Patent Publication Number: US-7223349-B2

Title: Method and apparatus for surface processing of printed wiring board

Description:
RELATED APPLICATION 
   This application is a continuation application of application Ser. No. 10/678,099 filed on Oct. 6, 2003, now U.S. Pat. No. 6,878,296 which is a divisional of application Ser. No.: 09/864,397 filed on May 25, 2001, now U.S. Pat. No. 6,673,194, the contents of which are hereby incorporated in its entirety by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a method and apparatus for a printed wiring board for forming a protective water-soluble pre-flux film on the surface of a conductor pattern facing outwards. 
   2. Description of Related Art 
   In a printed wiring board, a pre-flux film is routinely formed on its conductor pattern following the formation of the conductor pattern and prior to ultimate inspection such as substrate appearance inspection. For forming this pre-flux film, a solvent type pre-flux or a water-soluble pre-flux is used. 
   Meanwhile, since the solvent type pre-flux, which enables quality stability for the pre-flux film due to its high adhesion to a conductor pattern to assure stabilized film forming and also due to its superior solder wettability, is prepared using a large quantity of the volatile organic compounds (VOCs), the tendency is to use the solvent type pre-flux only in a limited quantity in view of environmental protection. 
   On the other hand, in a water-soluble pre-flux, not employing the VOCs, sufficient quality stability cannot be realized as compared to the solvent type pre-flux. For example, the water-soluble pre-flux is inferior to the solvent type pre-flux in adhesion to the conductor pattern, such that stable pre-flux films cannot be formed. In addition, the water-soluble pre-flux liquid is inferior in solder wettability. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a method and apparatus for surface treatment of a printed wiring board capable of forming a pre-flux film of stable quality on a conductor pattern using a water-soluble pre-flux. 
   In one aspect, the present invention provides a surface-processing apparatus for a printed wiring board including means for etching the surface of a conductor pattern formed on at least one surface of a printed wiring board, first rinsing means for rinsing the surface of the printed wiring board the conductor pattern of which has been etched by the etching means, air bubble removing means for removing air bubbles affixed to the surface of the printed wiring board by immersing the printed wiring board rinsed by the first rinsing means in a water-soluble pre-flux liquid in a processing vessel, pre-flux forming means for forming a pre-flux film on the conductor pattern on the printed wiring board in the pre-flux liquid, freed of air bubbles by the air bubble removing means, using an in-liquid spray provided in the pre-flux liquid in the processing vessel, liquid removing means for removing the pre-flux liquid from the surface of the printed wiring board carrying the pre-flux film and second rinsing means for rinsing the surface of the printed wiring board from the surface of which the pre-flux liquid has been removed by the liquid removing means. 
   In another aspect, the present invention provides a surface-processing method for a printed wiring board including the steps of etching the surface of a conductor pattern formed on at least one surface of a printed wiring board, rinsing the surface of the printed wiring board the conductor pattern of which has been etched by the etching step, removing air bubbles affixed to the surface of the printed wiring board by immersing the printed wiring board rinsed by the first rinsing step in a water-soluble pre-flux liquid in a processing vessel, forming a pre-flux film on the conductor pattern on the printed wiring board in the pre-flux liquid, freed of air bubbles, using an in-liquid spray provided in the pre-flux liquid in the processing vessel, removing the pre-flux liquid from the surface of the printed wiring board carrying the pre-flux film and transferred from the processing vessel, and rinsing the surface of the printed wiring board from the surface of which the pre-flux liquid has been removed by the liquid removing step. 
   According to the present invention, the conductor patterns on the printed wiring board are etched to remove surface oxides to provide for a planar surface. The liquid etchant then is rinsed off to form a pre-flux film. So, the pre-flux film may be improved in adhesion, while the pre-flux film is not affected by the surface oxides on the conductor patterns and hence may be a smooth surface. The pre-flux film is formed using an in-liquid spraying unit, so that it may be of uniform film thickness, while solder wettability is also improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view showing a printed wiring board. 
       FIGS. 2A to 2D  illustrate the structure of a surface processing apparatus for the printed wiring board shown in  FIG. 1 . 
       FIG. 3  illustrates a lower saucer provided below the bubble removing roll. 
       FIG. 4  illustrates a step for forming a pre-flux film on a land of the printed wiring board. 
       FIG. 5  is a cross-sectional view showing essential parts of the printed wiring board showing the state in which crests and recesses are formed by oxidation of a land surface. 
       FIG. 6  is a cross-sectional view of a printed wiring board the land surface of which has been flattened out as a result of soft-etching and oxidation of the land surface. 
       FIG. 7  is a cross-sectional view showing the state of formation of a pre-flux film on the land surface. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the drawings, a method and apparatus for surface-processing a printed wiring board for forming a pre-flux film on a land of each of the upper and lower surfaces of the printed wiring board carrying plural conductor patterns according to the present invention will be explained in detail. 
   Before proceeding to the description of the surface-processing method and apparatus, a printed wiring board used therein is explained. Referring to  FIG. 1 , the printed wiring board  1  includes inner layer substrates  2 ,  3 . The inner layer substrate  2  includes a conductor pattern  2   a , as a second layer, on its one surface, and a conductor pattern  2   b , as a third layer, on its opposite surface. The inner layer substrate  3  includes a conductor pattern  3   a , as a fourth layer, on its one surface, and a conductor pattern  3   b , as a fifth layer, on its opposite surface. The inner layer substrates  2 ,  3  are pressed together, with the conductor pattern  2   b  as the third layer facing the conductor pattern  3   a  as the fourth layer, with the interposition of a pre-preg  4 , comprised of glass fibers impregnated with an epoxy resin. 
   On the inner layer substrate  2  is formed a conductor pattern  5   a , as a first layer, with the interposition of an outer layer substrate  5  formed of a pre-preg. On the inner layer substrate  3  is formed a conductor pattern  6   a , as a first layer, with the interposition of an outer layer substrate  6  formed of a pre-preg. The outer layer substrate  5 , inner layer substrate  2 , pre-preg  4 , inner layer substrate  3  and the outer layer substrate  6  are layered in this order to form the printed wiring board  1 , through which a via-hole  7  is bored, such as with a drill. On the inner wall surface of this via-hole  7 , there is formed a plating layer  7   a , such as with an electrolytic copper plating method or an electroless copper plating method, to provide for electrical connection between the first layer of the conductor pattern  5   a  and the second layer of the conductor pattern  2   a , by way of an example. On the outer layer substrates  5 ,  6 , there are formed solder resists  8 ,  8 , in such a manner that lands  5   b ,  6   b , as part of the conductor patterns  5   a ,  6   a  will face outwards. These lands  5   b ,  6   b  are used for mounting electronic components thereon. There are formed protective pre-flux films  9 , mainly composed of an imidazole compound, on the lands  5   b ,  6   b.    
