Chip-on-glass Assembly Research Articles

The coupled effects of salt-spray corrosion, electrical current and mechanical load on the electrical and fatigue properties of COG assembly

It is well-known that chip-on-glass (COG) assembly working in the coastal areas is often subjected to the coupled effects of salt-spray corrosion, electrical current and cyclic mechanical loading in service. Therefore, the fatigue life and electrical property of COG assembly undergoing the coupled loads of salt-spray corrosion, electrical current and cyclic mechanical loading have been studied in the present work. It is found that the relative resistance of COG assembly increases with the increase of salt-spray corrosion time. Moreover, the salt-spray corrosion time has a great influence on the resistance variation during the fatigue process. Simultaneously, the fatigue life of the COG assembly decreases with the increasing corrosion time. Finally, Miner's linear damage rules could be used to define the damage of COG assembly caused by the salt-spray corrosion.

Study on fatigue life and electrical property of COG assembly under thermal–electric–mechanical coupled loads

It is well-known that chip-on-glass (COG) assembly is often subjected to the coupled effects of temperature, electrical current and cyclic mechanical loading in service. Therefore, the fatigue life and electrical property of COG assembly undergoing thermal–electric–mechanical coupled loads have been studied in the present work. Based on the present investigations, it was found that that the relative resistance of COG assembly in the fatigue process displayed different trends according to environmental temperature and mechanical loading amplitude. Moreover, the fatigue life of the COG assembly decreased with the increased temperature and the increased loading amplitude. Finally, the Basquin's equation can predict the fatigue life of COG assembly at different environmental temperatures well.

The coupling effects of temperature, electric current and stress on the adhesion and electrical properties of COG assembly

This paper reports the adhesion and electrical properties of chip-on-glass (COG) assembly undergoing the coupling loads of temperature, electric current and stress (hygrothermal stress or thermal stress). Firstly, the effects of loading rate and coupling loads on the adhesive force of COG assembly were studied by shear test. The maximum shear force of COG assembly firstly increases and then decreases with increasing loading rate in range of 10–70μm/s, peaks at the loading rate of 50μm/s. When the COG assembly was exposed in the coupling loads of temperature, electric current and hygrothermal stress, its maximum shear force decreases with the increase of hygrothermal aging time. However, as for thermal cycling aging time increases, the maximum shear force increases initially and then decreases for the COG assembly under the coupling loads of temperature, electric current and thermal stress. The functions of the maximum shear force with aging time were obtained by fitting experiment data. Secondly, the real-time resistances of COG assembly during shear test and aging process were detected using two-point probe. In shear process, the real-time resistance increases insignificantly in elastic deformation stage but increases rapidly in viscoelastic deformation stage prior to the fracture. Due to the combined influences of temperature, electric current and stress, the resistance increases remarkably with the increase of hygrothermal aging time and it increases slightly with the increase of thermal cycling aging time. However, the real-time resistance exhibits circulation changes corresponding to thermal cycling. Finally, the relationship of resistance with the maximum shear force of energized COG assembly versus environmental aging times was studied.

ACF-COG interconnection conductivity inspection system using conductive area

The liquid crystal display (LCD) module package mainly adopts the chip-on-glass (COG) process, in which the driver IC is assembled onto a glass substrate with anisotropic conductive film (ACF). With the higher demand on the display capacity, the stability of COG interconnection under the finer pitch package becomes more important. Currently bump conductive particle counting is used to assess the interconnection quality. However, it cannot verify the interconnection conductivity promptly and would be labor intensive in case that all the bumps were required to inspect. In this paper, a conductivity inspection system based on optical microscope is presented. The resistance prediction model used in the system is based on particle conductive area and has been verified with the published experimental data, which revealed it could calculate the resistance value with the mean of particle conductive area and the number of conductive particles trapped by bump. The model is more accurate than the existed models. A visual inspection system for bump interconnection is developed in this study to compute the particle conductive area and the particle number. The system has been tested with 228 bump images of the ACF-COG modules, and the predicted resistance, 163mΩ, is in the common range. The results show that the conductive area (CA) can be an integral index of bump conductivity and comply with a normal distribution. The resistance model and inspection system provide guidance for the COG interconnection conductivity online testing and will benefit the COG assembly reliability.

