大型液晶显示用COF带的现状和未来

概述了从TAB带到COF带的转换,大型LCD用的COF带的微细线路形成技术和高可靠性技术以及COF带制造技术的未来。     

液晶电视用新型高性能COF基材的开发与测试

随着COF封装技术的快速发展，其应用前景也更广阔，但由于COF基材在高电压条件容易发生短路，所以COF在大型液晶显示器方面的应用就受到了很大的限制。文章将从COF短路的机理分析基材高压短路的原因，并针对这一现象开发了新~OF基材。经过测试，新COF基材性能完全达到要求。     

COF精细线路的制作与相关技术

随着各种短、小、轻、薄液晶显示器越来越受到人们的欢迎,COF（chip on film）封装技术也得到了较快的发展。COF技术不仅仅是精细线路的制作和芯片的连接,而且该技术与其他的相关课题有着密切的联系。本文主要介绍了精细化线路COF基板的制作技术现状和未来需要进一步解决的相关技术。     

文献与摘要（60）

全球COF市场现况与机会分析本文介绍覆晶薄膜(COF)的定义和分类,对全球COF市场进行分析。文章指出:COF主要应用在显示器驱动的IC封装上,COF软板封装取代TCP载板的趋势仍在继续进行,COF软板的需求将持续增长,并且仍有技术发展的空间。从全球COF市场来看,日本厂商占有最大的市场份额。(工研院IEK零组件研究部,电路板会刊,2006/1,共6页)剥离强度实验Experiences with Peel Strength剥离强度是一个重要特性指标,用来表征在测试条件下铜箔与树脂之间的结合能力。本文主要从树脂的类型、铜箔的厚度、硬度及铜箔的表面粗糙度等方面进…     

COF技术—未来封装技术的主流

随着电子产品的小型、轻量化及多功能化的发展，特别是半导体芯片的高集成化与高I／O数的迅速发展，导致封装技术向芯片级封装的发展。对于高密度挠性电路的到装，未来市场的主流即是采用COF封装。本文概述了高密度的IC封装形式，COF封装的特点以及COF的三种连接方式。     

应用于COF的无胶基材尺寸稳定性研究

COF技术由于具备诸多优势，已经成为LCD驱动IC的主要封装技术。对三种无胶基材进行实验，通过测量孔径和误差之间的关系，得出1．5mm孔为引入误差最小的孔；测量真空层压后基材的尺寸稳定性，三种基材能够符合COF技术要求。     

大型液晶显示用COF带的细节距线路形成

概述了大型液晶显示用COF带的特征和制造技术以及细节距线路形成技术。     

埋置型叠层微系统封装技术

包含微机电系统(MEMS)混合元器件的埋置型叠层封装,此封装工艺为目前用于微电子封装的挠曲基板上芯片(COF)工艺的衍生物。COF是一种高性能、多芯片封装工艺技术,在此封装中把芯片包入模塑塑料基板中,通过在元器件上形成的薄膜结构构成互连。研究的激光融除工艺能够使所选择的COF叠层区域有效融除,而对封装的MEMS器件影响最小。对用于标准的COF工艺的融除程序进行分析和特征描述,以便设计一种新的对裸露的MEMS器件热损坏的潜在性最小的程序。COF/MEMS封装技术非常适合于诸如微光学及无线射频器件等很多微系统封装的应用。     

减成法制作双面COF印制电路板工艺研究

双面COF基板可以极大地缩小基板面积,满足产品的轻、薄、短小的要求,因此对于双面COF基板的需求也会逐渐增长.减成法工艺是生产FPC产品的主要工艺,技术与设备都非常成熟.本文对减成法工艺制作双面COF印制板进行了初步研究,讨论了微孔清洗方法的选择,比较了化学镀铜与黑孔化工艺的优劣,对应用液态感光抗蚀剂时的参数如曝光能量、显影速度、蚀刻速度及蚀刻压力等进行了优化,得到最佳工艺流程及工艺参数.     

封装内引脚键合过程的参数优化及模拟验证

覆晶软带封装(COF)以及带载芯片封装(TCP)是液晶显示驱动芯片普遍采用的封装方式.与传统封装的微焊球等技术不同,COF和TCP封装工艺采用内引脚键合(ILB)技术来实现驱动芯片与外部电路的电性连接,所以ILB工艺的可靠性对于封装质量起着至关重要的作用.利用改进的田口实验设计的方法,结合实际生产数据,获得了最优化的生产工艺,并利用FEA有限元模拟验证了实验参数.实际的生产结果显示,ILB引脚的可靠性有很大幅度的提高.     

