Lead free solder alloy and its preparation method

Abstract

The invention relates to a lead-free solder alloy for welding the electronic elements and its manufacturing method. The lead-free solder alloy is characterized in that the main components are Sn, Ag, Cu, and Ni, and In, Bi, Pd, P, Ge, Ga, Se, Te, La, Ce, Pr, Nd, Pm, Sm, Eu, Tm are added selectively. The preparation method is characterized by taking Sn, Ag, Cu, Ni and the additional elements in proportion and smelting them at the temperature of 1300 C. to 1500 C. to obtain the intermediate alloy by using water glass covering process; melting the residual Sn and the intermediate alloy at the temperature of 300 C. to 350 C. by using water glass covering process, and casting the molten materials into alloy pig and soldering tin rod at the temperature of between 250 C. and 350 C.. The lead-free solder alloy provided by the invention can be used for welding the Ag and Pd noble metal electronic element.

Description

Technical field [0001] The invention relates to a lead-free solder alloy for soldering electronic components and a preparation method thereof. The lead-free solder alloy of the present invention can also weld high-grade electronic components containing precious metals such as Ag and Pd, and the product does not contain lead; its preparation uses a covering process, and the obtained product has welding strength, aging resistance, oxidation resistance, wettability and The melting point is improved. Background technique [0002] Soldering is usually a reversible metallurgical joining method. In electrical and electronic applications, low temperature is especially important due to the temperature resistance limits of the materials involved and the necessity of reworking and replacing defective parts. Solder used in electrical and electronic production The alloy must have good wettability, good electrical conductivity, thermal conductivity and bonding strength. Traditional Sn-Pb...

AI Technical Summary

Problems solved by technology

[0002] Soldering is usually a reversible metallurgical joining method. In electrical and electronic applications, low temperature is especially important due to the temperature resistance limits of the materials involved and the necessity of reworking and replacing defective parts. Solder used in electrical and electronic production The alloy must have good wettability, good electrical conductivity, thermal conductivity and bonding strength. Traditional Sn-Pb alloys contain metal lead that is not easy to decompose, especially the waste of lead will pollute the soil. If it is absorbed by the human body, it will form Accumulated and difficult to be excreted, gathered in the human body, according to the report of the Centers for Disease Control and Prevention of the United States, if the content of lead in the blood exceeds 10 μg / dl, it will be fatal, and because of the accumulation in the body, it will lead to the decline of children's intelligence, which is required in the world Under the strong call for environmental protection, many countries have successively issued many regulations prohibiting the use of lead, and human society is eager for a green and environmentally friendly environment. Under the trend of such a general environment, the development of alternative lead-free solders has begun.

[0003] Among the traditional Sn-Ag alloys, it is well known that the Sn-3.5Ag alloy is a eutectic composition with a melting point of 221°C. When it is used as a welding alloy, the brazing temperature will be as high as 260°C. Sensitive electronic components will cause thermal damage, thereby reducing the performance of electronic components. It is mentioned in the CN1040303C patent that more than 6% of Bi is added to the lead-free solder based on Sn and Ag. Although the melting point is reduced, the elongation is higher. Poor, creep resistance is not ideal; in the Sn-Sb alloy system, the Sn-5Sb alloy has the lowest melting temperature, but its melting temperature is also as high as 235°C of the solidus line and 240°C of the liquidus line. Therefore, brazing The soldering temperature is 280°C, which is higher than the brazing temperature of Sn-3.5Ag alloy, and it is difficult to avoid damage to heat-sensitive high-end electronic components

For SnZn-based lead-free solder, in the CN1198117A patent, 10% Zn, 0.01-1% nickel, 0.1-3.5% Ag, and 0.1∽3% copper are mentioned. -Zn-based alloy solders are extremely vulnerable to impact and form gaps, the structure is not very precise, and it is easy to oxidize during welding, and has high requirements for flux; the use of Sn-Bi alloy solder is hard and brittle, so it is impossible Pull out the wire through plastic processing, as mentioned in CN1040302C Sn, Ag, In, Bi system, although the above-mentioned defects of Sn, Bi system can be improved, but because indium is very expensive, and the raw material is difficult, there is no Willing to use this alloy system in large quantities; CN1314229 mentions Sn, Ag, Cu, Ag, Bi, In, Sb multi-element alloy, because the Ag content exceeds 2.5%, the cost is higher; for Sn-Cu series lead-free solder, it is mentioned in CN1262638A Sn, Cu, Ni lead-free solder, the disadvantage is that the melting point is high

It can be seen from the above that the existing lead-free solders are not ideal in terms of cost effectiveness and other practical production applications, so it is difficult to find suitable solder substitutes from some simple combined alloy systems in the past