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Anisotropic conductive film (ACF) is an essential layer used in Micro-LEDs and is applied through laser processing during the repair process. However, research related to the repair process using step-by-step morphology processing of ACF has hardly been conducted so far. Therefore, in this study, we proposed and thoroughly investigated a processing morphology suitable for the repair process through step-by-step processing using femtosecond lasers with wavelengths of 1026 (NIR), 513 (Green), and 257 (DUV) nm. By appropriately processing the ACF according to the intended purpose, it is expected that the desired repair process can be applied and can also be applied to all fields where ACF is utilized. [ABSTRACT FROM AUTHOR]

Anisotropic conductive film (ACF) is an electrical and electronic material composed of conductive balls embedded in a polymer matrix. ACF plays a crucial role in connecting electrodes and chips in Micro-LEDs. It serves as the target material in the repair process, enhancing production yield. For the application of ACF in the Micro-LED display repair process, flawless selective micro-ablation is essential. However, little research related to ACF micro-ablation has been conducted so far. In this study, we investigated a detailed analysis of the ablation area and defects in ACF by using femtosecond lasers with three different wavelengths: 1026 nm (NIR), 513 nm (Green), and 257 nm (DUV) for selective micro-ablation. By conducting a comparative analysis of these wavelengths, we determined that the optimal ablation results were achieved using a 257 nm wavelength femtosecond laser. These results exhibited no-defect, uniform, reproducible, and symmetrical ablation characteristic, making it suitable for the Micro-LED display repair process. This research is expected to establish the foundation for micro-ablation in all applications where ACF is employed. [ABSTRACT FROM AUTHOR]

The demand for flexible displays (e.g. foldable and rollable displays) has recently increased, thus necessitating the development of various component technologies. An anisotropic conductive film, which is a conventional surface mount technology, is deemed more necessary than soldering for the implementation of a flexible display. However, it is still difficult to secure the electrical conductivity and reliability of the conductive ball used in the anisotropic conductive film. In this paper, a copper conductive ball having a lower resistance than the conventional conductive ball was fabricated. It has a lower contact resistance than nickel and gold, and the reliability issue, which is a disadvantage of copper, is secured by blocking the reaction with oxygen and coating a thin corrosive solution.

The demand for flexible displays (e.g. foldable and rollable displays) has recently increased, thus necessitating the development of various component technologies. An anisotropic conductive film, which is a conventional surface mount technology, is deemed more necessary than soldering for the implementation of a flexible display. However, it is still difficult to secure the electrical conductivity and reliability of the conductive ball used in the anisotropic conductive film. In this paper, a copper conductive ball having a lower resistance than the conventional conductive ball was fabricated. It has a lower contact resistance than nickel and gold, and the reliability issue, which is a disadvantage of copper, is secured by blocking the reaction with oxygen and coating a thin corrosive solution. [ABSTRACT FROM AUTHOR]

Electrochemical imaging with electrode arrays has been widely used to visualize chemicals and biomolecules. However, it is difficult to incorporate many sensors in a small area because of the large area of the leading connections and connector pads. To solve this problem, closed bipolar electrodes (BPEs) have been proposed as wireless electrochemical sensors, wherein many conductive materials are embedded in a thin film. However, it is laborious to prepare films with high-density BPEs. In this study, we demonstrate that commercially available anisotropic conductive films (ACFs) can be used as closed BPE films for electrochemiluminescence (ECL) imaging. Commercial ACFs are easily available without any fabrication equipment in a laboratory, which is a merit. The ACFs comprised conductive fibers embedded into a rubber film of 0.2 mm thickness. In the ACFs containing carbon fibers, the fiber diameter was 5–20 µm, and the fiber density was approximately 1 × 10³ fibers/mm². As the films were made of rubber, they bend and stretch easily, and thus are useful for bending and stretching applications during assays. During ECL imaging, redox compounds react at the cathodic poles of BPEs, and ECL chemicals are oxidized at the opposite poles. In this study, we characterized ACFs for ECL imaging. Additionally, we presented a novel configuration of electrodes for ECL imaging based on a BPE array film, where it is unnecessary to insert an electrode into the ECL chemical solution. Finally, a moving droplet was electrochemically visualized to study the crosstalk between BPEs. To the best of our knowledge, this is the first report concerning ECL imaging based on BPEs using commercially available ACFs. In the future, this strategy will be coupled with biosensing for cell analyses and immunoassays. [ABSTRACT FROM AUTHOR]

