【作者】 陈洁；

【导师】 沈骏；

【作者基本信息】 重庆大学 ， 材料加工工程， 2010， 硕士

【摘要】 微电子封装系统中,起到热、电和机械连接作用的无铅焊料合金与基板的界面反应直接影响焊点可靠性。本文以极具应用前景的Sn-Zn系和Sn-Ag系无铅焊料合金为研究对象,通过添加微量第三元素和异相纳米颗粒,结合微观组织分析,系统研究了不同第三组元的添加对二元无铅焊料合金与基板间界面反应的影响。同时采用高温时效处理模拟焊点的高温服役过程,揭示其组织中各相的演化规律、界面扩散行为以及金属间化合物层的生长机制。上述研究包括的主要内容和获得的结论是:通过将Sn-9Zn、Sn-8Zn-1Bi和Sn-8Zn-3Bi焊料合金在Cu板上回流焊接,系统研究了Bi组元的添加对Sn-Zn-xBi/Cu焊点界面形貌的影响。结果表明:随Sn-9Zn焊料合金中Bi含量的增加,减少了焊料合金与Cu板间线膨胀系数差值,降低了界面处裂纹形成倾向。并且Bi组元的添加降低了Sn-Zn焊料合金的熔点,因此,在相同的回流过程中熔点越低焊料合金处于液态的时间越长,导致其金属间化合物层厚度增加及晶粒粗化。此外,Bi在金属间化合物表面的局部偏聚,部分地阻挡了金属间化合物向熔体焊料的溶解,导致Sn-8Zn-3Bi焊料合金界面金属间化合物层呈现锯齿状形貌。研究了高温时效下Sn-3.5Ag-x(x=0, 0.75Ni, 1.0Zn和1.5In)/Cu界面金属间化合物的微观组织演变及其生长规律。结果发现:高温时效8分钟前Ni3Sn4/Cu6Sn5金属间化合物层在Sn-3.5Ag-0.75Ni/Cu界面处形成,当时效时间超过24分钟后,金属间化合物层转变为(Cu, Ni)6Sn5相,生长速度减缓。Cu6Sn5/Cu5Zn8金属间化合物层在Sn-3.5Ag-1.0Zn/Cu界面形成,而且其生长速度近似于Sn-3.5Ag/Cu界面金属间化合物层的生长速度。长时间时效后金属化合物层转变为Cu-Zn-Sn相,生长速度开始加快。Sn-3.5Ag焊料合金中添加In组元后界面处形成了Cu6(Sn, In微量)5金属间化合物颗粒,加快了其生长速度直到In被界面反应消耗殆尽。研究了时效过程中Sn-3.5Ag-1.5In焊料合金与Au/Ni/Cu焊盘间的界面反应,发现时效过程中Sn-3.5Ag/Au/Ni/Cu界面金属间化合物由(Ni, Au)Sn4相演化为Ni3Sn4相,但生长速度没有明显变化。高温时效初始阶段(Ni, Au)Sn4和Ni3Sn4相在Sn-3.5Ag-1.5In/Au/Ni/Cu界面形成。当In组元参与到界面反应后,促进了Sn原子的扩散,加快了Ni3(Sn,In)4相的生长速度,但长时间时效时,其影响作用逐渐减小。通过制备Sn-8Zn-1Bi-x纳米Ag和Sn-8Zn-1Bi-xMWCNTs复合焊膏,并将其置于Cu板上回流焊接,探讨了纳米Ag颗粒和MWCNT的添加对Sn-Zn-Bi焊料合金及界面金属间化合物层生长过程的影响。结果表明:在Sn-Zn-Bi焊料合金中添加纳米Ag颗粒后,在富Zn相的晶粒周围形成AgZn3金属间化合物颗粒,因此阻挡了水蒸气和氧气的扩散路径,抑制了ZnO在晶粒边界的形成;而部分AgZn3金属间化合物依附在Cu-Zn金属间化合物层上方形核生长,增加了界面整个金属间化合物层的厚度。在Sn-Zn-Bi焊料合金中添加MWCNT颗粒后,由于其表面吸附作用降低了焊料合金组织中富Zn相的晶粒表面能,细化了富Zn相的晶粒尺度,并且分布在界面处的MWCNT有效地阻碍了Sn、Zn和Cu原子的扩散,抑制了界面Sn-Cu-Zn金属间化合物层的生长。更多还原

