KR20180008635A - Improved fixed array ACF with multi-tier partially embedded particle morphology and method of making same - Google Patents

Abstract

An anisotropic conductive film (ACF), comprising: a substrate; An adhesive layer on the surface of the substrate; A first tier of conductive particles arranged in a non-random array embedded in the adhesive layer, the first tier being formed by transferring conductive particles from a carrier belt having a stitching line to a surface of the adhesive layer, The portion of the first tier corresponding to the stitching line is a first tier of conductive particles without or essentially free of conductive particles; And a second tier of conductive particles arranged in a non-random array embedded in the adhesive layer and overcoating a portion of the first tier corresponding to the stitching line. The tiers may be the same or different depths in the adhesive layer. Two or more tiers of conductive particles may be present in the ACF.

Description

Improved fixed array ACF with multi-tier partially embedded particle morphology and method of making same

Cross-reference to related patents

This application is a continuation-in-part of U.S. Application No. 13 / 678,935 (TS-023) filed on November 16, 2012 and US Application No. 13 / 233,360 (TS-011) filed on September 15, Some are still filing. Both of these applications are incorporated herein by reference in their entirety.

Anisotropic conductive film (ACF) is commonly used for flat panel display driver IC (integrated circuit) bonding. A typical ACF bonding process includes a first step of attaching an ACF onto an electrode of a panel glass, a second step of aligning the driver IC bonding pad with the panel electrode, and a second step of applying and heating the bonding pad to melt and cure the ACF It includes three steps. The conductive particles of the ACF impart anisotropic electrical conductivity between the panel electrode and the driver IC. ACF has also been widely used in applications such as flip chip bonding and photovoltaic module assembly.

US Published Application No. 2010/0101700 ("Liang '700") by Liang et al. Discloses a technique to overcome some of the disadvantages of ACFs with randomly dispersed conductive particles. Liang describes that the conductive particles are arranged in a predetermined array pattern on a fixed-array ACF (FACF). Non-random arrays of such conductive particles are capable of ultra-fine pitch bonding without the possibility of the same short circuit. On the other hand, the conductive particles of the stationary array ACF are pre-arrayed on the adhesive surface and exhibit significantly higher particle capture rates at lower particle concentrations than conventional ACFs. Because conductive particles are typically narrowly dispersed, expensive Au particles with a polymeric core, a fixed array ACF provides a significantly lower cost solution with better performance than conventional ACFs.

US Application No. 13 / 233,360 (recently granted) discloses a continuous belt or loop having an array of microcavities carrying conductive particles formed on one surface as a carrier web, ≪ / RTI > to produce an ACF. The belt is used in a manner similar to webs in the process described in Liang '700. The belt abuts the end surface of the web and is formed by securing them with an adhesive such as a pressure sensitive adhesive and a UV or thermosetting adhesive. The abutted end of the carrier web forms a stitching line, which can be less than 90 degrees (measured relative to the longitudinal edge of the web). One problem with the production of ACFs using continuous belts with stitching lines is that conductive particles can almost be carried on the belt in the region of the stitching line because the microcavities are filled with the adhesive in the region of the stitching line It is not. In order to minimize the frequency at which electrodes (e.g., electrodes in a device such as a microchip) oriented parallel to the cross-machine direction of the ACF do not contact a sufficient number of conductive particles to complete the circuit , The stitching line can be oriented at an angle of inclination.

The term "multi-tier" refers to two or more tiers of conductive particle arrays in which the array (s) of conductive particles are partially or wholly embedded in the surface of the ACF. The term "depth" refers to the portion of the conductive particle diameter below the top surface of the ACF adhesive. The particles can be completely and / or partially embedded in the adhesive layer. The term "corresponding to the stitching line" and its variants refers to that portion of the surface of the adhesive layer comprising the ACF, which is formed by the portion of the carrier web to which the abutment end of the carrier web is bonded, (For example, as described in U.S. Application Serial No. 13 / 233,360). The microcavities in this part of the carrier web are not well adapted to retain the conductive particles. The stitching lines interfere with the microcopy array on the belt, and then the array of conductive particles on the surface of the ACF. When the stitching line is oriented at 90 [deg.] With respect to the belt, i.e. in a direction parallel to the cross-machine direction of the belt, the conductive particle array of ACFs produced by transferring the conductive particles from the belt, do not include. However, by applying the conductive particles to the area of the adhesive layer corresponding to the stitching line, the stitching line can have any angle with respect to the machine direction of the substrate including not only the right angle but also the tilt angle. The implementation of the second transmission significantly improves the connection conductivity (reduction in connection resistance) in the stitching line region and improves the IC bonding yield. This also allows a wider tolerance in the stitching process. By the second transmission, a high yield of a high-resolution IC bonding application can be obtained with a wide range of stitching line widths and angles. Without a second transfer, a stitching line that is as narrow as the dimensions of patterned electrodes (typically 10 to 1000 microns) or IC bumps (typically 10 to 50 microns) is required to minimize conductive particles missing in the bonded area Will be. However, for high resolution IC connections, narrow stitching lines in the range of IC bump sizes tend to result in micro-cavity loops with high aspect ratio trenches with depths or step heights approximately equal to the substrate thickness 50 to 150 microns). Small conductive particles (2 to 5 microns in diameter) commonly used to connect IC bumps to prevent unwanted shorting are trapped inside a deep trench during microfluidic particle charging and transfer, . ACFs with conductive particle agglomerates are very undesirable for high resolution connections due to disconnection or shorting at electrical circuit connections. The edges of the two stitching ends of the fine cavity loop can be carefully polished and tapered to help reduce trapped particles and agglomerates. However, tapered edge approaches tend to result in significantly wider stitching lines and potential damage to the microcoupling array along the tapered line. For both high-resolution applications, both trade-offs will result in the disappearance of conductive particles along the stitching line and poor connectivity. Alternatively, the trench may be filled with a durable adhesive, such as a UV or thermoset adhesive. Unfortunately, filling and hardening glue on narrow trenches with a high aspect ratio is a very difficult and time consuming process. The surface smoothness and durability of the filled trenches are often not acceptable in the heavy duty microfluidic particle transfer process associated with the fabrication of stationary array ACFs. There is a clear need for a low cost structure and its manufacturing process for creating ultrafine pitch ACFs for high-end IC applications.

