PCB board short circuit problem
The biggest reason for the short circuit of the PCB is the improper design of the pad. At this time, the circular pad can be changed to an elliptical shape to increase the distance between the point and the point, so that the short circuit can be prevented.
Inappropriate design of the PCB board parts will also cause the board to be short-circuited, resulting in inoperability. If the foot of the SOIC is parallel to the tin wave, it is easy to cause a short circuit accident. In this case, the direction of the part can be modified to be perpendicular to the tin wave.
There is another reason that the PCB board is short-circuited, that is, the automatic plug-in bends. Because the IPC stipulates that the length of the line is less than 2mm and the part is too big when the angle of the bend is too large, it is easy to cause a short circuit. The solder joints are more than 2mm away from the line.
In addition to the three reasons mentioned above, there are some reasons that can cause short-circuit failure of the PCB board, such as too large substrate hole, too low tin furnace temperature, poor solderability of the board surface, solder mask failure, and board. Surface contamination, etc., are common causes of failure. Engineers can eliminate and check the above causes and failures one by one.
4 improvement methods for PCB fixed bit short circuit
The short-circuit of the fixed short-circuit of the short-circuit improvement of the PCB is mainly due to the scratching of the film line or the blockage of the garbage on the coated screen. The coated anti-plating layer is exposed to copper and causes short circuit of the PCB. The improvement is as follows:
- Films on the film must not have problems such as trachoma, scratches, etc. When placed, the film surface should be facing upwards, and should not be rubbed against other objects. When the film is copied, the film faces the film surface, and the appropriate film is loaded in time. Store in a film bag.
- When the film is facing, face the PCB surface. When taking the film, use both hands to pick up the diagonal. Do not touch other objects to avoid scratching the film surface. Each film must stop the alignment when the plate reaches a certain number. Check or replace it by hand. Put it in a suitable film bag and store it.
- The operator should not wear any decorations such as rings, bracelets, etc. The nails should be trimmed and kept in the garden. The surface of the table should not be placed with any debris, and the table tops should be clean and smooth.
- Before the screen version is produced, it must be strictly checked to ensure that there is no problem in the screen version. When applying the wet film, it is often necessary to check the paper to check if there is any jam on the screen. When there is no printing at intervals, the empty net should be printed several times before printing, so that the diluent in the ink dissolves the solidified ink sufficiently to ensure the smooth leakage of the screen.
PCB board short circuit inspection method
- If it is artificial welding, it is necessary to develop a good habit. First, visually inspect the PCB board before soldering, and use a multimeter to check whether the critical circuit ( especially the power supply and the ground) is short-circuited. Second, each time the chip is soldered. Use a multimeter to measure whether the power supply and ground are short-circuited. In addition, do not smash the soldering iron during soldering. If the solder is soldered to the soldering legs of the chip (especially surface-mount components), it is not easy to find.
- Open the PCB on the computer, illuminate the short-circuited network, and see where it is closest to it, the easiest to connect. Pay special attention to the internal short circuit of the IC.
- A short circuit was found. Take a board to cut the line (especially for single/double board). After secant, each part of the function block is energized separately, and some parts are excluded.
- Use short-circuit positioning analyzer, such as: Singapore PROTEQ CB2000 short circuit tracker, Hong Kong Lingzhi QT50 short circuit tracker, UK POLAR ToneOhm950 multilayer board short circuit detector.
- If there is a BGA chip, since all solder joints are not covered by the chip and are multi-layer boards (more than 4 layers), it is best to separate the power of each chip at the time of design, using magnetic beads or 0 ohms. The resistor is connected so that when the power supply is shorted to the ground, the magnetic bead is detected 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.
- Care must be taken when soldering small-sized surface-mount capacitors, especially power supply filter capacitors (103 or 104), which can easily cause short-circuit between 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.