Anisotropic conductive adhesive film with controlled fluidity of conductive particles

Abstract

The anisotropic conductive adhesive film according to the present invention fixes the conductive particles with a strong force through the high modulus of the polymer, minimizing the movement of the conductive particles during the compression process. In particular, the non-flowable conductive layer containing the conductive particles is formed through a semi-curing process to fix the conductive particles with the modulus force of the polymer resin, thereby minimizing the movement of the conductive particles when resin flow occurs due to pressure during the compression process. In addition, adhesive layers are formed on the upper and lower parts of the semi-cured polymer film layer to improve physical properties that are reduced by the semi-cured film, such as adhesive strength, reliability, and connection resistance, thereby optimizing the physical properties of the anisotropic conductive adhesive film.

Description

[Technical Field]

[0001] The present invention relates to a circuit connection technology using an anisotropic conductive adhesive, and more specifically to an anisotropic conductive adhesive for circuit connection that, when interconnecting two opposing circuit components, can electrically connect two opposing electrodes in the thickness direction while maintaining insulation between adjacent electrodes in the surface direction. [Background technology]

[0002] As electronic devices become smaller and thinner, circuit components are becoming denser and more precise. This has made it difficult to connect fine circuits using conventional methods such as welding or soldering. To address this issue, anisotropic conductive adhesives were developed (Japanese Patent Publication No. 51-21192). Anisotropic conductive adhesives are circuit-connecting components that incorporate conductive particles into adhesive components containing a curable resin, and by adjusting the content of conductive particles, they can electrically connect two opposing electrodes in the thickness direction while simultaneously maintaining insulation between adjacent electrodes in the planar direction. Such anisotropic conductive adhesives are widely used to electrically connect and bond various circuit components during the manufacture of display elements, semiconductor elements, and other devices.

[0003] In recent years, as the integration density of electronic circuits has increased, the pitch between electrodes has become increasingly finer, and as a result, the size (area) of circuit electrodes has also gradually become smaller. Furthermore, the development and commercialization of various wearable devices that can be attached to the body has accelerated. Therefore, there is a pressing need for an anisotropic conductive adhesive that can maintain the reliability of electrical connections between circuit components even when applied to electronic circuits with fine pitches between electrodes and / or flexible circuit boards.

[0004] In particular, with the trend toward higher resolution and smaller size of display devices, anisotropic conductive adhesive films used in COG (Chip on Glass) and COP (Chip on Plastic) connection structures have a high density of conductive particles, so preventing the interconnection of conductive particles is extremely important for signal stability. Also, in anisotropic conductive adhesive films with a high density of conductive particles, if the conductive particles aggregate due to the flowability of the resin during compression, this can be detrimental to the performance of the anisotropic conductive adhesive film. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention relates to an anisotropic conductive adhesive film, and more particularly to an anisotropic conductive adhesive film for ultra-fine pitch applications. The present invention aims to provide an anisotropic conductive adhesive film that fixes a polymer film layer containing conductive particles with a high resin modulus through semi-curing, and fixes the conductive particles with a strong fixing force when resin flow occurs due to pressure, thereby minimizing the movement of the conductive particles during the compression process.

[0006] The objects of the present invention are not limited to the objects mentioned above, and other objects not mentioned will be clearly understood from the following description. [Means for solving the problem]

[0007] The anisotropic conductive adhesive film according to the present invention comprises a non-flowable conductive layer obtained by semi-curing a thermosetting resin composition having conductive particles dispersed therein, the curing rate being 40% or more and 60% or less according to the following formula 1 measured using differential scanning calorimetry, and an adhesive non-conductive layer formed from the thermosetting resin composition and not containing conductive particles, and characterized in that the conductive layer and the non-conductive layer are laminated together.

[0008] [Formula 1] Cure rate (%) = [1 - (initial heat value) / (heat value after semi-curing)] x 100

[0009] Here, the modulus of the conductive layer is characterized by being 10,000 to 50,000 Pa·s.

[0010] The modulus of the conductive layer is at least twice as high as the modulus of the non-conductive layer.

[0011] The modulus of the non-conductive layer is characterized by being in the range of 1,000 to 5,000 Pa·s.

[0012] The non-conductive layer may include a first non-conductive layer and a second non-conductive layer, and the conductive layer may be interposed between the first and second non-conductive layers.

[0013] The thermosetting resin composition of the conductive layer and the non-conductive layer is characterized by containing an epoxy resin.

