2022-12-07
The causes of cavities and cracks caused by reflow welding during SMT chip processing.
Today, I will tell you what is the cause of cavities and cracks caused by SMT chip processing reflow welding. It is inevitable that various undesirable phenomena will occur during SMT chip processing. To solve these problems, it is necessary to analyze the causes of the undesirable phenomena. The causes of cavities and cracks caused by reflow welding during SMT chip processing mainly include the following factors:
Causes of cavities and cracks caused by reflow welding during SMT chip processing
1. Poor penetration between PCB welding plate and element electrode.
2. Solder paste was not controlled as required.
3. The expansion coefficients of welding and electrode materials do not match, and the solder joints are unstable during solidification.
4. The setting of reflow soldering temperature curve cannot volatilize the organic volatiles and water in the solder paste, and then enter the reflow area.
The problems of lead-free solder are high temperature, high surface tension and high viscosity. The increase of surface tension will inevitably make it more difficult for the gas to escape in the cooling phase, and the gas is not easy to discharge, so the proportion of the cavity is increased. Therefore, in SMT chip processing, there will be more holes and voids in lead-free solder joints.
In addition, since the temperature of SMT lead-free welding is higher than that of lead welding, especially for large, multilayer boards and components with high heat capacity, the peak temperature usually reaches about 260 ℃, and the temperature difference between the two is large. Cool and solidify to room temperature. Therefore, the stress of lead-free solder joints is also high. With more IMC, the thermal expansion coefficient of IMC is relatively large, and it is easy to crack under high temperature operation or strong mechanical impact.
QFP, CHIP and BGA welding spot holes and holes distributed in the welding interface will affect the connection strength of PCBA components. Solder joint crack of SOJ pin, BGA ball and disk interface crack defect, solder joint crack and welding interface crack will affect the long-term reliability of PCBA products.
The other is the hole or micropore at the weld interface. These holes are so small that they can only be seen with scanning electron microscopy (SEM). The location and distribution of voids may be a potential cause of electrical connection failure. In particular, hollow measurement of power components can increase thermal resistance and cause failures.
The research shows that the cavity (micropore) at the welding interface is mainly caused by the high solubility of copper. Due to the high melting point of lead-free solder and high tin solder, the copper dissolution rate in SMT lead-free welding is much higher than that in SN-PB welding. The high solubility of copper in lead-free solder will form "holes" on the copper solder interface, which may weaken the reliability of solder joints over time.
Causes of cavities and cracks caused by reflow welding during SMT chip processing
1. Poor penetration between PCB welding plate and element electrode.
2. Solder paste was not controlled as required.
3. The expansion coefficients of welding and electrode materials do not match, and the solder joints are unstable during solidification.
4. The setting of reflow soldering temperature curve cannot volatilize the organic volatiles and water in the solder paste, and then enter the reflow area.
The problems of lead-free solder are high temperature, high surface tension and high viscosity. The increase of surface tension will inevitably make it more difficult for the gas to escape in the cooling phase, and the gas is not easy to discharge, so the proportion of the cavity is increased. Therefore, in SMT chip processing, there will be more holes and voids in lead-free solder joints.
In addition, since the temperature of SMT lead-free welding is higher than that of lead welding, especially for large, multilayer boards and components with high heat capacity, the peak temperature usually reaches about 260 ℃, and the temperature difference between the two is large. Cool and solidify to room temperature. Therefore, the stress of lead-free solder joints is also high. With more IMC, the thermal expansion coefficient of IMC is relatively large, and it is easy to crack under high temperature operation or strong mechanical impact.
QFP, CHIP and BGA welding spot holes and holes distributed in the welding interface will affect the connection strength of PCBA components. Solder joint crack of SOJ pin, BGA ball and disk interface crack defect, solder joint crack and welding interface crack will affect the long-term reliability of PCBA products.
The other is the hole or micropore at the weld interface. These holes are so small that they can only be seen with scanning electron microscopy (SEM). The location and distribution of voids may be a potential cause of electrical connection failure. In particular, hollow measurement of power components can increase thermal resistance and cause failures.
The research shows that the cavity (micropore) at the welding interface is mainly caused by the high solubility of copper. Due to the high melting point of lead-free solder and high tin solder, the copper dissolution rate in SMT lead-free welding is much higher than that in SN-PB welding. The high solubility of copper in lead-free solder will form "holes" on the copper solder interface, which may weaken the reliability of solder joints over time.
