How to Find the Short Circuit Point of the Printed Circuit Board?

In the printed circuit board maintenance, it is often troublesome if it encounters a short circuit of the public power supply because there are many devices in the printed circuit board connected in parallel between VCC and GND. Chips, capacitors, transistors, and even the circuit board layers themselves will be short-circuited. The following will introduce some methods to find the short-circuit points in the printed circuit board for your reference.

Disconnect a certain pin of the device, for example, use an IC to cut a foot with diagonal pliers (be careful to cut from the center, do not cut all the roots). When a certain foot is cut, if the short circuit disappears, a certain chip or this capacitor There is a short circuit. After confirming the short-circuited device, remember to restore the cut part of the non-short-circuited device.

Use a stabilized power supply to adjust the open-circuit voltage to the power supply voltage level of the device under test, first adjust the current to the minimum, and apply this voltage to both ends of the circuit board under test, and then slowly increase the current. At the same time, touch the device by hand. When a certain device heats up obviously, this is often a damaged component. The main point of this method is that the voltage must not exceed the working voltage of the device.

We know that the copper foil on the circuit board also has resistance. If the thickness of the copper foil on the circuit board is 35um and the printed line width is 1mm, then every 10mm length, the resistance value is about 5mΩ, such a small resistance value, use ordinary The multimeter cannot be measured, but it can be measured with a milliohm meter.

We assume that a certain component is short-circuited. It is 0Ω measured with an ordinary multimeter, and it is about tens of milliohms to hundreds of milliohms when measured with a milliohm meter. When we test the short circuit board, when the resistance value obtained by measuring a certain component (including solder or copper foil) is the smallest, then the component is the key short-circuit target.

Generally speaking, more high-end short-circuit trackers use two methods: the first is the electric potential method, where the built-in current source of the machine is applied to the circuit board under test, and the electric potential of different parts of the circuit board is measured to find the short-circuit point; the second is In the current induction method, an excitation current is generated through a built-in excitation source, and the probe tracks the magnetic field changes generated by the current on the circuit board to find the short-circuit point. The advantage of the short-circuit tracker is that it does not damage the circuit board and can quickly find the short-circuit point.

The principle is that when the circuit board is short-circuited, the temperature rise of the short-circuited component is different from that of the normal component, and its infrared thermal image is also significantly different. Using this method, a normal device library is established. As long as the thermal image is scanned for abnormal circuit boards, the software will automatically locate the short-circuit point to be tested.

For different short-circuit situations, different detection methods and treatment measures are required, and some methods need to be used comprehensively. If you want to know more about the methods of printed circuit boards after reading the above, PCB Quick is happy to share more comprehensive solutions for you.

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