How many types of pads have you seen in PCB design?

btty038

How many types of pads have you seen in PCB design? [Copy link]

In PCB design, pad is a very important concept, and PCB engineers must be familiar with it. However, although they are familiar with it, many engineers have only a superficial understanding of pad.

Today, Xiaoyi will take you to understand the types of pads and the design standards of pads in PCB design.

Pads are the basic building blocks of surface mount assembly and are used to form the land pattern of a circuit board, which is a combination of pads designed for a particular component type.

A pad is a part of a conductive pattern used for electrical connection, device fixing, or both.

Types of PCB pads

1. Common pads

1. Square pads: This is often used when there are few large components on the printed circuit board and the printed conductors are simple. This type of pad is easy to use when making your own PCB.

2. Round pads - widely used in single-sided and double-sided printed circuit boards with regularly arranged components. If the density of the board allows, the pads can be larger so that they will not fall off during welding.

3. Island pad: The connection between pads is integrated. Commonly used in vertical irregular arrangement installation.

4. Polygonal pads - used to distinguish pads with similar outer diameters but different apertures, to facilitate processing and assembly.

5. Oval pad - This pad has enough area to enhance anti-peeling ability and is often used in dual in-line devices.

6. Open-shaped solder pads - often used to ensure that the manually repaired solder pad holes are not sealed by solder after wave soldering.

2. Special pads

1. Plum blossom pad

Plum blossom pads are usually used in large via grounding locations for the following reasons:

1) The fixing hole needs to be metallized and connected to GND. If the fixing hole is fully metallized, it is easy to block the hole during reflow soldering.

2) The use of internal metal screw holes may cause the grounding to be in a poor state due to installation or multiple disassembly, etc. However, the use of plum blossom hole pads can ensure good grounding regardless of how the stress changes.

2. Cross solder pad

The cross pad is also called hot pad, hot air pad, etc. Its function is to reduce the heat dissipation of the pad during welding to prevent cold soldering or PCB peeling caused by excessive heat dissipation.

1) When your pad is the ground wire, the cross can reduce the area of the ground wire, slow down the heat dissipation, and facilitate welding.

2) When your PCB needs machine placement and a reflow soldering machine, the cross soldering pad can prevent the PCB from peeling (because more heat is needed to melt the solder paste).

3. Teardrop Pad

This is often used when the traces connected to the pads are thin to prevent the pads from peeling and the traces from being disconnected from the pads. This type of pad is often used in high-frequency circuits.

Design standards for pads in PCB design

1. Design standards for the shape and size of PCB pads:

1. Call the PCB standard package library.

2. The minimum single-side diameter of the pad shall not be less than 0.25mm, and the maximum diameter of the entire pad shall not be greater than 3 times the component aperture.

3. Try to ensure that the distance between the edges of the two pads is greater than 0.4mm.

4. Pads with apertures exceeding 1.2mm or pad diameters exceeding 3.0mm should be designed as diamond or plum blossom-shaped pads.

5. In the case of dense wiring, it is recommended to use oval and oblong connection pads. The diameter or minimum width of the single-sided board pad is 1.6mm; the weak current line pad of the double-sided board only needs the hole diameter plus 0.5mm. If the pad is too large, it will easily cause unnecessary soldering.

2. PCB pad via size standards:

The inner hole of the pad is generally not less than 0.6mm, because holes smaller than 0.6mm are difficult to process when punching. Usually, the metal pin diameter plus 0.2mm is used as the inner hole diameter of the pad. For example, when the metal pin diameter of the resistor is 0.5mm, the inner hole diameter of the pad corresponds to 0.7mm. The pad diameter depends on the inner hole diameter.

3. Key points of reliability design of PCB pads:

1. Symmetry: To ensure the balance of surface tension of molten solder, the pads at both ends must be symmetrical.

2. Pad spacing: Too large or too small pad spacing will cause welding defects, so ensure that the spacing between the component ends or pins and the pads is appropriate.

3. The remaining size of the pad. The remaining size after the component end or pin is overlapped with the pad must ensure that the solder joint can form a meniscus.

4. The width of the pad should be basically consistent with the width of the component end or pin.

Source: Internet