The research status of
lead-free solder wire - the main component of lead-free solder wire is tin, the melting point is 232 ℃, and it forms an alloy system with other metals such as silver, bismuth, and zinc. The melting point of Sn-Ag system lead-free solder wire is 221℃, which is close to that of Sn-Pb system solder in many cases, and has many applications. In the Sn-Ag system, adding some copper appropriately, in addition to lowering the melting point, also improves the welding reliability.
The research goal of lead-free solder and lead-free tin wire - the lead-free solder should have roughly the same characteristics as Sn-Pb system solder.
The specific goals are as follows:
Weak toxicity, less impact on the environment.
The melting point should be close to the melting point (183°C) of Sn-Pb system solder, and should not exceed 200°C.
Low cost and good conductivity.
The mechanical strength and thermal fatigue resistance are roughly the same as those of Sn-Pb system solder.
The storage stability of solder is better.
Can be installed using equipment and current process conditions.
It can ensure good wettability and mechanical reliability after installation.
After welding, it is easy to repair various welding points and should have good electrical reliability.
As the biggest feature of Sn-Ag system lead-free solder wire, the thermal fatigue resistance is obviously better than Sn-Pb system solder. It is most suitable for use in machines that require long-term reliability of the joint. As a substitute for Sn-Pb system solder, the main problem of Sn-Ag system lead-free solder wire is the high melting point, and the cost is also higher than that of Sn-Pb system solder.
So far, no lead-free solder wire that can replace Sn-Pb based solder has been found, and lead-free solder wires have problems of one kind or another. lead-free solder wire needs to continue to study and improve, and gradually improve its performance to meet the reliability requirements of electronic products. But one thing is certain, with the further in-depth research and the requirements for environmental protection, lead-free solder wire will definitely replace Sn-Pb.
Sn-Zn-based lead-free solder wires are superior to Sn-Pb-based solders in tensile strength, initial strength, and long-term strength changes, and have the same ductility as Sn-Pb-based solders. In addition, Zn is also less toxic and less expensive. also low. Considering the mechanical strength, melting point, cost and toxicity of the solder alloy, Sn—Zn based lead-free solder wire is suitable to replace Sn—Pb based solder. However, Sn-Zn solders also have shortcomings: Zn is not stable and easy to oxidize; effective flux should be used.
Sn-Bi lead-free solder wire is characterized by a low melting point, which is beneficial for the soldering of electronic components with poor heat resistance. In addition, the storage stability of Sn-Bi lead-free solder wire is also good, and it can be used roughly the same as Sn-Pb solder. The flux is soldered in the atmosphere, and the wettability is no problem. The disadvantage of Sn-Bi lead-free solder wire is that with the addition of Bi, the solder becomes hard and brittle, the processing performance is greatly reduced, and the welding reliability is deteriorated. Therefore, the added amount must be controlled within an appropriate range.
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