Automotive navigation system PCBA, development and design solutions, OEM electronic products, OEM surface mount processing

Detailed explanation of the three major factors that cause soldering defects in circuit boards

There are three factors that can cause soldering defects in circuit boards:

1. The solderability of circuit board holes affects welding quality

Poor solderability of circuit board holes will result in virtual soldering defects, affecting the parameters of components in the circuit, leading to unstable conduction of multi-layer board components and inner wires, and causing the entire circuit function to fail. The so-called weldability refers to the property of the metal surface being wetted by molten solder, that is, the formation of a relatively uniform and continuous smooth attached film on the metal surface where the solder is located. The main factors affecting the solderability of printed circuit boards are: (1) the composition of the solder and the properties of the soldered material. Solder is an important component of the welding chemical treatment process, which is composed of chemical materials containing flux. The commonly used low melting point eutectic metals are Sn-Pb or Sn-Pb-Ag. The impurity content should be controlled in a certain proportion to prevent the oxide generated by impurities from being dissolved by the flux. The function of solder is to help wet the surface of the soldered board circuit by transferring heat and removing rust. Generally, white rosin and isopropanol solvents are used. (2) Welding temperature and surface cleanliness of the metal plate can also affect weldability. If the temperature is too high, the diffusion rate of solder will accelerate, and it has high activity, which will cause the melting surface of the circuit board and solder to quickly oxidize, resulting in welding defects. The contamination of the circuit board surface will also affect the solderability and cause defects, including tin beads, tin balls, open circuits, poor glossiness, etc.

2. Welding defects caused by warping

The circuit board and components undergo warping during the welding process, resulting in defects such as virtual soldering and short circuits due to stress deformation. Warping is often caused by temperature imbalance between the upper and lower parts of a circuit board. Large PCBs can also experience warping due to the weight of the board itself. A regular PBGA device is about 0.5mm away from the printed circuit board. If the device on the circuit board is large, as the circuit board cools down and returns to its normal shape, the solder joints will be under stress for a long time. If the device is raised by 0.1mm, it is enough to cause a virtual solder open circuit.

3. The design of circuit boards affects welding quality

In terms of layout, when the circuit board size is too large, although welding is easier to control, the printed lines are longer, the impedance increases, the noise resistance decreases, and the cost increases; If it is too small, the heat dissipation will decrease, and welding will be difficult to control, making it easy for adjacent lines to interfere with each other, such as electromagnetic interference from circuit boards. Therefore, it is necessary to optimize the PCB board design: (1) shorten the wiring between high-frequency components and reduce EMI interference. (2) Components with heavy weight (such as exceeding 20g) should be fixed with brackets and then welded. (3) Heating elements should consider heat dissipation issues to prevent significant surface damage to the components Δ Defects and rework caused by T should keep the thermistor away from the heat source. (4) The arrangement of components should be as parallel as possible, which is not only aesthetically pleasing but also easy to weld, making it suitable for mass production. The circuit board design is best with a 4:3 rectangle. Do not have sudden changes in wire width to avoid discontinuity in wiring. When a circuit board is heated for a long time, copper foil is prone to expansion and detachment. Therefore, it is advisable to avoid using large areas of copper foil.