PCB and components warp during the welding process, and defects such as virtual welding and short circuit due to stress deformation. Warpage is often caused by the temperature imbalance of the upper and lower parts of the PCB. For large PCB, warping will also occur due to the drop of the board’s own weight. The ordinary PBGA device is about 0.5mm away from the printed circuit board. If the device on the circuit board is larger, the solder joint will be under stress for a long time as the circuit board cools down and the solder joint will be under stress. If the device is raised by 0.1mm, it will be enough to cause Weld open circuit.

While the PCB warps, the components themselves may also warp, and the solder joints located in the center of the components are lifted away from the PCB, resulting in empty soldering. This situation often occurs when only flux is used and no solder paste is used to fill the gap. When using solder paste, due to deformation, the solder paste and the solder ball are connected together to form a short circuit defect. Another reason for the short circuit is the delamination of the component substrate during the reflow process. This defect is characterized by the formation of bubbles under the device due to internal expansion. Under X-ray inspection, it can be seen that the welding short circuit is often in the middle of the device. .