   For preparing the printed wiring board  1 , the conductor patterns  2   a ,  2   b  are formed on both sides of the inner layer substrate  2 , whilst the conductor patterns  3   a ,  3   b  are formed on both sides of the inner layer substrate  3 . The outer layer substrate  5 , having a copper foil bonded to its one surface, the inner layer substrate  2  carrying the conductor patterns  2   a ,  2   b , the prepreg  4 , the inner layer substrate  3 , carrying the conductor patterns  3   a ,  3   b , and the outer layer substrate  6 , having a copper foil bonded to its one surface, are hot-pressed together in vacuum to a unified structure. The via-hole  7  then is bored and the plating layer  7   a  is formed on the inner wall surface of the via-hole  7 , after which conductor patterns  5   a ,  6   a  are formed on the outer layer substrates  5  and  6 . The solder resists  8 ,  8  then are applied to the printed wiring board  1  so that the lands  5   b ,  6   b  will face outwards. The pre-flux film  9  then is formed on each of the lands  5   b ,  6   b  by e.g., a surface-processing device. 
   The surface-processing device  10  for forming the pre-flux film  9  surface-processes the lands  5   b ,  6   b  of the printed wiring board  1  prior to the formation of the pre-flux films  9 , that is the printed wiring board  1  carrying the solder resists  8 ,  8  on the surfaces of the outer layer substrates  5 ,  6 . Referring to  FIG. 2 , the surface-processing device  10  includes a rinsing unit  11  for rinsing the printed wiring board  1 , coated with the solder resists  8 ,  8 , and an etching unit  12  for etching the lands  5   b ,  6   b , as part of the conductor patterns  5   a ,  6   a , facing outwards from the solder resists  8 ,  8 . The surface-processing device  10  also includes a rinsing unit  13  for rinsing the printed wiring board  1 , having its lands  5   b ,  6   b  etched by the etching unit  12 , and a bubble removing unit  14  for removing the bubbles affixed to the surface of the printed wiring board  1  when the printed wiring board  1  rinsed by the rinsing unit  13  is dipped in a water-soluble pre-flux liquid. The surface-processing device  10  also includes a pre-flux forming unit  15  for forming pre-flux films  9  on the lands  5   b ,  6   b  facing outwards from the solder resists  8 ,  8  of the printed wiring board  1 , freed of bubbles by the bubble removing unit  14 , and a liquid removing unit  16  for removing the pre-flux liquid from the surface of the printed wiring board  1  on which the pre-flux film  9  has been formed. The surface-processing  10  also includes a rinsing unit  17  for rinsing the printed wiring board  1  carrying the pre-flux films  9  and freed of the liquid by the liquid removing unit  16 , a drying unit  18  for drying the printed wiring board  1  washed by the rinsing unit  17 , and a cooling unit  19  for cooling the printed wiring board  1  dried by the drying unit  18 . The printed wiring board  1  is continuously transported at a speed of 3 m/min in the horizontally laid state, by a transporting unit, in the direction indicated by arrow A in  FIG. 2 , through the rinsing unit  11 , etching unit  12 , rinsing unit  13 , bubble removing unit  14 , pre-flux forming unit  15 , liquid removing unit  16 , rinsing unit  17 , drying unit  18  and the cooling unit  19 , in this order. The rinsing unit  11 , to which is transported the printed wiring board  1 , coated with the solder resists  8 ,  8  and inspected as to the electrical conducting state, includes a transporting unit  21  for transporting the printed wiring board  1  in the horizontal position, and a spraying unit  22  for spraying the rinsing water, as shown in  FIG. 2A . The transporting unit  21  is made up of plural rolls arranged on upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transported in the horizontal position. The transporting unit  21  transports the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2A  at e.g., a transporting speed of 3 m/min for positively rinsing the printed wiring board  1 . As for the spraying unit  22 , two spraying units are provided on the upper surface side and on the lower surface side of the printed wiring board  1  transported to the transporting unit  21 , since the pre-flux films  9  need to be formed on both sides of the printed wiring board  1  and hence the both sides of the printed wiring board  1  need to be rinsed. These spraying units  22  spray well water at ambient temperature under a condition of the spraying pressure not less than 0.1 MPa. Thus, the rinsing unit  11  frees the surface of the printed wiring board  1  of impurities, such as dust and dirt, affixed to the surface of the printed wiling board  1 . 
   The etching unit  12 , used for etching the lands  5   b ,  6   b  of the printed wiring board  1 , the surfaces of which have been washed by the rinsing unit  11 , includes a processing vessel  24  in which to store an liquid etchant  24   a , and a transporting unit  25  for transporting the printed wiring board  1  through the liquid etchant  24   a . The liquid etchant  24   a  stored in the processing vessel  24  may, for example, be mainly composed of sulfurated water, such as PRT-01 (trade name of a product manufactured by MECK INC). The transporting unit  25  is made up of plural rolls arranged on upper and lower surface sides of the printed wiring board  1  for holding the printed wiring board  1  transported in a horizontal position. The transporting unit  25  transports the printed wiring board  1  at the same transporting speed of 3 m/min as the transporting unit  21  of the rinsing unit  11 , in the direction indicated by arrow A in  FIG. 2A , in order to positively remove oxides on the surfaces of the lands  5   b ,  6   b  by soft etching. The printed wiring board  1  is dipped e.g., for 30 seconds in the liquid etchant  24   a  at 30° C. so that the lands  5   b ,  6   b  as part of the conductor patterns  5   a ,  6   a  are etched e.g., by 1.5 to 2.5 μm. The soft etching of the lands  5   b ,  6   b  is represented by the following reaction formula:
 
Cu + +H 2 O 2 +H 2 SO 4 →CuSO 4 +2H 2 O.
 
   This removes oxides affixed to the lands  5   b ,  6   b  formed by the conductor patterns  5   a ,  6   a  being exposed to outside of the solder resists  8 ,  8 . 
   Referring to  FIGS. 2A and 2B , the rinsing unit  13  for washing the printed wiring board  1 , having its lands  5   b ,  6   b  etched by the etching unit  12 , includes a water washing unit  27  for washing the printed wiling board  1 , having its lands  5   b ,  6   b  etched, and an acid washing unit  28  for acid-washing the printed wiring board  1  water-washed by the water washing unit  27 . The rinsing unit  13  also includes a water washing unit  29  for water-washing the printed wiring board  1 , acid-washed by the acid washing unit  28 , an intermediate pressure water washing unit  30  for water-washing the printed wiring board  1  at a higher pressure than in the water washing unit  29 , and an abundant water washing unit  31  for washing the printed wiring board  1  with an abundant flow of rinsing water. The rinsing unit  13  also includes a second water washing unit  32  for further water-washing the printed wiring board  1  from the abundant water washing unit  31  and an air blower unit  33  for removing the moisture affixed to the surface of the printed wiring board  1 . 