The present invention relates to a method of manufacturing a conductive particle, wherein the conductive particles are arranged in two or more tiers in the surface of the ACF conductive adhesive layer and the particle depletion region of the conductive layer corresponding to the stitching line in one tier is at least By providing an ACF that is overcoated with conductive particles from one additional tier, the fixed array ACF of US Application No. 13 / 233,360 is increased. No. 13 / 111,300 ("Liang '300") discloses that conductive particles can be partially embedded in the adhesive resin such that at least a portion of the particles (e.g., about 1/3 to 3/4 of the diameter) But the multi-tier array further improves the particle capture rate and provides a lower contact resistance and more peeling force than a fixed array ACF without a tiered particle structure. ≪ RTI ID = 0.0 > High.

The present invention includes an ACF arrangement wherein at least one of these additional tiers is provided to apply conductive particles in a region of a first tier at least corresponding to a stitching line. One example of the available multi-tier effects, using a two-tier non-random fixed array particle morphology, as compared to a single plane morphology, is shown in the table below.

Although the particle density is slightly lower, ACFs with two-tier particle morphology have significantly higher particle capture rates, better contact resistance (lower), higher peel strengths, and other performance is essentially the same It is clear from Table 1 that it is maintained. The two-tier particle morphology also maintained well after the samples were aged for more than 3 months under normal storage conditions. By way of non-limiting example, by some of the particles embedded in the adhesive more than others in a given fixed array ACF, the unwanted turbulence effects caused by the melt flow of the adhesive during bonding are reduced and the effective The local bonding pressure increases. As a result, fewer particles are emitted from the connecting electrode, and the capturing rate is increased, the contact resistance is lowered, and the bonding strength is increased. Moreover, for the same particle densities, ACFs with multi-tiers produced by multiparticulate delivery steps have a lower standard deviation of particle density, resulting in a more uniform particle distribution, which tends to result in higher success rate devices . Without being limited by theory, it is believed that missing particles (e.g., at exactly the same point in a particle array produced by two or more successive low densities (e.g., using a particle array of 11.5 占 퐉 pitch for a particle density of about 9,000 pcs / , The process of particle filling and transfer is much lower than in a single high density array (e.g., a particle array of 8 um pitch with a particle density of about 18,000 pcs / mm < 2 >). Even if some missing particle regions are created in the first particle transfer process, the particles can be effectively filled in the area and transferred by a subsequent transfer process to form a multi-tier fixed array ACF having a low standard deviation of particle density .

In summary, in one embodiment of the present invention, in certain embodiments, the adhesive layer may include conductive particles dispersed within the surface of the adhesive layer in addition to the particles delivered in a non-random array. In other embodiments, the adhesive layer may not contain conductive particles dispersed therein. In addition, the tier of conductive particles over-coating the area corresponding to the stitching line can overcoat only the area corresponding to the stitching line, or overcoat the area adjacent to the area corresponding to the stitching line and the stitching line, All or a part of the entire surface of the conductive adhesive layer may be overcoated.

One aspect of the present invention is an anisotropic conductive film (ACF) comprising: (a) an adhesive layer; and (b) a plurality of conductive particles individually bonded to the adhesive layer, 1 and first and second tiers of non-random arrays of particles embedded at a second depth, wherein the depths at which the first array and the second array are embedded in the adhesive can be the same or different (e.g., For example, a difference of about 10% or more based on the diameter of the particles; a difference of about 0.3 [mu] m or more for particles of 3 [mu] m in diameter. The difference in embedded depths of the tiers may be at least 20%, at least 30%, even at least 80% of the particle diameter in the depth direction, and one of the tiers may be a first (e.g., At least some of the tears), otherwise there is little or no conductive particles.

Accordingly, the present invention provides an ACF comprising two or more fixed or non-random arrays of conductive particles embedded in one or more depths in an ACF, wherein the particles in one tier correspond to the stitching lines of the other tier Region, where there will be no or substantially no conductive particles in the overcoat due to the presence of stitching lines in the carrier belt. In a more particular embodiment, the adhesive layer itself contains conductive particles dispersed therein as well as particles delivered from the carrier belt. In another embodiment, the adhesive layer does not contain conductive particles dispersed therein. The combination of an adhesive layer containing randomly dispersed conductive particles and a first tier of conductive particles arranged in a non-random array has a single tier of conductive particles in a region corresponding to the stitching line, And provides an ACF having particles of two tiers in the region outside the region.

In another aspect, the ACF may comprise two tiers of a fixed or non-random array in which the conductive particles are partially embedded at the same or different depths on the surface of the adhesive layer of the ACF, One tier has particles not present in the region of the stitching line and the remaining tiers have particles at least present in the region corresponding to the stitching line of the first tier. In this embodiment, the adhesive layer may also optionally contain conductive particles that are randomly dispersed within it.

In another embodiment, one tier is a fixed or non-random array of conductive particles embedded by transfer to an adhesive layer, and the second tier is a random dispersion of conductive particles dispersed in the adhesive layer, Lt; / RTI > array of fixed or non-random arrays. Other aspects involving additional tiers of particle arrays, such as the second and third tiers, are also possible.

