We all know that “nothing can be accomplished without norms or standards”, the technology too. What specification should pay attention to when designing PCB ?
1. layout design specification
A,The distance to edge should be greater than 5mm or 197mil
B, first place the components that is close to the structure, such as connectors, switches, power sockets, etc
C, priority put core components of circuit function block and large components, and centering on the core components ,placed around the circuit components
D, components with large power are put in the position that is conductive to heat.
E, components with larger quality should be avoided on the center of the board,and should be putted close to the fixed boundary of the case.
F,components with high frequency connection should be as near as possible, to reduce the distribution of the high frequency signal and electromagnetic interference.
G,components of input should be away from components of output as far as possible .
H, components with a high voltage should be putted where the hand is not easy to reach when debugging.
I, thermal element should be far away from the heating element
J, adjustable components layout should facilitate of adjustment
K, considering the signal flow, layout with reasonable arrangement makes signal flow as consistent as possible
L, layout should be uniform, neat and compact
M, for SMT components, consistency of solder direction should be paid attention,which is good for PCB assembling and welding,and reduce the possibility of bridging.
N, decoupled capacitor should be at the location of the nearest power input.
O,the height of wave soldering components is limited 4mm.
P, for the PCB with double-sided components, IC with the larger density and plug-in components should be putted at the top of PCB board.Small components and SMD components with less pin and loose arrangement can only be putted at the bottom of board.
Q, adding the radiator for components with small size and high heat is particularly important.High power components can be heat dissipation by bonded copper, and try not to put heat sensitive components around these components .
R, high-speed element should be close to the connector as near as possible;
Digital circuit separate with analog circuit as far as possible.It is best that they are divided and single point grounding.
S, the distance between positioning hole to the nearby welding plate is not less than 7.62 mm (300 mil).The distance between positioning hole to surface mounting components is not less than 5.08mm(200 mil).
2 .wiring PCB design specification
A, line should avoid acute Angle, right Angle.Forty-five degrees should be used to trace.
B,signal lines of adjacent layer is the orthogonal direction
C, the high frequency signal is as short as possible
D, input and output signal as far as possible to avoid adjacent parallel lines.It is better to add ground wire between lines, in case of the back coupling.
E, the power cord of double-side board ,it is better that ground wire is consistent with the data flow direction, in order to enhance ability to resist noise.
F, digital and analog need to separate
The clock line and high frequency signal lines should consider line width according to the characteristic impedance requirements, to achieve the impedance matching
G, the wiring and drilling should be uniform in the whole circuit board .
H, The separate power layer and ground layer, the power lines and ground wire should be as short and thick as possible.Loops composed of power and ground should be as small as possible.
I, clock wiring should drill less holes, and try to avoid parallel lines with other signal lines,and should be far away from the general signal line, to avoid the interference to signal lines;At the same time avoiding the power part on the plate, to prevent mutual interference between power and clock;When a piece of circuit board has a number of different frequency clock, the clock line of two different frequency can not be parallel lines .The clock line should avoid close to output interface, to prevent high frequency clock coupled to the output CABLE line and launch out;If boards have special clock chip, its lower parts cannot place the line.Its lower part should be spread copper.If necessary , special cede territory for it;
J, paired difference signal lines generally parallel to the line, trying to drill a hole.If necessary,two lines should be drilled together, to achieve the impedance matching.
K,the space between two solder joint is very small, adn solder joint may not be directly connected ;Through-holes from the paste disc should be away from the PAD.