SnBi钎料电迁移机理及抑制的研究

发布时间：2018-07-24 11:22

【摘要】：随着电子产品向着微型化、多功能化方向发展,焊点电流密度急剧增大,电迁移现象已成为影响焊点可靠性的重要问题。Sn Bi钎料由于熔点低、低膨胀系数、性能高及环境协调性良好等优点而被广泛应用。但电迁移易导致Sn Bi钎料组织及性能发生恶化,严重影响焊点可靠性,故研究Sn Bi钎料电迁移行为在电子封装领域具有重要的意义。本文以Sn Bi钎焊接头作为研究对象,探究了电迁移对Sn Bi钎焊接头微观组织形貌、界面IMC及力学性能的影响。并进一步讨论Al2O3和Ce颗粒对Sn Bi钎料电迁移性能的影响。Sn Bi钎焊接头通电240h后,阴极界面产生了裂纹,焊缝组织中形成一条粗大的富Bi带。Bi原子在电子风力作用下不断从阴极向阳极迁移,阴极界面附近由于大量Bi原子离开产生空位并逐步演化为空洞和裂纹。当大量的Bi原子迁移到阳极界面附近时,持续通电导致接头温度上升,Bi相发生长大并形成富Bi带。此外,Sn Bi钎焊接头阳极界面IMC厚度随着通电时间的延长不断增加,当通电时间超过240h后,阳极IMC厚度的增加的速度不断加快,这可能是由于接头界面产生部分断裂,界面面积减小,电流密度增大,加速Bi原子的迁移。Al2O3颗粒有效地提升了Sn Bi钎料的电迁移抗性,Sn Bi-0.5%Al2O3钎焊接头随通电时间的加长,显微组织变化不大,IMC厚度变化程度也较小。这是由于Al2O3颗粒阻挡原子迁移的通道,使得原子迁移受阻,从而有效抑制了Sn Bi钎料的电迁移。Ce颗粒细化了Sn Bi钎料显微组织,改善钎料的力学性能。随通电时间延长,Sn Bi-0.5%Ce接头较稳定,当通电330h后发生断裂失效。接头阳极界面IMC形貌由扇贝状逐渐转变为层状,相比于Sn Bi钎料界面IMC厚度,Sn Bi-0.5%Ce钎料阴极和阳极界面IMC厚度变化程度较低。随着通电时间的增长,Sn Bi,Sn Bi-0.5%Al2O3和Sn Bi-0.5%Ce接头阴极侧显微硬度均逐渐降低,而阳极侧显微组织的显微硬度则逐渐增加。这是由于大量Bi原子从阴极向阳极迁移,阴极侧组织产生空洞和富Sn相,导致阴极侧硬度不断降低;而阳极侧形成大块的Bi相,由于Bi相为硬脆相,最终导致阳极侧组织的硬度不断上升。其中Sn Bi-0.5%Al2O3钎焊接头阴极和阳极侧显微硬度变化程度最低,这是由于Al2O3颗粒增强了钎料在电迁移过程的组织稳定性。通电200h后,Sn Bi,Sn Bi-0.5%Al2O3和Sn Bi-0.5%Ce钎焊接头抗拉强度分别为12MPa,33MPa和19 MPa。同时,Sn Bi-0.5%Al2O3和Sn Bi-0.5%Ce钎焊接头的延伸长度也相比于Sn Bi接头有明显的增加,且Sn Bi-0.5%Al2O3和Sn Bi-0.5%Ce钎焊接头拉伸断口中分布着撕裂痕,具有部分韧性断裂的特征,而Sn Bi接头的断口分布着大量解理台阶,为典型的脆性断裂形式,其中Sn Bi-0.5%Al2O3和Sn Bi-0.5%Ce钎焊接头呈现出比Sn Bi钎焊接头更优的力学性能。说明Al2O3和Ce颗粒都起到了抑制Sn Bi钎料电迁移的效果,且Al2O3颗粒的抑制效果更佳。
[Abstract]:With the development of electronic products towards miniaturization and multifunction, the current density of solder joint increases rapidly. The phenomenon of electromigration has become an important problem affecting the reliability of solder joint. Because of the low melting point, the expansion coefficient of Sn-Bi solder is low. High performance and good environmental coordination and other advantages are widely used. However, electromigration can lead to the deterioration of microstructure and properties of Sn-Bi solder, which seriously affects the reliability of solder joint. Therefore, it is of great significance to study the electromigration behavior of Sn-Bi solder in electronic packaging field. In this paper, the effect of electromigration on microstructure, interface IMC and mechanical properties of Sn-Bi brazed joints was investigated. The effect of Al2O3 and ce particles on the electromigration properties of Sn-Bi solder was further discussed. After the Sn-Bi brazing joint was electrified for 240 h, cracks occurred at the cathode interface. A coarse Bi-rich band. Bi atom in the weld microstructure is continuously migrated from cathode to anode under the action of electron wind. Due to a large number of Bi atoms leaving the cathode interface, a large number of Bi atoms leave to produce vacancies and gradually evolve into voids and cracks. When a large number of Bi atoms migrate to the anode interface, the continuous electrification leads to the increase of the junction temperature and the growth of the Bi phase and the formation of Bi-rich bands. In addition, the thickness