In summary, the ACF is characterized by comprising a first tier of conductive particles arranged in a non-random array deposited on the surface of the adhesive layer by transmission from a carrier belt comprising an area corresponding to the stitching line do. The non-random array of said first tier contains no, or essentially no or substantially no conductive particles in the region corresponding to the stitching line. To make the ACF suitable for use in ultrafine pitch applications, such as high resolution IC bonding, the particles may be applied to at least a portion of the second tier of the non-random array conductive particles And is provided in an area corresponding to the stitching line by transfer as a tier. The first and second tiers may each consist of particles of the same size or different sizes. The particles constituting each tier can be at the same depth or at different depths and they can have the same pitch of different pitches.

In a further aspect of the present invention, which provides an ACF suitable for ultrafine pitch applications, the ACF comprises a substrate, an adhesive layer optionally containing randomly dispersed conductive particles on the surface of the substrate, One or more tiers of conductive particles arranged in a non-random array and applied to the adhesive by transmission. By placing or releasing tiers so that the areas corresponding to the stitching lines of each tier do not overlap, an ACF suitable for ACF applications requiring fine pitch is provided.

Another aspect of the present invention is a laminate comprising: (a) an adhesive layer having a substantially uniform thickness; And (b) an anisotropic conductive film (ACF) comprising a plurality of conductive particles individually adhered to the adhesive layer, the conductive particles having a first non-random Type array, and a second non-random array of conductive particles partially embedded in the adhesive layer at the same or second depth, the second array covering an area of the stitching line in the first array.

It is understood that a tier may be placed to apply conductive particles only to an area corresponding to the stitching line of another tier or to an area covering the stitching line and to an area covering the entire surface of the adhesive layer, will be.

According to one aspect, a multi-tier ACF is created using a multiple delivery process that includes the following steps:

(a) transferring a first fixed array of particles to an adhesive layer, except for a region corresponding to a stitching line;

(b) optionally processing the first array to a desired level of embedding using, for example, heating and / or pressure rollers or calendaring;

(c) transferring at least the second fixed array of particles over the area of the first array corresponding to the stitching line to the adhesive; And

(d) optionally pressurizing the two arrays of particles to a desired degree of embedding such that the first array is buried in the adhesive to a greater extent than the second array.

According to another aspect, a multi-tier ACF is created using a multiple delivery process that includes the following steps:

(a) transferring a first fixed or non-random array of conductive particles except the array of stitching lines to an ACF having a substrate coated with an adhesive having conductive particles dispersed therein; And

(b) processing the first array to a desired level of embedding using, for example, heating and / or pressure rollers or calendering.

The ACF having a stitching line may be a sheet or a continuous film, or may be formed of the multi-tier particle morphology described herein, which may be a continuous film in the form of a reel or a roll. In one embodiment, the ACF can be fed from about 10 to 300 m (length) as a roll of about 1.0 to 2.0 mm (width) wound between plastic holders. In another embodiment, the ACF may be a continuous film or a reel having a multi-tier morphology as described herein.

FIG. 1A is an illustration of FIG. 8 of US Application No. 13 / 233,360, which illustrates the use of conductive particles for a series of 20 micron (width) x 1000 micron (length) electrodes after being bonded to an ACF having a 40 micron particle- Lt; / RTI > is a 400x micrograph of a bonded electronic device, showing the distribution of < RTI ID = 0.0 > Figure 1b shows a schematic of a simulated test kit comprising a series of IC bumps of 20 占 퐉 (width) 占 20 to 50 占 퐉 (length) bonded with a fixed array ACF having stitching lines of 10 占 퐉, 20 占 퐉 and 40 占 퐉 width .
Figure 2 shows a two-tier particle morphology and a two-tier particle corresponding to Figure 4 of U.S. Application No. 13 / 678,935, filed November 16, 2012, having the same pitch size with a corresponding distribution of particle buried depth Lt; RTI ID = 0.0 > ACF < / RTI >
3 is a schematic diagram of a two-tier fixed array ACF, wherein the microcavities used for the transfer of the two tiers of stationary array particles are shown in FIG. 5 of US Application No. 13 / 678,935, filed November 16, And have correspondingly different pitch sizes.
Figure 4 is a schematic diagram of an ACF with a two tiered fixed array that includes an optional overcoat.
5A is a schematic view of an ACF reel or roll with a micrograph (FIG. 5C) showing a two-tier structure of conductive particles according to the invention, wherein the second tier is transferred to the area of the stitching line and to the adjacent boundary area. 5B is a schematic view of a micro-cavity carrier belt stitched with a durable adhesive tape having, for example, a smooth surface.
Figure 6 is a schematic cross-sectional view of an ACF comprising a two-tier structure of conductive particles according to the present invention, wherein the second tier is confined to the area of the stitching line.
Figure 7 is a schematic cross-sectional view of an ACF comprising a dual tier structure of conductive particles according to the present invention, wherein the second tier fully switches the area of the stitching line and overlaps with a portion of the first tier structure.

U.S. Published Application No. 2010/0101700 and U.S. Patent Application No. 13 / 111,300, filed May 19, 2011 by Liang et al., Are hereby incorporated by reference in their entirety.

A carrier sheet or belt containing microcavities of about 6 占 퐉 (diameter) 占 4 占 퐉 (depth) 占 3 占 퐉 (partition), which is useful for delivering conductive particles to the surface of the adhesive layer, is preferably about 2 to 5 mil of a thermally stabilized polyimide To form a microcavity carrier by laser ablation on a polyester film such as polyimide (PI) or PET. The microcoupler array web is filled, for example, by coating with a conductive particle dispersion using a smooth rod, a doctor blade, or a slot die. One or more filling can be used to assure the unfilled microcavity. See Liang '300 and Liang' 700.

