 is a typical needle-bed tester structure, and the tester can obtain the information of all test points. Only those probes that need to be tested are actually installed. Although it is possible to test both sides of the circuit board using the pin-bed test, when designing the circuit board, all test points should be on the soldered side of the circuit board. Needle bed tester equipment is expensive and difficult to maintain. Different arrays of needles are selected according to their specific application.
A basic general-purpose grid processor consists of a bored board with pins spaced 100, 75, or 50mil apart at the center. Pins act as probes and make direct mechanical connections using electrical connectors or nodes on circuit boards. If the solder pads on the circuit board match the test grid, then the perforated polyvinegar film 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, which have been defined as the x-y coordinates of the pads. Since every network on the circuit board is checked for continuity. In this way, an independent test is completed. However, the proximity of the probes limits the effectiveness of the needle bed test.
The circuit board is small in size and complex in structure, so the observation of circuit board must use professional observation instrument. Generally, we use portable video microscope to observe the structure of the circuit board. Through video microcamera, we can clearly see the very intuitive microstructure of the circuit board from the microscope. In this way, it is easier to design and test circuit boards. The portable video microscope, the portable video microscope MSA200, VT101, because it can achieve “at any time observation, detection, many people to discuss” more convenient than the traditional microscope!
Flying probe test
The flying pin tester does not rely on pin patterns 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 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. The tester with two movable arms is based on measurements of capacitance. The circuit board is pressed against an insulating layer on a metal plate, which 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 small.
Test speed is an important criterion for selecting a tester. While the needle bed tester can accurately test thousands of test sites at a time, the flying needle tester can only test two or four sites at a time. In addition, a single pince-bed tester may cost as little as 20-305, depending on the complexity of the board, while a flying pince-bed tester may require Ih or more time to complete the same assessment. Shipley (19