导电胶固化状态对器件内部水汽含量的影响

气密性封装器件的芯腔内部如果存在大量的水汽，则会影响器件的可靠性，因此在封装的过程中，要对器件内部的水汽含量进行控制。但是目前的控制措施主要是从封帽环境、原材料等方面入手，对导电胶固化状态对器件内部水汽含量的影响研究得较少。因此，首先，对比了不同固化状态导电胶的固化度和吸水率；然后，对不同固化状态对器件内部水汽含量的影响进行了研究。结果表明，充氮烘箱的装载量会影响导电胶的固化状态。当导电胶在300℃下的固化时间为30 min时，其固化度为100%，吸水率约为0.45%；当在300℃下的固化时间为10 min时，其固化度约为92%，吸水率约为0.94%。导电胶固化不充分时，其在温度循环和高温烘烤中会继续固化，并释放出少量的水汽和大量的二氧化碳。固化不充分的导电胶会在双85试验中吸收水汽，即使器件在封帽前会进行烘烤，吸收的水汽也未能完全排出，导致器件内部水汽含量升高。随着烘烤时间的增加，器件内部水汽含量逐渐地减少，当将烘烤时间延长至13 h时，可有效地去除固化不充分导电胶吸收的水汽，使水汽含量低于1 000×10^-6。     

气密性金属封装内的水汽及气氛研究

从封装管壳、贴片材料、固化烘烤处理方式等方面,研究了封装内部的水汽和气氛。结果表明,管壳清洗后烘焙的水汽含量低于清洗后不烘焙的水汽含量。粘结材料(环氧树脂、氰酸酯树脂等)吸附于器件表面,其排放对封装内的水汽有严重的影响。对于环氧树脂H35和氰酸酯树脂JM7000两种导电胶,烘焙后的效果要好于未烘焙,且随着烘焙时间的延长,水汽含量逐步降低。对外壳清洗后进行150℃/8h的烘焙,对水汽和气氛都有好处。由于储能焊对导电胶的热冲击不大,两种导电胶的水汽和气氛排放并无明显差别。     

气密性封装内部水汽含量的控制

气密性封装内部水汽含量过高,会使芯片及电连接系统发生各种物理化学反应,从而造成器件参数不稳定甚至失效,为了保证空封半导体器件的可靠性,生产上不仅需要检测器件封装的气密性,而且需对器件内部水汽含量进行有效的控制。因国内许多生产单位不具备对内部水汽含量进行有效控制的条件和检测设备,因而通过本文的讨论并采用有效防止水汽存在或引入器件的内部,使水汽含量控制在规定的范围内(GJB548A-96、GJB33A-97规定内部水汽含量为:100±5℃,烘24小时以上,小于5000ppmV,且这是最低要求)。因要使器件(未经钝化处理)无因水汽引起的失效,最稳妥的办法是使器件内部水汽含量小于500ppmv;实际上,对大多数器件内部水汽含量若能保持在1000ppmv 以下即能保证器件可靠运行。我们采用合金烧结芯片、合金封帽的器件其内部水汽含量控制在300ppmV 左右,聚合物导电胶装片、合金封帽的在1200ppmV 左右,银玻璃装片、Pb-Sn-Ag 合金封帽的在3000ppmV 左右,即便有某些偏差,亦能保证内部水汽含量控制在较低的范围内,使生产的器件可靠性大大提高,并能100%通过水汽含量检测。     

内部水汽对半导体器件可靠性影响的研究

由于各种原因,国内对器件内腔水汽的危害还没给予充分重视和有效控制,器件内部水汽含量较高,使之在环境温度低于封装内水汽露点温度的条件下工作与贮存时容易发生失效,对器件可靠性直接造成威胁,是个急待解决的问题。本研究目的在于了解国产军用密封半导体器件内部水汽现状及其对可靠性的影响,探讨揭示内部水汽问题的有效试验方法,寻求降低水汽影响,提高器件可靠性的主要途径。     

光电耦合器内部水汽含量控制

分析了光电耦合器内部水汽的来源,在此基础上提出了降低产品内部水汽含量的方法,提高了元器件的质量和可靠性.对比了改进前后产品的内部水汽含量.     

