Apparatus and method for cleaning solid surface

Abstract: It is an object of the present invention to provide an apparatus and method for cleaning a solid surface which is effective for a substance to be cleaned having a complicated structure and which uses no solvent such as CFC or the like which destructs the environment of the earth. In the apparatus and method for cleaning a solid surface, a cleaning liquid is obtained by mixing insoluble particles in a liquid and brought into an eddy-flow state so that a surface to be cleaned can be uniformly cleaned.

Description: BACKGROUND OF THE INVENTION The present invention relates to an apparatus and method for cleaning a solid surface, and particularly to an apparatus and method for cleaning a part such as a metal workpiece, a print circuit board or the like, which has a surface having a complicated shape. In prior arts, there are disclosed cleaning apparatus and method using dry ice particles as disclosed in Japanese Patent Laid-Open No. 63-266836, and the ice fine particle generating apparatus using ice fine particles is disclosed in Japanese Patent Laid-Open No. 63-283133. In these methods and apparatuses, fine particles of dry ice or ice are blown out of a nozzle and sprayed on a substance to be cleaned for removing contaminants from the surfaces of the substance. In addition, in other prior arts, chlorine-type organic solvents such as trichloroethylene and the like and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113 in abbreviation) are generally used for cleaning out the oils, greases and waxes adhering to metal workpieces, print circuit boards and the like. In the above-described prior arts, the former method using fine particles is effective to clean a flat board such as a glass board, a Si wafer or the like. However, this method cannot uniformly clean the whole surface of a print circuit board on which many electronic parts are mounted, a part having a convex and concave surface or a complicated structure with holes because the motion of the dry ice used for cleaning in a constant direction causes a shadow portion on which the fine particles cannot be sprayed. In the prior arts, the latter method using a chlorine-type organic solvent such as trichloroethylene or the like has a danger of contaminating underground water, and, since CFC-113 depletes the stratospheric ozone, the use thereof is severely restricted. The German Patent DE-C-880 630, which forms the basis for the pre-characterising part of claims 1 and 5, discloses a device for removing a discloses a device for removing a substance of a decade tooth portion from a tooth. In the device the normal portion of the tooth is covered with a rubber cap having an opening at a position corresponding to the decade tooth portion. A sleeve of a middle ring is secured to the decade tooth through dental cement, the interior of the middle ring being filled with a liquid containing a disinfectant and abrasive particles and then being kept by a rubber plug. A shaft having a propeller is inserted in the middle ring through a small opening provided on the rubber plug. A deflow is caused to occur by rotating the shaft. The abrasive particles are colliding with the decade tooth portion to bear by remove the substance of the decade tooth portion. The device of the German Patent does not consider that a substance removed into liquids by the abrasive particles sticks again onto the surface to be cleaned. In the case of cleaning dirt such as solid fat or oil, it is impossible to prevent the solid fat or oil from sticking again on the surface to be cleaned since the solid fat or oil is hardly scattered in a liquid. The German Patent discloses the feature of AD-flow, but does not mention anything about the kind of substances to be used and the specific heating to be applied. The first object of the present invention is achieved by an apparatus according to claim 1. The means for bringing the cleaning liquid into an eddy-flow state may be a stirring apparatus. Alternatively, the means for bringing the cleaning liquid into an eddy-flow state may be a vibration generating apparatus. In a preferred form of the apparatus for cleaning a solid surface, the apparatus may further comprise means for mixing air bubbles in the cleaning liquid. The second object of the present invention is achieved by a method according to claim 5. Preferably, the state of the cleaning liquid obtained by mixing the insoluble particles in the liquid may be changed to an eddy-flow state by mixing air bubble in the cleaning liquid. Alternatively, the state of the cleaning liquid obtained by mixing the insoluble particles in the liquid may be changed to an eddy-flow state by vibrating the closed cleaning bath containing a vapor phase and the cleaning liquid. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic drawing of an apparatus of cleaning a solid surface in accordance with the present invention; Fig. 2 is a schematic drawing of an apparatus of the present invention for cleaning a solid surface which apparatus is effective for solid fats and oils to be cleaned off; and Fig. 3 is a drawing showing a relation between the cleaning temperature and the cleaning time when solid fat or oil is cleaned off by using an apparatus of the invention for cleaning a solid surface. DESCRIPTION OF THE PREFERRED EMBODIMENTS As a result of various experiments conducted by the inventors on an apparatus and method for cleaning a solid surface, the inventors obtained the following finding: The first object of the present invention can be achieved by an apparatus according to claim 1. The second object of the present invention can be achieved by a method according to claim 5. When a substance to be cleaned off is liquid or solid fat or oil, calcium carbonate particles having the property of adsorbing such liquid or solid fat or oil are used. The cleaning