Choosing six tips for PCB components

1, consider the choice of component packaging Throughout the schematic drawing stage, you should consider the component packaging and pad pattern decisions that need to be made at the layout stage. Some of the recommendations that need to be considered when selecting components based on component packaging are given below. Remember that the package includes the electrical pad connection and the mechanical dimensions (X, Y, and Z) of the component, ie the profile of the component body and the pins that connect the PCB. When selecting a component, it is necessary to consider any installation or packaging limitations that may exist on the top and bottom layers of the final PCB. Some components (if polar capacitors) may have a high clearance limit and 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 placed on some plans to use the large or location key components (such as connectors).  In this way, the virtual perspective of the circuit board (without wiring) can be viewed intuitively and visually and the relative positioning and component height of the relatively accurate circuit boards and components are given. This will help to ensure that the PCB components can be properly assembled into the outer packaging (plastic products, chassis, chassis, etc.). You can view the entire board by calling the 3D preview mode from the Tools menu. The pad pattern shows the actual pad or via shape of the welded device on the PCB. These copper patterns on the PCB also contain some basic shape information. The size of the pad pattern needs to be correct to ensure proper welding and to ensure correct mechanical and thermal integrity of the connected components. In the design of PCB layout, you need to consider how the circuit board will be manufactured, or manual welding, then how will the welding pad. Reflow (flux in a controlled high temperature furnace) can handle a wide range of surface mount devices (SMD). Wave soldering is generally used to weld the opposite side of the circuit board to secure the through-hole device, but it can also handle some surface-mount components placed on the back of the PCB. Often when using this technology, the bottom surface mount device must be arranged in a specific direction, and in order to adapt to this welding method, may need to modify the pad. The choice of components can be changed throughout the design process. In the early stages of the design process to determine which devices should use electroplated through-holes (PTH), which should be used to surface-mount technology (SMT) will contribute to the overall planning of the PCB. Factors to consider include device cost, availability, device area density, and power consumption. From the manufacturing point of view, the surface mount device is usually cheaper than the through-hole devices, and generally high availability. For small and medium-sized prototype projects, it is best to use a larger surface-mount devices or through-hole devices, not only convenient manual welding, but also conducive to troubleshooting and debugging process better connection pads and signals. If there is no ready-made package in the database, it is common to create custom packages in the tool.  2, use a good grounding method Ensure that the design has sufficient bypass capacitance and ground plane. When using an integrated circuit, make sure that the appropriate decoupling capacitor is used near the power supply to ground (preferably ground plane). The appropriate capacity of the capacitor depends on the specific application, capacitance technology and operating frequency. When the bypass capacitor is placed between the power supply and the ground pin, and close to the correct IC pin placed, you can optimize the circuit's electromagnetic compatibility and susceptibility.  3, the allocation of virtual components package Print a bill of materials (BOM) to check for virtual components. Virtual components are not associated with the package and will not be delivered to the layout phase. Create a bill of material and view all the virtual components in the design. The only entries should be power and ground signals, because they are considered virtual components, only in the schematic environment for specialized processing, will not be sent to the layout design. Unless used for simulation purposes, the elements shown in the virtual part should be replaced with a component with a package.  4, make sure you have complete bill of materials data Check if there is sufficient data in the bill of lading report. After creating a bill of material report, make a thorough review of the completeness of the incomplete device, supplier, or manufacturer information for all component entries.  5, according to the component label to sort To help sort and view the bill of materials, make sure that the component labels are numbered consecutively.  6, check the excess door circuit In general, all the extra gate inputs should have signal connections to avoid floating the input terminals. Make sure you check out all the extra or missing gates, and that all unconnected inputs are fully connected. In some cases, if the input is in a floating state, the entire system can not work correctly. Take the design used in the dual op amp is used. If a dual op amp IC component uses only one op amp in its www.pcblover.com, it is recommended that either another op amp be used or ground the unused op amp input and lay out a suitable Unit gain (or other gain) feedback network to ensure that the entire component is working properly. In some cases, the IC with the floating pin may not work properly within the target range. Usually only when the IC device or other gate in the same device is not working in a saturated state - the input or output is close to or in the component power rail, the IC can meet the requirements of the work. Simulation usually does not capture this situation because the simulation model generally does not connect multiple parts of the IC together to model the floating connection effect.