The names of circuit boards are: 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 Thin circuit boards, printed (copper etching technology) circuit boards, etc. The circuit board makes the circuit miniaturized and intuitive, and plays an important role in the mass production of fixed circuits and the optimization of the layout of electrical appliances. The circuit board can be called a printed circuit board or a printed circuit board, the English name is (Printed Circuit Board) PCB, (Flexible Printed Circuit board) FPC circuit board (FPC circuit board is also called flexible circuit board Flexible circuit board is based on polyimide Or polyester film as the base material is a highly reliable, excellent flexible printed circuit board. It has the characteristics of high wiring density, light weight, thin thickness and good bendability.) and soft and hard Combination board (reechas, Soft and hard combination plate) - The birth and development of FPC and PCB gave birth to the new product of soft and hard combination plate. Therefore, the flexible and rigid board is a flexible circuit board and a rigid circuit board, which are combined according to the relevant process requirements after pressing and other processes to form a circuit board with FPC characteristics and PCB characteristics.
Classification
Circuit boards are divided into three major categories: single-sided, double-sided, and multi-layer circuit boards according to the number of layers.
The first is single-sided. On the most basic PCB, the parts are concentrated on one side and the wires are concentrated on the other side. Because the wires only appear on one side, this kind of PCB is called a single-sided circuit board. Single panel is usually simple to make and low cost, but the disadvantage is that it cannot be applied to too complicated products.
Double-sided is an extension of single-sided. When single-layer wiring cannot meet the needs of electronic products, double-sided is used. Both sides have copper cladding and traces, and the lines between the two layers can be conducted through vias to form the required network connections.
A multi-layer board refers to a printed board with more than three conductive pattern layers and insulating materials in between, and the conductive patterns are interconnected as required. Multilayer circuit board is the product of the development of electronic information technology in the direction of high speed, multi-function, large capacity, small volume, thinning and light weight.
Circuit boards are divided into flexible boards (FPC), rigid boards (PCB), and rigid-flex boards (FPCB) according to their characteristics.
circuit board
FR-1: Flame retardant copper clad phenolic paper laminate. IPC4101 Detail Specification No. 02;Tg N/A;
FR-4: 1) Flame retardant copper clad epoxy E glass fiber cloth laminate and its bonding sheet material. IPC4101 Detail Specification No. 21; Tg≥100℃;
2) Flame-retardant copper-clad modified or unmodified epoxy E glass fiber cloth laminate and its bonding sheet material. IPC4101 Detail Specification No. 24; Tg 150℃~200℃;
3) Flame retardant copper clad epoxy/PPO glass cloth laminate and its adhesive sheet material. IPC4101 Detail Specification No. 25; Tg 150℃~200℃;
4) Flame retardant copper-clad modified or unmodified epoxy glass cloth laminate and its bonding sheet material. IPC4101 Detail Specification No. 26; Tg 170℃~220℃;
5) Flame retardant copper clad epoxy E glass cloth laminate (for catalytic addition method). IPC4101 Detail Specification No. 82; Tg N/A;
Inspection and repair
one. chip with program
1. EPROM chips should not be damaged in general. Because this chip requires ultraviolet light to erase the program, it will not damage the program during testing. However, there is information: due to the material used to make the chip, with the passage of time (the age is long), it may be damaged even if it is not used (mainly refers to the program). So make backups as much as possible.
2. EEPROM, SPROM, etc., as well as RAM chips with batteries, are very easy to destroy programs. Whether this type of chip has broken the program after using the <Tester> to scan the VI curve is not yet conclusive. Nonetheless, colleagues should be careful when encountering such a situation. The author has done many tests, the main reason may be: the leakage of the casing of the maintenance tools (such as testers, electric soldering irons, etc.).
3. For the chip with battery on the circuit board, do not easily remove it from the board.
two. reset circuit
1. When there are large-scale integrated circuits on the circuit board to be repaired, attention should be paid to the reset problem.
2. It is best to put it back on the device before the test, and turn it on and off repeatedly to try it. And press the reset button several times.
three. Functional and parametric testing
1. The detection of the device by <Tester> can only reflect the cut-off area, the amplification area and the saturation area. However, specific values such as the level of operating frequency and the speed of speed cannot be measured.