Characteristic study of anisotropic-conductive film for chip-on-film packaging

Chip-on-film (COF) is a new technology after tape-automated bonding (TAB) and chip-on-glass (COG) in the interconnection of liquid crystal module (LCM). The thickness of the film, which is more flexible than TAB, can be as thin as 44 μm. It has pre-test capability, while COG does not have. It possesses great potential in many product fabrication applications.In this study, we used anisotropic-conductive film (ACF) as the adhesive to bind the desired IC chip and polyimide (PI) film. The electric path was formed by connecting the bump on the IC and the electrode on the PI film via the conductive particles in the ACF. In the COF bonding process experimental-design method was applied based on the parameters, such as bonding temperature, bonding pressure and bonding time. After reliability tests of (1) 60 °C/95%RH/500 h and (2) −20 to 70 °C/500 cycles, contact resistance was measured and used as the quality inspection parameter. Correlation between the contact resistance and the three parameters was established and optimal processing condition was obtained. The COF samples analyzed were fabricated accordingly. The contact resistance of the COF samples was measured at varying temperature using the four points test method. The result helped us to realize the relationship between the contact resistance and the operation temperature of the COF technology. This yielded important information for circuit design.     

Development of chip-on-flex bonding using Sn-based bumps and non-conductive adhesive

We developed a reliable and low cost chip-on-flex (COF) bonding technique using Sn-based bumps and a non-conductive adhesive (NCA). Two types of bump materials were used for the bonding process: Sn bumps and Sn–Ag bumps. The bonding process was performed at 180 °C for 10 s using a thermo-compression bonder after dispensing the NCA. Sn-based bumps were easily deformed to contact Cu pads during the bonding process. A thin layer of Cu₆Sn₅ intermetallic compound was observed at the interface between Sn-based bumps and Cu pads. After bonding, electrical measurements showed that all COF joints had very low contact resistance, and there were no failed joints. To evaluate the reliability of COF joints, high temperature storage tests (150 °C, 1000 h), thermal cycling tests (−25 °C/+125 °C, 1000 cycles) and temperature and humidity tests (85 °C/85% RH, 1000 h) were performed. Although contact resistance was slightly increased after the reliability test, all COF joints passed failure criteria. Therefore, the metallurgical bond resulted in good contact and improved the reliability of the joints.     

Theoretical Prediction and Experimental Measurement of the Degree of Cure of Anisotropic Conductive Films (ACFs) for Chip-On-Flex (COF) Applications

The degree of cure of anisotropic conductive films (ACFs) was theoretically predicted and experimentally measured to investigate the effect of the degree of cure of ACFs on the electrical and mechanical stability of ACF joints and the␣reliability of chip-on-flex (COF) assemblies. The cure reaction of ACFs, observed by an isothermal differential scanning calorimetry (DSC) analysis, followed an autocatalytic cure mechanism, and the degree of cure of ACFs as a function of time and temperature was mathematically derived from an autocatalytic cure kinetics model. To simulate the ACF temperature field accurately during the COF bonding process, the thermal properties of the ACF such as the thermal diffusivity (α), specific heat capacity (C _p), and thermal conductivity (λ) were characterized experimentally. The degrees of cure of ACFs as functions of the bonding time during the COF bonding process were theoretically predicted by the incorporation of autocatalytic kinetics modeling and ACF temperature simulation. The predicted degrees of cure of ACFs were well matched with the experimental data measured by attenuated total reflectance/Fourier-transform infrared (ATR/FT-IR) analysis. The contact resistances of the ACF joints and the peel adhesion strengths of the COF assemblies were evaluated for electrical and mechanical interconnection stability. According to these results, the ACF contact resistances decreased and the ACF peel adhesion strengths increased as the degree of cure of ACFs increased. In addition, to investigate the effect of the degree of cure of ACFs on the reliability of COF assemblies, an 85°C/85% relative humidity (85°C/85% RH) test was performed. These results showed that the reliability of COF assemblies also strongly depends on the degree of cure of the ACFs.     

