What is the function of special pads (plum blossom pads, cross pads, teardrop pads, etc.)?
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1. Plum blossom soldering pad 1: The fixing hole needs to be non-metallized. During wave soldering, if the fixing hole is a metallized hole, the tin will block the hole during the reflow process. 2. The plum blossom soldering pad for the fixed mounting hole is generally for the GND network of the mounting hole, because the copper of the PCB is generally for the GND network. After the plum blossom hole is installed with the PCB shell device, it actually connects the GND to the earth, and in some occasions, the PCB shell plays a shielding role. Of course, some do not need to connect the mounting holes to the GND network. 3. The metal screw hole may be squeezed and broken, resulting in a zero boundary state between grounding and ungrounding, causing strange abnormalities in the system. The plum blossom hole can always keep the screw grounded regardless of how the stress changes. 2. Cross solder pad The cross solder pad is also called thermal solder pad, hot air solder pad, etc. Its function is to reduce the heat dissipation of the pad during welding to prevent cold solder joints or PCB peeling caused by excessive heat dissipation. 1 When your pad is a ground wire. The cross can reduce the area of the ground wire connection, slow down the heat dissipation speed, and facilitate welding. 2 When your PCB needs machine placement and a reflow soldering machine, the cross solder pad can prevent the PCB from peeling (because more heat is needed to melt the solder paste) 3. Teardrop solder pad [color=rgb(62, 62, Teardrop is the drop-type connection between pad and wire or wire and guide hole. The purpose of setting teardrop is to avoid disconnection of wire and pad or wire and guide hole when the circuit board is impacted by huge external force. In addition, setting teardrop can also make the PCB circuit board more beautiful. The role of teardrop is to avoid reflection caused by sudden decrease of signal line width, and to make the connection between trace and component pad smooth and transitional, solving the problem of easy breakage of connection between pad and trace. 1. In welding, it can protect the pad and avoid the pad from falling off due to multiple welding 2. Enhance the reliability of connection (in production, it can avoid uneven etching, cracks caused by offset vias, etc.) 3. Smooth impedance and reduce sharp impedance jumps In circuit board design, in order to make the pad more solid and prevent the pad and the wire from being disconnected during mechanical board making, a transition zone is often arranged between the pad and the wire with copper film. The shape is like a teardrop, so it is often called teardrop. Fourth, discharge teeth Have you seen that the serrated exposed copper foil is deliberately reserved under the common mode inductor of other people's switching power supplies? What is the specific function? [p=26, 2, This is called a discharge tooth, a discharge gap or a spark gap. Using a discharge gap (Sparkgaps) The discharge gap is a pair of triangles pointing to each other with sharp angles, and the fingertips are separated by a maximum of 10mil and a minimum of 6mil. One triangle is connected to the ground and the other is connected to the signal line. This triangle is not a component, but is made by using a copper foil layer during the PCB wiring process. These triangles must be set on the top layer (componentside) of the PCB board and cannot be covered by solder mask. During the switching power supply surge test or ESD test, high voltage will be generated at both ends of the common mode inductor, and arcing will occur. If the distance to the surrounding devices is close, the surrounding devices may be damaged. Therefore, a discharge tube or varistor can be connected in parallel to it to limit its voltage, thereby playing the role of arc extinguishing. Placing lightning protection devices is very effective but the cost is relatively high. Another way is to add discharge teeth at both ends of the common mode inductor during PCB design, so that the inductor discharges through the two discharge tips and avoids discharging through other paths, thereby minimizing the impact on surrounding and subsequent devices. The discharge gap does not require additional costs, and can be drawn when drawing the PCB board. However, it should be noted that this type of discharge gap is an air-type discharge gap and can only be used in environments where ESD is occasionally generated. If it is used in places where ESD often occurs, carbon deposits will be generated at two triangular points due to frequent discharges between the discharge gaps, and eventually a short circuit will be caused on the discharge gap, causing the signal line to be permanently shorted to the ground, thereby causing system failure.
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