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A theoretical investigation is performed into the bending behavior of FOF-ACF (Flex-On-Flex bonded by Anisotropic Conductive Film) packages bonded at different positions relative to the neutral surface position. The stresses and strains produced in the upper and lower regions of the ACF layer are investigated using Mode I fracture mechanics theory. The results show that the region of the ACF layer beneath the neutral surface of the FOF-ACF package experiences a negative stress, which prevents pre-existing cracks in the conductive particles from propagating further. However, at larger distances from the neutral surface, the compressive stress increases to such an extent that it may result in crumbling of the conductive particles. By contrast, the region of the ACF layer above the neutral surface experiences a positive stress, which promotes crack tip propagation. Moreover, the tension stress (i.e., the crack propagation effect) increases with an increasing distance from the neutral surface. The optimum bonding position for the ACF layer is found to be coincident with the neutral surface since, under this condition, the stresses and strains acting on the compressed particles present their minimum values. Consequently, the risk of fracture failure is reduced and the reliability of the ACF package is correspondingly improved.

As the display resolution has been rapidly increased, the pitch between two electrodes has been continuously decreased to less than $20~\mu \text{m}$ pitch. Therefore, fine-pitch interconnection technology has become very important in display technology. In our previous research results, anchoring polymer layer (APL) structure was successfully introduced into anisotropic conductive film (ACF) system to form fine pitch interconnection by suppressing the conductive particles movement during the ACF assembly. In general, the agglomerated conductive particles between two electrodes can cause short-circuit problems at ACF assembly. In this paper, the magnetic field was applied to the Ni-coated polymer conductive particles in the polyvinyl fluoride (PVDF) APL structure to disperse the conductive particles uniformly in the xy plane. Then the effects of the magnetic fields on the dispersion of the Ni-coated conductive particles in the PVDF APL structure and the characterization of fine-pitch chip-on-glass (COG) assembly using PVDF APL ACFs with magnetically dispersed conductive particles were investigated. By optimizing the magnetic fields on the PVDF APL structure, 80% dispersed particle rate was successfully obtained. After the ACF bonding process, the conductive particles capture rates and contact resistance properties of magnetically dispersed PVDF APL ACFs, and the PVDF APL ACFs with no magnetic field applied were investigated at 20- $\mu \text{m}$ -pitch COG applications. Both PVDF APL ACFs showed a similar capture rate of conductive particles and electrical insulation property at $20~\mu \text{m}$ pitch. The PVDF APL ACFs with no magnetic field applied showed 100% of insulation property at $20~\mu \text{m}$ , but short circuits at less than pitch. However, for less than 20- $\mu \text{m}$ pitch, only the PVDF APL ACFs with magnetically dispersed conductive particles showed 100% insulation circuit rate down to the 11- $\mu \text{m}$ pitch because the conductive particles were not agglomerated but existed as single particles, resulting in no electrical short between fine-pitch adjacent bumps. As a result, magnetically dispersed PVDF APL ACFs can be used as new ACF materials for ultrafine-pitch interconnection applications without any electrical short.

In the field of flat panel displays (FPD), packaging technology has significant influence on display performance. The electrical and mechanical interconnect between the liquid crystal displays (LCD) and its driver integrated circuit (IC) is a key issue that needs improvement to achieve finer pitch, easier assembly and greater connection reliability. With the decrease of the pixel size and the increase of pixel count for high-density LCD, the overall trend of the driver IC is packaged closer and closer to the LCD itself, even is onto the backside glass of the LCD. Bonding the driver IC chips directly to the glass substrate of the LCD panel might be a better choice when the pitch becomes less than 70–100 μm (Helge & Liu, 1998). Since the announcement by Citizen back in 1983 of a chip-on-glass (COG) driver assembly process for their LC pocket TV, many different types of COG assembly processes have been developed (Helge & Liu, 1998). In COG technology, the driver ICs are bonded directly to the indium-tin-oxide (ITO) traces on the glass without increasing the size of the panel, except for the finer bump pitch and smaller contact resistance, which can bring a significant reduction in the size of the FPD module. Because LCD is particularly heat sensitive and cannot withstand normal soldering temperatures, conductive adhesives are widely used to connect the driver IC to LCD. Usually, there are two different mechanisms used to cure the conductive adhesives, heat curing for thermosetting adhesives and UV curing for thermoplastic adhesives. Among them, heat curing appears to be most common. Nowadays interconnection using anisotropic conductive film (ACF) is the most major packaging method for production of FPD modules, to provide electrical conduction and mechanical adhesion between the driver ICs and the glass substrate with a high resolution, light weight, thin profile, and low power consumption (Myung & Kyung, 2006). Figure 1 presents a schematic illustration of a typical COG connection process using ACF. ACF is a thermosetting epoxy impregnated with small amount of electrically conductive particles, which can be pure metals such as gold, silver, or nickel, or metal-coated ones with plastic or glass cores. During ACF curing, when the heat and force are applied, the conductive particles are trapped between the mating bumps of IC and substrate to provide electrical conductivity, and the adhesive matrix is used to provide the necessary electrical insulation, to protect the metallic contacts from mechanical damage, and to provide stable O pe n A cc es s D at ab as e w w w .in te ch w eb .o rg

This study conducts an experimental investigation into the bending behavior and electrical resistance properties of Flex (PI with Cu)-On-Film (ITO–coated PET) packages considering the flexible effects under static bending loads with sequential bending cycles. The FOF packages, consisting of flex (with fine-pitch Cu circuits) and film (ITO–coated PET plastic) are bonded by Anisotropic Conductive Film (ACF). During the ACF bonding process, the deformed conductive particles in the adhesive matrix between the Cu electrodes and the ITO film under the effects of the compression force, and these broken conductive particles will play an electrical conductive role. In the subsequent bending tests (loading &unloading with many cycles), the conductive particles experience a compression or tension stress, which causes a further propagation of the cracks formed in the original packaging process. The results show the measured electrical resistance in the specified conductive channel increases with the bending cycles increasing, and the microscopic observations show that the higher electrical resistance is the result of a smaller overall contact area between the conductive ACF particles and the Cu electrode/ITO film due to fatigue crumbling of the particles.

