Patent Publication Number: US-2011056840-A1

Title: Electrolytic plating equipment and electrolytic plating method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electrolytic plating equipment and an electrolytic plating method. 
     2. Background Art 
     Electrolytic plating is used for forming wiring patterns on printed boards for example. In copper sulfate electrolytic plating for example, various additives including suppressors and promoters (called brighteners, carriers, levelers and the like) are added to the plating solution to obtain coating performance in terms of improved gloss, physical coating properties, throwing power, blind via hole filling and the like. 
     Of these additives, suppressors work effectively on the board surface, while promoters work effectively in the through holes and blind via holes to promote throwing of the through holes and filling of the blind via holes. If there is too much promoter in the plating solution, however, the ability of the suppressor to suppress growth of active nuclei will be reduced, resulting in a less dense coating with inferior physical properties. The effect of controlling precipitation on the board surface will also be reduced, causing problems with throwing of the through holes, filling of the blind via holes and the like. If there is too little promoter in the plating solution, on the other hand, it will be less able to promote formation of active nuclei, resulting in a less dense coating with inferior physical properties. The promoting effects within the through holes and blind via holes may also be insufficient, causing problems with throwing of the through holes, filling of the blind via holes and the like. Consequently, a suitable balance of the various additives in the plating solution is important. 
     The dissolved oxygen concentration of the plating solution is known as one factor the affects the coating performance of electroplate. The reasons for this are explained by means of an example using bis(3-sulfopropyl)disulfide (SPS), a common brightener in copper sulfate electrolytic plating. That is, a sequence of oxidation-reduction reactions such as the following occurs during plate processing. SPS is reduced on the surface of the cathode, becoming 3-mercapto-1-propane sulfonic acid (MPS). 
     SPS acts as a promoter by reducing copper ions when two MPS dimerizes to reform one SPS near the cathode. MPS not participating in this reaction is oxidized by dissolved oxygen to reform SPS. If the dissolved oxygen is insufficient, however, MPS binds to Cu + , and accumulates as Cu + -MPS. When Cu + -MPS accumulates the brightener concentration becomes too high, and the desired coating performance cannot be obtained. If the oxygen concentration is too high, more MPS is oxidized by the oxygen, and less MPS is available for reducing the copper ions, detracting from the promoting effects so that the desired coating performance are not sufficiently obtained. 
     Thus, the dissolved oxygen concentration in the plating solution needs to be adjusted to the appropriate range, but when soluble anodes are used, dissolved oxygen is expended in dissolving metal copper and the like, reducing the dissolved oxygen concentration of the plating solution, while when insoluble anodes are used, the dissolved oxygen concentration of the plating solution increases because the anodes generate oxygen. A variety of techniques have therefore been proposed for adjusting the dissolved oxygen concentration of the plating solution to a specific range. 
     For example, Japanese Patent Application Laid-open No. 2004-143478 discloses an electrolytic plating equipment using soluble anodes as the anodes. This equipment is provided with a plating tank for holding the plating solution and a separate tank apart from the plating tank, and has a structure in which the plating solution circulates between the plating tank and the separate tank. It is claimed that with this equipment, the problem of reduced coating quality can be solved by blowing air into the plating solution in the separate tank via an air blowing nozzle to thereby maintain the dissolved oxygen concentration of the plating solution at 5 ppm or more. 
     Japanese Patent Application Laid-open No. 2007-169700 discloses an electrolytic plating method using insoluble anodes as the anodes. It is claimed that with this method, non-penetrating holes in a material to be plated can be filled stably for a long period if the plating solution is agitated in the plating tank with air or inactive gas to maintain a dissolved oxygen concentration of 30 mg/liter or less. 
     The required level of plating quality has increased in recent years, however, as the wiring, through holes, blind via holes and the like in printed boards have become smaller. When there is floating foreign matter in the plating solution, for example, nodules (a portion in the form of a swelling) may form in part of the coating around this foreign matter, so electrolytic plating equipments are equipped with filter for separating foreign matter from the plating solution. This filter is capable of filtering out various kinds of foreign matter from the plating solution. 
     However, if many copper or other metal particles adhere to the filter for example, the dissolved oxygen in the plating solution may be expended by the metal particles, or additives (such as sulfur additives and the like) in the plating solution may be affected. Consequently, the filter must be replaced frequently to prevent a loss of quality of the plating. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electrolytic plating equipment and electrolytic plating method whereby the dissolved oxygen concentration of a plating solution can be adjusted and costs associated with filter replacement reduced. 
     The electrolytic plating equipment of the present invention includes: a plating tank for holding the plating solution; and a separate tank apart from the plating tank, for holding the plating solution circulating between the plating tank and the separate tank. This separate tank has therein a first space and a second space located downstream from the first space, and has a structure in which the plating solution in an amount exceeding a specific height in the first space flows from the first space into the second space, and the plating solution falls through air in the second space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the electrolytic plating equipment of the first embodiment of the present invention; 
         FIGS. 2A to 2F  show modified examples of the structure of the upper edge in the separate tank of the electrolytic plating equipment; 
         FIGS. 3A to 3E  show modified examples of the shape and arrangement of the source pipe; 
         FIG. 4  shows the separate tank of the electrolytic plating equipment of the second embodiment of the present invention; 
         FIG. 5  shows the separate tank of the electrolytic plating equipment of the third embodiment of the present invention; 
         FIG. 6  shows the electrolytic plating equipment of the fourth embodiment of the present invention; 
         FIG. 7  shows the electrolytic plating equipment of the fifth embodiment of the present invention; 
         FIGS. 8A and 8B  show the plating tank of the electrolytic plating equipment of the sixth embodiment of the present invention; 
         FIGS. 9A and 9B  show the plating tank of the electrolytic plating equipment of the seventh embodiment of the present invention; 
         FIG. 10  shows the electrolytic plating equipment of the eighth embodiment of the present invention; 
         FIG. 11A  shows the first partition of the separate tank of the electrolytic plating equipment of the ninth embodiment of the present invention, and  FIG. 11B  shows the XIB-XIB cross-section in  FIG. 11A ; 
         FIG. 12  shows the electrolytic plating equipment used in Example 1; 
         FIG. 13A  shows the electrolytic plating equipment used in Example 2, and  FIG. 13B  shows the XIIIB-XIIIB cross-section in  FIG. 13A ; 
         FIG. 14  shows the electrolytic plating equipment used in Example 3; 
         FIGS. 15A and 15B  are a cross-section for explaining the method of measuring pit of the blind via holes in Examples 1 and  3 ; 
         FIG. 16  is a plane view showing the shape of a test sample used to measure elongation and tensile strength in Examples 1 to 3; and 
         FIG. 17  is a cross-section for explaining the method of evaluating throwing power of the through holes in Example 2. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     Embodiments of the present invention are explained in detail below with reference to the drawings. In the following embodiments, the invention is explained with reference to examples in which an object is plated with copper. 
     First Embodiment 
     As shown in  FIG. 1 , electrolytic plating equipment  11  of the first embodiment of the present invention is provided with plating tank  13 , separate tank  15  apart from plating tank  13 , source pipe  29  that sends plating solution from plating tank  13  to separate tank  15 , and return pipe  41  that returns plating solution from separate tank  15  to plating tank  13 . 
     Plating tank  13  has roughly rectangular, open-topped tank body  47  and overflow tank  49 , which is integrated with tank body  47 . Anodes  55  are arranged inside tank body  47 . Tank body  47  is configured to allow insertion of cathode  57 , which is the object to be plated. 
     Anodes  55  are arranged on both sides of cathode  57 . Soluble anodes or insoluble anodes are used for anodes  55 . In the case of soluble anodes, copper plates can be used for example. Spherical copper (copper balls) contained in a titanium or other mesh container can also be used for the soluble anodes. These copper plates or copper balls may be formed from phosphate-containing copper for example. In the case of insoluble anodes, Ti—Pt coated with indium oxide can be used for example. 
     Each anode  55  is contained in an anode back  59 , which allows the passage of plating solution but not of anode slime. Anode backs  59  are formed from a material such as polypropylene or polyethylene for example. 
     Nozzles  61  are arranged vertically between cathode  57  and anodes  55 , facing cathode  57 . Each nozzle  61  is provided with multiple spray nozzles (not shown) for spraying plating solution supplied from separate tank  15  via source pipe  41  in the direction of cathode  57 . Plating solution around cathode  57  can be agitated by jets from such nozzles  61 . In addition to such agitation by jets, plating solution around cathode  57  can also be agitated mechanically with a mechanical agitator such as a squeegee or paddle (not shown). Agitation by jets can also be combined with mechanical agitation. 
     Voltage from a power source (not shown) is applied between anodes  55  and cathode  57 . Cathode  57  (the object to be plated) can be electroplated in this way. 
     Overflow tank  49  is attached integrally to the side of tank body  47 . Plating solution in tank body  47  spills over upper edge  53  of side wall  51  of tank body  47  into this overflow tank  49 . This overflow tank  49  can also be provided with a liquid level sensor (not shown) for detecting the liquid level inside the tank. The liquid level in overflow tank  49  can be adjusted by controlling the operation or shutoff of pump  63  based on the detection results from this liquid level sensor. 
