Tin bismuth cuprum series leadless solder and preparation method thereof

Abstract

The invention relates to a tin-bismuth-copper series lead-free solder and a manufacture method thereof. Counted by weight percentage, the invention is characterized by including 29 minus or plus 1 percent of Bi, 0.5 minus or plus 0.1 percent of Cu, equal to or more than 0.005 percent and equal to or less than 0.5 percent of Zn; the rest is tin. The solder has a higher reliability; the solidifying segregation of the element Bi is remarkably restrained; the tissues of the welding points are uniform and thin; no pure-Bi layers appear on a welding interface; the IMC (compound between metals) stability of the interface is improved; the interface has excellent technique property, mechanical property and using reliability. The tin-bismuth-copper series lead-free solder can be widely applied to the low-temperature encapsulation occasion and the multilevel encapsulation occasion of an electric product.

Description

technical field [0001] The invention relates to the technical field of manufacturing tin-based lead-free solder for low-temperature assembly in the electronics industry, in particular to a modified 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, with the recognition of the toxicity of Pb and the continuous improvement of solder requirements for electronic products, lead-free solder has become the mainstream. As a new type of lead-free electronic packaging solder, the general requirements are: it should have good process performance (low melting point, good wettability, good corrosion resistance and oxidation resistance, good mechanical properties, good conductivity), 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 cr...

AI Technical Summary

Problems solved by technology

However, bismuth also brings other problems, including the large change of its composition on the mechanical properties of the alloy, the problem of 'lead' pollution, the natural supply and high cost, and the instability of the interface layer. The reliability of higher temperature occasions is questioned, especially the monotectic alloy solder of Sn-Bi, due to the large melting range, it is prone to dendrite segregation and coarsening of the structure during the solidification process, and the unbalanced stress leads to easy peeling hazards , so the alloying of Sn-Bi solder and the rapid solidification of the welding process have become its development direction

[0005] Japanese patent application 2-70033 for this reason, 5-228685 and 8-132277 disclose a series of solders, 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 (as everyone knows, silver Price from 1.45 yuan / g in 2001 to 3.7 yuan / g now), and the obvious electromigration characteristics of Ag limit the promotion of Ag-containing solder

A typical example: Motorola’s patented alloy SnBi57Ag1, although its strength and reliability are greatly improved compared with the Sn-Bi eutectic type, but the alloy not only contains the precious metal silver but also has a Bi content as high as 57%. The economical development direction of products; the U.S. patent 6,156,132 applied by Fuji Electronics and the newly launched Sn-35Bi-1Ag low-temperature solder also contain 1% precious metal Ag, which doubles the cost; the limited resources of Bi and the total cost of Sn-Bi The large-scale application of crystalline solder has led to rapid growth of Bi price, so low-Bi content silver-saving (or silver-free) solder is urgently needed to be developed

The Sn-Bi-Cu component (containing 0.1-2.0% Cu, 1.0-7.5% Bi) disclosed in U.S. Patent 6,180,264, although the use of Ag is excluded, its Bi content is too low to make it still high Solder with tin content, which inevitably has high tin defects: such as corrosion to containers and equipment, high energy consumption for welding and smelting, high tin slag output, etc., the most important thing is that lower Bi content will lower the melting point of solder The effect is limited, and the impact damage to electronic components is increased during brazing

The monotectic alloy solder—silver-free Sn-Bi-Cu lead-free solder (CN200610089257.4) released by Beijing Kangpu Xiwei Solder Co., Ltd. and Beijing General Research Institute of Nonferrous Metals to a large extent suppresses the Bi element in the process of solder solidification. segregation, but it will inevitably form a weak zone of Bi-rich layer at the welding interface, resulting in poor reliability of solder joints (greater cracking tendency)

Images