An investigation is performed into the change in electrical resistance of flex-on-flex (FOF) assemblies under static bending loads. The FOF test vehicles are prepared via the face-to-face bonding of two identical flexible printed circuits by means of anisotropic conductive film (ACF). The FOF assemblies are then sandwiched between two thin flexible polycarbonate (PC) sheets in order to obtain the required bending radius in the range of 10–50 mm. In each bending test, the electrical resistance of 16 designated ACF conduction channels is measured, recorded and analyzed using a conventional digital ohmmeter. The electrical resistance of the FOF package under different bending radii is interpreted by reference to microscopic observations of the ACF conductive particle distribution within the Cu-electrode gaps and the effects of the bending moment on the deformation and crack damage of the particles, as observed through a microscope. The results show that the electrical resistance is determined mainly by the number of particles within the Cu-electrode gaps. However, the electrical resistance increases slightly with a reducing bending diameter due to the greater bending moment, which increases the propensity of the conductive particles toward cracking and therefore reduces the contact area between the metallic shell of the particles and the Cu-electrodes. In general, the present results show that the neutral axis of the bending load should be constrained to lie close to the center of the conductive particles, thereby minimizing the stress and strain acting on them and reducing the risk of critical fracture.

Anisotropic conductive film (ACF), is a lead-free material that is commonly used in fine-pitch interconnect manufacturing to make and maintain the electrical and mechanical connections between the micro-electrodes. A key issue about the circuit conductivity is the deformation, breakage, and number of conductive particles in the ACF packaging. For the field of vision, the Film-On-Glass (FOG) assembly on the glass-side is used to obtain excellent images in experimental observation. This paper utilizes the microscope technology to investigate the bonding properties of the conductive particles, and consider the electrical resistance effects after packaging. The results show the deformation shape, breakage type, and number of conductive particles will be quantitatively affect the electrical performances, and one can measure the area, diameter, and roundness of the deformed particles’ projection in the glass-side view to evaluate the ACF packaging quality.

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.

Anisotropic conductive film (ACF) is an essential component in the manufacture of liquid crystal displays (LCD), 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 enclose the imidazole curing agent to imbue the ACF with its latent behavior. A spray-drying method was used in the enclosing process, and this enclosed imidazole was mixed with epoxy resin to form the imidazole-epoxy resin system. A comparison with our previous our results showed that a smaller amount of polymeric material could be used in the enclosing process, and a superior latent behavior could be obtained.

Screen printed circuits on substrates such as thermoplastic polyurethane (TPU) have been usedfor many years in certain wearable applications such as heart rate monitors [...]

O_2 plasma treatment is a useful way to increase adhesion strength between polymer resins and adhered substrates in electronic packaging areas. However, a low adhesion strength of polymer adhesives on the adhered surfaces is a critical issue for anisotropic conductive film (ACF) joint reliability, especially when it comes to moisture-induced effects. This paper discusses the effects of oxygen plasma treatment (100W 20mTorr 3min) on the wettability and reliability of solder ACFs joints on Au/Ni metal electrodes. We carried out the surface analysis using surface energy, AFM, XPS, FTIR and joint resistances, peel adhesion strength, and reliability. By using the contact angle and surface energy, the un-wetted solder joining was explained from a spontaneous wettability to a hindered wettability, as a reason for poor electrical performance and reliability after oxygen treatment. Although the resin and electrode adhesion was increased, it was proven that the solder part played a more important role in determining joint reliability and mechanical property.

Integration technologies involving flexible substrates are receiving significant attention owing the appearance of new products regarding wearable and Internet of Things technologies. There has been a continuous demand from the industry for a reliable bonding method applicable to a low-temperature process and flexible substrates. Up to now, however, an anisotropic conductive film (ACF) has been predominantly used in applications involving flexible substrates; we therefore suggest low-temperature lead-free soldering and bonding processes as a possible alternative for flex-on-flex applications. Test vehicles were designed on polyimide flexible substrates (FPCBs) to measure the contact resistances. Solder bumping was carried out using a solder-on-pad process with Solder Bump Maker based on Sn58Bi for low-temperature applications. In addition, thermocompression bonding of FPCBs was successfully demonstrated within the temperature of 150 °C using a newly developed fluxing underfill material with fluxing and curing capabilities at low temperature. The same FPCBs were bonded using commercially available ACFs in order to compare the joint properties with those of a joint formed using solder and an underfill. Both of the interconnections formed with Sn58Bi and ACF were examined through a contact resistance measurement, an 85 °C and 85% reliability test, and an SEM cross-sectional analysis.

An anisotropic conductive film (ACF) can be utilized to simultaneously form mechanical bonds and electrical connections during flip-chip assembly. The electrical connection is created by trapping randomly dispersed metallized polymer spheres (MPS) in the ACF that are deformed during the bonding process. This work postulates that the reliability of interconnects formed with ACF depends on the degree to which the MPS are deformed. Silicon samples with fine-pitch electrical test structures were flip-chip assembled using an ACF and measured in-situ during environmental testing. Interconnects with MPS deformation below 60% proved more stable than interconnects with higher deformation during exposure to 85% relative humidity at 20 °C, 45 °C, 60 °C and 85 °C, as postulated. On the other hand, the stability of the interconnects did not show a dependence on MPS deformation during exposure to thermal shock cycling (TSC) (−55 °C / +125 °C, 7 s transit time, 700 cycles). The results suggest that deformation of MPS is a central factor with respect to reliability of ACF-bonded fine-pitch samples exposed to humid conditions, but the results also indicate that other failure mechanisms are more important for samples exposed to thermally unstable conditions.

