PCB News - PCB design skills-the choice of component packaging

Recently, when drawing PCB design, due to component selection, PCB layout design, routing design, I always encountered various problems, which led to the board that took a lot of time to make cannot be used in practice, so I I specially found some information about PCB design from the Internet, and found that there are really many points worth noting in the PCB design. What I am telling you today is the information I found in one of the articles, which is about some noteworthy points in the selection of PCB components.

This mainly refers to the selection of components from component packaging. The package of a component contains a lot of information, including the size of the component, especially the relative position of the pins, and the type of pad of the component. Of course, when we select components based on component packaging, there is another point to pay attention to is to consider the external dimensions of the components.

Pin position relationship: It mainly means that we need to correspond the actual component pins with the package size of PCB components. We choose different components. Although the functions are the same, the package of the components is likely to be different. We need to ensure that the PCB pad size and position are correct to ensure that the components can be soldered correctly.

The choice of the pad: This is the more we need to consider.

First include the type of pad. There are two types, one is plated through holes, and the other is surface mount type. We need to consider factors such as device cost, availability, device area density and power consumption. From a manufacturing perspective, surface-mount devices are generally cheaper than through-hole devices and generally have higher availability. For our general design, we choose surface mount components, which not only facilitates manual soldering, but also facilitates better connection of pads and signals in the process of error checking and debugging.

Secondly, we should also pay attention to the location of the pad. Because the different positions represent different positions in the actual components. If we do not arrange the location of the pads reasonably, it is very likely that the components in one area will be too dense, and the components in the other area will be sparse. Of course, the situation is even worse because the pads are too close, resulting in gaps between the components. It is too small to be soldered. The following is an example of my failure. I opened a through hole next to an optocoupler switch, but due to their close position, after the optocoupler switch is soldered, the through hole can no longer be used for screws.

Another situation is that we have to consider how the pads are soldered. In the actual process, we often arrange the pads in a specific direction, which is more convenient to solder.

Component dimensions: In practical applications, some components (such as polar capacitors) may have high headroom restrictions, so we need to consider them in the component selection process. When we first start the design, we can first draw a basic circuit board frame shape, and then place some large-scale or position-critical components (such as connectors) that we plan to use. In this way, the virtual perspective view of the circuit board (without wiring) can be seen intuitively and quickly, and the relative positioning and component height of the circuit board and components can be given relatively accurate. This will help ensure that the components can be properly placed in the outer packaging (plastic products, chassis, chassis, etc.) after the PCB board is assembled. Of course, we can also call the 3D preview mode from the Tools menu to browse the entire circuit board.