Method for cleaning object to be cleaned

Abstract

The present invention provides a method for cleaning an object to be cleaned, by which the composition and amount of a cleaning liquid are stabilized and the object to be cleaned can be stably cleaned. Provided is a method for cleaning an object to be cleaned, in which a cleaning liquid contact step for bringing the object to be cleaned into contact with a cleaning liquid and a cleaning liquid removal step for removing the cleaning liquid are performed once or repeatedly twice or more, and in which the object to be cleaned to which a flux residue adheres is cleaned using the cleaning liquid, wherein the cleaning liquid contact step includes a pressure reduction step for reducing the atmospheric pressure until the atmospheric pressure reaches 4.0 kPa to 26.3 kPa in a state in which the cleaning liquid is in contact with the object to be cleaned, and the temperature of the cleaning liquid is maintained at 45°C to 80°C in at least a part of the pressure reduction step.

Description

Washing method for an object to be washed

[0001] The present invention relates to a method for washing an object to be washed to wash and remove flux adhered to the object to be washed.

[0002] Conventionally, as a method for washing an object to be washed with flux residue adhered thereto, a method of reducing the pressure to 0.1 kPa to 7 kPa and immersing the object to be washed in a cleaning liquid in a cleaning tank is known (Patent Document 1).

[0003] WO2011 / 081071 A1

[0004] In the method of Patent Document 1, since the pressure is reduced to a very low level, there has been a problem that the cleaning liquid is discharged outside the cleaning tank due to the reduced pressure, the composition of the cleaning agent changes, or the amount of the cleaning liquid decreases. It becomes difficult to exhibit the assumed cleaning performance when the composition of the cleaning liquid changes or the amount of the cleaning liquid decreases.

[0005] The present invention has been completed in view of the above circumstances, and an object to be solved is to provide a method for washing an object to be washed in which the composition and amount of the cleaning liquid are stable and washing can be performed stably.

[0006] (1) As a result of diligent research, the inventors have found that the performance of the cleaning solution can be fully realized by appropriately controlling the degree of reduced pressure and the temperature of the cleaning solution in the cleaning process, and have completed the following invention. (2) That is, the cleaning method for an object to be cleaned according to the present invention is a cleaning method for cleaning an object to be cleaned to which flux residue is attached using the cleaning solution, comprising: a cleaning solution contact step of bringing the object to be cleaned into contact with the cleaning solution; and a cleaning solution removal step of removing part or all of the cleaning solution from the object to be cleaned, performed once or repeated two or more times, wherein the object to be cleaned in contact with the cleaning solution is exposed to a reduced pressure atmosphere, in which case the atmospheric pressure is reduced to 4.0 kPa to 26.3 kPa in at least a part of the reduced pressure step, and in which case the temperature of the cleaning solution is maintained at 45°C to 80°C in at least a part of the reduced pressure step. (3) A cleaning method for an object to be cleaned according to the present invention that further solves the above problems is a cleaning method for cleaning an object to be cleaned to which flux residue is attached using a cleaning solution, wherein the cleaning solution contact step of bringing the object to be cleaned into contact with a cleaning solution and the cleaning solution removal step of removing part or all of the cleaning solution from the object to be cleaned are repeated two or more times, the method comprising a depressurization step of exposing the object to be cleaned in contact with the cleaning solution to a depressurized atmosphere, in which at least a part of the depressurization step the temperature of the cleaning solution is maintained at 45°C to 80°C, and the depressurization step consists of a liquid depressurization step of depressurizing while immersing the object to be cleaned in the cleaning solution and an air depressurization step of depressurizing the object to be cleaned after removing it from the cleaning solution. (4) The depressurization step in (3) above is preferably a step of depressurizing until the pressure is reduced to 4.0 kPa to 26.3 kPa.

