Oxidation Prevention and Electrical Property Enhancement of Copper-Filled Isotropically Conductive Adhesives

This paper describes the development and characterization of isotropically conductive adhesives (ICAs) incorporating copper (Cu) powders as electrically conductive fillers, along with a silane coupling agent for oxidation protection of copper powders, for environmentally friendly, low cost and high thermal reliability applications in microelectronics packaging. The effect of silane coupling agent materials and concentration on the electrical conductivity, thermal stability and reliability of Cu-filled ICAs was investigated for potential alternatives of conventional silver-filled ICAs. The surface characteristics of silane thin films on copper surfaces, such as their hydrophobicity and thermal stability, were also evaluated to compare the performance of antioxidant behaviors of different silane coupling agents for Cu-filled ICAs. The low contact resistance and high thermal stability of the contact resistance of Cu-filled ICAs were achieved by addition of an optimized silane coupling agent. Greater thermal stability and improved reliability of Cu-filled ICAs under high temperature and humidity conditions were achieved with a silane coupling agent of high molecular weight and hydrophobicity. The bulk resistivity of ∼10⁻⁴ Ωcm of Cu-filled ICAs was achieved with bimodal filler loading.     

已二酸含量对导电胶性能的影响

通过在导电胶中直接添加短链二元羧酸已二酸对导电胶进行改性,研究了不同含量的已二酸对导电胶性能的影响规律。通过同步热分析仪对不同已二酸含量的导电胶的固化过程和固化后的热稳定性能分析表明,已二酸的添加会和环氧树脂进行反应,并且会促进导电胶的固化放热峰向低温方向偏移;同时已二酸的添加还会部分提高导电胶的热稳定性能。通过电子万能试验机对不同已二酸含量的导电胶的粘接强度进行分析表明,当已二酸质量分数低于0.5%时,随着已二酸含量的增加,导电胶的剪切强度逐步下降,当已二酸质量分数达到0.5%后,导电胶的剪切强度出现上升现象。通过四点探针测试仪对各不同导电胶的体积电阻率的测试,发现随着已二酸含量的增加,导电胶的体积电阻率逐渐减小。     

基于导电性能退化数据的导电胶可靠性评估

性能退化表征的是产品的工作能力随时间逐渐降低的现象。提出用指数退化模型来描述导电胶导电性能退化过程,并根据退化数据给出了一个某型导电胶在任意时河的性能特征值的分布模型。根据这个分布模型,提出了两种可靠性评估的方法：1）相对于传统的寿命分布模型,所推导的可靠度函数中的参数易以通过实时跟踪测量性能参数时间序列数据估计得到;2）给出了针对不同样本量时的可靠性评估方法,且简便易行。最后通过试验数据对导电胶在使用环境下的可靠性进行了评估。     

导电胶研究现状及其在LED产业中的应用

伴随中国战略性新兴LED产业的迅猛发展,LED芯片与基板之间的连接材料—导电胶,也成为了当前学术界和产业界的研究热点之一。分别从导电胶主要成分方面阐述了导电胶近年来的研究成果,为导电胶研发过程中的成分选择及优化处理提供参考。并展望了今后导电胶的发展趋势和应用前景。     

Effects of Trace Elements in Copper Fillers on the Electrical Properties of Conductive Adhesives

The properties of electrically conductive adhesives (ECAs) filled with Cu and Cu alloy fillers (with alloy elements Ag, Ge, Mg, and Zn) were investigated in terms of electrical conductivity, thermal stability, and the effects of the trace alloy elements on the oxidation resistance of the metallic fillers. Oxidation of metallic fillers under high-temperature exposure at 125°C was considered as the main reason that led to degradation of electrical conductivity in the ECAs. Cu fillers alloyed with a trace amount of Ag and Mg, respectively, had significant effects on the electrical conductivity and thermal stability of the ECAs as the electrical resistivity was substantially suppressed and a consistently high electrical conductivity could be maintained even after aging for 1000 h at 125°C.     