Figure 1 is a 400x micrograph of a bonded set of line electrodes of 18 占 퐉 (width) 占 1000 占 퐉 (length). Region 188 ' corresponds to a 60 " stitching line with a stitching gap of 40 [mu] m that does not contain conductive particles 112. [ In this particular example, the average diameter of the conductive particles is 3.2 占 퐉 and the distance or gap between the particles across the stitching line is 80 占 퐉 as measured along the electrode, which represents less than 10% of the 1,000 占 stitching line length. About 58 to 60 particles are in contact with the electrode across the stitching line, compared to about 64 to 66 particles in contact with the electrode not crossing the stitching line. The about 58 to 60 particles are much larger than the minimum number of particles required to establish a reliable electrical contact and are generally about 5 to 10 particles per electrode. The absence of conductive particles in the oblique stitching line obviously does not affect the connection to the long and wide electrodes, since reasonably sufficient conductive particles will still be trapped. However, in the case of high-resolution IC chip bonding, the IC bump dimensions are typically as small as 10 to 30 μm (width) × 20 to 50 μm (length), and the bump area corresponds to 300 to 1000 μm ² or less. For high quality connections, at least 3 to 5 trapped conductive particles are typically required for each bump.

1B shows a simulation including four series of chip bumps 302, 303, 304, and 305 having planar dimensions of 20 탆 20 탆, 20 탆 30 탆, 20 탆 40 탆, and 20 탆 50 탆, (300). ≪ / RTI > The test kits are bonded to a simulated fixed array ACF that includes three hypothetical 45 ° stitching gaps 310, 320, and 340 having widths of 10, 20, and 40 microns, respectively. In the figures, the conductive particles are not shown to be transferred to the gaps corresponding to the stitching lines 310, 320 and 340. 1b, the largest bump size 305 (20 占 퐉 50 占 퐉 or 1000 占 퐉 ² ) for the stitching gap 320 (20 占 퐉 gap) and the stitching gap 340 (40 占 퐉 gap) There are IC bumps that are essentially free of any trapped conductive particles. The best achievable resolution of a fixed array ACF with a stitching line wider than 20 占 퐉 would be 1000 占 퐉 ² or less. Stitching the gap (310) (10㎛ gap) of the ACF is more excellent in resolution has, however, a bump 305 for the small bumps than (1000㎛ ^2), in particular for a small bump more bumps (304) (800㎛ ²⁾ Bumps with insufficiently trapped particles can be observed.

It has been found that narrow stitch line widths of 2 to 10 mu m are required even in ACFs with high grain density (≥30,000 pcs / mm2) with oblique stitching lines. However, it is extremely difficult to produce a durable and high-resolution micro-cavity loop having such narrow stitching lines, and it often results in particle aggregation in subsequent microfluidic particle filling and delivery steps. Particle aggregation results in an undesirable short circuit in the bonded device

Figure 2 shows a first array of conductive particles 22 embedded at a first distance (e.g., d ₁ ) in the ACF adhesive 24 and a second array of conductive particles 22 embedded in the ACF at a second shallower distance (e.g., d ₂ ) Lt; RTI ID = 0.0 > 26 < / RTI > The pitch or distance between adjacent particles in a particular array (i.e., the first array designated by dashed hexagon 28 and the second array designated by dashed hexagon 29) has the same pitch. 2 is a graph showing the distribution of the depth of embedding. The graph shows that the distribution is bimodal, including two particle arrays at distinctly different embedded depths (d ₁ and d ₂ ).

3 shows a first array of particles 42 in which ACF 40 is embedded in ACF adhesive 44 at a first depth and a second array of particles 46 that are embedded in ACF adhesive at a shallower depth US patent application Ser. No. 13 / 678,935, which is incorporated herein by reference. The ACF 40 of FIG. 3 differs from the ACF 20 shown in FIG. 2 in that the pitches of the particles constituting the first and second arrays are different. The dotted line 48 representing the pitch of the second array of particles 46 is shorter than the dotted line 49 connecting adjacent particles 42 in the deeper first array of particles 42.

The two-tier (or multi-tier) ACF is obtained by a transfer process using a continuous carrier belt having stitching lines as described in U.S. Patent No. 13 / 233,360. The micro-cavity carrier belt may have the same or different micro-cavity pattern and pitch. Conductive particles are filled in the first micro-cavity belt, and the excess particles outside the cavity are, for example, a rubber wiper or rubber which carefully adjusts the gap and the pressure or tension between the micro-cavity film and the rubber wiper or rubber roller It is removed using a roller. For example, by laminating the filled microcavity film with an epoxy adhesive precoated onto the release liner, conductive particles of the microcavity film are transferred to the epoxy adhesive. As part of the laminating step or as a separate step, the thus delivered particles are further pressed into an adhesive film, for example by calendering, laminating or heating under pressure or shear, Approximately 0% of the diameter (i. E., Fully buried) to 95% (i. E. Partially buried) (more particularly about 0% to 80% of the particle diameter exposed on the adhesive surface) may be allowed or allowed. The particle filling and transfer process is repeated with a second microcavity film to produce a two-tier or multi-tier particle morphology, as shown in Figure 4, wherein two-tier (62 and 64) Any overcoat adhesive 50 covering the top surface of the containing ACF 60 is also shown. Due to the stitching line, some (if any) particles are present in the area of the stitching line in the first transmission. When the second transmission covers the entire area of the stitching line, the ACF includes a single layer of conductive particles in the stitching line and a double layer of conductive particles over the balance of ACF.