[0007] In the inventions described in (2) to (4) above, it is preferable to combine any one of the following inventions (5) to (7), (10), and (12). (5) The depressurization step includes a step of reducing the atmospheric pressure until bubbles expand if bubbles are attached to the surface of the object to be cleaned. (6) The cleaning solution comprises a first cleaning solution and a second cleaning solution having a lower content of non-volatile components than the first cleaning solution, and the cleaning solution contact step is repeated two or more times and comprises a step of bringing the object to be cleaned into contact with the first cleaning solution and a step of bringing it into contact with the second cleaning solution in at least the final step, the flux residue is attached to the object to be cleaned within a gap with a spacing of 100 μm or less, and the depressurization step is performed while maintaining the posture of the object to be cleaned so that the opening of the gap faces upward. (7) The depressurization step includes a cleaning solution recovery step of recovering the components of the cleaning solution contained in the exhaust gas that has been depressurized by the depressurization means and returning them to the cleaning solution, wherein if the depressurization means is not a dry depressurization means, the cleaning solution recovery step is a step of recovering the cleaning solution from the exhaust gas before the exhaust gas reaches the depressurization means. (8) In the case of the configuration of (7) above, the depressurization means is preferably a depressurization ejector. (9) In the case of the configuration of (7) above, the cleaning solution recovery step preferably includes a step of recovering the mist contained in the exhaust gas with a demister, and / or cooling the components of the cleaning solution contained in the exhaust gas that have evaporated to condense and recover the components of the cleaning solution. (10) After the depressurization step, there is a pressure-boosting step of increasing the ambient pressure while the object to be cleaned is in contact with the cleaning solution, wherein after the pressure-boosting step, the depressurization step, which is performed in overlap with the cleaning solution contact step, is performed once or twice or more. (11) In the case of the configuration of (10) above, one set of the depressurization step and the pressurization step is performed within 2 minutes. (12) The cleaning solution removal step includes a solvent evaporation removal step in which the object to be cleaned, which has been removed from the cleaning solution, is depressurized to evaporate and remove the solvent contained in the cleaning solution that has adhered to its surface.

[0008] The cleaning method for objects to be cleaned according to the present invention, having the above configuration, makes it possible to effectively clean objects that have narrow gaps.

[0009] The cleaning method for objects to be cleaned according to the present invention will be described in detail below based on embodiments. The numerical values ​​described herein can be used to define a range when making corrections, either as an upper or lower limit, and this range may or may not include the numerical value. Furthermore, the numerical range "x to y" described herein includes the lower limit x and the upper limit y. A new numerical range can be constructed by arbitrarily combining these upper and lower limits, as well as the numerical values ​​listed in the specification or examples. The new numerical range may also exclude one or both of the upper and lower limits. For example, a range greater than x or a range less than y can be adopted. Furthermore, any numerical value arbitrarily selected from any of the above numerical ranges can be used as the upper and lower limits of the new numerical range.

[0010] The cleaning method for the object to be cleaned according to this embodiment is a cleaning method that can be suitably used to remove flux residue as dirt remaining on a circuit board, which is the object to be cleaned, by cleaning. The object to be cleaned in which the cleaning method of this embodiment is suitably used is a manufacturing intermediate product including a circuit board and components soldered to the circuit board. Components soldered to the circuit board include semiconductor chips, chip-type capacitors, and other circuit boards.

[0011] When soldering, flux residue may remain in the gap between the circuit board and the components. If flux residue remains, malfunctions may occur, and the cleaning method of the object to be cleaned according to this embodiment is applied to remove this flux residue.

[0012] The gap in the object to be cleaned refers to the space formed between, for example, a circuit board and an interposer used for mounting components or semiconductors mounted on that circuit board. There are no particular limitations on the size of the gap, but examples include gaps where the size of the narrowest part, such as the shortest distance between the circuit board and the component, is in the range of 5 to 500 μm, 10 to 250 μm, or 20 to 100 μm. The width and depth of the gap depend on the size and spacing of the mounted components and electrodes on the circuit board, but examples include 0.5 to 100 mm, and especially 5 to 20 mm.

[0013] Flux residue adheres to the circuit board and components on the circuit board. Furthermore, it remains in the gaps between the circuit board and components, and between circuit boards themselves. The smaller the size of these gaps, the more advantageous it is to apply the cleaning method of the object to be cleaned according to this embodiment. For example, if the gap size is 100 μm or less (especially 50 μm or less, and even 20 μm or less), the cleaning solution and flux residue tend to remain in the gap, making thorough cleaning difficult.

[0014] While there are no specific limitations on the type of flux that forms the basis of the flux residue that causes contamination, commonly used rosin-based fluxes and water-soluble fluxes can be given as examples.