Electrical Properties of Isotropic Conductive Adhesives Composed of Silicone-Based Elastomer Binders Containing Ag Particles

The electrical properties of isotropic conductive adhesives (ICAs) with two different types of silicone-based binder containing Ag particles were examined. The ICAs were printed on glass substrates in order to prepare specimens for evaluating the electrical properties. In the case of adhesives containing a denatured silicone binder, both the curing and cooling steps in the isothermal curing process generated electrical conductivity. Adhesives that were cured at 120°C to 200°C exhibited similar values of electrical resistivity regardless of the different curing temperatures. By contrast, electrical conductivity was generated only during the cooling step when adhesives containing a dimethyl methylvinyl siloxane were isothermally cured. In this case, adhesives cured above 160°C exhibited high electrical resistivity. In evaluating the temperature dependence of the electrical resistivity, we found physical annealing to have significantly different effects on these specimens. In addition, we were able to make small sensitive variations in the properties of silicone-based ICAs by controlling the isothermal annealing and thermal cycling processes.     

Experimental Analysis of Mechanical and Electrical Characteristics of Metal-Coated Conductive Spheres for Anisotropic Conductive Adhesives (ACAs) Interconnection

An accurate characterization for the deformation behavior of conductive particles is important: 1) to understand the anisotropic conductive adhesive (ACA) interconnection and 2) to optimize the ACA bonding parameter. This paper introduces an experimental technique, which has been developed to allow continuous monitoring of deformation characteristics of a single conductive particle. The load-deformation curve of a single conductive particle is measured, which provides the quantitative estimation of the mechanical and electrical characteristics of metal-coated polymer spheres used in ACAs. Based on the load-deformation result of a single conductive particle and the number of trapped particles on a bump, equivalent spring models are used to predict the deformation degree of conductive particles after flip chip assembly. For two kinds of conductive particles with different polymer cores, the mechanical and electrical characteristics of ACA interconnection were studied. Such results are used to further achieve a more sophisticated approach of the ACA bonding process and contact reliability.     

Novel Isotropical Conductive Adhesives for Electronic Packaging Application

Isotropical conductive adhesives (ICAs) have recently received a lot of focus and attention from the researchers in electronic industry as a potential substitute to lead-bearing solders. In this paper, a novel kind of isotropical conductive adhesives was made by using silver (Ag) nanowires and nanosized silver particles as conductive fillers. These Ag nanowires with dismeters in the range of 30–50 nm and lengths of up to ${sim 50}~mu {rm m}$ could be synthesized by a solution-phase method, which was proceed by reducing silver nitrate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP). Electrical property including bulk resistivity and mechanical property including shear strength were investigated and compared with that of conventional ICA filled with micrometer-sized Ag particles or nanometer-sized Ag particles. Our results indicated that ICA filled Ag nanowires exhibited higher conductivity, higher shear strength and low percolation threshold value than traditional ICA. Possible conductive mechanism was discussed based on theory calculation.      

正弦激励下的导电胶非线性测试评价方法

目前由于电子产品中器件非线性引起的电磁可靠性问题变得越来越严重,为了准确评估不同导电胶产品在正弦信号激励下非线性特性的优劣,设计了一套基于窄带滤波器和微带线的简单且行之有效的非线性特性测试方法,在测试中使用滤波器排除测试系统固有的三次谐波。由于非线性效应会产生电压、电流的高次谐波成分,该方法以三次谐波的功率作为导电胶的非线性特性的衡量指标,通过测量不同导电胶的三次谐波功率来完成非线性特性的对比测试,为导电胶的测试评价及设计研发提供技术支撑。     

导电胶的力学性能研究

导电胶主要是由环氧树脂基体和导电粒子组成的复合导电聚合物,其力学性能主要是由聚合物基体决定,基体是粘弹性材料,具有时间和温度依赖性。文章建立了一个基于时间-温度、时间-固化度的宏观粘弹性本构关系来描述导电胶在固化过程中的粘弹性行为,通过动态力学试验（DMA）表征导电胶的粘弹性行为,测定导电胶的粘弹性参数。通过对导电胶粘弹性行为表征,能更好的优化固化工艺参数。     

