Warpage study in the welding process of PCB and components

PCBs and components are warped during soldering, and defects such as solder joints and short circuits are caused by stress deformation. Warpage is often caused by temperature imbalances in the upper and lower parts of the PCB. For large PCBs, warping occurs due to the weight of the board itself. The ordinary PBGA device is about 0.5mm away from the printed circuit board. If the device on the circuit board is large, the normal shape will be restored as the circuit board cools down, and the solder joint will be under stress for a long time. If the device is raised by 0.1mm, it is enough. Open welding.

While the PCB is warped, the components themselves may also be warped, and the solder joints at the center of the component are lifted off the PCB to produce an empty solder. This often happens when only flux is used and no solder paste fills the gap. When solder paste is used, the solder paste is bonded to the solder balls due to the deformation to form a short defect. Another reason for the short circuit is the delamination of the component substrate during the reflow process. The 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 soldering short circuit is often in the middle of the device. .

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