   Referring to  FIG. 2A , the water washing unit  27  for water-washing the printed wiring board  1 , having the lands  5   b ,  6   b  etched by the etching unit  12 , includes a transporting unit  35  for transporting the printed wiring board  1  in the horizontal state, and a spraying unit  36  for ejecting rinsing water. A plurality of transporting units  35  are arranged on the upper and lower surface sides of the printed wiring board  1 . The transporting unit  35  transports the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2A  at a transporting speed of, for example, 3 m/min, in order to remove the liquid etchant  24   a  affixed to the surface of the printed wiring board  1  with the rinsing water ejected from the spraying unit  36 . As for the spraying unit  36 , three spraying units each are provided on the upper and lower surface sides of the printed wiring board  1 , transferred by the transporting unit  35 , in order to remove the liquid etchant  24   a  affixed to both surfaces of the printed wiring board  1 . These spraying units  36  spray well water at ambient temperature under a spray pressure of 0.1 MPa or higher. This enables the water washing unit  27  to free the surface of the printed wiring board  1  of the liquid etchant  24   a.    
   The acid washing unit  28  for acid-washing the printed wiring board  1 , freed of the liquid etchant  24   a  by the water washing unit  27 , includes a transporting unit  38  for transporting the printed wiring board  1  in the horizontal position and a spraying unit  39  for ejecting sulfurated water. As for the transporting unit  38 , a plurality of transporting units  38  are provided on the upper and lower surface sides of the printed wiring board  1  for clamping the printed wiring board  1  transported in the horizontal position. The transporting units  38  transfer the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2A , at a transfer speed of e.g., 3 m/min, in order to positively remove the oxides from the lands  5   b ,  6   b  of the printed wiring board  1 . As for the spraying units  39 , there are provided each four spraying units  39  on the upper and lower surface sides of the printed wiring board  1 , being transferred by the transporting unit  35 , for positively forming the pre-flux films  9  on the surfaces of the lands  5   b ,  6   b . These spraying units  39  spray the 5% sulfuric acid sulfurated water at room temperature under a spraying pressure not lower than 0.2 MPa. This enables the acid washing unit  28  to positively remove the oxides of the lands  5   b ,  6   b  as part of the surface of the printed wiring board  1 . That is, the oxides on the lands  5   b ,  6   b  are removed positively by being etched by the etching unit  12  and acid-washed by the acid washing unit  28 , as shown in  FIGS. 5 and 6 . 
   Meanwhile, the sulfurated water is used for removing oxides on the surfaces of the conductor patterns  5   a ,  6   a , as described above, so that, if this sulfurated water is left in the via-hole  7  of the printed wiring board  1 , there is a risk that the plating layer  7   a  formed in the via-hole  7  be oxidized and ruptured. So, the rinsing unit  13  is designed so that, before forming the pre-flux film  9 , the sulfurated water will be removed positively by the water washing unit  29 , intermediate pressure water washing unit  30 , abundant water washing unit  31  and the water washing unit  32 . 
   The water washing unit  29  for water-washing the printed wiring board  1  washed with acid by the acid washing unit  28  includes a transporting unit  41  for transferring the printed wiring board  1  in the horizontal state, and a spraying unit  42  for spraying the rinsing water. As for the transporting unit  41 , plural transporting units  41  are provided on the upper and lower surface sides of the printed wiring board  1 . The transporting unit  41  transfers the printed wiring board  1  at e.g., a transfer speed of 3 m/min in the direction indicated by arrow A in  FIG. 2A  for positively rinsing the printed wiring board  1 . Since the pre-flux films  9  are formed on the lands  5   b ,  6   b  provided on both sides of the printed wiring board  1 , two each of the spraying units  42  are provided on the upper and lower surface sides of the printed wiring board  1  transferred by the transporting unit  41 . These spraying units  43  spray pure water at 35° C. under a condition of the spraying pressure not less than 0.1 MPa. The pure water at 35° C. is used for improving the water washing effect. If the water temperature is not lower than 35° C., the surfaces of the conductor patterns  5   a ,  6   a  tend to be oxidized. So, for washing the printed wiring board  1  until formation of the pre-flux film  9 , that is washing by the intermediate pressure water washing unit  30 , abundant water washing unit  31  and the water washing unit  32 , pure water at 35° C. is used. Thus, the water washing unit  29  removes the sulfurated water from the surface of the printed wiring board  1 . 
   The intermediate pressure water washing unit  30  for farther washing the printed wiring board  1  rinsed with water by the water washing unit  29  includes a transporting unit  44  for transferring the printed wiring board  1  in the horizontal position and a spraying unit  45  for ejecting rinsing water. As for the transporting unit  44 , plural transporting units  44  are provided on the upper and lower surface sides of the printed wiring board  1  for holding the printed wiling board  1  transferred in the horizontal position. The transporting unit  44  transfer the printed wiring board  1  at e.g., a transfer speed of 3 m/min in the direction indicated by arrow A in  FIG. 2B  to enable the sulfurated water to be rinsed off from the printed wiring board  1 . For rinsing the sulfurated water off from the printed wiring board  1 , four spraying units  45  are provided on the upper and lower sides of the printed wiring board  1  transferred by the transporting unit  44 . The spraying units  45  spray pure water at 35° C. at a pressure higher than that used for the water washing unit  29 , for example, at a spraying pressure not lower than 0.5 MPa. This allows the intermediate pressure water washing unit  30  to remove sulfurated water from the surface of the printed wiring board  1 . 
   The abundant water washing unit  31  for further washing the printed wiring board  1 , water-washed by the intermediate pressure water washing unit  30 , includes a transporting unit  47  for transferring the printed wiring board  1  in the horizontal state and a spraying unit  48  for ejecting rinsing water. A plurality of transporting units  47  are provided on the upper and lower sides of the printed wiring board  1  transferred by the transporting unit  44 . The transporting unit  47  transfers the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2B , at a transfer rate of e.g., 3 m/min, to enable the rinsing of the printed wiring board  1 . Two each of the spraying units  48  are provided on the upper and lower sides of the printed wiring board  1  transferred by the transporting unit  47 , in order to positively rinse sulfurated water off from both sides of the printed wiring board  1 . These spraying units  45  spray pure water at 35° C. with a higher water flow rate than the spraying unit  42  of the water washing unit  29 , for example, at a water flow rate not less than 5 liters/cm 2 . This allows the abundant water washing unit  31  to rinse the sulfurated water off from the surface of the printed wiring board  1 . 
