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After the PCB circuit board is completed, the quality inspection of the circuit board is indispensable. First, the quality of the circuit board is distinguished from the appearance. Under normal circumstances, the appearance of the PCB circuit board can be analyzed and judged by three aspects:
1. Standard rules for size and thickness.
The thickness of the PCB circuit board is different from that of the standard circuit board. Customers can measure and check the thickness and specifications of their own products.
2, the appearance of the weld.
Since there are many PCB circuit board parts, if the soldering is not good, the parts are easy to fall off the circuit board, which will seriously affect the soldering quality of the circuit board. The appearance is good. It is very important to identify carefully and have a stronger interface.
3. Light and color.
The external PCB circuit boards are 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 insulation board itself is not good.
Generally speaking, high-quality PCB circuit boards should meet the following requirements:
1, the 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, and it will be broken soon after oxidation;
3, no additional electromagnetic radiation;
4. The line width, line thickness, and line distance of the line meet the requirements to avoid line heating, open circuit, and short circuit;
5. High temperature, high humidity and resistance to special environments should also be considered;
6. The shape is not deformed, so as to avoid deformation of the shell and dislocation of the screw holes after installation. Now it is all mechanized installation, and the deviation of the hole position of the circuit board and the deformation of the circuit and the design should be within the allowable range.
SMT patch over reflow soldering affects the quality of reasons
When reflow soldering is used in SMT patch processing, some quality problems sometimes occur, which reduces the product yield. So what are the factors that affect the quality of reflow soldering? The following is an introduction for everyone.
1. The influence of solder paste
The quality of reflow soldering in SMT patch is affected by many factors. The most important factor is the temperature profile of the reflow oven and the composition parameters of the solder paste. Nowadays, the commonly used high-performance reflow soldering furnace can accurately control and adjust the temperature curve more conveniently. In contrast, in the trend of high density and miniaturization, the printing of solder paste has become the key to the quality of reflow soldering. .
The particle shape of the solder paste alloy powder is related to the soldering quality of narrow-pitch devices, and the viscosity and composition of the solder paste must also be selected appropriately. In addition, solder paste is generally stored in refrigeration. When taking it, it can only be opened after it has returned to room temperature. Special attention should be paid to avoid mixing the solder paste with moisture due to temperature differences. If necessary, use a mixer to stir the solder paste evenly.
2, the influence of reflow soldering process
After eliminating the quality abnormalities of the solder paste printing process and the placement process, the reflow soldering process itself will also cause the following quality abnormalities:
1) Cold welding is usually the reflow temperature is low or the time in the reflow zone is insufficient;
2), the circuit board or components are damp, and the moisture content is too much, which may cause the tin to explode and produce the tin;
3) The temperature rise in the preheating zone of the tin ball is too fast (generally required, the slope of the temperature rise is less than 3 degrees per second);
4) Cracks are generally caused by the temperature drop in the cooling zone too fast (generally, the temperature drop slope of lead soldering is less than 4 degrees per second);
3, the 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 that affect the soldering quality.
