Solder defects often delay new product launches,What factors will affect the poor soldering of the circuit board?
Solderability of circuit board holes affects soldering quality,The poor solderability of the circuit board holes in the PCB factory will cause virtual welding defects, which will affect the parameters of the components in the circuit, resulting in unstable conduction of the components and inner layers of the multi-layer board, causing the entire circuit to fail.
The so-called solderability is the property of the metal surface being 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 circuit boards are:
1.The quality of the solder affects the quality of the soldering
Solder is an important part in the process of soldering chemical treatment. It consists of chemical materials containing flux. Commonly used low-melting eutectic metals are Sn-Pb or Sn-Pb-Ag. The impurity content must be controlled in a certain proportion to prevent the oxides produced by the impurities from being dissolved by the flux. The function of the flux is to help the solder wet the circuit surface of the board being soldered by transferring heat and removing rust. – White rosin and isopropanol solvents are generally used.
Soldering temperature and cleanliness of the sheet metal surface also affect solderability. If the temperature is too high, the solder diffusion speed will be accelerated. At this time, it has high activity, which will rapidly oxidize the circuit board and the molten surface of the solder, resulting in soldering defects. The contamination of the surface of the circuit board in the PCB factory will also affect the solderability and cause defects. , these defects include solder balls, solder balls, open circuits, poor gloss, etc.
2. Welding defects caused by warpage
Circuit boards and components are warped during the soldering process, and defects such as virtual soldering and short circuits occur due to stress deformation. Warpage is often caused by an unbalanced temperature between the upper and lower parts of the board. For large PCBs, warpage will also occur due to the board’s own weight falling.
Ordinary PBGA devices are 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 and returns to its normal shape. If the device is raised by 0.1mm, it is enough to cause Weld open circuit.
3.Circuit board design affects soldering quality
In terms of layout, when the size of the circuit board is too large, although the welding is easier to control, the printed lines are long, the impedance increases, the anti-noise ability decreases, and the cost increases; if it is too small, the heat dissipation decreases, the welding is difficult to control, and adjacent lines are prone to appear Mutual interference, such as electromagnetic interference of circuit boards, etc. Therefore, the PCB board design of the PCB factory must be optimized:
- Shorten the connection between high-frequency components and reduce EMI interference.
- Components with heavy weight (such as more than 20g) should be fixed with brackets and then welded.
- The heating element should consider the heat dissipation problem to prevent defects and rework caused by large △T on the surface of the element, and the thermal element should be kept away from the heat source.
- The arrangement of the components should be as parallel as possible, which is not only beautiful but also easy to weld, and suitable for mass production. The circuit board design is best with a 4:3 rectangle. Do not change the wire width abruptly to avoid wiring discontinuities. When the circuit board is heated for a long time, the copper foil is easy to expand and fall off. Therefore, the use of large area copper foil should be avoided.
Based on the above, in order to ensure the overall quality of the PCB board, in the production process, it is necessary to use excellent solder, improve the solderability of the PCB board, and prevent warpage to prevent defects.