   The water washing unit  32  for further washing the printed wiring board  1  water-washed by the abundant water washing unit  31  includes a transporting unit  50  for transferring the printed wiring board  1  in the horizontal position, and a spraying unit  51  for ejecting the rinsing water. A plurality of the transporting units  50  are provided on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. Two each of the spraying units  51  are provided on the upper and lower sides of the printed wiring board  1 , transferred by the transporting unit  50 , in order to positively rinse sulfurated water off from both sides of the printed wiring board  1 . These spraying units  51  spray fresh water at a spray pressure not lower than 0.1 MPa. This allows the water washing unit  29  to remove sulfurated water off from the surface of the printed wiring board  1 . Here, new pure water, that is fresh water, is used as rinsing water. Thus, the water washing unit  32  is able to prevent the processing liquid affixed to the printed wiling board  1 , that is sulfurated water, from being carried to the next step. 
   The air blower unit  33  for removing water affixed to the surface of the printed wiring board  1 , washed with water by the water washing unit  32 , includes a transporting unit  53  for transferring the printed wiling board  1  in the horizontal position, and an air ejection unit  54  for ejecting air to the upper and lower sides of the printed wiring board  1 . A plurality of the transporting units  53  are provided on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The transporting unit  53  transfers the printed wiring board  1  at a transfer rate e.g., of 3 m/min in the direction indicated by arrow A in  FIG. 2B  in order to positively remove the moisture affixed to the the upper and lower sides of the printed wiring board  1 . The air ejection unit  54  is provided on each of the upper and lower sides of the printed wiling board  1  to eject air to the upper and lower sides of the printed wiring board  1  transferred by the transporting unit  53  to remove the moisture affixed to the printed wiring board  1 . The air blower unit  33  is able to remove the moisture positively from the the upper and lower sides of the printed wiring board  1  prior to formation of the pre-flux film  9 . 
   The printed wiring board  1 , positively freed of surface oxides from the lands  5   b ,  6   b  by the etching unit  12  and the acid washing unit  28 , is washed with water in four stages of different conditions using the water washing unit  29 , intermediate pressure water washing mechanism  30 , abundant water washing unit  31  and the second water washing unit  32 , so that sulfurated water remaining on the surface and especially in the via-hole  7  may be removed reliably. Moreover, the intermediate pressure water washing unit  30  ejects pure water on the upper and lower sides of the printed wiring board  1  under a pressure higher than in the ordinary water washing unit  27  or  29 , while the abundant water washing unit  31  ejects pure water at a water flow rate higher than in the ordinary water washing unit  27  or  29 , so that sulfurated water can be removed reliably from the printed wiring board  1 . In addition, in the rinsing with pure water, pure water at the water temperature of 35° C. is used to improve the water washing effect, while it is possible to prevent oxidation of the surface of the lands  5   b ,  6   b . Thus, with the printed wiring board  1 , it is possible to prevent sulfurated water from being left on the lands  5   b ,  6   b . to prevent the lands  5   b ,  6   b  from being oxidized and roughed, while it is also possible to prevent the plating layer  7   a  provided in the via-hole  7  from being oxidized and ruptured. 
   For forming the pre-flux film  9  on the lands  5   b ,  6   b  of the printed wiring board  1 , freed of surface water by the air blower unit  33 , the printed wiring board  1  is immersed in the pre-flux liquid  9   a  stored in a processing vessel  56 , as shown in  FIG. 2C . The printed wiring board  1  is transferred to the bubble removing unit  14  and to the pre-flux forming unit  15 . 
   This bubble removing unit  14  removes air bubbles  58  generated on the surface of the printed wiring board  1  when the printed wiring board  1  is immersed in the pre-flux liquid  9   a  of the processing vessel  56 , and includes a processing vessel  56  in which to store the pre-flux liquid  9   a  and a bubble removing roll  57  operating as a unit for transferring the printed wiring board  1  in the horizontal position through the pre-flux liquid  9   a  and also for removing air bubbles  58  generated on the surface of the printed wiring board  1  when the printed wiring board is immersed in the pre-flux liquid  9   a . The pre-flux liquid  9   a , stored in the processing vessel  56 , is the water-soluble type pre-flux mainly composed of acetic acid and imidazole, such as a pre-flux manufactured by SHIKOKU KASEI CO. LTD. under the trade name of TERFACE F2. 
   A plurality of bubble removing rolls  57  are provided on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The bubble removing roll  57  transfers the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2C  at the same transfer speed of 3 m/min as that of the other transporting units  21 ,  25 ,  38 ,  41 ,  44 ,  47 ,  50  and  53 . These bubble removing rolls  57  are formed like sponge rolls from e.g., chlorosulfonated polyethylene. The bubble removing roll  57 , contacting the printed wiring board  1 , is run in rotation to remove air bubbles affixed to the surface of the printed wiring board  1  and is able to form the pre-flux film  9  to a uniform thickness on the lands  5   b ,  6   b  at the next step. 
   The pre-flux forming unit  15  for forming the pre-flux film  9  on the lands  5   b ,  6   b  of the printed wiring board  1 , immersed in the pre-flux liquid  9   a  and freed of surface air bubbles  58  by the bubble removing unit  14 , includes a processing vessel  56  in which to store the pre-flux liquid  9   a , a transporting unit  60  for transferring the printed wiring board  1  transferred in the horizontal position through the pre-flux liquid  9   a  and an in-liquid spraying unit  61  for spraying the pre-flux liquid  9   a , as shown in  FIG. 2C . 
   The transporting unit  60  is made up of plural rolls arranged on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The rolls provided the upper and lower sides of the printed wiring board  1  are arranged with a gap C larger than the thickness t of the printed wiring board  1 , in-between, and are designed such that the roll pressure applied to the printed wiring board  1  is decreased and such that no roll marks will be left on the pre-flux film  9  during its formation to enable the pre-flux film  9  to be formed to a uniform thickness. For example, the gap C is set to 0.5 mm or less, preferably to 2 mm. The transporting unit  60  transfers the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2C , at a transfer rate e.g., of 3 m/min, as the printed wiring board  1  is immersed in the water-soluble type pre-flux liquid  9   a . The printed wiring board  1  is immersed for e.g., 120 seconds in the water-soluble type pre-flux liquid  9   a  in the processing vessel  56 . 
