Overview of conductive adhesive joining technology in electronics packaging applications
28 Sep 1998-pp 1-18
TL;DR: In this paper, the authors present an overview of the current status of use of conductive adhesives in various electronics packaging applications, focusing on recent developments in surface mount and flip-chip technology.
Abstract: This paper presents an overview of the current status of use of conductive adhesives in various electronics packaging applications. Strong emphasis is placed on recent developments in surface mount and flip-chip technology, as these methods in combination with conductive adhesives represent the latest developments in the area of electronics packaging. It is concluded that little practical use of conductive adhesives in surface mount has been found. In flip-chip applications, both isotropically and anisotropically conductive adhesives (ICAs and ACAs) have been used in real applications. Greater use is expected in the near future in this fast developing area.
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TL;DR: A review of both the tangible and intangible elements of manufacturing systems and a state-of-the-art survey of published work can be found in this article, where the evolution of research in manufacturing starting from past and current trends to future developments is discussed.
488 citations
TL;DR: In this paper, the authors investigated the changes in properties, especially in dimension (cure shrinkage), of an isotropic conductive adhesives (ICAs) during cure and to correlate them with the establishment of conductivity.
126 citations
TL;DR: In this paper, a double cantilever beam (DCB) test has been adopted to investigate the effects of environmental aging on ECA joints, revealing that conductive adhesives as well as substrate metallizations both play important roles in the durability of conductive joints.
79 citations
TL;DR: In this article, the reliability performance of the adhesive flip chip in the pressure cooker test and moisture sensitivity test conditions was investigated, and the failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact.
Abstract: Adhesive flip chip interconnect has been recognized as a promising substitute for solder interconnection due to its fine-pitch, lead-free, and low-temperature processing capabilities. As adhesives are made of polymers, moisture absorption by the polymeric resin remains as one of the principal contributors to adhesive joint failure mechanisms. In this research, the reliability performance of the adhesive flip chip in the pressure cooker test and moisture sensitivity test conditions was investigated. The failure modes were found to be interfacial delamination and bump/pad opening which may eventually lead to total loss of electrical contact. Different sizes of bump/pad opening in the interconnections were discussed in the context of the significance of mismatch in coefficient of moisture expansion (CME) between adhesive and other components in the package, which induces a hygroscopic swelling stress. The effect of moisture diffusion in the package and the CME mismatch were also evaluated from the standpoint of finite element modeling. In this study, it is concluded that hygroscopic swelling assisted by loss of adhesion strength upon moisture absorption is responsible for the moisture-induced failures in these adhesive flip chip interconnects.
68 citations
TL;DR: In this article, a new class of isotropic conductive adhesives was developed by using two different fillers, silver flakes and a lowmelting-point-alloy filler, into the ICA formulations.
Abstract: Conventional isotropic conductive adhesives (ICAs) are composed of a polymeric matrix and silver (Ag) flakes. As an alternative to lead-bearing solder, ICAs offer a number of benefits, but limitations do exist for ICA technology. ICAs filled with silver flakes generally show higher initial contact resistance, unstable contact resistance, and inferior impact strength. In this study, a new class of isotropic conductive adhesives was developed by using two different fillers, silver flakes and a low-melting-point-alloy filler, into the ICA formulations. After curing, the metallurgical connections between silver particles, and between silver particles and nickel (Ni) substrate were observed using scanning electron microscopy (SEM). Electrical properties including bulk resistance, initial contact resistance, and contact resistance shifts of the ICA were investigated and compared to those of a commercial ICA, an in-house ICA filled with only the silver flake, and a eutectic Sn/Pb solder. It was found that: (1) the low-melting-point alloy filler could wet the silver flakes and nickel substrate to form metallurgical connections, (2) this ICA had much lower bulk resistance than the commercial ICA and the in-house ICA filled with only the silver flake, and (3) this ICA showed especially low initial contact resistance and more stable contact resistance during aging on nickel metal compared to the ICA filled only with silver flakes.
68 citations
References
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TL;DR: In this article, surface characteristics, microstructure, reliability and failure mechanisms of tin/lead, copper and gold metallizations for conductive adhesive joining have been studied using electron spectroscopy for chemical analysis.