     Separate tank  15  has roughly rectangular, open-topped separate tank body  20  and first partition  21 , which divides this separate tank body  20  into two spaces. First partition  21  is a roughly rectangular partition extending upwards from the bottom surface of separate tank body  20 . This first partition  21  divides the inside of separate tank  15  into first space  17  and second space  19  located downstream from first space  17 . As shown in  FIGS. 1 and 2A , first partition  21  has partition body  25  extending from the bottom towards the top of separate tank  15 , and lip (extending portion)  27  extending from the top edge of partition body  25  towards second space  19 . 
     Upper edge  23  of first partition  21  is set at a specific height below the upper edge of separate tank body  20 . That is, separate tank  15  has a structure whereby that part of the plating solution that exceeds this specific height in first space  17  overflows upper edge  23  and flows from first space  17  into second space  19 . In separate tank  15 , first space  17  and second space  19  only communicate in the space above upper edge  23  of first partition  21 . In the structure of separate tank  15 , first space  17  and second space  19  are separated so that plating solution does not move between first space  17  and second space  19  below upper edge  23 . 
     The plating solution flowing into second space  19  falls through air in second space  19 . The liquid surface of the plating solution in second space  19  is adjusted to a position lower than the specific height of upper edge  23  of first partition  21  so as to cause the plating solution to fall through air in this way in second space  19 . 
     The liquid surface of the plating solution in second space  19  can be adjusted by controlling the operation or shutoff of pump  64  provided on return pipe  41  for example. Second space  19  can also be provided with a liquid level sensor (not shown) for detecting the liquid level inside this space. The liquid level in second space  19  can be adjusted by controlling the operation or shutoff of pump  64  based on the detection results from this liquid level sensor. 
     Lip  27  extends horizontally from the upper edge of partition body  25  toward second space  19 , and its end is separated from the side surface of partition body  25  facing second space  19 . With this lip  27 , plating solution flowing from first space  17  into second space  19  is conducted along lip  27  to the end of the lip  27 , where it separates from lip  27  and is released into air. Because the outer end of lip  27  is separated from the side surface of partition body  25 , the plating solution can be restrained from flowing down the side surface of partition body  25 . 
     In this embodiment, first partition  21  is explained by means of an example having a lip  27  such as that shown in  FIG. 2A , but lips  27  such as the modified examples shown in  FIGS. 2B to 2D  are also possible, as are embodiments without lips such as the modified examples shown in  FIGS. 2E and 2F . 
     In the modified example of  FIG. 2B , lip  27  extends upwards at an angle from the top of partition body  25  towards second space  19 . As in the embodiment of  FIG. 2A , in this modified example the end of lip  27  is separated from the side surface of partition body  25 . As a result, the plating solution can be restrained from flowing down the side surface of partition body  25 , but in comparison to  FIG. 2A , the plating solution is more likely to flow along the surface (lower surface) of lip  27  facing second space  19 . 
     In the modified example of  FIG. 2C , lip  27  extends downward at an angle from the top of partition body  25  towards second space  19 . As in the embodiment of  FIG. 2A , in this modified example the end of lip  27  is separated from the side surface of partition body  25 , and the plating solution can be restrained from flowing down the side surface of partition body  25 . Moreover, because lip  27  extends downwards at an angle, the plating solution is almost completely prevented from contacting the lower (inner) surface of lip  27 . In this respect the modified example of  FIG. 2C  is superior to the embodiment of  FIG. 2A . 
     In the modified example of  FIG. 2D , lip  27  has horizontal part (lateral part)  27   a  extending horizontally towards second space  19  from the top of partition body  25 , and vertical part (lower part)  27   b  extending downwards from the lateral end of horizontal part  27   a . The lower end of this vertical part  27   b  is separated from the side surface of partition body  25 . As in  FIG. 2A , in this modified example plating solution can be restrained from flowing down the side surface of partition body  25  because the end of lip  27  is separated from the side surface of partition body  25 . Moreover, in this embodiment plating solution flowing into second space  19  from first space  17  is first conducted along horizontal part  27   a  to the end of this part, and then flows downward along vertical part  27   b . There is a large distance between this edge and the side surface of partition body  25 . Consequently, plating solution is prevented almost completely from contacting the inner surface of lip  27 . In this respect, the modified example of  FIG. 2D  is superior to the embodiment of  FIG. 2A . 
     In the modified examples of  FIGS. 2E and 2F , first partition  21  has no lip. In the modified example of  FIG. 2E , first partition  21  is disposed vertically. In the modified example of  FIG. 2F , first partition  21  is arranged at an angle to the perpendicular direction. The first partition  21  of this modified example is slanted so that the lower part is downstream from the upper part. 
     The upstream ends of source pipe  29  are connected to the bottom of overflow tank  49  and to side wall  51  of tank body  47 , communicating with overflow tank  49  and tank body  47 . The downstream end of source pipe  29  is provided with supply port  29   a , which supplies plating solution to separate tank  15 . 
     As shown in  FIGS. 1 and 3A , supply port  29   a  is located above the liquid surface of the plating solution in first space  17 , and does not contact the plating solution. Consequently, when plating solution discharged from supply port  29   a  flows downward from supply port  29   a  to contact plating solution held in first space  17 , it administers some degree of shock to this plating solution. This causes some fluid movement of the plating solution in first space  17 . 
     In the modified examples of  FIGS. 3B to 3E , supply port  29   a  of source pipe  29  is located below the aforementioned specific height. That is, supply port  29   a  may also be located below the liquid surface of the plating solution in first space  17 , so as to be immersed in the plating solution. In these modified examples, the plating solution discharged from supply port  29   a  is supplied directly within the plating solution held in first space  17 . The shock to the plating solution in first space  17  is thus less than in the embodiment of  FIG. 3A , in which the plating solution from supply port  29   a  is first discharged into air before falling onto the liquid surface of the plating solution held in first space  17 . 
     In the modified example of  FIG. 3C , the downstream end of source pipe  29  is bent so that the plating solution from supply port  29   a  is directed towards inner surface  20   a  of separate tank body  20 . In this modified example, fluid movement of the plating solution held in first space  17 , and particularly plating solution located towards the bottom of the tank, is suppressed more than in the embodiment of  FIG. 3B , in which the plating solution is discharged downwards. 
     In the modified example of  FIG. 3D , the downstream end of source pipe  29  is branched (into 6 in this modified example), having multiple supply ports  29   a  for discharging plating solution. The discharge speed of the plating solution discharged from each supply port  29   a  is thus less than in the modified example of  FIG. 3B . Consequently, it is possible to suppress fluid movement of plating solution held in first space  17 , and particularly plating solution located towards the bottom of the tank. 
     In the modified example of  FIG. 3E , source pipe  29  has a structure in which the inner diameter of the downstream end of the pipe is wider than at other sites. The discharge speed of the plating solution discharged from supply port  29   a  is thus less than in the modified example of  FIG. 3B . Consequently, it is possible to suppress movement of plating solution held in first space  17 , and particularly plating solution located towards the bottom of the tank. 
     As shown in  FIG. 1 , the upstream end of return pipe  41  is connected to the side of separate tank body  20 , communicating with second space  19 . The downstream end of return pipe  41  is branched into multiple ends (3 in this embodiment). Two of these multiple ends,  41   a  and  41   b , are connected to the aforementioned pair of nozzles  61 , communicating with nozzles  61 . The remaining end  41   c  of a plurality of pipe ends is connected to the bottom of tank body  47 , communicating with the inside of tank body  47 . This end  41   c  is located near the side of tank body  47  opposite overflow tank  49 . 
     Filter  65  is attached to return pipe  41  upstream from the branches. Pump  64  is provided on return pipe  41  upstream from this filter  65 . Operating this pump  64  and the aforementioned pump  63  causes plating solution to circulate between plating tank  13  and separate tank  15 . Filter  65  can filter the plating solution to separate out various kinds of foreign matter from the liquid. 
     The bath volume ratio of the plating tank  13  and separate tank  15  (volume of plating tank  13 :volume of separate tank  15 ) is preferably between 0.1:1 and 30:1 or more preferably between 0.3:1 and 10:1. If the volume of plating tank  13  is less than 0.1 times the volume of separate tank  15 , separate tank  15  will be so large as to be impractical. If the volume of plating tank  13  is more than 30 times the volume of separate tank  15 , on the other hand, the ability to adjust the dissolved oxygen in separate tank  15  may be inadequate. 
     The circulating volume (turns) is calculated as circulation speed (liters/minute)×60 (minutes/hour)/total capacity (liters), and is preferably 5 to 100 turns or more preferably 10 to 80 turns relative to total bath volume (total amount of plating solution circulating in the electrolytic plating equipment). A circulating volume of less than 10 turns may be insufficient for adjusting the dissolved oxygen in separate tank  15 . On the other hand, a circulating volume of more than 100 turns is impractical because it necessitates a large circulation pump or several circulation pumps. 
     A copper sulfate plating solution for example is used as the plating solution. A copper sulfate plating solution comprises a specific amount of sulfuric acid added to copper sulfate as the copper source. Various additives can be added as necessary to this copper sulfate plating solution. These additives may be organic additives such as suppressors and promoters, called brighteners, levelers and carriers. Examples of these organic additives include nitrogen-containing organic compounds, sulfur-containing organic compounds, oxygen-containing organic compounds and the like. Specific examples of sulfur-containing compounds include sulfur compounds selected from the following formulae (1) to (4) below. 
     
