Analysis of the types of pads and design standards in PCB design

Pads are a very important concept inPCB Design and PCB engineers are no stranger to it. However, although familiar, many engineers have little knowledge of the pad. The types and design standards of the pads in the PCB design are detailed below.

First, the type of pad

In general, the pads can be divided into 7 categories, according to the shape of the following

Square pads - large and small components on printed boards, and used when printed conductors are simple. This type of pad is easy to implement when making a PCB by hand.

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

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

Teardrop Pads - Used when the traces on the pad are thinner to prevent pad ping, routing, and pad disconnection. Such pads are commonly used in high frequency circuits.

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

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

Open-type pad - In order to ensure that the pad holes for manual repair welding are not sealed by solder after wave soldering.

Second, the design of the shape and size of the pad in the PCB design

  1. All pads have a minimum of 0.25 mm on one side and a maximum diameter of not more than 3 times the aperture of the component.

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

  3. In the case of dense wiring, it is recommended to use oval and oblong lands. The diameter or minimum width of the single-panel pad is 1.6 mm; the weak-circuit pad of the double-panel requires only 0.5 mm of the hole diameter. If the pad is too large, it may cause unnecessary soldering, and the hole diameter exceeds 1.2 mm or the pad diameter. Pads over 3.0 mm should be designed as diamond or plum-shaped pads.

  4. For plug-in components, in order to avoid copper foil breakage during soldering, and the single-sided lands are completely covered with copper foil; the minimum requirements for double-panel should be filled with teardrops.

  5. All machine insert parts should be designed as drip pads along the bend direction to ensure that the solder joints at the bends are full.

  6. Pads on large areas of copper should be daisy-like pads, not just soldered. If there is a large area of ​​ground and power line area on the PCB (area over 500 mm2), it should be partially opened or designed as a grid fill.

Third, PCB manufacturing process requirements for the pad

  1. Test points should be added to the components of the chip that are not connected to the plug-in components. The test point diameter is equal to or greater tha1.8 mm to facilitate the online tester test.

  2. The IC pad with dense pitch should be added with test pad if it is not connected to the hand pad. If it is a chip IC, the test point cannot be placed in the chip IC silk screen. The test point diameter is equal to or greater than 1.8 mm for on-line tester testing.

  3. If the pad pitch is less tha0.4 mm, white oil should be applied to reduce the over-peak soldering.

  4. The ends and ends of the chip components shall be designed with lead-in solder. The width of the lead-in solder is recommended to b0.5 mm. The length is generally 2 or 3 mm.

  5. If there is a hand-welded component on a single panel, the tin bath should be opened, the direction is opposite to the direction of the tin, and the width of the hole is 0.3MM to 1.0MM.

  6. The spacing and size of the conductive rubber buttons should match the size of the actual conductive rubber buttons. The PCB board connected to this should be designed as a gold finger and the corresponding gold plating thickness should be specified.

  7. The pad size and spacing should be the same as the chip component size.

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