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  • Six skills of selecting components in PCB design
    Date :2017-4-14

    One, Component selection
    At the time of selecting the components, the final PCB top layer and the bottom layer may be considered for any installation or packaging restrictions. Some components (such as a polar capacitor) may have a high clearance limit and need to be considered in the component selection process. At the beginning of the design, you can draw a basic outline of the circuit board shape, and then put on some of the plans to use large or position critical components (such as connectors). In this way, we can see the visual view of the circuit board visually and quickly, and give the relative precision of the relative position and the height of the circuit board and the components. This will help ensure that the PCB can be properly packed into the outer packaging (plastic, chassis, frame, etc.). From the tools menu, you can browse the entire board.
    In the design of PCB layout, it is necessary to consider how the circuit board will be manufactured, or manual welding, the welding pad will be how. Reflow soldering (flux melting in a controlled high temperature furnace) can handle a wide variety of surface mount devices (SMD). Wave soldering is generally used to weld the reverse side of the circuit board to fix the hole through the device, but can also be placed on the back of the PCB to handle some of the surface mount components.
    In general, when the technique is used, the underlying surface mount devices must be arranged in a particular direction, and in order to adapt to this type of welding, it may be necessary to modify the pads. The selection of components can be changed throughout the design process. In the early stages of the design process to determine which devices should be plated through hole (PTH), which should be using the PCB (SMT) will help the overall planning. Factors to consider include device cost, availability, device area density, power consumption, etc.. From a manufacturing perspective, surface mount devices usually by hole device, cheap, and generally high availability. For small and medium scale prototype projects, it is best to choose a larger surface mount device or through the hole device, not only to facilitate manual welding, but also conducive to error checking and debugging process better connection pad and signal.


    Two, use a good grounding method
    Ensure that the design has adequate bypass capacitance and ground plane. In the use of integrated circuits, ensure that the appropriate decoupling capacitors are located near the power supply to the ground (preferably the ground plane). The appropriate capacity of the capacitor depends on the specific application, capacitance and operating frequency. When the bypass capacitor is placed between the power supply and the ground pin and is placed near the correct IC pin, the electromagnetic compatibility and susceptibility of the circuit can be optimized.


    Three, distribution of virtual component packaging
    Print a list of materials (BOM) for checking virtual components. Virtual components are not related to the package, will not be sent to the layout stage. Create a list of materials and see all the virtual components in the design. The only entries should be power and ground signals, because they are considered virtual elements, only in the schematic environment for special processing, will not be transferred to the layout design. Unless it is used for simulation purposes, the components shown in the virtual part should be replaced with encapsulated components.


    Four, Make sure you have a complete list of materials
    Check the material list report for sufficient data. After the material list report has been created, it should be carefully checked to complete the incomplete information of all components, suppliers or manufacturers.


    Five, according to the component label sorting
    To help sort and view the list of materials, make sure that the component labels are numbered consecutively.


    Six, check the redundant door circuit
    In general, the input of all redundant doors should be connected to the signal, so as to avoid the input suspended. Make sure you check all the redundant or missing door circuits, and all the inputs that are not connected are fully connected. In some cases, if the input is in suspension, the whole system is not working properly. Take the design of the dual operational amplifier. If the dual op amp IC element only one operational amplifier, a suggestion or put another op amps used up, or will not have the operational amplifier is connected with the input end, and placed a suitable unit gain (or gain) feedback network, so as to ensure the whole device can work normally.
    In some cases, the presence of a suspension pin of the IC may not function properly within the target range. This IC is usually used only when the IC device or other gate in the same device does not work in saturation state, when the input or output is close to or on the component supply rail. Simulation is not usually possible to capture this situation, because the simulation model is generally not connected to a number of parts of the IC used to model the suspension connection effect.


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