Effects of anisotropic nonconductive film properties on 3D IC integration

Driven by technology trends towards 2.5D and 3D IC integration for higher bandwidth and small form factor, the demand for high thermal conductivity materials is growing in order to facilitate thermal management. At the same time, constraints in critical dimensions at the bondline set new challenges for materials and processing. This study analyzes both advancement in high thermal conductivity materials and improvements in integration for thermal management. Polymeric matrix materials often used as underfill in advanced packaging currently was forced to the use of small fillers for 3D IC integration. This reduction of filler size in polymer composite tends to reduce its ability to improve thermal conductivity. Presently, however, the increasing development and adoption of wafer level packaging offers new processing capability and cost reduction. Nonconductive film has evolved as a new form for underfill materials associated with laminating processes. Thermal conductivity improvement in underfill can therefore be categorized into two categories, the improvement of composite materials and the consideration of new alternative materials. This study uses mathematical models to explain the evolution of anisotropic properties of high thermal conductivity nonconductive film materials. Finite element analysis is conducted to assess the ability of hot spot reduction in a 3D IC system with the innovative anisotropic thin film composite underfill. The high bandwidth memory JEDEC standard 3D IC structure (HBM2) integrated with anisotropic thin film composite underfill is used as an example for this study. Discussions are expanded to cost analysis due to the needs of additional process steps to integrate the new materials into advanced packaging for 3D IC integration.