A wafer-scale packaging structure with monolithic microwave integrated circuits and passives embedded in a silicon substrate for multichip modules for radio frequency applications

Abstract

A wafer-level packaging structure with chips and passive components embedded in a silicon substrate for multichip modules (MCM) is proposed for radio frequency (RF) applications. The packaging structure consists of two layers of benzocyclobutene (BCB) films and three layers of metalized films, in which the monolithic microwave ICs (MMICs), thin film resistors, striplines and microstrip lines are integrated. The low resistivity silicon wafer with etched cavities is used as a substrate. The BCB films serve as interlayer dielectrics (ILDs). Wirebonding gold bumps are used as electric interconnections between different layers, which eliminate the need of preparing vias by costly procedures including dry etching, metal sputtering and electroplating. The chemical mechanical planarization (CMP) is used to uncover the gold bumps, and the BCB curing profile is optimized to obtain the appropriate BCB film for CMP process. In this work, the thermal, mechanical, electrical as well as RF properties of the packaging structure are investigated. The packaging thermal resistance can be controlled below 2 • C W −1 . The average shear strength of the gold bumps on the BCB surface is about 70 MPa. In addition, a Kelvin test structure is fabricated for resistance testing of the vertical vias. The performances of MMIC and interconnection structure at high frequency are simulated and tested. The testing results reveal that the slight shifting of S-parameter curves of the packaged MMIC indicates perfect transmission characteristics at high frequency. For the transition structure of transmission line, the experimental results are compatible with the simulation results. The insertion loss (S 21 ) is below 0.4 dB from 0 to 40 GHz and the return loss (S 11 ) is less than −20 dB from 0 to 40 GHz. For a low noise amplifier (LNA) chip, the S 21 shifting caused by the packaging structure is below 0.5 dB, and S 11 is less than −10 dB from 8 GHz to 14 GHz.

System-on-Package Platform with Thick Benzocyclobutene Layer for Millimeter-Wave Antenna Application

“…There are many reports that organic materials have a very poor interfacial fracture resistance (adhesion) to gold. [11][12][13][14] However, the adhesion between BCB and inorganic materials, such as SiO 2 and SiN x is good. 15) Thus, the insertion of a layer of inorganic materials between gold and BCB can improve the adhesion.…”

“…The roughness average (R a ) of the BCB surface after CMP was about 3.2 nm, which is comparable with other groups' results. 13,28) 77 GHz patch array antennas were fabricated with an additional multilayer thin-film process. Details of our previous SOP technology are shown in ref.…”

Wafer-level multilayer integration of RF passives with thick BCB/metal interlayer connection in silicon-based SiP

“…The differences of these two processes are marked out by dark backgrounds. Details of these processes can be referred to Geng et al (2009) andTang et al (2011), respectively. There are some notes to be mentioned for the sake of subtle differences of these two processes.…”

A study on the effect of wire bonding interconnects of BCB capped CPW to CPW on LTCC substrate

“…Multidie package can be realized using multiple die bond and lamination process. In another way, chips can be embedded on a common Si substrate using BCB polymer coating and via patterning . Through common metal interconnect lines on BCB surfaces, RF chips have a benefit of short interconnect resulting in large operation frequency range.…”