Thin-film Multichip Module Research Articles

Thin-Film Flip-Chip Assembly for High-Temperature Geothermal Application

A thin-film multichip module technology has been developed and evaluated for packaging high-temperature (300 °C) geothermal well instrumentation. Since a measurement-while-drilling tool is exposed to a combination of high-temperature and shock/vibration loading, flip-chip technology was selected to avoid vibration-related problems with bond wires. Thermocompression flip-chip bonding was characterized in thermal aging, thermal cycling, and thermal shock/vibration tests. Three digital circuit boards were fabricated and electrical characteristics of the digital circuit boards were evaluated. The experimental results show that thin-film substrates combined with flip-chip assembly are a viable approach for fabrication of digital circuit boards for use in extreme environments.

Thin-Film Multichip Packaging for High-Temperature Geothermal Application

A thin-film multichip module substrate technology has been developed and evaluated for packaging high-temperature (300 °C) geothermal well instrumentation. The base substrate technology selected was AlN to minimize the difference in the coefficient of thermal expansion between the substrate and the SiC digital die. The conductor was vacuum deposited Ti/Ti:W/Au followed by an electroplated Au. A plasma-enhanced chemical vapor-deposited silicon nitride was used for the interlayer dielectric. The substrate was characterized as a function of temperature and after aging at 300 °C. The electrical properties and adhesion remained stable after 2000 h at 300 °C.

Electrical characterization and reliability study of integrated GaN power amplifier in multi-layer thin-film technology

In this work, the degradation of a GaN power amplifier (PA) integrated in a thin film multi-chip module (MCM-D) interconnect technology is investigated by means of DC and RF measurements. Failure analysis has demonstrated that improper thermal contact may cause the PA module performance degradation. Moreover, we have experimentally studied the thermal effects on the RF performance of MCM-D and low-temperature co-fired ceramic (LTCC) PAs. It shows that the device exhibits a higher output power density on a thinned MCM-D substrate than on an LTCC substrate with thermal vias, and also that the output power density can be further improved by reducing the heat spread distance between active devices and heat sink.

Photo‐induced millimeter wave losses in coplanar waveguide on high resistivity silicon

AbstractWe report on a multifunctional optoelectronic radio frequency attenuator for millimeter wave applications, designed in a multilayer thin‐film multichip module technology on high resistive silicon. Insertion loss of measurements and electromagnetic simulations of a coplanar waveguide line under illumination demonstrate a contrast of 40 dB at 100 GHz. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 808–810, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22288

Innovation via Photosensitive Polyimide and Poly(benzoxazole) Precursors-a Review by Inventor

In order to work out indispensable criteria for a promising process of innovation, a historical review is given for two paths of innovation, which the author was involved in as an chemist in electrical industry from the initial idea up to commercialization and application in the field of microelectronics and electronics. The examples concern the approach to thermally stable organic patterns via photosensitive precursors of polyimides (negative mode) and of poly(benzoxazoles) (positive mode). After direct photolithographic patterning the precursor layers can be thermally converted into polyimide and poly(benzoxazole), respectively. The photoresists have been commercialized by licensed chemical companies. They have been and still are mainly applied to memory and logic devices as protective and buffer coatings to reduce the stress caused by an encapsulating resin, and to thin film multichip modules as planarizing interlayer dielectrics.

Single-package integration of RF blocks for a 5 GHz WLAN application

Transceivers for future digital telecommunications applications (third generation cellular, wireless LAN) need to be portable (compact), battery-powered and wireless. Today's single-chip solutions for RF front-ends do not yield complete system integration. For example, they typically still need external components for impedance matching, for antenna switches, for power amplifiers and for RF bandpass filters (BPFs). Furthermore, problems of substrate coupling (either manifesting as analog crosstalk or as noise coupling from the digital part to the analog part on mixed-signal chip) become more important with increasing integration. A system-in-a-package (SiP) approach can address these problems. High quality components can be integrated in the package, avoiding lower quality on-chip passives or circumventing expensive chip technology adaptations. Virtually all external components can be integrated, as shown in this paper for the case of the bandpass filters and the impedance matching. Even the antenna is a candidate for integration in the package. Further, a clever chip partitioning can reduce the substrate coupling problem. Partitioning also allows using the best IC-technoiogy for each component. This paper reports on a fully integrated single-package RF prototype module for a 5 GHz WLAN receiver front-end, which is intended to demonstrate the concept of SiP integration. The approach, that is illustrated here with prototype RF blocks for a 5 GHz WLAN application, is implemented with a thin film multichip module (MCM-D) interconnect technology. This technology also allows the integration of high quality passive components. With these passives, low-loss filters can be implemented. The use of passives, filters and off-the-shelf, active, bare die components opens the way to successful system integration.