Abstract: In this paper, surface characteristics, microstructure, reliability and failure mechanisms of tin/lead, copper and gold metallizations for conductive adhesive joining have been studied. Electron spectroscopy for chemical analysis (ESCA) and Auger electron spectroscopy (AES) have been used to analyze Sn37Pb, copper and gold metallizations. The analyzes show that copper and nickel may be present as impurities on the gold plated surface. The tin and lead oxides present on the Sn37Pb plated surface were found to be 74 /spl Aring/ and 26 /spl Aring/, respectively. The microstructures were studied using scanning and transmission electron microscopy (SEM and TEM). The chemical analysis of the consisting compounds were analyzed using energy dispersive X-ray analysis (EDX). The conductive adhesive joints were exposed to constant humidity treatment at 85/spl deg/C, 85% RH up to 2000 h. The mechanical and electrical performance were measured using a shear tester and an Ohmmeter after various humidity treatment times. After the 85/spl deg/C/85% RH treatment, an increase in electrical resistance of the copper joints was found with increasing testing time due to the formation of Cu/sub 2/O. Also, there was a decrease in mechanical strength and an increase in electrical resistance due to oxidation of Pb. The best electrical performance was observed on the gold metallization after the constant humidity test.
55 citations
TL;DR: In this paper, an epoxy-based anisotropically conductive adhesive joints (ACA) were measured and simulated on three different types of connection: flip-chip bonded Si test chip and a transmission line gap bridged by Cu foil.
Abstract: In this paper, we present results from measurement and simulation of epoxy-based anisotropically conductive adhesive joints (ACA). We studied two different types of connection: flip-chip bonded Si test chip and a transmission line gap bridged by Cu foil. Test chips were mounted on three substrates: rigid FR-4 PCB, flexible PCB and high frequency teflon-based duroid substrate. Equivalent electrical models are discussed based on physical considerations and parameters were fitted to measurement data in the HP MDS high-frequency CAD tool. A HP8510 network analyser was used to measure S-parameters on rigid FR-4 and flex boards in the 500 MHz-8 GHz frequency range for both flip-chips and bridges, and for duroid mounted flip-chips and bridges over 1-30 GHz. ACA microstructures were studied by cross-sectioning and SEM. LF results for 500 MHz-8 GHz indicated that ACA flip-chip joints and bridge joints on FR-4 or flex can be used. For HF applications (1-30 GHz), ACA flip-chip joints and bridge joints on duroid can be used. For flip-chip joints and bridge joints, ACA was as good as or better than the solder joint for FR-4 over 45 MHz-2 GHz and for duroid substrates over 1-30 GHz. The largest contribution to transmission loss is due to Si chip resistivity in the flip-chip assembly. HP momentum analysis showed that for duroid, Si-chip crosstalk also gave power losses, which is not the case for FR-4 or flex. HP momentum analysis of flip-chip on FR-4 and flex showed that FR-4 and flex substrate losses also should be considered. Different ACA particle sizes and materials made little difference to ACA joint electrical behaviour.
38 citations
TL;DR: In this paper, it is shown by the electric network percolation theory that the isotropic conductive adhesive (ICA) using a bimodal distribution of metal fillers is expected to have a decreased metal loading for better mechanical performance while its electrical and manufacturing processing properties remain unchanged.
34 citations
TL;DR: In this paper, the characteristics of conductive particles in anisotropic conductive adhesives (ACA) were studied by optical microscopy observation and nano indenter measurements, and the indentation measurement was performed at the particles in ACA joints using different bonding forces.
Abstract: The characteristics of conductive particles in anisotropically conductive adhesives (ACA) were studied by optical microscopy observation and nano indenter measurements. The indentation measurement was performed at the particles in ACA joints using different bonding forces. The load-displacement curves and microhardness values are obtained, which indicate that the nano indenter could be used for quantitative estimation of the electrical and mechanical characteristics of conductive particles in ACAs.
20 citations
08 Dec 1998
TL;DR: In this paper, the authors present simulation results of the thermal characteristics of epoxy-based anisotropically conductive adhesive (ACA) flip-chip joints, compared with the thermal properties of ICA and wire-bonded modules.
Abstract: In this paper, we present simulation results of the thermal characteristics of epoxy-based anisotropically conductive adhesive (ACA) flip-chip joints. The results are compared with the thermal characteristics of isotropically conductive adhesive (ICA) flip-chip joints, soldered flip-chip modules and wire bonded modules. The simulated thermal parameters are the overall thermal resistance from the active chip surface down to the substrate as well as the unsteady/transient state characteristics time constant. In modern telecommunication applications, the thermal behaviour (temperature response) caused by electronic high power pulses are of great interest. The unsteady state characteristics are discussed and presented as time constants under different conditions. The thermal simulation software used is an IVF-developed software designed for electronic packaging applications. In order to study the effect of different ACA joint shapes on the thermal characteristics, a joint thermal crack model was developed and simulated for various sets of parameters. The purpose of the investigation of a nonperfect ACA joint is to see how thermal characteristics are affected by ACA joint shape. Simulation of isotropically electrically conductive adhesive joints was done for 35 /spl mu/m thick joints. Simulations were made for two different bondline thicknesses for soldered flip-chip modules. Finally, simulations have been done on a wire bonded module and on an ideally contacted ACA mounted flip-chip module with 400 I/Os in order to compare the two cases.
8 citations