Cleaning method

Abstract

A cleaning method to prevent connection failures when mounting micro LED chips onto a circuit board. [Solution] The present invention is a method for manufacturing an LED mounting substrate, comprising the step of cleaning an LED chip 5, which has been transferred from a sapphire substrate to a receptor substrate 2 by laser lift-off, with an alkaline cleaning solution 6. This provides a method for manufacturing an LED mounting substrate that can selectively remove the metal Ga adhering to the LED chip transferred from the sapphire substrate to the receptor substrate by laser lift-off without dissolving or altering other metals, a cleaning solution that can be used therefor, a cleaning method for selectively removing gallium 4 adhering to an LED chip without dissolving or altering other metals, and a cleaning method for selectively removing gallium from a component having gallium and other metals on its surface without dissolving or altering the other metals.

Description

Technical Field

[0007] ,

[0001] The present invention relates to a method for manufacturing an LED mounting substrate, a cleaning liquid, and a cleaning method.

Background Art

[0008] During the LLO process, opaque metallic Ga deposits form on the surface of the detached micro-LED chips. When these deposited metallic Ga deposits were removed from the LED chips using an acidic cleaning solution and the cleaned LED chips were mounted onto a substrate, connection failures occurred. The inventors investigated various possibilities to determine the cause of these connection failures and noticed that the shape of the bumps had changed from their original state before connection. They then determined that this change was due to the bumps dissolving or deforming due to the acidic cleaning solution used in the cleaning process.

[0009] Here, when the LED chip was LLO'd from the sapphire substrate to the receptor substrate, the side with the bumps was adhered to the receptor substrate and appeared to be protected from the cleaning solution, yet dissolution and deformation occurred during the cleaning process. In other words, it was thought that a gap existed between the LED chip and the receptor substrate due to steps such as bumps, and that the cleaning solution penetrated through this gap, dissolving and deforming the bumps.

[0010] As shown in Figure 5, the metals used in the bumps (such as In and SnAgCu alloys (SAC)) and Ga (gallium) are often close together in the periodic table, making it difficult to selectively remove gallium when the bumps and gallium are in contact with the cleaning solution. Therefore, the inventors first considered protecting the bumps from the cleaning solution by deeply embedding them in the adhesive layer of the receptor substrate. However, it was found that while this method could protect the bumps from the cleaning solution, it made it difficult to peel the adhesive layer from the bumps in subsequent steps.

[0011] Here, being close to gallium in the periodic table means being close to the position of gallium in the 4th period and group 13. For example, it may be a position in the range of the 3rd to 6th periods and groups 11 to 15, or it may be a position in the range of the 3rd to 5th periods and groups 11 to 14.

[0012] Thus, it has become clear that there is a need for a cleaning method or cleaning solution that can selectively remove metallic Ga from components such as LED chips that have metallic Ga and other metals on their surface, without affecting the metals other than metallic Ga.

[0013] The present invention has been made to solve the above problems, and aims to provide a method for manufacturing an LED mounting substrate that can selectively remove the metal Ga (hereinafter sometimes simply referred to as "Ga" or "gallium") adhering to an LED chip transferred from a sapphire substrate to a receptor substrate by laser lift-off, without dissolving or altering other metals, a cleaning solution that can be used therefor, a cleaning method for selectively removing gallium adhering to an LED chip without dissolving or altering other metals, and a cleaning method for selectively removing gallium from a component having gallium and other metals on its surface without dissolving or altering the other metals. [Means for solving the problem]

[0014] To achieve the above objective, the present invention provides a method for manufacturing an LED mounting substrate, which includes a step of cleaning an LED chip transferred from a sapphire substrate to a receptor substrate by laser lift-off with an alkaline cleaning solution.

[0015] This method of manufacturing LED mounting substrates allows for the removal of unwanted gallium without dissolving or altering metals such as bumps on the LED chips, thereby enabling the production of high-quality LED mounting substrates.

[0016] At this time, the LED chip transferred onto the receptor substrate has gallium on the side opposite to the receptor substrate, and the gallium can be removed by the cleaning process.

[0017] The cleaning step in the method for manufacturing an LED mounting substrate of the present invention is particularly effective when removing gallium from such LED chips.

