【作者】 刘平；

【导师】 姚琲；

【作者基本信息】 天津大学 ， 材料学， 2009， 博士

【摘要】 本文选择Sn3.8Ag0.7Cu（SAC）无铅焊料,首先研究了在Cu和Ni上经过多次焊接（1-10次）和150oC时效（50-1000小时）后的界面反应和剪切强度,并与Sn37Pb（SP）进行了对比;然后通过机械混合方法成功制备了SiC纳米颗粒复合焊料SAC-xSiC和Ni颗粒复合焊料SAC-xNi,重点研究了SAC-xNi/Cu（Ni）焊点在焊接和时效过程中的界面反应和剪切强度。结果表明:焊接过程中,SAC（SP）/Cu界面扇贝状的Cu6Sn5 IMC的生长受晶界扩散控制,而SAC（SP）/Ni界面层状IMC的生长受体扩散控制,Ni-Sn IMC晶粒和反应的速度都小于Cu-Sn。时效过程中,Cu和Ni上的IMC生长都由体扩散控制,时效50小时后,SAC（SP）/Cu界面IMC为双层结构（Cu₆Sn₅和Cu₃Sn）;而SAC（SP）/Ni界面保持单层结构。焊接次数和时效对焊点剪切强度影响较小,富Pb相合并生长降低了SP焊点的强度,SAC的焊点强度一直高于SP。首次选用SiC纳米颗粒与焊料成功复合,复合焊料SAC-xSiC的熔点有所下降,焊料内部IMC颗粒和β-Sn相的亚晶粒显著细化,复合焊料硬度值比SAC增加30-44%。由于表面吸附效应,SiC纳米颗粒抑制了焊料中Ag3Sn的生长,强化了合金的性能,位错绕过理论的预测值与实验测得的强化结果紊合良好。SAC-xNi的工艺性能与SAC相当,Ni颗粒起形核剂的作用,复合焊料凝固过程中发生了非均匀形核,减小了过冷度,得到了颗粒Ni与焊料合金良好润湿性的判据。焊接过程中,SAC-xNi/Cu焊点界面（CuNi）6Sn5 IMC由疏松和致密的两层构成,与SAC相比,复合焊料SAC-xNi与Cu的反应速度大大增加,界面IMC晶粒显著细化,IMC的生长由反应扩散和体扩散双重控制,本文利用热-动力学理论讨论了颗粒Ni对反应速度和晶粒尺寸的影响。焊料中自由活动的Cu原子数量对SAC-xNi/Ni界面IMC的形貌和结构起决定性作用。由于Ni颗粒的添加,SAC-xNi/Cu（Ni）剪切强度有所增加,焊点断裂呈韧性特征。时效50小时后,SAC-xNi/Cu焊点界面变为双层结构即（CuNi）6Sn5和Cu3Sn层,IMC的生长受体扩散控制,添加Ni颗粒抑制了Cu3Sn层的生长。时效过程中,SAC-xNi焊料中的Cu原子逐渐扩散到Ni界面,除了SAC-2Ni/Ni外,界面都形成了双层IMC结构即（CuNi）6Sn5和（NiCu）3Sn4。500小时时效后的SAC-1Ni/Cu（Ni）和SAC-2Ni/Cu（Ni）剪切焊点,断裂区域部分发生在界面。更多还原

【Abstract】 In the first, the interfacial evolution and shear strength of SAC lead free solder were studied in detail on Cu and Ni substrate during multiple reflows and isothermal aging at 150oC. The eutectic SP solder were used as the control. Then the particle reinforced composite solders were successfully prepared by mechanically dispersing SiC nanoparticles and dendrite Ni micro-particles into the SAC solder paste. The Surface Adsorption Effect and reinforced mechanism rendered by nanoparticles were revealed. Lastly the research was emphasized on the intermetallic compound (IMC) microstructure, morphology and shear strength of SAC-xNi/Cu(Ni) joints in the process of reflow and aging. More details were given as following.During multiple reflows, the scallop like Cu6Sn5 IMC at interfaces of SAC(SP)/Cu grew by grain boundary diffusion controlling. Whereas for SAC(SP)/Ni joints, the IMC growth was controlled by the volume diffusion. The growth rate and grain size of Ni-Sn IMC was less than that of Cu-Sn. During aging, the IMC growth on Cu and Ni substrate was controlled by volume diffusion. After 50 h aging, duplex layer structure was displayed at the solder/Cu interface. They are Cu6Sn5 close to solder and Cu3Sn adjacent to Cu substrate. The strength of SAC joints was always higher than that of SP.Composite solder SAC-xSiC was fabricated, which never was reported in literatures. In comparison to SAC, the melting temperature of SAC-xSiC solders was lower by 1oC. The grain size ofβ-Sn sub-grain and Ag3Sn decreased significantly in the composite solder matrix. Addition of SiC nanoparticles in the SAC solder could improve the microhardness by 30-44%, which was in good agreement with the prediction of the classic theory of dispersion strengthening.The process characteristics of SAC-xNi composite solders were equal to that of the non-composite solder. Ni particles could wet well with SAC solder. During multiple reflows, the SAC-xNi/Cu interfaces showed two distinct Ni bearing (CuNi)6Sn5 regions in the IMC layer. The reaction between Cu and SAC-xNi composite solder was accelerated with the Ni addition increasing, but IMC grains were refined. IMC growth at SAC-xNi/Cu interfaces was controlled by the combination of volume diffusion and reaction diffusion. The quantity of free Cu atoms in the solder bulk influenced the IMC morphology and crystal structure of solder/Ni interfaces. The shear strength of SAC-xNi/Cu(Ni) was enhanced by Ni particle additions, and the joint fracture presented ductile mode.After aging 50h at 150oC, the interfacial IMC in SAC-xNi/Cu joints become duplex layer structure, i.e. (CuNi)6Sn5 and Cu3Sn. The volume diffusion is the main controlling process for each IMC layer growth. The addition of Ni particles could depress the growth of Cu3Sn layer. After aging, except for SAC-2Ni joint with single (NiCu)3Sn4 IMC layer, the interface of all joints presented duplex IMC layers, whose upper and lower IMC layers were comprised of (CuNi)6Sn5 and (NiCu)3Sn4, respectively. Shear test result showed partial brittle fractures at interfaces of SAC-1Ni/Ni(Cu) and SAC-2Ni/Ni(Cu) after 500h aging.更多还原