Dispersion of functionalized SiO2 particles into a Liquid Crystal Polymer matrix for a reliable HF package

The development of a new generation of innovative thermoplastics for microelectronics and photonics applications is essential to make cavity packages able to compete with ceramic packages in terms of weight, cost and design flexibility (transparent materials for optical components). Among plastic materials, thermoplastic resins such as Liquid Crystal Polymer (LCP) offer attractive properties including low gas permeation, high temperature resistance, thermal stability and low dielectric constant (3.1 at 1 MHz and 2.8 at 10 GHz). In order to reduce anisotropic mechanical properties inducing a discrepancy in CTE and Young´s modulus values various approaches are currently studied in particular the addition of mineral fillers into the LCP. Silicon dioxide (SiO₂) is commonly used as additive compound because both it improves mechanical properties of polymers and has a low dielectric constant. However agglomeration of fillers affects the dispersion into LCP. An original approach consists in a chemical functionalization of SiO₂ particles to enhance the dispersion. Two chemical functions (phenyl and hydroxyl) are studied using various filler contents (10 and 20%wt in the LCP). Composite materials are analyzed by Scanning Electron Microscopy to observe the spatial distribution of the functionalized particles. Thermal and mechanical properties (CTE and Young´s modulus) of each composite are characterized and compared. In a final point, long-term reliability based on the proposed formulations of the LCP composite is evaluated by FEM simulations.