Types of pads in PCB design, how many have you seen?

In PCB design, the pad is a very important concept, but many experienced PCB engineers on the knowledge of the pad but also half-knowledge, today we will take you to understand the knowledge of the pad.

Pad, that is, the surface mount assembly of the basic components of the unit, used to constitute the circuit board pad pattern (land pattern), that is, a variety of special component types designed for the combination of pads.

Pad for electrical connection, device fixation or both part of the conductive pattern.

Types of PCB pads

First, the common pad

  1. Square pads – printed circuit board components large and small, and printed wires are simple to use. In the handmade PCB, the use of this pad is easy to realize.
  2. Round pads – widely used in the regular arrangement of components in a single, double-sided printed circuit board. If the density of the board allows, the pad can be larger, welding does not fall off.
  3. Island-shaped pads – pads and pads between the line into one. Commonly used in vertical irregular arrangement of the installation.
  4. Polygonal pads – used to distinguish between the outer diameter close to the aperture of different pads, easy to process and assemble.
  5. Oval pad – this pad has enough area to enhance the peeling resistance, commonly used in double in-line devices.
  6. Open pads – in order to ensure that the wave soldering, so that the handmade pad holes are not sealed by the solder commonly used.

Second, special pads

1.Plum pads

Plum pads are usually used in large holes grounded position, so the design has the following reasons:

(1) The fixed hole needs to be metallized and GND connected, if the fixed hole is fully metallized, in the reflow soldering is easy to block the hole.

(2) The use of internal metal screw holes may cause the ground to be in a bad state due to installation or multiple disassembly. And the use of plum blossom hole pads, no matter how the stress changes, can ensure good grounding.

2.Crosshatch pads

Crosshatch pads, also known as hot pads, hot air pads, etc.. Its role is to reduce the pad in the welding of heat dissipation to the outside, in order to prevent false soldering or PCB skinning caused by excessive heat dissipation.

(1) When your pad is ground. The crosshair can reduce the area of the connected ground line, slow down the heat dissipation and facilitate soldering.(

(2) When your PCB is required to machine patch, and reflow soldering machine, crosshatch pads can prevent PCB skinning (because more heat is needed to melt the solder paste).

3.Tear drop pads

When the pad is connected to the alignment of the thinner often used to prevent the pad skinning, alignment and pad disconnect. This pad is often used in high-frequency circuits.

PCB design pad design standards

First, the shape and size of the PCB pad design standards:

  1. Call the PCB standard package library.
  2. There are pads on one side of the minimum is not less than 0.25mm, the entire pad diameter is not greater than the maximum component aperture diameter of 3 times.
  3. Try to ensure that the distance between the two pad edges is greater than 0.4mm.
  4. Aperture diameter of more than 1.2mm or pad diameter of more than 3.0mm pad should be designed as a diamond or plum-shaped pad.
  5. Wiring denser case, the recommended use of oval and oblong connection plate. Single-panel pad diameter or minimum width of 1.6mm; dual-panel weak line pad only hole diameter plus 0.5mm can be, the pad is too large easily caused by unnecessary continuous welding.

Second, the PCB pad hole size standards:

Pad hole is generally not less than 0.6mm, because less than 0.6mm hole mold punching is not easy to process, usually to the value of the metal pin diameter plus 0.2mm as the diameter of the pad hole, such as resistors of the metal pin diameter of 0.5mm, the diameter of the pad hole corresponds to 0.7mm, the pad diameter depends on the diameter of the hole.

Third, the reliability of the PCB pad design points:

  1. Symmetry, in order to ensure the balance of surface tension of molten solder, the two ends of the pad must be symmetrical.
  2. Pad spacing, pad spacing is too large or too small will cause welding defects, so make sure that the component ends or pins and pad spacing is appropriate.
  3. The remaining size of the pad, component ends or pins and pads after the lap of the remaining size must ensure that the solder joints can form a curved moon face.
  4. The width of the pad, should be basically the same as the width of the component end or pin.
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