The name of the circuit board is: ceramic circuit board, alumina ceramic circuit board, aluminum nitride ceramic circuit board, circuit board, PCB board, aluminum substrate, high frequency board, thick copper plate, impedance board, PCB, ultra-thin circuit board, ultra-thin circuit board, printed (copper etching technology) circuit board. The circuit board makes the circuit miniaturized and intuitive, and plays an important role in the mass production of fixed circuit and optimizing the layout of electrical appliances. Circuit boards may be called printed circuit boards or printed circuit boards, The English name is (Printed Circuit Board) PCB, (Flexible Printed Circuit board) FPC circuit board (FPC circuit board, also known as flexible circuit board) Flexible circuit board is made of polyimide or polyester film as a substrate with high reliability, Excellent flexible printed circuit board. It has the characteristics of high wiring density, light weight, thin thickness and good bending. and Soft and hard combination plate (reechas, soft and hard combination plate) - the birth and development of FPC and PCB, gave birth to the soft and hard combination plate this new product. Therefore, the soft and hard combined board is the flexible circuit board and the hard circuit board, after pressing and other processes, according to the relevant process requirements combined together to form a circuit board with FPC characteristics and PCB characteristics.
The circuit board is divided into three large categories according to the number of layers: single panel, double panel, and multi-layer circuit board.
a. Single panel, on the most basic PCB, the parts are concentrated on one side, and the wires are concentrated on the other side. Because the wire only appears on one side, this PCB is called a single-sided circuit board. Single panel is usually simple to make, low cost, but the disadvantage is that it can not be applied to too complex products.
b. Double panel is an extension of the single panel, when the single-layer wiring can not meet the needs of electronic products, it is necessary to use double panel. Both sides are covered with copper and have wiring, and the line between the two layers can be guided through the hole to form the required network connection.
c. Multi-layer board refers to a printed board with more than three layers of conductive graphics layer and the insulating material between them are separated by layers, and the conductive graphics between them are interconnected as required. Multilayer circuit board is the product of the development of electronic information technology to high speed, multi-function, large capacity, small volume, thin shape and light weight.
According to the characteristics of the circuit board is divided into soft board (FPC), hard board (PCB), soft and hard combined board (FPCB).
Circuit board board
FR-1: Flame retardant copper clad phenolic paper laminate. IPC4101 Specification Number 02; Tg N/A;
FR-4: a. Flame retardant copper clad epoxy E glass fiber cloth laminate and adhesive sheet material. IPC4101 Detail Specification Number 21; Tg≥100℃; b. Flame retardant copper clad modified or unmodified epoxy E glass fiber cloth laminate and its adhesive sheet material. IPC4101 Detail Specification No. 24; Tg 150℃~200℃; c. Flame retardant copper clad foil epoxy /PPO glass cloth laminate and adhesive sheet material. IPC4101 Detail Specification No. 25; Tg 150℃~200℃; d. Flame retardant copper clad foil modified or unmodified epoxy glass cloth laminate and its adhesive sheet material. IPC4101 Detail Specification Number 26; Tg 170℃~220℃; E. Flame retardant copper-clad epoxy e glass cloth laminate (for catalytic addition process). IPC4101 Detail Specification number 82; Tg N/A;
Circuit board inspection and repair
1. Chip with program
(1). The EPROM chip should not be damaged. Because the chip requires ultraviolet light to erase the program, it will not damage the program during testing. However, some information is introduced: because of the material used to make the chip, it may be damaged (mainly referring to the program) with the passage of time (the years are long). So back it up as much as possible.
(2) EEPROM,SPROM, etc., and RAM chips with batteries are easy to destroy the program. Whether such chips break the program after using the < tester > for VI curve scanning has not been determined. Nevertheless, colleagues should be careful in such situations. The author has done many tests, the main reason may be: maintenance tools (such as tester, soldering iron, etc.) caused by leakage of the shell.
(3) For the chip with a battery on the circuit board, do not easily remove it from the board.
2. Reset circuit
(1) When there is a large-scale integrated circuit on the circuit board to be repaired, attention should be paid to the reset problem.
(2) Before the test, it is best to put it back on the equipment, and repeatedly open and close the machine to try. And press the reset button more than once.
3. Function and parameter testing
(1). The detection of the device by the tester can only reflect the cutoff region, the amplification region and the saturation region. However, it is not possible to measure specific values such as the working frequency and speed.
(2) Similarly, for TTL digital chips, it can only know that there are high and low level output changes. There is no way to find out the speed of its rising and falling edges.
4, crystal oscillator
(1). Usually only oscilloscope (crystal oscillator needs to be powered up) or frequency meter test, multimeter can not be measured, otherwise only substitution method can be used.
