固态金属锡表面晶须自发生长行为及机理研究

项目名称： 固态金属锡表面晶须自发生长行为及机理研究

项目编号： No.50871119

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 机械、仪表工业

项目作者： 冼爱平

作者单位： 中国科学院金属研究所

项目金额： 35万元

中文摘要： Sn晶须是一种细丝状金属晶体，在室温条件下它可自发的从表面生长出来。在电子封装密度不断提高和电子设备更加小型化的趋势下，Sn晶须的自发生长已成为电子器件内部短路而致故障或失效的一个重要原因，严重影响电子产品长期使用或储存的可靠性。本项目主要研究这一固态金属锡表面晶须自发生长现象，以及相关的微观机制。主要研究内容包括晶须生长的原因和主要的驱动力，晶须形核的位置，晶须生长的方式，晶须生长速度及影响因素，微量稀土，杂质元素等对晶须萌生和生长行为的影响，以及控制晶须生长形貌的影响因素等。通过对晶须生长机制的研究，提出从根本上防治锡晶须问题的解决方案，以适应在电子工业无铅化后，提高电子器件或设备的长期工作可靠性的需要。

中文关键词： 锡;稀土;金属间化合物;晶须

英文摘要： Sn whisker is an interesting phenomenon, which has been studied by scientists for many years, while it has also been a problem in electronic industry. The electro-circuit breakdown caused by the whiskers will significantly decrease the reliability of the electronic device with high dense packaging. Generally, whiskers form on the Sn plating rather than the bulk Sn alloy. In present project, the whisker growth behavior and mechanism for the RE-doping solders or Sn-RE compound are studied. The main results include the following. By doped with Nd (0.1-5 wt%), the whiskers grow on the surface of both the bulk Sn-Cu solder and the Sn-Pb solder; The whiskers only nucleate and grow at the area of Sn-RE compound in the solders, but never grow at the area of the Sn matrix. In the case of In3Nd or Pb3La, the whiskers also grow on the surface of the IMCs after exposure them to room ambient. Since the whisker growth will be not avoided in the solders doped with RE, it make a question for the design of the RE-doping solder, which is the "hot point" recently in the area of the lead free solder. The in-situ observation of the single whisker was carried out by the optics microscope, the whisker growth rate on Sn3Nd was up to 8-15?/s (in the case of powder sample, 73?/s).With the whisker growth, a new RE-hydroxide Nd(OH)3 formed, which reflects the significant influence of the trace water in exposed environment on the whisker formation. The detail microstructure of the whisker was observed by TEM, it was showed that the whisker is a βn single crystal with a growth axis of [111]. A native oxide film with about 15-18nm thickness covered on the surface of the whisker. Based on the results, a new growth mechanism of whisker, the chemical potential driving, was suggested. The free Sn atoms (released by decomposition of Sn-RE compound) may have high chemical potential, so that they must diffuse then nucleate to decrease the energy, this driving force will result in the whiskers formation and growth. Since the residual stress is not necessary in the mechanism, it will give a challenge to the traditional compressive stress mechanism.

英文关键词： Sn;RE;IMCs;whiskers