[0014] The thickness of the conductive layer is also characterized in that it does not exceed 2 μm relative to the average particle size of the conductive particles. [Effects of the Invention]

[0015] According to the present invention, when connecting circuit components using an anisotropic conductive adhesive film, the movement of conductive particles that occurs during the compression bonding process is minimized, the number of captured conductive particles between electrodes is increased, and the aggregation of leached conductive particles is minimized, thereby improving the connection reliability of electrical elements. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is an image showing a cross section of an anisotropic conductive adhesive film according to the present invention. [Figure 2] 1 is a differential scanning calorimetry analysis result for the conductive layer of the anisotropic conductive adhesive film according to the present invention, showing a heat capacity graph before and after the semi-curing process. [Figure 3] 1 is a graph showing the correlation between the capture rate and connection resistance of an anisotropic conductive adhesive film depending on the curing rate of the conductive layer. [Figure 4]Graph (1) shows the temperature-dependent viscosity change for a conductive layer and a non-conductive layer. [Figure 5] Graph (2) shows the temperature-dependent viscosity change for conductive and non-conductive layers. [Figure 6] Graph (3) showing the temperature-dependent viscosity change for conductive and non-conductive layers. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Best Mode for Carrying Out the Invention> The anisotropic conductive adhesive film according to the present invention comprises a non-flowable conductive layer obtained by semi-curing a thermosetting resin composition having conductive particles dispersed therein so that the cure rate according to the following formula 1 measured using differential scanning calorimetry is 40% or more and 60% or less, and an adhesive non-conductive layer formed from the thermosetting resin composition and not containing conductive particles, and characterized in that the conductive layer and the non-conductive layer are laminated together.

[0018] [Formula 1] Cure rate (%) = [1 - (initial heat value) / (heat value after semi-curing)] x 100

[0019] Here, the modulus of the conductive layer is characterized by being 10,000 to 50,000 Pa·s.

[0020] The modulus of the conductive layer is at least twice as high as the modulus of the non-conductive layer.

[0021] The modulus of the non-conductive layer is characterized by being in the range of 1,000 to 5,000 Pa·s.

[0022] The non-conductive layer may include a first non-conductive layer and a second non-conductive layer, and the conductive layer may be interposed between the first and second non-conductive layers.

[0023] The thermosetting resin composition of the conductive layer and the non-conductive layer is characterized by containing an epoxy resin.

[0024] The thickness of the conductive layer is also characterized in that it does not exceed 2 μm relative to the average particle size of the conductive particles.

[0025] <Mode for carrying out the invention> The present invention can be modified in various ways and can have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail through the detailed description. However, this is not intended to limit the present invention to the specific embodiments, and it should be understood that the present invention includes all modifications, equivalents, and alternatives that fall within the spirit and technical scope of the present invention. Furthermore, when describing the present invention, if it is determined that detailed descriptions of related publicly known technologies may obscure the gist of the present invention, such detailed descriptions will be omitted.

[0026] The present invention minimizes the movement of conductive particles during the compression process by strongly fixing the conductive particles through the high modulus of the polymer. In particular, the non-flowable conductive layer containing the conductive particles is formed through a semi-curing process to fix the conductive particles using the modulus of the polymer resin, thereby minimizing the movement of the conductive particles when resin flow occurs due to pressure during the compression process. In addition, adhesive layers are formed on the top and bottom of the semi-cured polymer film layer to improve properties that are reduced by the semi-cured film, such as adhesive strength, reliability, and connection resistance, thereby optimizing the physical properties of the anisotropic conductive adhesive film.

[0027] The anisotropic conductive adhesive film according to the present invention can be manufactured by laminating a conductive layer containing dispersed conductive particles and an adhesive non-conductive layer containing no conductive particles, wherein the conductive layer and the non-conductive layer are formed from a thermosetting resin composition, and the conductive layer contains conductive particles and the non-conductive layer does not contain conductive particles.

[0028] The thermosetting resin compositions used in the conductive layer and the non-conductive layer may each contain a curable resin and a curing agent.

[0029] The curable resin may be, but is not limited to, an epoxy resin, an acrylic resin, etc. For example, an epoxy resin such as a bisphenol A type epoxy resin, a bisphenol F type epoxy resin, a novolac type epoxy resin, or a modified epoxy resin may be used, and the acrylic resin may be, for example, an acrylic resin such as methyl acrylate, ethyl acrylate, isopropyl acrylate, isobutyl acrylate, epoxy acrylate, or ethylene glycol diacrylate.

[0030] The curing agent may be selected appropriately depending on the type of cured resin, for example, a radical curing agent such as an organic peroxide, or a latent curing agent such as a sulfonium salt or an onium salt.

[0031] The thermosetting resin composition may further contain a phenoxy resin or the like as a film-forming resin, and may further contain a coupling agent, if necessary, to improve adhesion to circuit components. The coupling agent is not particularly limited, and for example, an epoxy-based silane coupling agent, an acrylic-based silane coupling agent, or the like can be used to improve the connectivity and insulating properties of the anisotropic conductive adhesive film.

