Investigation of intermetallic compound formation,Kirkendall void nucleation and failure in solder joints

微电子电路单元包括几个连接，特别是将多层单元保持在适当位置的不同金属层之间的焊点。焊料合金的时效、沿电极形成的金属间化合物(IMC)以及气孔和裂纹的形核和生长都会影响焊点的性能，并可能显著影响整个电路单元的寿命。虽然这一课题具有很高的实用价值，但到目前为止，大多数关于焊料中IMC生长的研究都是观察性的，还没有得到IMC生长、空穴形核和裂纹形成的预测模型。该研究项目的目标是为模拟铜-焊接头中金属间化合物的生长和长期时效提供一个数值工具。为此，我们将推导出焊料在热、机械和电载荷作用下的微观结构的耦合相场模型。在典型载荷的影响下，Kirkendall空洞的形核、随后的孔洞生长和裂纹的形成将成为关注的中心。根据现有的实验和热力学数据，我们计划在铜垫上模拟纯锡焊球和传统的共晶锡铅焊料。这两种焊点都有两个不同的IMC，Cu6Sn5在块体和界面上，Cu3Sn在铜垫上。总而言之，该项目将导致对铜垫上焊球系统的全三维模拟，从而能够预测实际应用中的相分解、IMC增长、空洞形核和裂纹扩展。

Microelectronic circuits units include several connections, in particular solder joints between different metal layers which hold the multi-layered unit in position. Aging of the solder alloy, formation of intermetallics (IMCs) along the electrodes as well as nucleation and growth of pores and cracks influence the properties of the joints and may significantly affect the life expectation of the whole circuit unit. Though this topic is of high practical relevance, by today most investigations of IMC growth in solder are observantly, preditive models for IMC growth, void nucleation and crack formation are not available. The goal of the proposed research project is to provide a numerical tool for simulations of intermetallic growth and long-term aging in solder-copper connections. To this end we will derive a coupled phase-field model of the solder's microstructure subjected to thermal, mechanical and electrical loading. The nucleation of Kirkendall voids, their subsequent growth to pores and the formation of cracks under the influence of typical loadings will be in the center of attention. Regarding the available experimental and thermodynamical data we plan to model pure Sn-solder balls and traditional eutectic Sn-Pb solder on copper pads. Both solder connections have two distinct IMCs, Cu6Sn5 in the bulk and along the interfaces and Cu3Sn along the copper pad. In conclusion, the project will lead to fully three-dimensional simulations of the system solder-ball-on-copper-pad which allow for predictions of phase decomposition, IMC growth, void nucleation and crack propagation in real world applications.