Multichip Module Applications Research Articles

Recent advances in hermetic equivalent flip-chip hybrid IC packaging of microelectronics

Recent advances in polymeric materials and integrated circuit (IC) encapsulants have made high-reliability very large-scale integration (VLSI) plastic packaging a reality. High-performance silicone gel possesses excellent electrical and physical properties for IC protection. With their intrinsic low modulus and soft gel-like nature, silicone gels have become very effective encapsulants for larger, high I/O, wire-bonded and flip-chip VLSI chips. Furthermore, the recently developed silica-filler modified epoxies, with the well-controlled thermal coefficient of expansion (TCE), have enhanced the flip-chip and chip-on-board hybrid IC encapsulation. Recent studies indicate that, with adequate IC chip surface protection with high-performance silicone gels and epoxies, plastic packages could replace conventional ceramic hermetic packages. This paper reviews the IC technological trends, and IC encapsulation materials and processes. Special focus is placed on the high-performance silicone gel, epoxies and polyimides, their chemistry and use as VLSI device encapsulants for single and multi-chip module applications.

Novel techniques for millimeter-wave packages

A new millimeter-wave package architecture with supporting electrical, mechanical and material science experiment and analysis is presented. This package is well suited for discrete devices, monolithic microwave integrated circuits (MMIC's) and multichip module (MCM) applications. It has low-loss wideband RF transitions which are necessary to overcome manufacturing tolerances leading to lower per unit cost. Potential applications of this new packaging architecture which go beyond the standard requirements of device protection include integration of antennas, compatibility to photonic networks and direct transitions to waveguide systems. Techniques for electromagnetic analysis, thermal control and hermetic sealing were explored. Three dimensional electromagnetic analysis was performed using a finite-difference time-domain (FDTD) algorithm and experimentally verified for millimeter-wave package input and output transitions. New multi-material system concepts (AlN, Cu, and diamond thin films) which allow excellent surface finishes to be achieved with enhanced thermal management have been investigated. A new approach utilizing block copolymer coatings was employed to hermetically seal packages which met MIL STD-883. >

Chip on Board: Technologies for Multichip Modules

Preface Acknowledgments A brief introduction to wire bonding, tape automated bonding, and flip chip on board for multichip module applications Making COB testing tractable: chip pretest and system diagnostics Chip level interconnect wire bonding for multichip modules Chip level interconnect: wafer bumping and inner lead bonding Chip level interconnect: solder bumped flip chip Chip attachment Wire bonding chip on board Tape automated bonding chip on board and on MCM-D Solder bumped flip chip attach on SLC board and multichip module Micron bump bonding chip on board chip on board encapsulation Underfill encapsulation for flip chip applications Index

Evaluation of polymeric coatings for MCM applications

An effort was initiated under the Reliability without Hermeticity (RwoH) project to evaluate the performance of nonhermetic coatings for multichip module (MCM) applications. As a means of selecting coating materials, Sandia ATCO1 test chips, with and without chip passivation (SiN), were coated with three nonhermetic polymer materials: a silicone gel, a filled epoxy, and a polyimide. Some of the coated parts were preconditioned (500 temperature cycles and 96 h of salt spray), and some were not. The coated parts were subjected to either pressure cooker test (PCT-121/spl deg/C, 99.6% RH, no bias) or temperature-humidity-bias (THB-85/spl deg/C, 85% RH, 40 V bias) tests, for 7000 and 10 000 h, respectively. In this paper, the moisture protection performance of the coatings on nonpassivated test chips is presented in detail. In addition, some overall comparisons of the failures in passivated and nonpassivated chips are given. For the preconditioned parts, THB median lives (times to 50% failures) in excess of 10 000 h were obtained for the epoxy and the gel coatings. Polyimides exhibited a THB median life of 6950 h. In PCT, the three coatings exhibited similar median lives in the range of 350-400 h, but, much different failure kinetics. Based on earlier published studies, these median lives are representative of good coating performance. The failures in the nonpreconditioned coated parts were much lower (20-50%) for the gel and the polyimide coatings, at the end of THB tests. Epoxies on the other hand did not exhibit such influence of preconditioning steps on failures. The comparison of passivated and nonpassivated coated ATC01's revealed that the presence of passivation enhances the moisture protection performance of all three coatings. This effect was especially pronounced for the silicone gel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Open repair technologies for MCM-D

IBM has developed various technologies for repairing defects in thin film circuitry, primarily for Multichip Module (MCM) applications. This paper discusses five technologies: laser chemical vapor deposition (LCVD), wire bond, laser-sonic bonding, solder repair, and self-induced repair, with focus on the process parameters and tooling aspects of the three established in IBM's production environment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laser system for fine pitch Tape Automated Bonding

A system has been developed for implementing a solderless fine pitch Tape Automated Bonding (TAB) process. The process was applied to multichip module (MCM) packages with lead pitch of 100 μm. The technology can be extended to ultrafine pitch as low as 25 μm and can be used for both inner lead bonding and outer lead bonding. The technology is based on metal to metal diffusion at the lead to pad interface using a ‘‘hot’’ tip energized by a laser. A closed end flat tip was used to comply with safety requirements and provide uniform temperature distribution across the footprint of the tip. The tip has shown no degradation during the initial testing of 25 000 bonds. The technology is much simpler compared to the solder based TAB process. It is easily controlled, does not require any pretreatment of the pads and is less sensitive to pad contamination and surface nonplanarity. It can be applied to various sets of pad-lead metallurgies such as Au–Au, Au–Sn, Cu–Au, and Ni–Au. The study shows that the process can be designed to be reworkable which makes it suitable for MCM applications.

