Patent Publication Number: US-2005124091-A1

Title: Process for making circuit board or lead frame

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation-in-part (CIP) application of U.S. patent application Ser. No. 10/822,825 filed on Apr. 13, 2004, the contents being incorporated therein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a process for making a circuit board or a lead frame. In particular, the present invention relates to a process for making a circuit board with a conductor pattern formed on an insulating substrate by the subtractive method, or a process for making a lead frame or a fine pattern from a metal plate using a patterning technique.  
      2. Description of the Related Art  
      The subtractive method is an inexpensive, simple method and has conventionally been used most widely for fabricating circuit boards. With the recent trend toward a higher integration and a finer structure of semiconductor devices and various electronic appliances, however, this method is disadvantageous when producing a fine conductor pattern for the circuit board.  
      FIGS.  1 ( a ) to  1 ( d ) are sectional views showing the conventional process of fabricating a circuit board by the subtractive method disclosed in Japanese Unexamined Patent Publication No. (JP-A) 62-115891 or Japanese Unexamined Patent Publication NO. (JP-A) 2-175825, and show the process of forming a conductor pattern, on a resin substrate, by etching. As shown in  FIG. 1 ( a ), a board member  3  with a copper foil  2  attached to a resin substrate  1  is prepared. As shown in  FIG. 1 ( b ), the copper foil  2  is formed with a dry film resist (DFR) or coated with a liquid resist for masking to thereby form a resist  4 . The resist  4  is exposed and developed by a well-known method thereby to form a resist pattern  4   b.  Next, as shown in  FIG. 1 ( c ), an etching solution is applied to etch the portions  4   a  other than the portions of the copper foil  2  formed with the resist pattern thereby to leave a copper pattern. As shown in  FIG. 1 ( d ), the resist pattern  4   b  is then removed, so that the remaining copper foil portion constitutes a conductor pattern  5 .  
      According to the conventional method of fabricating a circuit board described above, however, as shown in  FIG. 1C , each portion of the conductor pattern  5  tends to assume a substantially trapezoidal shape in which the width (a) of the upper part formed with the resist is smaller than the pattern width (b) near to the boundary surface  6  between the resin substrate  1  and the copper foil  2 . This is due to the fact that during the progress of the etching process, the etching solution is applied also to the portion immediately under the masking  4  so that the copper foil  2  is side etched. Especially, the boundary surface  6  between the resin substrate  1  and the copper foil  2  generally has a fine unevenness as shown, and therefore it requires considerable time before the etching solution is sufficiently applied to the uneven boundary surface  6 . During this time, the etching solution is undesirably applied also to the portion immediately under the masking  4 , as described above.  
      An attempt to reduce the width of each pattern portion  5  or the pitch (c) between adjacent pattern portions would make it difficult to secure a sufficient width especially at the upper part of the pattern  5  far from the resin substrate  1 , which in turn makes it difficult to achieve a fine structure.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of this invention to provide a method of fabricating a circuit board or a lead frame with a fine conductor pattern by use of an inexpensive, simple subtractive method or a patterning technique and an etching technique, and a circuit board or a lead frame fabricated by the method.  
      According to the present invention, there is provided a process for forming a metal pattern, such as a lead frame, comprising the following steps of: (a) half-etching a metal plate from one or respective sides thereof by means of first masking which is positioned on one or respective surfaces of the metal plate; (b) applying positive liquid resist on the half-etched metal plate from one or respective sides of the first masking; (c) exposing the positive liquid resist with light from one or respective sides of the first masking; (d) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured liquid resist is removed; (e) half-etching again the metal plate from one or respective sides thereof by means of second masking composed of the first masking and the protected positive liquid resist; (f) repeating the steps (b) to (e) until a metal pattern is obtained from the metal plate; and (g) removing the first masking, and the second or subsequent masking of the unexposed positive liquid resist, from the metal plate.  