[0015] Rosin-based fluxes are composed of rosin as the base resin, an organic solvent, activators such as carboxylic acids and amines to effectively remove the oxide film from solder during soldering, and a thixotropic agent to modify viscosity. By mixing and stirring this rosin-based flux with solder powder, it is commonly used as solder paste. Water-soluble fluxes use water-soluble polymers such as polyoxyethylene alkyl ethers as the base resin.

[0016] The components of the cleaning solution are not particularly limited, but examples include water, organic solvents such as glycol ether, and amine compounds such as monoethanolamine, diethanolamine, methyldiethanolamine, methylmonoethanolamine, and ethylmonoethanolamine.

[0017] Furthermore, at least two cleaning solutions can be used, including a first cleaning solution containing non-volatile cleaning components and a second cleaning solution containing less non-volatile cleaning components than the first cleaning solution. Three or more cleaning solutions can also be used.

[0018] First, by performing cleaning with a first cleaning solution followed by a second cleaning solution, and so on, ultimately cleaning with a cleaning solution that contains a low amount of non-volatile cleaning components, it is possible to suppress the residue of non-volatile cleaning components contained in the cleaning solution on the object being cleaned. It is especially preferable that the second cleaning solution does not contain non-volatile cleaning components. The second cleaning solution, which does not contain non-volatile cleaning components, acts as a so-called rinsing solution. When using three or more cleaning solutions with different concentrations of non-volatile cleaning components, it is preferable to use the cleaning solution with the lowest amount of non-volatile cleaning components in the final cleaning solution contact step. Alternatively, multiple cleanings may be performed using the cleaning solution with the lowest amount of non-volatile cleaning components.

[0019] The cleaning method for the object to be cleaned in this embodiment comprises a cleaning solution contact step, a cleaning solution removal step, and a depressurization step. The cleaning solution contact step and the cleaning solution removal step are performed once or two or more times in combination. By repeating these combinations two or more times, flux residue can be removed from the object to be cleaned more effectively. There is no particular upper limit to the number of repetitions, but approximately 100 times is a possible example.

[0020] ・Cleaning liquid contact process The cleaning liquid contact process is a process in which the object to be cleaned comes into contact with the cleaning liquid by immersing it in a storage tank containing the cleaning liquid. In the cleaning liquid contact process, flux residue attached to the object to be cleaned is dissolved into the cleaning liquid and removed by immersing it in the cleaning liquid. In the storage tank, the dissolution of flux residue into the cleaning liquid can be promoted by creating a flow of cleaning liquid through stirring or by applying ultrasonic irradiation. When immersing an object to be cleaned that has gaps in it into the cleaning liquid, it is preferable to have the opening of the gap facing upward. In addition to flux residue, gas is present in the gap, so it is preferable to control the position of the object to be cleaned so that the opening faces upward in order to discharge the gas in the cleaning liquid. Here, "the opening is facing upward" means that the opening is facing upward from the horizontal direction.

[0021] When a storage tank is used, the inside is depressurized during the depressurization process, so it is constructed to withstand the reduced pressure. The storage tank is large enough to accommodate the object to be cleaned. When cleaning multiple objects simultaneously, it is large enough to accommodate multiple objects.

[0022] The storage tank has a temperature control means for adjusting the temperature of the cleaning solution stored inside. The temperature control means can control the temperature of the cleaning solution within a range of 45°C to 80°C. Examples of upper limits for the cleaning solution temperature include 70°C and 80°C, and lower limits include 45°C and 50°C, and these lower and upper limits can be combined arbitrarily. As for the temperature control means, in addition to installing a heating means such as a heater inside the storage tank, a device can also be used to heat the cleaning solution externally before introducing it into the storage tank. The externally heated cleaning solution can be used to replenish the storage tank, or it can be used to heat the cleaning solution after removing it from the storage tank and then returning it. The temperature of the cleaning solution may be controlled within the above range for at least a portion of the depressurization process described later, and may also be controlled within the steam temperature range for other times. For example, the temperature may be controlled within the above temperature range while the object to be cleaned is in contact with the cleaning solution.

