Talking about the selection of PCB components from packaging

- Apr 21, 2017-

In a recent painting PCB design, the component selection, PCB layout design, wiring design always encounter a variety of problems, leading to the final spent lots of time doing out of the board can not be used in practice, so I specially from the Internet to find some information about the design of the PCB, PCB design there are really a lot of interesting places.

This is mainly from the component package to select components. The package contains a lot of information, including the size of the components, especially the relative position of the pin, as well as the type of the components. Of course, we have a choice of components according to the component when there is a need to pay attention to the place is to consider the external dimensions of the components.

Pin position relationship: mainly refers to the actual components of the pin and PCB components of the package size corresponding. We choose different components, although the same function, but the components of the package may not be the same. We need to ensure that the size of the PCB pad is correct to ensure that the components are properly welded.

The choice of pad: This is a lot of places we need to consider. First, including the type of pad. Its type includes two kinds, one is plating through hole, one is the surface paste type. We need to consider factors such as device cost, availability, device area density and power consumption. From a manufacturing perspective, surface mount devices usually by hole device, cheap, and generally high availability. For our general design, we choose to stick to the table components, not only to facilitate manual welding, but also in favor of troubleshooting and debugging process better connection pad and signal.

Second, we should also pay attention to the location of the pad. Because of the different position, it represents the actual location of the components. If we do not arrange the pad position, it is possible to appear a regional element too close, while another area element is sparse, of course, the situation is even worse because the pad position too close, resulting in the gap between the components is too small to be welded, the following is an example of my failure, I opened the hole at the side of a optocoupler switch, but because their position is too close, after leading optocoupler switch welding up, through holes to the screw placement.

Another situation is that we have to consider how the welding pad. In the actual process, we often arrange a pad in a specific direction, welding is more convenient.

Component dimensions: in practical applications, some components may have high headroom limitations, so we need to be considered in the component selection process. At the beginning of our design, we can draw a basic outline of the circuit board, and then place some of the major or key components to be used. In this way, the Virtual Perspective of the circuit board can be seen visually and quickly. This will help ensure that the PCB is properly packed into the outer package after assembly. Of course, we can also call the menu from the three dimensional preview mode to view the entire circuit board.

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