      According to another aspect of the present invention, there is provided a process for forming a metal pattern, such as a lead frame, comprising the following steps of: (a) coating one or respective surfaces of a metal plate with first resist and patterning the first resist; (b) forming light-block film on the patterned first resist; (c) half-etching the metal plate from one or respective side thereof by means of first masking composed of the first resist and the light-block film; (d) applying positive liquid resist on the half-etched metal plate from one or respective side of the first masking; (e) exposing the positive liquid resist with light from one or respective sides of the first masking; (f) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured liquid resist is removed; (g) half-etching again the metal plate from one or respective side thereof by means of second masking composed of the first masking and the protected positive liquid resist; (h) repeating the steps (d) to (g) until a metal pattern is obtained from the metal plate; and (i) removing the first masking, and the second or subsequent masking of the unexposed positive liquid resist, from the metal plate.  
      In the step of exposing the positive liquid resist with light from the upper and lower sides of the respective first masking, a parallel light perpendicular to the metal plate is used.  
      According to still another aspect of the present invention, there is provided a process for forming a metal pattern comprising the following steps of: (a) forming a first metal layer on a metal plate from one or respective sides thereof; (b) applying a first resist on the first metal layer and patterning the first resist to provide it with openings; (c) etching selectively only the first metal layer through the openings of the patterned first resist; (d) half-etching the metal plate by means of a first masking composed of the first resist and the first metal layer located just under the first resist; (e) applying a positive liquid, second resist on the half-etched metal plate from an upper side of the first masking; (f) exposing the positive liquid resist with light from the upper side of the first masking; (g) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured positive liquid resist is removed; (h) half-etching again the metal plate by means of a second masking composed of the first masking and the protected positive liquid resist; (i) repeating the steps of (e) to (h) until a metal pattern is obtained from the metal plate; and (g) removing the first masking, and the second or subsequent masking of the unexposed positive liquid resist, from the metal plate.  
      According to still another aspect of the present invention, there is provided a process for forming a metal pattern comprising the following steps of: (a) forming a first metal layer on a metal plate from one or respective sides thereof; (b) applying a first resist on the first metal layer and patterning the first resist to provide it with openings; (c) etching selectively only the first metal layer through the openings of the patterned first resist; (d) half-etching the metal plate by means of a first masking composed of the first resist and the first metal layer located just under the first resist; (e) applying a positive liquid, second resist on the half-etched metal plate from an upper side of the first masking; (f) exposing the positive liquid resist with light from the upper side of the first masking; (g) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured positive liquid resist is removed; (h) half-etching again the metal plate by means of a second masking composed of the first masking and the protected positive liquid resist; and (i) repeating the steps of (e) to (h) until a metal pattern is obtained from the metal plate.  
      According to still another aspect of the present invention, there is provided a process for making a circuit board comprising the following steps of: (a) half-etching a metal layer formed on an insulating substrate by means of a first masking which is positioned on an upper surface of the metal layer; (b) applying a positive liquid resist on the half-etched metal layer from an upper side of the first masking; (c) exposing the positive liquid resist with light from the upper side of the first masking; (d) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured to be positive liquid resist is removed; (e) half-etching again the metal layer by means of a second masking composed of the first masking and the protected positive liquid resist; (f) repeating the steps of (b) to (e) to form a conductive pattern on the insulating substrate; (g) removing the first masking, and the second or subsequent masking of the unexposed positive liquid resist, from the metal layer.  
      According to still another aspect of the present invention, there is provided a process for making a circuit board comprising the following steps of: (a) forming a first metal layer on an insulating substrate and forming a second metal layer on the first metal layer, the second metal layer having smaller thickness than that of the first metal layer; (b) applying a first resist on the second metal layer and patterning the first resist to provide it with openings; (c) etching selectively only the second metal layer through the openings of the patterned first resist; (d) half-etching the first metal layer by means of a first masking composed of the first resist and the second metal layer located just under the first resist; (e) applying a positive liquid, second resist on the half-etched first metal layer from an upper side of the first masking; (f) exposing the positive liquid resist with light from the upper side of the first masking; (g) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured positive liquid resist is removed; (h) half-etching again the metal layer by means of a second masking composed of the first masking and the protected positive liquid resist; (i) repeating the steps of (e) to (h) to form a conductive pattern on the insulating substrate; and (j) removing the first masking, and the second or subsequent masking of the unexposed positive liquid resist, from the metal layer.  