Polymer matrix composites, reinforced with aligned carbon nanotubes (CNT), have a great potential in myriads of applications including flexible electronic and biomedical devices. However, effectively aligning the CNTs inside any matrix has always been a challenge. Present study deals with fabrication of an aligned carbon nanotube reinforced polymer matrix composite and effect of the methods of alignment on anisotropic properties of the composite. Multi-walled carbon nanotubes (MWCNT) reinforced Polyvinylidene fluoride (PVDF) composite with uniform dispersion and alignment of CNTs is fabricated by solution casting technique. CNTs are aligned with the application of alternating voltage as well as pulsed current. The voltage-assisted films have shown good dispersion and alignment of CNTs inside PVDF matrix. On the other hand, the current-assisted alignment led to the formation of shortest, continuous path for the flow of electrons and hence, resulted in formation of highly anisotropic conductive film. Directly current passage assisted alignment of CNTs in the composite film records an impressive 360% improvement in conductivity in the direction parallel to the alignment as compared to the structure with randomly aligned CNT. At the same time, the composite in transverse direction to the alignment was totally insulating, indicating the efficiency of alignment. With the addition of only 0.5 wt% CNTs to PVDF matrix, film shows improvement of elastic modulus and tensile strength by 180% and 150%, respectively, as compared to pure PVDF film. However, the films behaved mostly isotropic in terms of mechanical properties, showing improvement in all the directions with CNT reinforcement. This study provides effective way to align CNT in thermoplastic matrix to tailor the directional electrical conductivity significantly.

Ultrathin chip-in-flex (CIF) packages using anisotropic conductive film (ACF) as an interconnecting material were demonstrated as one of the flexible electronic packages for wearable electronics applications. In this paper, the effects of ACF resin material and conductive ball type on the CIF package bending properties were investigated. Various ACFs with different moduli were fabricated by adding silica particle to polymer resin. For the conductive ball type, solder ball, metal-coated polymer ball, and Ni ball were used. To quantify the bending properties of the CIF packages, dynamic bending test was performed. It was found that the lowest modulus resin (0.54 GPa) resulted early delamination between the conductive ball and the electrode interface. For the resin modulus of 1.04 GPa, the conductive balls and electrodes interface delamination was significantly suppressed due to lower deformation of ACFs. However, when the modulus was increased to 1.3 GPa, chip crack failure occurred presumably due to the internal stress increase at the chip area. Therefore, it is suggested that the optimal modulus of the ACF resin was around 1 GPa. In addition, among the various conductive ball types, metal-coated polymer balls showed no electrical and mechanical failure even after 160k dynamic bending cycles. The metal-coated polymer balls had better compliance compared with the solder ball and Ni ball, which eventually prevented chip crack and ACF contact loss to occur.

A study of the failure mechanism and the enhanced reliability performance of SnBi58 solder ACF joints were investigated by considering the total influence of polymer viscoelastic and hygroscopic properties on the cross-sectional morphologies and the electrical properties of Sn58Bi solder joints in a pressure cooker test (PCT) for 120 h. The Sn58Bi solder failure mechanism is demonstrated that, when polymer resin absorbed moisture, the $T_{g}$ values of polymer resins decreased, and the coefficient of thermal expansion (CTE) values of polymer resins increased, due to a hydroswelling effect. Considering the total influence of polymer viscoelastic and hygroscopic properties on the cross-sectional morphologies and the reliability of Sn58Bi solder joints in a PCT for 120 h, four typical polymer resins were evaluated. As a result, cationic epoxy (128 ppm/°C) with the smallest CTE mismatch (112 ppm/°C) with SnBi58 solder joints (16 ppm/°C) in a PCT aging test (121 °C, 100% humidity, and 2 atm) showed a stable electrical property in terms of joint contact resistance and remained a complete cross-sectional Sn58Bi solder joint morphology after PCT reliability for 120 h.

Generally, anisotropic conductive films (ACFs) used for bonding in communication devices and displays are manufactured by applying pressure to conductive particles at desired positions. The conventional production process has serious disadvantages that waste of conductive particles and the non-uniform number of particles captured, etc. In order to overcome these disadvantages, the film production using electrohydrodynamic (EHD) ink jet printing technique is proposed in this work. The EHD printing results are greatly affected by the ink properties and printing conditions. Therefore, polymer inks suitable for EHD ink jet printing are developed, and then the variation of the meniscus according to the intensity of the voltage was evaluated. As a main material of ACFs, conductive particles are added to the polymer inks to assess the feasibility of generating the ACFs using EHD technology. The results show that the electrical conductivity of the manufactured ink with conductive particles shows good performance.

Anisotropic conductive film (ACF) is used for finepitch bonding in liquid crystal display (LCD) packaging. The film is typically composed of 3-10 $\mu$m conductive particles incorporated into an epoxy based film matrix.Smaller particles (e.g., 3 $\mu$ m) are used to obtain a finerpitch, driven by a demand for higher resolution. Using smaller particlesleads to a reduction in the effective contact area resulting in an increasein the resistivity. Smaller particles also exhibit a reduced tolerance forvariations in the bond line thickness which may affects the repeatability of interconnects and reliability. In this paper, we investigate the relation ofparticle deformation to the resistance of both free particles(electromechanical test) and particles embedded in an adhesive film (ACF bonding). The presence of adhesive film has resulted in a much higherparticle contact resistance and affected interconnect repeatability. Theeffect of the adhesive film is strongly dependent on the bump surface topography, and a smooth surface tends to increase the contact resistance.

Micron sizes solder metallurgical joints have been applied in a thin film application of anisotropic conductive film and benefited three general advantages, such as lower joint resistance, higher power handling capability, and reliability, when compared with pressure based contact of metal conductor balls. Recently, flex-on-board interconnection has become more and more popular for mobile electronic applications. However, crack formation of the solder joint crack was occurred at low temperature curable acrylic polymer resins after bonding processes. In this study, the mechanism of SnBi58 solder joint crack at low temperature curable acrylic adhesive was investigated. In addition, SnBi58 solder joint cracks can be significantly removed by increasing the storage modulus of adhesives instead of coefficient of thermal expansion. The first approach of reducing the amount of polymer rebound can be achieved by using an ultrasonic bonding method to maintain a bonding pressure on the SnBi58 solder joints cooling to room temperature. The second approach is to increase storage modulus of adhesives by adding silica filler into acrylic polymer resins to prevent the solder joint from cracking. Finally, excellent acrylic based SnBi58 solder joints reliability were obtained after 1000 cycles thermal cycling test.