封装腔体内氢气含量控制

目前,对密封腔体内的水汽、二氧化碳、氧气含量的研究比较多,内部水汽含量控制在≤5 000 ppm、氧气控制在≤2 000 ppm、二氧化碳控制在≤4 000 ppm、氦气控制在≤1 000 ppm的密封工艺技术已解决[9],氢气含量控制的研究则未见报道。对于一些气密性要求高的封装应用领域,还需要控制氢气含量,如MEMS、GaAs电路等。分析了平行缝焊、Au80Sn20合金封帽的导电胶、合金烧结的器件的内部氢气含量,并分析了125℃168 h和125℃1 000 h贮存前后氢气含量的变化情况;在试验的基础上,提出了氢气的主要来源和针对性的工艺措施,并取得了期望的结果：密封器件经过125℃、1 000 h贮存后的氢气含量也能控制在≤4 000 ppm。     

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。     

高分辨率红外相机单窗与劈窗陆表温度反演精度分析研究

针对高分辨率热红外传感器单通道和劈窗设置,全面分析了影响陆表温度反演的各种因素,探讨劈窗和单窗对温度反演总精度的影响.首先利用辐射传输模型MODTRAN4.0,结合大量的TIGR探空廓线数据,建立广义劈窗算法和普适性单窗算法.接着进行算法拟合精度分析,以及地表比辐射率、等效噪声温度和水汽含量等不确定度对陆表温度反演精度的敏感性分析.最后得出不同比辐射率下,不同水汽含量下,劈窗和单窗算法地表反演总精度.研究表明单窗算法拟合精度低于劈窗算法,且随水汽含量增大而精度降低;水汽含量不确定度、地表比辐射率不确定及通道亮温NE△T对陆表温度反演总精度均有贡献,该贡献大小与水汽含量,比辐射率和地表温度均有关;影响单窗算法精度主要因素是算法拟合精度,影响劈窗算法精度主要因素是通道NE△T.在水汽含量较低时,单窗算法总精度与劈窗算法差不多,都在1K左右,水汽含量越大,单窗算法总精度越低,在2K左右,而劈窗算法总精度则变化不大.     

氟硅凝胶对陶瓷封装隔离器漏电流的影响

陶瓷封装隔离器具有高可靠性，灌胶可加强其绝缘性能，但还需要考虑灌胶对隔离器漏电流的影响。以GL3200C型陶瓷封装隔离器为研究对象，研究了氟硅凝胶通过内部水汽对陶瓷封装隔离器漏电流的影响，对隔离器在不同温度下进行稳定性烘焙10 h后测量其内部水汽含量，并分析内部水汽含量对隔离器漏电流的影响。结果表明，在不超过150℃的条件下，氟硅凝胶会分解产生烃类物质并释放至GL3200C封装内，但并不释放水汽，灌胶不会影响陶瓷封装隔离器的漏电流指标，满足隔离器的可靠性要求，但是存在稳定性不足和引入腐蚀性离子的风险。研究结果为工程应用上灌胶的选择提供了参考。     

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。     

导电胶粘接可伐载板工艺的仿真与优化

导电胶是一种很有潜力的互连材料,其粘接可靠性是制约其应用的主要因素。基于对某混频模块粘接失效的分析,探索温度试验条件及载板尺寸对可伐载板粘接可靠性的影响。通过仿真和试验设计,研究不同温度试验条件下不同尺寸载板在粘接界面处的应力分布情况,并优化了可伐载板粘接工艺。结果表明,温度试验条件越严苛,载板尺寸越大,可伐载板粘接可靠性越差,可采取环氧绝缘胶加固或柔性导电胶粘接的方式对其粘接工艺进行优化。     

微波芯片元件的导电胶粘接工艺与应用

导电胶常用于微波组件的组装过程,其粘接强度、导电、导热和韧性等性能指标严重影响其应用范围.分析了导电胶的国内外情况和主要性能参数,总结了混合微电路对导电胶应用的指标要求.通过微波芯片元件粘接工艺过程,分析了导电胶的固化工艺与粘接强度和玻璃化转变温度的关系、胶层厚度与热阻的关系、胶点位置和大小与粘片位置控制等方面的影响关系.测试结果显示,经导电胶粘接的芯片元件的电性能和粘接强度等指标均满足设计和使用要求,产品具有较好的可靠性和一致性.     