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We report a miniaturized, minimally invasive high-density neural recording interface that occupies only a 1.53 mm2 footprint for hybrid integration of a flexible probe and a 256-channel integrated circuit chip. To achieve such a compact form factor, we developed a custom flip-chip bonding technique using anisotropic conductive film and analog circuit-under-pad in a tiny pitch of 75 μm. To enhance signal-to-noise ratios, we applied a reference-replica topology that can provide the matched input impedance for signal and reference paths in low-noise aimpliers (LNAs). The analog front-end (AFE) consists of LNAs, buffers, programmable gain amplifiers, 10b ADCs, a reference generator, a digital controller, and serial-peripheral interfaces (SPIs). The AFE consumes 51.92 μW from 1.2 V and 1.8 V supplies in an area of 0.0161 mm2 per channel, implemented in a 180 nm CMOS process. The AFE shows > 60 dB mid-band CMRR, 6.32 μVrms input-referred noise from 0.5 Hz to 10 kHz, and 48 MΩ input impedance at 1 kHz. The fabricated AFE chip was directly flip-chip bonded with a 256-channel flexible polyimide neural probe and assembled in a tiny head-stage PCB. Full functionalities of the fabricated 256-channel interface were validated in both in vitro and in vivo experiments, demonstrating the presented hybrid neural recording interface is suitable for various neuroscience studies in the quest of large scale, miniaturized recording systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new concept of photosensitive dual-anisotropic conductive Janus film is advanced. • Film has bi-anisotropic conduction, luminescence and magnetism on light irradiation. • Anisotropic conduction is firstly realized by utilizing photoconductive effect. • Multi-functionalities of Janus film can be switched by controlling light irradiation. • Novel 3D Janus-type tube and 2D plus 3D complete flag-like structures are obtained. A new photosensitive dual-anisotropic conductive Janus film (PDCJF) is proposed for the first time. It is rationally designed and manufactured by facile electrospinning. PDCJF is firstly constructed using 2,7-dibromo-9-fluorenone (DBF) with photoconductive and luminescent properties. Janus nanofibers are respectively used as the building units to construct the top layer (T-PDCJF) and the bottom layer (B-PDCJF) of PDCJF. The two layers are tightly bonded to form PDCJF. Under light irradiation, there is photosensitive dual-anisotropic conduction in PDCJF, but there is no anisotropic conduction without light. Thus, the transition of PDCJF from mono-functional magnetism to tri-functionalities is realized under light and without light. The luminescence color of PDCJF is tunable and it emits white-light. This is made possible by modulating the amounts of luminescent substances and excitation wavelength. The microscopic Janus nanofibers used as building units and macroscopic Janus film structure ensure high photosensitive dual-anisotropic conduction and excellent fluorescence in PDCJF. The two-dimensional (2D) PDCJF is rolled to obtain three-dimensional (3D) Janus-type tubes and 2D plus 3D complete flag-like structures with exceptional multi-functionalities. The new findings can strongly guide in developing advanced multi-functional nanostructures. [ABSTRACT FROM AUTHOR]

The development of an anisotropic conductive film was attempted using original microfabrication (stick-slip (SS) processing) involving SS accompanying abrasion. During SS processing, the film surface was periodically scraped with a razor. For a metal-deposited polyethylene terephthalate (PET) film (metal/PET film), fine periodic structures (line and space (L/S)-like patterns) were formed on its surface because the metal layer was periodically scraped. This result proved that SS processing can be applied not only to polymers but also to metals. Moreover, the line interval of an SS-processed metal/PET film shortened as the contact force decreased, and the depth of the line became shallower in proportion to the line interval. In addition, SS-processed copper/PET (Cu/PET) film did not conduct electricity in the direction perpendicular to the Cu line; however, it conducted electricity in the direction parallel. Thus, this study shows the possibility of using SS processing for fabricating an anisotropic conductive film. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Novel sandwich-structured composite pellicle was firstly designed and constructed. • Conductive aeolotropism, magnetism and luminescence were integrated into 2D pellicle. • Partition of three independent domains in 2D pellicle is macroscopically actualized. • Partitioned structure helps reduce detrimental interactions among various materials. • Partitioned structure can be extended to prepare other materials with multifunction. Abstract The novel sandwich-structured composite pellicle equipped with electrically conductive anisotropy, magnetism and photoluminescence is successfully constructed via electrospinning for the first time. Exceptionally-designed electrospun [polyaniline (PANI)/polymethylmethacrylate (PMMA)]//PMMA Janus nanobelts are utilized as constitutional and conductive elements to construct anisotropic electrically conductive array layer, Fe 3 O 4 /polyvinylpyrrolidone (PVP) nanofibers and Eu(BA) 3 phen/polyacrylonitrile (PAN) nanofibers are respectively applied as building units to form magnetic and luminescent non-array layers, then the three layers are firmly unified together to form the 2D sandwich-structured composite pellicle with tri-functionality. By the aid of the exceptive sandwich-like structure, electrical, magnetic, and luminescent substances are mutually and efficaciously segregated, and thus the mutually detrimental interferences among them can be absolutely avoided, leading to the fact that the sandwich-structured composite pellicle coinstantaneously possesses superior conductive anisotropy, luminescence and magnetism tri-functionality. The conductive anisotropy and magnetism of composite pellicle can be respectively adjusted via regulating PANI and Fe 3 O 4 NPs contents. Owing to the unique nanostructure made of Janus nanobelts in the anisotropic conductive array layer, the conduction ratio reaches 108 times between conductive and insulating direction of the sandwich-structured composite pellicle. Under the excitation of 280-nm ultraviolet light, prominent red emission at 615 nm can be clearly observed in the luminescent layer. The novel sandwich-structured composite pellicle with concurrent trifunctionality has potential applications in many fields. Above all, this academic thought and manufacturing means will provide supports for the design and manufacture of new-typed anisotropic conductive films with multifunctionality. [ABSTRACT FROM AUTHOR]

