PCB packaging is actually to display various parameters (such as size, length and width, pad size, etc.) of components and chips in a graphical way, so that they can be invoked when drawing PCB drawings. So before the design of PCB, the choice of components becomes the most important. Otherwise, there will always be some problems in the design, which will lead you to spend a lot of time designing PCB boards that can never be used in practice.
PCB packaging is actually to display various parameters (such as size, length and width, pad size, etc.) of components and chips in a graphical way, so that they can be invoked when drawing PCB drawings. So before the design of PCB, the choice of components becomes the most important. Otherwise, there will always be some problems in the design, which will lead you to spend a lot of time designing PCB boards that can never be used in practice. Today, I will introduce some points that need to be paid attention to when choosing PCB components.
How to Select Components Based on Packaging
This article mainly talks about the skill of analyzing and selecting components from PCB design package. The package of components contains a lot of information, including the size of components, especially the relative position of pins, and the type of pad of components. Of course, when we choose components according to their packaging, we should also pay attention to the shape and size of the components.
Pin position relationship: mainly refers to the need to match the actual pin of the component with the packaging size of the PCB component. We choose different components, although the functions are the same, but the packaging of components is likely to be different. We need to ensure the correct size and position of PCB pad to ensure that the components can be welded correctly.
Pad selection: This is what we need to consider more.
First of all, it includes the type of pad. Its type includes two kinds, one is electroplating through hole, the other is surface mounting type. We need to consider factors such as device cost, availability, device area density and power consumption. From the manufacturing point of view, surface mounted devices are usually cheaper than through-hole devices, and generally have higher usability. For our general design, we choose the table-mounted components, which is not only convenient for manual welding, but also conducive to better connection of pads and signals in the process of error investigation and debugging.
Secondly, we should pay attention to the position of the pad. Because different locations represent different locations in the actual components. If we do not arrange the position of the pad reasonably, it is likely that one area element is too dense, while the other area element is very sparse. Of course, the situation is worse because the pad position is too close, resulting in too small gap between components to weld. Here is an example of my failure. The through holes are opened beside the optocoupler switches, but because of their close position, the through holes can not be placed with screws after the optocoupler switches are welded.
Another case is that we have to consider how the pads are welded. In practice, we often arrange the pads in a specific direction, which is more convenient to weld.
Component dimensions: In practical applications, some components (such as polar capacitors) may have a high clearance limit, so we need to consider it in the process of component selection. When we first started the design, we could draw a basic circuit board frame shape and then place some large or location-critical components (such as connectors) that we planned to use. In this way, the Virtual Perspective of PCB (without wiring) can be seen intuitively and quickly, and the relative positioning and component height of PCB and components with relative accuracy are given. This will help to ensure that PCB components are properly packaged into the outer packaging (plastic products, chassis, frame, etc.) after assembly. Of course, we can also browse the whole circuit board by calling the three-dimensional preview mode from the tool menu.
For the selection of components, besides the design requirements, we should also choose the products manufactured by the regular manufacturers, so as to ensure the realization of your design goals.