Phase Field Modeling of Joint Formation During Isothermal Solidification in 3DIC Micro Packaging

Abstract

In this paper, a computational multi-phase field approach is utilized to study the formation of the Cu/Sn/Cu micro-joint in 3-Dimensional Integrated Circuits (3DICs). The method considers the evolution of the system during isothermal solidification at 250°C for the case of two different interlayer thicknesses (5 and 10 lm). The Cu/Sn/Cu interconnection structure is important for the micro packaging in the 3DIC systems. The thermodynamics and kinetics of growth of gCu 6 Sn 5 and e-Cu 3 Sn interfacial intermetallics (IMCs) are investigated by coupling the multiphase field method with CALPHAD approach. The interaction of the phases is addressed by assuming a metastable condition for the Cu/Sn reacting system. The simulations start with the nucleation and rapid growth of the g-Cu 6 Sn 5 IMCs at the initial stage, the nucleation and growth of e-Cu 3 Sn IMCs at the intermediate stage ending with the full consumption of Sn layer and the domination of e-Cu 3 Sn IMCs at the later stages. In addition, comparing different diffusion rates through the grain boundary of g phases show that their morphology is the direct consequence of balance of kinetic forces. This work provides a valuable understanding of the dominant mechanisms for mass transport in the Cu/Sn/Cu low volume interconnections. The results show that the phase field modeling is successful in addressing the morphological evolution and growth of IMC layers in the 3DIC joint formation.

On the interfacial phase growth and vacancy evolution during accelerated electromigration in Cu/Sn/Cu microjoints

“…We used similar values as estimated by our previous studies for larger size solder systems. The assumption by [50] for σ ηL interface energy is one order of magnitude smaller than what we already used in our previous phase-field modeling study [18]. The Arrhenius diffusivity relations, interfacial mobilities, interfacial energies and other material properties used in our simulations are summarized in Table 3.…”

“…The study shows that the reaction rate is independent of solder volume or substrate area fraction and it is more dependent on the amount of bulk and interfacial diffusive features in the microstructure. We avoid providing further details of the reaction process during TLPB here, and readers may refer to our previous work [18]. An example morphological comparison between the current phase-field study and the experimental study of Cu/Sn/Cu sandwich interconnection with 15 µm interlayer thickness is illustrated in fig.…”

“…A summary of the experimental microstructures of the Cu/Sn/Cu sandwich interconnection is provided in Table 1. Apart from the experimental studies, numerous numerical models (FDR [16], LSW [17], phase-field [18,19]) have been utilized to study the growth and ripening process of IMCs during soldering and conventional transient liquid phase bonding (TLPB) processes. This work specifically covers the EM-mediated growth of individual IMCs and distinguishes the distinct nature of the interchange between the anode and cathode layers by carrying out the simulations in one domain.…”

“…This goal makes it necessary to consider different, potentially multi-scale microstructural processes [21] in the materials to gain an understanding of the underlying physical phenomena responsible for the observed responses while breaking the evolving discontinuities among these scales [22]. Accordingly, we have built an integrated computational framework to incorporate the multi-phase-field method [18,19], addressing the microstructural evolution in the Cu/Sn/Cu sandwich structure during complex liquid and solid state reactions with the EM and vacancy evolution models. In this way, we couple the modified phase-field approach with the electric charge continuity equation to study the evolution of the miscrostructure of the interconnection under external electric fields.…”

Multiscale Modeling of Discontinuous Precipitation in U‐Nb

“…Although this information mediates the understanding why specific length scales, growth rates, and phase compositions are selected, it does not infer explanations for the occurrence and growth of γ during DP, especially with the phase's composition residing near the center of miscibility gap's unstable region (see [10][11][12] To shed some light towards the addressing of these questions, we attempt, in the current work, the investigations of DP's origin from the fundamental thermodynamic and kinetic points of view. We choose to take our views from the interesting perspective of phase-field theory that accounts both thermodynamic and kinetic factors towards microstructural evolutions [13][14][15][16][17]. The proposed phase-field framework for the current analyses is the phase-field model with finite interface, or in short interface dissipation model, recently developed by Zhang and Steinbach et al [18,19].…”