导电胶粘接元件接触电阻的稳定性研究

为解决导电胶粘接元件接触电阻不稳定的问题,研究了在温度及压力应力条件下,导电胶在不同界面的导电性和体电阻率的变化情况,分析了导电胶接触电阻不稳定的机理。试验结果表明,导电胶粘接片式元件的接触电阻的稳定性不仅与工艺加工过程有关,而且与元件端头金属基材表面金属化层的电极电动势密切相关;采用Ag基或Au基端头元件时,其导电胶粘接元件的接触电阻在粘接装配工艺过程中是最稳定的。     

固化工艺参数对导电胶导电性的影响

用四点探针法的原理设计了一种测试导电胶电阻的新方法。研究了固化温度、时间及导电胶层厚度对导电胶固化后导电性的影响。结果表明:夹具经预热导电胶,在80~140℃固化较好;未预热时在110~150℃固化较好,但固化时间较长;随着导电胶层厚度增加,固化时间和固化后的最低电阻都有一定的增大;最佳的固化效果是固化到电阻变化很微小时停止固化。     

导电PBO织物的制备及其吸波性能

以离子注入法制备了导电聚对苯撑苯并二噁唑(PBO)织物,并对其表面形貌、结构和导电性能进行了表征。以导电PBO织物制备了频率选择表面(FSS),研究了FSS对纳米碳纤维(CNF)复合材料吸波性能的影响。     

Hygrothermal Stability of Electrical Contacts Made from Silver and Graphite Electrically Conductive Pastes

The hygrothermal stability of electrical contacts made from silver and graphite electrically conductive pastes is comparatively evaluated by measurement of the increase in contact electrical resistance during immersion in water at 15°C and 40°C. The pastes are silver paint, silver paint with a nonconductive epoxy overcoat, silver epoxy, and graphite colloid. Each electrical contact is made between a seven-strand tin-coated copper wire and the surface of a carbon fiber epoxy-matrix composite. Silver paint and graphite colloid penetrate the spaces among the 130-μm-diameter strands, but silver epoxy does not. Partly due to its low penetrability and the silver flake (15 μm) preferred orientation, silver epoxy gives contacts of significantly higher resistance than silver paint. Graphite colloid is comparable to silver epoxy in the resistance. Among the four pastes, silver paint with an epoxy overcoat is most durable, though it gives slightly higher resistance than silver paint without epoxy. Silver epoxy is less durable than silver paint without an epoxy overcoat, particularly at 40°C, due to the low hygrothermal stability of epoxy. Graphite colloid is even less durable than silver epoxy, due to its being water based.     

Wearable Personal Network Based on Fabric Serial Bus Using Electrically Conductive Yarn

E‐textile technology has earned a great deal of interest in many fields; however, existing wearable network protocols are not optimized for use with conductive yarn. In this paper, some of the basic properties of conductive textiles and requirements on wearable personal area networks (PANs) are reviewed. Then, we present a wearable personal network (WPN), which is a four‐layered wearable PAN using bus topology. We have designed the WPN to be a lightweight protocol to work with a variety of microcontrollers. The profile layer is provided to make the application development process easy. The data link layer exchanges frames in a master‐slave manner in either the reliable or best‐effort mode. The lower part of the data link layer and the physical layer of WPN are made of a fabric serial‐bus interface which is capable of measuring bus signal properties and adapting to medium variation. After a formal verification of operation and performances of WPN, we implemented WPN communication modules (WCMs) on small flexible printed circuit boards. In order to demonstrate the behavior of our WPN on a textile, we designed a WPN tutorial shirt prototype using implemented WCMs and conductive yarn.     

