According to different components and welding processes, the pads in the printed circuit board can be divided into two types: non-via pads and via pads. Non-via pads are mainly used for soldering of surface mount components, and via pads are mainly used for soldering of stitched components. The choice of pad shape is related to factors such as the shape, size, layout, heating and force direction of the components, and the designer needs to make a choice after comprehensive consideration.
In most PCB design tools, the system can provide designers with different types of pads such as round (Round) pads, rectangular (Rectangle) pads and octagonal (Octagonal) pads.
1. Round pad
In printed circuit boards, circular pads are the most commonly used pads. For the via pad, the main size of the circular pad is the size of the via hole and the size of the pad. There is a proportional relationship between the size of the pad and the size of the via. For example, the size of the pad is generally twice the size of the space. Non-via-type circular pads are mainly used as test pads, positioning pads, and reference pads, etc., and their main size is the pad size.
2. Rectangular pad
Rectangular pads include square pads and rectangular pads. The square pad is mainly used to identify the first pin on the printed circuit board for mounting components. Rectangular pads are mainly used as pin pads for surface mount components. The size of the pad is related to the pin size of the corresponding component, and the pad size of different components is different. In order to avoid device deviation and tombstoning after reflow soldering, pads at both ends of chip components below 0805 and 0805 after reflow soldering should ensure heat dissipation symmetry, and the width of the connection between the pad and the printed wire should not be greater than 0.3 mm (for asymmetric pads).
3. Octagonal Pad
Octagonal pads are relatively seldom used in printed circuit boards. It is mainly set to meet the requirements of the wiring of printed circuit boards and the soldering performance of pads. In the PCB design process, designers can also use some special-shaped pads according to the specific requirements of the design. For example, for some pads with high heat generation, high force and high current, they can be designed in a teardrop shape.
