Some issue of Welding quality problems

///Some issue of Welding quality problems

1.The solderability of the circuit board hole affect the quality of welding

The solderability of the circuit board hole is not good, and it will cause the false weld defect, which will affect the parameters of the components in the circuit, leading to the instability of the multilayer component and the inner layer wire, causing the entire circuit function to fail. The so-called solderability is the property that the metal surface is wetted by the molten solder, that is, the surface of the metal on which the solder is formed forms a relatively uniform, continuous, smooth and adherent film. The factors influencing the solderability of printed circuit boards are: (1) the composition of the solder and the properties of the solder. (2) The soldering temperature and the cleanness of the metal plate surface also affect the solderability.2.welding defects caused by warping

2. 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 the board’s own weight drop. 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.
3.the design of the circuit board affects the quality of welding

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) Components with a large weight (eg more than 20g) should be fixed with 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 is likely to swell and fall off. Therefore, large-area copper foil should be avoided.

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