各向异性导电胶粘剂膜的研究进展

介绍了ACF的结构、原理、组成、应用及发展前景,详述了导电粒子、粘结剂、添加剂等组分在体系中的作用和对ACF性能的影响,综述了热固性树脂中离子聚合树脂型ACF和自由基聚合树脂型ACF的现状,并指出自由基聚合树脂型ACF是将来的发展趋势。     

Enhancement of Electrical Properties of Ferroelectric Polymers by Polyaniline Nanofibers with Controllable Conductivities

Conductive nanofibers are adopted to enhance the electric properties of ferroelectric polymers. Polyaniline (PANI) nanofibers doped by protonic acids have a high dispersion stability in vinylidene fluoride‐trifluoroethylene copolymers [P(VDF‐TrFE)] and lead to percolative nanocomposites with enhanced electric responses. About a 50‐fold rise in the dielectric constant of the ferroelectric polymer matrix has been achieved. Percolation thresholds of the nanocomposites are relevant to doping levels of PANI nanofibers and can be as low as 2.9 wt% for fully doped nanofibers. The interface between the conductive nanofiber and the polymer matrix plays a crucial role in the dielectric enhancement of the nanocomposites in the vicinity of the percolation threshold. Compared with other dopants, perfluorosulfonic acid resin is better at improving the performance of the nanofibers in that it serves as a surface passivation layer for the conductive fillers and suppresses leakage current at low frequency. The nanofibers drastically reduce the electric field strength required to switch spontaneous polarization of P(VDF‐TrFE). The nanocomposites can be utilized for potential applications as high energy density capacitors, thin‐film transistors, and non‐volatile ferroelectric memories.     

Investigation of Mechanical and Electrical Characteristics for Cracked Conductive Particle in Anisotropic Conductive Adhesive (ACA) Assembly

In an anisotropic conductive adhesive (ACA) assembly, the electrical conduction is usually achieved with the conductive particles between the bumps of integrated circuit (IC) and corresponding conductive tracks on the glass substrate. Fully understanding of the mechanical and electrical characteristics of ACA particles can help to optimize the assembly process and improve the reliability of ACA interconnection. Most conductive particles used in the ACA assembly are with cracks in the metal coating of the particles after the ACA bonding. This paper introduced the fracture analysis by applying the cohesive elements in the numerical model of the nickel-coated polymer particle and further simulating the cracks initiation and propagation in the nickel coating during the ACA bonding. The simulation results showed that the stress distribution on the nickel-coated particle with cracks was significantly different from that on the nickel-coated particle without crack, indicating that the stress analysis by taking the crack into consideration is very important for the reliability assessment of the ACA interconnection. The stress analysis of cohesive elements indicated that the cracks initiated at the central area of the nickel coating and propagated to the polar area. Furthermore, by the introduction of a new parameter of the virtual resistance, a mathematical model was established to describe the electrical characteristics of the nickel-coated particle with cracks. The particle resistance of the nickel-coated particle with cracks was found to be much higher than that of the particle without crack in the optimized bonding pressure range, indicating that it is necessary to take the crack into consideration for the particle conduction analysis as well. Therefore, the fracture analysis on the conductive particle by taking the crack into consideration could accurately evaluate the reliability of ACA interconnection and avoid serious reliability issues.     

Obtaining Electrically Conductive Structures by Electrochemical Deposition of Copper onto Substrates of Anodized Aluminum Using Polyfluorochalcones as a Photoresist Layer

Russian Microelectronics - The approaches used to the form electrically conductive structures on aluminum and anodized aluminum substrates using such photoresists as synthesized triacrylamide...     

Thermoelectric Property Dependence and Geometry Optimization of Peltier Current Leads Using Highly Electrically Conductive Thermoelectric Materials

Thermoelectric materials are promising candidates for use in energy-saving devices in many fields. They are also useful in superconducting applications such as those using Peltier current leads (PCLs) to reduce system heat loss. In the case of PCLs, consideration must be given to Joule heating. Furthermore, the performance of PCLs is intricately dependent on their thermoelectric properties. In addition to the figure of merit Z, consideration of the electrical conductivity is also important for the design of high-performance PCLs. In this paper, we discuss the resistivity dependence of the performance of PCLs using model parameters obtained from real devices.