[0023] ・Cleaning liquid removal process After the cleaning liquid contact process, a cleaning liquid removal process is performed. The cleaning liquid removal process is the process of removing the cleaning liquid from the object to be cleaned. In order to remove the cleaning liquid from the object to be cleaned, the cleaning liquid and the object to be cleaned must be separated. Specifically, this can be achieved by lifting the object to be cleaned from the cleaning liquid in the storage tank or by discharging the cleaning liquid from the storage tank to the outside. When discharging the cleaning liquid to the outside, methods such as using free fall by providing an outlet at the bottom of the storage tank to reduce the amount of energy supplied from the outside, or generating an ejector effect by creating a flow of cleaning liquid and air as it is discharged, thereby creating a pressure difference in the gap, and quickly discharging the cleaning liquid from the gap can be employed. The diameter of the outlet should be as large as possible to increase the discharge speed of the cleaning liquid.

[0024] When using a first cleaning solution and a second cleaning solution, the removal of the first cleaning solution can be accelerated by using the second cleaning solution after cleaning with the first cleaning solution. The second cleaning solution is preferably composed only of volatile substances that can be removed by drying. Examples of solvents for the second cleaning solution include water, alcohol, and mixtures thereof.

[0025] Furthermore, the process may include a solvent evaporation and removal step in which the object to be cleaned is heated or a gas such as air is sprayed onto the object to be cleaned to evaporate and remove splash components in the cleaning solution. The gas to be sprayed can be selected to be dry or heated to facilitate drying when sprayed onto the object to be cleaned.

[0026] As a solvent evaporation removal step, another method involves adjusting the conditions of the vacuum step described later to reduce the atmospheric pressure to a level equivalent to or different from that of the vacuum step, thereby evaporating the cleaning solution.

[0027] In the solvent evaporation removal step, it is preferable to remove the cleaning solution adhering to the surface until it is 50% or less of the volume of the gap, and more preferably 30% or less, 20% or less, 10% or less, or even completely removed. In addition to the above criteria, in the solvent evaporation removal step, a criterion can also be adopted in which it is sufficient to remove the cleaning solution from a state in which the gap is filled with cleaning solution (a state in which cleaning solution adhering to one surface of the gap's surface connects the cleaning solution adhering to another surface opposite that surface, creating a connection between the two surfaces with cleaning solution) until the filled state is eliminated and the cleaning solution uniformly covers the surface of the gap.

[0028] The solvent evaporation and removal step is a step that creates conditions that allow the solvent contained in the cleaning solution to evaporate, and it is particularly preferable that this step evaporates all of the volatile components contained in the cleaning solution.

[0029] In the solvent evaporation removal process, by employing conditions that allow the solvent to evaporate, it becomes possible to introduce new cleaning solution into the gaps as the solvent evaporates, effectively replacing the cleaning solution in the gaps with fresh solution. The cleaning solution dissolves and removes dirt adhering to the object to be cleaned, but depending on the amount of dirt present in the gaps, it is anticipated that the cleaning solution present in the gaps may not be able to dissolve it sufficiently. Therefore, by effectively replacing the cleaning solution in the gaps, the cleaning solution's ability to dissolve dirt is restored, making cleaning more effective.

[0030] The vacuum step and cleaning liquid contact step include a vacuum step. The vacuum step is performed while the cleaning liquid is in contact with the object to be cleaned. After the cleaning liquid contact step, unless the cleaning liquid has been completely removed by some method, some cleaning liquid will remain on the object to be cleaned. It is especially preferable to perform the vacuum step in conjunction with the cleaning liquid contact step. This allows the cleaning liquid to effectively penetrate into the gaps.

[0031] The depressurization process is preferably carried out in a storage tank that holds the cleaning solution inside. By depressurizing while the object is immersed in the cleaning solution in the storage tank (depressurization in liquid), the cleaning solution can be continuously supplied to the surface of the object to be cleaned, and the cleaning solution can be effectively introduced into gaps. When the object to be cleaned is immersed in the cleaning solution, air may remain in gaps where the cleaning solution cannot easily penetrate. By depressurizing while such air remains in the gaps and the cleaning solution is in contact with the surface, if there is air (bubbles) remaining in the gaps, these bubbles will expand and push the cleaning solution remaining in the gaps out of the gaps. After that, when the object to be cleaned is immersed in the cleaning solution again, the cleaning solution, which has a high solubility for flux residue, can penetrate into the gaps, and cleaning in the gaps will proceed. Furthermore, depressurization can also be carried out while the object is removed from the cleaning solution, whether inside or outside the storage tank (depressurization in air). When using a storage tank, depressurization is carried out by discharging the atmospheric gas inside the storage tank. The degree of depressurization is preferably within the range of 4.0 kPa to 26.3 kPa. After reaching the desired pressure, maintaining that reduced pressure for a predetermined time promotes the expulsion of air from the gaps in the object being cleaned, and after the air is expelled, the penetration of the cleaning solution proceeds. An example of a predetermined time is 10 seconds or more and 60 seconds or less, with 20 seconds or more and 40 seconds or less being preferred.