       
         
         
             
             
         
       
     
     (wherein R 1 , R 2  and R 3  are each C 1-5  alkyl groups, M is a hydrogen atom or alkali metal, a is an integer from 1 to 8 and b, c and d are each either 0 or 1.) 
     Well-known nitrogen-containing organic compounds can also be used, such as tertiary amine compounds, quaternary ammonium compounds and the like for example. Known oxygen-containing compounds can be used, such as polyethylene glycol and other polyether compounds for example. 
     When the components of the copper sulfate plating solution have become decreased by continuous electrolytic copper plating, they can be replenished as necessary by adding a replenishing solution. Continuous electrolytic copper plating is thus possible. Copper ions can also be replenished from the soluble anodes when soluble anodes are used. When insoluble anodes are used, a tank capable of supplying copper ions can be provided separately from plating tank  13 , and copper ions in the plating tank can be replenished from this tank. 
     Next, the operations of electrolytic plating equipment  11  of this embodiment are explained. During the initial bath makeup, specific quantities of plating solution are deposited in tank body  47  and overflow tank  49  of plating tank  13 , and in first space  17  and second space  19  of separate tank  15 . 
     Next, pump  63  and pump  64  are operated to circulate the plating solution between plating tank  13  and separate tank  15 . The liquid levels in overflow tank  49  and second space  19  are adjusted by controlling the operation or shutoff of pump  63  and pump  64 . Under these conditions, cathode  57  as the object to be plated is immersed in the plating bath in tank body  47 , and current is applied between anodes  55  and cathode  57 . The object to be plated is copper electroplated in this way. When electrolytic plating is complete, the object to be plated is replaced with another object, and successive electrolytic copper plating is performed. 
     Next, the flow of plating solution is explained. When pump  64  operates, plating solution is supplied to the inside of tank body  47  via return pipe  41 . When plating solution is supplied to this tank body  47 , plating solution in the same quantity as the liquid supplied flows over top edge  53  of side wall  51  of tank body  47 , and into overflow tank  49 . 
     When pump  63  operates, the plating solution in overflow tank  49  and tank body  47  is supplied to first space  17  of separate tank  15  via source pipe  29 . Foreign matter such as for example slough from cathode  57  or copper particles resulting from slime generated by the soluble anodes are floating in the plating solution. Copper particles that are denser than the plating solution drop down in first space  17  of separate tank  15  to settle at the bottom of first space  17 . 
     When plating solution is supplied to first space  17  via source pipe  29 , meanwhile, plating solution in the same amount as the supplied liquid flows over upper edge  23  of first partition  21  and into second space  19 . Plating solution entering second space  19  falls through air in second space  19  to arrive at the surface of the plating solution held in second space  19 . Exposing plating solution to air in this way as it falls serves to adjust the dissolved oxygen concentration of the plating solution. Specifically, when soluble anodes are used for anodes  55 , a drop in the dissolved oxygen concentration of the plating solution can be prevented by incorporating oxygen from air into the plating solution during plating. If insoluble anodes are used for the anodes, on the other hand, a rise in the dissolved oxygen concentration of the plating solution can be prevented by discharging oxygen as necessary into air from the plating solution during plating. 
     The dissolved oxygen concentration is adjusted by changing the time during which the plating solution falls through air, the surface area of contact with air as it falls through air and the like. The time during which the plating solution falls through air and the surface area of contact of the plating solution with air as it falls through the air can be adjusted by changing the distance between the top edge  23  of first partition  21  and the surface of the plating solution in second space  19  for example, or the width of upper edge  23  overflowed by the plating solution. 
     The dissolved oxygen concentration of the plating solution in tank body  47  of plating tank  13  can preferably be 4 to 20 mg/liter. If the dissolved oxygen concentration is less than 4 mg/liter or more than 20 mg/liter, the quality of the plate may be adversely affected. Specifically, physical coating properties such as the elongation and tensile strength of the plating may decline, or the throwing power (TP) of the through holes in the printed board may be reduced, or filling of the blind via holes may be reduced (increased pit). 
     Since in this embodiment the plating solution in first space  17  overflows into second space  19  as described above, air is incorporated into the plating solution as it falls due to this overflow. The dissolved oxygen concentration of the plating solution can thus be made to approach the saturated dissolved oxygen concentration. Air consists primarily of oxygen (about 20%) and nitrogen (about 80%). As a benchmark, the saturated dissolved oxygen concentration of water at 25° C. is about 8.1 mg/liter. When the dissolved oxygen concentration of the plating solution is below the aforementioned desirable range (4 to 20 mg/liter), oxygen from the air dissolves into the plating solution as it overflows and falls through the air, bringing the dissolved oxygen concentration of the plating solution closer to the saturated dissolved oxygen concentration. The dissolved oxygen concentration of the plating solution can thus be easily adjusted to the desirable range. When the dissolved oxygen concentration of the plating solution is above the aforementioned desirable range, on the other hand, part of the oxygen that dissolved into the plating solution as it overflowed and fell through the air is released appropriately into air due to the effect of the nitrogen in the air, bringing the dissolved oxygen concentration of the plating solution closer to the saturated dissolved oxygen concentration. The dissolved oxygen concentration of the plating solution can thus be easily adjusted to the desirable range. 
     The distance (drop) between upper edge  23  of first partition  21  and the surface of the plating solution in second space  19  is not particularly limited, but is preferably at least cm or more preferably at least 15 cm for purposes of efficiently adjusting the dissolved oxygen concentration. The drop should also be no more than 100 cm so that separate tank  15  does not become too large. 
     In this embodiment, a configuration in which separate tank has only one partition and the plating solution overflows only once is given as an example, but as explained below, overflow can be made to occur more than once in separate tank  15  by providing multiple partitions within the separate tank body. The number of overflows in separate tank  15  is preferably 2 or more from the standpoint of allowing more efficient adjustment of the dissolved oxygen concentration. The number of overflows is preferably 5 or less so that separate tank  15  does not become too large. 
     As explained above, in the first embodiment that part of the plating solution that exceeds a specific height flows from first space  17  into second space  19 , while that part at or below the specific height remains in first space  17 . As a result, metal particles in the plating solution remaining in first space  17  can be made to settle at the bottom of first space  17 . If the metal particles settle and accumulate in this way at the bottom of first space  17 , it is possible to efficiently remove metal particles in the plating solution by a collection means such as scheduled collection of the metal particles for example. In this way, it is possible to reduce the frequency of replacing filter  65  in electrolytic plating equipment  11 , and in some cases filter  65  may not be necessary. The dissolved oxygen concentration of the plating solution can also be adjusted by causing that part of the plating solution in first space  17  that exceeds a fixed height to flow into second space  19  and fall through air in second space  19 , or in other words by exposing the plating solution in a flowing state to air. Consequently, with the first embodiment it is possible to adjust the dissolved oxygen concentration of the plating solution and also reduce the costs associated with filter replacement. 
     Specifically, when soluble anodes are used as the anodes, it is possible to prevent a drop in dissolved oxygen concentration of the plating solution because oxygen from air is incorporated into the plating solution during plating. When insoluble anodes are used as the anodes, it is possible to prevent a rise in dissolved oxygen concentration of the plating solution because a suitable amount of oxygen is released into air from the plating solution during plating. 
     In the first embodiment, upper edge  23  extends towards second space  19 , and its end has lip  27 , which is separated from the side of the first partition  21 . Thus, plating solution flowing from first space  17  into second space  19  is conducted along lip  27  to the end of the lip  27 , where it separates from lip  27  and is released into air. As a result, in the first embodiment plating solution is prevented from falling along the side of first partition  21 . It is thus possible to increase the area of contact of the plating solution with air as it falls, and thus to more efficiently adjust the dissolved oxygen concentration of the plating solution. 
     Second Embodiment 
       FIG. 4  shows separate tank  15  of electrolytic plating equipment  11  of the second embodiment of the present invention. In this second embodiment, the structure of first space  17  of separate tank  15  is different from that of the first embodiment. Components that are the same as in the first embodiment are indicated by the same symbols (reference numbers), and detailed explanations are omitted. 
     As shown in  FIG. 4 , separate tank  15  has second partition  35  in addition to separate tank body  20  and first partition  21 . This second partition  35  is roughly rectangular, and extends vertically from the bottom of separate tank body  20 . Second partition  35  divides the inside of first space  17  into two spaces. One space is supply space  33  to which plating solution is supplied from supply port  29   a  of source pipe  29 , while the other space, located downstream from supply space  33 , is settling space  31  for settling metal particles  32  from the plating solution. 
     Second partition  35  has multiple communicating holes communicating between settling space  31  and supply space  33 . These communicating holes are provided below the aforementioned specific height, or in other words below the height of upper edge  23  of first partition  21 . Plating solution in first space  17  can move from supply space  33  to settling space  31  through these multiple communicating holes. A resin plate, metal plate or the like having multiple through holes arranged at fixed intervals across the entire surface can be used as second partition  35  for example. The communicating holes are adjusted to a size that allows at least the passage of metal particles. 
     In the second embodiment, first space  17  is divided by second partition  35  into settling space  31  and supply space  33 , and plating solution is supplied from supply port  29   a  of source pipe  29  to supply space  33 . Therefore, even if plating solution held in supply space  33  undergoes fluid movement when plating solution is supplied, this movement should not be communicated to settling space  31 . As a result, metal particles  32  can be deposited more efficiently than if there were no second partition  35  dividing first space  17 . 
     Moreover, in the second embodiment second partition  35  has multiple communicating holes provided below a specific height that communicate between settling space  31  and supply space  33 . As a result, plating solution supplied to supply space  33  is dispersed as it moves through the multiple communicating holes of second partition  35  into settling space  31 . Fluid movement of the plating solution held in settling space  31  can be suppressed because the plating solution is dispersed as it flows through the multiple communicating holes into settling space  31 . 
     Other configurations, actions and effects are not mentioned here because they are the same as in the first embodiment. 
     Third Embodiment 
       FIG. 5  shows separate tank  15  of electrolytic plating equipment  11  of the third embodiment of the present invention. In this third embodiment, the structure of first space  17  of separate tank  15  is different from those of the first and second embodiments. Constituent elements that are the same as in the first embodiment are indicated by the same symbols, and detailed explanations are omitted. 
     As shown in  FIG. 5 , separate tank  15  has second partition  35  in addition to separate tank body  20  and first partition  21 . This second partition  35  is rectangular, and extends vertically from the bottom of separate tank body  20  as in the second embodiment above. Second partition  35  divides the inside of first space  17  into supply space  33  and settling space  31 . The difference between this and the second embodiment is that second partition  35  of the third embodiment does not have multiple communicating holes. 
     In the third embodiment, upper edge  35   a  of second partition  35  is positioned below the aforementioned specific height so that the height of upper edge  35   a  of second partition  35  is lower than the surface of the plating solution held in settling space  31 . In this way, plating solution in first space  17  can move from supply space  33  to settling space  31  over upper edge  35   a  of second partition  35 . 
     Consequently, because the third embodiment has second partition  35 , the fluid movement of plating solution that occurs when plating solution is supplied to supply space  33  from supply port  29   a  is unlikely to be communicated to settling space  31 . Moreover, because the plating solution flows into settling space  31  from supply space  33  over upper edge  35   a  of second partition  35 , it is possible to prevent metal particles  32  that have settled at the bottom of the settling space from being stirred up again. 
     Other configurations, actions and effects are not explained because they are the same as in the first embodiment. 