of IMC at the anode interface of Sn-Bi brazed joint increases with the prolongation of the electrification time, and the increasing speed of the thickness of the anode IMC increases continuously when the electrification time exceeds 240 h, which may be due to the partial fracture of the interface of the joint. With the decrease of interface area and the increase of current density, accelerating the migration of Bi atoms. Al _ 2O _ 3 particles can effectively enhance the electromigration resistance of Sn Bi solder and the microstructure of Sn-Bi brazed joints increases with the time of electrification, and the change of microstructure is not so great as to change the thickness of Sn-Bi solders. This is due to the blocking of atom migration by Al2O3 particles, which effectively inhibits the electromigration of Sn Bi solder. Ce particles refine the microstructure of Sn-Bi solder and improve the mechanical properties of the filler metal. The Sn-Sn Bi-0.5 joint is stable with the prolongation of the power on time, and fracture failure occurs after 330 hours of electrification. The IMC morphology of the anode interface of the joint changed from scalloped to layered, and the thickness of Sn Bi-0.5 solder cathode and anode interface IMC changed less than that of Sn-Bi brazing metal interface. The microhardness of the cathode side of the Sn Bi-Sn Bi-0.5%Al2O3 and Sn Bi-0.5 joints decreases gradually with the increase of the electrification time, while the microhardness of the anode side increases gradually. This is due to the migration of a large number of Bi atoms from the cathode to the anode, and the formation of voids and Sn rich phases in the cathode side, which leads to the decrease of the hardness of the cathode side, while the formation of bulk Bi phase on the anode side, because the Bi phase is hard and brittle. Finally, the hardness of the anodic side structure increases continuously. The microhardness of Sn Bi-0.5%Al2O3 brazing joint is the lowest, which is due to the enhancement of the microstructure stability of the solder during electromigration by Al2O3 particles. The tensile strength of Sn-Bi-Sn Bi-0.5%Al2O3 and Sn Bi-0.5 brazed joints is 12 MPA and 19 MPA, respectively. At the same time, the elongation length of Sn Bi-0.5%Al2O3 and Sn Bi-0.5 brazed joints is also significantly longer than that of Sn Bi joints, and the tensile fracture of Sn Bi-0.5%Al2O3 and Sn Bi-0.5 brazing joints is characterized by partial ductile fracture. However, there are a lot of cleavage steps on the fracture surface of Sn-Bi joints, which are typical brittle fracture modes. The mechanical properties of Sn Bi-0.5%Al2O3 and Sn Bi-0.5 brazed joints are better than that of Sn-Bi brazed joints. The results show that both Al2O3 and ce particles can inhibit the electromigration of Sn-Bi solder, and Al2O3 particles have better inhibition effect.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG425

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