[0032] The lower limits for pressure reduction can be 4.5 kPa, 5.0 kPa, 5.5 kPa, 6.3 kPa, 7.0 kPa, and 8.0 kPa, while the upper limits can be 26.3 kPa, 22.0 kPa, and 18.0 kPa. These lower and upper limits can be combined in any way.

[0033] In the depressurization process, it is preferable to control the depressurization rate so that it is between 3 kPa / s and 7 kPa / s when the ambient pressure passes near the vapor pressure of the cleaning solution. When the pressure is reduced to near the vapor pressure of the cleaning solution, evaporation from the surface of the cleaning solution becomes active, and if the depressurization rate is too high, there is a risk of bumping, so it is preferable to set an upper limit on the depressurization rate. Setting a lower limit on the depressurization rate is to ensure that the depressurization process proceeds quickly. At ambient pressures higher than the vapor pressure of the cleaning solution, there is less risk of bumping of the cleaning solution, so it is preferable to set the depressurization rate faster than the above. The depressurization rate is adjusted by changing the capacity of the depressurization means. In particular, when using a depressurization ejector, the depressurization rate can be controlled by using multiple depressurization ejectors and changing the number of depressurization ejectors being operated.

[0034] The method of depressurization is not particularly limited, but it is carried out by depressurization means. Examples of conventional depressurization means include depressurization pumps and depressurization ejectors. It is preferable to employ a dry depressurization means. A dry depressurization means is a depressurization means that does not use liquids such as hydraulic oil when discharging the atmospheric gas. By employing a dry depressurization means, vapors and mists derived from cleaning fluids mixed in the discharged atmospheric gas can be recovered without the risk of contamination with hydraulic oil, etc., and returned to the storage tank. As a dry depressurization means, a depressurization ejector that uses compressed air as the working fluid is preferred.

[0035] By performing a depressurization process while the cleaning solution is in contact with the object being cleaned, if the cleaning solution has not completely penetrated the gaps in the object being cleaned, any air remaining in the gaps will expand and escape. Furthermore, when the system is released to the atmosphere, the expanded air will rapidly contract. As a result, the cleaning solution in contact with the object replaces the gaps left by the escaping and contracted air, filling the gaps and allowing the cleaning solution to come into contact with the flux residue present within the gaps, thus effectively removing the flux residue.

[0036] To recover vapors and mists originating from the cleaning solution that are mixed into the discharged atmospheric gas, a cleaning solution recovery process is employed in which the discharged atmospheric gas is passed through cleaning solution recovery means such as demisters and traps to recover the vapors and mists originating from the cleaning solution. A demister is formed from an aggregate of woven fabric made of metal wires or from a porous material, and is a means of recovery when the mist-like cleaning solution adheres to the surface of the aggregate or porous material as it passes through the woven fabric aggregate or porous material.

[0037] A trap is a means of condensing and recovering vapors derived from the cleaning solution by cooling the exhaust gas containing these vapors. The recovered cleaning solution components can be returned directly to the storage tank, thus maintaining the composition of the cleaning solution. As a method of cooling the discharged atmospheric gas, in addition to using commonly available refrigeration equipment, exhaust gas generated from a decompression ejector can be adiabatically expanded to lower its temperature, and this lowered exhaust gas can then be used as a cooling source.

[0038] To prevent the cleaning solution from adhering to the vacuum mechanism, it is preferable to perform the cleaning solution recovery process before it flows into the vacuum mechanism. In particular, if the vacuum mechanism is not a dry type, there is a concern about the cleaning solution mixing with the hydraulic oil, so it is desirable to perform the cleaning solution recovery process before the atmospheric gas discharged to the vacuum mechanism reaches it.