   For forming the pre-flux film  9  of a uniform film thickness on each of the surfaces of the printed wiring board  1 , 10 each of in-liquid spraying units  61  are provided on the upper and lower sides of the printed wiring board  1  transferred by the transporting unit  60 . These in-liquid spraying units  61  are comprised of flat nozzles and are of the radiating angle of approximately 90° to permit the water-soluble pre-flux liquid  9   a  to be ejected over a wide range. These in-liquid spraying units  61  spray the water-soluble pre-flux liquid  9   a  of 35° C. onto the the upper and lower sides of the printed wiring board  1  under a spraying pressure not less than 0.1 MPa. Since the pre-flux liquid  9   a  is ejected onto the printed wiring board  1  by the in-liquid spraying units  61  in the pre-flux liquid  9   a , the pre-flux film  9  of a uniform film thickness of 0.2 to 0.3 μm is formed on the lands  5   b ,  6   b . The pre-flux film  9 , formed on the lands  5   b ,  6   b  formed by copper foils, is mainly composed of an imidazole compound, and is formed in accordance with the chemical formula 1: 
   
     
       
       
           
           
       
     
   
   In the previous process, the lands  5   b ,  6   b  are soft-etched by the etching unit  12  and further acid-washed by the acid washing unit  28  to remove the surface oxides and to rinse sulfurated water off positively and hence are of flat surfaces. Thus, the pre-flux film  9  adheres to the lands  5   b ,  6   b  intimately and is moreover of a flat surface. So, the pre-flux form  9  adherers positively to the lands  5   b ,  6   b  and is superior in solder wetting properties. 
   When the pre-flux film  9  has been formed by the lands  5   b ,  6   b  by the pre-flux forming unit  15 , the printed wiring board  1  is taken out from the processing vessel  56 . The printed wiring board  1 , taken out from the processing vessel  56 , is transferred to the liquid removing unit  16  to remove the liquid attached to its surface. This liquid removing unit  16  serves as a transfer unit for transferring the printed wiring board  1  taken out from the processing vessel  56  in the horizontal position, and includes upper and lower liquid removing rolls  62  for removing the liquid attached to its surface, and a lower saucer  63  arranged below the lower liquid removing roll  62 , as shown in  FIGS. 2C and 3 . 
   A plurality of the liquid removing rolls  62  are provided on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The liquid removing rolls  62  transfer the printed wiring board  1  in the direction indicated by arrow A in  FIGS. 2C and 3  at the same transfer rate e.g., of 3 m/min as that of the other transporting units  21 ,  25 ,  38 ,  41 ,  44 ,  47 ,  50 ,  53 ,  57  and  60 . The liquid removing rolls  62  are formed as water-absorbent sponge rolls from e.g., chlorosulfonated polyethylene and is designed to apply its own gravity to the printed wiring board  1 . 
   On the lower side of the printed wiring board  1 , transferred by the liquid removing rolls  62 , there is provided the lower saucer  63  of e.g., vinyl chloride for holding substantially the lower half of the liquid removing rolls  62 . Within this lower saucer  63 , which is a storage part for the pre-flux liquid  9   a , the water-soluble pre-flux liquid  9   a  is circulated at a rate of 5 to 10 liters/min. This permits the liquid removing rolls  62  to be immersed at all times in the new water-soluble pre-flux liquid  9   a  to prevent the liquid immersing the liquid removing rolls  62  from being oxidized to exfoliate the pre-flux liquid  9   a.    
   The aforementioned liquid removing unit  16  is able to form the surface of the pre-flux film  9  to a flat shape by the sponge-like liquid removing rolls  62  removing the excess pre-flux liquid  9   a  affixed to the surface of the printed wiring board  1  when the printed wiring board  1  is taken out of the processing vessel  56 . In particular, the lower liquid removing roll  62  is sponge-like and is partially covered by the lower saucer  63  in which is circulated the pre-flux liquid  9   a . So, the liquid component, in which is immersed the liquid removing rolls  62 , may be prevented from being oxidized to prevent exfoliation of the pre-flux film  9 . 
   The rinsing unit  17  for rinsing the printed wiring board  1 , freed of the surface pre-flux liquid  9   a  by the liquid removing unit  16  and for rinsing the printed wiring board  1  carrying the pre-flux film  9 , includes a water washing unit  66  for washing the printed wiring board  1  carrying the pre-flux film  9 , a water washing unit  67  for further water-washing the printed wiring board  1  washed with water by the water washing unit  66 , and an air blower unit  68  for removing the moisture affixed to the surface of the printed wiring board  1 , as shown in  FIG. 2D . 
   The rinsing unit  66  for washing the printed wiring board  1 , carrying the pre-flux film  9 , includes a transporting unit  71  for transferring the printed wiring board  1  transferred in the horizontal position, and a spraying unit  72  for ejecting the rinsing water, as shown in  FIG. 2D . A plurality of the transporting unit  71  are arranged on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The transporting unit  71  transfers the printed wiring board  1  at a transfer rate e.g., of 3 m/min in the direction indicated by arrow A in  FIG. 2D  for removing unneeded pre-flux liquid  9   a  affixed to the surface of the printed wiring board  1  and which has not been removed by the liquid removing unit  16 . Three of the spraying units  72  are provided on the upper and lower sides of the printed wiring board  1 , transferred by the transporting unit  71 , for removing the pre-flux liquid  9   a  affixed to the surface of the printed wiring board  1 . These spraying units  72  spray new water, that is fresh pure water, at ambient temperature, under a spraying pressure not less than 0.1 MPa. This permits the water washing unit  66  to remove the pre-flux liquid  9   a  from the surface of the printed wiring board  1 . On the other hand, by using fresh water, the pre-flux liquid  9   a  may be prevented from being carried to the next process step. 
   The second water washing unit  67  for further water-washing the printed wiring board  1 , water-washed by the water washing unit  66 , includes a transporting unit  74  for transferring the printed wiring board  1  transferred in the horizontal position and a spraying unit  75  for ejecting the rinsing water. A plurality of the transporting unit  74  are provided on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The transporting unit  74  transfers the printed wiring board  1  at a transfer rate e.g., of 3 m/min in the direction indicated by arrow A in  FIG. 2D  for removing unneeded pre-flux liquid  9   a  affixed to the surface of the printed wiring board  1  and which has not been removed by the liquid removing unit  66 . Two each of the spraying units  75  are provided on the upper and lower sides of the printed wiring board  1 , transferred by the transporting unit  74 , for removing the pre-flux liquid  9   a  affixed to the surface of the printed wiring board  1 . These spraying units  72  spray new water at ambient temperature, under a spraying pressure not less than 0.1 MPa, that is, the water washing unit  67  uses the new rinsing water, that is fresh water, without using the rinsing water used in the water washing unit  66 , for preventing the processing liquid, that is the pre-flux liquid  9   a , from being carried into the water washing unit  67  to make the rinsing water acidic to peel off the pre-flux film  9 . This permits the water washing unit  67  to remove the pre-flux liquid  9   a  positively from the surface of the printed wiring board  1 . 
