Method for forming active coating film on solder particles

Abstract

The method for forming an active coating film on solder particles according to the present invention comprises: a step for cleaning solder particles and a solvent by adding the solder particles and the solvent to a stirrer; a step of further adding an active agent into the stirrer, and forming an active coating film on the surfaces of the solder particles by press-fitting through collision of the plurality of falling solder particles; and a step of removing the solvent from the solder particles and drying the solder particles.

Description

Technical Field

[0001] The present invention relates to a method for forming an active coating film on solder particles, and more particularly, to a method for forming an active coating film on solder particles by compression bonding, wherein the active coating film is provided in a resin film and is used to form a soldering portion between terminals. Background Art

[0002] Generally, in order to manufacture electronic devices, electronic components such as semiconductor chips or terminals of various substrates are connected to each other. To achieve this connection, anisotropic conductive films or solder pastes are used.

[0003] Anisotropic conductive films are not only used for connecting semiconductor chips and flexible printed circuit boards (COF, Chip On Film), but also for connecting flexible printed circuit boards and glass substrates (FOG, Film On Glass), and connecting flexible printed circuit boards and glass epoxy boards (FOB, Film On Board).

[0004] In the anisotropic conductive film, conductive particles are dispersed in a resin film.

[0005] The conductive particles are made of metal particles such as nickel or metal-plated resin particles. The anisotropic conductive film is generally prepared by mixing the conductive particles in a thermosetting resin and then hardening and processing the mixture into a film form.

[0006] The method of forming a connection structure using an anisotropic conductive film is as follows.

[0007] When the anisotropic conductive film is inserted between the first connection object part and the second connection object part and heated and pressurized, the plurality of terminals of the first connection object part and the second connection object part are electrically connected via the pressurized conductive particles, and the resin film melted by the heat hardens again, thereby maintaining the electrical connection.

[0008] In the case of anisotropic conductive films, there are problems such as high manufacturing costs of conductive particles, and conductive particles made of metal particles penetrate into the terminals and damage the terminals. Metal-plated resin particles have residual stress acting in the direction of separating the distance between the terminals, thus negatively affecting the durability and connection reliability of the connection structure.

[0009] Also, the connection method using an anisotropic conductive film has a problem in that the connection process takes a long time until the resin particles are completely hardened and the distance between the terminals can be maintained.

[0010] On the other hand, solder paste is formed by mixing solder particles, flux and activator in resin paste. After applying the solder paste to the terminals of the first connection object part and the second connection object part by screen printing, the solder particles melt and self-assemble through the reflow process, thereby achieving electrical connection between the terminals. Connection using solder paste has the following problems: it is difficult to accurately adjust the amount of solder paste applied, and it is also difficult to apply the solder paste only to a local area, making it difficult to achieve electrical connection on ultra-fine circuit boards.

[0011] In addition, the solder particles used in solder paste are mainly processed into the particle form of lead-tin material, and then can be used by coating the surface with antistatic agent, etc. This coating is mainly achieved by dipping or spraying, and there is a problem that the coating often peels off due to its weak adhesion strength.

[0012] Furthermore, depending on the situation, a connection structure formed of solder paste may require an underfill that fills a space between the first connection target component and the second connection target component with a resin, and thus a separate underfill formation process may be required after forming the connection structure.

[0013] On the other hand, as the solder particles used in the conventional soldering surface, as disclosed in Korean Patent No. 1205839, metal nanoparticles are sometimes pressed into the ball milling device by the falling and collision of the ball milling balls. However, the patent discloses that the solder particles have a diameter of 5 to 50 μm, and when they collide with ordinary ball milling balls with a minimum diameter of about 800 μm, the solder particles tend to deform, or the solder particles aggregate together, resulting in the problem of difficulty in filtering them out in subsequent screening work.

[0014] In order to solve the problems of the conventional connection method using anisotropic conductive film and solder paste, the present applicant filed a patent application for solder particles having an active coating film formed by an activator, and a connection film made of such solder particles.

[0015] When solder particles are mixed into the film for connection, it is difficult to supply the activator separately by including it in the resin film, so it is necessary to form the activator in the form of a coating on the solder particles. However, according to the conventional coating method, the coating cannot be uniformly formed on the surface of the particles and is easily peeled off, so in the actual connection process, there is a problem that the activator cannot be accurately supplied to the welding area. Summary of the invention

[0016] Technical issues

[0017] The object of the present invention is to provide a method for forming an active coating film by forming an active agent by press bonding, so as to smoothly cause interface phenomena such as adsorption, dissolution, penetration and diffusion on the surface of solder particles during soldering.

[0018] Solutions to the problem

[0019] The method for forming an active coating on solder particles of the present invention comprises:

[0020] The step of adding solder particles and solvent to a blender for cleaning;

[0021] A step of further adding an activator to the mixer and forming an active coating film on the surface of the solder particles by pressing the plurality of falling solder particles together through collision; and

[0022] The step of removing the solvent from the solder particles and performing drying.