[0018] In this case, the alkalinity of the alkaline cleaning solution can be set to 0.5% by mass or more and below the saturation concentration. The temperature of the alkaline cleaning solution can be set to 5°C or more and 80°C or less. The cleaning time with the alkaline cleaning solution can be set to 10 seconds or more and 1 hour or less.

[0019] Under these conditions, gallium can be selectively removed more stably and reliably.

[0020] In this case, the LED chip on the side that is bonded to the receptor substrate may have bumps.

[0021] The method for manufacturing an LED mounting substrate of the present invention is particularly effective when manufacturing an LED mounting substrate having bumps from such LED chips.

[0022] In this case, the bumps may be formed from lead-free solder. Furthermore, the bumps may have at least one selected from SnAgCu alloys, SnZnBi alloys, SnCu alloys, SnAgInBi alloys, SnZnAl alloys, and indium as their main component.

[0023] The method for manufacturing an LED mounting substrate according to the present invention is particularly effective when dealing with LED chips having such bumps.

[0024] At this time, the LED chip transferred onto the receptor substrate can be cleaned by immersing the receptor substrate together with the LED chip in the alkaline cleaning solution.

[0025] Thereby, the LED mounting substrate can be manufactured more easily.

[0026] The present invention also provides a cleaning liquid for cleaning an LED chip provided on a sapphire substrate after transferring it to a receptor substrate by laser lift-off, the cleaning liquid being alkaline.

[0027] According to such a cleaning liquid, unnecessary gallium can be selectively removed without dissolving or denaturing metals such as bumps of the LED chip.

[0028] At this time, the cleaning liquid can have a pH of 9.5 to 14.0. Further, the cleaning liquid can be an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium hydrogen carbonate, and potassium acetate.

[0029] Thereby, simpler and more stable cleaning can be performed.

[0030] The present invention also provides a cleaning method for cleaning an LED chip separated from a sapphire substrate by laser lift-off, the cleaning method being performed using an alkaline cleaning liquid.

[0031] According to such a cleaning method for cleaning an LED chip, unnecessary gallium can be selectively removed without dissolving or denaturing metals such as bumps of the LED chip.

[0032] At this time, the LED chip can be transferred onto a receptor substrate.

[0033] The cleaning method of the present invention is particularly effective when cleaning such an LED chip.

[0034] The present invention also provides a cleaning method for selectively removing gallium from a part having gallium and a metal other than gallium on its surface, wherein the part is cleaned using an alkaline cleaning solution.

[0035] This cleaning method, which selectively removes gallium, allows for the selective removal of gallium in a simple manner without dissolving or altering other metals.

[0036] In this case, the alkaline cleaning solution can be brought into contact with the gallium and other metals during the cleaning process.

[0037] This allows for the selective removal of gallium without dissolving or altering other metals, using a simpler method.

[0038] In this case, the component may be in the form of a substrate, fixed to another substrate during cleaning, the gallium may be present on the side of the component opposite to the side facing the other substrate, and the metals other than gallium may be present on the side facing the other substrate.

[0039] The cleaning method of the present invention is particularly effective when cleaning such parts.

[0040] In this case, the metal other than gallium may be at least one metal selected from the group consisting of aluminum, copper, zinc, silver, indium, tin, and bismuth. Furthermore, the metal other than gallium may be at least one metal selected from the group consisting of copper, silver, indium, and tin. Furthermore, the metal other than gallium may be copper, silver, and tin.

[0041] Other metals besides gallium are less likely to dissolve or denature, making them more stable. [Effects of the Invention]

[0042] As described above, the method for manufacturing an LED mounting substrate according to the present invention makes it possible to selectively remove unwanted gallium without dissolving or altering metals such as bumps on the LED chips, thereby manufacturing a high-quality LED mounting substrate and reducing connection failures of LED chips.

[0043] Furthermore, the cleaning solution of the present invention can selectively remove unwanted gallium without dissolving or altering metals such as bumps on the LED chip, thereby reducing connection failures of the LED chip.

[0044] Furthermore, the cleaning method for cleaning LED chips separated from a sapphire substrate by laser lift-off according to the present invention makes it possible to selectively remove unwanted gallium without dissolving or altering metals such as bumps on the LED chip, thereby reducing connection failures of the LED chip.

