Printed Circuit Design & Fab - February 2009 - (Page 22)

PackaGinG embedded active Components in MulTilaYer lCp paCKageS Embedded active technology offers advantages in reduced parasitics and form factors, but thermal dissipation and rework issues are delaying commercialization. by SWAPAN K. BHATTACHARyA, NICKoLAS KINGSLEy, CHAD PATTERSoN and JoHN PAPAPoLyMERoU Embedding integrated circuits (IC) within a multilayer package dates back to the work of Gene Weiner at MIT’s Lincoln Laboratory in 1950. The team placed devices within resin and routed interconnections by mechanical drilling.1 However, the leapfrog work is credited to General Electric. In the early 1990s, the company accomplished the real embodiment of chips in a multilayer package.2 Since the inception of GE’s "chip first" process, several approaches have been undertaken in embedding chips into polymer and other thin core matrices. Such innovations can be encompassed by three major categories: cavity formation to the size or volume of the chip, lamination similar to the LTCC process adopted in ceramics with the chip within the multilayer laminated sheets and over-molding upon placement of the chips.3 Besides reduction in thickness, another key advantage in embedding actives is the decreased interconnect length. An analysis of parasitics in different package configurations was conducted by Daum2 at GE. Results showed that HDI with embedded components and actives could lead to a significant reduction in parasitics.2 In recent years, Liquid Crystal Poly22 mer (LCP) has received attention as a high-frequency substrate material. LCP has low dielectric constant (~2.97), low dielectric loss and temperature stability up to 125o C across a wide frequency range up to 110 GHz.4-6 The coefficient of thermal expansion (CTE) of LCP can be engineered to match that of copper, silicon or GaAs. The availability of two types of LCP substrates with different melting temperatures makes it possible to realize multi-layer architectures. LCP is uniquely positioned at a frequency band where conventional organic dielectrics, such as FR 4, degrade in performance (at around 5 GHz). Nevertheless, to date, the major constraint for the commercialization of LCP has been its processability, such as surface treatment, handling of thin flexible films and layer-to-layer registration and via formation and plating. These issues have been addressed by several academic7-8 and industrial organizations, such as Endicott Interconnect Technologies9 and Foster-Miller Inc.10 Embedded devices in LCP have been realized by the lamination process with micro-machined cavities, as well as by the molding process with a liquid polymer. A combined path in embed- ding chips and passives and enhancing thermal performance of the embedded IC in a flex circuitry was first reported by Torikka11 using LCP and liquid Benzocyclobutene (BCB). BCB provides the lowest dielectric loss (Dk = 0.0008) among the polymers. The key advantages in combined solid LCP/liquid BCB processes are thermal cooling from the back of the chip and feasibility of coreless packaging.12 Comprehensive research and prototypes have been published leading to the realization of embedded RF components and devices in all LCP packages.4-6 A conceptual layout of an all-LCP organic package with micro-machined cavities to host actives such as amplifiers and oscillators, discrete components and MEMS is depicted in FiGurE 1. The following FiGurE 1. A cross-sectional view of LCP package with embedded components. FEBRUARY 2009 printEd CirCuit dESign & fAB

Table of Contents Feed for the Digital Edition of Printed Circuit Design & Fab - February 2009

Printed Circuit Design & Fab - February 2009 Contents Our Line Market Watch Around the World Happenings ROI Tip Jar BGA Bulletin Interconnect Strategies Final Finsh Forum Defects Database Embedded Active Components In Multilayer LCP Packages Simulation: The Need for Speed Advanced Registration Systems The DC Design Squeeze Ad Index Do You Really Want a Better Autorouter? Designing With Conductive Materials, Part 1 Off th eShelf Marketplace On the Forefront

Printed Circuit Design & Fab - February 2009

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