PCB Related Basic Concepts Explained
A. PCB Appearance
A bare board (no parts on the board) is often called a "Printed Wiring Board (PWB)". The substrate of the board itself is made of insulating and non-bending material. The small lines that can be seen on the surface are made of copper foil, which originally covered the entire board, but during the manufacturing process some of the copper foil is etched away, leaving the remaining portion as a mesh of small lines. These lines are called conductors (conductor pattern) or wiring, and are used to provide circuit connections to parts on the PCB.
Usually the color of the PCB is green or brown, which is the color of the solder mask. It is an insulating layer that protects the copper wires and prevents short circuits caused by wave soldering and saves the amount of solder used. The solder mask is also printed on a silk screen. Often, text and symbols (mostly white) are printed on this screen to indicate the location of each component on the board. The silk screen is also called the legend.
Integrated circuits, transistors, diodes, passive components (e.g. resistors, capacitors, connectors, etc.), and a variety of other electronic parts are mounted on the board when it is made into the final product. By connecting the wires, it can form the electronic signal connection and due function.
B. PCB Assembly Specification
- a, Circuit board board width ≤ 260mm (SIEMENS line) or ≤ 300mm (FUJI line); if you need automatic dispensing, PCB board width × length ≤ 125mm × 180mm.
- b, The shape of the patchwork board as close to square, recommended 2 × 2, 3 × 3, ...... patchwork board; but do not put together into a yin and yang board.
- c, The outer frame (clamping edge) of the circuit board splicing board should be closed-loop design to ensure that the PCB splicing board will not be deformed after it is fixed on the fixture.
- d, The center distance between the small board control between 75mm ~ 145mm.
- e, The outer frame of the piecing board and the internal small board, small boards and small boards can not be near the connection point of large devices or outstretched devices, and components and the edge of the PCB board should leave more than 0.5mm of space to ensure that the cutting tool operates normally.
- f, Four positioning holes in the four corners of the outer frame of the patchwork board, aperture 4mm ± 0.01mm; the strength of the holes should be moderate, to ensure that in the process of up and down the board will not break; aperture and positional accuracy should be high, the hole wall is smooth and burr-free.
- g, The circuit board within the patchwork of each small board at least three positioning holes, 3mm ≤ aperture ≤ 6mm, edge positioning holes within 1mm does not allow wiring or patch.
- h, Used for circuit board positioning of the whole board and for fine-pitch device positioning datum symbols, in principle, the pitch is less than 0.65mm QFP should be set in its diagonal position; used for collocation of circuit board positioning datum symbols should be used in pairs, arranged in the positioning elements of the diagonal.
- i, Set the reference positioning point, usually around the positioning point than its larger than the 1.5 mm non-resistive soldering zone
C. Main Advantages of PCB
The main advantages of using printed circuit boards are:
- a, Since the graphics have repeatability (reproducibility) and consistency, it reduces wiring and assembly errors and saves time for maintenance, debugging and inspection of equipment;
- b, The design can be standardized, facilitating interchangeability;
- c, High wiring density, small size, light weight, conducive to the miniaturization of electronic equipment;
- d, Conducive to mechanization, automated production, improve labor productivity and reduce the cost of electronic equipment.
- e, FPC flexible board bending resistance, precision should be better to high-precision instruments (such as cameras, cell phones, video cameras, etc.).
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