Collaborative Research: Mechanisms and Processing Strategies for Sn Whisker Mitigation

细节距镀锡电气互连线上锡须的生长在无铅电子元件中造成了灾难性的短路问题。过去，这个问题是通过添加几个百分点的铅来缓解的，但由于世界范围内对铅的禁令，这不再是允许的。这项研究旨在通过两种不同的机制来制定强有力的策略来减缓锡晶须的生长。提出的一种方法是通过在电镀液中添加掺杂剂来改变电镀化学，以模拟使铅能够赋予晶须对锡的生长阻力的机制。另一种是改变沉积条件，以促进近等轴晶结构，而不是典型的普遍存在的柱状晶，允许吸收质量流而不生长晶须。为了实现这一目标，该项目将把合金设计/微结构的智能组件与可交付的制造组件集成在一起。为了辅助合金设计，将进行分子动力学(MD)模拟，以深入了解掺杂元素对TiN中晶界能和扩散系数的影响。预期的结果将是减少镀锡过程中的应力，并深入了解晶须形成的关键机制，包括工艺条件对晶须尺寸和密度的影响。如果成功，这里提出的工艺技术将对电子制造业产生重大影响。这一结果将与电力、航天和军事电子行业特别相关，这些行业的寿命是以几十年为单位衡量的，因此胡须的形成是一个严重的问题。这项工作将整合新墨西哥理工大学和华盛顿州立大学的研究和研究生培训，促进发现、与行业互动、在会议上传播成果，以及指导本科生和高中生。它将为学生提供与工业相关的技术方面的实践经验，其中材料加工、微观结构、力学和热力学都被捆绑在一起，形成一个具有全球影响的单一问题。

The growth of tin whiskers on fine pitched tin-plated electrical interconnect lines poses catastrophic short circuit problems in lead-free electronic components. In the past, this problem was mitigated by adding a few percent lead, which is no longer permissible due to a world-wide ban on lead. This research is aimed at developing robust strategies for mitigating tin-whisker growth by two different mechanisms. One path proposed is to alter the plating chemistry by adding dopants in the electroplating bath to emulate mechanisms that enable lead to impart whisker growth resistance to tin. Another is to modify deposition conditions to promote a near-equiaxed grain structure instead of typically prevalent columnar grains, allowing absorption of mass flow without whisker growth. To achieve this, the project will integrate an intellectual component of alloy-design/microstructure with a deliverable manufacturing component. To aid alloy-design, molecular dynamics (MD) simulations will be performed to provide insight into the influence of dopant elements on grain boundary energy and diffusivity in tin. The expected outcomes will be stress reduction in the tin plating as well as insight into the key mechanisms of whisker formation, including the impact of process conditions on the size and density of whiskers produced.If successful, the process technology proposed here will have significant impact on the electronics manufacturing industry. The results will be particularly relevant for the power, space and military electronics industries, where lifetimes are measured in decades making whisker formation an egregious problem. The work will integrate research and graduate student training at New Mexico Tech and Washington State University by fostering discovery, interactions with the industry, dissemination of results in conferences, as well as mentoring of undergraduate and high school students. It will provide students with hands-on experience in an industrially relevant technology, where materials processing, microstructure, mechanics, and thermodynamics are all tied together in a single problem of world-wide impact.