Issues in Assembly Process of Next-Generation Fine-Pitch Chip-On-Flex Packages for LCD Applications

Some of the current assembly issues of fine-pitch chip-on-flex (COF) packages for LCD applications are reviewed. Traditional underfill material, anisotropic conductive adhesive (ACA), and nonconductive adhesive (NCA) are considered in conjunction with two applicable bonding methods including thermal and laser bonding. Advantages and disadvantages of each material/process combination are identified. Their applicability is further investigated to identify a process most suitable to the next-generation fine-pitch packages (less than 35 mum). Numerical results and subsequent testing results indicate that the NCA/laser bonding process is advantageous for preventing both lead crack and excessive misalignment compared to the conventional bonding process     

倒装芯片各向异性导电胶互连的剪切结合强度

采用冲击试验方法研究了各向异性导电胶膜(ACF)互连的玻璃和柔性基板上倒装芯片(COG和COF)的剪切结合强度.结果表明:COF比COG的剪切强度高.ACF的固化程度达85 %时有最大的结合强度.键合温度、导电颗粒状态、缺陷等因素对ACF互连的结合强度有较大影响,而键合压力的影响不大.     

Studies on various chip-on-film (COF) packages using ultra fine pitch two-metal layer flexible printed circuits (two-metal layer FPCs)

Various fine pitch chip-on-film (COF) packages assembled by (1) anisotropic conductive film (ACF), (2) nonconductive film (NCF), and (3) AuSn metallurgical bonding methods using fine pitch flexible printed circuits (FPCs) with two-metal layers were investigated in terms of electrical characteristics, flip chip joint properties, peel adhesion strength, heat dissipation capability, and reliability. Two-metal layer FPCs and display driver IC (DDI) chips with 35 μm, 25 μm, and 20 μm pitch were prepared. All the COF packages using two-metal layer FPCs assembled by three bonding methods showed stable flip chip joint shapes, stable bump contact resistances below 5 mΩ, good adhesion strength of more than 600 gf/cm, and enhanced heat dissipation capability compared to a conventional COF package using one-metal layer FPCs. A high temperature/humidity test (85 °C/85% RH, 1000 h) and thermal cycling test (T/C test, ?40 °C to + 125 °C, 1000 cycles) were conducted to verify the reliability of the various COF packages using two-metal layer FPCs. All the COF packages showed excellent high temperature/humidity and T/C reliability, however, electrically shorted joints were observed during reliability tests only at the ACF joints with 20 μm pitch. Therefore, for less than 20 μm pitch COF packages, NCF adhesive bonding and AuSn metallurgical bonding methods are recommended, while all the ACF and NCF adhesives bonding and AuSn metallurgical bonding methods can be applied for over 25 μm pitch COF applications. Furthermore, we were also able to demonstrate double-side COF using two-metal layer FPCs.     

The effect of different bonding temperatures on the mechanical and electrical performance of NCF-bonded flip-chip-on-flex packages

Liquid crystal displays (LCDs) and organic light emitting diodes (OLEDs) are the technology involved in electronic displays in order to get a better viewing angle and high-density resolution products. Fine-pitch, flip-chip interconnection is one method which is able to enhance the display performance with high color resolution. Nonconducting film (NCF) is a novel material developed for fine-pitch applications. This study investigates the temperature effect on the electrical contact performance of an NCF-bonded chip-on-flexible (COF) substrate package. The changes in contact resistance after reflow at a peak temperature of 260/spl deg/C for three times were measured with a four-point probe method. The bonding temperature has a significant effect on the peel strength of the NCF-bonded COF. A high peel strength for the NCF COF bonded at a high temperature indicated that the NCF obtained sufficient mechanical strength to hold the interconnection joints. A low bonding temperature is preferable to obtain good electrical contact, but sufficient high temperature is needed to ensure a good mechanical and reliable joint. An excessively high bonding temperature is to be avoided because it gives instant curing at the contact point which restricts good electrical conduction. An NCF with a curing degree of /spl sim/86% was needed to ensure sufficient and reliable electrical joints in the COF.     

Process optimization to overcome void formation in nonconductive paste interconnections for fine-pitch applications

Nonconductive paste (NCP) is becoming an alternative material for chip-on-flexible (COF) substrate, where it is able to achieve a very fine-pitch interconnection for high resolution products. The application of NCP faces the problem that it is initially a high viscosity liquid, which easily causes voids in the inter-connection. Voids in the interconnection reduce the mechanical strength in the joints and create moisture entrapment sites, which shorten the reliable performance of the interconnection. They were revealed using optical microscopy and nondestructive C-mode scanning acoustic microscopy (C-SAM). This study reveals the factors involved during process control in order to minimize void entrapment in the interconnection. These parameters include the following: (a) substrate pretreatment, (b) the speed at which the tool heater descends, (c) bonding force, (d) bonding temperature, and (e) holding time on the bonding stage. These parameters permitted a modification to the surface, and also brought chemical reaction and viscosity changes to the NCP during the bonding process, which leads to the minimization of void formation in the specimen.