国外微电子组装用导电胶的研究进展

介绍导电胶的组成、分类、较之于传统共晶锡铅焊料的优点以及导电胶的研究现状。重点阐述国外在导电胶导电机理研究、可靠性研究及新型高性能导电胶研制方面的现状和进展。     

叠孔导通用导电胶研究进展

随着电子产品的小型化、高密度化以及人类环保意识的增强,导电胶取代传统的填孔电镀已成为国内外的研究热点。文章简述了叠孔填充用导电胶的组成及机理,总结了导电胶的优点及现存问题,并阐述了国内外研究现状。     

导电胶的研究进展

导电胶作为无铅连接材料的一种,近年来在电子封装中得到越来越多的重视。导电机理、组成及老化性能的研究成为导电胶实用化的关键因素。各向异性导电胶是连接用Pb/Sn合金的理想替代材料。     

各向异性导电胶粘接可靠性研究进展

介绍各向异性导电胶导电机理和粘接工艺,以及影响它的粘接可靠性因素和最佳参数的研究,如粘接温度、固化时间、粘接压力、粒子含量等。对各向异性导电胶粘接可靠性中的开路、短路、接触电阻与粘接压力和温度循环的关系进行了讨论,并介绍了各向异性导电胶可靠性的理论计算模型。     

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。     

金属粉末-聚合物复合导电胶研究进展

随着电子封装工艺的发展,越来越多的人们致力于研发更高性能、环境友好的新连接材料,以聚合物为基体的复合导电胶在电子封装领域的应用也由此越来越广泛。文章介绍了导电胶的分类和组成,以及改善导电胶性能的方法与技术,从宏观和微观角度对导电机理进行了探讨并对研究前景做了展望。     

导电胶在倒装芯片互连结构中的应用进展

介绍了导电胶的基本分类以及导电胶的渗透理论;讨论了各向异性导电胶(ACA)、各向同性导电胶(ICA)、绝缘粘合剂(NCA)在倒装芯片互连结构中的应用;分析了导电胶互连的可靠性。最后展望了导电胶的发展趋势。     

钽电容器用石墨导电胶的研究

以石墨粉和热固性树脂混合配成导电胶,分析了石墨粉、稀释剂的用量,固化温度,固化时间等与电阻的关系。结果表明:当石墨含量在25%～35%,稀释剂含量在20%～25%(均为质量分数)时,在150℃下固化2～3 h得到的导电胶导电性最好,能够满足作为钽电容器阴极引出材料的需要。并用“逾渗理论”解释了导电胶的导电机理,与实验所得结论相符。     

微波器件用导电胶变色机理及其对接触电阻的影响

针对导电胶变色的现象,分析了变色导电胶的外观、微观结构及成分,研究了导电胶变色现象对接触电阻的影响。找出了导电胶变色的原因,导电胶固化后裸露在环氧树脂表面的银粒子被硫化生成黑色的硫化银所致,且随着硫化银的增多颜色由浅变深。试验结果表明导电胶变色现象对接触电阻无影响。     

导电胶在固化中电阻的自动测量采集系统设计研究

导电胶作为元铅连接材料的一种，近年来在微电子封装、组装中越来越受重视。本文简单介绍了导电胶的分类、组成，重点介绍一种新的导电胶电阻的测试方法和导电胶在固化过程中电阻的自动测量采集系统设计，通过最后选用的导电胶实验证明本文设计的系统完全能够满足导电胶电阻的测试要求。     

Conductivity mechanisms of isotropic conductive adhesives (ICAs)

Isotropic conductive adhesives (ICAs) are usually composites of adhesive resins with conductive fillers (mainly silver flakes). The adhesive pastes before cure usually have low electrical conductivity. The conductive adhesives become highly conductive only after the adhesives are cured and solidified. The mechanisms of conductivity achievement in conductive adhesives were discussed. Experiments were carefully designed in order to determine the roles of adhesive shrinkage and silver (Ag) flake lubricant removal on adhesive conductivity achievement during cure. The conductivity establishment of the selected adhesive pastes and the cure shrinkage of the corresponding adhesive resins during cure were studied. Then conductivity developments of some metallic fillers and ICA pastes with external pressures were studied by using a specially designed test device. In addition, conductivity, resin cure shrinkage, and Ag flake lubricant behavior of an ICA which was cured at room temperature (25°C) were investigated. Based on the results, it was found that cure shrinkage of the resin, rather than lubricant removal, was the prerequisite for conductivity development of conductive adhesives. In addition, an explanation of how cure shrinkage could cause conductivity achievement of conductive adhesives during cure was proposed in this paper     

Determining the impact resistance of electrically conductive adhesives using a falling wedge test

This study was conducted to determine the impact resistance of electrically conductive adhesives (ECAs). A novel falling wedge test that was used to quantitatively characterize the impact resistance of conductive adhesives at a material level has been described, and some important findings obtained from the falling wedge test are presented. This unique impact resistance testing method is not only a substitution of the conventional drop test which has several severe drawbacks, but also provides some useful information for screening adhesives at the materials level and helping formulate new conductive adhesives with improved impact performance. Three model conductive adhesives were studied in this work and the impact fracture energies of the adhesive materials were measured utilizing the falling wedge test. The effect of test temperature on the fracture behavior of ECAs was examined and the correlation between the impact resistance and damping property of the conductive adhesive was also investigated. This study suggests that 1) the falling wedge test is able to discriminate between adhesives and this technique is capable of screening adhesives for bonding purposes; 2) the viscoelastic energy has played an important role in the fracture behavior of the conductive adhesives. As a measure of the internal friction, the loss factor tan/spl delta/ is found to be a good indicator of a conductive adhesive's ability to withstand impact loading.     