(2) The common faults of crystal vibration are: a. internal leakage, b. internal open circuit c. metamorphic frequency deviation d. peripheral capacitance leakage. The leakage phenomenon here should be measured by the VI curve of the < tester >.
(3) Two judgment methods can be used when the whole board is tested: a. The relevant chip near the crystal oscillator does not pass the test. b. No other fault points were found except crystal vibration.
(4). There are two common crystal oscillators: a. two feet. b. Four pins, of which the second foot is added to the power supply, pay attention not to short circuit.
5. Distribution of fault symptoms
(1) Incomplete statistics of circuit board fault parts:
a. Chip damage 30%, b. Discrete component damage 30%,c. Cable (PCB copper wire) is broken 30%, d. 10% of programs are broken or lost (with an upward trend).
(2) From the above, when the circuit board to be repaired has a connection and a program problem, there is no good board, neither familiar with its connection, can not find the original program. The board is unlikely to be repaired.
Electromagnetic compatibility refers to the ability of electronic devices to work harmoniously and effectively in various electromagnetic environments. The purpose is to enable the electronic equipment to suppress various external interference, so that the electronic equipment can work normally in a specific electromagnetic environment, and at the same time reduce the electromagnetic interference of the electronic equipment itself on other electronic equipment.
(1) Choose a reasonable wire width Because the impact interference caused by the transient current on the printed line of the PCB circuit board is mainly caused by the inductive component of the printed wire, so the inductance of the printed wire should be minimized.
(2) The use of the correct wiring strategy using equal wiring can reduce the inductance of the wire, but the mutual inductance and distributed capacitance between the wires increase, if the layout allows, it is best to use the well pattern network wiring structure, the specific practice is one side of the printed board horizontal wiring, the other side longitudinal wiring, and then connected with metalized holes at the cross hole.
(3) In order to suppress the crosstalk between the PCB circuit board wires, in the design of wiring should try to avoid long-distance equal wiring, as far as possible to open the distance between the line and the line, the signal line and the ground and the power line as far as possible do not cross. Crosstalk can be effectively suppressed by setting a ground printed line between some signal lines that are very sensitive to interference.
The circuit board is mainly composed of welding pad, through hole, mounting hole, wire, components, connectors, filling, electrical boundary, etc. The main functions of each component are as follows:
Pad: A metal hole for welding the pin of a component.
Through holes: There are metal through holes and non-metal through holes, wherein the metal through holes are used to connect the component pins between the layers.
Mounting hole: used to secure the circuit board.
Wire: Electrical network copper film used to connect component pins.
Connector: A component used to connect circuit boards.
Filling: Copper coating for ground wire network can effectively reduce impedance.
Electrical boundary: Used to determine the size of the board, all components on the board can not exceed this boundary.
Circuit board systems are classified into the following three types:
Single-sided - We just mentioned that, so we call this type of PCB single-sided. Because a single panel has many strict restrictions on the design circuit (because there is only one side, the wiring can not cross * and must go around a separate path), only early circuits used such boards.
Dual panel - This circuit board has wiring on both sides. However, in order to use the wires on both sides, there must be a proper circuit connection between the two sides. This "bridge" between circuits is called a pilot hole (via). A pilot hole is a small hole filled with or coated with metal on the PCB, which can be connected with wires on both sides. Because the area of the dual panel is twice as large as that of the single panel, and because the wiring can be interlaced (can be wound around the other side), it is more suitable for use in more complex circuits than the single panel.
Multilayer board - For more complex applications, the circuit can be arranged into a multi-layer structure and pressed together, and the through hole circuit is arranged between the layers to connect the layers.
Copper foil substrate is first cut to size suitable for processing production. Before pressing the substrate film, it is usually necessary to roughen the copper foil on the surface of the plate by brush grinding, micro-etching and other methods, and then attach the dry film to it with appropriate temperature and pressure. The substrate with dry film photoresist is sent to the UV exposure machine for exposure, and the photoresist will produce polymerization reaction after ultraviolet irradiation in the film transmission area (the dry film in this area will be retained as an etching resistance in the later development and copper etching steps), and the line image on the negative will be transferred to the dry film photoresist on the plate surface. After the protective film on the film surface is torn off, the unilluminated area on the film surface is developed and removed with sodium carbonate aqueous solution, and then the exposed copper foil is corroded and removed with hydrochloric acid and hydrogen peroxide mixed solution to form a circuit. Finally, the successfully retired dry film was photowashed with sodium hydroxide aqueous solution. For the inner circuit board with more than six layers (including), the automatic positioning punch is used to flush out the rivet reference hole of the interlayer line alignment.
In order to increase the area that can be wired, the multilayer board uses more single or double sided wiring boards. The multilayer board uses several double panels and is glued (pressed) by placing a layer of insulation between each layer.