Effects of ultrasonic bonding process on polymer-based anisotropic conductive film joints in chip-on-glass assemblies

Polymer-based anisotropic conductive film has become widely used in many electronic packaging interconnect applications. In this study, thermosonic flip chip bonding technology for anisotropic conductive film (ACF) joints in Chip-on-Glass (COG) assemblies is investigated. The effects of ultrasonic bonding process parameters on the degree of cure and bond strength of polymer-based anisotropic conductive film joints are discussed. Results show that (1) the bond strength and degree of cure both increase with increase of the bonding time and the optimum bonding time is 3 s; (2) the effects of the bonding force on the bond strength are not significant; (3) the bond strength of the ACF joints firstly increases and then rapidly decreases when the ultrasonic power is continuously increased; (4) the degree of cure of ACF material increases with increase of the ultrasonic power. When the ultrasonic power is 3.52 W, the degree of cure of ACF material can reach 94%. Hence, the optimum value of ultrasonic power is about 3.5 W for the studied COG assembly.

Effect of Material Properties of Anisotropic Conductive Films (ACFs) on the Reliability of Chip-On-Glass (COG) Assembly

The effect of material properties of anisotropic conductive films (ACFs) on the reliability of chip on glass (COG) assemblies was investigated. Two types of ACF were used in this study. ACF-A (50 wt%) is designed to have higher rubber resin content than ACF-B (11 wt%), in order to reduce the warpage of COG assembly. From the study on basic material properties, such as elastic modulus (E′), coefficient of thermal expansion (CTE) and glass transition temperature (Tg), ACF-B showed better properties than ACF-A. The temperature cycle reliability test showed that there were little differences between two ACF COG assemblies in spite of their different warpage level. But, results of high temperature storage test (100°C and 1000 hours) exhibited that the ACF-B COG assembly showed better performances due to the better material properties of ACF-B.

A Study of Process-Induced Deformations of Anisotropic Conductive Film (ACF) Assembly

The warpage of glass substrate in chip-on-glass (COG) assemblies were believed to be the main cause of the so-called "Mura" phenomenon in thin-film transistor liquid crystal display (TFT-LCD) panels. The main objective of the study is to characterize the process-induced deformations of an anisotropic conductive film (ACF) type of COG assembly during the ACF bonding process. For effectively modeling the process-dependent thermal-mechanical behaviors of the ACF assembly, a process-dependent simulation methodology that integrates both thermal and thermal-mechanical finite element (FE) analyses and a "death-birth" meshing scheme is proposed. In the investigation, two various types of mircobump bonding technologies, i.e., the Au alloy and composite bumps, are explored. To substantiate the validity of the proposed methodology, the modeled results are extensively compared against experimental data. Moreover, the alternative goal of the study is to provide a design guideline through the exploration of the individual or combined effect of some essential parameters on the process-induced deformations. Both the modeled and experimental results reveal that in addition to the coefficient of thermal expansion (CTE) mismatch between the die and substrate, the process-induced temperature gradient appears to be the key factor causing the deformation of the assembly, and the deformed shape of the substrate is totally opposed to that obtained from isothermal modeling. Evidence also suggests that a preheated substrate could effectively ease the maximum process-induced warpage of the substrate, while the ACF fillet would unfortunately enlarge it. Besides, it is not surprising to find that an increase of the die length would enhance the maximum process-induced warpage of the substrate, but what surprises many is that an increase of the die width would diminish it

Anisotropic conductive films (ACFs) for ultra-fine pitch Chip-On-Glass (COG) applications

This paper describes the development of anisotropic conductive films (ACFs) for ultra-fine pitch Chip-On-Glass (COG) application. In order to have reliable COG interconnects using ACF at fine pitch, the number of conductive particles trapped between the bump and substrate pad should be enough and less conductive particle between adjacent bumps. The ACF in this paper has double-layered structure, in which ACF and nonconductive film (NCF) layer thickness is optimized, to have as many conductive particles as possible on bump after COG bonding. In ACF layer, non-conductive particles of diameter 1/5 times smaller than the size of conductive particles were added to prevent electrical short between the bumps of COG assembly. The conductive particles are naturally insulated by the non-conductive particles even though conductive particles are flowed into and agglomerated in narrow gap between bumps during COG bonding. Also, flow property of the conductive particles is restrained due to increased viscosity of ACF layer with non-conductive particles, and the number of the conductive particles is constantly maintained. To ensure the insulation property at the level of 10 μm gap, insulating coated conductive particles were used in ACF layer composition. The double-layered ACF using low temperature curable binder system was also effective in reducing the warpage level of COG assembly due to low modulus and low bonding temperature.