Is a PCB complete when the layout is completed and no problems are found with connectivity and spacing?
The answer, of course, is no. Many beginners, even including some experienced engineers, due to limited time or impatient or too confident,
tend to be hurry, ignoring the late checking, there have been some very low-level bugs, such as line width is not enough, components label printing
pressure and outlet holes had too close, signals in the loop, etc., lead to electrical or process problems, serious to play board, wasteful. Therefore,
post-inspection is an important step after a PCB has been laid out.
1. Component packaging
(1) Pad spacing. If it is a new device, to draw their own components package, ensure that the spacing is appropriate. Pad spacing directly affects the welding of components.
(2) Via size (if any). For plug-in devices, the size of the hole should be retained enough margin, generally not less than 0.2mm is more appropriate.
(3) Outline of the silk screen. The contour screen printing of the components should be
larger than the actual size to ensure that the device can be installed smoothly.
(1) IC should not be near the board edge.
(2) The components of the circuit in the same module should be placed close to each other. For example, the decoupling capacitor should be
close to the power supply pin of IC, and the components that constitute the same functional circuit should be placed in the same area with clear hierarchy
to ensure the realization of functions.
(3) Arrange the socket location according to the actual installation. Socket is connected to other modules through the lead, according to the actual structure,
in order to install convenient, generally use nearby principle arrangement socket position, and generally near board edge.
(4) Pay attention to the outlet direction. Socket needs a direction, if the direction is opposite, wire needs to be done it. For a flat socket, the orientation of the socket should be towards the outside of the board.
(5) There should be no devices in the keep out area.
(6) The interference source should be far away from the sensitive circuit. High speed signal, high speed clock or high current switch signal are interference sources, should be away from the sensitive circuit (such as reset circuit, analog circuit). They can be separated by a floor.