Committee Members:  

Prof. C. P. Wong, Advisor, MSE

Prof. Seung Soon Jang, MSE 

Prof. Zhiqun Lin, MSE  

Prof. Madhavan Swaminathan, MSE/ECE 

Dr. Mohanalingam Kathaperumal, ECE 

High thermal conductivity epoxy composites in the application of 3D semiconductor packaging

Abstract: 

With the ultra-fast development of high-performance semiconductor devices through the increase of power and on-chip integration density, heterogeneous integration heat dissipation is becoming more crucial to maintain desired operating temperatures for chips. Excellent thermal management in 3D electronic encapsulation is very important because it can ensure the performance and reliability of the electronic device. Epoxy-based composites are one of the most common thermal management materials in electronic packaging due to their excellent adhesion strength, low cost, light weight, good processability, etc. However, epoxy itself only has a thermal conductivity of around 0.2 W/mK, so it needs to combine with thermally conductive fillers, such as aluminum oxide, aluminum nitride, and metal particles to improve its thermal conductivity. However, traditional thermal management materials struggle to dissipate large amounts of heat efficiently to meet the requirements of next generation microelectronic devices. Therefore, new epoxy composites, especially those with novel nanofillers, need to be explored to maximize heat transfer efficiency. 

In this dissertation, graphene nanosheets are chosen as one of fillers to combine with epoxy for achieving a high thermal conductivity because of its ultrahigh thermal conductivity of 3500–5300 W/mK and large surface area of 2630 m2/g. However, graphene nanosheets easily aggerate, similar to particulate graphite platelets with low surface area, due to strong van der Waals attraction. Additionally, their surface is too smooth, resulting in poor interfacial connections with the polymer matrix. This ultimately causes phonon scattering that lowers the thermal conductivity of composites. Thus, modifying graphene nanosheets, including surface modification and morphology change, are discussed to solve these issues. In addition to the thermal conductivity of graphene-based epoxy composites, other properties like viscosity, CTE, storage modulus, and so on are also discussed for meeting the requirements of electronic packaging materials. Another filler is boron nitride nanosheets (BNNS), also known as white graphene, and it has attracted much attention due to its high thermal conductivity (200–600 W/mK), low density, and a large band gap (nearly 5.9 eV), excellent thermal stability, and superior anti-oxidation ability. These properties make it suitable for applications, requiring electrical insulation, in thermal management materials in semiconductor packaging. The modification of BNNS and pre-formed network of BNNS will also be explored. These two nanofillers can be used to create epoxy composites whose resulting properties could support the idea that these composites have potential to be applied in the next generation of semiconductor packaging materials for high-power and high-density ICs.