   The air blower unit  68  for removing the moisture affixed to the surface of the printed wiring board  1 , washed with water by the water washing unit  67 , includes a transporting mechanism  77  for transferring the printed wiring board  1  in the horizontal position, and air blowers  78  for ejecting air onto the upper and lower sides of the printed wiring board  1 . A plurality of the transporting units  77  are provided on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The transporting unit  77  transfers the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2D  at a transfer rate e.g., of 3 m/min in order to positively remove the moisture affixed to the printed wiring board  1 . The air blowers  78  are provided on the upper and lower sides of the printed wiring board  1  for positively ejecting air onto the upper and lower sides of the printed wiring board  1  of the printed wiring board  1  transferred by the transporting unit  77 . The air blower unit  68  is able to remove the moisture positively from the upper and lower sides of the printed wiring board  1  carrying the pre-flux film  9 . 
   The drier unit  18  for drying the printed wiring board  1 , completely freed of the unneeded pre-flux liquid by water washing, includes a transporting unit  81  for transferring the printed wiring board  1  in the horizontal position and a heater  82  for heating the the upper and lower sides of the printed wiring board  1 . A plurality of the transporting units  81  are provided on the upper and lower sides of the printed wiring board  1 . The transporting unit  81  transfers the printed wiring board  1  in the direction indicated by arrow A in  FIG. 2D  at a transfer rate e.g., of 3 m/min for positively removing the moisture affixed to the printed wiring board  1 . The heater  82  heats the inside of a processing chamber to approximately 150° C. The printed wiring board  1 , transferred by the transporting unit  81 , is positively dried by heating for approximately 30 seconds. 
   The cooling unit  19  for cooling the printed wiring board  1  from the drying unit  18  includes a transporting unit  84  for transferring the printed wiring board  1  in the horizontal position. A plurality of transporting units  84  are mounted on the upper and lower sides of the printed wiring board  1  for holding the printed wiring board  1  transferred in the horizontal position. The transporting unit  84  cools the printed wiring board  1  at ambient temperature for approximately 20 seconds at a transfer rate e.g., of 3 m/min. 
   The method for forming the pre-flux film  9  on the lands  5   b ,  6   b  using the surface-processing device  10  constructed as described above is now explained by referring to  FIGS. 2A to 2D . 
   First, at step S 1 , the printed wiring board  1 , coated with the solder resists  8 ,  8  and tested for current conduction, is transferred by a transporting unit, not shown, to the rinsing unit  11 . The printed wiring board  1  is transferred by a transporting unit  21  at a transfer rate e.g., of 3 m/min and rinsed as the well water at ambient temperature is sprayed thereon under a spraying pressure not less than 0.1 MPa by each two spraying units  22  provided on the upper and lower sides of the printed wiring board  1 . This removes foreign matter, such as dust and dirt, deposited on the surface of the printed wiring board  1  prior to formation of the pre-flux film  9 . The printed wiring board  1  thus rinsed is transferred from the transporting unit  21  to the transporting unit  25  of the etching unit  12 . 
   Meanwhile, the lands  5   b ,  6   b  present irregularities due to surface oxidation, as shown in  FIG. 5 . If the pre-flux film  9  is formed on the lands  5   b ,  6   b  in a state shown in  FIG. 5 , the pre-flux film  9  is inferior in adhesion to the lands  5   b ,  6   b . Moreover, the irregularities on the lands  5   b ,  6   b  affect the pre-flux film  9  such that the surface of the pre-flux film  9  is also indented to worsen solder wettability. So, the lands  5   b ,  6   b  are planarized by acid-washing their surfaces by soft etching to remove surface irregularities, that is oxides. 
   That is, the lands  5   b ,  6   b  of the printed wiring board  1 , having their surfaces washed, are soft-etched at step S 2  by the etching unit  12 . Specifically, the printed wiring board  1  is transferred at a transfer rate e.g., of 3 m/min through the liquid etchant  24   a  in the processing vessel  24 , mainly composed of sulfurated water, whereby the copper foils making up the lands  5   b ,  6   b  are etched by 1.5 to 2.5 μm in 30 seconds. This removes the oxides affixed to the lands  5   b ,  6   b . The printed wiring board  1 , the lands  5   b ,  6   b  of which have been soft-etched is transferred from the transporting unit  25  to a transporting unit  35  of the water washing unit  27 . 
   The printed wiring board  1 , the lands  5   b ,  6   b  of which have been etched by the etching unit  12 , is freed at step S 3  of the liquid etchant  24   a  affixed to the entire surface of the printed wiring board  1  by the water washing unit  27 . That is, as the printed wiring board  1  is transferred by the transporting unit  35  at a transfer rate e.g., of 3 m/min, well water at ambient temperature is sprayed under a spraying pressure not less than 0.1 MPa by each three spraying units  36  provided the upper and lower sides of the printed wiring board  1 , whereby the excess liquid etchant  24   a  affixed to the surface of the printed wiring board  1  is removed. The printed wiring board  1 , rinsed by the water washing unit  27 , is transferred from the transporting unit  35  to a transporting unit  38  of the acid washing unit  28 . 
   The printed wiring board  1  freed of the liquid etchant  24   a  by water washing by the water washing unit  27 , is freed at step S 4  of oxides on the lands  5   b ,  6   b  by the acid washing unit  28 . Specifically, as the printed wiring board  1  is transferred at a transfer rate e.g., of 3 m/min in by the transporting unit  38 , 5% sulfuric acid sulfurated water at ambient temperature is sprayed on the upper and lower sides of the printed wiring board  1  under a spraying pressure not less than 0.2 MPa by each four spraying units  39  provided on the upper and lower sides of the printed wiring board  1 , whereby the oxides of the lands  5   b ,  6   b  may be removed positively. 
   That is, the surfaces of the lands  5   b ,  6   b  are soft-etched at step S 2  by the etching unit  12  and acid-washed at step S 4  by the acid washing unit  28 . That is, the two-stage oxide removing process positively removes the oxides to planarize the surface of the lands  5   b ,  6   b . This improves adhesion of the pre-flux film  9  to the lands  5   b ,  6   b , while also improving solder wettability. 
