Circuit boards and components are warped during the welding process, and defects such as cold welding and short circuits are generated due to stress deformation. Warpage is often caused by temperature imbalances in the upper and lower parts of the board. For large PCBs, warpage may also occur due to board weight falling. Ordinary PBGA device is about 0.5mm away from the printed circuit board. If the device on the circuit board is large, the solder joint will be under stress for a long time as the circuit board cools down. If the device is raised by 0.1mm, it will be enough to cause Welded open circuit.
In the layout, when the circuit board size is too large, although the welding is easier to control, the printed lines are longer, the impedance is increased, the anti-noise ability is decreased, and the cost is increased; when the size is too small, the heat dissipation is decreased, the welding is not easy to control, and adjacent lines easily appear. Mutual interference, such as the electromagnetic interference of the circuit board. Therefore, PCB design must be optimized: (1) Shorten the connection between high-frequency components and reduce EMI interference. (2) Heavy components (eg more than 20g) shall be fixed by brackets and then welded. (3) The heat-generating component should consider the heat dissipation problem to prevent the component surface from having a large ΔT defect and rework, and the heat-sensitive component should be far away from the heat source. (4) The arrangement of the components is as parallel as possible, which is not only aesthetic but also easy to solder, and mass production is preferred. The circuit board is designed to have a 4:3 rectangle best. Do not change the width of the wire to avoid wiring discontinuities. When the circuit board is heated for a long time, the copper foil easily expands and falls off. Therefore, large-area copper foil should be avoided.