liquid contains the insoluble particles dispersed therein so that the insoluble particles are caused to collide with a board surface by virtue of the kinetic energy, thereby cleaning the surface. A predetermined number of collisions of the insoluble particles in the cleaning liquid causes cleaning of the surface. The use of a small amount of insoluble particles requires much time for cleaning, while the use of a large amount of insoluble particles requires only a little time for cleaning. Thus, the composition of the cleaning fluid has no relation to the cleaning capability. A stirring apparatus, a vibration generating apparatus or the like is used as the means for providing an eddy flow in the cleaning liquid. In order to improve the effect of the means for forming an eddy flow in the cleaning liquid, the means for mixing bubbles in the cleaning liquid may be used in combination with the above means forming an eddy flow. The present invention is described below with reference to embodiments. (Embodiment 1) Fig. 1 is a schematic drawing of an apparatus for cleaning a solid surface of the present invention. In the drawing, reference numeral 1 denotes a cleaning liquid; reference numeral 2, a cleaning bath; reference numeral 3, a part to be cleaned; reference numeral 4, a cage in which the part 3 is placed; reference numeral 5, a stirring apparatus; reference numeral 6, fine particles; reference numeral 7, a contaminant, reference numeral 8, a hole of the part 3 to be cleaned; reference numeral 9, a gas supply; and reference numeral 10, a bubble generator. The operation of the apparatus is described below. The part 3 to be cleaned having a surface provided with a complicated shape was placed in the exclusive jig 4 which has a mesh structure or the like so as to prevent the cage 4 from interrupting the flow of the cleaning liquid 1, and the part 3 was immersed in the cleaning liquid 1 containing the fine particles 6 in the cleaning bath 2. The cleaning bath was equipped with the stirring apparatus 5 such as a rolling fan for causing the cleaning liquid 1 to flow which can accurately cause a liquid current by rotation. The fine particles 6 contained in the cleaning liquid 1 were moved together with the liquid current, caused to collide with the surface of the part 3 by virtue of inertia so as to separate the contaminant 7 adhering to the surface of the part 3 and entrap the contaminant 7 in the cleaning liquid 1, thereby removing the contaminant 7. The stirring apparatus 5 was provided with the function of controlling the rotational speed, rotational direction and the angle with respect to the part 3 for converting the liquid flow into an eddy flow so as to cause a flow in the hole 8. The contaminant 7 in the hole 8 of the part 3 to be cleaned having a complicated structure was thus able to be removed by causing the particles 6 to collide with the entire internal surface of the hole 8, whereby the overall surface of the part 3 was cleaned. The cleaning apparatus may be provided with a gas supply 9 for supplying bubbles in the cleaning liquid 1 and a bubble generator 10 for generating fine bubbles of gas by employing ultrasonic waves, both of which are provided together with the stirring apparatus 5 or in place of the apparatus 5 so that the cleaning efficiency in the hole 8 can be further increased. The above cleaning method mainly utilizes the liquid dynamic effect of the cleaning liquid. Other considerable effects include the temperature effect of the cleaning liquid and the effect of characteristics of the fine particles in the cleaning liquid. In regard to the temperature effect, for example, the efficiency of removal of the rosin wax fused on a glass board was increased by several times when the temperature of the cleaning liquid is increased to 60 to 80°C. The type of the fine particles mixed in the cleaning liquid and the results of measurement of the mixing state, particle size, specific gravity, hardness and so on of the particles are described below. The type of the particles, which is effective for cleaning, was particles of calcium carbonate, which were insoluble in the cleaning liquid. A particle size of several µm to several mm was effective. The specific gravity of the particles may be a value which allows the particles to suspend in a liquid state (stirring function) (which may allows the particles to sediment in the liquid in a stationary state). Although the hardness of the particles had a relation to the material of the part to be cleaned and the flow rate of the liquid, it was necessary to select a degree of hardness which caused no flaw on a surface. Although the influences of the factors on an increase in the cleaning efficiency are related to each other and complicated, it was effective to use calcium carbonate particles when a precision part such as a print circuit board was cleaned by using as a cleaning liquid pure water. Pure water was used as the cleaning liquid because of its easy handling, safety and low cost. (Embodiment 2) Fig. 2 is a schematic drawing of a cleaning apparatus which is particularly effective to a substance to be cleaned off such as solid fat or oil. In Fig. 2, reference numeral 1 denotes a cleaning liquid; reference numeral 2, a cleaning bath; reference numeral 3, a part to be cleaned; reference numeral 4, a jig in which the part 3 is placed; reference numeral 5, a stirring apparatus; reference numeral 6, fine particles; reference numeral 8, a hole of the part 3 to be cleaned; reference numeral 11, a heating heater; reference numeral 12, a temperature measuring device; reference numeral 13, a temperature controller; and reference numeral 14, a solid fat or oil contaminant. The operation of the apparatus is described below. The part 3 to be cleaned having a surface having a complicated shape was placed in the exclusive jig 4 which has a mesh structure or