A diffusion-viscous analysis and experimental verification of defect formation in sintered silver bond-line

Abstract

The low-temperature joining technique (LTJT) by silver sintering is being implemented by major manufacturers of power electronic devices and modules for bonding power semiconductor chips. A common die-attach material used with LTJT is a silver paste consisting of silver powder (micrometer-or nanometer-sized particles) mixed in organic solvent and binder formulation. It is believed that the drying of the paste during the bonding process plays a critical role in determining the quality of the sintered bond-line. In this study, a model based on the diffusion of solvent molecules and viscous mechanics of the paste was introduced to determine the stress and strain states of the silver bond-line. A numerical simulation algorithm of the model was developed and coded in the C11 programming language. The numerical simulation allows determination of the time-dependent physical properties of the silver bond-line as the paste is being dried with a heating profile. The properties studied were solvent concentration, weight loss, shrinkage, stress, and strain. The stress is the cause of cracks in the bond-line and bond-line delamination. The simulated results were verified by experiments in which the formation of bond-line cracks and interface delamination was observed during the pressure-free drying of a die-attach nanosilver paste. The simulated results were consistent with our earlier experimental findings that the use of uniaxial pressure of a few mega-Pascals during the drying stage of a nanosilver paste was sufficient to produce high-quality sintered joints. The insight offered by this modeling study can be used to develop new paste formulations that enable pressure-free, low-temperature sintering of the die-attach material to significantly lower the cost of implementing the LTJT in manufacturing.

Effect of heating rate on bonding strength of pressure-free sintered nanosilver joint

“…1 a and parameters to demonstrate the aste during drying. The detailed ur previous work [11]. During the drying process, the paste is constrained on the x-y plane by the chip and substrate, and both the chip and substrate are considered as rigid bodies undergoing no deformation.…”

“…In our recent studies, we developed a mathematical model based on diffusion of solvent molecules and viscousflow mechanics of a silver paste to show that drying of the paste in the bonding process is a critical step in determining the bond-line microstructural and mechanical quality [11]. Our modeling results showed that stresses and strains generated in the shrinking silver paste were responsible for observed delamination and cracking in the sintered bond-line [12].…”

Effect of Various Parameters on the Shear Strength of Solid-State Nanoporous Cu Bonding in Cu–Cu Disks for Power Device Packaging

“…Loading [MathJax]/jax/output/CommonHTML/jax.js An alternative bonding approach, that has been investigated to address the abovementioned limitations, is nanoparticle sintering. Various sintering nanoparticles have been explored by virtue of their high melting temperatures and superior electrical and thermal conductivities [15][16][17][18][19]. Unlike Ag-nanoparticle sintering, that is not suitable for practical application because of the high cost and low ion-migration resistance of Ag nanoparticles [20].…”

“…However, Cu nanoparticle sintering is unsuitable for electronic devices because of the weak oxidation resistance of Cu [22]. Besides, the nanoparticle paste contains, various organic substances, including solvents, capping molecules and binders, which are added to tailor the properties of the paste [19]. For example, polyvinylpyrrolidone serves as a capping molecule to control the size of the nanoparticles and protect them against oxidation [23][24][25].…”

Effect of various parameters on the shear strength of solid-state nanoporous Cu bonding in Cu–Cu disks for power device packaging

“…An alternative bonding approach, that has been investigated to address the abovementioned limitations, is nanoparticle sintering. Various sintering nanoparticles have been explored by virtue of their high melting temperatures and superior electrical and thermal conductivities [15][16][17][18][19]. Unlike Ag-nanoparticle sintering, that is not suitable for practical application because of the high cost and low ion-migration resistance of Ag nanoparticles [20].…”