5A shows an ACF roll comprising an area 112 having a first grain array, a stitching line area 106 having a second tier grain array, and an overlap area 110 having both first and second grain arrays, Is a schematic view of a reel (70). Figure 5c shows regions 112, 110 and 106 and the corresponding boundary regions 111 (left) and 113 (right) of the two-tier structure shown schematically by the rectangle A of Figure 5a ). ≪ / RTI > Fig. 5B shows a schematic view of the stitching area of the microcavity carrier belt stitched, for example, with a durable adhesive tape 106T having a smooth surface for forming a closed loop. As described in U.S. Patent No. 13 / 233,360, conductive particles are filled into microcavities and transferred onto a precoated adhesive layer on a release liner to provide a particle-to-particle ratio corresponding to the area covered by the stitching tape 106T, Containing stitching region 106 and a region 112 comprising the first tear particles. The stitching line 106 is then overcoated with a second tier of conductive particles such that there is a continuous layer of conductive particles over the surface of the adhesive layer comprising the stitching line 106. [

6, the ACF includes a substrate 100, an adhesive layer 102 on the surface of the substrate 100, an adhesive in which conductive particles are optionally dispersed, a non-random array of non- Wherein at least one tier of conductive particles 104 is formed by transferring conductive particles from a carrier belt having a stitching line to a surface of an adhesive layer wherein the surface of the adhesive layer corresponding to the stitching line 106 Is overcoated with a second tier of conductive particles 108 arranged in a non-random array by transmission from a carrier belt covering at least a portion 106 of the first tier corresponding to the stitching line. 6, the ACF comprises a single layer of conductive particles, particles outside the stitching line are applied in the first transmission, and the area of the stitching line Are applied at the time of the second transfer. Figure 6 shows an embodiment wherein the conductive particles are completely buried and at different depths, but the invention includes ACFs in which the particles are partially buried and / or have different depths. In addition, although only two tiers are shown, the present invention encompasses embodiments in which two, three, four, five or more tiers are present at the same or different depths.

Figure 7 shows a further embodiment. 7, when the second tier 108A is selectively applied over the overlap region 110 adjacent to the area of the stitching line 106 and the stitching line, A double layer of particles in the region 110 where the first transmission and the second transmission overlap, and a single layer 112 of particles in the region of the first transmission outside the region of the stitching line.

According to a further aspect of the present invention, an ACF having any of the foregoing structures is overcoated with an adhesive layer 50 as shown in Fig. 4 to improve the tackiness or adhesion of the ACF to the electrode Where an adhesive 50 overcoat is deposited or laminated onto a conductive adhesive layer 60 comprising a first tier 62 and a second tier 64 of conductive particles. The adhesive may be the same as the adhesive on the surface of the ACF as described in more detail below. Such an overlay adhesive does not require conductive particles, but conductive particles can be included in the adhesive, if necessary.

In another aspect, an ACF can be obtained by delivering one or more tiers of a fixed array of conductive particles onto a layer of adhesive where the conductive particles are randomly dispersed and completely embedded in the conductive adhesive layer. For example, alternatively, an adhesive layer having randomly dispersed conductive particles in the adhesive may be formed, a fixed, non-random array of particles may be delivered to the surface of the ACF adhesive, Lt; RTI ID = 0.0 > tier < / RTI > ACF. Any of the previously taught conductive particles for use in an ACF may be used in the practice of the present disclosure. In one embodiment, gold coated particles are used. In one embodiment, the conductive particles have a narrow particle size distribution with a standard deviation of less than 10%, preferably less than 5%, even more preferably less than 3%. The particle size is preferably in the range of about 1 to 250 mu m, more preferably about 2 to 50 mu m, even more preferably about 2.5 to 10 mu m. Two types of commercially available conductive particles useful in the present invention include those sold by the company JCI USA (New York, USA), a subsidiary of Nippon Chemical Industrial Co., Ltd. Ni particles available from Nippon Chemical through Inco Special Products (WickOff, New Jersey, USA), and Ni particles available from Inco Special Products (Wick Off, New Jersey, USA). In one embodiment, the conductive particles may have a 2-mode or multimodal particle size distribution. In one embodiment, the sizes of the microcavity and the conductive particles are selected such that each microcavity has a limited space for containing only one conductive particle. In certain embodiments, the electrically conductive particles or microcavities have a diameter or depth ranging from about 1 to about 20 mu m. In another embodiment, the electrically conductive particles or microcavities have a diameter or depth ranging from about 2 to about 5 mu m. In another embodiment, the electrically conductive particles or microcavities have a diameter or depth with a standard deviation of less than about 10%.

In another preferred embodiment, the electrically conductive particles or microcavities have a diameter or depth with a standard deviation of less than about 5%. In another preferred embodiment, the adhesive layer comprises a thermoplastic, thermosetting, or precursor thereof.

In one embodiment, conductive particles comprising a polymeric core and a metal shell are used. Useful polymer cores include, but are not limited to, polystyrene, polyacrylates, polymethacrylates, polyvinyls, epoxy resins, polyurethanes, polyamides, phenols, polydienes, polyolefins; Aminoplastics such as melamine formaldehyde, urea formaldehyde, benzoguanamine formaldehyde; And oligomers, copolymers, blends or complexes thereof. When the composite material is used as a core, nanoparticles or nanotubes of carbon, silica, alumina, BN, TiO ₂ and clay are preferred as fillers in the core. Suitable materials for the metal shell include but are not limited to Au, Pt, Ag, Cu, Fe, Ni, Sn, Al, Mg and alloys thereof. Conductive particles with interpenetrating metal shells such as Ni / Au, Ag / Au, and Ni / Ag / Au are useful for hardness, conductivity and corrosion resistance. Particles having a spike of rigidity, such as Ni, carbon, graphite, are useful for enhancing the reliability of the connection of the electrode which, if present, permeates the corrosive film and is susceptible to corrosion. These particles are available from Sekisui KK under the trade designation MICROPEARL under the trade designation DYNOSPHERES by Dyno AS from Nippon Chemical Industrial Co. under the trade designation BRIGHT, (Norway).

In another embodiment, the conductive particles may have a so-called spiked surface. The spikes can be formed by doping or depositing a small amount of foreign particles, such as silica, onto the latex particles before the electroless plating step of Ni and then partially replacing the Ni layer with Au. In one embodiment as described in more detail in the aforementioned application, the conductive particles are formed into spikes. These spikes may be formed without limitation as sharp spikes, nodular, notch, wedge, or groove. In yet another embodiment, a thin insulating layer may be precoated with an insulating polymer layer, preferably with a melt flow temperature close to or lower than the bonding temperature.