     Fourth Embodiment 
       FIG. 6  shows electrolytic plating equipment  11  of the fourth embodiment of the present invention. This fourth embodiment differs from the first embodiment in having re-supply pipe  43 . Constituent elements that are the same as in the first embodiment are indicated by the same symbols, and detailed explanations are omitted. 
     As shown in  FIG. 6 , in this fourth embodiment electrolytic plating equipment  11  is also provided with re-supply pipe  43  for returning plating solution discharged from separate tank  15  to first space  17 . One end  43   a  of this re-supply pipe  43  is connected to the lower side of separate tank body  20 , communicating with second space  19 . The other end  43   b  is located above first space  17 . Re-supply pipe  43  is provided with pump  66  and filter  68 . 
     Consequently, in the fourth embodiment part of the plating solution in second space  19  of separate tank  15  can be supplied again to first space  17  via re-supply pipe  43  before being returned to plating tank  13 . Foreign matter in the plating solution can thus be removed even more efficiently. 
     Other configurations, action and effects are not explained but are the same as in the aforementioned first embodiment. 
     Fifth Embodiment 
       FIG. 7  shows electrolytic plating equipment  11  of the fifth embodiment of the present invention. This fifth embodiment differs from the first embodiment in that underflow divider  45  is provided in second space  19 . Constituent elements that are the same as in the first embodiment are indicated with the same symbols, and detailed explanations are omitted. 
     As shown in  FIG. 7 , in this fifth embodiment divider  45  is provided in second space  19  downstream from first space  17 . This divider  45  is a plate arranged so that there is a gap between the bottom of separate tank body  20  and the lower edge of divider  45 , and second space  19  above the gap is divided into two regions of an upstream region and a downstream region. As a result, plating solution flowing from first space  17  into second space  19  always passes through this gap as it moves from the upstream region to the downstream region within second space  19 . This results in a more uniform agitation of the liquid in second space  19 . 
     Other configurations, actions and effects are not explained in detail, but are the same as in the first embodiment. 
     Sixth Embodiment 
       FIGS. 8A and 8B  show part of plating tank  13  of electrolytic plating equipment  11  of the sixth embodiment of the present invention.  FIG. 8A  shows part of plating tank  13  from the side, and  FIG. 8B  shows it from the top. In the sixth embodiment, the structure of overflow tank  49  of plating tank  13  is different from that of the first embodiment. Constituent elements that are the same as in the first embodiment are indicated with the same symbols, and detailed explanations are omitted. 
     As shown in  FIGS. 8A and 8B , in this sixth embodiment overflow tank  49  of plating tank  13  contains upstream space  71  and downstream space  73 , which is located downstream from upstream space  71 . Overflow tank  49  is composed of two tanks, first tank  75  and second tank  77 . Upstream space  71  is the space delineated by first tank  75  and side wall  51  of tank body  47 , while downstream space  73  is the space delineated by second tank  77  and side wall  51  of tank body  47 . 
     Looking at the upper edge  53  of side wall  51  of tank body  47 , the upper edge of first tank  75  and the upper edge of second tank  77 , the upper edge of second tank  77  is the highest while the upper edge of first tank  75  is the lowest. As shown in  FIG. 8B , the upper edge of first tank  75  is provided with a pair of overflow parts  81 . These overflow parts  81  are lower than the other parts so that plating solution can overflow from first tank  75  into second tank  77 . Through hole  79  connecting to source pipe  29  is provided at the bottom of second tank  77 . 
     Thus, plating solution overflows upper edge  53  of side wall  51  of tank body  47  into upstream space  71  of first tank  75 , then overflows the upper edge of first tank  75  into downstream space  73  of second tank  77 , and then flows into source pipe  29  via through hole  79 . Thus, the sixth embodiment is configured so that plating solution falls through air twice. As a result, the dissolved oxygen concentration of the plating solution can be adjusted not only in separate tank  15  but also in overflow tank  49  of plating tank  13 . 
     In this sixth embodiment in particular, the dissolved oxygen concentration can be adjusted efficiently as the plating solution flows from upstream space  71  to downstream space  73  and falls through air if the drop from the upper edge of first tank  75  to the liquid surface in second tank  77  is 10 cm or more. 
     Upper edge  53  of side wall  51  of tank body  47  preferably has a lip similar to that shown in  FIG. 2 . Similarly, the upper edge of first tank  75  preferably has a lip similar to that shown in  FIG. 2 . When the upper edge has a lip in this way, plating solution flowing from tank body  47  into first tank  75  and plating solution flowing from first tank  75  into second tank  77  is conducted along the lip to the end of the lip, where it separates from the lip and is released into the air. As a result, the plating solution can be prevented from flowing along the side surface of side wall  51  of the tank body  47  or the side surface of first tank  75 . In this way, the dissolved oxygen concentration of the plating solution can be adjusted more efficiently because the area of contact of the falling plating solution with air can be increased. 
     Other configurations, actions and effects are not explained but are the same as in the first embodiment. 
     Seventh Embodiment 
       FIG. 9A  and  FIG. 9B  show one part of plating tank  13  of electrolytic plating equipment  11  of the seventh embodiment.  FIG. 9A  shows part of the plating tank  13  from the side, while  FIG. 9B  shows it from the top. In the seventh embodiment, the structure of overflow tank  49  of plating tank  13  is different from that of the first embodiment, and the structure of first tank  75  is different from that of the sixth embodiment. Constituent elements that are the same as in the first embodiment and sixth embodiment are indicated with the same symbols, and detailed explanations are omitted. 
     As shown in  FIG. 9A  and  FIG. 9B , in the seventh embodiment first tank  75  has through holes  85  on the bottom surface, and discharge pipes  83  connected to these through holes  85 . Plating solution in upstream space  71  flows through these discharge pipes  83  to fall through air into downstream space  73 . The bottom of first tank  75  is positioned above the bottom of second tank  77 . Discharge pipes  83  can be omitted. 
     Other configurations, actions and effects are not explained but are the same as in the first embodiment. 
     Eighth Embodiment 
       FIG. 10  shows electrolytic plating equipment  11  of the eight embodiment of the present invention. This eighth embodiment differs from the first embodiment in that there are two overflows in separate tank  15 . Constituent elements that are the same as in the first embodiment are indicated with the same symbols, and detailed explanations are omitted. 
     As shown in  FIG. 10 , in this eighth embodiment separate tank  15  is provided with third partition  91 . This third partition  91  is rectangular in shape and extends vertically from the bottom of separate tank body  20 . The inside of separate tank  15  is divided by this third partition  91  into second space  19  and third space  93  located downstream from this second space  19 . In this way, the dissolved oxygen concentration of the plating solution can be adjusted even more efficiently. 
     In this eighth embodiment, moreover, second space  19  and third space  93 , which are downstream from first space  17  for settling metal particles, are provided with underflow dividers  45 . As in the fifth embodiment of  FIG. 7 , these dividers  45  are plates arranged so that there are gaps between the bottom of separate tank body  20  and the lower edges of dividers  45  in second space  19  and third space  93 , and second space  19  above the gap is divided into two regions, an upstream region and a downstream region, while third space  93  above the gap is also divided into two regions, an upstream region and a downstream region. As a result, plating solution flowing from first space  17  into second space  19  always passes through this gap as it moves from the upstream region to the downstream region within second space  19 , and plating solution flowing from second space  19  to third space  93  always passes through the gap as it moves from the upstream region to the downstream region within third space  93 , resulting in a more uniform mixing of the plating solution in second space  19  and third space  93 . 
     Upper edge  24  of third partition  91  has a structure similar to that of upper edge  23  of first partition  21 . That is, like upper edge  23  of first partition  21 , upper edge  24  of third partition  91  has lip  27 , so plating solution flowing from second space  19  into third space  93  is conducted along lip  27  to the end of the lip, where it separates from lip  27  and is released into air. As a result, plating solution can be prevented from flowing along the side surface of third partition  91 . It is thus possible to increase the contact area of the plating solution with air as it falls, and to more efficiently adjust the dissolved oxygen concentration of the plating solution. 
     Other configurations, actions and effects are not explained but are the same as in the first embodiment. 
     Ninth Embodiment 
       FIGS. 11A and 11B  show first partition  21  of the separate tank of the electrolytic plating equipment of the ninth embodiment. In this ninth embodiment, plating solution does not overflow the upper edge of first partition  21  as in the previous embodiments, but instead flows from first space  17  into second space  19  via through hole  95  provided at the aforementioned specific height in first partition  21 . 
     In the ninth embodiment, the plating solution may fall along the side surface of first partition  21  as it flows from first space  17  into second space  19 , but preferably falls without contacting the side surface of first partition  21 . For example, as shown in  FIG. 11B , first partition  21  preferably has lip  95   a  protruding laterally from the lower edge of through hole  95  in the side of the partition facing second space  19 . In this case, plating solution flowing from first space  17  into second space  19  is conducted along lip  95   a  to the end of the lip  95   a , where it separates from lip  95   a  and is released into the air. It is thus possible to prevent the plating solution from flowing along the side surface of first partition  21 . In this way, the contact area of the plating solution with air is increased as it falls, and the dissolved oxygen concentration of the plating solution can be more efficiently adjusted. 
     Other configurations, actions and effects are not explained but are the same as in the first embodiment. 
     Other Embodiments 
     The present invention is not limited to the aforementioned embodiments, and various changes and improvements are possible to the extent that they do not deviate from the intent of the invention. 
     For example, in the aforementioned embodiments an object to be plated was plated with copper in the examples given, but in addition to electrolytic copper plating the present invention is applicable to electrolytic nickel plating, electrolytic gold plating and the like for example. 
     In the aforementioned embodiments, separate tank  15  is divided by a partition or partitions into 2 or 3 spaces, but separate tank  15  can also be divided into 4 or more spaces. 
     Moreover, a re-supply pipe such as that of the fourth embodiment could also be provided in the electrolytic plating equipment of another embodiment. 
     The electrolytic plating equipment and electrolytic plating method using it of the aforementioned embodiments can be used favorably for forming wiring patterns on such plated objects as printed boards, wafers and the like, but applications thereof are not particularly limited. 
     The embodiments are summarized below as follows. 
     The electrolytic plating equipment of the aforementioned embodiments includes: a plating tank for holding the plating solution; and a separate tank apart from the plating tank, for holding the plating solution circulating between the two tanks. The separate tank has therein a first space and a second space located downstream from the first space, and has a structure in which the plating solution in the first space in an amount exceeding a specific height flows from the first space into the second space, and the plating solution falls through air in the second space. 
     With this configuration, since that part of the plating solution that exceeds a specific height flows from the first space into the second space while that part that is at or below the specific height remains in the first space, metal particles in the plating solution remaining in the first space can be allowed to settle at the bottom of the first space. If metal particles settle and accumulate in this way at the bottom of the first space, it is possible to efficiently remove metal particles in the plating solution by a collection means such as scheduled collection of the metal particles for example. In this way, filter exchange frequency can be reduced in the electrolytic plating equipment, or in some cases the filter can be eliminated altogether. 
     The dissolved oxygen concentration of the plating solution can also be adjusted by causing that part of the plating solution in the first space that exceeds a specific height to flow into the second space and fall through air in the second space, or in other words by exposing the plating solution in a fluid state to air. 
     In this way, as discussed above, not only can the dissolved oxygen concentration of the plating solution be adjusted, but costs associated with filter replacement can also be reduced. 
     A specific example of the structure of such a separate tank has a partition extending vertically so as to divide the first space from the second space, and has a structure in which the plating solution in the first space overflows an upper edge located at the aforementioned specific height on the partition, and flows into the second space. 
