【作者】 吴翠平；

【导师】 沈骏；

【作者基本信息】 重庆大学 ， 材料加工工程， 2011， 硕士

【摘要】 微电子封装工艺中,无铅焊料合金组织中的金属间化合物（intermetallic compound, IMC）起到热、电和机械连接作用,其形态和分布直接影响着该合金的连接性能。焊料在基板上的焊接性能直接决定着焊点的可靠性,进而影响整个电子设备的服役寿命。稀土元素以其特殊的性能被添加到无铅焊料中,得到了许多研究者的关注。本文以极具应用前景的Sn30Bi0.5Cu、Sn35Bi1Ag和Sn57Bi1Ag无铅焊料合金为基体,分别添加不同质量分数的混合稀土元素（rare earth, RE）制备新型无铅焊料合金。研究了新型无铅焊料与Cu基板焊接后其焊接接头的微观组织演变,时效过程中界面处金属间化合物的生长规律及稀土元素的添加对无铅焊料硬度的影响机制。又同时研究了Sn58Bi无铅焊料与电镀不同元素的Cu基板反应,其焊接接头微观组织和界面金属间化合物的演变。全文主要内容和结论如下:稀土元素的添加对SnBiCu-xRE和SnBiAg-xRE（x=0, 0.25和0.5）无铅焊料合金的熔点略有影响。微量稀土元素的添加细化了焊料合金基体中的β-Sn相、Cu6Sn5相和Ag3Sn相,并使其均匀分布在焊料合金基体中。随着稀土元素的添加,焊料合金的显微硬度明显升高。当添加0.5wt.% RE时,由于基体组织中少量脆性富Bi相枝晶的析出,SnBiAg焊料合金的显微硬度增长缓慢;焊接接头处金属间化合物层Cu6Sn5相的生长受到抑制,这是因为添加的稀土元素抑制了Sn元素的活性,降低了Cu6Sn5层生长的驱动力。通过对Sn57Bi1Ag-xRE/Cu（x=0, 0.25,0.5,0.75和1.0）焊料合金微观组织演变的研究发现:随着微量稀土元素的添加,Sn57Bi1Ag-xRE焊料的固相线下降,糊状温度区间略有上升。当添加微量稀土元素时,焊料合金中的富Bi相得到细化,但是过量稀土元素的添加导致RE（Bi,Sn）3金属间化合物的形成,使稀土元素对富Bi相枝晶的吸附作用减弱,从而促进了富Bi相的生长。由于稀土元素在界面处的吸附作用,使得界面处金属间化合物Cu6Sn5层的生长受到抑制。通过时效处理SnBiAg-xRE/Cu焊接接头,探讨了焊接接头界面处金属间化合物的生长规律。结果表明:焊料界面处金属间化合物的生长和厚度变化受稀土元素对Cu6Sn5相吸附作用的影响。稀土元素对富Bi相晶粒的细化作用会促进金属间化合物的生长,而其在界面处Cu₆Sn₅相表面的吸附会抑制金属间化合物的生长。这使得SnBiAg -0.5RE/Cu界面处的金属间化合物的厚度生长速度最小。研究了Sn58Bi/x（x=Cu,Ni/Cu,Au/Ni/Cu,Ag/Cu和Zn/Cu）焊接接头微观组织及界面金属间化合物层的演变。研究发现:Sn58Bi焊料合金在不同基板上焊接时,界面形成的金属间化合物是不同的,且其厚度也不相等。电镀Au和Ag的焊接接头微观组织中分别出现了长条状的AuSn₄相和Ag₃Sn相,而界面处出现了不同的金属间化合物,比如AuSn₄相、Ag3Sn相和Ni₃Sn₄相。电镀Au和Ni元素后,微观组织中的富Bi相尺寸减小,得到细化。而电镀所有元素后,与没有电镀相比,界面处金属间化合物层的厚度增加。更多还原

【Abstract】 The interfacial compound in the solder alloy acts as thermal, electronic and mechanical connections in microelectronic packaging process, and their morphology and distribution influence the solder connection directly. Solder-substrate reaction determines the reliability of the solder joint and then affects the lifetime of the whole electronic equipment. Rare earth （RE） elements, as active elements added into solder alloys, get many attentions by many researchers. In this paper, different amounts of RE elements were added into Sn30Bi0.5Cu, Sn35Bi1Ag and Sn57Bi1Ag lead-free solders respectively. Microstructure evolutions and the microhardness of the solder joints and the influence of RE additions on the growth of IMC in solder joints were investigated. The results are given as follows:The results indicated that with the additions of RE, the melting property of the SnBiCu–xRE and SnBiAg–xRE （x= 0, 0.25 and 0.5） solder alloys changed slightly. The microstructures of theβ-Sn phase, Cu6Sn5 and Ag3Sn intermetallic compounds （IMCs） in the solder matrices were refined due to the surface adsorption effect of RE. In addition, the microhardness of the solder alloys increased remarkably with the additions of RE because of the refined microstructures. Moreover, the formed Cu6Sn5 IMC layers in SnBiCu–xRE/Cu and SnBiAg–xRE/Cu solder joints were much thinner than those in the undoped-RE SnBiCu/Cu and SnBiAg/Cu solder joints after reflowing and aging tests. This is because the RE decreased the interfacial energy of Cu6Sn5 IMC layer and then suppressed the Cu atoms to react with Sn atoms to form Cu6Sn5 IMC layer. The results indicated that with the increase of RE additions, the solidus temperature decreased and the mushy temperature zone increased slightly in SnBiAg–xRE （x= 0, 0.25, 0.5, 0.75 and 1.0） solder alloys. The microstructures of the Bi–rich dendrites in SnBiAg–xRE solder alloys were refined by the additions of minor RE elements.However, too many RE elements added into solder matrices led to the formation of large RE（Bi,Sn）3 intermetallic compound （IMC） which weakened the adsorption effect of RE elements on the Bi–rich dendrites. In addition, the thickness of the Cu6Sn5 IMC layers of SnBiAg–xRE/Cu solder joints were reduced remarkably due to the adsorption effect of RE elements at the interfaces of the Sn element and the Cu6Sn5 IMC layer. Evolution of IMCs in SnBiAg-xRE/Cu solder joints during aging were investigated by scanning electron microscopy. The results indicated that the growth and thickness of Cu6Sn5 IMC layers were influenced by the absorption of RE on the grain boundaries of Cu6Sn5 phase. The refinement of Bi-rich phase increased the growth of IMC layers, while the reduction of surface energy of the Cu6Sn5 phases suppressed the growth of IMC layers after the RE additions. In addition, the thickness of Cu₆Sn₅ IMC layers in SnBiAg-0.5RE/Cu solder joints were the lowest during aging.The microstructure evolution of Sn58Bi/x （x=Cu, Ni/Cu, Au/Ni/Cu, Ag/Cu and Zn/Cu） solder joints were investigated. In the Sn58Bi/Au/Ni/Cu and Sn58Bi/Ag/Cu solder joints, the elongated AuSn4 and Ag₃Sn phases were formed in the solder matrices and the AuSn4, Ag3Sn and Ni₃Sn₄ phases were formed in the solder joints. The microstructure of the Bi-rich phase was refined and the size was decreased in the Sn58Bi/Au/Ni/Cu and Sn58Bi/Ni/Cu solder joints. In addition, the thicknesses of the IMC layers in the electroplated solder joints were thicker than the unelectroplated solder joint.更多还原