   Meanwhile, the sulfurated water is used for removing surface oxides on the lands  5   b ,  6   b , as described above, so that, if this sulfurated water is left in the via-hole  7  of the printed wiring board  1 , the plating layer  7   a  provided in the via-hole  7  tends to be oxidized and ruptured. So, at step S 5 , the printed wiring board  1 , the lands  5   b ,  6   b  of which have been acid-washed by the acid washing unit  28  and which has been transferred by the transporting unit  38 , is water-washed by the water washing unit  38 . That is, as the printed wiring board  1  is transferred at a transfer rate e.g., of 3 m/min by the transporting unit  41 , pure water at 35° C. is ejected under a spraying pressure not less than 0.1 MPa by each two spraying units  42  provided on the upper and lower sides of the printed wiring board  1 . This rinses sulfurated water off from the printed wiring board  1 . The printed wiring board  1 , washed with water by the water washing unit  29 , is transferred from the transporting unit  38  to a transporting unit  44  of the intermediate pressure water washing unit  30 . 
   The printed wiring board  1 , water-washed at step S 6  by the water washing unit  29 , is water-washed at a high ejection pressure by the spraying units  42  of the water washing unit  29  of the intermediate pressure water washing unit  30 . Specifically, the printed wiring board  1  is transferred by the transporting unit  44  at a transfer rate e.g., of 3 m/min and has its upper and lower surfaces sprayed with pure water at 35° C. under a spraying pressure not less than 0.5 MPa by each four spraying units  45  provided on the upper and lower sides of the printed wiring board  1 . This rinses the sulfurated water off from the printed wiring board  1 . The printed wiring board, washed with water by the intermediate pressure water washing unit  30 , is transferred from the transporting unit  44  to the transporting unit  47  of the abundant water washing Unit  31 . 
   The printed wiring board  1 , washed with water by the intermediate pressure water washing mechanism  30 , is washed at step S 7  with an abundant flow of water by the spraying units  42  of the water washing unit  29  of the abundant water washing unit  31 . Specifically, the printed wiring board  1  is transferred by the transporting unit  47  at a transfer rate e.g., of 3 m/min and sprayed with 35° C. pure water at a flow rate not less than 5 lit/cm 2  by each two spraying units provided on the upper and lower sides of the printed wiring board  1 . This rinses sulfurated water off from the printed wiring board  1 . The printed wiring board  1 , washed with water by the abundant water washing unit  31 , is transferred from the transporting unit  47  to the transporting unit  50  of the abundant water washing unit  32 . 
   At the next step S 8 , the printed wiring board  1 , washed with water by the abundant water washing unit  31 , is washed with new water by the water washing unit  32 . That is, as the printed wiring board  1  is transferred by the transporting unit  50  at a transfer rate e.g., of 3 m/min, it is sprayed with fresh water at 35° C. under a spraying pressure not less than 0.1 MPa by each two spraying units  51  provided the upper and lower sides of the printed wiring board  1 . This completely rises sulfurated water off from the printed wiring board  1 . Here, new pure water, that is fresh water, is used as the rinsing water, to prevent the processing liquid, that is sulfurated water, affixed to the printed wiring board  1 , from being carried to the following process step. The printed wiring board  1 , washed with water by the water washing unit  32 , is transported from the transporting unit  50  to the transporting unit  53  of the air blower unit  33 . 
   The printed wiring board  1 , washed with fresh water by the water washing unit  32 , is freed at step S 9  of water affixed to its surface by the air blower unit  33 . Specifically, as the printed wiring board  1  is transferred by the transporting unit  53  at a transfer rate e.g., of 3 m/min, air is ejected from an air blower  54  onto the upper and lower sides of the printed wiring board  1  to remove the moisture positively from the upper and lower sides of the printed wiring board  1  immediately before formation of the pre-flux film  9 . 
   By the four stages of water washing under different conditions employing the water washing unit  29 , intermediate pressure water washing unit  30 , abundant water washing unit  31  and the second water washing unit  32  at steps S 5  to S 8 , the sulfurated water left on the surface of the printed wiring board  1 , especially in the via-hole  7 , may be removed positively. Moreover, in the rinsing at the steps S 5  to S 8  employing pure water at 35° C., the water-washing effect may be improved, whilst surface oxidation of the lands  5   b ,  6   b  may be prevented from occurring. By using fresh water as the rinsing water at step S 8 , the processing liquid affixed to the printed wiring board  1 , that is sulfurated water, may be prevented from being transferred to the next step. 
   Thus, with the printed wiring board  1 , it is possible to prevent the lands  5   b ,  6   b , planarized by soft etching at step S 2  and acid washing at step S 4 , from being oxidized and being again hardened in its surface by the sulfurated water left on the lands  5   b ,  6   b . Moreover, with the printed wiring board  1 , it is possible to prevent the plating layer  7   a  in the via-hole  7  from berring oxidized and ruptured. On the lands  5   b ,  6   b , thus planarized, there is then formed the pre-flux film  9 . 
   That is, the printed wiring board  1 , freed of redundant water by the air blower unit  33 , is transported from the transporting unit  53  of the air blower unit  33  to a transporting unit, comprised of the bubble removing rolls  57  of the bubble removing unit  14 , so as to be immersed in the pre-flux liquid  9   a  stored in the processing vessel  56 . At this time, air bubbles  58  are generated on the surface of the printed wiring board  1 . If the pre-flux film  9  is formed as the air bubbles  58  are generated in this manner, the pre-flux film  9  cannot be formed to a uniform film thickness. So, the printed wiring board  1 , on the surface of which are attached the air bubbles  58 , is transferred at a transfer rate e.g., of 3 m/min by the bubble removing rolls  57  provided on the upper and lower sides of the printed wiring board  1  for removing the air bubbles  58 . The printed wiring board  1 , freed of the air bubbles  58  on immersion in the pre-flux liquid  9   a  in the processing vessel  56 , is transferred from the transporting unit comprised of the bubble removing rolls  57  to the transporting unit  60  of the pre-flux forming unit  15 . 
   On the lands  5   b ,  6   b  of the printed wiring board  1 , from the surface of which the air bubbles  58  have been removed, the pre-flux film  9  is formed at step S 11  by the pre-flux forming unit  15 . Specifically, as the printed wiring board  1  is transferred by the transporting unit  60  at a transfer rate e.g., of 3 m/min through the water-soluble pre-flux liquid  9   a  in the processing vessel  56 , mainly composed of acetic acid and imidazole on the surface of the printed wiring board  1  in the pre-flux liquid  9   a , the water-soluble pre-flux liquid at 35° C. is sprayed under a spraying pressure not less than 0.1 MPa by each ten in-liquid spraying units  61  provided on the upper and lower sides of the printed wiring board  1 . This forms the pre-flux film  9 , mainly composed of the imidazole compound, to a uniform film thickness of 0.2 to 0.3 μm, on the lands  5   b ,  6   b . Since these lands  5   b ,  6   b  are formed to flat surfaces by soft etching at step S 2  and by acid washing at step S 4 , as previous steps, as shown in  FIG. 7 , the pre-flux film  9  is intimately affixed to the lands  5   b ,  6   b  and formed to a planar surface. This enables the pre-flux film  9  to be generated with high adhesion properties with respect to the lands  5   b ,  6   b  and excellent solder wettability. The upper and lower paired rolls, making up the transporting unit  60 , are arranged at the intervals larger than the thickness of the printed wiring board  1 . So, the roll pressure applied to the surface of the printed wiring board  1  is reduced to prevent roll marks from being left on the surface of the pre-flux film  9  being formed to rough the surface. The printed wiring board  1 , now carrying the pre-flux film  9  on its lands  5   b ,  6   b , is transferred from the transporting unit  60  to the liquid removing unit  16 . Meanwhile, the printed wiring board  1  is immersed for 120 seconds in the pre-flux liquid  9   a  in the processing vessel  56 . 
