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          What should we pay attention to when designing circuit board?

          2021-07-17 347

            1. Spacing between patches

            It is a problem that engineers need to pay attention to the spacing between chip components in layout. If the spacing is too small, it is difficult to print solder paste and prevent solder continuity.

            The interval claims are as follows

            Requirements for equipment spacing between patches:

            Same kind of equipment: ≥ 0.3mm

            Heterogeneous equipment: ≥ 0.13 * H + 0.3mm (H is the height difference of adjacent components)

            The isolation requirements between the components that can only be used for technical mounting: ≥ 1.5mm

            The above ideas are for reference only, and can be in accordance with the PCB process design specifications of their respective companies

            2. Distance between in line equipment and patch

            As shown in the figure above, the gap between the in-line resistor and the chip should be 1-3mm. Due to the difficulty in processing, the use of in-line plug-ins is rare now.

            3. On the placement of decoupling capacitors in IC

            Decoupling capacitors should be placed near the power ports of each IC, and the position should be as close as possible to the power ports of the IC. When a chip has multiple power ports, decoupling capacitors should be placed at each port.

            4. Pay attention to the placement direction and spacing of components on the edge of PCB board

            Because PCB is usually made of tailor-made boards, the demand of equipment near the edge meets two conditions.

            The most important thing is to be parallel to the cutting direction (so that the mechanical stress of the equipment is uniform. For example, assuming that the equipment is placed according to the method on the left side of the figure above, the stress direction of the two pads of the patch is different when the panel is to be split, which may cause the element and pad to fall off)

            Then, the equipment can not be installed within a certain interval (to prevent the equipment from being damaged when the board is cut)


            5. Pay attention to the situation that adjacent pads are connected

            Assuming that the adjacent pads need to be connected, it is first recognized that the connection should be carried out outside, so as to prevent the connection from forming a group to form a bridge, and pay attention to the width of copper wire at this time.

            6. Assuming that the pad falls on the general area, the heat dissipation should be considered

            Assuming that the pad falls in the paved area, the method on the right should be used to connect the pad and the paved area, and whether to connect one wire or four wires should be determined according to the current magnitude.

            If we choose the left side method, it is difficult to weld or repair the equipment. Because the temperature is loose through the copper, the welding can not be done.

            7. If the lead wire is smaller than the plug-in pad, you need to add tears

            Assuming that the wire is smaller than the pad of in-line equipment, we need to add the method on the right side of the figure above.

            There are two advantages of adding teardrops

            To prevent the signal linewidth from suddenly becoming smaller and forming reflection, the connection between the wire and the component pad tends to be smooth transition.

            The problem that the connection between pad and wire is cracked by impact force is solved.

            Setting teardrop can also make PCB more beautiful.

            8. The width of lead wires at both ends of the component pad should be the same

            The width of lead wire at both ends of the component pad should be the same

            9. Pay attention to keep the unused pin pad and ground

            Pay attention to keep the unused pin pad and ground it correctly.

            For example, the two pins of a chip in the figure above should not be used. However, there are various pins in the chip. Suppose that the two pins are suspended as shown in the method on the right of the figure above, which is very simple to cause trouble. It is assumed that the addition of pads and the grounding of pads can prevent interference.

            10. Don't punch the through hole on the pad

            Pay attention that the through hole should not be punched on the pad, which may cause solder leakage.

            11. Pay attention to the distance between the wire or component and the edge of the board

            It should be noted that the lead wires or components should not be too close to the edge of the board, especially the single panel. Generally, the single panel is mostly paper board, which will crack slightly after being stressed. It is assumed that the connection at the edge or the components will be affected.

            12. It is necessary to consider that the ambient temperature of electrolytic capacitor is far away from heat source

            The first thing to consider is whether the ambient temperature of the electrolytic capacitor meets the requirements, and the second thing is to keep the capacitor away from the heating area as far as possible, so as to prevent the liquid electrolyte inside the electrolytic capacitor from drying.

                 The article comes from:http://www.marysbrideandformals.com


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