Thermosonic bonding (TSB) and thermocompression bonding (TCB) are common interconnections technique in flip chip (FC). Both techniques are used in chip to chip interconnection and both have been studied in this paper. Coining and anisotropic conductive film are used in TCB assembly process. Whereas, TSB process flow are solder free and simpler compared to TCB. It was found that TSB has lower 5.5 % electrical resistance compared to TCB. In term of physical analysis, TCB sample has an open joint after temperature cycling (TC) 500 whereas TSB still in a good joint. Therefore, TSB method is suitable for system in package.

Purpose – The purpose of this paper is to determine: how the thermal cycling aging affects the ratcheting behavior of anisotropic conductive adhesive film (ACF); how the loading conditions and loading history affect the ratcheting strain and strain rate of ACF with different thermal cycling aging histories. Design/methodology/approach – The ACF of CP6920F was cured at 190°C in an electro-thermal vacuum drying apparatus for 30 s. The cured specimens were put into the thermal cycling chamber (−40-150°C) for aging to 25, 50, 100, 200 and 500 cycles. A series of uniaxial ratcheting tests of aged ACF after different thermal cycles was carried out under stress control at 80°C. Findings – The ACF subjected to larger number of thermal aging cycles exhibits less ratcheting strain under the same loading conditions. The ACF with the same thermal cycling aging history shows more ratcheting strain and a higher ratcheting strain rate when loaded under a larger mean stress or stress amplitude or a lower loading rate. The ratcheting behavior of aged ACF is found to be more sensitive to the lower loading rate. The higher mean stress (or stress amplitude) enhances the deformation resistance and consequently restrains the ratcheting strain of subsequent cycling with a lower mean stress (or stress amplitude). The prior lower loading rate accelerates the plastic deformation more significantly than the higher one. Originality/value – The influencing trends of thermal cycling aging, loading condition and loading history on ratcheting behavior of ACF are obtained, which is important for the design and safety assessment of ACF joints.

In this paper, in order to improve the reliability of anisotropic conductive film (ACF) interconnections, solder ACF joints were investigated in terms of solder joint morphology. ACFs are film-type interconnection adhesive materials that consist of polymer adhesive resins and randomly dispersed conductive particles. Recently, in order to obtain high reliability of ACF joints, solder ACFs that use solder particles as conductive particles of ACFs have been introduced combined with an ultrasonic bonding method. However, further researches are needed in the area of crack initiation and the propagation of solder ACF joints at high temperature and high humidity conditions due to the stress generated by hygroscopic expansion of ACF resin. Therefore, in order to solve the crack initiation of solder ACF joints, solder ACF joint morphology should be controlled and optimized to minimize the solder crack-related reliability problems. In this paper, solder ACF joint reliability was investigated depending on the solder morphologies of ACF joints bonded with various bonding pressures and temperatures. According to the results, as bonding pressure increased from 2 to 6 MPa, aspect ratio (joint diameter/joint gap) increased due to the increased joint area and decreased joint gap. In the pressure cooker test (PCT) reliability tests, as solder aspect ratio increased, electrical resistances were more stable after 60 h of the tests due to higher joint strength. In the target bonding temperature profile of 250 °C, solder joints showed a concave shape. However, joints bonded at in the target bonding temperature profile of 200 °C showed a convex shape. It is mainly due to the lower degree of cure of resin when ACF temperature reached to solder Melting Point (MP) in the target bonding temperature profile of 250 °C compared with that in the target bonding temperature profile of 200°, because ACF temperature reached to solder MP in shorter time in the target bonding temperature profile of 250 °C. Concave-shaped solder joints showed higher PCT reliability than the convex-shaped solder joints due to the lower stress concentration. These results indicate that solder ACF joint morphology was a significantly important factor for highly reliable solder ACF joints in high temperature and high humidity reliability conditions.

Anisotropic conductive film (ACF) has been used for more than 30 years in flat panel display (FPD) module package. In this paper, the technical trends and development of ACF are described. Among all of them, ACF material design for flexible substrate bonding is critical for the development of flexible display. According to different process flow of flexible AMOLED, flexible substrate bonding technologies can be classified as “PI/Glass” and “Film type” substrate bonding. That is to say the flexible substrate bonding process can be implemented before and after PI substrate separation from the original carrier glass substrate. Based on the current results, soft conductive particles of ACF are developed and chosen in the PI/Glass substrate bonding. For the film type substrate bonding, especially in IC bonding, the design of ACF is very important in avoiding the insufficient conductive particle deformation issue induced by the sink of plastic substrate. Here, we present a feasible and simple flexible substrate bonding technology to package driver IC, FPC or COF for flexible AMOLED application.

In this paper, inclined conductive bumps (ICBs) are proposed as a substitute for the anisotropic conductive film (ACF). The new interconnection method ICBs can provide controlled bump deformation, uniform electrical conductivity, and fine pitch interconnection without short circuit. The ACF is widely used in the chip-substrate bonding process in today's display and semiconductor industries. This is due to the fact that the ACF has various advantages, such as low bonding temperature, low cost, and small packaging sizes, when compared with those of wire bonding. However, as the bump pitch decreases, the short-circuit problem can occur by lumped conductive particles of the ACF between adjacent bumps. In addition, the electrical conductivity of package varies due to the number of the trapped ACF particles between bonded bumps. Various alternatives, such as coating a thin insulating layer at the outside of the particle and utilizing an array of metal pillars instead of the random distributed particles have been attempted to overcome these shortcomings of the conventional ACF. As another alternative, the ICBs, which are the inclined and hollow copper bumps directly fabricated on electrodes, are suggested. In addition, in this paper is the finite element analysis, which has been conducted to predict the elastic-plastic deformations of the ICBs and their reliability issues. Then, the fabrication processes of the ICB is explained. In such process, the ICBs are fabricated on a test wafer with the inclined angles of 70° and 80°. The ICBs are selectively formed on a target pad at a pitch of 30 μm. A singulated chip with ICBs is assembled on an organic substrate using thermo-compressive bonding. After bonding, the ICBs show reasonable contact resistances of 12-27 mΩ.

