What are the functions of the "special pads" on the PCB board?
Plum blossom pad
1. The fixing holes need to be non-metallized. During wave soldering, if the fixing hole is a metalized hole, tin will block the hole during reflow soldering.
2. Fixing mounting holes as quincunx pads is generally used for mounting hole GND network, because generally PCB copper is used to lay copper for GND network. After quincunx holes are installed with PCB shell components, in fact, GND is connected to the earth. On occasion, the PCB shell plays a shielding role. Of course, some do not need to connect the mounting hole to the GND network.
3. The metal screw hole may be squeezed, resulting in a zero-boundary state of grounding and ungrounding, resulting in a strange abnormality of the system. The plum blossom hole, no matter how the stress changes, can always keep the screw grounded.
Cross flower pad
Cross flower pads are also called thermal pads, hot air pads, etc. Its function is to reduce the heat dissipation of the pad during soldering to prevent the virtual soldering or PCB peeling caused by excessive heat dissipation.
1. When your pad is ground. The cross pattern can reduce the area of the ground wire, slow down the heat dissipation speed, and facilitate welding.
2. When your PCB requires machine placement and is a reflow soldering machine, the cross-pattern pad can prevent the PCB from peeling (because more heat is needed to melt the solder paste)
Teardrops are excessive dripping connections between the pad and the wire or the wire and the via. The purpose of the teardrop is to avoid the contact point between the wire and the pad or the wire and the via when the circuit board is hit by a huge external force. Disconnect, in addition, set teardrops can also make the PCB circuit board look more beautiful.
The function of teardrop is to avoid the sudden decrease of the signal line width and cause reflection, which can make the connection between the trace and the component pad become a smooth transition, and solve the problem that the connection between the pad and the trace is easily broken.
1. When soldering, it can protect the pad and avoid the falling off of the pad due to multiple soldering.
2. Strengthen the reliability of the connection (production can avoid uneven etching, cracks in via deviation, etc.)
3. Smooth impedance and reduce the sharp jump of impedance
In the design of the circuit board, in order to make the pad stronger and prevent the pad and the wire from being disconnected during the mechanical manufacturing of the board, a copper film is often used to arrange a transition area between the pad and the wire, which is shaped like a teardrop, so it is often called Teardrops.