PCB News - Reasons that affect the quality of PCB board welding

1. The solderability of PCB board holes affects soldering quality
PCB board hole solderability is not good, it will produce false soldering defects, affecting the parameters of the components in the circuit, resulting in unstable conduction of multi-layer board components and inner wires, causing the entire circuit to fail. The so-called solderability is the property that the metal surface is wetted by molten solder, that is, a relatively uniform continuous smooth adhesion film is formed on the metal surface where the solder is located. The main factors that affect the solderability of printed PCB boards are: (1) The composition of the solder and the nature of the solder. Solder is an important part of the welding chemical treatment process. It is composed of chemical materials containing flux. Commonly used low-melting eutectic metals are Sn-Pb or Sn-Pb-Ag, and the impurity content must be controlled by a certain proportion., In order to prevent the oxides generated by impurities from being dissolved by the flux. The function of the flux is to help the solder wetting the surface of the circuit to be soldered by transferring heat and removing rust. White rosin and isopropanol solvents are generally used. (2) The welding temperature and the cleanliness of the metal plate surface will also affect the weldability. If the temperature is too high, the solder diffusion speed will increase. At this time, it will have a high activity, which will cause the PCB board and the solder melt surface to oxidize rapidly, resulting in soldering defects. The contamination of the PCB board surface will also affect the solderability and cause defects. These defects Including tin beads, tin balls, open circuits, poor gloss, etc.

2. Welding defects caused by warpage
PCB boards 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 between the upper and lower parts of the PCB. For large PCBs, warping will also occur due to the drop of the board's own weight. Ordinary PBGA devices are about 0.5mm away from the printed PCB board. If the components on the PCB board are larger, the solder joints will be under stress for a long time as the circuit board cools down and the solder joints will be under stress. If the device is raised by 0.1mm, it will be enough to cause Weld open circuit.
3. The design of the PCB board affects the welding quality
In the layout, when the PCB board size is too large, although the soldering is easier to control, the printed lines are long, the impedance increases, the anti-noise ability is reduced, and the cost increases; Mutual interference, such as electromagnetic interference of circuit boards. Therefore, the PCB board design must be optimized: (1) Shorten the wiring between high-frequency components and reduce EMI interference. (2) Components with heavy weight (such as more than 20g) should be fixed with brackets and then welded. (3) The heat dissipation problem should be considered for heating elements to prevent defects and rework caused by large ΔT on the surface of the element, and the thermal element should be far away from the heat source. (4) The arrangement of components should be as parallel as possible, so that it is not only beautiful but also easy to weld, and it is suitable for mass production. The PCB board is best designed as a 4:3 rectangle. Do not change the wire width to avoid wiring discontinuities. When the PCB board is heated for a long time, the copper foil is easy to expand and fall off. Therefore, avoid using large-area copper foil.

The above are several reasons that affect the quality of PCB board welding. ipcb company also provides PCB manufacturers, circuit board manufacturing, etc.