Polyaniline (PANI) was investigated for use in bonding packages of flexible printed circuit boards (FPCB). The contact resistance of the anisotropic conductive film used in the current study was significantly lower than that of the PANI powder, with an average contact resistance of 0.47 Ω, as compared to 7.1 Ω for the PANI powder. Nevertheless, the suitability of PANI for conductive ball bonding was investigated via bonding of a FPCB, and the possibility for the use of PANI as the core polymer in conductive balls was determined by simulating the ohmic loss and signal distortion.

In this paper, the electrical and reliability properties of various solder anisotropic conductive film (ACF) joints for flex-on-board (FOB) assembly using ultrasonic bonding were assessed in terms of short circuits, contact resistance, current handling capability, wetted solder areas, and reliability evaluation. It was found that the wetted solder areas increased and reliability was enhanced as the size and content of the solder ball increased. Regardless of solder ball size and content, the contact resistances of solder ACF joints were almost the same, because the current went through the electrode/electrode contact, which is like a short circuit to the solder joint. In addition, the exact value of current handling capability of all the ACF joints could not be evaluated, because metal lines of printed circuit board were burnt before ACF joint failure. After 120 h of pressure cooker test (PCT), the open-circuit failures were mainly observed at Ni ACFs, and 5–15- $\mu $ m solder ball size from 10 to 30 wt% solder content and 25–32- $\mu $ m size and 10 wt% solder content of solder ACFs, presumably due to lower wetted solder areas on metal electrodes. In addition, the crack was noted after 120 h of PCT in the solder ACF joints who has lower wetted solder areas. As a result of this paper, the solder ball size and content of solder ACFs joints were optimized at 25–32- $\mu $ m sizes and above 30 wt% content for 300- $\mu $ m pitch FOB assembly.

FOG(Flexible Printed Circuit On Glass) ACF(Anisotropic Conductive Film) bonding achieves electric conductivity interconnection by ACF material. The conductive microspheres from ACF material are trapped between ITO(Indium Tin Oxides) bumps and substrate pads, which are the fundamental cause of achieving electric conductivity interconnection. Prior work has studied the mechanism of achieving electric conductivity interconnection and the interconnection resistance calculation model, presenting the quantity and distribution of trapped conductive microspheres determine the contact resistance of FOG ACF bonding. But those studies haven't presented the mechanism of trapped conductive microspheres in LCD FOG ACF bonding. In this paper, the problem has been researched by Ripley's K function, K-S(Kolmogorov-Smirnov) test and PPP(Poisson Point Process) theory. It has been proved that the distribution of trapped microspheres in each bump belongs to the random distribution and the distribution of trapped microspheres' quantity can be calculated with PPP module in LCD FOG bonding. Finally, we have analyzed the probability of trapped certain number of conductive microspheres in different conductive microsphere density in ACF material and bumps' size, which is useful to optimize ACF bonding and improve the packaging reliability in LCD module industry.

We report the feasibility of forming Ni bumps directly on Cu pads in CMOS image sensor (CIS) logic elements formed by Cu wires with diameters of less than 65 nm. The direct Ni bump process proposed in this study simplifies the fabrication process and reduces costs by eliminating the need for Al pad process. In addition, this process can secure the margin of the final layer, enabling the realization of thin camera modules. In this study, we evaluated the effect of pad annealing on the direct formation of Ni bumps over Cu pads. The results suggest that the morphology of the Cu pad varies depending on the annealing sequence, and post-passivation annealing resulted in fewer defects than pad etch annealing. The shear stress of the Ni bumps was 57.77 mgf/m2, which is six times greater than the corresponding reference value. Furthermore, we evaluated the reliability of a chip with an anisotropic conductive film (ACF) and a non-conducting paste (NCP) by using high-temperature storage (HTS), thermal cycling (TC), and wet high-temperature storage (WHTS) reliability tests. The evaluation results suggest the absence of abnormalities in all samples. Open image in new window

In this paper, a method to reduce the contact resistance of lateral thermosonic bonding with an anisotropic conductive film (ACF) is proposed. Despite the various advantages of the ACF-based bonding process, it suffers from higher contact resistance between a chip and a substrate, which increases the power consumption and decreases the reliability. The contact resistance largely relies on the conductive particle density. However, in the thermosonic process, a large portion of conductive particles flow out along with the adhesives at the reflow state. To tackle this issue, an intaglio-shaped bump is newly proposed. Thanks to the proposed bump, more conductive particles remain inside the intaglio shape after the reflow state, which results in increment of the conductive particles' density. Through the experiments with a commercialized ACF, it will be shown that the proposed intaglio-shaped bump does increase the conductive particle density of the lateral thermosonic bonding process.

In this paper, the assessment of the electrical and mechanical performance of the Cu nanowire anisotropic conductive film (NW-ACF) flip-chip interconnects has been performed. The influence of bonding conditions (bonding temperature and bonding force) has been studied in order to understand their impact on bonding resistance and shear strength for two types of NW-ACF based on different templates with varying porosity and thickness. An overgrowth-stripping method has been employed to obtain uniform NW (200 and 220 nm) arrays in the track-etch polymer membranes. The bonding substrate was coated with indium so that a diffusion soldering between Cu NWs and bulk In film can occur at a relatively low eutectic point (156.6°C). The bonding interface and the fractural surface of NW-ACFs have been characterized by scanning electron microscope and energy dispersive X-ray analysis. Under optimized fabrication conditions, process at the bonding profile of 200°C, 20 N shows that the z-axis resistance can be below 1 mΩ and the shear strength can be above 10 MPa, which is very promising for the fine pitch, 3-D interconnection applications in the future.

