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PCB manufacturing board pad types and through holes setting specifications

316 Published by FASTPCBA 9月 09,2019

PCB manufacturing board pad types and through holes setting specifications

Pad is basic constituent unit of a surface mount assembly during pcb manufacturing, used to form the land pattern of a board, that is, a variety of pad combinations designed for a particular component type.

pcb manufacturing

pcb manufacturing

 

First, the type of pad

In general, the pads can be divided into 7 categories, which are distinguished by shape as follows:

  1. Square pad—The components on the printed pcb manufacturing board are large and less, and which is used for simple printed wiring. This type of pad is easy to implement formanual pcb manufacturing.

 

  1. Round pads – are widely used in single and double-sided pcb manufacturing boards with regularly arranged components. If the density of the board permits, the pad can be larger enough and will not fall off during soldering.

 

  1. Island-shaped pad – the connection between the pad and the pad is integrated. Often used in vertical irregular arrangement installation. Such pads are often used in tape recorders.

 

  1. Teardrop Pads – used for thetraces of the pad connections are thin, to prevent the pads from peeling, the traces from being disconnected from the pads. Such pads are commonly used in high frequency pcb manufacturing circuitboards.

 

  1. Polygon Pads – Used to distinguish pads with different outer diameters and apertures for easy processing and assembly.

 

  1. Elliptical Pads – These pads have sufficient area to enhance stripping resistance and are commonly used in dual in-line devices.

 

  1. Open-type pad – In order to ensure that the pad hole of the manual repair welding is not sealed by solder after wave soldering.

 

Second, the thermal peering of the pad

When the pins of the SMD device are connected to the large-area tube foil, thermal isolation treatment is required. Otherwise, soldering defects may occur due to uneven heat at both ends of the device during pcb manufacturing.

Third, the reflow soldering process through hole setting

  1. The diameter of the general via hole is not less than 0.75mm;
  2. Except for SOIC, QFP, PLCC and other devices, it is not possible to setthrough holes under other components;
  3. The via hole cannot be designed in the middle of the two pads of the chip component on the soldering surface;
  4. It is not allowed to directly use the via hole as the pad of the BGA device;
  5. A thin wire coated with a solder mask should be connected between the via and the pad. The length of the thin wire should be greater than 0.5mm; the width should be greater than 0.4mm.

It is absolutely necessary to avoid the placement of the via holes in the surface mount pads. The via holes should be placed within 0.635 mm from the surface mount pads. The vias should be connected through a small length of wire and the solder drain channel should be blocked by solder resist during pcb manufacturing. Otherwise, defects such as “slices” or “insufficient solder”.

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