[0032] The conductive particles contained in the conductive layer are used to electrically connect opposing electrodes in a bonded structure in which circuit members are bonded, and although the conductive particles are not particularly limited, they are preferably 1 μm to 10 μm in size in order to connect circuit members having an extremely fine pitch. The conductive particles may be conductive metal particles or particles in which the surface of resin particles is coated with a metal.

[0033] The examples described below use 45 to 55 wt.% of epoxy resin as the thermosetting resin composition, 5 to 10 wt.% of 4-hydroxyphenylmethyl-1-naphthylmethylsulfonium as the initiator, and 10 to 15 wt.% of phenoxy resin as the film-forming resin, and 5 to 10 wt.% of nickel balls as the conductive particles.

[0034] The anisotropic conductive adhesive film according to the present invention comprises a conductive layer and a non-conductive layer. The conductive layer is formed by dispersing conductive particles in a thermosetting resin composition and then semi-curing the composition. The semi-cured conductive layer electrically connects to the electrodes of the circuit component during the bonding process due to the flow of the polymer layer surrounding the conductive particles. Figure 1 shows a cross-section of the anisotropic conductive adhesive film according to the present invention. The thickness of the conductive layer is preferably formed so as not to exceed 2 μm relative to the average particle size of the conductive particles. This is because, if the thickness of the conductive layer exceeds 2 μm relative to the average particle size of the conductive particles, the semi-cured resin surrounding the surfaces of the conductive particles may remain on the surfaces of the conductive particles during the bonding process, and the thicker conductive layer reduces the pressure load applied to the conductive particles.

[0035] The conductive layer 110 is formed by dispersing conductive particles 130 in a thermosetting resin composition containing an epoxy resin as a curing resin and a curing agent, and then performing a semi-curing process by adjusting the drying temperature conditions to 50 to 100°C and the coating speed to approximately 1 to 5 m / min to optimize the thermal reaction time of the epoxy resin. The non-conductive layer 120 is formed using a thermosetting resin composition containing the same curing resin and curing agent as the conductive layer, and is laminated on the conductive layer that has completed the semi-curing process, and is manufactured using an anisotropic conductive adhesive film.

[0036] The semi-curing process for the conductive layer involves applying a thermosetting resin composition to a base film, and then adjusting the drying temperature and coating speed in the drying section to control the thermal reaction time of the cured resin. The semi-cured state of the conductive layer can be confirmed by measuring the curing rate. To calculate the curing rate of the conductive layer 110, the heat capacity was measured before and after semi-curing using differential scanning calorimetry (DSC). Figure 2 shows a graph of heat capacity measured before (initial heat value of the non-fluid layer) and after (heat value after drying the non-fluid layer) the semi-curing process at a temperature increase rate of 10°C per minute. Based on the heat capacity analysis results, the curing rate was calculated using the following equation:

[0037] [Formula 1] Cure rate (%) = [1 - (initial heat value) / (heat value after semi-curing)] x 100

[0038] Each sample (conductive layer film sample) with a cure rate of 30 to 70% was laminated under the same conditions to produce the final anisotropic conductive adhesive film. Then, to evaluate the physical properties of each anisotropic conductive adhesive film, a bump area of ​​1500 μm was used. 2 The bonding process was carried out on a chip containing circuit components with a pitch of 20 μm, and the capture rate and connection resistance were measured for each sample. The measurement results are shown in Table 1 below.

[0039] [Table 1]

[0040] As is clear from Table 1, when the cure rate is less than 40% (Sample 1), the connection resistance increases due to a decrease in the number of captured conductive particles. When the cure rate is more than 60% (Sample 5), the connection resistance increases due to insufficient compression. Figure 3 shows the correlation between the cure rate of the conductive layer and the capture rate and the connection resistance confirmed in this example.