[0039] It is preferable to have a pressure-boosting step in which the ambient pressure is increased after the pressure reduction step while the object to be cleaned is in contact with the cleaning solution. Even if air cannot completely escape from the gap after the pressure reduction step, the pressure-boosting step compresses the air in the gap, and the cleaning solution penetrates into the gap as a result. The pressure can be increased to atmospheric pressure. The time required for the pressure-boosting step can be exemplified as 1 second or more and 30 seconds or less, preferably 2 seconds or more and 15 seconds or less, and more preferably 10 seconds or less. The pressure-boosting step is a step in which a gas such as air is introduced from the outside, and by spraying the introduced gas onto the object to be cleaned, it becomes possible to remove the cleaning solution from the surface of the object to be cleaned.

[0040] Therefore, by combining a decompression step and a pressure increase step, the cleaning liquid can effectively penetrate into the gap, and as a result, sufficient removal of flux residues can be achieved. The decompression step and the pressure increase step can be combined within 2 minutes (preferably within 1 minute, more preferably multiple times within 1 minute) to improve the cleaning speed of the flux residues.

[0041] In particular, by performing the combination of the decompression step and the pressure increase step multiple times, the removal of flux residues by the cleaning liquid will further progress. Also, even if a pressure increase step is performed before the decompression step, the air present in the gap is compressed and the penetration of the cleaning liquid into the gap can be realized, so that the removal of flux residues can be effectively performed.

[0042] - Other steps It is possible to have a step of detecting a change in the composition of the cleaning liquid and supplementing the insufficient components. For example, since it is assumed that the solvent component such as water evaporates from the cleaning liquid during the decompression step and the concentration of the cleaning liquid becomes high, a sensor for measuring the concentration of the solvent component (a moisture meter when the solvent is water) is provided and controlled to reach the required solvent concentration. Also, when many flux residues dissolve in the cleaning liquid and deterioration progresses, the performance of the cleaning liquid is maintained by replacing part or all of the cleaning liquid.

[0043] In order to manage the concentration of the cleaning liquid, by measuring the refractive index with a refractometer, fluctuations in the refractive index due to a decrease in the amount of solvent and fluctuations in the refractive index due to the dissolution of flux residues can be detected. When fluctuations above a certain level are detected, the solvent is added or part or all of the cleaning liquid is replaced.

[0044] For the cleaning liquid corresponding to rosin-based flux, the amount of dissolved flux residues can be estimated by detecting fluctuations in pH. Also, for the cleaning liquid corresponding to water-soluble flux, the purity of the cleaning liquid can be estimated by measuring the electrical conductivity.

[0045] When the variation in the composition of the cleaning liquid is detected by the above detection, in addition to reducing the components recovered in the cleaning liquid recovery step, the reduced components can also be separately supplemented. Further, when the flux residue concentration in the cleaning liquid rises above a predetermined value due to the progress of the cleaning of the object to be cleaned, it is preferable to replace part or all of the cleaning liquid to maintain the cleaning performance of the cleaning liquid above a certain level.

[0046] The cleaning method of the object to be cleaned according to the present invention will be described in detail based on the following examples. - Preparation of the object to be cleaned A semiconductor mounted product was prepared as the object to be cleaned. Rosin-based flux was attached to the object to be cleaned as dirt. A gap (width of the opening is 150 μm, length is 10 mm, depth is 50 μm) was formed in the object to be cleaned, and the gap was filled with dirt.

[0047] - Cleaning test (Test Example 1) As the first cleaning liquid, 25 L of a semi-aqueous cleaning liquid was used. The temperature of the cleaning liquid was 40°C. The object to be cleaned was immersed in this first cleaning liquid (cleaning liquid contact step), and the pressure was reduced to 6.3 kPa and held for 30 seconds (pressure reduction step). Then, the pressure was returned to normal pressure and the liquid was drained.

[0048] After performing these operations 50 cycles as one cycle, it was immersed in 2 L of normal-temperature pure water as the second cleaning liquid (rinse liquid = pure water) (cleaning liquid contact step). Further, it was immersed in 25 L of 50°C pure water as the second cleaning liquid (cleaning liquid contact step), and the pressure was reduced to 6.3 kPa and held for 30 seconds (pressure reduction step). Then, the pressure was returned to normal pressure and the liquid was drained.