     In the electrolytic plating equipment according to the above embodiment, the upper edge of the partition has preferably an extending portion extending towards the second space, and the extending portion preferably has an end that is separated from the side of the partition. 
     In this configuration, plating solution flowing from the first space into the second space is conducted along the extending portion to the end of the extending portion, where it separates from the extending portion and is released into air. That is, when the upper edge of the partition is not provided with this extending portion, the plating solution flowing from the first space into the second space is likely to contact the side surface of the partition and flow along this side surface, but in the present configuration the plating solution can be prevented from flowing along the side surface. This serves to increase the area of contact of the plating solution with air as it falls, so that the dissolved oxygen concentration of the plating solution can be adjusted more efficiency. 
     In the electrolytic plating equipment according to the above embodiment, the extending portion preferably has a lateral part extending laterally towards the second space and a lower part extending downwards from a lateral end of the lateral part, and the end of the extending portion is a lower end of the lower part, the lower end is separated from the side surface of the partition. 
     In this configuration, plating solution can be restrained from flowing along the side surface of the partition because plating solution flowing from the first space into the second space is first conducted along the lateral part to the end of this part, thereby increasing its distance from the side surface of the partition, and then flows downwards along the lower part. 
     In the electrolytic plating equipment according to the above embodiment, the separate tank may have a partition extending vertically so as to divide the separate tank into the first space and the second space, and the partition may have a through hole located at the specific height, and the separate tank may have a structure in which the plating solution in the first space passes through the through hole to flow into the second space. 
     Preferably, the electrolytic plating equipment according to the above embodiment further includes a source pipe that sends plating solution from the plating tank to the separate tank, this source pipe has a supply port for supplying the plating solution to the first space, and this supply port is located below the aforementioned specific height. 
     In this configuration, because the supply port of the source pipe is located below the aforementioned specific height or in other words below the surface of the plating solution held in the first space, plating solution supplied to the first space from the supply port can be supplied directly inside the plating solution held in the first space. When plating solution is thus directly supplied inside the plating solution in the first space, the shock to the plating solution in the first space is less than when plating solution discharged once into air from the supply port falls the surface of plating solution held in the first space. Thus, the fluid movement of plating solution held in the first space can be controlled, and metal particles can be made to settle more efficiently in the first space. 
     In the electrolytic plating equipment according to the above embodiment, when plating solution is discharged from the supply port towards the inner side of the separate tank, moreover, fluid movement of plating solution held in the first space, and particularly movement of plating solution in the lower part of the space, can be controlled better than when the discharge is directed downward for example. In this way, it is possible to control interference with settling of metal particles in the first space by preventing metal particles that have settled in the first space from being stirred up again. 
     The electrolytic plating equipment according to the above embodiment may further includes a source pipe for sending the plating solution from the plating tank to the separate tank, the separate tank may have a first partition extending vertically so as to divide the separate tank into the first space and the second space and a second partition extending vertically so as to divide the first space into a settling space for settling metal particles in the plating solution and a supply space located upstream from the settling space wherein plating solution is supplied from the supply port of the source pipe. 
     In this configuration, because the first space is divided by the second partition into a settling space and a supply space, and the plating solution is supplied to the supply space from the supply port of the source pipe, the fluid movement of plating solution held in the supply space that occurs when plating solution is supplied to the supply space is unlikely to be communicated to the settling space. As a result, metal particles can be made to settle more efficiently than if there were no second partition in the first space. 
     In the electrolytic plating equipment according to the above embodiment, when the second partition has a plurality of communicating holes provided below the aforementioned specific height and communicating between the settling space and the supply space, the plating solution supplied to the supply space is dispersed as it moves through the multiple communicating holes in the second partition into the settling space. Fluid movement of the plating solution held in the settling space can be controlled if the plating solution is dispersed in this way as it passes through multiple communicating holes into the settling space. 
     In the electrolytic plating equipment according to the above embodiment, if the upper edge of the second partition is located at or below the aforementioned specific height, the height of the upper edge of the second partition will be the same as or lower than the surface of the plating solution held in the settling space. As a result, since the surface of the plating solution in the settling space and the surface of the plating solution in the supply space are at roughly the same height, there is less shock when the plating solution flows from the supply space into the settling space. It is therefore possible to control the stirring up of metal particles that have settled in the settling space for example, and to prevent interference with settling of metal particles in the settling space. 
     The electrolytic plating equipment according to the above embodiment may further includes: a return pipe for returning plating solution from the separate tank to the plating tank; and a re-supply pipe for returning plating solution discharged from the separate tank back to the first space. In this configuration, part of the plating solution in the separate tank can be re-supplied to the first space via the re-supply pipe before being returned to the plating tank. This allows foreign matter in the plating solution to be separated more efficiently. 
     In the electrolytic plating equipment according to the above embodiment, when a mechanical agitator further includes a mechanical agitator provided in a space downstream from the first space, the plating solution can be agitated with this mechanical agitator in the downstream space after the metal particles have settled in the first space. This allows fine adjustments to be made to the dissolved oxygen concentration of the plating solution. 
     In the electrolytic plating equipment according to the above embodiment, the plating tank may have: a tank body for holding plating solution; and an overflow tank provided integrally with the tank body in which the plating solution from the tank body overflows the upper edge of the side wall of the tank body to flow into the overflow tank, and this overflow tank may contain an upstream space and a downstream space located downstream from the upstream space, and the plating solution falls through air to flow from the upstream space into the downstream space. 
     In this configuration, the dissolved oxygen concentration of the plating solution can be adjusted not only in the separate tank but also in the overflow tank of the plating tank. In this overflow tank, the dissolved oxygen concentration is adjusted as the plating solution falls through air when flowing from the upstream space into the downstream space. 
     In the electrolytic plating equipment according to the above embodiment, when the upper edge of the tank body has a extending portion extending towards the overflow tank, and this extending portion has an end that is separated from the side of the tank body, the plating solution flowing from the tank body into the overflow tank is conducted along the extending portion to the end of the extending portion, where it separates from the extending portion and is released into air. As a result, in this configuration the plating solution can be restrained from flowing along the side wall of the tank body. This increases the contact area of the plating solution with air when the plating solution falls, and allows the dissolved oxygen concentration of the plating solution to be adjusted more efficiently. 
     In the electrolytic plating equipment according to the above embodiment, a drop through which the plating solution falls through air in the second space is preferably 10 cm or more. The dissolved oxygen concentration of the plating solution in the separate tank can be adjusted still more efficiently if this drop is 10 cm or more. 
     The electrolytic plating method of this embodiment uses an electrolytic plating equipment provided with a plating tank for holding plating solution, and a separate tank separated from this plating tank, with the plating solution circulating between the plating tank and the separate tank. The separate tank contains a first space and a second space located downstream from the first space. In this method, the first space is filled with plating solution up to a specific height, and metal particles in the plating solution are allowed to settle at the bottom of the first space. In this method, moreover, that part of the plating solution in the first space that exceeds the specific height flows into the second space, and the dissolved oxygen concentration of the plating solution is adjusted by causing it to fall through air in this second space. In this way, the dissolved oxygen concentration of the plating solution can be adjusted, while metal particles can be effectively removed from the plating solution. 
     In the electrolytic plating equipment and electrolytic plating method according to the above embodiment, the plating solution is used for copper plating, which is particularly desirable when a sulfur-containing organic compound is included as a brightener. 
     The present invention is explained in more detail below using examples, but the present invention is not limited by these examples. 
     Example 1 
     Objects to be plated (Samples Nos. 1 to 8) were copper electroplated under the following conditions using an electrolytic plating equipment. The electrolytic plating equipment  11  shown in  FIG. 12  was used for Samples Nos. 2 to 4. In this electrolytic plating equipment  11 , plating tank  13  has the same structure shown in  FIG. 1 , while separate tank  15  has a structure in which separate tank body  20  is divided by first partition  21  and third partition  91  into three spaces: first space  17 , second space  19  and third space  93 . The plating solution overflows the upper edge of first partition  21  to flow from first space  17  into second space  19 , and overflows the upper edge of third partition  91  to flow from second space  19  into third space  93 . Second space  19  is equipped with underflow divider  45 . 
     For Samples Nos. 1 and 5 to 8, partitions  21  and  91  were removed from separate tank  15  of the electrolytic plating equipment  11  shown in  FIG. 12 . 
     As shown in Table 2 below, the structures of the upper edges of first partition  21  and third partition  91  are Structure A (structure shown in  FIG. 2D ) in the case of Sample No. 4 and Structure B (structure shown in  FIG. 2E ) in the case of Samples Nos. 2 and 3. 
     The drop from the upper edges of first partition  21  and third partition  91  to the surface of the plating solution was set to three levels, 5 cm, 10 cm and 20 cm, as shown in Table 2 below. 
     Stainless steel plates and substrates with blind via holes (printed boards with blind via holes) were used as the objects to be plated (cathodes). The opening size of the blind via hole in the plate was 100 μm, and the blind via hole depth was 75 μm. 
     The other electrolytic copper plating conditions were as follows. 
     Bath volume of plating tank  13  (combined bath volume of tank body  47  and overflow tank  49 ): 4300 liters 
     Bath volume of separate tank  15  (combined bath volume of first space  17 , second space  19  and third space  93 ): 800 liters 
     Bath volume: 5100 liters 
     Plating solution: Copper sulfate plating solution (containing 200 g/L copper sulfate pentahydrate, 50 g/L sulfuric acid and 50 mg/L chloride ions). 
     Additive added to plating solution: C.Uyemura “Thru-Cup EVF-T” 
     Plating solution circulation speed: 860 liters/minute 
     Anodes: Soluble anodes (titanium case filled with sulfur-containing copper balls, enclosed in a polypropylene anode back) 
     The objects to be plated were copper electroplated under these conditions, and the dissolved oxygen concentration, coating properties, and pit of the blind via hole were evaluated. The coating properties (elongation and tensile strength) were evaluated using the aforementioned stainless steel plates plated with 50 μm of copper. Pitting of the blind via holes was evaluated using the aforementioned substrates with blind via holes plated with 20 μm of copper. 
     In this Example 1, the stainless steel plates were pretreated, copper electroplated, and post-treated in the following steps 1 to 8. 
     Step 1: Acid wash cleaner (C.Uyemura “MSC-3-A”) 
     Step 2: Hot water wash 
     Step 3: Water wash 
     Step 4: Acid wash 
     Step 5: Water wash 
     Step 6: Electrolytic copper plating 
     Step 7: Water wash 
     Step 8: Dry 
     The substrates with blind via holes were desmeared and chemically copper plated (0.3 μm) by well-known methods, and then pretreated, copper electroplated, and post-treated by the same steps 1 to 8. 
     The electrolytic copper plating conditions in Example 1 were as shown in Table 1. The electrolytic copper plating temperature (plating solution temperature) was 25° C. The cathode current density is given in Table 1 in units of A/dm 2 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Stainless steel 
                 Substrate with 
               