Failure mechanisms of ACF joints under isothermal ageing

The possible failure mechanisms of anisotropic conductive film (ACF) joints under isothermal ageing conditions have been identified through experiments. It has been found that ACF joints formed at higher bonding temperatures can prevent increases in the contact resistance for any ageing temperature. The higher the ageing temperature the higher the electrical failure rate is. The formation of conduction gaps between the conductive particles and the pads and damages to the metal coatings of the particle have been identified as the reasons behind the electrical failures during ageing. In order to understand the mechanism for the formation of the conduction gap and damages in metal coatings during the isothermal ageing, computer modelling has been carried out and the results are discussed extensively. The computer analysis shows that stresses concentrate at the edges of the particle-pad interface, where the adhesive matrix meets the particle. This could lead to subsequent damages and reductions in the adhesion strength in that region and it is possible for the conductive particle to be detached from the pad and the adhesive matrix. It is believed that because of this a conduction gap appears. Furthermore, under thermal loading the thermal expansion of the adhesive matrix squeezes the conductive particle and damages the metal coatings. Experimental evidences support this computational finding. It is, therefore, postulated that if an ACF-based electronic component operates in a high temperature aging condition, its electrical and mechanical functionalities will be at risk.     

Effects of different bonding parameters on the electrical performance and peeling strengths of ACF interconnection

The effects of different bonding parameters, such as temperature, pressure, curing time, bonding temperature ramp and post-processing, on the electrical performance and the adhesive strengths of anisotropic conductive film (ACF) interconnection are investigated. The test results show that the contact resistances change slightly, but the adhesive strengths increase with the bonding temperature increased. The curing time has great influence on the adhesive strength of ACF joints. The contact resistance and adhesive strength both are improved with the bonding pressure increased, but the adhesive strengths decrease if the bonding pressure is over 0.25 MPa. The optimum temperature, pressure, and curing time ranges for ACF bonding are concluded to be at 180–200 °C, 0.15–0.2 MPa, and 18–25 s, respectively. The effects of different Teflon thickness and post-processing on the contact resistance and adhesive strength of anisotropic conductive film (ACF) joints are studied. It is shown that the contact resistance and the adhesive strength both become deteriorated with the Teflon thickness increased. The tests of different post-processing conditions show that the specimens kept in 120 °C chamber for 30 min present the best performance of the ACF joints. The thermal cycling (−40 to 125 °C) and the high temperature/humidity (85 °C, 85% RH) aging test are conducted to evaluate the reliability of the specimens with different bonding parameters. It is shown that the high temperature/humidity is the worst condition to the ACF interconnection.     

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     

Flip chip attachment on flexible LCP substrate using an ACF

In this study the reliability of a flip chip bonding process using anisotropic conductive adhesives (ACA) was evaluated. The flexible substrates used were made of liquid crystal polymer (LCP), which is an interesting new material having excellent properties for flexible printed circuit boards. The test samples were prepared using two different anisotropic conductive films (ACF) having the same fast-cure resin matrix, but different conductive particles. The reliability of the test samples was studied by accelerated environmental tests. In the constant humidity test the temperature was 85 °C and the relative humidity was 85%. The temperature cycling test was carried out between temperatures of −40 °C and 85 °C. To determine the exact time of a failure the resistance of each test sample was measured using continuous real-time measurement. A clear difference between the behaviour of the conductive particles was seen in the test. While the adhesive having polymer particles had only one failure during testing, the adhesive having nickel particles had a considerable number of failures in both tests. Cross sections of the samples were made to analyze the failure mechanisms.     

环境对各向异性导电胶膜性能参数的影响

各向异性导电胶膜(ACF)的玻璃转化温度T_g是它的一个重要性能参数,用差示扫描热示计(DSC)分别测定商用各向异性导电胶膜固化前和固化后的玻璃转化温度,并确定不同的固化时间对它的玻璃转化温度的影响,以及高温高湿(85℃,85%RH)环境对它的玻璃转化温度影响,得到各向异性导电胶玻璃转化温度下降是其粘接强度下降的原因之一。     

环境对各向异性导电胶膜性能参数的影响

各向异性导电胶膜(ACF)的玻璃转化温度Tg是它的一个重要性能参数,用差示扫描热示计(DSC)分别测定商用各向异性导电胶膜固化前和固化后的玻璃转化温度,并确定改变固化时间对它的玻璃转化温度的影响,以及高温高湿(85℃,85%RH)环境对它的玻璃转化温度的影响,得到各向异性导电胶玻璃转化温度下降是其粘接强度下降的原因之一。