NER: Nanostructured Adaptive Solder for Microelectronic Packaging

根据半导体行业路线图，未来微电子封装中的焊球尺寸将继续逐步缩小到20微米(人类头发直径)或更小，同时受到不断上升的温度的影响。这将使芯片(通常是硅)界面附近的焊料受到严重的热机械应变。为了应对这些不可避免地会降低连接寿命和封装寿命的恶劣条件，该计划设想开发包含纳米尺寸形状记忆合金(SMA)颗粒的自适应无铅焊料。研究人员先前已经证明，微米级的NiTiSMA颗粒在热机械循环过程中对焊料基质施加反向剪应力，并有效地降低焊料中的非弹性应变。然而，应变集中问题和焊球尺寸的减小要求使用纳米尺寸的SMA颗粒，以便在低体积分数时获得更扩散的应变场以及渗流的可能性。将对固态和液态加工路线进行调查。衡量成功与否的标准将是纳米SMA增强材料在降低热机械循环过程中的非弹性应变范围方面的有效性。这项研究的广泛结果将是能够设计出比微米级可行的热机械可靠性高得多的活性纳米复合材料微结构。这项研究将对纳米SMA颗粒的作用产生新的机理见解，并对成功制造纳米尺度颗粒提供实用见解。这项工作还将有助于对美国两个不同机构的平民学生和军官进行纳米材料加工和理解的科学和技术方面的教育。在整个项目中，调查人员计划利用与微电子行业的现有关系来开发处理/测试方法，这些方法最终可以转移到工业

According to the semiconductor industry roadmap, the size of solder balls in future microelectronic packages will continue to shrink progressively to 20 microns size (diameter of human hair) or smaller, while being subjected to ever increasing temperatures. This will subject the solder near the chip (typically Si) interface to severe thermo-mechanical strain. To counteract these severe conditions, which will invariably reduce joint life and hence package life, the program envisions developing adaptive lead-free solders containing nanometer size shape-memory alloy (SMA) particles. The investigators have demonstrated previously that micron size NiTi SMA particles impose reverse shear stress on the solder matrix during thermo-mechanical cycling, and are effective in reducing the inelastic strain in the solder. However, strain concentration problems and the decreasing size of solder balls necessitates the use of nanometer size SMA particles, such that a more diffused strain field is obtained along with the possibility of percolation at low volume fraction. Both solid-state and liquid based processing routes will be investigated. The metric of success will be the effectiveness of nano-SMA reinforcements in reducing inelastic strain range during thermo-mechanical cycling. The broad outcome of this study will be the ability to design active nanocomposite microstructures with much greater thermomechanical reliability than that feasible at the micron scale. The research will generate new mechanistic insights on the role of nanoscale SMA particles, and practical insights on successful manufacturing with nanosize particles. The work will also contribute to educating civilian students and military officers at two different U.S. institutions in the science and technology of nanomaterial processing and understanding. Throughout the project, the investigators plan to leverage existing relationships with the microelectronics industry to develop processing/testing methodologies that can be eventually transferred to the indust