How to control the relationship between line width and current when designing PCB?Finished Aluminium Substrate Pcb Production_Shenzhen StarLight Industrial Development Co., Ltd.

How to control the relationship between line width and current when designing PCB?Finished Aluminium Substrate Pcb Production

source:Other information release time:2023-04-19 Hits: Popular:PCB Assembly company: Share:

　　When we draw PCB, we generally have a common sense, that is, the large current (such as 50mil, even above) where the large current is taken, and the signal of small current can be used in thin lines (such as 10mil).

　　For some mechanical and electrical control systems, sometimes the current current flowing in the wiring can reach more than 100A, so that the thin lines will definitely have problems.

　　A basic experience value is: 10A/square mm, that is, the current value that can pass the line with a cross -sectional area of 1 square millimeter is 10A. If the wire width is too thin, it will be burned when the large current is overdue. Of course, the current burning wiring must also follow the energy formula: Q = i*i*T. For example, for a 10A current, a 100A current burr suddenly appears. It must be able to bear it. (At this time, another problem will occur. The turbid inductance of the wire will have a strong reverse electromotive force under the action of this inductance, which may damage other devices. The larger, the more the length of the comprehensive wire is considered.) The general PCB drawing software often has several options when paving the copper of the perforated pads of the device pins: right -angle spokes, 45 -degree angle spokes, straight paving. What is the difference between them? Novices often don't care much, choose one casually, just beautiful.

　　actually not. There are two main considerations:

　　The first is to consider not to heat dissipation too fast, and the other is to consider the current ability. The characteristics of the use of straight paving are that the over -current capacity of the pad is very strong. For device pins on high -power circuits, you must use this method. At the same time, its thermal conductivity is also very strong. Although it is good for the heat dissipation of the device to work, it is a difficult problem for the circuit board welding personnel, because the pile of heat dissipation is too fast and it is not easy to hang tin. The higher welding temperature reduces production efficiency. The use of right -angle spokes and 45 -angle spokes will reduce the contact area of pin and copper foil. Slow heat dissipation, and it is easier to weld.

　　Therefore, the connection method of choosing a pore pads should be considered according to the application occasion, and the comprehensive over -current ability and heat dissipation capacity should be considered. Do not use straight paving with a small -power signal line. For large -current pads shop. As for the right angle or 45 degrees, it depends on the beauty.

　　Why did you mention this? Because I have been studying a motor driver for a while, the device of the H bridge in this driver has always been burned, and the reason can be found for four or five years. After my hard work, I finally discovered that the pads of a device in the power circuit used the copper paving method of right -angle spokes when the copper was paved (and because of the poor paving copper painting To. This has greatly reduced the over -current capacity of the entire power circuit.

　　Although there is no problem in the normal use process, it is completely normal to work under 10A current. However, when the H bridge has a short circuit, the current will appear about 100A on the circuit, and the two spokes will be burned instantly (US level). Then, the power circuit has become a disconnection. The energy stored on the motor is distributed through all possible channels without the laxes and drop channels. This energy will burn the liquid and related op amp device and destroy the bridge road control chip. In the signal and power supply of the digital circuit part, causing serious damage to the entire equipment. The whole process was as thrilling as a big mine with a hair.

　　Then you may have to ask, why do you use only two spokes on the pad in the power circuit? Why not let the copper foil spread directly? Because, huh, the person in the production department said that the pin is too difficult to weld! The designer was listening to the production staff, so ... Alas, I found that this problem can really take me some brains. If the hole of VIA is less than 0.3mm, there is no way to use mechanical drilling. If you want to use laser drilling, the production and processing of the board will increase. So my personal idea is that if it does not need the minimum to be 0.5mm /0.3mm. But such as computer motherboards, memory, dense BGA packaging, etc., sometimes it may be as small as 14mil/8mil.

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