Silver-free tin-bismuth-copper leadless solder and preparation method

Abstract

The invention relates to a tin-base leadless solder without silver, and relative production. Wherein, it comprises Bi at 7.5-60% (without 7.5%), Cu at 0.1-3.0%, and the left is tin; and it also can contain Zn, Ni, P, Ge, Ga, In, Al, La, Ce, Sb, Cr, Fe, Mn, or Co while the total amount of micro alloy element is not higher than 1.0%. And the production comprises that in protective gas or vacuum, smelting middle alloy Sn-Cu10; then smelting into leadless solder alloy ingot which can be used as solder directly or be made into bar band, wire plate or powder. The inventive solder has low cost while its fusion point can be controlled between 140 and 230Deg. C. And it has strong anti-oxidization and anti-corrosion properties.

Description

technical field [0001] The invention relates to the technical field of manufacturing tin-based lead-free solder, in particular to a silver-free tin-bismuth-copper-based lead-free solder and a preparation method thereof. Background technique [0002] Solder is widely used in connecting materials such as electronic appliances. However, as a new type of lead-free electronic packaging solder, it should have good process performance (low melting point, good wettability, good corrosion and oxidation resistance, good mechanical properties, electrical conductivity Good), high process yield (fast spreading speed, high welding yield, high slag formation rate), good reliability of solder joints (high joint strength of solder joints, good creep resistance), easy operation, and low cost. [0003] Several major alloy systems currently developed for lead-free solder: Sn-Ag system (including Sn-Ag-Cu system), Sn-Cu system, Sn-Zn system, Sn-Bi system, if measured according to the user's valu...

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Problems solved by technology

[0003] Several major alloy systems currently developed for lead-free solder: Sn-Ag system (including Sn-Ag-Cu system), Sn-Cu system, Sn-Zn system, Sn-Bi system, if measured according to the user's value equation, all There are inherent defects: Sn-Ag solder can provide good reliability and process yield, but it contains a lot of Ag, the cost of Ag is high, and the oxidation and corrosion resistance is not satisfactory; Sn-Cu eutectic solder and its modification The alloys are cheap and easy to obtain, but there are certain problems in soldering reliability, process yield and oxidation resistance; and the most serious problem is that the melting point of these two systems of solder is much higher than that of the original general-purpose Sn-Pb solder (about 34 ~44℃), which is a huge test for the equipment usually used for Sn-Pb soldering, and it is also the biggest obstacle for the lead-free process

Although Sn-Zn solder has obvious advantages in terms of melting point and cost, it is obviously at a disadvantage due to its oxidation resistance and spreading due to its activity, as well as the difficulty in preparing and selecting matching fluxes; Sn-Bi solder It has the advantages of low melting point, convenient welding, high efficiency, etc., but its reliability and its inherent disadvantages in higher temperature applications are also the fundamental driving force for its modification or innovation

Japanese patent application 2-70033, 5-228685 and 8-132277 disclose a series of solders for this reason, yet because all contain Ag in these patent compositions, have increased the consumption of combat readiness resource Ag, have also increased the cost of solder

The Sn-Bi-Cu component disclosed in US Patent 6,180,264 (containing 0.1-2.0% Cu, 1.0-7.5% Bi), although the use of Ag is excluded, the lower Bi and Cu content determines that it is Solder with high tin content, which inevitably has high tin defects: such as corrosion to containers and equipment, etc., and the lower Bi content has limited effect on lowering the melting point of solder

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