The narrowly dispersed polymer particles can be prepared, for example, by seed emulsion polymerization as taught in U.S. Patent Nos. 4,247,234, 4,877,761 and 5,216,065, and by the method described in Adv., Colloid Interface Sci., 13, 101 ); J. Polym. Sci ., 72, 225 (1985) and "Future Directions in Polymer Colloids ", ed. El-Aasser and Fitch, p. 355 (1987), Martinus Nijhoff Publisher]. In one embodiment, monodisperse polystyrene latex particles of about 5 탆 diameter are used as a deformable elastic core. The particles are first treated in methanol with gentle agitation to remove excess surfactant and create a microporous surface on the polystyrene latex particles. The thus treated particles are then activated in a solution containing PdCl ₂ , HCl and SnCl ₂ , then washed with water and filtered to remove Sn ⁴⁺ , and then electroless, including Ni complexes and a hydrophosphite Ni plating solution (for example, from Surface Technology Inc. (Trenton, NJ)) at 90 占 폚 for about 30 to about 50 minutes. The thickness of the Ni plating is controlled by the plating solution concentration and the plating temperature and time.

In order to improve the transfer of conductive particles onto the adhesive layer, the release layer may be applied on the microcavity. The release layer may comprise a fluoropolymer or oligomer, a silicone oil, a fluorosilicon, a polyolefin, a wax, a poly (ethylene oxide), a poly (propylene oxide), a surfactant with a long chain hydrophobic block or branch, or a copolymer or blend thereof May be selected from the list containing. The release layer is applied to the surface of the microcavity array by methods including but not limited to coating, printing, spraying, vapor deposition, plasma polymerization or crosslinking. As illustrated in Liang '300 application, in another embodiment, the method further comprises the step of using a microcostal array closed loop. In another embodiment, the method further comprises the step of using a cleaning device to remove residual adhesive or particles from the microcavity array after the particle shear step. In a different embodiment, the method further comprises the step of applying the release layer onto the microcavity array prior to the particle filling step. In yet another aspect, to further reduce the risk of shorting in the X-Y plane, the conductive particles may be encapsulated or coated with a thermoplastic or thermosetting insulating layer, as described in U.S. Patent Nos. 6,632,532; 7,291, 393; 7,410,698; 7,566,494; 7,815,999; 7,846,547 and U.S. Patent Application 2006/0263581; 2007/0212521; And 2010/0327237. According to one embodiment, the conductive particles are treated / coated with a coupling agent. The coupling agent improves not only the corrosion resistance of the conductive particles but also the wetting or wetting of the particles to electrodes having metal-OH or metal oxide moieties on the electrode surface, So that the conductive particles are readily available for electrical device bonding. More importantly, the surface treated conductive particles can be better dispersed while reducing the risk of agglomeration in the non-contact area or the adhesive in the spacing area between the electrodes. As a result, the risk of shorting in the X-Y plane is significantly reduced, especially in fine pitch applications.

Examples of coupling agents useful for the pretreatment of conductive particles include titanate, zirconate, 3-glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, gamma-mercapto ("SCA") such as organotrialkoxysilane comprising bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) do. Coupling agents containing thiol, disulfide and tetrasulfide functional groups are particularly useful for pretreating Au particles because they form Au-S bonds even under mild reaction conditions. See, for example, J. Am. Chem. Soc., 105 , 4481 (1983) Adsorption of Bifunctional Organic Disulfides on Gold Surfaces. The coupling agent may be present in an amount of about 5% to 100% of the surface coverage, more particularly about 20% to 100% of the surface coverage, and more particularly 50% to 100% of the surface coverage Can be applied to the surface. J. Materials Sci., Lett., 8, 99], 1040 (1989); Langmuir , 9 (11), 2965-2973 ( 1993 ); Thin Solid Films, 242 (1-2), 142 (1994); Polymer Composites, 19 (6), 741 (1997); see and "Silane Coupling Agents", 2 nd Ed., by EP Plueddemann, Plenum Press, (1991) and those of the reference document.

The microcaval array may be formed directly on the carrier web or on a cavity-forming layer that is pre-coated on the carrier web. Suitable materials for the web include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polycarbonate, polyamide, polyacrylate, polysulfone, polyether, polyimide, and liquid crystal polymers and blends thereof , Composites, laminates, or sandwich films. Suitable materials for the cavity-forming layer may include, but are not limited to, a thermoplastic material, a thermoset material or precursor thereof, a positive or negative photoresist, or an inorganic material. To achieve a high particle delivery yield, the carrier web may preferably be treated with a thin layer of release material to reduce the adhesion between the microcavity carrier web and the adhesive layer. The release layer can be applied by coating, printing, spraying, vapor deposition, thermal transfer, or plasma polymerization / crosslinking before or after the micro-cavitation step. Suitable materials for the release layer include fluoropolymers or oligomers, silicone oils, fluorosilicones, polyolefins, waxes, poly (ethylene oxide), poly (propylene oxides), surfactants with long chain hydrophobic blocks or branches, But are not limited to, coalescence or blends.

In one embodiment, particle deposition can be performed by applying a fluid particle distribution and trapping process, wherein each conductive particle is entrapped into one microcavity. A number of capture processes can be used. For example, in one embodiment described in Liang '700, a roll-to-roll continuous fluid particle distribution process can be used to capture only one conductive particle into each microcavity. The entrapped particles can then be transferred from the microcavity array to a predetermined location on the adhesive layer. Typically, the distance between these transferred conductive particles must be greater than the percolation threshold, which is the density threshold at which the conductive particles agglomerate.

The various pattern dimensions, shapes and spacings of the microcavities are described in US Patent Publication US 2006/0280912 to Liang and Liang '700. Fixed array patterns can vary. In the case of a circular microcavity, the pattern can be represented by X-Y, where X is the diameter of the cavity and Y is the distance between the edges between adjacent cavities in microns. Typical fine cavity pattern pitches include 4-3, 5-3, 5-5, 5-7, and 6-2 patterns. The selected pattern depends in part on the number of particles required for each electrode. The micro-cavity pattern can be staggered to reduce the minimum bonding space of the electrodes.

