Electronic Manufacturing,PCB assembly,PCB Manufacturing

PCB Assembly

PCB layout and design specifications

PCB design must know the PCB layout and design specifications
    We all know that "no rules no standards," technology is the same, that in PCB design time and need to pay attention to what spec?
    Layout design specifications
    A, should be greater than the distance from the plate edge 5mm = 197mil
    B, first place and close structural elements, such as connectors, switches, power sockets, etc.
    C, placing priority circuit block of core components and bulky components, and then to the center of the core element is placed around the circuit components
    D, power components placed in favor of the position of the heat
    E, greater quality components should be avoided on the center plate, should be close to the chassis side fixed placement
    F, a high-frequency connection element as close as possible to reduce the electromagnetic interference and distribution of high-frequency signal
    G, input and output devices as far away
    H, components with high pressure as possible on the commissioning of the reach of the hand
    I, thermal element away from the heating element
    Layout J, adjustable element should be easy to adjust
    K, consider the signal flow, reasonable arrangement of the signal flow of the layout consistent as possible
    L, the layout should be uniform, neat, compact
    M, SMT components should note pad direction far as possible, in order to facilitate assembly and welding, to reduce the possibility of bridging
    N, decoupling capacitors should be close to the location of the power input
    O, element surface wave height limit of 4mm
    P, has a double-sided element PCB, larger denser IC, plug-in components on the top plate, the bottom element only put a small number of pins and small and loosely arranged chip components
    Q, small size and high calorie plus radiator element is particularly important to dissipate heat through the copper can lower power elements, and these elements try not to put around the thermal element
    R, high speed element as close to the connector; digital and analog circuits widely apart, separated by the best land, and then single-point ground
    S, near the positioning hole to pad distance not less than 7.62mm (300mil), from the positioning hole to the edge of the surface-mount device is not less than 5.08mm (200mil)
    Wiring design specifications
    A, the line should be avoided at an acute angle, right angle, forty-five degrees should be used to trace
    B, adjacent layers in the orthogonal direction to the signal line
    C, high-frequency signal as short as possible
    D, input and output signals to avoid adjacent parallel lines, between the best online plus ground, to prevent feedback coupling
    E, dual panel power lines, ground toward the best consistent with the data flow, in order to enhance noise immunity
    F, digital ground, analog ground should be separated. Clock and high-frequency signal line according to the characteristic impedance of the line width asked to consider, so that impedance matching
    G, block board wiring, drilling should be uniform
    H, separate power and ground planes, power lines, ground as short and thick, loop power supply and constructed as small as possible
    I, the clock wiring should be less played the hole, try to avoid walking and other signal lines and lines, and away from the general signal line, to avoid interference with the signal line; at the same time the power supply is part of the board, power and clock to prevent mutual interference ; when a circuit board has a plurality of different frequency clock, two different frequencies of the clock line and can not walk the line; avoid going near the clock line output interface, to prevent high-frequency clock output coupled to the cABLE line and transmitted; as board on a dedicated clock generation chip, which can not go below the line, shall be covered in copper below, if necessary, its specialized annexations
    J, paired differential signal lines generally parallel lines, played sparingly hole punch when necessary, should play with two lines, in order to achieve impedance matching
    K, two spot pitch is very small, can not be directly connected between the pads; from mount pad via leads as far away from the pad farther.
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