[0049] After performing these operations 50 cycles as one cycle, it was dried with hot air at 100°C for 10 minutes. Then, the amount of dirt remaining in the gap was visually evaluated in three levels. If the ratio of the flux that could be removed was 70% or more and less than 85%, it was rated as △, if it was 85% or more and less than 95%, it was rated as ○, and if it was 95% or more, it was rated as ◎. The results and test conditions are shown in Table 1. Note that "draining the liquid" in the table means flowing out the cleaning liquid (rinse liquid) from the cleaning tank (rinse tank).

[0050] (Test Examples 2-5) Tests and evaluations were conducted under the same conditions as in Test Example 1, except for the changes shown in Table 1. In Test Example 5, after the cleaning solution contact step using the first cleaning solution and after the cleaning solution contact step using the second cleaning solution, the volatile components contained in the cleaning solution were removed from the liquid and the pressure was reduced to 6.3 kPa and held for 30 seconds (indicated as "reduced pressure in air" in the table: solvent evaporation removal step). In the solvent evaporation removal step used in Test Example 5, the ambient temperature was approximately 40°C. Therefore, in the solvent evaporation removal step, the second cleaning solution could be quickly evaporated and removed by reducing the pressure to 6.3 kPa, which is below the saturated vapor pressure of water, the main component of the first and second cleaning solutions. The evaluation results are shown in Table 1.

[0051]

[0052] As is clear from the table, the results of Test Examples 1 to 3, in which the temperature of the first cleaning solution was varied, showed that Test Example 3, in which the temperature of the cleaning solution was 70°C, exhibited high cleaning performance. Furthermore, a strict comparison of Test Examples 1 and 2 showed that Test Example 2, with its higher temperature of the first cleaning solution, exhibited higher cleaning performance.

[0053] Furthermore, the results from Test Examples 3 and 4, in which the degree of reduced pressure was varied, showed that lower pressure resulted in higher cleaning performance. In addition, Test Example 5, which employed a solvent evaporation removal process, showed even higher cleaning performance compared to Test Example 3, which did not employ this process.

Claims

1. A method for cleaning an object to be cleaned to which flux residue is attached, comprising: a cleaning liquid contact step of bringing the object to be cleaned into contact with a cleaning liquid; and a cleaning liquid removal step of removing part or all of the cleaning liquid from the object to be cleaned, repeated two or more times, wherein the cleaning liquid method includes a depressurization step of exposing the object to be cleaned in contact with the cleaning liquid to a depressurized atmosphere, wherein the depressurization step includes a step of reducing the atmospheric pressure until bubbles expand if bubbles are attached to the surface of the object to be cleaned, wherein the temperature of the cleaning liquid is maintained at 45°C to 80°C in at least a part of the depressurization step, wherein the depressurization step consists of a liquid depressurization step of reducing the pressure while immersing the object to be cleaned in the cleaning liquid, and an air depressurization step of reducing the pressure of the object to be cleaned after it has been removed from the cleaning liquid, wherein the cleaning liquid removal step includes a solvent evaporation removal step of reducing the pressure of the object to be cleaned after it has been removed from the cleaning liquid to evaporate and remove the solvent contained in the cleaning liquid attached to its surface, The depressurization step is a step of reducing the pressure from 4.0 kPa to 26.3 kPa, the cleaning solution comprises a first cleaning solution and a second cleaning solution having a lower content of non-volatile components than the first cleaning solution, the cleaning solution contact step is repeated two or more times and comprises a step of bringing the object to be cleaned into contact with the first cleaning solution and a step of bringing the object to be cleaned into contact with the second cleaning solution in at least the final step, the depressurization step includes a cleaning solution recovery step of recovering the components of the cleaning solution contained in the exhaust gas that has been depressurized by the depressurization means and returning them to the cleaning solution, the cleaning solution recovery step is a step of recovering the cleaning solution from the exhaust gas before the exhaust gas reaches the depressurization means if the depressurization means is not a dry depressurization means, the depressurization means is a depressurization ejector, and / or recovering the mist contained in the exhaust gas by recovering the mist contained in the exhaust gas with a demister, and / or cooling the volatile components of the cleaning solution contained in the exhaust gas to condense and recover the components of the cleaning solution, The process includes a pressure-boosting step in which the atmospheric pressure is increased while the object to be cleaned is in contact with the cleaning liquid after the pressure-boosting step, and the pressure-boosting step is repeated once or twice or more while at least a portion of the object is in contact with the cleaning liquid.A method for cleaning an object to be cleaned, wherein the depressurization step and the pressurization step are completed within a total of two minutes, the depressurization rate in the depressurization step is 3 kPa / s to 7 kPa / s when the ambient pressure passes near the vapor pressure of the cleaning liquid, the flux residue is attached to the object to be cleaned within a gap of 100 μm or less, and the depressurization step is performed while maintaining the position of the object to be cleaned so that the opening of the gap faces upward.