[0023] Preferably, the weight ratio of the solder particles added to the mixer to the solvent is 1.5 to 3.5:1.

[0024] Preferably, the solvent is one or more of acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), water or alcohol.

[0025] Preferably, the diameter of the solder particles is in the range of 1 to 100 μm.

[0026] Preferably, the active agent of the present invention is selected from at least one of the group consisting of butylamine hydrobromide, butylamine hydrochloride, ethylamine hydrobromide, pyridine hydrobromide, cyclohexylamine hydrobromide, ethylamine hydrochloride, 1,3-diphenylguanidine hydrobromide, 2,3-dibromo-1-propanol, oxalic acid, malonic acid, succinic acid, adipic acid, pimelic acid, palmitic acid, DL-malic acid and suberic acid.

[0027] Preferably, the step of forming the active coating film on the surface of the solder particles by pressure bonding is performed by adding an active agent in an amount of 1 to 6% of the weight of the added solder particles and running a stirrer for 5 to 30 hours.

[0028] Preferably, the step is performed by adding 0.5-5.5% of the activator by weight of the solder particles and running the mixer for 2-28 hours, and then further adding 0.5-5.5% of the activator by weight of the solder particles and running the mixer for 2-28 hours.

[0029] Preferably, the stirrer rotates at 150 rpm to 250 rpm.

[0030] Preferably, the drying step is a step of drying at a temperature of 50 to 90° C. under vacuum for 10 to 24 hours.

[0031] Effects of the Invention

[0032] According to the present invention, there is an effect that the adhesion strength of the active coating film formed on the solder particles can be increased, and thus the solder particles can be contained in the resin film for use. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The following are photographs showing solder particles before and after forming an active coating film according to an embodiment of the present invention.

[0034] Figure 2 To show Figure 1 Photographs of the melting morphologies of multiple solder particles. DETAILED DESCRIPTION

[0035] Hereinafter, the present invention will be described in more detail based on examples.

[0036] The diameter of the solder particles used in the present invention is in the range of 1 to 100 μm. In the embodiment, taking into account the size of the region where the solder particles are to be used, it is preferred to select a diameter range of 25 to 45 μm, 8 to 25 μm, or 3 to 8 μm.

[0037] As solder particles for connecting ultrafine circuit boards, solder particles having a diameter of less than 5 μm are preferably used.

[0038] As the solder particles, it is preferable to use a tin (Sn)-bismuth (Bi)-based low melting point solder material.

[0039] In order to form an active coating film on solder particles, first, the solder particles are added to a stirrer together with a solvent.

[0040] The solvent used in this embodiment is a ketone solvent, preferably acetone, methyl ethyl ketone (MEK) or methyl isobutyl ketone (MIBK). As the solvent, water or alcohol is also preferably used.

[0041] The solder particles and the solvent are added in a weight ratio of 1.5 to 3.5:1.

[0042] After adding the solder particles and the solvent, the stirrer is operated at a rotation speed of 150 to 250 rpm. If the rotation speed is less than 150 rpm, the rotation speed is slow, resulting in low productivity, and if the rotation speed is more than 250 rpm, the solvent and the solder particles rotate together with the rotating barrel due to centrifugal force, so cleaning or pressing cannot be performed.

[0043] The plurality of solder particles that rise to a predetermined height along the rotating drum collide with each other when falling, thereby removing and cleaning the oxide scale on the surface. This cleaning step is preferably performed within a range of 30 minutes to 2 hours.

[0044] After the cleaning step, the active agent is added to the rotating drum.

[0045] In this embodiment, the active agent is selected from at least one of the group consisting of butylamine hydrobromide, butylamine hydrochloride, ethylamine hydrobromide, pyridine hydrobromide, cyclohexylamine hydrobromide, ethylamine hydrochloride, 1,3-diphenylguanidine hydrobromide, 2,3-dibromo-1-propanol, oxalic acid, malonic acid, succinic acid, adipic acid, pimelic acid, palmitic acid, DL-malic acid and suberic acid.

[0046] Preferably, the amount of the active agent added is 1-6% of the weight of the solder particles added. If the amount of the active agent added is less than 1%, the mixer must run too long to obtain the desired active coating, and if it is greater than 6%, a large amount of active agent will remain after the active coating is formed.

[0047] If the stirrer is rotated after the activator is added, multiple solder particles collide with each other, and the activator is pressed onto the outer surface of the collided solder particles to form an active coating. As described in this embodiment, when the active coating is formed by the collision force between the solder particles, the close adhesion strength of the active coating can be greatly improved.

[0048] Furthermore, unlike conventional ball milling, since the solder particles collide with each other due to their own weight, multiple solder particles will not aggregate together or their particle shapes will not change.