High performance conductive adhesives

Isotropic conductive adhesives (ICAs) have been developed as an alternative for traditional tin/lead (Sn/Pb) solders for electronic applications. Compared to mature soldering technology, conductive adhesive technology is still in its infant stage, therefore, there are some limitations for current commercial ICAs. Two critical limitations are poor impact performance and unstable contact resistance with nonnoble metal finished components. These limitations seriously hindered the wide applications of ICA's. No current commercial ICAs show both desirable impact performance and stable contact resistance. In this paper, novel conductive adhesives were formulated using mixtures of an epoxide-modified polyurethane resin and a bisphenol-F type epoxy resin and a corrosion inhibitor. Cure profiles, rheology, and dynamic mechanical properties of the conductive adhesives were studied using a differential scanning calorimeter (DSC), a rheometer, and a dynamic mechanical analyzer (DMA), respectively. Impact strength and contact resistance with several nonnoble metals (Sn/Pb, Sn, and copper) of these conductive adhesives were tested and compared to those of a commercial conductive adhesive. It was found that these in-house conductive adhesives showed superior impact performance and substantially stable contact resistance with nonnoble metal finished components during elevated temperature and humidity aging     

Conductivity enhancement of nano silver-filled conductive adhesives by particle surface functionalization

Five different types of surfactants were employed for nanoparticle functionalization and the effects of the surfactants on electrical properties of nano silver (Ag)-filled conductive adhesives were investigated. The Ag nanoparticles pretreated with the surfactants were incorporated into isotropic conductive adhesives (ICA) formulations as conductive fillers. By using the surfactants (S3, S4, and S5), the reduced resistivity of the nano Ag-filled adhesives could be achieved with 2×10⁻⁴ Θ-cm. The morphology studies showed that the low resistivity resulted from the sintering of nanoparticles.     

Effect of Gold Stud Bump Topology on Reliability of Flip Chip on Flex Interconnects

The flip chip technique using conductive adhesives have emerged as a good alternative to solder flip chip methods. Different approaches of the interconnection mechanism using conductive adhesives have been developed. In this paper, test chips with gold stud bumps are flip-chipped with conductive adhesives onto a flexible substrate. An experimental study to characterize the bonding process parameters is reported. Initial results from the environmental studies show that thermal shock test causes negligible failure. On the other hand, high humidity test causes considerable failure in flip chip on flex assemblies. Improvements in the reliability of the assembly are achieved by modifying the shape of the gold stud bumps.     

Development of conductive adhesives for solder replacement

Develops conductive adhesives with stable contact resistance and desirable impact performance. Effects of purity of the resins and moisture absorption on contact resistance are investigated. Several different additives (oxygen scavengers and corrosion inhibitors) on contact resistance stability during elevated temperature and humidity aging are studied, and effective additives are identified. Then, several rubber-modified epoxy resins and two synthesized epoxide-terminated polyurethane resins are introduced into ECA formulations to determine their effects on impact strength. The loss factor, tan δ, of each formulation is measured using a dynamic mechanical analyzer (DMA) and impact strength is evaluated using the National Center for Manufacturing Science (NCMS) standard drop test procedure. Finally, high performance conductive adhesives are formulated by combining the modified resins and the effective additives. It is found that 1) purity of the resins and moisture absorption of the formulation affect the contact resistance stability of an ECA; 2) the oxygen scavengers and corrosion inhibitors can delay contact resistance shift; 3) one of the corrosion inhibitors is very effective in stabilizing the contact resistance; 4) some rubber-modified epoxy resins and the epoxide-terminated polyurethane resins can provide the conductive adhesives with superior impact performance; and 5) conductive adhesives with stable contact resistance and desirable impact performance are developed     

用于微电子组装的导电胶粘接剂的研究现状

综述了当前电子组装业中导电胶粘接剂的研究情况,主要介绍国外正在重点研究的几大类导电胶粘接剂及其组成,与传统锡铅焊料的对比,以及它们的电性能、机械性能、热性能等,并简要介绍其发展趋势。     

Mechanisms underlying the unstable contact resistance of conductiveadhesives

One critical obstacle of current conductive adhesives is their unstable contact resistance with nonnoble metal finished components during high temperature and humidity aging. It is commonly accepted that metal oxide formation at the interface between the conductive adhesive and the nonnoble metal surface is responsible for the contact resistance shift. Two different mechanisms, simple oxidation and galvanic corrosion, both can cause metal oxide formation, but no prior work has been conducted to confirm which mechanism is the dominant one. Therefore, this study is aimed at identifying the main mechanism for the metal oxide formation and the unstable contact resistance phenomenon of current conductive adhesives. A contact resistance test device, which consists of metal wire segments and conductive adhesive dots, is specially designed for this study. Adhesives and metal wires are carefully selected and experiments are systematically designed. Based on the results of this systematic study, galvanic corrosion has been identified as the underlying mechanism for the metal oxide formation and for the observed unstable contact resistance phenomenon of conductive adhesives