Graduation Semester and Year
Summer 2024
Language
English
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Mechanical Engineering
Department
Mechanical and Aerospace Engineering
First Advisor
Dr. Dereje Agonafer
Second Advisor
Dr. Abdolhossein Haji-Sheikh
Third Advisor
Dr. Miguel Amaya
Fourth Advisor
Dr. Amir Ameri
Fifth Advisor
Dr. Tushar Jashvantbhai Chauhan
Abstract
Moore’s law has predicted the growth of semiconductor industry for the last 50 years by providing a template for silicon scaling and homogenous system on chip integration of multiple circuits. Lately, this trend has been declining due to the increased power density and functionality and increasing chip size to accommodate this. Moving forward, heterogeneous integration of chiplets will improve the silicon yield by integrating multiple multi-functional chiplets that are of smaller area onto an interposer or a substrate in 2.5D, 3D or 3.5 D architectures. In this study, computational analysis is done on the impact of design parameters and material properties on the reliability of a quarter-symmetric model of a 2.5D package with an ASIC (Application Specific Integrated Circuit) and 4 HBM (High Band-width Memory) modules around integrated through an interposer. JEDEC standard loading of thermal cycling loads are applied on the package to emulate long term thermal loads that the package is subjected to -40°C to 125°C at a ramp time of 300 sec and dwell time of 1800 seconds is applied to the entire package. All three different kinds of interposers namely Si, glass and organic interposers are evaluated for their impact on the total deformation, Von-Moises stress on the solders, die and the substrate.
The bump-less direct Cu-Cu hybrid bonding interconnection technology is crucial for achieving high-density and fine-pitch applications, such as in high-performance computing. This technology provides significantly lower electrical resistivity and reduced electromigration compared to traditional methods like C4 (controlled collapse chip connection) solder bumped flip assembly and C2 (chip connection, micro-bump, or Cu-pillar with solder cap) bumped flip chip assembly. This study employs a multi-level sub-modeling approach to evaluate the reliability of bump-less Cu-Cu bonded interconnects in a 2.5D TSV package during the Cu-Cu thermal compression bonding (TCB) process. Typically, direct Cu-Cu TCB necessitates the diffusion of Cu atoms across the interface to form monolithic copper at high temperatures (350 – 400°C). Fracture mechanics parameters are calculated at the Cu-Cu bonded region, the Si/TSV region, and the back-end Cu/dielectric stack under TCB thermal loads. Furthermore, a multivariable design optimization is conducted to enhance the reliability of these advanced interconnects.
Datacenter industry has been inclining towards Immersion cooling in recent years owing to the increase in power densities in the processors. Air cooling is found to be incapable of maintaining a safe junction temperature on these processors and liquid cooling also has its limitations moving towards high chip powers. Two-phase Immersion cooling has the best Power Usage Efficiency (PUE) compared to single-phase immersion cooling technology. As the entire server is immersed in a two-phase dielectric fluid, all the other components are also in contact with the fluid. Therefore, detailed study of material compatibility of the various electronics packaging materials for immersion cooling is essential to understand their failure modes and reliability. Modulus and thermal expansion are critical material properties for electronics mechanical design. Substrate is a critical component of electronic packaging and heavily influences failure mechanism and reliability of electronics. The non-halogenated low Coefficient of Thermal Expansion (CTE) bismaleimide triazine (BT) resin laminate is used for its ultra-low CTE in high frequency applications which in turn reduces the warpage of substrate. Moreover, the substrate has high glass transition temperature and high stiffness suitable for the application which requires high heat resistance. The substrate is aged in a two-phase dielectric fluid, and air for 720 hours at room temperature and 45°C (just below its boiling point). The complex modulus is characterized before and after aging for all kinds of substrates and compared to draw the relationship between the modulus of the material and the impact of immersion on the thermo-mechanical properties.
Keywords
2.5D IC, Reliability, Substrates, Two-phase Immersion, CTE mismatch, Hybrid bonds, Interconnects, Interposers, J-Integral, Fracture, Crack Propagation, Modulus
Disciplines
Electro-Mechanical Systems
License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License
Recommended Citation
Lakshminarayana, Akshay Boovanahally, "Reliability Assessment of 2.5D Heterogenous Integrated Circuits, Cu-Cu Hybrid Bonded Interconnects & Thermo-Mechanical Assessment of Substrates in Two-Phase Immersion Cooling" (2024). Mechanical and Aerospace Engineering Dissertations. 260.
https://mavmatrix.uta.edu/mechaerospace_dissertations/260