PCBA Tech - Checking Methods for PCBA Short Circuit in PCBA Manufacturer

PCBA manufacturer's PCBA circuit board short-circuit check methods, first of all, to open the PCB design on the computer, to light up the network of short-circuit PCB board, to see where is closest and most easily connected to one, especially the short-circuit situation inside IC.

If it is the manual welding in the PCBA plant, good habits should be formed: 1. Before the PCB board is welded, check the PCB board visually once and check whether the key circuit (especially the power supply and the ground) is short-circuited with the multimeter; 2. Use a multimeter to check whether the power supply and the ground are short-circuited after each chip is welded. 3. Do not shake the iron indiscriminately during welding. If you shake the solder onto the foot of the chip (especially the surface-mounted element), it will not be easy to find out that there is a short-circuit phenomenon. Take a piece of board to cut the line (especially for single/double-layer boards). After cutting the line, power each part of the functional block separately and gradually exclude it.

With short-circuit positioning analyzer, if there is a BGA chip, because all solder joints are not visible by the chip and are also multi-layer plates (more than 4 layers), it is best to divide the power supply of each chip at design time and connect with magnetic beads or 0-Euclidean resistance. In this way, when power supply and ground short circuit occur, it is easy to locate a chip by disconnecting magnetic beads detection. Due to the difficulty of BGA welding, if it is not for machine automatic welding, the adjacent power supply will be short-circuited to the two balls without a little attention.

Be careful when welding small surface capacitors, especially power filter capacitors (103 or 104), which can easily cause short-circuit between power supply and ground. When repairing PCBA circuit boards, the faults that encounter short-circuit of public power supply are often very large, because many electronic components on PCBA circuit boards share the same power supply. Every component that uses this power supply has the suspicion of short-circuit. If there are not many electronic components on PCBA circuit board, the way of "hoing the earth" can eventually find the short-circuit point. If there are too many components, "hoing the earth" Whether you can hoe or not depends on your luck. Plug-in capacitors on PCB circuit boards can be cut one foot with beveled pliers (be careful to cut from the center, not from the root or from the circuit board). Plug-in IC can cut the power supply VCC foot. When a short circuit disappears when one foot is cut, a chip or capacitor will be short-circuited. If it is a patch IC, the IC power foot can be tilted after melting the tin with an electric solder to leave the VCC power source. After replacing the short circuit element, weld the cut or the raised part again.

Another quick way to do this is to use a special gauge: the milliohm meter. We know that copper foil on PCBA circuit boards also has resistance. If the thickness of copper foil on PCB is 35um and the width of printed line is 1mm, the resistance value is about 5m per 10mm long. Such a small resistance value can not be measured with ordinary multimeter, it can be measured with the milliohm meter.

Now let's assume that one of the components on the PCBA circuit board has a short circuit. All measured by a common universal meter are 0, while those measured by a millimeter are probably tens to hundreds of milliohms. When we measure a short circuit component on the PCB board exactly with a pen on its feet, the resistance value will be the smallest. (Since the resistance value also includes the resistance value of the copper foil on the printed circuit board when measuring on the feet of components placed on other PCBA circuit boards), we may decide to compare the resistance value of the milliohm meter when a component is detected (the same is true if there is a short circuit in solder or copper foil) When the minimum resistance value is obtained, the components of the PCBA board are the focus of suspicion so that obstacles can be quickly found.