Development of hermetic LCP for electronic device packages

Abstract

In this paper, a new method is utilized to develop the hermetic thermoplastics through modification of conventional LCP resins. Thermoplastic materials are synthesized for producing a hermetic barrier with a cavity structure made based on the materials compositions: near-hermetic liquid crystalline polymers (LCP), nano-sized mineral fillers, adhesion promoters, compatibilizers, inorganic microparticles and anti-oxidants. Near-hermetic LCP is used as the matrix resin to provide robust mechanical strength, heat resistant stability and electrical insulation. Nano-sized mineral fillers with large aspect ratio are incorporated into LCP matrix resin to increase its hermeticity without sacrificing the outstanding performance of LCP resins and simultaneously reduce the coefficient of thermal expansion (CTE) of LCP resins. Adhesion promoters are added into the LCP resin systems in order to improve the bonding strength with metallic substrates (copper / alloy 42 lead frame etc.) that provide the electrical input/output (I/O) path to electronic packages. Compatibilizers are used to modify the above-mentioned LCP systems with potential multicomponent phase separation and hence (to the fullest) make use of the benefits from each component in the composites. Inorganic microparticles are optional to either solve the processability or promote the functionality of the hermetic LCP systems. The synthetic methods are based on the mechanical blending through injection molding process at an elevated temperature. Anti-oxidants are required to prevent the thermo-oxidative degradation in synthesis of modified LCP nano-composites and subsequent applications, for example, pre-molded cavity quad flat no-lead (QFN) packages. The as-formed LCP resin systems possess high hermetic performance which is comparable to electrical glass with excellent dimensional stability in a wide range of application, especially for advanced electronic packages such as the open cavity QFN substrates for MEMS packages. The hermeticity of 8.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> atm-cc/s can be achieved. The adhesion of modified LCP to Ni/Pd/Au-coated copper lead frame can also meet the requirement for MEMS packaging.