Adopting the particle filling procedure described in this embodiment, a surface-treated polyimide (PI) microcavity sheet having an array configuration of 6 mu m (open) x 2 mu m (spacing) x 4 mu m (depth) was filled with the particles. An epoxy film was prepared to a target thickness of about 15 mu m. The microporous sheet and the epoxy film were attached to the steel sheet face to face. The steel sheet was pushed through a commercially available HRL 4200 dry film roll laminator from Think & Tinker. The lamination pressure and lamination rate are adjusted such that this first array of particles has a good efficiency (greater than about 90%, preferably greater than about 95%) and a desired filling rate (e.g., For example about 40 to 90%), optionally using a calendaring or heating process, to allow a higher level of landfill. The second array of particles is then transferred to the film and the deposition pressure and deposition rate are adjusted to obtain the desired degree of embedding. The delivery of the second fixed array of particles may be further filled with an adhesive as a first array of particles according to the conditions. The pressure, temperature and velocity of the second array lamination are adjusted such that the first and second arrays are embedded in the epoxy adhesive at different desired different depths for the first and second arrays of particles. By tiering the depth of embedding in this manner, improved connection performance is achieved. In one embodiment, the first array is filled to about 40 to 90%, more typically about 50 to 80%, of the diameter of the particle. The second array is buried at about 10 to 60%, more typically about 30 to 60%, of the diameter of the particle, and the buried percentage is larger in one array than the remaining array. In particular, it is preferred that the first array particles are embedded in the adhesive by at least about 20%, preferably 30% deeper, than the depth of embedding of the second array particles.

The adhesive used in the ACF may be thermoplastic, thermoset, or a precursor thereof. Useful adhesives include, but are not limited to, pressure sensitive adhesives, hot melt adhesives, heat or radiation curable adhesives. The adhesive may be, for example, an epoxy, a phenol resin, an amine-formaldehyde resin, a polybenzoxazine, a polyurethane, a cyanate ester, an acrylate, an acrylate, a methacrylate, a vinyl polymer, a poly (styrene- And block copolymers thereof, polyolefins, polyesters, unsaturated polyesters, vinyl esters, polycaprolactones, polyesters, and polyamides. Epoxides, cyanate esters and polyfunctional acrylates are particularly useful. Catalysts or curing agents comprising latent curing agents may be used to control the curing power of the adhesive. Curing agents useful in epoxy resins include dicyanodiamide (DICY), adipic dihydrazide, 2-methylimidazole and its encapsulated products, such as liquids from Asahi Chemical Industry Novacure HX dispersion in bisphenol A epoxy; Ethylenediamine, diethylenetriamine, triethylenetetramine, BF3 amine adducts, amines such as Amicure from Ajinomoto Co. Inc.; But are not limited to, sulfonium salts such as diaminodiphenylsulfone, p-hydroxyphenylbenzylmethylsulfonium hexafluoroantimonate, and the like. In one embodiment, the particles may be coated with a coupling agent. Coupling agents including, but not limited to, titanates, zirconates and silane coupling agents such as glycidoxypropyltrimethoxysilane and 3-aminopropyltrimethoxysilane may also be used to improve the durability of ACFs . The effect of the curing agent and coupling agent on the performance of the epoxy-based ACF is described in [S. Asai, et al., J. Appl. Polym. Sci., 56, 769 (1995). A literature review is incorporated herein by reference. The dry adhesive thickness is typically in the range of 5 to 30 mu m, preferably in the range of 10 to 20 mu m.

Fluid assemblies of IC chips or solder balls into recessed regions or holes of a substrate or web of display material are disclosed, for example, in U.S. Patent Nos. 6,274,508, 6,281,038, 6,555,408, 6,566,744 and 6,683,663 have. Charging and top sealing of electrophoretic fluid or liquid crystal fluid into microcups of an embossed web is described, for example, in U.S. Patent Nos. 6,672,921, 6,751,008, 6,784,953, 6,788,452, and 6,833,943. The preparation of abrasive composite slurries comprising a plurality of abrasive particles dispersed in a precisely spaced abrasive article, a curable binder precursor, by filling the recesses of the embossed carrier web is described, for example, in U.S. Patent Nos. 5,437,754, 5,820,450, 5,219,462. All of the aforementioned U.S. patents are incorporated herein by reference in their entirety. In the aforementioned field, recesses, holes or microcups have been formed on the substrate by, for example, embossing, stamping or lithography processes. Subsequently, various devices for various applications including active matrix thin film transistor (AM TFT), ball grid array (BGA), electrophoresis and liquid crystal display were filled in recesses or holes. In a particular embodiment, the ACF is formed by fluid filling of conductive particles comprising only one conductive particle and a polymeric core and a metal shell in each microcavity or recess, as described in U.S. Patent Nos. 20150072109, 20120295098, As taught in these references, wherein the metal shell is encapsulated with an insulating polymer or coated with a coupling agent, more specifically a silane coupling agent, and the particles are partially embedded in the ACF adhesive layer.

The microcavity can be formed directly on a plastic web substrate with or without additional co-forming layer. Alternatively, the microcavity can be formed without an embossing mold, for example, by laser cutting or by a lithography process using a photoresist, followed by development and optionally etching or electroforming. Suitable materials for the cavity-forming layer may include, but are not limited to, a thermoplastic material, a thermoset material or precursor thereof, a positive or negative photoresist, or an inorganic or metallic material. In laser cutting, one aspect has a power ranging from about 0.1 W / cm < 2 > to about 200 W / cm < 2 > or more, applying from about 1 pulse to about 100 pulses using a pulse frequency of about 0.1 Hz to about 500 Hz Thereby generating an excimer laser beam for cutting. In a preferred embodiment, the laser cutting power is in the range of about 1 W / cm 2 to about 100 W / cm 2, using a pulse frequency of about 1 Hz to about 100 Hz and using about 10 pulses to about 50 pulses. It is also preferable to supply the carrier gas under vacuum to remove the residue.

