TY - THES

T1 - Development and Characterisation of 3D-Stacks with Porous Metal Layers

AU - Krainer, Rudolf

N1 - embargoed until 28-05-2023

PY - 2020

Y1 - 2020

N2 - The development of new low-cost, lead-free bonding materials for interconnects in power devices is currently of high interest. Printed and subsequently thermally processed metal sinter pastes, notably Copper (Cu), have shown to form highly reliable metal-metal interconnects on a chip level, whilst taking advantage of the cost-efficient handling on a wafer level. Within the scope of this thesis, pre-selected Cu sinter pastes with different levels of porosity after pre-conditioning with pressureless sintering were investigated in their capability to form mechanically resilient three dimensional interconnects between stacked Silicon (Si) chips through thermocompression bonding. The optimisation of the bonding process to a mild, but sufficient, process parameter set was achieved through a systematic design of experiment (DoE). In detail, the parameter set consisted of pre-conditioning, bonding temperature, bonding pressure and an optional annealing step. The formed sinter joints were assessed through a preliminary optical inspection with a light microscope and a scanning acoustic microscope. The microstructure of the sintered layer was assessed in a detailed inspection by a scanning electron microscope. The shear strength of the sinter joints was tested in a subsequent shear test and represented the decisive factor in the evaluation of the quality of the formed interconnects. The ideal process parameter set for each sinter paste was evaluated by a linear regression analysis of the DoE of the bonded three dimensional chip stacks. In summary, the processed metal sinter paste layers showed a shear strength of up to 79 MPa for thermocompression bonding with bonding process parameters of up to 400°C and 50 MPa.

AB - The development of new low-cost, lead-free bonding materials for interconnects in power devices is currently of high interest. Printed and subsequently thermally processed metal sinter pastes, notably Copper (Cu), have shown to form highly reliable metal-metal interconnects on a chip level, whilst taking advantage of the cost-efficient handling on a wafer level. Within the scope of this thesis, pre-selected Cu sinter pastes with different levels of porosity after pre-conditioning with pressureless sintering were investigated in their capability to form mechanically resilient three dimensional interconnects between stacked Silicon (Si) chips through thermocompression bonding. The optimisation of the bonding process to a mild, but sufficient, process parameter set was achieved through a systematic design of experiment (DoE). In detail, the parameter set consisted of pre-conditioning, bonding temperature, bonding pressure and an optional annealing step. The formed sinter joints were assessed through a preliminary optical inspection with a light microscope and a scanning acoustic microscope. The microstructure of the sintered layer was assessed in a detailed inspection by a scanning electron microscope. The shear strength of the sinter joints was tested in a subsequent shear test and represented the decisive factor in the evaluation of the quality of the formed interconnects. The ideal process parameter set for each sinter paste was evaluated by a linear regression analysis of the DoE of the bonded three dimensional chip stacks. In summary, the processed metal sinter paste layers showed a shear strength of up to 79 MPa for thermocompression bonding with bonding process parameters of up to 400°C and 50 MPa.

KW - copper pastes

KW - sintering

KW - 3D-stack

KW - thermocompression bonding

KW - Kupferpasten

KW - Sintern

KW - 3D-Stacks

KW - Thermokompressionsbonden

U2 - 10.34901/mul.pub.2023.105

DO - 10.34901/mul.pub.2023.105

M3 - Master's Thesis

ER -