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6 inspection methods for short circuit of PCB boards

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    Published by Pinsheng Electronics Co., Ltd October 16,2019

    The short circuit might occur in the PCB production or use, which will cause troubles or even economic loss to you. Although we have eliminated the possibility of short circuit in PCB manufacturing,  it still exists in the use. It will save time and money if you are able to find the causes quickly and turn to repair.

     

    First, take a look at the common types of short circuit

    Short circuits can be classified according to their functionality:

    • Short circuits can be classified according to their functionality:
    • Short-circuit (such as: tin), 
    • Short circuit of PCB (such as: residual copper, hole deviation, etc.), Short circuit of devices, 
    • Short circuit of PCB assembly
    • ESD/EOS breakdown, 
    • Micro-short circuit in the inner layer of a circuit board, 
    • Electrochemical short circuit (such as chemical residue, Electromigration), 
    • Short circuit caused by other causes.

    Short circuits can be classified according to the wiring characteristics as:

    • Wire-to-wire short circuit, 
    • Line-to-face (layer) short circuit, 
    • Face-to-face (layer-to-layer) short circuit.

     

    Six methods for short circuit analysis

    1. Open the PCB design with a PC, illuminate the short circuit network, and observe which locations are closest to each other, which is the easiest to connect to. In particular, you need to pay attention to the short circuit inside the IC.

    inspect short circuit in PCB drawing

    2. If it is hand soldered, you need to develop a good habit:

    a. Visually inspect the PCB once before soldering, and use a multimeter to check whether the critical circuit (especially the power supply and ground) is short circuited;
    b. Use a multimeter to measure whether the power supply and ground are short circuited each time a chip is soldered.
    c. Do not smash the soldering iron when soldering, if the solder is rubbed onto the soldering feet of the chip (especially surface mount components), it is not easy to find.
    d. A short circuit was found. Take a board to cut the line (especially suitable for single/double board), after each line is cut, each part of the function block is energized separately and gradually eliminated.

    3. A short circuit was found, take a board to cut the line (especially suitable for single/double board), after each line is cut, each part of the function block is energized separately and gradually eliminated.

    4. Using short circuit positioning analysis instruments, the instrumentation is more efficient and the detection accuracy is higher for some conditions in certain situations.

    5. If there is a BGA chip, since all the solder joints are invisible by the chip cover, and it is a multi-layer board (more than 4 layers), it is better to separate the power supply of each chip at the time of design, and connect it with a magnetic bead or a 0-ohm resistor. In this way, when the power supply and the ground are short circuited, the magnetic bead detection is disconnected, and it is easy to locate a certain chip. Because the BGA is difficult to solder, if it is not the machine's automatic soldering, the adjacent power supply and ground solder balls will be short circuited with a little care.

    BGA

    6. Care must be taken when soldering small-sized surface-mount capacitors, especially for power supply filter capacitors (103 or 104), which can easily cause a short circuit between the power supply and ground. Of course, sometimes the luck is not good, the capacitor itself is short circuited, so the best way is to check the capacitance before soldering.

    There is another quicker method, but a special instrument is used: milliohm meter.

    milliohm meter

    We know that the copper foil on the circuit board is also resistant. If the thickness of the copper foil on the PCB is 35um and the printed line width is 1mm, the resistance value is about 5

    We assume that a component is short circuited, measured with a versatile multimeter, and measured with a milliohm meter, which is about tens of milliohms to several hundred milliohms. When we measure the test probe on both feet of the short circuit component, we get The resistance is definitely the smallest (because if the resistance is measured on the two legs of the other components, the resistance obtained also includes the resistance of the copper foil trace on the circuit board), so we can compare the resistance difference of the milliohm meter. When a component is measured (if the solder or copper foil is short circuited), the resistance is the smallest, then the component is a key suspicion. Resolving this essential can quickly find obstacles.

     

    Advanced technologies and more rigorous testing allowed us to eliminate short circuit at the electronic manufacturer end, in order to further reduce short circuit at the user end, as a reliable PCB manufacturer, PS Electronics provide free inspection and after-sales tracking for delivering maximum protection.

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