A direct Ku-band linear subharmonically pumped BPSK and I/Q vector modulator in multilayer thin-film MCM-D

A direct Ku-band linear subharmonically pumped binary phase-shift keying (BPSK) and in-phase/quadrature (I/Q) vector modulator have been developed using multilayer thin-film multichip module (MCM-D) technology. All passives are integrated in the low cost MCM-D substrate. To the authors knowledge, this is the first modulator based on thin-film integrated passive components. The subharmonic mixing is performed using a beam-lead antiparallel diode pair mounted onto the MCM using thermocompression. A custom diode model has been developed and verified using nonlinear network analyzer measurements: an excellent agreement between the measured and simulated powers and phases for more than nine harmonics is demonstrated. Additionally, it is shown that an optimal reactive termination for the third harmonic of the local oscillator (LO) exists such that a very flat BPSK mixer conversion is obtained. This is validated by measurements that indicate a /spl plusmn/0.25-dB variation on the conversion loss for an LO frequency varying from 6.8 to 7.6 GHz. The I/Q vector modulator consists of a Wilkinson power divider, a coplanar-waveguide Lange coupler, and two BPSK modulators. It has a measured image rejection better than -27 dB over the RF range of 13.4-15.2-GHz band (corresponding to a vector phase and amplitude error lower than 2/spl deg/ and 1%). The image rejection is even better than -32 dB over the very small aperture terminal band (RF: 14-14.5 GHz).

Chip-package codesign of a low-power 5-GHz RF front end

Future high-performance wireless communication applications such as wireless local area networks (WLANs) around 5 GHz require low-power and highly integrated transceiver solutions. The integration of the RF front end especially poses a great challenge in these applications, as traditional front-end implementations require a large number of external passive components. In this paper, we present the single-package integration of complete transceivers based on a thin-film multichip module (MCM) technology with integrated passives. The MCM substrate is a a common carrier onto which different ICs are mounted. passive components such as RF bandpass filters, inductors, capacitors, and resistors are directly integrated into the MCM substrate with the use of the multilayer structure of the MCM technology. The "system-on-a-package" approach is illustrated with a voltage-controlled oscillator for Digital European Cordless Telephone (DECT) applications and a 5-GHz WLAN front end. These examples indicate that this approach yields a compact low-power implementation of complete transceivers for high-performance wireless applications.

Generalized analysis of coupled lines in multilayer microwave MCM-D technology-application: integrated coplanar Lange couplers

In this paper, the design and realization of coplanar Lange couplers integrated in a multilayer thin-film multichip module deposition (MCM-D) technology is discussed. The MCM-D technology has been well established for the interconnection of high-speed digital circuits, and is now being recognized to be very useful for the integration and interconnection of microwave components. In this way, passive structures, such as spiral inductors, filters, and couplers, may be realized efficiently and more cost effective in MCM-D compared to monolithic microwave integrated circuits. The presented coplanar Lange couplers have been designed using an equivalent coupled-line model. A general and computationally efficient method for the determination of the required modal characteristic impedances and the related geometrical parameters in a microwave multilayer coupled-line topology is presented. Also, a way to calculate the optimum coupled line length is given. Using the described method, coplanar Lange couplers have been realized and then measured. Comparison between the measurement results and HP Momentum simulations show good agreement and indicate the feasibility of designing and integrating such components in MCM-D.