2. Similarly, for TTL digital chips, only the output changes of high and low levels can be known. And it is impossible to find out the speed of its rising and falling edges.
Four. crystal oscillator
1. Usually, it can only be tested with an oscilloscope (the crystal oscillator needs to be powered on) or a frequency meter.
2. Common faults of crystal oscillators are: a. Internal leakage, b. Internal open circuit c. Deterioration frequency deviation d. Peripheral connected capacitor leakage. The leakage phenomenon here should be detected by the VI curve of the <Tester>.
3. Two judgment methods can be used in the whole board test: a. During the test, the related chips near the crystal oscillator and the surrounding area do not pass. b. No other fault points were found except the crystal oscillator.
4. There are two common crystal oscillators: a. Two feet. b. Four pins, of which pin 2 is powered, be careful not to short-circuit at will.
five. Distribution of fault phenomena
1. Incomplete statistics of faulty parts of circuit boards: 1) Chip damage 30%, 2) Discrete component damage 30%,
3) 30% breakage of wiring (copper wire on PCB board), 4) 10% program damage or loss (there is an upward trend).
2. It can be seen from the above that when there is a problem with the connection and the program of the circuit board to be repaired, there is no good board, neither is it familiar with its connection, and the original program cannot be found. This board is unlikely to be repaired.
Compatible 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 suppress various external interference, make the electronic equipment work normally in a specific electromagnetic environment, but also reduce the electromagnetic interference of the electronic equipment itself to other electronic equipment.
1. Choose a reasonable wire width. The impact interference generated by the transient current on the printed lines of the PCB circuit board is mainly caused by the inductance component of the printed wires, so the inductance of the printed wires should be minimized.
2. Adopting the correct wiring strategy Using equal wiring can reduce the wire inductance, but the mutual inductance and distributed capacitance between the wires increase. If the layout allows, it is best to use a well-shaped mesh wiring structure. The specific method is that one side of the printed board is horizontal Route, run lengthwise on the other side, and then connect with metallized vias at cross holes.
3. In order to suppress the crosstalk between the wires of the PCB circuit board, the long-distance equal wiring should be avoided as much as possible when designing the wiring, and the distance between the wires should be widened as much as possible. cross. Setting a grounded trace between some signal lines that are very sensitive to interference can effectively suppress crosstalk.
composition
The circuit board is mainly composed of pads, vias, mounting holes, wires, components, connectors, fillings, electrical boundaries, etc. The main functions of each component are as follows:
Pad: A metal hole for soldering component pins.
Vias: There are metal vias and non-metal vias, where metal vias are used to connect component pins between layers.
Mounting holes: used to fix the circuit board.
Wire: An electrical network copper film used to connect component pins.
Connector: A component used for connection between circuit boards.
Filling: The copper used for the ground wire network can effectively reduce the impedance.
Electrical Boundary: Used to determine the size of the circuit board, and all components on the circuit board must not exceed this boundary.
main classification
Circuit board systems are classified into the following three categories:
single panel
Single-Sided Boards
We just mentioned it, so we call this kind of PCB single-sided (Single-sided). Because the single board has many strict restrictions on the design circuit (because there is only one side, the wiring cannot cross * and must go around a separate path), so only early circuits used this type of board.
Double panel
Double-Sided Boards
This board has wiring on both sides. However, to use two sides of the wire, there must be a proper circuit connection between the two sides. Such "bridges" between circuits are called vias. Vias are small holes on a PCB, filled or painted with metal, that can be connected to wires on both sides. Because the area of the double-sided board is twice as large as that of the single-sided board, and because the wiring can be interleaved (can be wound to the other side), it is more suitable for use on more complex circuits than single-sided boards.