Properties of Metal / Polyphenylquinoxaline Interfaces

ABSTRACTWe have investigated the microscopic properties of copper and chromium layers deposited on polyphenylquinoxaline (PPQ). PPQ is a thermostable polymer used for multichip module applications. The metal is deposited under ultra-high vacuum conditions and analysed in-situ by X-ray photoemission (XPS) and atomic force microscopy (ex situ). Copper does not react significantly with the PPQ and tends to diffuse into the polymer matrix upon annealing. On the contrary, chromium strongly reacts with the polymer surface at room temperature. With increasing metal coverage, chromium grows in a layer-by-layer mode and the reacted interface is progressively burried under the pure metal layer.

Comparison of the metallization of chemically and laser-etched structures in BPDA-PDA polyimide

Polyimide is an insulating polymer that is used in multichip module applications as a dielectric material. For high density packaging, structures in polyimide have to be minimized to features of about 20 mu m by 20 mu m. The metallization of such vias has to be optimized for this purpose. The authors studied chemical and laser etching of vias and lines and compared the influence of the resulting features on the metallization. For the laser etching an excimer laser with a wavelength of 248 nm was used. The metallization was performed using a standard electroless copper bath. To start the metallization a layer of gold was employed. The authors could observe no visible damage to the PI layer even after 4 h in the electroless copper bath. >

Interconnect technologies and the thermal performance of MCM

The thermal performances of multichip modules (MCMs) are compared on the basis of their interconnection technologies. The comparisons are made for hermetic and conduction cooled use environments. The thermal performances of the chip-first-type high density interconnect (HDI) technology, the flipped chip (FCP) technology, and the flipped tape automated bond (FTAB) technology are analyzed and compared for the MCM applications. The results show the thermal performance of each interconnect technology and the most effective ways of improving the performance of MCMs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Film Stress in High Density Thin Film Interconnect

AbstractHigh density thin film interconnects are expected to be widely used for multi-chip module application to accommodate next generation high I/O and high speed integrated circuits. These interconnects typically use polyimide as the dielectric, and aluminum or copper (with protective overcoat) as the conductor. The interconnects are typically built on silicon or alumina substrates. Large film stress occurs due to the high processing temperature required to cure polyimide and due to the mismatch in thermal coefficients of expansion (TCE) between the film materials and substrate materials. This work studies film stress for these materials.An instrument which measures thin film stress in-situ at temperatures between 25 and 450°C was used to characterize the stress in polyimide, nickel, and copper films. Two substrate materials, silicon and sapphire, were used in order to extract the TCE and elastic modulus for each film material. Three polyimide materials were evaluated. One of the polyimides studied showed complete stress relaxation at temperatures above 300°C and was almost completely elastic upon heating and cooling between 25 and 300°C. The TCE was calculated to be 41×10−6/°C and the biaxial elastic modulus was 4.0×109 Pascal. The nickel had very low stress asplated, however, high tensile stress was observed after 350°C annealing as a result of TCE mismatch. After first annealing, the nickel was almost completely elastic upon cooling and repeated heating and cooling between 25 and 350°C. Copper, on the other hand, was not completely elastic under similar thermal treatments. High thermal stress caused plastic deformation to occur in copper films. The room temperature stress in copper film after 350°C annealing depended on yield strength instead of TCE mismatch. The stress in these materials and its effects on processing and reliability for high density interconnect will be reported.

Susceptibility of semiconductor devices to thermal second breakdown : N. S. Cohn. Proc. IEEE Reliab. Phys. Symp. 90 (1974)

Recent advances in polymeric materials and integrated circuit (IC) encapsulants have made high-reliability very large-scale integration (VLSI) plastic packaging a reality. High-performance silicone gel possesses excellent electrical and physical properties for IC protection. With their intrinsic low modulus and soft gel-like nature, silicone gels have become very effective encapsulants for larger, high I/O, wire-bonded and flip-chip VLSI chips. Furthermore, the recently developed silica-filler modified epoxies, with the well-controlled thermal coefficient of expansion (TCE), have enhanced the flip-chip and chip-on-board hybrid IC encapsulation. Recent studies indicate that, with adequate IC chip surface protection with high-performance silicone gels and epoxies, plastic packages could replace conventional ceramic hermetic packages. This paper reviews the IC technological trends, and IC encapsulation materials and processes. Special focus is placed on the high-performance silicone gel, epoxies and polyimides, their chemistry and use as VLSI device encapsulants for single and multi-chip module applications.