Mini/Micro LED are recognized as the fourth generation display technology due their superior performance. Backlights based on active‐matrix Mini‐LED (AM‐MLED) have been adopted in LCD modules and would soon be put into mass production. In this paper, a novel Sn paste free method was developed to manufacture Mini‐LED displays. This method is more simple and could successfully solve the short problem which is common for conventional approach. We believe this result would further extend the application of Mini‐LED in direct display area. [ABSTRACT FROM AUTHOR]

This paper reports a novel assembly method for 3-dimensional (3D) microelectrode array with the aid of anisotropic conductive film (ACF). For this purpose, a unique silicon probe with trenches encircled bonding pads was fabricated to realize the ACF-bonding with flexible cable. This design is meaningful because it can realize planar bonding for subsequently convenient 3D stacking and the time-consuming plating is not needed to form bumping on pads. The reliability of the ACF-bonding is demonstrated by measuring the electrochemical impedance spectra (EIS) of the bonded probes with different structural and dimensional bonding pads. The bonded probes are further assembled into 3D arrays and integrated with micro-drive for chronic neural recordings. The excellent recording performance indicates that the ACF-bonded probes are reliable and suitable for chronic neural recordings. [ABSTRACT FROM AUTHOR]

Although cationic epoxy was optimized for low-melting SnBi58 solder ACF joints with the lowest coefficient of thermal expansion (CTE) in terms of reliability, cationic epoxy also showed a faster curing property than any other types of adhesives. In fact, solder joint shapes at 250 °C bonding are very different from those shapes at 200 °C bonding. In this paper, four adhesive film types were investigated in terms of Sn-3Ag-0.5Cu solder ACF joint shapes on the electrical performances and reliability in a pressure cooker test (PCT). Thermal stability of adhesive films was tested to be first. Resin curing speeds were measured in a 250 °C isothermal mode differential scanning calorimetry, resin viscosities were checked by a parallel-plate rheometer, and adhesive thermomechanical properties, such as modulus and CTE, were characterized. Then, four different types of ACF resins containing the same weight percentages of Sn-3Ag-0.5Cu solders were assembled by the same thermocompression bonding parameter (250 °C 10s 2MPa on bump) on a 500- \mu \textm -pitch flex-on-board (FOB) application, and different solder joint morphologies were verified. Various bonded solder ACFs joints were compared in terms of solder wetting areas, electrical performances by a four-point-probe method, and the reliability of PCT (121 °C 100% humidity 2atm) for 120 h. This paper aims at optimizing the best adhesive film candidate for SAC305 solder ACF joints of FOB application. [ABSTRACT FROM PUBLISHER]

The microstimulation of specific neural populations of the brain is one of the facile and reliable methods used in neuroscience for deduction of functional movement, complex behavior and even long-range connectivity. Recent advanced biomedical tools now employ flexible optoelectronic devices combined with optogenetic mouse models to induce high spatiotemporal modulation of specific brain activity. However, most current applications are limited to activation of small functional regions using blue-light driven channelrhodopsin. In this report, we introduce flexible AlGaInP vertical light-emitting diodes (VLEDs) for perturbation of specific functional areas of mouse cortex. Micro-scaled LEDs effectively compress the conductive balls dispersed in anisotropic conductive film (ACF) resulting red light emissions with high optical power density, capable of stimulating motor neurons deep below layer III from the brain surface. Selective operation of pulsed red light from f-VLEDs induces mouse body movements and synchronized electromyogram (EMG) signals. The expression of chrimson, red-shifted channelrhodopsin, enables red-light excitation of targeted functional area of motor cortex. This demonstration opens new opportunities for entire cortical mapping, to explore the connectivity between undefined motor areas in the mouse brain. [ABSTRACT FROM AUTHOR]

