Effect of materials on the reliability of lead-free solder joints
Release time:
2022-10-05
【Summary Description】 The choice of solder is extremely important. At present, most of the tin-silver-copper alloy series are used, and the liquid phase temperature is 217 ~ 22l ℃, which requires reflow soldering to have a higher peak temperature. As mentioned above, solder and conductor materials (such as Cu foil) are easy to oxidize at high temperature, and intermetallic compounds grow rapidly. Because in the welding process, when the molten solder is in contact with the welding substrate, a layer of metal intermetallic compound (IMC) is formed at the interface due to high temperature. Its formation is not only controlled by reflow temperature and time, but also its thickness increases with time in the later use process. Studies have shown that intermetallic compounds on the interface are a key factor affecting the reliability of solder joints. The existence of an excessively thick intermetallic compound layer will seriously cause the solder joint to fracture, and the toughness and low-cycle fatigue resistance will decrease, which will cause the reliability of the solder joint to decrease. In addition, since the lead-free solder and the conventional Sn-Pb solder have different compositions, their reaction rates and reaction products with the pad materials, such as Cu, Ni, AgPd, etc., may be different, so that the solder joints may also exhibit different reliability. At the same time, the compatibility of solder and flux will also have a great impact on the reliability of solder joints. Studies have shown that the incompatibility between the components of solder and flux will lead to a decrease in adhesion, in addition, due to the mismatch of thermal expansion coefficients, it will accelerate the periodic fatigue failure of the solder. Therefore, special attention should be paid to the selection of solder and flux with excellent compatibility to withstand the high temperature impact of lead-free reflow soldering. In addition, each solder interconnection component comes from different manufacturers, so the quality of the components is inevitably uneven, such as poor solderability of the device pins, which has a great impact on the reliability of the lead-free solder joints.
The choice of solder is extremely important. At present, most of the tin-silver-copper alloy series are used, and the liquid phase temperature is 217 ~ 22l ℃, which requires reflow soldering to have a higher peak temperature. As mentioned above, solder and conductor materials (such as Cu foil) are easy to oxidize at high temperature, and intermetallic compounds grow rapidly.
Because in the welding process, when the molten solder is in contact with the welding substrate, a layer of metal intermetallic compound (IMC) is formed at the interface due to high temperature. Its formation is not only controlled by reflow temperature and time, but also its thickness increases with time in the later use process. Studies have shown that intermetallic compounds on the interface are a key factor affecting the reliability of solder joints. The existence of an excessively thick intermetallic compound layer will seriously cause the solder joint to fracture, and the toughness and low-cycle fatigue resistance will decrease, which will cause the reliability of the solder joint to decrease. In addition, since the lead-free solder and the conventional Sn-Pb solder have different compositions, their reaction rates and reaction products with the pad materials, such as Cu, Ni, AgPd, etc., may be different, so that the solder joints may also exhibit different reliability.
At the same time, the compatibility of solder and flux will also have a great impact on the reliability of solder joints. Studies have shown that the incompatibility between the components of solder and flux will lead to a decrease in adhesion, in addition, due to the mismatch of thermal expansion coefficients, it will accelerate the periodic fatigue failure of the solder. Therefore, special attention should be paid to the selection of solder and flux with excellent compatibility to withstand the high temperature impact of lead-free reflow soldering. In addition, each solder interconnection component comes from different manufacturers, so the quality of the components is inevitably uneven, such as poor solderability of the device pins, which has a great impact on the reliability of the lead-free solder joints.
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