[0045] Furthermore, the cleaning method for selectively removing gallium according to the present invention makes it possible to selectively remove unwanted gallium from parts having gallium and other metals on their surface in a simple manner without dissolving or altering the other metals.

[0046] In this invention, it is preferable that metals such as bumps and metals other than gallium are not dissolved at all. However, if the amount of gallium removed is greater than the amount of metals such as bumps and metals other than gallium removed, and gallium can be selectively removed, then metals such as bumps and metals other than gallium may be dissolved to a degree that is practical. [Brief explanation of the drawing]

[0047] [Figure 1] This is a diagram illustrating an example of a cleaning process according to the present invention. [Figure 2] The conditions and evaluation results for Examples 1-3 and Comparative Examples 1 and 2 are shown. [Figure 3] The evaluation results for Example 4 are shown below. [Figure 4] The evaluation results for Comparative Example 3 are shown below. [Figure 5] This is a diagram (periodic table) illustrating examples of metal elements that are removed or not removed by cleaning. [Figure 6] This is a schematic diagram illustrating gap-laser lift-off (Gap-LLO). [Figure 7] This is a schematic diagram illustrating Contact-Laser Lift-Off (LLO). [Modes for carrying out the invention]

[0048] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0049] As described above, there was a need for a method for manufacturing an LED mounting substrate that can selectively remove metallic Ga attached to an LED chip transferred from a sapphire substrate to a receptor substrate by laser lift-off without dissolving or altering other metals, a cleaning solution that can be used therefor, a cleaning method that selectively removes gallium attached to an LED chip without dissolving or altering other metals, and a cleaning method that selectively removes gallium from a component having gallium and other metals on its surface without dissolving or altering the other metals.

[0050] As a result of diligent research into the above-mentioned problems, the inventors have discovered that a method for manufacturing an LED mounting substrate, which includes a step of cleaning the LED chips transferred from a sapphire substrate to a receptor substrate by laser lift-off with an alkaline cleaning solution, can selectively remove unwanted gallium without dissolving or altering metals such as bumps on the LED chips, thereby enabling the manufacture of high-quality LED mounting substrates and reducing LED chip connection failures. This has led to the completion of the present invention.

[0051] The inventors have also discovered that a cleaning solution for cleaning an LED chip provided on a sapphire substrate after it has been transferred to a receptor substrate by laser lift-off, which is alkaline, can selectively remove unwanted gallium without dissolving or altering metals such as bumps on the LED chip, thereby reducing connection failures of the LED chip, and thus completed the present invention.

[0052] The inventors have also discovered a cleaning method for cleaning LED chips separated from a sapphire substrate by laser lift-off, which uses an alkaline cleaning solution to selectively remove unwanted gallium without dissolving or altering metals such as bumps on the LED chips, thus completing the present invention.

[0053] The present inventors have also found that a cleaning method for selectively removing gallium from a part having gallium and a metal other than gallium on its surface, wherein the part is cleaned using an alkaline cleaning solution, makes it possible to selectively remove unwanted gallium in a simple manner without dissolving or altering the metal other than gallium, thus completing the present invention.

[0054] The following explanation will be given with reference to the drawings.

[0055] As described above, the inventors diligently studied to solve the aforementioned problems and, surprisingly, discovered that by using an alkaline aqueous solution as a cleaning solution, gallium can be selectively removed without affecting metals other than gallium, even without physically protecting the bumps. The fact that gallium can be selectively removed using such a simple method as an alkaline aqueous solution as a cleaning solution can lead to simplification of the production process and improvement of yield, representing a significant step towards reducing the cost of micro-LED displays, which are said to cost tens of millions of yen per unit. The present invention will be described in more detail below.

[0056] [Cleaning solution] The cleaning solution according to the present invention is an alkaline cleaning solution for cleaning LED chips that have been placed on a sapphire substrate after being transferred to a receptor substrate by laser lift-off. With the cleaning solution according to the present invention, unwanted gallium can be selectively removed without dissolving or altering metals such as bumps on the LED chip, thereby reducing connection failures of the LED chip.

[0057] Such cleaning solutions are not particularly limited as long as they are alkaline, but those with a pH of 9.5 to 14.0 are preferred. This allows for stable and reliable selective removal of Ga without dissolving or denaturing metals such as bumps on LED chips.

