What Factors Do We Need to Consider when Choosing PCB Components?

Printed circuit boards are mainly composed of PCB boards and various components, and are widely used in various electronic equipment. If the printed circuit board wants to play its due function, it is necessary to pay attention to the following techniques for selecting PCB components.

In the entire schematic drawing stage, the component packaging and land pattern decisions that need to be made in the layout stage should be considered. Some suggestions to consider when selecting components based on component packaging are given below.

(1) The package includes the electrical pad connections and mechanical dimensions (X, Y, and Z) of the component, that is, the appearance of the component body and the pins that connect to the PCB. When selecting components, you need to consider any mounting or packaging restrictions that may exist on the top and bottom layers of the final PCB.

(2) Some components (such as polar capacitors) may have high headroom restrictions, which need to be considered in the component selection process. At the beginning of the design, you can first draw a basic circuit board frame shape, and then place some large-scale or position-critical components (such as connectors) that you 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, frame, etc.) after the PCB is assembled. You can browse the entire circuit board by calling the 3D preview mode from the tools menu.

(3) The land pattern shows the actual land or via the shape of the soldered device on the PCB. These copper patterns on the PCB also contain some basic shape information. The size of the land pattern needs to be correct to ensure correct soldering and the correct mechanical and thermal integrity of the connected components.

(4) When designing the PCB layout, it is necessary to consider how the circuit board will be manufactured, or how the pad will be soldered if it is manually soldered. Reflow soldering (the flux is melted in a controlled high-temperature furnace) can handle a wide range of surface mount devices (SMD).

Wave soldering is generally used to solder the reverse side of the circuit board to fix through-hole devices, but it can also handle some surface mount components placed on the back of the PCB.

Usually, when this technology is used, the bottom surface mount devices must be arranged in a specific direction, and in order to adapt to this soldering method, the pads may need to be modified.

(5) The selection of components can be changed during the entire design process. Determining which devices should use plated through holes (PTH) and which should use surface mount technology (SMT) early in the design process will help the overall planning of the PCB. Factors that need to be considered include device cost, availability, device area density, power consumption, and so on.

From a manufacturing perspective, surface mount devices are generally cheaper than through-hole devices and generally have higher availability. For small and medium-scale prototype projects, it is best to use larger surface mount devices or through-hole devices, which not only facilitate manual soldering but also facilitate better connection of pads and signals during error checking and debugging.

(6) If there is no ready-made package in the database, it is generally to create a customized package in the tool.

Ensure that the design has sufficient bypass capacitors and ground planes. When using an integrated circuit, make sure to use a suitable decoupling capacitor near the power terminal to the ground (preferably a ground plane). The appropriate capacity of the capacitor depends on the specific application, capacitor technology, and operating frequency.

When the bypass capacitor is placed between the power and ground pins and placed close to the correct IC pin, the electromagnetic compatibility and susceptibility of the circuit can be optimized.

Print a bill of materials (BOM) for checking virtual components. Virtual components have no associated packaging and will not be transferred to the layout stage. Create a bill of materials and then view all the virtual components in the design.

The only items should be power and ground signals because they are considered virtual components, which are only processed in the schematic environment and will not be transferred to the layout design. Unless used for simulation purposes, the components displayed in the virtual part should be replaced with encapsulated components.

Check whether there is sufficient data in the bill of materials report. After creating the bill of materials report, it is necessary to carefully check and complete the incomplete device, supplier, or manufacturer information in all component entries.

To facilitate the sorting and viewing of the bill of materials, ensure that the component numbers are consecutively numbered.

Generally speaking, the inputs of all redundant gates should have signal connections to avoid dangling the input terminals. Make sure that you have checked all redundant or missing gate circuits, and all unwired input terminals are completely connected. In some cases, if the input terminal is suspended, the entire system cannot work correctly.

If you want to know more about printed circuit boards after reading the above, you can refer to our past news.

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