Liquid Crystal Polymer for microwave and millimeter-wave multi-layer packages and modules

Hermetic packages are used to protect microwave and millimeter-wave monolithic integrated circuits (MMICs) against harsh environmental conditions, including changes in atmospheric pressure, humidity, moisture, and other natural hazards that would otherwise disrupt electrical connections or damage delicate electronics. Microelectromechanical systems (MEMS) require hermetic packaging to prevent against contaminating particles and moisture. Hermetic packages have a fine helium leak rate of around 1×10
^-11
atm-cc/sec and are known to provide the reliability in harsh environments. Current hermetic packages are based on metal and ceramic materials. Ceramic and metal packages are heavier, bulkier, and more expensive than organic counterparts. At the wafer-level packaging, high temperature wafer bonding is used to form hermetic cavities that result in tall structures. While organic packaging technology cannot provide true hermeticity, can it have a low enough leak rate to achieve competitive reliability? This is referred as “reliability without hermeticity” or near hermetic packaging. In this lecture, we will review the concept of hermeticity and near-hermeticity in electronic packages. Liquid Crystal Polymer (LCP), which has permeation close to glass, will be introduced as the next generation organic material for near-hermetic packaging. We will discuss results of LCP material characterization. We will then present the development of sealing techniques of LCP onto LCP and LCP onto semiconductor materials to form near hermetic cavities for housing MEMS and MMICs. Using the newly developed sealing techniques, we will demonstrate LCP wafer-level packages, surface mount packages and multi-chip modules to 40 GHz. Examples of wafer-level packages include the lamination of LCP onto Si to cap or package RF MEMS switches and a phase shifter with LCP-packaged MEMS. We will also present the development of low-loss surface mount LCP packages to 40 GHz. These surface mount packages are designed with novel feedthroughs that achieve a measured insertion loss of ~0.2 dB to 0.4dB up to 40 GHz and provide embedded filters. We will discuss bond wire compensation schemes, package to printed circuit board transition design techniques, electrical repeatability, and thermal performance of millimeter-wave surface mount packages. Reliability evaluation will be presented to demonstrate the robustness and reliability of LCP packages. Examples of the environmental tests include 1000 hours of 85°C and 85% humidity, temperature cycles, thermal shock, etc. Finally, we demonstrate the development of compact wide bandwidth passive components, multi-chip modules, and phased array antennas in multi-layer LCP boards at Ka-band.