Components are the basic elements that constitute a circuit, and are the final result of circuit principle analysis and calculation. In the circuit principle analysis, it is necessary to know the structure, characteristics and parameters of each component, its role in the circuit, and its influence on the entire circuit; in the circuit parameter calculation, each component parameter is the circuit calculation. The final result is convenient for the reasonable selection of the specifications and models of the components. Correct selection of components is the key to realizing circuit functions, and selection methods and skills are very important. So how to quickly select components in pcb design? The following six skills are briefly analyzed for your reference.

1. Consider the choice of component packaging

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

Remember, the package includes the electrical pad connections and mechanical dimensions (X, Y, and Z) of the component, that is, the outline of the component body and the pins that connect to the PCB. When selecting components, consider any mounting or packaging constraints that may exist on the top and bottom layers of the final PCB. Some components, such as polar capacitors, may have height headroom constraints that need to be considered during the component selection process. At the beginning of the design, you can draw a basic circuit board outline shape, and then place some large or location-critical components (such as connectors) that you plan to use. In this way, a virtual perspective view of the circuit board (without routing) can be seen quickly and intuitively, 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 fit properly into the outer packaging (plastics, chassis, chassis, etc.) after the PCB is assembled. Invoke the 3D preview mode from the Tools menu to view the entire board.

The land pattern shows the actual pad or via 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 proper soldering and to ensure the correct mechanical and thermal integrity of the connected components. When designing a PCB layout, you need to consider how the board will be fabricated, or if hand soldered, how the pads will be soldered. Reflow soldering (flux melting in a controlled high temperature furnace) can handle a wide variety of surface mount devices (SMDs). Wave soldering is generally used to solder the reverse side of a circuit board to hold through-hole devices, but can also handle some surface mount components placed on the backside of a PCB. Typically with this technique, the underlying surface mount devices must be aligned in a specific orientation, and pads may need to be modified to accommodate this type of soldering.

The selection of components can be changed throughout the design process. Determining which components should use plated through holes (PTH) and which should use surface mount technology (SMT) early in the design process will help with overall PCB planning. Factors to consider are device cost, availability, device area density, and power consumption. From a manufacturing standpoint, surface-mount devices are generally less expensive than through-hole devices and generally have higher availability. For small and medium-scale prototype projects, it is better to choose larger surface mount devices or through-hole devices, which not only facilitates manual soldering, but also facilitates better connection pads and signals during troubleshooting and debugging.

If there are no ready-made wrappers in the database, custom wrappers are typically created in the tool.

2. Use a good grounding method

Make sure the design has adequate bypass capacitors and ground planes. When using integrated circuits, make sure to use appropriate decoupling capacitors close to the power supply to ground (preferably a ground plane). The appropriate capacitance of the capacitor depends on the specific application, capacitor technology and operating frequency. Electromagnetic compatibility and susceptibility of the circuit can be optimized when bypass capacitors are placed between the power and ground pins and close to the correct IC pins.

3. Assign virtual component packages

Print a bill of materials (BOM) for checking virtual components. Virtual components have no associated footprint and are not passed to the layout stage. Create a bill of materials and view all the virtual components in your design. The only entries should be the power and ground signals, as they are considered virtual components and are only handled exclusively in the schematic environment and are not carried over to the layout design. Components shown in the dummy section should be replaced by components with encapsulation unless used for simulation purposes.

4. Make sure you have complete BOM data

Check that there is enough complete data in the BOM report. After the BOM report is created, double-check and complete any component entries that are incomplete with device, supplier, or manufacturer information.

5. Sort by component label

To aid in the sorting and viewing of the Bill of Materials, ensure that the component numbers are numbered consecutively.

6. Check for redundant gate circuits

In general, all redundant gate inputs should have signal connections to avoid floating inputs. Make sure you check for any redundant or missing gates and that all unwired inputs are fully wired. In some cases, the entire system does not work correctly if the input is left floating. Take the dual op amps that are often used in designs. If only one op amp is used in the dual op amp IC component, it is recommended to either use the other op amp, or ground the input of the unused op amp, and place a suitable unity gain (or other gain) ) feedback network to ensure that the entire element works properly.

In some cases, ICs with floating pins may not work properly within the specifications. Typically, the IC will only meet specifications if the IC device or other gates in the same device are not operating in saturation with the input or output close to or at the component power rails. Simulation often fails to capture this because simulation models generally do not connect parts of an IC together to model floating connection effects.

This article can only lead you to a preliminary understanding of the selection of pcb components. I hope it will be helpful to you. At the same time, you need to keep summarizing, so as to improve your professional skills. You are also welcome to discuss some knowledge points of the article.