the like so as to prevent the jig 4 from interrupting the flow of the cleaning liquid 1, the part 3 being immersed in the cleaning liquid 1 containing the fine particles 6 in the cleaning bath 2. The cleaning bath was equipped with the stirring apparatus 5 such as a rolling fan which accurately caused a liquid current by rotation for causing the cleaning liquid 1 to flow. At the same time, the cleaning liquid 1 was heated to a desired temperature by the heating heater 11, the temperature of the cleaning liquid 1 being measured by the temperature measuring device 12. The heating heater 11 was turned on and off by the temperature controller 13 which received the measurement results from the temperature measuring device 12. The solid fat or oil contaminant 14 adhering to the part 3 to be cleaned was heated and softened by the cleaning liquid 1 heated by the heating heater 11. The fine calcium carbonate particles 6 contained in the cleaning liquid 1 were moved together with the flow of the cleaning liquid 1 and caused to collide with a surface of the parts 3 by virtue of inertia so as to separate the softened solid fat or oil contaminant 14 adhering to the surface and entraped the contaminant 14 in the cleaning liquid 1, thereby removing the contaminant 14. The stirring apparatus 5 was provided with the function of controlling the rotational speed, rotational direction and the angle with respect to the part 3 for converting the liquid flow into an eddy flow so as to cause a flow in the hole 8. The contaminant 7 in the hole 8 of the part 3 to be cleaned having a complicated structure was thus able to be removed by causing the particles 6 to collide with the entire internal surface of the hole 8, whereby the overall surface of the part 3 can be cleaned. Fig. 3 shows a relation between the temperature of the cleaning liquid and the cleaning time when solid fat or oil contaminant was cleaned off by the cleaning apparatus in accordance with the present invention. Table 1 shows the time required for removing each of the five types of wax including the stick wax, sky wax, hot wax, apiezon wax and hot melt, which were used as solid fat or oil, by cleaning using a cleaning liquid at two temperatures, a temperature below the softening point of the wax and a temperature above the softening point of the wax. In Table 1, mark x represents the cleaning result that the fat or oil could not be removed by cleaning for 20 minutes. It can be seen from Table 1 that any one of the wax types used can be removed by cleaning using the cleaning liquid at a temperature near the softening point of the wax for a time of about 1 minute. It can also be seen that much time is required for cleaning by using the cleaning liquid at a temperature below the softening point. The present invention therefore enables the contaminant adhering to a surface of a substrate to be cleaned, which surface has a complicated shape and a structure with a hole, a recess or the like, to be easily and efficiently removed by cleaning. The present invention also enables the contaminant adhering to a surface of a substance to be cleaned having a complicated shape and a structure with a hole, a recess or the like to be easily and efficiently removed by cleaning for a short time. Particularly, the present invention has the significant effect of cleaning off solid fats and oils without using CFC or a chlorocarbon-type organic solvent which has at present an environmental problem all over the world.

Claims: Apparatus for cleaning a solid surface (3) containing a solid fat or oil (7) thereon, comprising a cleaning bath (2) containing a cleaning liquid (1) and means (5) for bringing said cleaning liquid into an eddy-flow state, characterized by said cleaning liquid (1) being a mixture of pure water and calcium carbonate particles (6), and by means (11) for heating the cleaning liquid (1) up to a temperature near to softening point of said solid fat or oil (7 or 4). Apparatus for cleaning a solid surface (3) according to claim 1, wherein said means (5) for bringing said cleaning liquid into an eddy-flow state is a stirring device (5). Apparatus for cleaning a solid surface (3) according to claim 1, wherein said means (5) for bringing said cleaning liquid into an eddy-flow state is a vibration generating device (5). Apparatus for cleaning a solid surface (3) according to claim 1, further comprising means (10) for mixing bubbles in said cleaning liquid (1). Method of cleaning a solid surface (3) by bringing a cleaning liquid (1) into contact with said solid surface (3) to be cleaned in a cleaning bath (2), which solid surface (3) includes a solid fat or oil (7) thereon, comprising the following steps: mixing pure water and calcium carbonate particles (6) insoluble in water to thereby prepare said cleaning liquid (1), heating the cleaning liquid up to a temperature near to the softening point of said solid fat or oil (7), and making the cleaning liquid (1) to be in an eddy-flow state, whereby the softened solid fat or oil (14) is removed. Method of cleaning a solid surface (3) according to claim 5, further comprising the step of mixing bubbles (10) in said cleaning liquid (1) so that the pure water and the calcium carbonate particles (6) insoluble in water are mixed in an eddy-flow state. Method of cleaning a solid surface (3) according to claim 5, further comprising the steps of closing the cleaning bath (2) and vibrating the cleaning bath (2) so that the mixture (1) of pure water and calcium carbonate particles (6) is in an eddy-flow state.

Inventors: HAMANO MEGUMI HACHIMANYAMA APA, OTAKE MITSUYOSHI, TAKIZAWA YOSHIHARU, WATANABE MASAHIRO, HAMANO, MEGUMI HACHIMANYAMA APATO 126, OTAKE, MITSUYOSHI, TAKIZAWA, YOSHIHARU, WATANABE, MASAHIRO
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1991
Main classification: B24B31
IPC codes: B08B7, B08B3, H01L21, B24B31, H05K3