[0058] Furthermore, the cleaning solution according to the present invention may be an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium bicarbonate, and potassium acetate. Such aqueous solutions are relatively easy to obtain and handle, and are low-cost.

[0059] Preferred conditions for cleaning using the cleaning solution according to the present invention will be described later.

[0060] [Manufacturing method for LED mounting boards] The method for manufacturing an LED mounting substrate according to the present invention includes a step of cleaning the LED chip, which has been transferred from a sapphire substrate to a receptor substrate by laser lift-off, with an alkaline cleaning solution. The laser lift-off method is not particularly limited, but gap-laser lift-off (Gap-LLO) and contact-laser lift-off (Contact-LLO) are applicable. These methods will be described in general terms below with reference to Figures 6 and 7.

[0061] In Gap-LLO, first, as shown in Figure 6(a), a sapphire substrate 1 equipped with, for example, an LED chip 5 to be transferred, and a receptor substrate 2, such as a quartz substrate, which has an adhesive layer 3 such as silicone on its surface, are placed facing each other with a space between the LED chip 5 and the adhesive layer 3, i.e., a gap is created. In this state, a laser 20 is shone from a laser oscillator 110 through the side of the sapphire substrate 1 opposite to the LED chip 5, onto the interface 11 between the multiple LED chips 5 and the sapphire substrate 1. Generally, the laser 20 is shone one by one onto the entire surface of the interface 11 between each LED chip 5 and the sapphire substrate 1 in sequence.

[0062] For example, in the case of a sapphire substrate 1 equipped with multiple LED chips 5, each containing a gallium nitride-based semiconductor layer such as a GaN layer at the interface 11, irradiation with a laser 20 causes the GaN layer to decompose (ablate). When the bonding force (adhesion, bonding force, etc.) between the LED chips 5 and the sapphire substrate 1 weakens due to ablation, the LED chips 5 are peeled off from the sapphire substrate 1. In addition, the decomposition of the GaN layer generates gas (e.g., nitrogen gas). The pressure of this gas provides a propulsion force for the peeled LED chips 5 toward the receptor substrate 2, causing them to move through the space between the sapphire substrate 1 and the receptor substrate 2 and reach the adhesive layer 3 on the receptor substrate 2. In this way, the LED chips 5 are transferred onto the receptor substrate 2. Next, as shown in Figure 6(b), the sapphire substrate 1 is removed. This completes the transfer of the LED chips 5 from the sapphire substrate 1 to the receptor substrate 2.

[0063] Contact-LLO is similar to Gap-LLO, except that when the laser 20 is irradiated, the sapphire substrate 1 equipped with the LED chip 5 to be transferred and the receptor substrate 2 having an adhesive layer 3 on its surface are placed facing each other with the LED chip 5 and the adhesive layer 3 in contact, as shown in Figure 7(a). After irradiation with the laser 20, the transfer of the LED chip 5 from the sapphire substrate 1 to the receptor substrate 2 is completed by removing the sapphire substrate 1 as shown in Figure 7(b).

[0064] In such an LLO process, metallic Ga remains on components such as the LED chip 5 due to the decomposition of gallium nitride-based semiconductor layers such as the GaN layer. In this invention, the LED chip 5 is cleaned using an alkaline cleaning solution to remove this metallic Ga. This allows for the selective removal of unwanted gallium without dissolving or altering metals such as bumps on the LED chip, thereby reducing connection failures of the LED chip.

[0065] The alkaline cleaning solution used here can be the alkaline cleaning solution described above.

[0066] The alkalinity of the alkaline cleaning solution is preferably 0.5% by mass or more, and below the saturation concentration. The temperature of the alkaline cleaning solution is preferably 5°C or higher and 80°C or lower. The temperature of the cleaning solution is preferably 5°C or higher, so as not to freeze. If the temperature is too high, the gallium removal effect will not change, so it is fine to keep it below 80°C. Furthermore, the cleaning time with the alkaline cleaning solution is preferably 10 seconds or more and 1 hour or less. By cleaning for 10 seconds or more, Ga can be removed selectively and more stably and reliably. If the cleaning time is too long, the gallium removal effect will not change, so it is fine to keep it below 1 hour. In addition, by appropriately combining the alkalinity, temperature of the alkaline cleaning solution, and cleaning time mentioned above, gallium can be removed selectively and even more stably and reliably.

