TY - THES

T1 - Mean-Field-Model Development for Void Formation in SAC305-Solder Bumps

AU - Huber, Alexander

N1 - embargoed until 28-06-2029

PY - 2024

Y1 - 2024

N2 - The formation of pores is frequently observed during the ageing process of soldered semiconductor components in the microelectronics industry. Sn-Ag-Cu-based solders used in the industry form the intermetallic phases Cu3Sn and Cu6Sn5, which expedites the problem. Insights into the formation of pores and their distribution are of significant importance for the assessment of the operating limits and are analysed in the present Master's thesis. A mean-field model is developed from a model based on thermodynamic considerations in a non-equilibrium state. This is generalised with regard to the geometry, initial pore and vacancy distribution and the characterisation of the individual phases. A descriptive differential equation is obtained from the considerations on vacancy diffusion underlying the pore evolution characterisation. In addition to the intermetallic phases, the pure phases Cu and Sn also occur. Moreover to the contributions of the surface energy and chemical bonding energy, the mechanical portion of the Gibbs energy must be taken into account through the strain energy. Therefore, the stress and strain state of the material points of the continuum must be represented. In particular, the anisotropy, the plastic material behaviour including hardening mechanisms and the creep behaviour must be realistically implemented in the numerical model. The implementation of the model is performed by means of the finite element method. Various subroutines are used to flexibly design the interpolation of the material behaviour between the individual phases. Furthermore, a suitable constitutive law is derived in order to be able to determine the influence of pore formation on the stiffness of the solder joint and the consideration of transformation strains. The modelling is followed by the validation of initial simulation results using the experimental data provided and by fitting previously unknown parameters to predict dissipative influences. An essential aspect is the evaluation of impurities in the solder, especially through an increasing Cl-content. The influence is to be taken into account by adapting the thermodynamic parameters.

AB - The formation of pores is frequently observed during the ageing process of soldered semiconductor components in the microelectronics industry. Sn-Ag-Cu-based solders used in the industry form the intermetallic phases Cu3Sn and Cu6Sn5, which expedites the problem. Insights into the formation of pores and their distribution are of significant importance for the assessment of the operating limits and are analysed in the present Master's thesis. A mean-field model is developed from a model based on thermodynamic considerations in a non-equilibrium state. This is generalised with regard to the geometry, initial pore and vacancy distribution and the characterisation of the individual phases. A descriptive differential equation is obtained from the considerations on vacancy diffusion underlying the pore evolution characterisation. In addition to the intermetallic phases, the pure phases Cu and Sn also occur. Moreover to the contributions of the surface energy and chemical bonding energy, the mechanical portion of the Gibbs energy must be taken into account through the strain energy. Therefore, the stress and strain state of the material points of the continuum must be represented. In particular, the anisotropy, the plastic material behaviour including hardening mechanisms and the creep behaviour must be realistically implemented in the numerical model. The implementation of the model is performed by means of the finite element method. Various subroutines are used to flexibly design the interpolation of the material behaviour between the individual phases. Furthermore, a suitable constitutive law is derived in order to be able to determine the influence of pore formation on the stiffness of the solder joint and the consideration of transformation strains. The modelling is followed by the validation of initial simulation results using the experimental data provided and by fitting previously unknown parameters to predict dissipative influences. An essential aspect is the evaluation of impurities in the solder, especially through an increasing Cl-content. The influence is to be taken into account by adapting the thermodynamic parameters.

KW - SAC305

KW - Porösität

KW - Lötstellen

KW - Kirkendall-Effekt

KW - FEM

KW - Porenwachstum

KW - Cl-Kontamination

KW - SAC305

KW - porosity

KW - solder bumps

KW - Kirkendall-effect

KW - FEM

KW - pore growth

KW - Cl-contamination

M3 - Master's Thesis

ER -