[0041] Figures 4 to 6 show the results of measuring the viscosity (unit: Pa s) of the conductive layer and non-conductive layer using a rheometer machine at temperatures ranging from 25 to 200°C when the conductive layer cure rate was 40% (Figure 4), 50% (Figure 5), and 60% (Figure 6) (measurement conditions: ramp rate: 10°C / min, angular frequency: 1.0 rad / s). The fluidity of each layer when the anisotropic conductive adhesive film was bonded was confirmed. As is clear from Figures 4 to 6, the modulus (minimum melt viscosity) of the semi-cured conductive layer 110 increases with the cure rate. By controlling the cure rate between 40 and 60%, the modulus of the conductive layer can be adjusted to 10,000 to 50,000 Pa·s. (From Figure 4, the modulus of the conductive layer with a 40% cure rate is 29,800 Pa·s; from Figure 5, the modulus of the conductive layer with a 50% cure rate is 40,100 Pa·s; and from Figure 6, the modulus of the conductive layer with a 60% cure rate is 49,905 Pa·s.) In this case, the resin flow phenomenon that occurs during the bonding process minimizes the number of conductive particles that flow away without being involved in contact between the electrodes, thereby achieving stable connection resistance. If the modulus of the conductive layer is less than 10,000 Pa·s, the resin has high flowability during final compression bonding, resulting in a large amount of conductive particles flowing away between the electrodes. Furthermore, if the modulus of the conductive layer exceeds 50,000 Pa·s, the hardness of the resin increases, significantly reducing the bonding effect during final bonding and significantly increasing the connection resistance. Furthermore, the modulus of the conductive layer is preferably at least twice that of the non-conductive layer. When the modulus of the conductive layer is at least twice that of the non-conductive layer, loss of conductive particles due to resin flow in the non-conductive layer during the bonding process can be minimized. Furthermore, the modulus (minimum melt viscosity) of the non-conductive layer is preferably in the range of 1,000 to 5,000 Pa·s (in this example, the modulus of the non-conductive layer was confirmed to be 2,178 Pa·s; see Figures 4 to 6).If the modulus of the non-conductive layer is less than 1,000 Pa·s, bubbles may be generated during the compression process due to high fluidity, and if it exceeds 5,000 Pa·s, the filling ability to the connection structure is reduced due to low fluidity.

[0042] From the viewpoint of the adhesive properties and reliability of the anisotropic conductive adhesive film, the non-conductive layers 120 arranged on the top and bottom, which embody the adhesive properties, can improve interlayer compatibility and increase reliability by using the same thermosetting resin as the conductive layer 110.

[0043] The high viscosity of the conductive layer minimizes the loss of conductive particles between circuit electrodes. While conventional anisotropic conductive adhesive films have a particle capture rate of approximately 30%, the anisotropic conductive adhesive film of the present invention can significantly improve the capture rate to 40% to 60%. When using an anisotropic conductive adhesive film with such an improved capture rate, electrical short circuits caused by the flow and subsequent aggregation of conductive particles in fine pitch connections can be fundamentally resolved. Therefore, since the particle capture rate has increased, the same level of capture rate can be achieved at fine pitches even when the content of expensive conductive particles is significantly reduced compared to conventional anisotropic conductive adhesive films, thereby significantly reducing the manufacturing cost of the anisotropic conductive adhesive film.

[0044] In particular, anisotropic conductive adhesive films for COG and COP require fine pitch, so the planar connection cross-sectional area is designed to be narrow, and the number of conductive particles participating in conduction between the bump and the panel is small. Therefore, in the case of conventional anisotropic conductive adhesive films for COG and COP, the density of conductive particles is tens of thousands of pcs / mm 2 When the anisotropic conductive adhesive film according to the present invention is used in the connection structure of COG and COP, the flow of conductive particles can be controlled remarkably even if the content of conductive particles is significantly reduced, so that a stable number of captured conductive particles can be ensured even at a low conductivity density.

[0045] In addition, in the case of COG, the substrate has physical properties in which a rigid lower substrate is applied to an upper substrate having a chip structure, while in the case of COP, the substrate has physical properties in which a lower substrate having a film structure is applied to an upper substrate having a chip structure. In the present invention, a multilayer structure is designed in which a conductive layer is sandwiched between two non-conductive layers, and non-conductive layers with different physical properties can be applied to the non-conductive layers arranged above and below the conductive layer, so it is possible to provide an anisotropic conductive adhesive film that is optimized for substrates with different structures.

[0046] Although the preferred embodiments of the present invention have been described above, those skilled in the art will recognize that modifications may be made without departing from the essential characteristics of the present invention. Therefore, the embodiments of the present invention described herein should be considered from an illustrative rather than a restrictive perspective, and the scope of the present invention is defined by the claims, not the above description, and all variations within the scope of the claims should be considered to be within the scope of the present invention.

Claims

1. a non-flowable conductive layer formed by semi-curing a thermosetting resin composition containing an epoxy resin as a thermosetting resin and conductive particles dispersed therein so that the cure rate measured by differential scanning calorimetry according to the following formula 1 is 40% or more and 60% or less; an adhesive non-conductive layer formed of a thermosetting resin composition containing an epoxy resin as a thermosetting resin and not containing conductive particles; An anisotropic conductive adhesive film formed by laminating the conductive layer and the non-conductive layer. [Formula 1] Cure rate (%) = [1 - (calorie value after semi-curing) / (initial calorie value)] x 100

2. 2. The anisotropic conductive adhesive film according to claim 1, wherein the non-conductive layer comprises a first non-conductive layer and a second non-conductive layer, and the conductive layer is interposed between the first and second non-conductive layers.

3. 2. The anisotropic conductive adhesive film according to claim 1, wherein the thickness of the conductive layer is not more than 2 μm compared to the average particle size of the conductive particles.

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