Flex-on-fabric (FOF) interconnections using anisotropic conductive films (ACFs) and ultrasonic bonding method were investigated for wearable devices applications. In this paper, the conduction mechanism of FOF and the effects of the conductive fabrics porosity and ACFs materials on the FOF interconnection were investigated. Two types of conductive fabrics with different porosities such as knitted and woven fabrics, and different viscosities of ACFs resin were used. For the conductive particle of ACFs, metal-coated polymer ball was used. According to the results, the conduction of FOF consists of both conductive balls and fabrics to metal electrode direct contacts. Among these two conduction paths, fabric direct contact was the major conduction path because the contact resistance of the ACFs conductive balls to metal contact is about ten times larger than that of the fabric to metal direct contact. In addition, it was found that laminated nonconductive films cover layer and the increased ACFs minimum viscosity (from 940 to 27000 Pa \cdot \texts ) substantially increased the peel adhesion strength twice due to the decreased resin flow through the pore of fabrics and increased FOF joint gap size. Finally, both conductive fabrics showed no electrical failure after 500 h 85°/85% relative humidity reliability test. However, among two types of fabric, knitted fabric had better humidity reliability performance than the woven fabric presumably due to its better compliance. [ABSTRACT FROM AUTHOR]

Anisotropic conductive film ( ACF) is an essential component in the manufacture of liquid crystal displays, and an imidazole-epoxy resin system that exhibits a latent behavior is generally used as an adhesive in the ACF. In this study, a new copolymer was synthesized using methacrylic acid and dodecyl methacrylate, and this copolymer was used to encapsulate an imidazole curing agent to endow the ACF with latent behavior. A spray-drying method was used in the encapsulation process, and this encapsulated imidazole was mixed with epoxy resin to form an imidazole-epoxy resin system. A comparison with our previous results showed that a smaller amount of polymeric material could be used in the encapsulating process, and a superior latent behavior could be obtained. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The pressing deformation of conductive microspheres in Anisotropic Conductive Film(ACF) bonding mainly decides the interconnection resistance and bonding quality. Prior works have studied the formation mechanism of microspheres’ pressing deformation and bonding resistance, but haven't theorized how to obtain them. This paper has propose to accurately inspect the pressing deformation by differential interference contrast(DIC) imaging and images analyzing. By the deformation inspection, it further proposed to calculate the bonding resistance with the resistance model. Experimental results show it can accurately inspect the conductive microspheres’ pressing deformation and interconnection resistance, showing that the unacceptable bumps have a big resistance, over 300 mΩ, while the acceptable bumps have a small resistance, about 126 mΩ. The inspection result is more consistent with the actual resistance than ones from the references for it doesn't have the shortages of parameters acquisition in the references. This paper has theorized how to inspect the ACF bonding resistance which will be useful to electronic packaging, especially in LCD module industry. [ABSTRACT FROM AUTHOR]

Anisotropic conductive film (ACF) bonding is widely used in the liquid crystal display (LCD) industry. It implements circuit connection between screens and flexible printed circuits or integrated circuits. Conductive microspheres in ACF are key factors that influence LCD quality, because the conductive microspheres' quantity and shape deformation rate affect the interconnection resistance. Although this issue has been studied extensively by prior work, quick and accurate methods to inspect the quality of ACF bonding are still missing in the actual production process. We propose a method to inspect ACF bonding effectively by using automated optical inspection. The method has three steps. The first step is that it acquires images of the detection zones using a differential interference contrast (DIC) imaging system. The second step is that it identifies the conductive microspheres and their shape deformation rate using quantitative analysis of the characteristics of the DIC images. The final step is that it inspects ACF bonding using a back propagation trained neural network. The result shows that the miss rate is lower than 0.1%, and the false inspection rate is lower than 0.05%. [ABSTRACT FROM AUTHOR]

In order to assemble a driver IC onto a LCD glass panel, Chip on glass (COG) bonding technology using Anisotropic conductive film (ACF) has been widely implemented. The key process parameters in the technology are the temperature, pressure and time during the thermo-compression bonding. These factors mainly affect the quality of the assembled ACF joint being represented by the contact resistance and adhesion strength. This study purposes to obtain the optimal process conditions for high reliability of the ACF joint. In order to determine the optimal condition, the experiments based on the response surface methodology were designed. Based on the experiments and statistical analysis, the empirical model of second-order polynomials approximating the relationships between the process conditions and the response variables of contact resistance and adhesion strength were obtained. The optimal process condition to lead lower contact resistance and higher adhesion strength of the ACF joint was also calculated from the relationships. The optimization was verified through the bonding experiments conducted under the derived optimal process condition. In addition, the reliability of the ACF joints according to the variation of the process conditions was evaluated in high temperature and humidity environment (85°C/85%RH). Consequently, it was shown that the reliability of ACF joints assembled under the optimal process conditions was superior to others after the 85°C/85%RH tests. [ABSTRACT FROM AUTHOR]