In order to improve the transfer efficiency, the diameter of the conductive particles and the diameter of the cavity have specific tolerances. In order to achieve a high delivery rate, the diameter of the cavity preferably has a specific tolerance of from about 5% to less than about 10%, and the standard deviation requirement is based on the basis described in U.S. Patent Application Publication No. 2010/0101700.

In one embodiment, the particles in the non-random ACF microcavity array may have a particle size range that is approximately a single average particle size value, typically distributed from about 2 [mu] m to about 6 [mu] m, Lt; RTI ID = 0.0 > standard deviation. ≪ / RTI > In other embodiments characterized by a narrow distribution, it may be desirable for the narrow particle size distribution to have a standard deviation of less than about 5% from the average particle size. Typically, cavities having a selected cavity size are formed to accommodate particles having a selected particle size that is slightly smaller than the selected cavity size. To prevent the formation of particle clusters in the ACF, preferably, the average diameter of the cavity openings is slightly larger than the particle diameter but less than twice the particle diameter. More preferably, the average diameter of the cavity openings is greater than 1.5 times the particle diameter but less than twice the particle diameter.

Thus, in one embodiment, the microcavities in the non-random ACF microcavity arrays can have a coarse size range generally distributed at a single average cavity size value, typically from about 2 microns to about 6 microns, Include a narrow cavity size distribution with an average particle size of less than about 10% standard deviation. In other embodiments characterized by a narrow distribution, it may be desirable for the narrow cavity size distribution to have a standard deviation of less than 5% from the average cavity size.

In particular aspects, the present invention further describes a method of making an electronic device. The method comprises the steps of placing a plurality of electrically conductive particles in an array of microcavities comprising a coupling agent or an electrically conductive shell surface treated or coated with an insulating layer and a core material and then overcoating the layer of adhesive over the filled microcavity or And laminating. In one embodiment, placing the plurality of surface treated conductive particles in the array of microcavities includes using a fluid particle distribution process to trap each conductive particle into a single microcavity.

According to the above description, drawings and examples, the present invention is directed to a non-random fixed array in an adhesive layer at a predetermined two-tiered non-randomized particle location, (ACF) comprising treated particles, wherein the non-randomized particle position is selected from the group consisting of a plurality of predetermined microcostal positions of an array of microcavities for transporting and delivering the electroconductive particles to the adhesive layer ≪ / RTI > Conductive particles are sequentially transferred to the adhesive layer in the first and second arrays and are buried at different depths.

In addition to the above aspect, the present invention further describes an electronic device having an electronic part connected to the ACF of the present invention. In certain embodiments, the electronic device includes a display device. In another aspect, an electronic device includes a semiconductor chip. In another aspect, an electronic device includes a printed circuit board having printed wires. In another preferred embodiment, the electronic device comprises a flexible printed circuit board having printed wires.

Although the present invention has been described in detail with reference to specific embodiments thereof, it will be apparent that many modifications and variations are possible without departing from the scope of the following claims.

Claims (16)

As an anisotropic conductive film (ACF)
Board; An adhesive layer on the surface of the substrate; A first tier of conductive particles arranged in a non-random array embedded in the adhesive layer, the first tier comprising a carrier belt having a stitching line, ) Of the conductive particles to the surface of the adhesive layer, the portion of the first tier corresponding to the stitching line being essentially or essentially free of conductive particles; And a second tier of conductive particles arranged in a non-random array embedded in the adhesive layer and overcoating a portion of the first tier corresponding to the stitching line. 2. The method of claim 1, wherein the ACF comprises a first non-random array of particles partially or entirely embedded in the adhesive layer at a first depth, and a second non-random array of particles partially or entirely embedded at the same or second depth in the adhesive layer. Lt; RTI ID = 0.0 > ACF < / RTI > 3. The ACF of claim 2, wherein in the first or second array, at least about 10% of the partially buried conductive particles are exposed on the surface of the adhesive layer, based on the diameter of the particles. 4. The ACF of claim 3, wherein at least about 30% of the partially buried particles are exposed on the surface of the adhesive layer. 3. The method of claim 2, wherein the first array of conductive particles is about 40-90% embedded and the second array of conductive particles is about 10-60% embedded, with the depth of the first and second arrays Apparently different, ACF. 2. The ACF of claim 1, wherein in addition to the particles in the first and second tiers, the adhesive layer contains conductive particles dispersed therein. 7. The method of claim 6, wherein the ACF transfers a first tier of a stationary array of conductive particles to a surface of an adhesive layer of an ACF, excluding a region of the stitching line, and at least a second tier of a stationary array of conductive particles, Lt; RTI ID = 0.0 > ACF < / RTI > 7. The ACF of claim 6, wherein the ACF further comprises a separate, non-conductive adhesive layer superimposed on a tier of conductive particles. The ACF of claim 1, wherein the adhesive layer has orthogonal X and Y directions, and wherein the particles in the stationary, non-random array have a pitch of about 3 to 30 micrometers in the X and / or Y direction. 10. The ACF of claim 9, wherein the particle sites are arranged in an array having a pitch of about 4 to 12 micrometers in the X and / or Y direction. 4. The ACF of claim 3 wherein the first and second tiers are at least partially overlaid. 12. The ACF of claim 11, wherein the adhesive layer is about 5 to 30 占 퐉 thick. 13. The ACF of claim 12, wherein the adhesive layer is about 10 to 25 占 퐉 thick. 3. The ACF of claim 2 wherein two or more tiers of conductive particles are present. 3. The ACF of claim 2, wherein the depths of the first and second tiers are different. 3. The ACF of claim 2, wherein the depths of the first and second tiers are the same.

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