[0049] Furthermore, the step of pressing and forming an active coating on the surface of the solder particles is preferably carried out in the following two stages: first, 0.5 to 5.5% of the weight of the solder particles is added as an activator and the mixer is operated for 2 to 28 hours (first stage pressing), and then 0.5 to 5.5% of the weight of the solder particles is further added as an activator and the mixer is operated for 2 to 28 hours (second stage pressing).

[0050] More preferably, the first stage pressing is performed for 16 hours and the second stage pressing is performed for 7 hours.

[0051] Dividing the lamination process into two stages as described above means that in the first stage, the active agent is evenly physically pressed onto the solder particle surface, and in the second stage, the active agent is again pressed onto the active coating film formed by the pressing, so that a uniform and dense active coating film can be formed on the solder particle surface. (See Figure 1 )

[0052] In this embodiment, the mixer is described as allowing multiple solder particles that rise to a specified height along a rotating barrel to collide with each other when falling, but any device that can move the solder particles and make them collide with each other, such as a device that lifts multiple solder particles by rotating a screw and causes them to fall and collide, should be considered to fall within the scope of the mixer of the present invention.

[0053] After the coating film is formed, the solder particles are separated from the solvent and then added to a vacuum oven and dried at a temperature range of 50 to 90°C for 10 to 24 hours.

[0054] Once the drying step as described above is completed, the work of pressure-forming the active coating film on the surface of the solder particles is completed.

[0055] Figure 1 Part (a) is an electron micrograph of solder particles before the active coating is formed, part (b) is an electron micrograph of solder particles with active coating formed by immersion, and part (c) is an electron micrograph of solder particles with active coating formed by the lamination method of this embodiment. The active coating formed by lamination penetrates into the surface irregularities of the solder particles better than the active coating formed by immersion, forming a smooth spherical shape, and it can be confirmed that the active coating is uniformly formed even on solder particles of about 2 to 3 μm.

[0056] Figure 2 For the general Figure 1 The photo was taken 5 seconds after multiple particles were placed on an aluminum dish with a surface temperature of 240°C. The multiple solder particles without active coatings did not melt at all, the solder particles with active coatings formed by immersion only partially melted, and the solder particles with active coatings formed by the lamination method of this embodiment melted completely. Figure 2 It was confirmed that the solder particles having the active coating film formed thereon by the pressure bonding method of this example melt more easily.

[0057] On the other hand, the solder particles having the active coating film formed by immersion were oxidized at 198° C., while the solder particles having the active coating film formed by the press bonding method of this example were oxidized at 225° C., and thus had excellent oxidation resistance.

[0058] Industrial Applicability

[0059] The present invention can be used industrially by forming an active coating film by compression bonding on solder particles that are provided in a resin film and are used to form a soldering portion between terminals.

Claims

1. A method for forming an active coating on solder particles, characterized in that: include: The step of adding solder particles and solvent in a weight ratio of 1.5 to 3.5:1 into a mixer for cleaning; A step of further adding an activator in an amount of 1 to 6% of the weight of the solder particles added to the mixer, and causing the plurality of solder particles that have risen to a predetermined height to fall and collide with each other as the mixer rotates, thereby forming an active coating film on the surface of the solder particles by pressing; and The step of removing the solvent from the solder particles and performing drying.

2. The method for forming an active coating on solder particles according to claim 1, characterized in that: The solvent is one or more of acetone, methyl ethyl ketone, methyl isobutyl ketone, water or alcohol.

3. The method for forming an active coating on solder particles according to claim 1, characterized in that: The diameter of the solder particles is in the range of 1 to 100 μm.

4. The method for forming an active coating on solder particles according to claim 1, characterized in that: The active agent is at least one selected from the group consisting of butylamine hydrobromide, butylamine hydrochloride, ethylamine hydrobromide, pyridine hydrobromide, cyclohexylamine hydrobromide, ethylamine hydrochloride, 2,3-dibromo-1-propanol, oxalic acid, malonic acid, succinic acid, adipic acid, pimelic acid, DL-malic acid and suberic acid.

5. The method for forming an active coating on solder particles according to claim 1, characterized in that: The step of forming the active coating film on the surface of the solder particles by pressure bonding is performed by operating a stirrer for 5 to 30 hours after adding the activator.

6. The method for forming an active coating on solder particles according to claim 5, characterized in that: The step is performed by adding 0.5 to 5.5% of the activator by weight of the solder particles and running the stirrer for 2 to 28 hours, and then further adding 0.5 to 5.5% of the activator by weight of the solder particles and running the stirrer for 2 to 28 hours.

7. The method for forming an active coating on solder particles according to claim 1, characterized in that: The stirrer rotates at 150 rpm to 250 rpm.

8. The method for forming an active coating on solder particles according to claim 1, characterized in that: The drying step is a step of drying at a temperature of 50 to 90° C. under vacuum for 10 to 24 hours.

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