What are the alloy components of lead-free medium-temperature solder paste? A brief discussion.

The composition of lead-free medium-temperature solder paste consists of two parts: solder alloy powder and flux paste. The general composition of the solder alloy is:Sn64.7Bi35Ag0.3,Sn64Bi35Ag1,Sn59.9Bi4Cu0.1,Sn69.5Bi30CU0.5,Sn82.5Bi17Cu0.5There are five specifications.

The solder alloy part accounts for the total weight of lead-free medium-temperature solder paste90%-95%Between the two, solder alloy powder is composed of several alloy materials such as tin, silver, tin and copper, and the standard content of impurity residues in the alloy powder is required to be: oxide less than0.50%Antimony is lower than0.50%Zinc is lower than0.005%Iron is less than0.001%Copper is lower than0.08%Phosphorus is lower than0.01%Sulfur is lower than0.005%Cadmium is lower than0.002%Aluminium is lower than0.001%/.

The size, particle size, shape and surface oxidation degree of solder alloy powder have a direct impact on the solderability of lead-free medium-temperature solder paste. The smaller the particle size, the greater the viscosity, but the surface after soldering processing is prone to oxidation. If the particle size is also larger, the viscosity will become smaller and smaller. Although it is not very easy to oxidize, it will still affect the soldering processing. The particles of solder alloy powder can be detected under a microscope. The most reasonable solder alloy powder is spherical particles with a highly consistent number of particles, and the length ratio of the solder alloy powder should not exceed1.5:1Spherical alloy powder has a particularly small surface area and a low degree of oxidation. The solder paste processed from it has a low viscosity and good printing performance.

Meanwhile, the different proportions of similar alloy components will cause a slight difference in the melting point of lead-free medium-temperature solder paste, such as:Sn59.9Bi4Cu0.1,Sn69.5Bi30CU0.5,Sn82.5Bi17Cu0.5The melting points of these three types of medium-temperature solder pastes are respectively:170℃,189℃,203℃. The properties of lead-free medium-temperature solder pastes with different alloy compositions are quite different. For instance, the activity of medium-temperature solder paste containing silver is slightly higher than that of medium-temperature solder paste containing copper.

The above is the answer from JJY solder Paste ManufacturerLead-free medium-temperature solder pasteThe explanation of alloy composition knowledge is hoped to be helpful to everyone. Please feel free to point out any shortcomings.