System-in-a-Package on Low-Cost Liquid Crystal Polymer Substrate

Doktorsavhandling, 2005

System-in-a-Package (SiP) is one of the most advanced approaches to meet the requirements for future high-density electronics packaging. In this thesis, a 3D system-in-a-package concept with embedded active and passive components is proposed, where a liquid crystal polymer (LCP) was used as the base substrate. The high frequency properties of LCP were studied first. The relative dielectric constant and loss tangent were measured using a ring resonator. In the frequency range of 3GHz to 35GHz, the measured relative dielectric constant of LCP is about 3.0. The measured loss tangent is below 0.0045. This means that LCP has RF properties similar to Teflon based substrate materials and therefore can be used for high frequency electronics packaging applications. To demonstrate a SiP using LCP, a GaAs MMIC switch chip was embedded into a LCP substrate and connected to outside by bonding wires. The high frequency performance of this wire-bonding module was tested using a network analyzer. The test results show that the embedded MMIC works well. It proves that the embedded structure with LCP substrate is feasible to realize SiP. A fully planar SiP module and integrated passive components including inductors, capacitors and resistors were fabricated using the thin-film multi-chip module technique (MCM-D) where the standard clean-room processes, such as spin-coating, lithography, thin film deposition, were adopted. The high frequency performance was analyzed. Lumped element model of the integrated passive components were proposed. Good agreement is achieved between the measured and modeled data. Anisotropic Conductive Adhesive (ACA) offers a promising alternative for flip-chip interconnection due to its fine pitch and simpler processing capability. ACA is becoming an alternative for electronic packaging flip-chip interconnection. Using 3D finite difference in time domain (FDTD) method, the RF performance of a single ACA flip-chip joint is investigated. The simulation results show that the number and the distribution of the conductive particles in ACA have little influence on the high frequency transition of the ACA flip-chip joint. The adhesive resin also has limited effect on the high frequency performance of the ACA flip-chip joint. An equivalent circuit model of a single ACA flip-chip joint was proposed. The MMIC used in SiP was also flip-chip assembled using ACA as interconnection method. The high frequency and thermal mechanical performances of the flip-chip structure were studied. The high frequency performance has been simulated using a lumped element model. The finite element method (FEM) computation of the thermal mechanical characterization of the ACA flip chip assembly in a cooling process was performed. The simulation results show that LCP has good high frequency performance. The LCP substrate has better thermal mechanical performance than a Teflon substrate.