Radiation curable acrylated epoxy oligomer was found to be an effective resin system for application to electron beams (EB) on curing of anisotropic conducting film. To study curing degree as a function of EB dosage, we irradiated bisphenol-A type acrylate epoxy oligomer samples with doses of 5 to 600 kGy of EB. To investigate the effect of a metal barrier for potential industrial application, a 3 mm thick Al plate was placed in front of the samples, and the curing parameters were compared with the ones irradiated without an Al plate. As the dosage of the EB irradiation was increased, the glass transition temperature of the sample ranged from 46.8 to 62.2 °C for the epoxy composites without placing an Al plate, and from 46.4 to 64.1 °C for their counterparts with a 3 mm thick Al plate. These results confirm that enhancement of the curing degree with increasing EB irradiation is possible even in the presence of a metal plate. The scanning electron microscope images of the fracture surfaces are presented as evidence of the morphological changes of the EB cured epoxy samples.

An anisotropic conductive film (ACF) is a thin adhesive epoxy layer that is widely used to connect circuits in highly-integrated electronic devices. To bind two electric circuits, an ACF is pasted between the circuits and pressed with an optimum pressure so that the joints can be electronically connected. For the curing of the resin, electron-beam (E-beam) irradiation is known to be an environmentally friendly technique and exhibits many technical advantages over conventional thermal curing in terms of low temperature and reduced curing time. In this method, the applied pressure and electron-beam dose are critical parameters to maximize the conductivity without a failing of the connection between the circuits. For the minimization of the contact resistance after curing by using E-beam irradiation, curable epoxy resin was mixed with conductive particles made of Ni/Au-plated polymer spheres with a mean particle size of 10 µm in a ratio of 5: 1 by weight. The mixed resin was pasted on rigid boards having circuits of 100-µm pitch and was irradiated by using an E-beam. The optimum dose for E-beam irradiation for a reasonable curing, the contact resistance values, and the reliability of the cured film were systematically investigated as functions of E-beam dose, applied pressure and temperature. The lowest contact resistance values were obtained when the specimens were irradiated by an 80-kGy E-beam under a constant pressure of 5 kgf/cm2. At this condition, the minimum contact resistance was 80 ± 0.015 mΩ, which is significantly lower than the values obtained from commercial products, and the values were maintained within a 5% increase when the samples were kept at 100 °C for 294 hours. Our results demonstrate that an E-beam irradiation technique can be applied for curing ACFs for commercial electronic devices.

To investigate the effect of the sintering temperature on the electrical properties of a chip on glass (COG) module, a screen-printed conductive circuit was sintered at various temperatures, viz. 150, 200, 250 and 300^oC for 30min. An anisotropic conductive film (ACF) is a suitable bonding material for the interconnection between a device and printed circuit, because of the conductive particles within it. We expected that the conductive particles in the ACF would provide a good electrical connection and reliability in our study. The electrical properties of the printed Ag circuits improved with increasing sintering temperature. The conductive particles in the ACF were well deformed in between the Au bumps and printed Ag pads after the bonding process. The resistances of the interconnections drastically decreased with increasing sintering temperature. Also, the temperature-humidity reliability of the ACF was investigated by measuring the resistance after the temperature-humidity test (THT) at 85^oC and 85% relative humidity. After the THT, the resistance shows a tendency to decrease when sintered below 200^oC, whereas it increases when sintered over 250^oC. The increase in the resistance due to the effect of surface oxidation is negligible.

Recently, the flip-chip bonding technology using adhesives has been widely used in the packaging industry because of environmental friendliness (elimination of lead material and flux cleaning), low temperature process (no soldering process), fewer processing steps (no underfill process), and the fine pitch capability. In flip-chip assembly using adhesives, the electrical interconnection is established by mechanical contact between the bumps on the chip and the corresponding pads on the substrate after the adhesive is cured. The adhesive can be categorized into two types with respect to the presence of the conductive particles: anisotropic conductive film (ACF) and nonconductive adhesive (NCA). ACF is the adhesive polymer film with dispersed conductive particles, and NCA is just adhesive which contains no conductive particles. In this review, the bonding technologies with ACF and NCA are introduced, and the principle and characteristics of each bonding method are discussed.

In this paper, we investigate the mechanical and electrical properties of an anisotropic conductive film (ACF) on the basis of high-density vertical fibers for a wafer-level packaging (WLP) application. As part of the WaferBoard, a reconfigurable circuit platform for rapid system prototyping, ACF is used as an intermediate film providing compliant and vertical electrical connection between chip contacts and a top surface of an active wafer-size large-area IC. The chosen ACF is first tested by an indentation technique. The results show that the elastic-plastic deformation mode as well as the Young's modulus and the hardness depend on the indentation depth. Second, the efficiency of the electrical contact is tested using a uniaxial compression on a stack comprising a dummy ball grid array (BGA) board, an ACF, and a thin Al film. For three bump diameters, as the compression increases, the resistance values decrease before reaching low and stable values. Despite the BGA solder bumps exhibit plastic deformation after compression, no damage is found on the ACF film. These results show that vertical fiber ACFs can be used for nonpermanent bonding in a WLP application.

The failure probability of anisotropic conductive film (ACF) packages is critically dependent on the volume fraction of conductive particles within the adhesive resin. In this study, the V-shaped curve method is used to determine the optimal volume fraction of conductive particles as a function of the bonding geometric parameters, the pad array dimension, and the misalignment offset between the upper and lower pads. In evaluating the corresponding failure probability of the ACF package, the probability of an opening failure is determined in accordance with a Poisson function model, while the probability of a bridging failure is derived using a box model. In computing the opening and bridging probabilities, the two models are modified to take account of the effects of package misalignments on the effective conductive area between opposing pads and the bridging path length between neighboring pairs of opposing pads, respectively. The opening and bridging probabilities are then combined using probability theory to establish the overall failure probability of the ACF package. In general, the results show that, for given bonding geometric parameters and misalignment offset, the optimal volume fraction of conductive particles remains approximately constant as the pad array dimension is increased. However, for given bonding geometric parameters and pad array dimension, the optimal volume fraction of conductive particles increases with an increasing misalignment error. Overall, the results show that, for any given values of the bonding geometric parameters, pad array dimension, and misalignment offset, the failure probability of the ACF package can be minimized by setting the volume fraction of conductive particles equal to the value corresponding to the tip of the V-shaped curve.

