VISION AND STRATEGY
Thermal management has always been a major barrier for high performance systems such as PCs, workstations, mainframes and super computers that dissipate 100s of watts. The PRC’s SOP adds another barrier, this time for mobile products dissipating only few watts. The SOP trend towards ultra-miniaturization with 3D systems dramatically enhances the thermal density due to miniaturized volume. While liquid cooling architectures have been and continue to be used in high performance systems that could afford their size and cost, these are not acceptable technologies for handheld consumer applications.
PRC’s approach to thermal management involves four steps, as shown in fig.1.
1) Modeling and characterization
2) thermal interface materials(TIM) starting with silicon surface
3) thermal distribution across larger surfaces and
4) system level dissipation.
Miniaturized 3D systems require advanced thermal interface materials and bonding interfaces for efficient heat dissipation. Traditional polymer composite based thermal grease and gels may not be able to meet the thermal resistance targets between the active device layers and the heat spreaders.
Figure 1: Thermal management focus in PRC.
CURRENT RESEARCH PROJECTS
1. 3D Package Design, Materials and Structures for Thermal Management
Increasing chip heat fluxes and localized hot spots, along with die-thinning, and three-dimensional stacking will place ever-stringent demands on thermal management. The objective of this project is to lower the temperature in the die by: 1.) Design of via layers with high conductivity metallization, 2.) Die assembly with advanced die bonding materials, heat spreaders and inclusion of heat dissipation structures such as heat pipes. Thermal profiles are modeled for various packaging architectures with novel designs and materials to analyze thermal behavior of 3D systems. Advanced models that incorporate refinements from the new structures and materials are being developed to accurately predict the thermal profiles in the 3D system.
Figure 2: Numerical simulation example for a flip chip package.
2. Nanoscale Thermal Interface Materials
The objective of this project is to lower the TIM resistance to less than 0.01 C cm2/W with thin nanoscale thermal structures of CNT and graphite nanocomposites (Figure 3 and 4). The focus is on addressing the interfacial thermal resistance with unique nanostructured bonding layers that have phonon match and chemical compatibility with CNT. This project will also address the characterization methodologies and thermomechanical reliability issues along with the cost impact of advanced TIM.
Figures 3 & 4: CNTs and solder-graphite nanocomposites as thermal interface materials.
3. 3D Packaging with Fluidic Cooling
Package integrated fluidic channels combined with heat sinks is a promising solution to address the increasing heat dissipation needs in 3D ICs. This project integrates low-cost polymer channels with MEMS to integrate micropumps and fluidic channels for direct heat dissipation from the active device layers through advanced packaging design, materials and processes.
D. Advanced Phase Change Materials
The objective of this project is to incorporate phase change materials that can prevent temperature raise in the TIM and heat spreaders during transient peak loads. Nanocomposites of high conductivity CNTs and graphene combined with low melting solders and polymers (Figure 5) are explored to simultaneously enhance the thermal conductivity and latent heat of phase change while lowering the melting temperature.
Figure 5: Advanced Phase Change Materials (PCM) for thermal management in portable devices.
INDUSTRY CONSORTIA WITH THERMAL TECHNOLOGIES RESEARCH
1. Embedded MEMS, Actives and Passives (EMAP)
SELECTED PUBLICATIONS
1. Dong-won Yoo; Joshi, Y.K.; Energy efficient thermal management of electronic components using solid-liquid phase change materials, Device and Materials Reliability, IEEE Transactions on, Volume: 4 , .Issue: 4 Publication Year: 2004 , Page(s): 641 - 649
2. Reddy, G. Prashant; Raj, P. Markondeya; Nataraj, Nikhilesh; Rajesh, P. M.; Jha, Gopal; Choudhury, Abhishek; Kumbhat, Nitesh; Tummala, Rao; Brese, Nathaniel; Toben, Michael; Szocs, Edit; Co-electrodeposited graphite and diamond-loaded solder nanocomposites as thermal interface materials, Electronic Components and Technology Conference (ECTC), 2010 Proceedings 60th , Publication Year: 2010 , Page(s): 1708 – 1712.
3. Khiabani, R.H.; Joshi, Y.; Aidun, C.K.; Thermal characteristics of TIMs with elliptical particles Semiconductor Thermal Measurement and Management Symposium, 2010. SEMI-THERM 2010. 26th Annual IEEE , Publication Year: 2010 , Page(s): 100 – 106.
4. Lingbo Zhu, Yangyang Sun, Dennis W. Hess, and Ching-Ping Wong, “Well-Aligned Open-Ended Carbon Nanotube Architectures: An Approach for Device Assembly”, Nano Letters, 2006, Vol. 6, No. 2, 243-247.
5. Gerty, D.; Gerlach, D.W.; Joshi, Y.K.; Glezer, A.; Development of a prototype thermal management solution for 3-D stacked chip electronics by interleaved solid spreaders and synthetic jets, Thermal Investigation of ICs and Systems, 2007. THERMINIC 2007. 13th International Workshop on, Publication Year: 2007 , Page(s): 156 – 161.
6. Shinotani, K.-I.; Raj, P.M.; Seo, M.; Bansal, S.; Sakurai, H.; Bhattacharya, S.K.; Tummala, R.; Components and Packaging Technologies, IEEE Transactions on Evaluation of alternative materials for system-on-package (SOP) substrates Volume: 27 , Issue: 4, Publication Year: 2004 , Page(s): 694 – 701.
7. D. Yoo and Y. Joshi. 2004. Energy Efficient Thermal Management of Electronic Components Using Solid Liquid Phase Change Materials. IEEE Transactions on Device Materials and Reliability 4, 641-649.
RECENT INVENTIONS
1. Solder-assisted CNT transfer, C. P. Wong and L. Zhu, US patent pending.