   At step S 12 , the printed wiring board  1 , now carrying the pre-flux film  9 , is taken out from the processing vessel  56 , and transferred to the liquid removing rolls  62  making up the liquid removing unit  16  for removing the redundant portion of the pre-flux liquid  9   a . That is, the printed wiring board  1 , carrying the pre-flux liquid  9   a , is passed through the sponge-like liquid removing rolls  62  so as to be thereby freed of the unneeded portion of the pre-flux liquid  9   a . The lower liquid removing roll  62  below the printed wiring board  1  is partially hidden in the lower saucer  63  in which is circulated the pre-flux liquid  9   a . So, the fresh pre-flux liquid  9   a  is circulated at all times in the lower saucer  63  to prevent the liquid, component immersing the liquid removing roll  62  from being oxidized to cause peeling of the pre-flux film  9 . The printed wiring board  1  freed of the surface pre-flux liquid  9   a , is transferred to a transporting unit  71  of the water washing unit  66  from the liquid removing rolls  62  also operating as transporting means. 
   The printed wiring board  1 , freed of the surface pre-flux liquid  9   a  by the liquid removing unit  16 , is freed at step S 13  of the redundant portion of the pre-flux liquid  9   a  affixed to its surface by the water washing unit  66 . Specifically, as the printed wiring board  1  is transferred by the transporting unit  71  at a transfer rate e.g., of 3 m/min, it is sprayed with new water at ambient temperature, that is new fresh water, under a spraying pressure not less than 0.1 MPa, by each three spraying units  71  provided on the the upper and lower sides of the printed wiring board  1 . This rinses the pre-flux liquid off from the printed wiring board  1 . By using fresh water for water washing in this step, the pre-flux liquid  9   a  is prevented from being transferred to the next step. The printed wiring board  1 , washed with water by the water washing unit  66 , is transported from the transporting unit  71  to the transporting unit  74  of the water washing unit  67 . 
   The printed wiring board  1 , washed with water at step S 14  by the water washing unit  66 , is freed of excess pre-flux liquid  9   a , affixed to its surface, by the water washing unit  67 . Specifically, as the printed wiring board  1  is transferred by the transporting unit  74  at a transfer rate e.g., of 3 m/min, it is sprayed with new water at ambient temperature, that is new fresh water, under a spraying pressure not less than 0.1 MPa, by each two spraying units  71  provided on the the upper and lower sides of the printed wiring board  1 . This completely rinses the pre-flux liquid off from the printed wiring board  1 . By using fresh water for water washing in this step, the pre-flux liquid  9   a  is prevented from being transferred to the next step. The printed wiring board  1 , washed with water by the water washing unit  66 , is transported from the transporting unit  74  to the transporting unit  77  of the air blower unit  68 . 
   The printed wiring board  1 , now carrying the pre-flux film  9 , is washed with water in two stages by the water washing units  66 ,  67 , whereby the excess pre-flux liquid  9   a  affixed to its surface can be removed positively. By using fresh water as rinsing water at the time of removing the excess pre-flux liquid  9   a  attached to the printed wiring board  1  at steps S 12  and S 13 , the pre-flux liquid  9   a  may be prevented from being transferred to the next step. 
   The printed wiring board  1 , washed with new water by the water washing unit  67 , is freed of the moisture affixed to its surface by the air blower unit  68 . Specifically, as the printed wiring board  1  is transferred by the transporting unit  77  at a transfer rate e.g., of 3 m/min, air is ejected by the air blowers  78  onto the upper and lower sides of the printed wiring board  1  to remove the moisture positively from the upper and lower sides of the printed wiring board  1 . 
   The printed wiring board  1 , freed of the excess moisture by the air blower unit  68 , is dried at step S 16  by the drier unit  18 . That is, as the printed wiring board  1  is transferred by the transporting unit  84  at a transfer rate e.g., of 3 m/min; it is cooled at ambient temperature for approximately 20 seconds at ambient temperature. 
   At step S 17 , the printed wiring board  1  from the drying unit  18  is cooled by a cooling unit  19 . That is, the present printed wiring board  1  is transferred by the transporting mechanism  84  at a transfer rate e.g., of 3 m/min and cooled at ambient temperature for approximately 20 seconds. 
   In the above-described surface-processing method and apparatus  10  for forming the water-soluble pre-flux film  9  on the lands  5   b ,  6   b , the lands  5   b ,  6   b  are soft-etched by the etching unit  12  at step S 2  and substantially acid-washed by the acid washing unit  28 , by way of performing two-stage oxide removing step, where by the oxides may be positively removed and the lands  5   b ,  6   b  are processed to a planar surface, as shown in  FIG. 6 . By the four stages of water washing at steps S 5  to S 8  under different conditions employing the water washing unit  29 , intermediate pressure water washing unit  30 , abundant water washing unit  31  and the second water washing unit  32 , the sulfurated water left on the surface of the printed wiring board  1 , especially in the via-hole  7 , may be removed positively. 
   So, with the printed wiring board  1 , it is possible to prevent the lands  5   b ,  6   b , planarized by soft etching at step S 2  and acid washing at step S 4 , from being oxidized and being again roughed in its surface by the sulfurated water left on the lands  5   b ,  6   b . Moreover, with the printed wiring board  1 , it is possible to prevent the plating layer  7   a  in the via-hole  7  from being oxidized and ruptured. By forming the pre-flux film  9  on the lands  5   b ,  6   b , processed to planar surfaces, as shown in  FIG. 6 , it is possible to form the pre-flux film  9  having improved adhesion to the lands  5   b ,  6   b , while it is possible to planarize the surface of the pre-flux film  9  to improve its solder wettability. 
   Although the foregoing description is made of a multi-layered printed wiring board, having the lands  5   b ,  6   b  formed on its upper and lower sides, the present invention may also be applied to the forming of the pre-flux film  9  on a land of a printed wiring board carrying an electrically conductive layer on only one surface thereof.