Anisotropic conductive film (ACF), is a lead-free and fine-pitch interconnect materials that is commonly used in liquid crystal display (LCD) manufacturing to make and maintain the electrical and mechanical connections from the driver IC to the substrate. A key issue in the ACF technology is the packaging yield or failure probability, and performance of ACF’s material formula composition. This paper utilizes the V-shaped curve method to analyze the failure probability of composite ACF packages with a smart composition or a functional formula. In the proposed model, the probability of opening failures is modeled using a Poisson function, modified to take into account the average conception on the effective conductive area between opposing pads. Meanwhile, the probability estimation of bridging failures is based on the Box-Strip-Brick model between the neighboring pad pairs in the array. The results show the derived probability formulation can involve the probability conceptions of the composite ACF into a complete evaluation computation.

In this paper, a thermosonic flip-chip bonding process using lateral ultrasonic vibration is proposed. To enhance the reliability of the specimen after the lateral thermosonic process, a sliding mechanism is adopted with investigation of equivalent stiffness of the anisotropic conductive film (ACF) joint. By a tensile test, it is shown that the equivalent stiffness of the ACF joint gradually increases as curing proceeds. Based on these results, the sliding point where the vibration amplitude of the chip specimen begins to decrease can be adjusted by the applied pressure. Thanks to the sliding mechanism, forced excitation to the sufficiently cured chip specimen can be naturally avoided. In addition, the robustness of the degree of cure against the bonding time variation can be improved in spite of the short bonding time. To demonstrate the feasibility of the proposed sliding mechanism in practice, experiments are conducted with a commercialized driver chip assembly of a liquid crystal display with an ACF.

An innovative bonding approach applied to flexible substrate bonding is proposed in this research. Thin-film metal pad is fabricated as bonding medium to provide vertical stacking. As compared to other bonding methods, such as anisotropic conductive film (ACF) or non-conductive paste (NCP), thin-film metal pad bonding approach provides the most attractive advantage of fine-pitch. The bonding condition at low temperature exhibits good electrical performance, proving its great potential in the applications of flexible substrate stacking.

A new concept of anisotropic conductive film (ACF) called nanofiber/solder ACF combined with an ultrasonic bonding method can overcome limitations of fine pitch flex-on-flex (FOF) assembly using conventional ACF, such as short circuit issues, low current-handling capability, and poor reliability. To fabricate the nanofiber/solder ACF, SAC305 (96.5% Sn, 0.5% Cu, and 3% Ag) conductive solder balls are added to polyacrylonitrile polymer solution and ejected as nanofibers containing SAC305 conductive solder balls by an electrospinning method. This new concept of nanofiber/solder ACF successfully prevents short circuits between neighboring conducting electrodes by limiting the free movement of conducting balls and insulating individual conductive solder balls with coated nanofiber layers. Moreover, SAC305 conductive solder balls in nanofiber/solder ACF are completely melted and made metallurgical alloy contact between FOF electrodes during the ultrasonic bonding, resulting in 41% more electrical power being carried, and showing significant improvement in reliability performance compared with conventional nickel ball ACF.

The voids at the interface of anisotropic conductive film (ACF) to glass are typically formed during bonding process for Chip-On-Glass (COG) packages. The low temperature (∼23 °C) Ar H 2 plasma pretreatment on glasses are investigated to enhance the void-free bonding of ACF to glass for COG packages. The void fraction of glass with ACF is significantly reduced from 52% of untreated-glass to 0% of Ar H 2 plasma-pretreated glass. The improved void-free ACF bonding is found to be highly dependent on the surface characteristics of glass. The surface energies, surface morphologies and surface compositions of glasses are discussed how to affect the enhanced void-free bonding of ACF to glass by low temperature Ar H 2 plasmas. The surface energies, such as total surface energies, polar surface energies and dispersive surface energies of glasses are obtained by calculating the basis of the measured contact angles of three various surface tensions of liquids. The surface morphologies of glasses are observed by field emitted scanning electron microscopy (FESEM). The surface compositions, such as atomic compositions and chemical bond compositions of glasses are analyzed using X-ray photoelectron spectroscopy (XPS).

We have utilized a transmission ratio (TR) between curtain-shaped (Curtain) Mura and non-Mura zones as a key parameter to characterize the optical appearance of Curtain Mura occurred on a 13.3-in TFT–TN panel (Mura sample) after bonding process to place silicon-based driver-IC chips on one of the panel substrates using anisotropic conductive film as a binder (COG ACF process). Our measured TRs of the Mura sample at zero applied voltage were in good agreement with calculated TRs using optical parameters of the Mura sample derived from the measured Stokes parameters of the liquid crystal (LC) medium in that sample. We conclude that the occurrence of Curtain Mura is dominant by the stress-induced change in the twist angle, less sensitive and insensitive to the corresponding induced changes in the cell gap and pretilt angle of the in-panel-LC medium, respectively. By simulation, we also point out a way to reduce the occurrence of Curtain Mura by designing the cell gap for a 90°-twsit TN panel to satisfy the condition of Gooch–Terry first minimum.

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.