Performance analysis of MCM systems

When a new interconnection technology is developed, it is of interest to accurately characterize its electrical features from a system's perspective and evaluate its possible application areas and boundary limits. Accurate design models can then be extracted and used for a correct design and implementation of electronic systems. This paper describes a case study used to characterize a five-layer thin-film multichip module (MCM) technology developed for high speed digital applications. The high frequency characterization of the substrate has been combined with the electrical models of the input/output (I/O) buffers of a complementary metal-oxide-semiconductor (CMOS) technology to accurately analyze the signal propagation with a network simulation tool. A test chip and MCM module have been developed to evaluate how the maximum system frequency is influenced by different quantities such as line length, type of driver or noise. Experimental results, showing a good match with simulations, demonstrate the effectiveness of this approach. It is also shown how it is possible to take advantage of some apparently limiting features of thin-film MCM's to actually improve the system performance.

Analysis of a multilayered-metal thin-film transmission line

In this study, a perturbed-TEM analysis was conducted on a two-wire transmission line with a two-layered metal system that represents a typical metallurgy used in thin-film multichip modules (MCM's). Closed-form solutions were obtained for the current density, resistance, inductance, attenuation, and phase velocity. The proximity effects were clearly illustrated in the current density plots. It was shown that the increase in the attenuation and the resistance was caused by the skin effect and the power loss in the cladding conductor (copper line clad with 0.1-/spl mu/m thick chromium), and the increase (decrease) in the phase velocity (internal inductance) of the thin-film lines was caused by the penetration of the magnetic field into the conductors. >

SURF: rubber-band routing system for multichip modules

Current PCB (printed circuit board)-based routing tools cannot meet the performance and cost constraints presented by today's packaging technologies, including thin-film multichip modules. The authors describe SURF, a routing system designed specifically to meet these challenges. The strength of the SURF system comes from its extremely flexible rubber-band data representation. The rubber-band model is an ideal framework for performance-driven and cost-driven routing and naturally supports rectilinear, octilinear, and all-angle wiring patterns: one-and-a-half-layer routing; even wiring distribution; and powerful manual editing. The integrated spoke-based design-rule-checking/enforcement mechanism supports an incremental design style. As objects are moved or wires are resized, the wires are adjusted incrementally so that they maintain the same wiring topology. By working in the topological domain instead of the geometrical one, the designer can focus on higher-level design issues while the tool handles the precise geometrical details.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

α α′ α″ α‴ Poly-tetrafluoro-p-xylylene as an interlayer dielectric for thin film multichip modules and integrated circuits

α α′ α″ α‴ Poly-tetrafluoro-p-xylylene (PA-f ) has been evaluated as an interlayer dielectric for multichip modules and integrated circuits, and its properties are reported. It has a lower dielectric constant and higher thermal stability than parylene-n (PA-n). The as-deposited films have very low crystallinity. The crystallinity increases as the film is annealed. Thermogravimetric analysis has shown that these films lose weight at temperatures higher than 480 °C. A shrinkage in the films of ∼10% was observed when annealed in a vacuum at a temperature of 425 °C. The as-deposited film has a low dielectric constant of 2.38 and a volume resistivity of 1.3×1016 Ω cm. The refractive index at optical wavelengths was 1.3 for as-deposited samples and it increased with annealing temperature. The stress levels observed after annealing are also lower (20 MPa) than for PA-n (40 MPa). The hardness, as determined by a microindentor, of PA-f was 0.56 GPa in the bulk, but the surface hardness was ∼1.0 GPa. The conformal nature of these films permitted successful coating of micron-sized gaps having an aspect ratio of 1.5–2. Diffusion of Cu into PA-f is reported here and is contrasted with Cu/PMDA-ODA polyimide. Scanning electron microscopy of film cross sections shows microstructure changes above 350 °C. The low dielectric constant and high thermal stability of PA-f makes it a good insulator for high-speed interconnection applications.

