PCB post-inspection after PCB designing

When PCB layout completed, and already ensured connectivity and distance, is a PCB completed? The answer of course is no. Many beginners included many experienced engineers ignoring the post-inspection due to impatient or too confident. These may cause some very basic BUG, such as line width is not enough, sockets too close, and the signal loop occurs. These details may cause electrical problems or process problems. Some serious problems result to re-board and waste. So after PCB layout done, a very important step is to post-inspection. PCB inspection include many details. Nod Electronics listed some basic error-prone elements.

1.Component packaging

(1) The pad pitch. If it’s new devices, draw their element package to ensure proper spacing, because pad pitch directly affects weld elements.

(2) The hole size. For plug-in devices, vias size should retain sufficient margin, generally mores than 0.2mm.

(3) Outline silk-screen. Outline silk-screen should be bigger than the actual size, to ensure that the device can be successfully installed.

2.Layout

(1) IC should not be close to the plate edges.

(2) The same module circuit devices should be placed close. Such as decoupling capacitors should be close to the IC power pin to form a functional circuit with a device placed in a priority area, structured, ensure the realization of the function.

(3) The location of the actual installation socket arrangement according to. Sockets are lead to other modules, according to the actual structure, in order to facilitate the installation, the general principle of proximity, position socket arrangement, and generally close to the plate edges.

(4) Note outlet direction. There are outlet direction, the direction is reversed, the wire must re customized. For flat plug sockets, socket should be directed toward the plate away.

(5) Keep Out area can not have the device.

(6) The source of interference away from sensitive circuits. High-speed signals, high-speed clock or high current switching signals are interference sources, should stay away from sensitive circuits, such as a reset circuit, an analog circuit. You can use the floor to separate them.

3.Wiring

(1) Line width. Considering  technology and carrying capacity to choose width,it can not be less than the minimum line width of the minimum line width PCB manufacturers. While ensuring that the current carrying capacity, generally 1mm / A to select the appropriate width.

(2) The differential signal lines. For USB, Ethernet, differential line, pay attention to alignment to wait long, parallel with the plane spacing by impedance.

(3) Note that the high-speed line return path. High speed line prone to electromagnetic radiation, if the wire path and return path formed area is too large, it will form a single coil radiate electromagnetic interference, as shown in Figure 1. So take the time to pay attention to the line next to the return path, plywood provided with the power and ground planes can effectively solve this problem.

(4) Note that the analog signal line. Analog and digital signal lines should be separated from traces to avoid interference sources (such as clock, DC-DC power supply) walked by, and traces as short as possible.