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Reliability Studies in Advanced Halogen-Free Organic Laminates for Ultra-Fine Pitch 3D Packaging
Keywords: Halogen-free materials, electrochemical migration, Flip-chip reliability
High I/O density and “green” materials are two major drivers of package substrates for flip-chip and 3D IC packaging. Future organic laminate substrates will require 5-25μm lines and spaces and through package via (TPV) pitch of 50-250μm. This ultra fine pitch requirement will lead to serious substrate failures due to electrochemical migration and conductive anodic filament (CAF). While CAF reliability in halogenated materials has been reported at board-level, there has been limited research data available on halogen-free materials at board and package level at very fine pitch. Therefore, there is a need to investigate the electro-migration reliability in ultra-fine pitch halogen-free substrates because of the recent limitations in use of halogenated materials. This work focuses on four areas, 1) Novel halogen-free organic materials 2) Surface insulation resistance (SIR) on fine lines and spaces 3) Conductive anodic filament (CAF) in fine pitch TPVs and 4) Flip-chip package reliability. The substrate materials selected for this study include novel resin formulations that incorporate halogen-free flame retardants onto the polymer backbone, reducing the need for particulate flame retardants. For comparison with state-of-the-art, conventional resin formulations were also studied. The SIR was studied on substrates with finely spaced (30µm and 50 µm) copper traces and CAF was studied with TPVs of 100 µm, 150 µm and 500 µm spacing. The SIR and CAF tests were carried out at 85OC and 85% RH with 100V DC bias. Flip- chip test vehicles were subjected to Moisture Sensitivity Level 3 (MSL3) and 3x reflow (peak temperature 260OC) preconditioning prior to subjecting them to Thermal Cycling Test (TCT), Unbiased-Highly Accelerated Stress Test (U-HAST) and High Temperature Storage (HTS) test. SEM and EDS analysis was performed to understand the failure mechanisms in halogen-free systems. The halogen-free substrates were observed to show better electrochemical migration resistance in comparison to brominated FR-4.
Koushik Ramachandran, Graduate Research Assistant
Georgia Institute of Technology; 3D Systems Packaging Research Center
Atlanta, GA

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