               
                   
                 plate 
                 blind via hole 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Cathode current 
                 1.0 
                 1.0 
               
               
                   
                 density (ASD) 
               
               
                   
                 Plating time 
                 226 
                 90 
               
               
                   
                 (minutes) 
               
               
                   
                 Plating thickness 
                 50 
                 20 
               
               
                   
                 (μm) 
               
               
                   
                   
               
            
           
         
       
     
     The results are shown in Table 2. Table 3 gives the test procedures for each sample. Table 4 shows the dissolved oxygen concentration after 30, 60 and 90 minutes of electrolysis with the partitions  21  and  91  shown in  FIG. 12  attached to the separate tank after plating of Sample No. 1 was completed. In order to maintain a roughly uniform flow volume of plating solution to the object to be plated (cathode  57 ) from each nozzle  61 , part of the plating solution supplied to tank body  47  via return pipe  41  was supplied via pipe end  41   c . The dissolved oxygen concentration of plating solution collected from a valve (not shown) attached to the pipe near pipe end  41   c  in  FIG. 12  was measured. 
     Pitting of the via was evaluated by first applying copper plating  103  as shown in  FIG. 15B  to the substrate with blind via hole  101  shown in  FIG. 15A , and then measuring the difference Δh in height (dimension in direction of thickness) between the lowest part of the surface of copper plating  103  formed inside blind via hole  101   c  and the surface of copper plating  103  formed around blind via hole  101   c  ( FIG. 15B ). Substrate with blind via hole  101  in  FIG. 15A  is provided with resin layer  101   a  and copper layer  101   b  formed on the surface of this resin layer  101   a , with blind via hole  101   c  formed therein. 
     Elongation and tensile strength were measured as follows using the test piece shown in  FIG. 16 . That is, a stainless steel plate was copper plated to 50 μ±5 μm, and the copper plating layer (copper foil) was peeled carefully from the stainless steel plate so as to avoid wrinkles or damage. This copper foil was heat treated for 2 hours at 120° C., and then punched with a dumbbell to the shape shown in  FIG. 16  to prepare a test piece. The film thickness at the center of this test piece was measured with a fluorescence x-ray film thickness meter, and the measured value was taken as the film thickness d (mm) of the test piece. Next, the test piece was fixed between the chucks of a tensile tester with a distance of 40 mm between chucks, and with the part of the test piece having a round portion exposed outside the chucks, and tested at a tension rate of 4 mm/minute. Next, the maximum tensile strength F (kgf) was derived from a chart obtained from the test, and this F (kgf) was divided by the cross-sectional area of the test piece to obtain the tensile strength values (kgf/mm 2 ) shown in Tables 2, 6 and 9. The cross-sectional area of the test piece was the width 10 mm of the center of the test piece times the film thickness dmm. The elongation E (%) was calculated by first measuring the elongation ΔL (mm) from the beginning of tension to breakage of the test piece, and then dividing this ΔL (mm) by the dimension (20 mm) of the straight part of the central part of the test piece before tension. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Dissolved 
                 Coating properties 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Separate 
                   
                 oxygen 
                   
                 Tensile 
                 Blind 
               
               
                 Sample 
                 tank specs 
                   
                 concentration 
                 Elongation 
                 strength 
                 via hole 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 No. 
                 Partition 
                 Drop 
                 Circulation 
                 mg/liter 
                 (%) 
                 (kgf/mm 2 ) 
                 pit μm 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 1 
                 No partition 
                 — 
                 10 turns 
                 2.4 
                 25.6 
                 35.6 
                 28.5 
               
               
                 2 
                 Structure B 
                  5 cm 
                 10 turns 
                 3.7 
                 31.2 
                 32.4 
                 19.2 
               
               
                 3 
                 Structure B 
                 20 cm 
                 10 turns 
                 7.7 
                 32 
                 33.1 
                 15.2 
               
               
                 4 
                 Structure A 
                 10 cm 
                 10 turns 
                 7.4 
                 31.5 
                 32.8 
                 14.5 
               
               
                 5 
                 No partition 
                   
                 10 turns 
                 6 
                 32 
                 33 
                 15.2 
               
               
                 6 
                 No partition 
                   
                 10 turns 
                 4.3 
                 30.7 
                 32.2 
                 16.3 
               
               
                 7 
                 No partition 
                   
                 10 turns 
                 3.4 
                 31.1 
                 33.3 
                 18.1 
               
               
                 8 
                 No partition 
                   
                 10 turns 
                 2.6 
                 31 
                 33.3 
                 24.4 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Sample 
                   
               
               
                 No. 
               
               
                   
               
             
            
               
                 1 
                 Electrolyzed for 30 hours at cathode current density 1.0 ASD 
               
               
                   
                 using separate tank with no partition. Stainless steel plate and 
               
               
                   
                 substrate with blind via hole then plated. 
               
               
                 2 
                 Electrolyzed for 24 hours at 1.0 ASD using separate tank 
               
               
                   
                 shown in FIG. 14. Stainless steel plate and substrate with blind 
               
               
                   
                 via hole then plated. 
               
               
                 3 
                 Electrolyzed for 24 hours at 1.0 ASD using separate tank 
               
               
                   
                 shown in FIG. 14. Stainless steel plate and substrate with blind 
               
               
                   
                 via hole then plated. 
               
               
                 4 
                 Electrolyzed for 24 hours at 1.0 ASD using separate tank 
               
               
                   
                 shown in FIG. 14. Stainless steel plate and substrate with blind 
               
               
                   
                 via hole then plated. 
               
               
                 5 
                 Electrolyzed for 8 hours following Sample No. 4 with plating 
               
               
                   
                 solution circulating using separate tank with no partition. 
               
               
                   
                 Stainless steel plate and substrate with blind via hole then plated. 
               
               
                 6 
                 Electrolyzed for 8 hours following Sample No. 5 with plating 
               
               
                   
                 solution circulating using separate tank with no partition. 
               
               
                   
                 Stainless steel plate and substrate with blind via hole then plated. 
               
               
                 7 
                 Electrolyzed for 8 hours following Sample No. 6 with plating 
               
               
                   
                 solution circulating using separate tank with no partition. 
               
               
                   
                 Stainless steel plate and substrate with blind via hole then plated. 
               
               
                 8 
                 Electrolyzed for 8 hours following Sample No. 7 with plating 
               
               
                   
                 solution circulating using separate tank with no partition. 
               
               
                   
                 Stainless steel plate and substrate with blind via hole then plated. 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Dissolved oxygen 
               
               
                   
                 Electrolysis time (minutes) 
                 concentration (mg/liter) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 30 
                 4 
               
               
                   
                 60 
                 5.9 
               
               
                   
                 90 
                 7.6 
               
               
                   
                   
               
            
           
         
       
     
     From the results for Sample No. 1 in Table 2, it can be seen that using a separate tank without partitions  21  and  91 , the dissolved oxygen concentration of the plating solution was low, and the amount of pit in the blind via holes tended to be greater. 
     From the results for Samples Nos. 2 to 4, it can be seen that the dissolved oxygen concentration is increased by providing partitions  21  and  91  in separate tank  15  to cause overflow of the plating solution. The dissolved oxygen concentration is increased dramatically by providing a drop of 10 cm or more for the plating solution during overflow as in Samples Nos. 3 and 4. In the case of these Samples Nos. 3 and 4, the dissolved oxygen concentration did not decrease even after long-term electrolysis. 
     From the results for Samples Nos. 5 to 8, which were plated after Sample No. 4, it can be seen that when partitions  21  and  91  are removed from separate tank  15 , the dissolved oxygen concentration after during long-term electrolysis, and the amount of pit in the blind via hole tends to increase. 
     As shown in Table 4, moreover, the dissolved oxygen concentration increased over time during electrolysis with partitions  21  and  91  attached to the separate tank following plating of Sample No. 1. 
     Example 2 
     Objects to be plated (Samples Nos. 9 to 14) were copper electroplated under the following conditions using the electrolytic plating equipment shown in  FIG. 13A  and  FIG. 13B . A separate tank having the same partitions  21  and  91  as the equipment of  FIG. 12  was used as separate tank  15  for Samples Nos. 12 to 14. As shown in  FIG. 13A  and  FIG. 13B , moreover, plating tank  13  was provided with tank body  47  and overflow tank  49 , so that plating solution overflowing from tank body  47  flowed into overflow tank  49 . A plate-shaped object to be plated was arranged roughly horizontally in tank body  47  as cathode  57 , and multiple anodes  55  were arranged above and below this cathode  57 . Nozzles  61  were also arranged above and below cathode  57 . Each nozzle  61  was provided with multiple spray nozzles (not shown) for spraying plating solution supplied from separate tank  15  via return pipe  41  in the direction of cathode  57 . 
     For Samples Nos. 9 to 11, partitions  21  and  91  were removed from separate tank  15 . 
     The drop of the plating solution from the upper edges of first partition  21  and third partition  91  to the surface of the plating solution was set to three heights as shown in Table 6 below: 5 cm, 10 cm and 20 cm. 
     A stainless steel plate and a plate with through hole were used as the objects to be plated (cathodes). The inner diameter of the through hole in the plate was 0.3 mm, and the plate thickness was 1.6 mm. 
     The other electrolytic copper plating conditions and the like were as follows. 
     Bath volume of plating tank  13  (combined bath volume of tank body  47  and overflow tank  49 ): 1000 liters 
     Bath volume of separate tank  15  (combined bath volume of first space  17 , second space  19  and third space  93 ): 1400 liters 
     Capacity: 2400 liters 
     Plating solution: Copper sulfate plating solution (containing 100 g/L copper sulfate pentahydrate, 200 g/L sulfuric acid and 50 mg/L chloride ions) 
     Additive added to plating solution: C.Uyemura “Thru-Cup ETN” 
     Circulation speed of plating solution: 3000 liters/minute 
     Anodes: Insoluble anodes (Ti—Pt coated with indium oxide) 
     In this Example 2, the stainless steel plates were pre-treated, copper electroplated and post-treated in the same steps 1 to 8 as in Example 1. 
     The plates with through holes were first desmeared and chemically copper plated (0.3 μm) by well-known methods as in Example 1, and then pre-treated, copper electroplated and post-treated in the same steps 1 to 8 as in Example 1. 
     The electrolytic copper plating conditions for Example 2 are shown in Table 5. The electrolytic copper plating temperature (temperature of plating solution) was 25° C. The cathode current density is given in Table 5 in units of A/dm 2 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Stainless steel 
                 Substrate with 
               
