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The contact resistance and reliability of anisotropically conductive film (ACF)
No full textThe effect of bonding pressure on the electrical and mechanical properties of anisotropic conductive film (ACF) joint using nickel particles and metal-coated polymer bah-filled ACF's was investigated. The contact resistance decreases as the bonding pressure increases, Contact resistance of ACF is determined by the contact area change between particles and contact substrates. Electrical conduction through the pressure engaged contact area between conductive particles and conductor substrates is the main conduction mechanism in ACF interconnection. In addition, environmental effects on contact resistance and adhesion strength such as thermal aging, high temperature/humidity aging and temperature cycling were also investigated. Interestingly, the contact resistances of the excessively bonded samples deteriorated more than those of optimally bonded ones. Increasing contact resistance and decreasing adhesion strength after harsh environmental tests were mainly due to the loss of contact by thermal stress effect and moisture absorption, and also partially due to the formation of metal oxide on the conductive particles
Recent advances on anisotropic conductive adhesives (ACAs) for flat panel displays and semiconductor packaging applications
No full textAnisotropic conductive films (ACFs) consist of conducting particles and adhesive polymer resins in a film type and have been widely used for the flat panel display module to be high-resolution, light weight, thin profile and low power consumption in forms of out lead bonding (OLB), flex to printed circuit board bonding (PCB), chip-on-glass (COG) and chip-on-film (COF) in last decades. As the interconnection pitch between driver IC and flex is decreasing, ACF materials have been evolved to meet the fine pitch capability, low-temperature curing and strong adhesion requirements. Multi-layered ACF structures such as double and triple-layered ACFs were developed for the same reason. Flip chip technology has been well-known as one of the solutions to meet today's semiconductor packaging needs of miniaturization of package size as well as reduction in interconnection distance, resulting in high electrical performance. Especially, nip chip assembly using anisotropic conductive adhesives (ACAs) has been gaining Much attention for its simple and lead-free processing as well as cost-effective packaging method. High mechanical reliability, good electrical performance at high-frequency range and effective thermal conductivity for high current density are the required properties for the ACF material for wide use in the flip chip application, In this paper, an overview on the principles, recent development and applications of ACF materials for flat panel displays and semiconductor packaging applications, with focus on the fine pitch capability, low-temperature bonding process, electrical/ mechanical/thermal performance and wafer level package using ACFs are described. (C) 2005 Elsevier Ltd. All rights reserved.The authors would like to acknowledge that part of
this work was supported by Center for Electronic
Packaging Materials of Korea Science and Engineering
Foundation
Effect of nonconducting filler additions on ACA properties and the reliability of ACA flip-chip on organic substrates
No full textIn this paper, we investigated the effect of nonconducting fillers on the thermomechanical properties of modified anisotropic conductive adhesive (ACA) composite materials and the reliability of flip chip assembly on organic substrates using modified ACA composite materials. For the characterization of modified ACAs composites with different content of nonconducting fillers, dynamic scanning calorimeter (DSC), and thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), and thermomechanical analyzer (TMA) were utilized. As the nonconducting filler content increased, CTE values decreased and storage modulus at room temperature increased. Tn addition, the increase in the content of filler brought about the increase of Tg(DSC) and Tg(TMA). However, the TGA behaviors stayed almost the same. Contact resistance changes were measured during reliability tests such as thermal cycling, high humidity and temperature, and high temperature at dry condition, The reliability results were significantly influenced by CTEs of ACA materials, especially at the thermal cycling tests. Results showed that flip chip assembly using modified ACA composites with lower coefficients of thermal expansion (CTEs) and higher modulus by loading nonconducting fillers exhibited better contact resistance behavior than conventional ACAs without nonconducting fillers.The authors would like to thank D. Lu and Z. Zhang, Packaging
Research Center (PRC), Georgia Institute of Technology,
Atlanta, for their useful help and discussion. Part of this work
was performed during the author’s visit, from June 1999 to August
1999 at the PRC through exchange visitor’s program
New Anisotropic Conductive Adhesives for Low Cost and Reliable Flip Chip on Organic Substrates Applications
No full textFlip chip assembly on organic boards using anisotropic conductive adhesives (ACAs) and nickel/gold bumps
No full textEffect of filler content on the dielectric properties of anisotropic conductive adhesives materials for high-frequency flip-chip interconnection