[0067] As described above, the LED chip transferred onto the receptor substrate has gallium on the side opposite to the receptor substrate. The LED chip also has bumps on the side that is bonded to the receptor substrate. The gallium on the side opposite to the receptor substrate can be easily removed by cleaning with an alkaline cleaning solution.

[0068] In the method for manufacturing an LED mounting substrate according to the present invention, the bumps are preferably formed from lead-free solder, and more preferably have at least one selected from SnAgCu(SAC) alloy, SnZnBi alloy, SnCu alloy, SnAgInBi alloy, SnZnAl alloy, and indium as the main component. In particular, when such bumps are used, even when cleaning with an alkaline cleaning solution, the dissolution and deformation (damage) of the bumps can be reliably and stably prevented.

[0069] Figure 1 shows an example of a process for cleaning an LED chip with an alkaline cleaning solution. As shown in Figure 1, in the process of cleaning an LED chip with an alkaline cleaning solution in the method for manufacturing an LED mounting substrate according to the present invention, it is preferable to clean the LED chip 5, which has been transferred onto the receptor substrate 2, by immersing the receptor substrate 2 together with the LED chip 5 in the alkaline cleaning solution 6. This allows for the selective removal of gallium 4 more simply, reliably, and stably. More specifically, as shown in Figure 1, the receptor substrate 2 on which the LED chip 5 has been transferred is immersed in a cleaning container filled with the alkaline cleaning solution 6, and then the substrate can be cleaned with pure water or the like an appropriate number of times and dried (air-dried).

[0070] [How to clean LED chips] The present invention also provides a cleaning method for cleaning LED chips separated from a sapphire substrate by laser lift-off as described above, using an alkaline cleaning solution. With such a cleaning method, gallium can be selectively removed by cleaning without dissolving or altering metals other than gallium, and as a result, connection failures of the LED chips can be reduced. Furthermore, in the cleaning method according to the present invention, it is preferable that the LED chips are transferred onto a receptor substrate. A specific example of the LED chip cleaning method is the same as that described with reference to Figure 1 above.

[0071] [Cleaning method for selectively removing gallium from parts] As described above, the inventors have found that by cleaning LED chips separated from sapphire substrates by laser lift-off using an alkaline cleaning solution, gallium can be selectively removed without dissolving or altering other metals. Further research has shown that this method is not limited to LED chips; even when selectively removing gallium from components having gallium and other metals on their surface, gallium can be selectively removed without dissolving or altering other metals by cleaning the components with an alkaline cleaning solution, using an extremely simple method.

[0072] In such cleaning methods, it is particularly preferable to clean gallium and other metals by contacting them with an alkaline cleaning solution. This allows for the selective removal of gallium without dissolving or altering other metals, making the process simpler.

[0073] Furthermore, it is preferable that the component to be cleaned is in the form of a substrate and is fixed to another substrate during cleaning, and that gallium is present on the side of the component opposite to the other substrate side, while other metals are present on the side of the component that is opposite to the other substrate side.

[0074] The metal other than gallium is preferably at least one metal selected from the group consisting of aluminum, copper, zinc, silver, indium, tin, and bismuth, more preferably at least one metal selected from the group consisting of copper, silver, indium, and tin, and even more preferably copper, silver, and tin. This is because if the metal other than gallium is of this type, dissolution and modification during cleaning can be suppressed more stably.

[0075] In this invention, the gallium to be removed may exist in a state of 100% purity, or in the form of oxides or nitrides. Furthermore, these states may be present in combination. The gallium content of the material to be removed is effective when it is 50% by volume or more, preferably 70% by volume or more, and more preferably 90% by volume or more.

[0076] Furthermore, in this invention, a higher selectivity ratio, which is the ratio of the dissolution rate of gallium to the dissolution rate of other metals, is more effective. This selectivity ratio may be 1 or more, 5 or more, or 10 or more. From the viewpoint of the working environment and workability, the upper limit of this selectivity ratio may be around 100, around 50, or around 20.