               
                   
                 plate 
                 through hole 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Cathode current 
                 5.0 
                 5.0 
               
               
                   
                 density (ASD) 
               
               
                   
                 Plating time 
                 45 
                 27 
               
               
                   
                 (minutes) 
               
               
                   
                 Plating thickness 
                 50 
                 30 
               
               
                   
                 (μm) 
               
               
                   
                   
               
            
           
         
       
     
     The objects to be plated were copper electroplated under these conditions, and the dissolved oxygen concentration, coating properties, and through hole throwing power (TH-TP) were evaluated. The results are shown in Table 6. Table 7 gives the test procedures for each sample. The dissolved oxygen concentration was evaluated by measuring dissolved oxygen in plating solution collected from a valve (not shown) attached to return pipe  41  downstream from filter  65  in  FIG. 13 . 
     The throwing power is defined as the ratio of the thickness of the copper plating on the plate surface near the through hole to the thickness of the copper plating half way through the through hole. That is, as shown in  FIG. 17 , after copper plating  107  is performed to substrate  105  in which through hole  105   a  is formed under these conditions, the throwing power (TH-TP) is obtained by entering the thicknesses e and f of the copper plating halfway through the through hole and the thicknesses a through d of the copper plating on the surface of the plate near the through hole into the following Formula (5): 
         TH - TP (%)=2( e+f )/( a+b+c+d )×100  (5)
 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 Dissolved 
                 Coating properties 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Separate 
                   
                 oxygen 
                   
                 Tensile 
                   
               
               
                 Sample 
                 tank specs 
                   
                 concentration 
                 Elongation 
                 strength 
                 TH- 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 No. 
                 Partition 
                 Drop 
                 Circulation 
                 mg/liter 
                 (%) 
                 (kgf/mm 2 ) 
                 TP % 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 9 
                 No Partition 
                 — 
                 75 turns 
                 7.4 
                 30.4 
                 33.6 
                 75.7 
               
               
                 10 
                 No Partition 
                 — 
                 75 turns 
                 23.4 
                 23.5 
                 37.8 
                 70.7 
               
               
                 11 
                 No Partition 
                 — 
                 75 turns 
                 38.5 
                 15.4 
                 43.4 
                 65.6 
               
               
                 12 
                 Structure B 
                  5 cm 
                 75 turns 
                 21.5 
                 24.5 
                 37.5 
                 72.5 
               
               
                 13 
                 Structure B 
                 20 cm 
                 75 turns 
                 15.6 
                 30.3 
                 31.2 
                 76.2 
               
               
                 14 
                 Structure A 
                 10 cm 
                 75 turns 
                 18.5 
                 30.1 
                 32.2 
                 75.6 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                 Sample 
                   
               
               
                 No. 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 9 
                 Stainless steel plate and substrate plated with plating solution 
               
               
                   
                 circulated using separate tank without partition. 
               
               
                 10 
                 Electrolyzed for 3 hours following Sample No. 9. Stainless steel 
               
               
                   
                 plate and substrate then plated. 
               
               
                 11 
                 Electrolyzed for 3 hours following Sample No. 10. Stainless 
               
               
                   
                 steel plate and substrate then plated. 
               
               
                 12 
                 Electrolyzed for 24 hours at cathode current density 5.0 ASD 
               
               
                   
                 using separate tank with partition. Stainless steel plate and 
               
               
                   
                 substrate then plated. 
               
               
                 13 
                 Electrolyzed for 24 hours at 5.0 ASD using separate tank with 
               
               
                   
                 partition. Stainless steel plate and substrate then plated. 
               
               
                 14 
                 Electrolyzed for 24 hours at 5.0 ASD using separate tank with 
               
               
                   
                 partition. Stainless steel plate and substrate then plated. 
               
               
                   
               
            
           
         
       
     
     The results for Sample No. 9 in Table 6 show good coating properties with a dissolved oxygen concentration of 7.4 mg/liter at the start of plating. However, the results for Samples Nos. 10 and 11 show the dissolved oxygen concentration increasing as the electrolysis time increases, with poor coating properties and lower TH-TP for Sample No. 10 after 3 hours, and poor coating properties and the TH-TP decreasing to 65.6% for Sample No. 11 after 6 hours. 
     In the case of Samples Nos. 12 to 14, on the other hand, the increase in dissolved oxygen concentration was controlled by providing partitions  21  and  91  in separate tank  15 , causing overflow of the plating solution. The effect of controlling the increase in dissolved oxygen concentration is particularly remarkable when the drop of the plating solution during overflow is 10 cm or more as in Samples Nos. 13 and 14. In the case of these Samples Nos. 13 and 14, it was possible to reduce the dissolved oxygen concentration to 20 mg/liter or less, resulting in good coating properties with a TH-TP of 75% or more. 
     Example 3 
     Objects to be plated (Samples Nos. 15 to 18) were electrolytic copper plating under the following conditions using the electrolytic plating equipment shown in  FIG. 14 . A separate tank having the same partitions  21  and  91  as the equipment of  FIG. 12  was used as separate tank  15  for plating Samples Nos. 17 and 18. Plating tank  13  is provided with tank body  47  and overflow tank  49  as shown in  FIG. 14 , so that overflowing plating solution from tank body  47  flows into overflow tank  49 . 
     The inside of tank body  47  is divided into two spaces by separating membrane  99 . A Yuasa Membrane Systems “Y-9205T” was used for this separating membrane  99 . An object to be plated was arranged as cathode  57  in one space, while anode  55  was arranged in the other space. Nozzle  61  was arranged near cathode  57 . Nozzle  61  is provided with a spray nozzle (not shown) for spraying plating solution supplied from separate tank  15  via return pipe  41  in the direction of cathode  57 . 
     For Samples Nos. 15 and 16, partitions  21  and  91  were removed from separate tank  15 . 
     The drop of the plating solution from the upper edges of first partition  21  and third partition  91  to the surface of the plating solution was set to two heights as shown in Table 9 below: 10 cm and 20 cm. 
     A stainless steel plate and a wafer with a blind via hole were used as the objects to be plated (cathodes). The opening size of the blind via hole in the plate was 15 μm, and the blind via hole was 25 μm deep. 
     The other conditions for electrolytic copper plating were as follows. 
     Bath volume of plating tank  13  (combined bath volume of tank body  47  and overflow tank  49 ): 50 liters 
     Bath volume of separate tank  15  (combined bath volume of first space  17 , second space  19  and third space  93 ): 150 liters 
     Bath volume: 200 liters 
     Plating solution: Copper sulfate plating solution (containing 200 g/L copper sulfate pentahydrate, 50 g/L sulfuric acid and 50 mg/L chloride ions) 
     Additive added to plating solution: C.Uyemura “Thru-Cup ESA-21” 
     Circulation speed of plating solution: 100 liters/minute 
     Anodes: Soluble anodes (phosphor-containing copper balls enclosed in a titanium case) 
     In this Example 3, the stainless steel plates were pre-treated, copper electroplated and post-treated in the same steps 1 to 8 as in Example 1. 
     The wafers were first given a barrier layer and seed layer by known methods, and then pre-treated, copper electroplated and post-treated in the same steps 1 to 8 as in Example 1. 
     The conditions for electrolytic copper plating in Example 3 were as shown in Table 8. The electrolytic copper plating temperature (temperature of the plating solution) was 25° C. In Table 8, the cathode current density is given in units of A/dm 2 . 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Stainless steel 
                   
               
               
                   
                 plate 
                 Wafer 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Cathode current 
                 1.0 
                 1.0 
               
               
                   
                 density (ASD) 
               
               
                   
                 Plating time 
                 226 
                 23 
               
               
                   
                 (minutes) 
               
               
                   
                 Plating thickness 
                 50 
                 5 
               
               
                   
                 (μm) 
               
               
                   
                   
               
            
           
         
       
     
     The objects to be plated were copper electroplated under these conditions, and the dissolved oxygen concentration, coating properties, and blind via hole pit were evaluated. The results are shown in Table 9. Table 10 gives the test procedures for each sample. The dissolved oxygen concentration (DOC) was evaluated by measuring dissolved oxygen in plating solution collected from a valve (not shown) attached to return pipe  41  downstream from filter  65  in  FIG. 14 . 
     During plating of Sample No. 15, air was agitated in first space  17  of separate tank  15  by using air agitator  94  to supply air to the plating solution. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 9 
               
             
            
               
                   
                   
               
               
                   
                 Separate tank 
                   
                 Coating properties 
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 specs 
                   
                 Tensile 
                 Blind 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Air 
                 DOC 
                 Elongation 
                 strength 
                 via hole 
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 No. 
                 Partition 
                 Drop cm 
                 agitation 
                 mg/liter 
                 % 
                 kgf/mm 2   
                 pit μm 
                 Filter 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 15 
                 No Partition 
                 — 
                 Use 
                 3.8 
                 30.5 
                 33.4 
                 7.4 
                 Black 
               
               
                 16 
                 No Partition 
                 — 
                 Not use 
                 7.1 
                 31.3 
                 33.1 
                 3.5 
                 Replaced 
               
               
                 17 
                 Structure B 
                 20 
                 Not use 
                 7.7 
                 30.7 
                 32.6 
                 2.7 
                 White 
               
               
                 18 
                 Structure A 
                 10 
                 Not use 
                 7.5 
                 31.4 
                 32.3 
                 3.3 
                 White 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                 TABLE 10 
               
               
                   
               
               
                 Sample No. 
               
               
                   
               
             
            
               
                 15 
                 Electrolyzed for 24 hours at cathode current density 1.0 
               
               
                   
                 ASD using separate tank without partition. 
               
               
                 16 
                 Stainless steel plate and substrate plated immediately 
               
               
                   
                 after replacement of filter following plating of Sample No. 
               
               
                   
                 15. 
               