No full textThe dielectric property of anisotropic conductive film (ACF) as an interconnect materials in the flip-chip joints is becoming important concern for device packaging solution at high-frequency due to low parasitic effect on the signal transfer. The effects of non-conductive, dielectric filler content on dielectric properties of ACA materials, like dielectric constant, loss factor and loss tangent, and conductivity at high-frequency were investigated. Frequency is dominating factor in determining dielectric constant, loss factor, and conductivity. However, the filler content is dominant only on dielectric constant, not on the loss factor, and conductivity at low-frequency range. The effect of low dielectric constant (low-k) filler addition on high-frequency behavior of ACF interconnection in flip-chip assembly was also investigated. Impedance parameters of low-k ACF with Ni filler and low-k SiO2 filler extracted from measurement were compared with that of conventional ACF with only Ni filler. The resonant frequency of conventional ACF flip-chip interconnect was 13 GHz, while the resonant frequency of low-k ACF including low-k SiO2 filler was found at 15 GHz. This difference is originated from capacitance decrease of polymer matrix between bump and substrate pad due to change in dielectric constant of polymer matrix, which was verified by measurement-based modeling. The high-frequency property of the conductive adhesive flip-chip joint, such as resonant frequency can be enhanced by low-k polymer matrix. (c) 2005 Elsevier B.V. All rights reserved.The authors would like to ackonowledge the financial support by Center for Packaging Materials (CEPM) of Korea Science and Engineering Foundation
Effects of thermoplastic resin content of anisotropic conductive films on the pressure cooker test reliability of anisotropic conductive film flip-chip assembly
No full textThe flip-chip technology using anisotropic conductive films (ACFs) is gaining growing interest due to its technical advantages such as environmentally friendly, simpler, and lower cost processes. Electrical performances and reliability of ACF flip-chip assembly depend on thermomechanical properties of ACF polymer resins. In this paper, the changes in ACF resin morphology due to the phase separation of thermoplastics, and subsequent changes of physical and mechanical properties were investigated as a function of thermoplastic contents of ACF formulation. Furthermore, the pressure cooker test (PCT) reliability of ACF flip-chip assemblies with various thermoplastic contents was also investigated. As thermoplastic contents increased, coefficient of thermal expansion (CTE) of ACFs increased, and elastic modulus (E') of ACFs decreased. In contrast, water absorption rate decreased as thermoplastic content increased. As a result, PCT reliability of ACF flip-chip assembly was improved adding up to 50 wt.% content of thermoplastic.Financial support from the Center for Electronic
Packaging Materials (CEPM) of Korea Science and
Engineering Foundation is gratefully acknowledged
Effects of epoxy functionality on the properties and reliability of the anisotropic conductive films for flip chips on organic substrates
No full textThe effects of the functionality of an epoxy monomer on the composite properties and reliability of anisotropic conductive films (ACFs) in a flip-chip package were investigated. Three epoxy monomers with different functionalities (f = 2-4) were considered. The ACFs prepared using epoxy monomers with higher functionality resulted in lower molecular weight between crosslinks (M-c). As the M-c decreased, the elastic modulus (E') and coefficient of thermal expansion (CTE) were improved. These results were highly consistent with the rubber elasticity theory. The reliability performance of the flip chip on organic substrate assemblies using ACFs were also investigated as a function of epoxy functionality. The ACFs prepared by using higher functional epoxy monomers showed improved reliability performance.Financial support from Center for Electronic
Packaging Materials (CEPM) of the Korea Science
and Engineering Foundation (KOSEF) is gratefully
acknowledged
Reduced thermal strain in flip chip assembly on organic substrate using low cte anisotropie conductive film
No full textFlip chip assembly directly on organic boards offers miniaturization of package size as well as reduction in interconnection distances, resulting in a high performance and cost-competitive packaging method, This paper describes the usefulness of low cost flip-chip assembly using electroless Ni/Au bump and anisotropic conductive films on organic boards such as FR-4, As bumps for flip chip, electroless Ni/Au plating was performed as a low cost bumping method. Effect of annealing on Ni bump characteristics informed that the formation of crystalline nickel with Ni3P precipitation above 300 degrees C causes an increase of hardness and an increase of the intrinsic stress. As interconnection material, modified ACFs composed of nickel conductive fillers for conductive fillers, and nonconductive fillers for modification of him properties, such as coefficient of thermal expansion (CTE), were formulated for improved electrical and mechanical properties of ACF interconnection. Three ACF materials with different CTE values were prepared and bonded between Si chips and FR-4 boards for the thermal strain measurement using moire interferometry, The thermal strain of the ACF interconnection layer, induced by temperature excursion of 80 degrees C, was decreased according to the decreasing CTEs of ACF materials. This result indicates that the thermal fatigue life of ACF flip chip assembly on organic boards, limited by the thermal expansion mismatch between the chip and the board, could be increased by low CTE ACF.This work
was supported by KOSEF and Electronic Packaging Research Center in KAIST
Effect of conductive particle properties on the reliability of anisotropic conductive film for Chip-On-Glass (COG) applications
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