[0077] Here, the dissolution rate (μm / min) can be measured, for example, by the methods shown in (A) to (G) below. (A) Prepare 1 liter of an alkaline cleaning solution to be used for cleaning, for example, a 5% by mass KOH (potassium hydroxide) aqueous solution. (B) Prepare a gallium substrate and a substrate of a metal other than gallium, both in the form of a plate measuring 1 cm in length, 1 cm in width, and 1 mm in thickness, and measure their mass W0. If there is a native oxide film or the like on the surface of the substrate, remove it beforehand. (C) Divide the alkaline aqueous solution into two containers, each containing 500 ml. Immerse the gallium substrate and the substrate of a metal other than gallium in the alkaline aqueous solution, adjusted to the planned washing conditions, for example, 25°C, in each container for 3 minutes. Adjust the position of each substrate in each container during immersion so that the two substrates do not differ drastically and affect the amount of solubility. If the substrates are to dissolve completely, increase the thickness of the substrates prepared in (B) above. (D) Remove each substrate from the alkaline solution and wash it at room temperature. (E) Measure the mass W1 of each substrate after cleaning. (F) The dissolution rate (μm / min) is calculated from the difference between the mass W0 and the mass W1 and the specific gravity of each substrate. At this time, the calculation is performed assuming that the substrate dissolves only in the thickness direction. (G) Calculate the selection ratio from the obtained dissolution rate values ​​according to the following formula. Selectivity ratio = Dissolution rate of gallium (μm / min) / Dissolution rate of other metals (μm / min)

[0078] Furthermore, if the contact area between the metal other than gallium and the cleaning solution is sufficiently smaller than the contact area between gallium and the cleaning solution, the selectivity ratio may be less than 1.

[0079] The above describes a cleaning method for objects containing gallium and other metals. However, the technical concept of the present invention can also be applied to cleaning methods for objects containing other combinations of metals. For example, a cleaning method for objects containing a combination of a specific metal and a metal adjacent to that metal in the periodic table (for example, a metal within the range of ±2 of the period and ±2 of group of the specific metal). [Examples]

[0080] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0081] LED chips with bumps formed on one side were prepared by transferring them to a receptor substrate using laser lift-off, and then a cleaning process was performed. LED chips using In (indium) bumps and SAC bumps were prepared.

[0082] (Pre-cleaning evaluation) First, before cleaning, the LED chips were observed using an optical microscope, and it was confirmed that gallium was adhering to the surface of the LED chip opposite to the bump-forming surface. The presence or absence of gallium adhesion after cleaning, and the presence or absence of bump dissolution due to cleaning, can be distinguished by the difference in color. The observation results are shown in Figure 2, "Pre-cleaning photograph".

[0083] (Example 1) As a cleaning solution, a 5% by mass aqueous solution of KOH (potassium hydroxide), an alkaline cleaning solution, was used for cleaning. The receptor substrate on which the LED chips were transferred was immersed in the cleaning solution, and the cleaning was performed for 3 minutes at a cleaning temperature of 25°C (room temperature). Similar to the pre-cleaning evaluation, the LED chips were observed using an optical microscope to evaluate the presence or absence of gallium adhesion and the occurrence of bump dissolution.

[0084] (Example 2) The cleaning and evaluation were carried out in the same manner as in Example 1, except that a 2.34% by mass aqueous solution of TMAH (tetramethylammonium hydroxide), which is an alkaline cleaning solution, was used as the cleaning solution.

[0085] (Example 3) Except for using a 10% by mass aqueous solution of Na2CO3 (sodium carbonate), which is an alkaline cleaning solution, as the cleaning solution, the cleaning and evaluation were carried out in the same manner as in Example 1.

[0086] (Comparative Example 1) The cleaning and evaluation were carried out in the same manner as in Example 1, except that a 12.3% by mass aqueous solution of HCl (hydrochloric acid), which is an acidic cleaning solution, was used as the cleaning solution.

[0087] (Comparative Example 2) Except for using a 6% by mass aqueous solution of H2SO4 (sulfuric acid), which is an acidic cleaning solution, as the cleaning solution, the cleaning and evaluation were carried out in the same manner as in Example 1.

