Formation and Growth of Intermetallic Compound Cu6Sn5 at Early Stages in Lead-Free Soldering

Abstract

In this work, the early stages of the formation and growth of the intermetallic compound Cu 6 Sn 5 during soldering reactions between a Cu substrate and liquid Sn are examined through phase-field simulations. The liquid Sn-based solder (L phase) and the copper substrate (a phase) are considered to be under metastable equilibrium conditions that eventually lead to nucleation of the Cu 6 Sn 5 intermetallic compound (IMC) (g phase) at the solid/liquid interface. Nucleation is incorporated into the model through a classical treatment considering that individual nucleation events follow a Poisson distribution function. The driving forces for the nucleation and phase transformations are obtained by coupling the phase-field simulations to CALPHAD models. In the phase-field simulations, physical properties such as liquid surface as well as IMC interfacial energies are treated parametrically to probe the behavior of the system under various growth conditions. The simulations are compared with previous works and are shown to have good (qualitative) agreement with recent detailed studies on the early stages of the interaction between Cu and liquid Sn.

Size effect on IMC growth in micro-scale Sn-3.0Ag-0.5Cu-0.1TiO2 solder joints in reflow process

“…D h ¼ 1:28 Â 10 À11 e À53:92=RT m 2 =s are chosen to be used from a reference[24]. Meanwhile, the grain boundary is assumed to have a constant width (d ¼ 0.05 mm)[23,25].…”

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

“…In general, the suggested value is of the order of 10 39±1 (m À3 s À1 ) in volumetric nucleation and 10 31±1 (m À2 s À1 ) for surfacebased nucleation. [7,16] In the calculation of the stochastic probability of nucleation, we accounted for the variation in nucleation rate constant and the contact angle of the embryo with the substrate. In addition, T is the temperature and k is the Boltzmann constant.…”

“…Such a phenomenon previously observed for the conventional lead-free soldering as well. [15,16] 3.2.2 Intermediate Stages. Intermediate stages of the growth of the low volume soldering system are dominated by the nucleation and evolution of e-Cu 3 Sn phases.…”

“…[8,15,16] The thickness of the interlayer is selected based on the current trends for microbump size in the industry. In current 3DIC technologies, there are several thousands of these microbumps in a 3DIC pack.…”

“…While fully quantitative prediction of microstructural processes through the phase-field method is limited due to the phenomenological nature of the approach-many model parameters are difficult to measure experimentally or may not have a physical motivation at all-the multiphase-field approach has proven to be a very useful tool to simulate the microstructural evolution during soldering reactions in a qualitative and semi-quantitative manner. [15][16][17] In section 2 of the present paper, the multi-phase field modeling with dynamic coupling to the classical nucleation approach is explained. In addition, integration of phase field model with the thermodynamics and kinetics of phase transformation in the low volume interconnection system is discussed.…”