               
                 17 
                 Electrolyzed for 24 hours at 1.0 ASD using separate tank 
               
               
                   
                 with partition. Stainless steel plate and substrate then 
               
               
                   
                 plated. 
               
               
                 18 
                 Electrolyzed for 24 hours at 1.0 ASD using separate tank 
               
               
                   
                 with partition. Stainless steel plate and substrate then 
               
               
                   
                 plated. 
               
               
                   
               
            
           
         
       
     
     In the case of Sample No. 15 in Table 9, which was electrolyzed with air agitation in first space  17  of separate tank  15 , the dissolved oxygen concentration of plating tank  13  was 3.8 mg/liter as shown in Table 9, while at the same time the dissolved oxygen concentration of separate tank  15  was 7.2 mg/liter. Thus, the dissolved oxygen concentration of the separate tank can be maintained within a good range by means of air agitation, but because air agitation interfered with settling of copper particles in first space  17 , many copper particles were found adhering to filter  65  (filter  65  was black as shown in Table 9). Since dissolved oxygen is expended by these copper particles adhering to filter  65 , the dissolved oxygen concentration in the plating tank declines, and pit of the blind via hole tends to increase. 
     The results for Sample No. 16 show almost no copper particles adhering to filter  65  immediately after replacement, with a good dissolved oxygen concentration in the plating tank and little pit of the blind via hole. 
     In the case of Samples Nos. 17 and 18, there were almost no copper particles adhering to filter  65  (which was a white as new), indicating effective settling of copper particles in first space  17 . Causing plating to overflow a partition provided in the separate tank in this way is an effective way not only of increasing the dissolved oxygen concentration but also of separating out copper particles from the plating solution. The dissolved oxygen concentration in the plating tank is also maintained within a desirable range, and pit of the blind via hole is reduced. 
     Reference Examples 
     The dissolved oxygen concentration, brightener concentration and Ar value of the plating solution were measured by cyclic voltammetric stripping (CVS). 
     The method for measuring CVS is as follows. 
     1) Ar Measurement Method 
     A rotating platinum electrode as the working electrode, a copper bar as the counter electrode and a silver/silver chloride double junction electrode as the reference electrode were immersed in the plating solution, the potential supplied to the rotating platinum electrode was varied as the plating step, stripping step and washing step were repeated, a potential-current curve (voltammogram) was prepared, and the area in the stripping step (Ar value) was derived from this potential-current curve. 
     The results shown in Tables 11 and 12 below were obtained by applying the CVS measurement method described above, and show changes over time in Ar values obtained by continuous repeated scanning in this method. 
     2) Measurement Instrument and Measurement Conditions Used in Ar Measurement 
     Measurement Instrument: ECI “QL-5” 
     Measurement conditions: Rotating platinum electrode rpm: 
     2500; potential sweep speed: 100 mV/second; temperature: 25° C. 
     3) Measurement Solution 
     The measurement solution was prepared as follows. 30 mL of the VMS described below was placed in a container, and 30 mL of the plating solution to be measured was added and mixed to obtain the measurement liquid. 
     4) VMS and Plating Solutions to be Measured 
     The plating solutions to be measured are shown in Table 11 for Samples Nos. 19 to 23 and in Table 12 for Samples Nos. 24 to 28. That is, in the case of Sample No. 19 the plating solution to be measured is plating solution collected from a valve (not shown) attached to a pipe near pipe end  41   c  in  FIG. 12  during plating of Sample No. 1 in Example 1, while in the case of Sample No. 20, the plating solution to be measured is plating solution collected at the same location during plating of Sample No. 3 in Example 1. In the case of Sample No. 24, the plating solution to be measured is plating solution collected from a valve (not shown) attached to return pipe  41  downstream from filter  65  in  FIG. 13  during plating of Sample No. 11 in Example 2, while in the case of Sample No. 25 the plating solution to be measured is plating solution collected at the same location during plating of Sample No. 13 in Example 2. 
     In the case of Samples Nos. 21 to 23 and Samples Nos. 26 to 28, the plating solution to be measured was prepared in a beaker so as to obtain the values shown in Tables 11 and 12 for dissolved oxygen concentration (DOC) of each measurement liquid after preparation for each sample. 
     C.Uyemura “Thru-Cup EVF-T” was used as the additive in the plating solutions to be measured for Samples Nos. 19 to 23, while C.Uyemura “Thru-Cup ETN” was used as the additive in the plating solutions to be measured for Samples Nos. 24 to 28. 
     For Samples Nos. 19 to 23 in Table 11, a copper sulfate plating solution (containing 200 g/L copper sulfate pentahydrate, 50 g/L sulfuric acid and 50 mg/L chloride ions) was used as the virgin makeup solution (VMS), while for Samples Nos. 24 to 28 in Table 12, a copper sulfate plating solution (containing 100 g/L copper sulfate pentahydrate, 200 g/L sulfuric acid and 50 mg/L chloride ions) was used. 
     5) Measurement Results 
     The measurement results are shown in Table 11 and Table 12. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 11 
               
             
            
               
                   
                   
               
               
                   
                 Plating 
                 Ar value (mC) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sample 
                 solution 
                   
                 DOC 
                 Brightener 
                   
                 15 
                 30 
                 45 
                 60 
                 75 
                 90 
                 105 
                 120 
               
               
                 No. 
                 measured 
                 Additive 
                 (mg/L) 
                 (%) 
                 0 
                 min 
                 min 
                 min 
                 min 
                 min 
                 min 
                 min 
                 min 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 19 
                 Sample 1 
                 EVF-T 
                 2.4 
                 100 
                 1.249 
                 1.2 
                 1.176 
                 1.166 
                 1.163 
                 1.16 
                 1.157 
                 1.152 
                 1.155 
               
               
                   
                 Solution 
               
               
                 20 
                 Sample 3 
                   
                 7.7 
                 100 
                 1.142 
                 1.143 
                 1.144 
                 1.145 
                 1.144 
                 1.144 
                 1.144 
                 1.142 
                 1.142 
               
               
                   
                 Solution 
               
               
                 21 
                 Beaker 
                   
                 8 
                 100 
                 1.155 
                 1.158 
                 1.16 
                 1.162 
                 1.157 
                 1.158 
                 1.157 
                 1.16 
                 1.157 
               
               
                   
                 makeup 
               
               
                   
                 bath 
               
               
                 22 
                 Beaker 
                   
                 8 
                 200 
                 1.211 
                 1.212 
                 1.214 
                 1.209 
                 1.207 
                 1.21 
                 1.214 
                 1.218 
                 1.213 
               
               
                   
                 makeup 
               
               
                   
                 bath 
               
               
                 23 
                 Beaker 
                   
                 8 
                 20 
                 1.11 
                 1.104 
                 1.111 
                 1.113 
                 1.114 
                 1.111 
                 1.104 
                 1.1 
                 1.102 
               
               
                   
                 makeup 
               
               
                   
                 bath 
               
               
                   
               
            
           
         
       
     
     65 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 12 
               
             
            
               
                   
                   
               
               
                   
                 Plating 
                 Ar value (mC) 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sample 
                 solution 
                   
                 DOC 
                 Brightener 
                   
                 15 
                 30 
                 45 
                 60 
                 75 
                 90 
                 105 
                 120 
               
               
                 No. 
                 measured 
                 Additive 
                 (mg/L) 
                 (%) 
                 0 
                 min 
                 min 
                 min 
                 min 
                 min 
                 min 
                 min 
                 min 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 24 
                 Sample 11 
                 ETN 
                 38.5 
                 100 
                 1.907 
                 1.918 
                 1.923 
                 1.935 
                 1.95 
                 1.955 
                 1.959 
                 1.963 
                 1.964 
               
               
                   
                 solution 
               
               
                 25 
                 Sample 13 
                   
                 15.6 
                 100 
                 1.967 
                 1.965 
                 1.963 
                 1.963 
                 1.963 
                 1.965 
                 1.966 
                 1.964 
                 1.967 
               
               
                   
                 solution 
               
               
                 26 
                 Beaker 
                   
                 8 
                 100 
                 1.97 
                 1.973 
                 1.973 
                 1.974 
                 1.972 
                 1.969 
                 1.972 
                 1.973 
                 1.975 
               
               
                   
                 makeup 
               
               
                   
                 bath 
               
               
                 27 
                 Beaker 
                   
                 8 
                 200 
                 2.01 
                 2.009 
                 2.012 
                 2.013 
                 2.011 
                 2.008 
                 2.007 
                 2.008 
                 2.009 
               
               
                   
                 makeup 
               
               
                   
                 bath 
               
               
                 28 
                 Beaker 
                   
                 8 
                 20 
                 1.899 
                 1.89 
                 1.892 
                 1.892 
                 1.892 
                 1.9 
                 1.9 
                 1.898 
                 1.893 
               
               
                   
                 makeup 
               
               
                   
                 bath 
               
               
                   
               
            
           
         
       
     
     66 
     The measured Ar value reflects the concentration of the brightener. In Table 11, the Ar value is about 1.14 to 1.16 when the dissolved oxygen concentration and brightener concentration are suitable as in Samples Nos. 20 and 21. When the brightener concentration is suitable but the dissolved oxygen concentration is too low as in Sample No. 19, the initial Ar value is about 1.2, which is about what it is when the brightener concentration is too high (Sample No. 22). Over time, the Ar value for this Sample No. 19 drops to about 1.15, or about the same as for Sample No. 20. 
     In Table 12, the Ar value is about 1.97 when the dissolved oxygen concentration and brightener concentration suitable as in Samples Nos. 25 and 26. When the brightener concentration is suitable but the dissolved oxygen concentration is excessive as in Sample No. 24, the initial Ar is about 1.91, which is about what it is when the brightener concentration is too low (Sample No. 28). Over time, the Ar value for this Sample No. 24 rises to about 1.96, or about the same as for Sample No. 25. 
     The reason why the Ar values for Samples Nos. 19 and 24 above approach the Ar values for Samples No. 20 and 25 over time is as follows. That is, when potential scanning is repeated continuously, air dissolves into the measurement liquid, and the dissolved oxygen concentration fluctuates as shown in Tables 11 and 12, approaching the suitable concentration. Air dissolves into the measurement liquid because it is being agitated by the rotating platinum electrode, and because the dissolved oxygen concentration of the VMS is close to the saturation concentration of air. 
     This application is based on Japanese Patent Application No. 2009-207286 filed on Sep. 8, 2009, the contents of which are hereby incorporated by reference.