2. A method for cleaning an object to be cleaned to which flux residue is attached, comprising: a cleaning liquid contact step of bringing the object to be cleaned into contact with a cleaning liquid; and a cleaning liquid removal step of removing part or all of the cleaning liquid from the object to be cleaned, performed once or repeated two or more times, the method comprising: a depressurization step of exposing the object to be cleaned in contact with the cleaning liquid to a depressurized atmosphere, wherein in at least a portion of the depressurization step the atmospheric pressure is reduced to 4.0 kPa to 26.3 kPa, and in at least a portion of the depressurization step the temperature of the cleaning liquid is maintained at 45°C to 80°C.

3. A method for cleaning an object to be cleaned to which flux residue is attached, comprising: a cleaning liquid contact step of bringing the object to be cleaned into contact with a cleaning liquid; and a cleaning liquid removal step of removing part or all of the cleaning liquid from the object to be cleaned, repeated two or more times, wherein the cleaning liquid comprises a depressurization step of exposing the object to be cleaned in contact with the cleaning liquid to a depressurized atmosphere, wherein in at least a part of the depressurization step the temperature of the cleaning liquid is maintained at 45°C to 80°C, and the depressurization step comprises a liquid depressurization step of depressurizing while immersing the object to be cleaned in the cleaning liquid, and an air depressurization step of depressurizing the object to be cleaned after removing it from the cleaning liquid, and a method for cleaning an object to be cleaned.

4. The method for cleaning an object to be cleaned according to claim 3, wherein the depressurization step is a step of reducing the pressure until it reaches 4.0 kPa to 26.3 kPa.

5. The method for cleaning an object to be cleaned according to any one of claims 2 to 4, wherein the depressurization step further includes reducing the atmospheric pressure until bubbles expand if bubbles are adhering to the surface of the object to be cleaned.

6. The cleaning solution comprises a first cleaning solution and a second cleaning solution having a lower content of non-volatile components than the first cleaning solution, the cleaning solution contact step is repeated two or more times and comprises a step of bringing the object to be cleaned into contact with the first cleaning solution and a step of bringing the object to be cleaned into contact with the second cleaning solution in at least the final step, the object to be cleaned has the flux residue attached to a gap with a spacing of 100 μm or less, and the depressurization step is performed while maintaining the posture of the object to be cleaned so that the opening of the gap faces upward, the cleaning method for an object to be cleaned according to any one of claims 2 to 4.

7. The method for cleaning an object to be cleaned according to any one of claims 2 to 4, wherein the depressurization step comprises a cleaning solution recovery step of recovering the components of the cleaning solution contained in the exhaust gas that has been depressurized by the depressurization means and returning them to the cleaning solution, and the cleaning solution recovery step is a step of recovering the cleaning solution from the exhaust gas before the exhaust gas reaches the depressurization means if the depressurization means is not a dry depressurization means.

8. The method for cleaning an object to be cleaned according to claim 7, wherein the depressurization means is a depressurization ejector.

9. The cleaning method for an object to be cleaned according to claim 7, further comprising the steps of: recovering the mist contained in the exhaust gas using a demister; and / or cooling the volatile components of the cleaning liquid contained in the exhaust gas to condense and recover the components of the cleaning liquid.

10. A method for cleaning an object to be cleaned according to any one of claims 2 to 4, further comprising a pressure-boosting step in which the object to be cleaned is in contact with the cleaning liquid after the pressure-boosting step, wherein the pressure-boosting step, which is performed in overlap with the cleaning liquid contact step, is repeated once or two or more times after the pressure-boosting step.

11. The method for cleaning an object to be cleaned according to claim 10, wherein a set of the depressurization step and the pressurization step is performed within two minutes.

12. The cleaning method for an object to be cleaned according to any one of claims 2 to 4, wherein the cleaning solution removal step is further comprising a solvent evaporation removal step of removing the object to be cleaned from the cleaning solution by reducing the pressure and evaporating the solvent contained in the cleaning solution that has adhered to its surface.

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