In this work, thermal cycling (T/C) reliability of anisotropic conductive film (ACF) flip chip assemblies having various chip and substrate thicknesses for thin chip-on-board (COB) packages were investigated. In order to analyze T/C reliability, shear strains of six flip chip assemblies were calculated using Suhir’s model. In addition, correlation of shear strain with die warpage was attempted. The thicknesses of the chips used were 180 μm and 480 μm. The thicknesses of the substrates were 120, 550, and 980 μm. Thus, six combinations of flip chip assemblies were prepared for the T/C reliability test. During the T/C reliability test, the 180 μm thick chip assemblies showed more stable contact resistance changes than the 480 μm thick chip assemblies did for all three substrates. The 550 μm thick substrate assemblies, which had the lowest CTE among three substrates, showed the best T/C reliability performance for a given chip thickness. In order to investigate what the T/C reliability performance results from, die warpages of six assemblies were measured using Twyman–Green interferometry. In addition, shear strains of the flip chip assemblies were calculated using measured material properties of ACF and substrates through Suhir’s 2-D model. T/C reliability of the flip chip assemblies was independent of die warpages; it was, however, in proportion to calculated shear strain. The result was closely related with material properties of the substrates. The T/C reliability of the ACF flip chip assemblies was concluded to be dominatingly dependent on the induced shear strains of ACF layers.

We developed a new ultra-fine pitch chip-on-glass (COG) bonding technique using insulated metal bumps and anisotropic conductive film (ACF). An insulating layer was formed by spin coating a photosensitive insulating polymer and subsequently exposing it without any mask. The shape of the insulating layer coverage on the side walls of the metal bumps can be controlled by changing the exposure time and the viscosity of the photosensitive insulating polymer. In our experiment, we successfully fabricated COG joints with a 25 μm pitch using Au bumps with an insulating layer on their side walls and a conventional single-layer ACF. When the bumps were covered with the photosensitive insulating polymer, a few conductive particles were trapped between neighboring bumps and many conductive particles were embedded between bumps and pads. The electrical resistance between neighboring bumps was measured by the two-point probe method. The resistances were measured only in uncoated specimens. The measured resistance indicates that electrical shorting between neighboring bumps occurred in uncoated specimens. Therefore, electrical shorting was successfully prevented by the insulating layer on the side walls of the bumps.

The effects of conductive particles on the electrical stability and reliability of anisotropic conductive film (ACF) joints for chip-on-board applications were investigated. In this paper, two types of conductive particles were prepared. One was a conventional Ni/Au-coated polymer ball, and the other was a Ni/Au-coated polymer ball with Ni/Au-projections. According to the results of a nano-indentation experiment of a conductive particle, the elastic recovery of a single conductive particle decreased as the applied load and the deformation of the conductive particle increased. The evaluated conductive particles which had the same polymer core showed the similar load-deformation behaviors regardless of the existence of Ni/Au-projections. The contact resistances of ACF joints using each conductive particle as a function of bonding pressure were measured, and the results showed that the contact resistances of ACF joints with the metal-projection-type conductive particles were lower and more stable than those with the conventional conductive particles. Especially at lower bonding pressure, ACF joints with the metal-projection-type conductive particles were much more stable and had lower contact resistances than the conventional ACF joints. According to the results of thermal cycling (T/C) reliability test, the metal-projection-type conductive particles also enhanced T/C reliability of ACF joints when compared with the conventional conductive particles.

This paper describes how anisotropic conductive film (ACF) properties including viscosity affect the electrical stability of ACF interconnections for fine pitch chip-on-glass (COG) applications. In this study, new ACFs for COG applications were designed by combining a high viscosity ACF layer and a low viscosity NCF layer to prevent the electrical shortage between bumps. As expected, the viscosity-controlled ACF showed better electrical insulation stability than a conventional ACF in fine pitch COG assemblies. According to the results of thermo-mechanical analysis (TMA) and dynamic-mechanical analysis (DMA), the viscosity-controlled ACF showed the improved thermo-mechanical properties such as lower coefficient of thermal expansion (CTE), higher storage modulus (E 0 ) at higher temperature region, and higher glass transition temperature (Tg) than the conventional ACF. Furthermore, hot air reliability test and pressure cooker test (PCT) results showed that the viscosity-controlled ACF with higher Tg had better hot air test and PCT reliabilities than the conventional ACF.

This paper develops a computational model for predicting the failure probability of multilayered packages fabricated using anisotropic conductive film (ACF). The ACF and NCA are stacked layers by layers, and spaced with each other. The analyzed pads array 10x10 combined with specified geometry parameters in the IC/ Substrate are used to analyze the failure probability. The computational results indicate that the multilayered analysis developed in this study can provide lower failure probability by means of reducing bridging effects for improving the ACF packaging yield.

Polymer-based anisotropic conductive film has become widely used in many electronic packaging interconnect applications. The ultrasonic flip chip bond technology for anisotropic conductive film (ACF) joints in Chip-on-Glass (COG) assemblies has been investigated in part 1 of this paper [1]. In Part 2, the ultrasonic flip chip bond process for polymer-based anisotropic conductive film joints in chip-on-FR4 organic rigid board assemblies is discussed. The effects of ultrasonic bond process parameters, including the bonding time, bonding force, substrate temperature and ultrasonic power on the degree of cure and bond strength of ACF joints between chip and FR4 organic rigid board are investigated in detail. The optimized ultrasonic bonding process conditions for the Chip-on-FR4 organic rigid board assemblies are obtained as: (1) the bonding time can be from 2500 ms to 3000 ms; (2) the bonding force should be over 10 N; (3) the substrate temperature should be higher than 70 °C; (4) the optimum ultrasonic power is about 2.80 W.

Monodispersed polyaniline-coated (PANi) microspheres with a mean diameter of 5.174 μm and a 3.53% coefficient of variation were successfully prepared through an in-situ chemical oxidation polymerization of aniline on the surface of high-crosslinked polystyrene-divinylbenzene (PSDVB) particles with the mass ratio of 1: 0.12 between PSDVB particles and aniline. The microspheres were characterized by the scanning electron microscopy (SEM), FTIR and elemental analysis. A very thin layer of polyaniline, about 10.5% in weight, was found to evenly cover on the PSDVB, The microspheres were demonstrated to be thermal stable below 450 °C by thermogravimetric analysis (TGA) measurements and have a bulk conductivity of 6.67 × 10-3 S.cm-1 by AC impedance method. The good thermal stability suggested that PANi/PSDVB microspheres could be a promising material to replace the conventional metallic anisotropic conductive film (ACF) particles if the conductivity could be further improved in the future.

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.