【Abstract】 Interfacial reactions between lead-free solders which act as thermal, electronic and mechanical connections in microelectronic packaging process and common substrates affect the reliability of the solder joints directly. In the paper, Sn-Zn and Sn-Ag lead-free solder alloys were selected and the interfacial reactions were explored systematically by the addition of minor thirds elements and nanoparticles and the means of metallographic analysis. In addition, the evolution of phases in the solder matrices, the diffusion of elements and the growth mechanism of IMC (intermetallic compound) layers of the solder joints, which serviced under high-temperature environment were investigated by high-temperature aging treatment and the results are given as follows.Three types of Sn-9Zn, Sn-8Zn-1Bi and Sn-8Zn-3Bi solders were adopted for reflowing on Cu substrate to investigate the influence of minor Bi additions on the evolution of the interfacial morphology in Sn-Zn-xBi/Cu solder joints. The addition of Bi into Sn-Zn solder reduced the tendency of the formation of cracks at the solder joints because alloying of Bi reduced the mismatch of CTE (coefficient of thermal expansion) between the solder alloys and the Cu plate. Moreover, alloying with Bi reduced the melting temperature of the Sn-Zn solder so as to increase the molten period of the Bi-containing solders during reflow. This increased the thicknesses and grain/particle sizes of IMC layers/particles.The microstructural evolution of IMCs in Sn-Ag-X(X = 0, Ni, Zn and In)/Cu solder joints and their growth mechanisms during liquid aging were investigated. The results indicate that compared with the growth of single IMC layer in Sn-Ag/Cu solder joint, there was a two-phase (Ni3Sn4 and Cu6Sn5) IMC layer formed in Sn-Ag-Ni/Cu solder joint during their initial liquid aging stage (in the first 8 minutes). However, after long time aging (more than 24 minutes), the rate of growth of the IMC layer in Sn-Ag-Ni/Cu solder joint decreased due to the phase transformation (from two Ni3Sn4 and Cu6Sn5 phases to a (Cu, Ni)6Sn5 phase). The IMC layers with two Cu6Sn5 and Cu5Zn8 phases formed initially in Sn-Ag-Zn/Cu solder joint during the liquid aging and the rate of growth of these IMC layer was close to that of the layer in Sn-Ag/Cu solder joint. After long time liquid aging, IMC layer with two phases transformed into a Cu-Zn-Sn phase which speeded up its growth. The addition of indium into the Sn-Ag solder alloy to form a Cu6(Snx,In1-x)5 phase speeded up the growth of the IMC layer in Sn-Ag-In/Cu solder joint until the indium became exhausted due to the interfacial reaction.The interfacial reaction between Sn-3.5Ag-1.5In solder and a Au/Ni/Cu pad in BGA package during solid aging were investigated and compared with that between Sn-3.5Ag solder and the Au/Ni/Cu pad. The results indicate that during the solid state aging, the IMC layer in Sn-3.5Ag/Au/Ni/Cu solder joint evolved from a (Ni, Au)Sn4 phase to Ni3Sn4 phase, but the rate of growth did not change greatly. In Sn-3.5Ag-1.5In/Au/Ni/Cu solder joint, the phases evolved from the (Ni, Au)Sn4 and Ni3Sn4 phases into a Ni3(Sn,In)4 phase. The participation of indium atoms in the interfacial reaction accelerated the diffusion of Sn atoms and speeded up the rate of growth of the whole IMC layer, but this effection was reduced gradually after prolonged aging.Ag nano-particles and MWCNT reinforced Sn-8Zn-1Bi composite solders were prepareded and reflowed on a Cu plate to investigate the influence of minor Ag nano-particles and MWCNT additions on the evolution of the interfacial morphology in Sn-Zn-Bi/Cu solder joints. The results indicate that the addition of Ag nano-particles into Sn-8Zn-1Bi solder led to the formation of a AgZn3 phase around the Zn-rich particles, which inhibited the diffusion of water vapor and oxygen along the grain boundaries and restrained the formation of ZnO at the grain boundaries. However, parts of AgZn3 IMC particles were found to adhere on the top of surface of Cu-Zn IMC layer, which increased the entire thickness of the IMC layer. The addition of MWCNT into Sn-Zn-Bi solder refined the microstructure of the Zn-rich particles greatly by reducing the surface energy of the Zn-rich phase due to the Surface Adsorption Effect. In addition, the MWCNT which distributed in the IMC layer inhibited the diffusion of Sn, Cu and Zn atoms effciently and decreased the growth of Sn-Cu-Zn IMC layer.更多还原