Evaluation of thin film MCM materials for high-speed applications

The role of material properties in thin-film multichip module (MCM-D) performance as signal frequencies increase above 100 MHz is examined. Specifically, the impact on system performance of dielectric constant, dielectric loss tangent, interconnect metal resistance, and interconnect metal skin depth is discussed. These properties are compared for common MCM-D materials.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Processing and performance of gold MCMs

The use of gold metallization in multichip modules (MCMs) has been investigated for the purpose of achieving simplified processing and high reliability. A process has been developed for producing multilayered, gold metallization thin film MCM (MCM-D) structures which reduces the number of processing steps compared to copper metallization. Multilayered gold-polymer and gold-SiO/sub 2/ test devices have been fabricated to evaluate the electrical and mechanical properties of the structures. The adhesion of a variety of dielectrics has been achieved by blanket coverage of the noble metal with a single step adhesion layer. The processing, performance, adhesion layer, and cost of gold MCM-D structures on silicon substrates have been analyzed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Guidelines governing the need for low-impedance drivers for MCM's

High-speed, large-area integrated circuits (ICs) require packages with high-density, small cross-sectional interconnections. This trend toward more resistive interconnections is particularly clear for advanced thin-film multichip modules (MCMs). To obtain high clock speeds with these ICs and these packages requires a combined design of drivers, lines, and loads. By extending traditional impedance-matched design to a generalization that adjusts load, line, and driver for overshoot-controlled performance, maximum line lengths and driver impedances are found beyond which underdamped (i.e., rapid) response is not possible. These limits are provided for on-chip, MCM, and printed-circuit-board (PCB) interconnections. For line lengths typical of advanced thin-film MCM interconnections, an underdamped circuit response requires a driver with impedance significantly less than the characteristic impedance of a lossless interconnection line of the same geometry. As a result, drivers are required with impedances below the normal impedance-matched condition. Alternatively, wiring cross-sections can be increased with a corresponding decrease in wiring density or an increase in the number of wiring layers. >

Stress in thermally annealed parylene films

Stress is a problem for thin film Multichip Modules (MCM) fabrication and reliability. Stress can cause adhesion failure, wire cracking and fracture of the polymer. Parylene can be deposited in a low compressive stress state, and here we explore its temperature-stress behavior. The stress generated by thermal coefficient of expansion (TCE) mis-match between thick parylene-n (PA-n) films (4-7 μm)and Si substrates has been studied as a function temperature. Measurements of stress were made on as-deposited films; after thermal annealing and also in-situ. The as-deposited films are under compressive stress of 20 MPa. As the films are annealed, the stress decreases and then becomes tensile, peaking at about 53 MPa. It was observed that stress was reduced in PA-n films during the crystal phase transformations at around 200 and 270°C. The stress has been compared to reported data from other sources and found to agree. Stress in PA-c (chlorinated), and co-polymerized PA-n ande (ethyl) films, and a fluorinated parylene (PA-f) are also evaluated. The effective glass transition temperatures and the linear coefficient of expansion have also been estimated.

Multichip Module Technology: The Transition from Research to Manufacture

The benefits of the thin film multichip module (MCM‐D) approach to high density packaging for VLSI devices have now been amply demonstrated by a number of research groups. The successful emergence of a viable multichip module industry from this research base will, however, depend upon the installation of an industry‐wide manufacturing infrastructure. This will have to provide the necessary range of concurrent design capabilities, make pretested bare die available, and include multichip module vendors who can offer an integrated capability in module design, substrate layout and manufacture, advanced module assembly, packaging and test. Each of these areas of MCM‐D technology merits detailed attention in its own right, sufficient to justify many individual papers and presentations. This present paper focuses on just one of these topics and addresses the approach taken by GEC Plessey Semiconductors (GPS) to the development and control of a highly manufacturable MCM‐D silicon substrate process. The GPS ‘Process I’ four‐layer metal, aluminium‐polyimide substrate technology is described, the technology development and process control test structures are detailed and process characterisation data presented.

Crisis in technology: the questionable US ability to manufacture thin-film multichip modules

It is argued that even though the technology choices are available, the ability to procure deposited multichip modules (MCM-D) in the US is seriously threatened by the inability to obtain volume orders. The result is the withdrawal of capital at just the time when the capabilities are more and more certain. The future capability in the necessary thin-film multichip module technology may not exist if the companies with capability fold before volume orders are placed. A prescription to stimulate volume production of thin-film MCMs is offered.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Engineering software-multichip routing and placement

The demands being placed on CAD systems by current advances in packaging technology, in particular, the need to design interconnecting networks for thin-film multichip modules (MCMs), are discussed. The approaches embodied in several recently developed software packages are described. These include interactive placement and routing, warping, shape-based routing, rubber-band routing, and correct by design. The role of concurrent engineering in the design process is examined. >