Multilayer board
[Multilayer board] In the case of more complex application requirements, the circuit can be arranged into a multi-layer structure and pressed together, and through-hole circuits are arranged between the layers to connect the circuits of each layer.
inner line
The copper foil substrate is first cut into a size suitable for processing and production. Before the substrate is laminated, it is usually necessary to properly roughen the copper foil on the board surface by brushing, micro-etching, etc., and then stick the dry film photoresist on it with an appropriate temperature and pressure. The substrate with the dry film photoresist is sent to the UV exposure machine for exposure, and the photoresist will polymerize after being irradiated by UV light in the light-transmitting area of the negative film (the dry film in this area will be later developed and copper-etched in the steps of etching. Keep it as an etch resist), and transfer the circuit image on the negative to the dry film photoresist on the board. After peeling off the protective film on the film surface, first use sodium carbonate aqueous solution to develop and remove the unilluminated area on the film surface, and then use a mixed solution of hydrochloric acid and hydrogen peroxide to etch and remove the exposed copper foil to form a circuit. Finally, the dry film photoresist that has been successfully removed is washed away with an aqueous solution of sodium hydroxide. For inner-layer circuit boards with more than six layers (inclusive), use an automatic positioning punching machine to punch out the riveting reference holes for the alignment of the interlayer lines. Multi-Layer Boards
In order to increase the area that can be wired, more single or double-sided wiring boards are used for multilayer boards. Multi-layer boards use several double-sided boards, and put an insulating layer between each board and then glue (press-fit).
The number of layers of the board represents several independent wiring layers, usually the number of layers is even, and includes the outermost two layers. Most motherboards are 4 to 8-layer structures, but technically, nearly 100-layer PCB boards can be achieved. Most large supercomputers use fairly multi-layer motherboards, but because such computers can be replaced by clusters of many ordinary computers, ultra-multi-layer boards have gradually fallen out of use. Because the layers in a PCB are so tightly bound, it's generally not easy to see the actual number, but if you look closely at the motherboard, you might be able to.
The automatic detection technology of circuit boards has been applied with the introduction of surface mount technology, and the packaging density of circuit boards has increased rapidly. Therefore, even for low-density, general-number boards, automatic board detection is not only basic, but also economical. In complex circuit board inspection, two common methods are bed of needles testing and dual or flying probe testing.
DetectorEdit
According to the material characteristics of the circuit board and the wide application fields, in order to save the volume more effectively and achieve a certain accuracy, the characteristics of the three-dimensional space and the thin thickness can be better applied to digital products, mobile phones and notebook computers. Recommended instruments for circuit board (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.
testing method
needle bed method
This method consists of spring-loaded probes connected to each detection point on the board. The springs apply 100 - 200g of pressure to each probe to ensure good contact at each test point, and such probes are called a "bed of needles". Under the control of the testing software, the testing points and testing signals can be programmed. Figure 14-3 is a typical structure of a bed of needles tester, and the tester can obtain the information of all testing points. Only the probes for the test points that need to be tested are actually installed. Although it is possible to test on both sides of the board using the bed of needles method, when designing the board, all test points should be on the solder side of the board. Bed of needles tester equipment is expensive and difficult to maintain. The needles are selected in different arrangements of probes according to their specific application.
A basic general-purpose raster processor consists of a drilled board with pins 100, 75, or 50 mil center-to-center. The pins function as probes and make direct mechanical connections using electrical connectors or nodes on the circuit board. If the pads on the board mate with the test grid, a polyester film perforated to specification is placed between the grid and the board to facilitate design-specific probing. 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 net on the board is checked for continuity. In this way, an independent test is completed. However, the proximity of the probes limits the performance of the bed of needles test.
observation
The circuit board is small in size and complex in structure, so the observation of the circuit board must also use a professional observation instrument. Generally, we use a portable video microscope to observe the structure of the circuit board. Through the video microscope camera, 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 microscopes currently used in the factory, and the portable video microscopes MSA200 and VT101, are more convenient than traditional microscopes because they can realize "observation at any time, detection at any time, and discussions with multiple people"!
Flying probe test
Flying probe testers do not rely on pin patterns mounted on a fixture or bracket. Based on this system, two or more probes are mounted on tiny heads that can move freely in the x-y plane, and the test points are directly controlled by CADI Gerber data. The dual probes can be moved within 4 mils 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 can move back and forth is based on the measurement of capacitance. The circuit board is pressed against the insulation on a metal plate that acts as the other metal plate for the capacitor. If there is a short between the lines, the capacitance will be larger than at a certain point. If there is an open circuit, the capacitance will become smaller.
Test speed is an important criterion for selecting a tester. A bed of needles tester can accurately test thousands of test points at a time, while a flying probe tester can only test two or four test points at a time. Also, bed of needles testers may only cost 20 - 305 for single-sided testing, depending on the complexity of the board, while flying probe testers take Ih or more to complete the same