采用液相法在室温下合成了直径为10 nm以下的Sn3.5Ag0.5Cu纳米颗粒, 并采用SEM, TEM, XRD及EDS表征其形貌、结构、物相及元素组成特征, 研究了不同温度和时间烧结时纳米颗粒的尺寸变化, 测试了经过不同压力钎焊后的Cu/纳米钎料/Cu的三明治结构的剪切强度. 结果表明: 10 nm以下的纳米钎料颗粒呈现颈缩团聚的趋势; 烧结温度越高, 纳米颗粒的颈缩团聚越明显, 整个过程发生越迅速; 在230 ℃可以实现钎焊, 低于传统微米尺度的Sn3.5Ag0.5Cu钎料的温度(250 ℃左右), 且钎焊界面强度受钎焊压力影响较大, 当压力为10 N时, 三明治结构的剪切强度达到最大, 为14.2 MPa. 钎焊键合过程为首先通过纳米颗粒颈缩团聚减少气孔, 随着温度的升高, 熔化的钎料与固态母材之间的溶解扩散过程形成牢固的冶金连接.

Solder has been long playing an important role in the assembly and interconnection of integrated circuit (IC) components on substrates, i.e., ceramic or organic printed circuit boards. The main function of solder is to provide electrical, thermal, and mechanical connections in electronic assemblies. Lead, a major component in Sn/Pb solder, has long been recognized as a health threat to human beings, which is the main reason for the requirement of environmental-friendly lead-free solder. A variety of lead-free solder alloys have been investigated as potential replacements for Sn/Pb solders, but there is still no perfect alternative. Three alloy families, Sn-Ag-Cu, Sn-Ag and Sn-Cu, seem to be of particular interest. However, concerns with this alloy family, including higher soldering temperature, poorer wettability due to their higher surface tension, and their compatibility with existing soldering technology and materials, have impeded their steps in completely replacing Sn/Pb solder. As the melting point can be dramatically decreased when the size of the particles is reduced to nanometer size, especially under 20 nm, and nanosolders have much better wettability at the same time. Furthermore, after heated and cooled, nanomaterials become bulk materials, which make them have the ability to endure a higher function temperature. Thus it is of great significance to conduct in-depth investigation on the synthesis of nanosolders and their soldering performance. In this work, Sn3.5Ag0.5Cu nanoparticles as a promising alternative of Sn/Pb solder was developed. The morphology, atomic structure, phase composition, and element composition of nanoparticles were characterized by SEM, TEM, XRD, and EDS, respectively. Size change of Sn3.5Ag0.5Cu nanoparticles under different sintering temperatures and sintering times was discussed. Microstructure of Cu/nanosolder/Cu sandwich structure under different soldering peak temperatures and soldering times was investigated. Shear strength and failure mode of the Cu/nanosolder/Cu sandwich structure under different pressure were also discussed. The results showed that the average diameter of nanoparticles was less than 10 nm with an agglomeration growth tendency. When sintering temperature was relatively low, the neck size increased steadily as temperature and time increased. In contrast, when sintering temperature was relatively high, the agglomeration mainly happened in the initial process and neck size changed little as the time increased. Thickness of intermetallics of Cu/nanosolder/Cu sandwich structure increased with the soldering temperature increased while the size and quantity of voids decreased. Shear strength of bonded sample increased with the increasing pressure, and got the maximum 14.2 MPa when the pressure reached 10 N.