The number of layers of the board represents several independent wiring layers, usually an even number of layers, and contains the outermost two layers. Most of the host board is a 4 to 8 layer structure, but it is technically possible to achieve nearly 100 layers of PCB board. Most large supercomputers use a fairly multilayer mainframe, but since such computers can be replaced by clusters of many ordinary computers, ultra-multilayer boards have fallen out of use. Because the layers in the PCB are tightly combined, it is generally not easy to see the actual number, but if you look closely at the host board, you may be able to see it.
With the introduction of surface mount technology, automatic detection technology of circuit board has been applied, and the packaging density of circuit board has increased rapidly. Therefore, even for the low density, the average number of circuit boards, automatic detection of circuit boards is not only basic, but also economical. In complex circuit board inspection, two common methods are the needle bed test and the double probe or flying needle test.
According to the characteristics of the material of the circuit board and the wide application field, in order to save the volume more effectively and achieve a certain accuracy, the characteristics of the three-degree space and the thin thickness are better applied to digital products, mobile phones and laptops. The recommended instruments for circuit board (FPC) inspection are 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.
Circuit board test method
A. Needle bed method - This method consists of a probe with a spring attached to each detection point on the circuit board. The spring makes each probe have a pressure of 100-200g to ensure that each detection point contacts well, so that the probe is arranged together called the "needle bed". Under the control of the detection software, the detection point and the detection signal can be programmed. Figure 14-3 is a typical structure of the needle bed tester, and the detector can know the information of all the test points. In fact, only the probes for the test points that need to be tested are installed. Although it is possible to inspect both sides of the board at the same time using the needle bed test method, when designing the board, all inspection points should be on the welded side of the board. Needle bed tester equipment is expensive and difficult to maintain. Different arrangements of probes are selected according to the specific application of the needle.
A basic general-purpose grid processor consists of a drilled board with pins with center spacing of 100, 75, or 50mil. The pins act as probes and make direct mechanical connections using electrical connectors or nodes on the circuit board. If the pad on the circuit board matches the test grid, the polyvinegar film drilled according to the specification is placed between the grid and the circuit board to facilitate the design of a specific probe. 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 tested for continuity. Thus, an independent test is completed. However, the proximity of the probes limits the effectiveness of the needle bed test.
b. Observation - The circuit board is small in size and complex in structure, so the observation of the circuit board must also use professional observation instruments. In general, we use a portable video microscope to observe the structure of the circuit board, through the video microscope camera, you can clearly see the very intuitive microscopic structure of the circuit board from the microscope. In this way, it is relatively easy for us to design and test the circuit board. The portable video microscope used in the factory site, the portable video microscope MSA200, VT101, because it can achieve "any time observation, any time detection, many people discuss" than the traditional microscope is more convenient!
c. Flying needle test - 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 magnetic heads that can move freely 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 are able to 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 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 become smaller.
Test speed is an important criterion for choosing a tester. Needle bed testers can accurately test thousands of test points at a time, while flying needle testers can only test two or four test points at a time. In addition, single-sided testing with the needle bed tester may only cost 20-305, depending on the complexity of the board, while flying needle testing
Ih or more time is required to complete the same assessment. Shipley (1991) explained that even though manufacturers of high-volume printed circuit boards find moving flypin testing techniques slow, this method is a good choice for manufacturers of complex circuit boards with lower volumes.
For bare board testing, there are special test instruments (Lea,1990). A more cost-effective approach would be to use a general-purpose 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 grid for boards and surface-mount devices with pin components is 2.5mm. At this time, the test pad should be greater than or equal to 1.3mm. For Imm grids, the 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 accurate and economical. Another approach 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 heights of pads treated with hot air smoothing will hinder the connection of test points.
The following three levels of detection are usually carried out: a. Bare board detection; b. Online testing; c. Function test. The use of a general type of tester can be used to detect a class of style and type of circuit board, but also can be used for 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 boards in various industries is also increasing, after the damage of the industrial control board, the high cost required to replace the circuit board (as little as thousands of yuan, more than tens of thousands or hundreds of thousands of yuan) has become a very headache for 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, and the time used is much shorter than that of foreign fixed boards. 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 one or some of the devices caused by damage, The idea of circuit board maintenance is based on the above factors established. Circuit board maintenance is divided into two parts: inspection and maintenance, in which inspection occupies a very important position. Test the basic knowledge of each device on the circuit board until the bad parts are found and replaced, then a circuit board is repaired.
Circuit board inspection is the process of finding, determining and correcting the fault of each electronic component on the circuit board. In fact, the entire testing process is the thinking process and the testing process of providing logical reasoning clues, so the testing 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. Then from the fault phenomenon to the cause of the fault, the box-type maintenance method is an important maintenance method. As long as the circuit board detects the problem, it is easy to repair. The above is the basic knowledge of circuit board maintenance.
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