PCB News - FR4 double-sided circuit board/How much do you know about pads?

FR4 double-sided circuit board/How much do you know about pads?

The land is the basic unit of PCB boardmounting and assembly, and the tool used to compose the land pattern of the circuit board. It is indispensable to be an excellent PCB engineer to have a stock of common sense of the land.

According to the component manual to draw a lot of people and cities, but when you draw, you should pay attention to how to draw the best pad. Sharing some small skills above will make you more advanced and more complete.

Variety of pad

Generally speaking, the pads can be divided into 6 categories. According to the shape, the following are distinguished:

1. Square pads-more used when the printed circuit board components are large and few, and the printed wires are simple. In the manual cheap PCB, it is easy to adopt this kind of pads.

2. Circular pads-commonly used in single and double-sided printed boards where the component rules are arranged. If the board density permits, the pad can be larger so that it will not fall off during soldering.

3. Island-shaped pad-the connection between the pad and the pad is integrated. It is often used in vertical illegal placement installation. For example, these types of pads are often used in radio tape recorders.

4. Teardrop pads-when the traces connected to the pads are thinner, it is often used to prevent the pads from peeling and the traces are disconnected from the pads. Such pads are often used in high-frequency circuits.

5. Polygonal pads-used to distinguish pads with close outer diameters but different apertures, which is convenient for processing and assembly.

6. Oval pad-this type of pad has sufficient area to enhance the anti-stripping ability, and is often used in dual in-line devices. Tooth-shaped pad-In order to ensure that after wave soldering, the manually repaired pad hole is not sealed by solder.

The dimensions of the shape and size of the pad in the PCB design

1. The minimum single side of all pads is not less than 0.25mm, and the maximum diameter of all pads is not more than 3 times the component aperture.

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

3. In a dense wiring environment, it is recommended to adopt oval and oblong adjacent disks. The diameter or minimum width of the single-sided board pad is 1.6mm; the weak-current circuit pad of the double-sided board only needs to add 0.5mm to the hole diameter. If the pad is too large, it will easily cause unnecessary continuous soldering. The hole diameter exceeds 1.2mm or the diameter of the pad. Pads that span 3.0mm should be considered diamond-shaped or quincunx pads.

4. For plug-in components, in order to prevent copper foil breakage during soldering, the single-sided adjoining plate is completely covered with copper foil; the minimum requirement for double-sided panels should be to make up for teardrops.

5. All machine insert parts need to be designed as drip pads along the bent foot mark to ensure that the solder joints at the bent foot are full.

6. The pads on the large-area copper skin should be chrysanthemum-shaped pads, so that there is no false soldering. If there is a large area of ground and power lines on the PCB (with an area spanning 500 square millimeters), part of the window should be opened or the grid should be supplemented.

PCB manufacturing process requirements for pads

1. The two ends of the chip components are not connected to the plug-in components should add test points, the diameter of the test point is or greater than 1.8mm, so as to facilitate the online tester test.

2. If the IC pin pads of the pin spacing set are not connected to the plug-in pads, test pads need to be added. For SMD ICs, the test points cannot be placed in the SMD IC silk screen. The diameter of the test point is 1.8mm or greater, which is convenient for online tester testing.

3. If the pad spacing is less than 0.4mm, white oil must be applied to reduce continuous soldering when the wave crest is exceeded.

4. The two ends and ends of the SMD component should be drawn with tin. The width of the lead should be 0.5mm wire, and the length is generally 2 or 3mm.

5. If there are hand-soldering components on the single panel, the tin bath should be removed. The purpose of the marking is opposite to the purpose of the tin marking. The size of the width viewing hole is 0.3MM to 1.0MM.

6. The spacing and size of the conductive rubber buttons should be consistent with the actual size of the conductive rubber buttons. The PCB board connected to this should be assumed to be a gold finger, and the corresponding gold plating thickness should be defined.

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