[0088] Figure 2 shows the evaluation results. In Examples 1-3, it was confirmed that the metallic Ga attached to the LED chip was removed regardless of the type of cleaning solution used. On the other hand, neither the In bump nor the SAC bump dissolved due to cleaning. It was found that cleaning with an alkaline cleaning solution selectively dissolved and removed only the metallic Ga. In contrast, in Comparative Examples 1 and 2, where cleaning was performed with an acidic cleaning solution, it was confirmed that the In bump dissolved. However, dissolution of the SAC bump was not observed.

[0089] (Example 4) After immersion treatment of SAC bumps in the same alkaline cleaning solution as in Example 1 (5% by mass KOH (potassium hydroxide) aqueous solution), an IPA solution of abietic acid, a component of flux, was applied and dried at 40°C. Then, it was heated to 250°C on a hot plate. Figure 3 shows the evaluation results using an optical microscope. As shown in Figure 3, the color of the bumps changed after heating at 250°C, indicating that the SAC bumps dissolved. Flux is used to improve the meltability and wettability of solder by reducing the oxide film on the bump surface, thereby ensuring electrical connection. Therefore, the fact that the SAC bumps melted after treatment as in Example 4 means that the SAC bumps did not denature due to the cleaning treatment in Example 4. The composition of the SAC bumps used was Sn=96.5% by mass, Ag=3.0% by mass, and Cu=0.5% by mass.

[0090] (Comparative Example 3) After immersion treatment in the same acidic cleaning solution (12.3% by mass HCl aqueous solution (hydrochloric acid)) as in Comparative Example 1, an IPA solution of abietic acid, a component of the flux, was applied to the SAC bumps and dried at 40°C. Then, they were heated to 250°C on a hot plate. Figure 4 shows the evaluation results using an optical microscope. As shown in Figure 4, the color of the bumps did not change before and after heating at 250°C, indicating that the SAC bumps did not dissolve. This is thought to be because the Sn / Ag / Cu alloy composition changed due to cleaning with the acidic cleaning solution, raising the melting point, and thus the bumps were modified from their normal state. In other words, although the SAC bumps themselves did not dissolve due to the acidic cleaning solution, their composition and other properties changed, resulting in a change in the electrical characteristics of the LED chip. This suggests the possibility of connection failure.

[0091] As described above, it has been found that, according to the embodiments of the present invention, gallium can be removed by washing without dissolving or altering metals other than gallium.

[0092] This specification includes the following embodiments: [1]: A method for manufacturing an LED mounting substrate, comprising the step of cleaning an LED chip that has been transferred from a sapphire substrate to a receptor substrate by laser lift-off with an alkaline cleaning solution. [2]: A method for manufacturing an LED mounting substrate according to [1], wherein the LED chip transferred onto the receptor substrate has gallium on the side opposite to the receptor substrate, and the gallium is removed by the cleaning step. [3]: A method for manufacturing an LED mounting substrate according to [1] or [2] above, wherein the alkaline concentration of the alkaline cleaning solution is 0.5% by mass or more and less than or equal to the saturation concentration. [4]: A method for manufacturing an LED mounting substrate according to [1], [2], or [3] above, wherein the temperature of the alkaline cleaning solution is 5°C or higher and 80°C or lower. [5]: A method for manufacturing an LED mounting substrate according to [1], [2], [3], or [4] above, wherein the cleaning time with the alkaline cleaning solution is 10 seconds or more and 1 hour or less. [6]: A method for manufacturing an LED mounting substrate according to [1], [2], [3], [4] or [5], wherein the surface of the LED chip that is bonded to the receptor substrate has bumps. [7]: The method for manufacturing the LED mounting substrate according to [6], wherein the bumps are formed by lead-free solder. [8]: The method for manufacturing an LED mounting substrate according to [6] or [7], wherein the bumps have as a main component at least one selected from SnAgCu alloy, SnZnBi alloy, SnCu alloy, SnAgInBi alloy, SnZnAl alloy and indium. [9]: A method for manufacturing an LED mounting substrate according to [1], [2], [3], [4], [5], [6], [7], or [8], wherein the LED chip transferred onto the receptor substrate is cleaned by immersing the receptor substrate together with the LED chip in the alkaline cleaning solution.

[10] : A cleaning solution, which is alkaline, for cleaning an LED chip provided on a sapphire substrate after it has been transferred to a receptor substrate by laser lift-off.

