PCB quality SMT over reflow soldering affects quality

PCB quality SMT over reflow soldering affects quality
PCB board quality
After the completion of PCB, the quality inspection of PCB is essential. First of all, the quality and appearance of the circuit board are different. Under normal conditions, the appearance of PCB can be analyzed and judged from three aspects:
Standard rules for dimensions and thicknesses.
The thickness of PCB is different from that of standard PCB. Customers can measure and check the thickness and specifications of their products.
2. Weld appearance.
Due to the large number of PCB parts, if the welding is not good, the parts are easy to fall off from the PCB, which will seriously affect the welding quality of the PCB. Very good appearance. It is important to identify carefully and have a stronger interface.
3. Light and color.
The external PCB circuit board is covered with ink, and the circuit board can play an insulating role. If the color of the board is not bright and the ink is less, the insulating board itself is not good.

In general, high-quality PCB circuit boards shall meet the following requirements:
1. Copper skin is not easy to fall off under high temperature;
2. The copper surface is not easy to oxidize, which affects the installation speed. It will be broken soon after oxidation;
3. No additional electromagnetic radiation;
4. The line width, line thickness and line spacing of the line shall meet the requirements to avoid heating, open circuit and short circuit of the line;
5. High temperature, high humidity and special environment resistance shall also be considered;
6. The appearance shall not be deformed to avoid shell deformation and screw hole dislocation after installation. Now it is a fully mechanized installation, and the hole bit deviation, circuit deformation and design of the circuit board should be within the allowable range.
Causes of SMT chip over reflow soldering affecting quality
When reflow soldering is used in SMT chip processing, some quality problems sometimes occur, thus reducing the product output. So, what are the factors that affect the quality of reflow soldering? The following is an introduction to you.
1. Effect of solder paste
The quality of SMT reflow soldering is affected by many factors. The most important factors are the temperature distribution of the reflow furnace and the composition parameters of the solder paste. At present, the commonly used high-performance reflow furnace can more easily control and adjust the temperature curve accurately. In contrast, under the trend of high density and miniaturization, solder paste printing has become the key to determine the quality of reflow soldering.
The particle shape of solder paste alloy powder is related to the welding quality of narrow spacing devices, and the viscosity and composition of solder paste must be properly selected. In addition, solder paste is usually stored in the freezer. When taking it, it can only be opened after it is restored to room temperature. Special attention shall be paid to avoid mixing solder paste with water due to temperature difference. If necessary, use a blender to stir the solder paste evenly.
2. Effect of reflow soldering process
After eliminating the quality anomalies in the solder paste printing process and placement process, the reflow soldering process itself will also cause the following quality anomalies:
1) Cold welding usually has low reflow temperature or insufficient time in reflow zone;
2) The circuit board or component is affected with damp, and the water content is too high, which may lead to tin explosion and tin production;
3) The temperature rise in the solder ball preheating area is too fast (generally, the temperature rise slope is less than 3 degrees per second);
4) The crack is usually caused by too fast temperature drop in the cooling zone (usually, the temperature drop slope of lead welding is less than 4 degrees per second);
3. Influence of SMT welding equipment
Sometimes the excessive vibration of the conveyor belt of the reflow soldering equipment itself is also one of the factors affecting the welding quality.