Nithin Nedumthakady 

(Advisor: Prof. Vanessa Smet, Co-advisor: Prof. Rao Tummala) 

will defend his doctoral thesis entitled, 

Magnetoelectrodeposition of Copper-Graphene Composites:  

A New Method to Tailor Properties of Copper in Advanced Packaging 

on 

Monday, December 4th, 2023 at 1:00PM EST 

Pettit Microelectronics Building – Room 102A 

and 

Via Microsoft Teams 

https://teams.microsoft.com/l/meetup-join/19%3ameeting_Nzk2MjY3YjUtYzcxZC00ZTJiLWI5NjYtN2Q0ZWVmNzRhZTRh%40thread.v2/0?context=%7b%22Tid%22%3a%22482198bb-ae7b-4b25-8b7a-6d7f32faa083%22%2c%22Oid%22%3a%226601c060-850a-4925-9bf3-b07f7d7f7982%22%7d  

Meeting ID: 224 519 609 146
Passcode: ofHwmT  

As device performance continues to scale, so too does the need for increased integration of metals, specifically electrodeposited copper (Cu), which has traditionally been the conductor of choice for many electronic applications due to its low electrical resistivity (1.72 μΩ⋅cm), excellent thermal conductivity (398 W/mK), ease of integration allowing for patterning of interconnects and thermal structures on package substrates, and relatively low cost. However, the biggest drawback of Cu within electronic packages remains its relatively high coefficient of thermal expansion (CTE) of ~17 ppm/K compared to traditional semiconductor and substrate core materials: ~3 ppm/K for Si, ~4 ppm/K for silicon carbide, ~4.5 ppm/K for gallium nitride (GaN), and a tailorable ~3 - 9.5 ppm/K for glass. This CTE mismatch prevents the desired increased integration and density of Cu within electronic packages. For example, fully-filled through-package vias provide incredible performance enhancements over conformal ones, particularly at high aspect ratios; however, these vias have various critical stress points due to CTE mismatches between the substrate and the via Cu, and thus limits and constrains what can be designed and manufactured reliably today. In parallel, thermal densification of electronic packages is driving the need for more integrated, near-junction passive heat spreading solutions such as thermal vias or heat slugs. However, the amount of metal, specifically Cu, that can be integrated within electronic packages is limited by CTE-mismatch driven thermomechanical stresses that induce warpage, delamination, or, more severely, cracking of semiconductor devices. Materials such as Cu-Mo-Cu or Cu-W have been explored to help mitigate CTE mismatch, but while such materials may mitigate stress, they come with the tradeoff of deteriorated electrical and thermal performance. Thus, the best way to design a material that meets or exceeds the desired properties for advanced packages is through the development of metal matrix composites (MMCs) where the reinforcement material has properties that exceed that of Cu. 

Graphene (Gr) reinforcement of metals has recently gained momentum to not only enhance electrical, thermal, and mechanical properties but also control the metal matrix composites' grain structure and its evolution at the nanoscale. Specifically, electrodeposited copper-graphene (CuGr) composites have been explored as a material that maintains or exceeds all the electrical, thermal, ease of use, and cost benefits of Cu while retaining electronic package processability. The final composition is mainly governed by the initial volume loading of Gr in the plating bath and any applied agitation methods, giving, so far, limited returns in terms of property improvements. Achieving the theoretical maximum material performance requires 1) a high Gr relative content, 2) homogeneous dispersion of Gr throughout the composite, and 3) controlled alignment of Gr within the material. To address this grand challenge, a novel magneto-electrodeposition process is proposed in this paper wherein a low-magnitude magnetic field is applied during plating to tailor the microstructure, composition and, subsequently, the material properties of CuGr composites. 

This thesis will focus on assessing the effect of applied magnetic fields on electrodeposited copper-graphene composites in terms of their material composition, microstructure, morphology, and subsequent electrical, mechanical, and thermomechanical properties for use in next-generation advanced packaging. Key results will demonstrate the effects of magnetic fields on graphene, establish theories for the effects of Gr-reinforcement in Cu matrices, experimental setup, methodology, and proof-of-concept for magneto-electrodeposition of copper-graphene composites, characterization of morphology and mechanical and electrical property improvements, theoretical modeling of potential property improvements of graphene-reinforcement of copper, and finite-element modeling to evaluate the potential benefits of copper-graphene composites in various advanced packaging applications. 

Committee:  

• Prof. Vanessa Smet – George W. Woodruff School of Mechanical Engineering (Advisor) 
• Prof. Rao Tummala – School of Electrical and Computer Engineering, School of Materials Science and Engineering (Co-Advisor) 
• Prof. Preet Singh – School of Materials Science and Engineering 
• Prof. Eric Vogel – School of Materials Science and Engineering 
• Dr. Jobert van Eisden, MKS Instruments, Inc.