What exactly does the“Special pad” on the PCB board do?
2024-07-27
Cross plum pads
1. The fixing hole needs to be non-metallic. In wave soldering, if the fixing hole is a metallized hole, the tin will block the hole during the reflow soldering process.
2. The fixed mounting hole is generally used to install the GND network for the installation hole, because the general PCB copper is poured for the GND network, and after the plum hole is installed with the PCB shell device, it is actually connected to the GND and the earth, and the PCB shell plays a shielding role on some occasions. Of course, some do not need to connect the mounting holes to the GND network.
3. The metal screw hole may be squeezed out, resulting in the zero boundary state of grounding and non-grounding, resulting in the wonderful abnormality of the system.
Cross-solder pads
Also known as hot pads, hot air pads, etc. Its function is to reduce the heat dissipation of the pads during soldering to prevent virtual soldering or PCB peeling due to excessive heat dissipation.
1. When your pad is ground. The cross flower can reduce the area of the ground wire, slow down the heat dissipation, and facilitate soldering.
2. When your PCB needs machine mounting, and it is a reflow soldering machine, the cross-solder pad can prevent the PCB from peeling (because more heat is needed to melt the solder paste)
Teardrop pads
The purpose of setting teardrops is to avoid the contact point between the wire and the pad or the wire and the guide hole when the circuit board is hit by a huge external force, and in addition, setting the teardrop can also make the PCB circuit board appear more beautiful.
The function of TearDrop is to avoid reflection caused by the sudden reduction of the signal line width, which can make the connection between the trace and the component pad tend to be a smooth transition, and solve the problem that the connection between the pad and the trace is easy to break.
1. In welding, the pad can be protected to avoid multiple soldering is the fall off of the pad
2. Strengthen the reliability of the connection (production can avoid uneven etching, cracks in the deviation of vias, etc.)
3. Smooth impedance and reduce the sharp jump of impedance
In the design of circuit boards, in order to make the pads stronger and prevent the disconnection between the pads and the wires during mechanical board making, a transition area is often arranged with a copper film between the pads and the wires, which is shaped like teardrops, so it is often called teardrops
Discharge teeth
Discharge teeth are also a type of "special pad", which are a pair of triangles pointing at acute angles opposite each other, made by using a layer of copper foil during the PCB design and routing process. These triangles need to be placed on another layer of the PCB board components and cannot be covered by green oil.
It is mainly used to avoid damage to the circuit board by static electricity. The discharge teeth are able to absorb static electricity that comes into contact with the circuit board and direct it to the ground or ground wire, thus preventing the accumulation and release of static electricity, protecting the electronic components on the circuit board from static damage.
During surge testing or ESD testing, high voltage is generated across the common mode inductor, resulting in arcing. If you are in close proximity to surrounding devices, you may damage them. So you can connect a discharge tube in parallel on it to suppress its voltage. For example, the gas discharge tube is connected in parallel at both ends of the common mode inductor to play the effect of arc extinguishing. Although the suppression effect of gas discharge tubes is good, the cost is relatively high.
Therefore, in many cases, discharge teeth can be placed at both ends of the common mode inductor so that the common mode inductor can be discharged through the tip of the discharge tooth, which can reduce or avoid discharging through other paths, thus protecting the surrounding and subsequent devices.
This discharge tooth is discharged in the form of air, so it should be paid attention to the different aspects of the common mode inductor when designing, although it can play a certain effect, but for the occasion where it is often associated with inrush current voltage and ESD, if this discharge tooth is used, it will be easy to produce carbon deposits, and it will cause a short circuit after a long time.
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