[11] : The cleaning solution is the cleaning solution of

[10] above, having a pH of 9.5 to 14.0.

[12] : The cleaning solution according to

[10] or

[11] above, wherein the cleaning solution is an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium bicarbonate, and potassium acetate.

[13] : A cleaning method for cleaning LED chips separated from a sapphire substrate by laser lift-off, the method comprising cleaning with an alkaline cleaning solution.

[14] : The cleaning method of

[13] above, wherein the LED chip is transferred onto a receptor substrate.

[15] : A cleaning method for selectively removing gallium from a part having gallium and a metal other than gallium on its surface, wherein the part is cleaned using an alkaline cleaning solution.

[16] : The cleaning method of

[15] , wherein the gallium and metals other than gallium are brought into contact with the alkaline cleaning solution during the cleaning.

[17] : The cleaning method of

[15] or

[16] above, wherein the component is in the form of a substrate and is fixed to another substrate during cleaning, the gallium is present on the side of the component opposite to the side of the other substrate, and the metals other than gallium are present on the side of the component that is on the side of the other substrate.

[18] : The cleaning method according to

[15] ,

[16] , or

[17] , wherein the metal other than gallium is at least one metal selected from the group consisting of aluminum, copper, zinc, silver, indium, tin, and bismuth.

[19] : The cleaning method according to

[15] ,

[16] ,

[17] or

[18] , wherein the metal other than gallium is at least one metal selected from the group consisting of copper, silver, indium and tin.

[20] : The cleaning method of

[15] ,

[16] ,

[17] ,

[18] or

[19] , wherein the metal other than gallium is copper, silver, and tin.

[0093] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A cleaning method for selectively removing gallium from a part having gallium and a metal other than gallium on its surface, The metals other than gallium are metals in the period 3 to 5 and groups 11 to 14 of the periodic table. The aforementioned component is in the form of a substrate, and the cleaning is performed while it is fixed to another substrate. The gallium is present on the side of the component opposite to the other substrate side. The metals other than gallium are present on the other substrate side of the component. A cleaning method for the aforementioned parts, wherein an alkaline cleaning solution comes into contact with the gallium and other metals, and selectively removes the gallium.

2. A cleaning method for selectively removing gallium from a part having gallium and a metal other than gallium on its surface, The metal other than gallium is at least one metal selected from the group consisting of aluminum, copper, zinc, silver, indium, tin, and bismuth. The aforementioned component is in the form of a substrate, and the cleaning is performed while it is fixed to another substrate. The gallium is present on the side of the component opposite to the other substrate side. The metals other than gallium are present on the other substrate side of the component. A cleaning method for the aforementioned parts, wherein an alkaline cleaning solution comes into contact with the gallium and other metals, and selectively removes the gallium.

3. A cleaning method for selectively removing gallium from a part having gallium and bumps on its surface, The bump is formed with lead-free solder. The aforementioned component is in the form of a substrate, and the cleaning is performed while it is fixed to another substrate. The gallium is present on the side of the component opposite to the other substrate side. The bump is located on the other substrate side of the component, A cleaning method for the aforementioned parts, wherein an alkaline cleaning solution comes into contact with the gallium and the bumps, and selectively removes the gallium.

4. The cleaning method according to claim 1 or 2, wherein the metal is at least one metal selected from the group consisting of copper, silver, indium, and tin.

5. The cleaning method according to claim 1 or 2, wherein the metals are copper, silver, and tin.

6. The cleaning method according to any one of claims 1 to 3, wherein the alkaline concentration of the alkaline cleaning solution is 0.5% by mass or more and less than or equal to the saturation concentration.

7. The cleaning method according to any one of claims 1 to 3, wherein the temperature of the alkaline cleaning solution is 5°C or higher and 80°C or lower.

8. The cleaning method according to any one of claims 1 to 3, wherein the cleaning time with the alkaline cleaning solution is 10 seconds or more and 1 hour or less.

9. The cleaning method according to any one of claims 1 to 3, wherein the alkaline cleaning solution has a pH of 9.5 to 14.

0.

10. The cleaning method according to any one of claims 1 to 3, wherein the alkaline cleaning solution is an aqueous solution containing at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide, magnesium hydroxide, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, sodium carbonate, sodium bicarbonate, and potassium acetate.

Images