      According to still another aspect of the present invention, there is provided a process for making a circuit board comprising the following steps of: (a) preparing an insulating substrate having first and second surfaces, with a metal layer formed on at least one of the surfaces; (b) laminating a dry-film resist on the metal layer and patterning the dry-film resist; (c) coating the patterned dry-film resist with a light-blocking film to form a first masking; (d) half-etching the metal layer formed on the insulating substrate by means of the first masking; (e) applying a positive liquid resist on the half-etched metal layer from an upper side of the first masking; (f) exposing the positive liquid resist with light from the upper side of the first masking; (g) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured to be positive liquid resist is removed; (h) half-etching again the metal layer by means of a second masking composed of the first masking and the protected positive liquid resist; (i) repeating the steps of (e) to (h) to form a conductive pattern on the insulating substrate; (j) removing the first masking, and the second or subsequent masking of the unexposed positive liquid resist, from the metal layer.  
      According to further aspect of the present invention, there is provided a process for making a circuit board comprising the following steps of: (a) preparing an insulating substrate having first and second surfaces, with a metal layer formed on at least one of the surfaces; (b) laminating a dry-film resist on the metal layer and patterning the dry-film resist; (c) coating the patterned dry-film resist with a light-blocking film to form a first masking; (d) half-etching the metal layer formed on the insulating substrate by means of the first masking; (e) applying a positive liquid resist on the half-etched metal layer from an upper side of the first masking; (f) exposing the positive liquid resist with light from the upper side of the first masking; (g) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured to be positive liquid resist is removed; (h) half-etching again the metal layer by means of a second masking composed of the first masking and the protected positive liquid resist; (i) repeating the steps of (e) to (h) to form a conductive pattern on the insulating substrate; (j) selectively removing the light-blocking film; and (k) removing the dry-film resist, and the second or subsequent masking of the unexposed positive liquid resist, from the metal layer.  
      According to further aspect of the present invention, there is provided a process for making a circuit board comprising the following steps of: (a) forming a first metal layer on an insulating substrate and forming a second metal layer on the first metal layer, the second metal layer having smaller thickness than that of the first metal layer; (b) applying a first resist on the second metal layer and patterning the first resist to provide it with openings; (c) etching selectively only the second metal layer through the openings of the patterned second metal layer; (d) half-etching the first metal layer by means of a first masking composed of the first resist and the second metal layer located just under the first resist; (e) applying a positive liquid, second resist on the half-etched first metal layer from an upper side of the first masking; (f) exposing the positive liquid resist with light from the upper side of the first masking; (g) developing the positive liquid resist in such a manner that unexposed positive liquid resist located under the first masking is protected and exposed, uncured positive liquid resist is removed; (h) half-etching again the metal layer by means of a second masking composed of the first masking and the protected positive liquid resist; and (i) repeating the steps of (e) to (h) to form a conductive pattern on the insulating substrate.  
      In the step of exposing the positive liquid resist with light from the upper side of the first masking, a parallel light perpendicular to the metal layer is used.  
      The insulating substrate is flexible so that a tape automated bonding (TAB) type circuit board is thus made. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      FIGS.  1 ( a ) to  1 ( d ) are sectional views of a circuit board fabricated by the conventional subtractive method;  
      FIGS.  2 ( a ) to  2 ( f ) are sectional views showing the process of fabricating a circuit board by the subtractive method according to the invention;  
      FIGS.  3 ( a ) to  3 ( f ) are sectional views showing the process of fabricating a circuit board according to a second embodiment of the invention;  
      FIGS.  4 ( a ) to  4 ( f ) show a modification of the fabrication process shown in  FIG. 3 ;  
      FIGS.  5 ( a ) to  5 ( f ) are sectional views showing the process of fabricating a lead frame according to a third embodiment of the invention;  
      FIGS.  6 ( a ) to  6 ( f ) are sectional views showing the fabrication process according to a modification of the second embodiment of the invention;  
      FIGS.  7 ( a ) to  7 ( f ) are sectional views showing the fabrication process according to a further modification of the modification shown in  FIG. 4 ;  
       FIG. 8  is a sectional view showing a portion coated with a positive photosensitive permanent resist;  
      FIGS.  9 ( a ) to  9 ( f ) are sectional views the process of fabricating a circuit board by the subtractive method according to a fourth embodiment of the invention;  
      FIGS.  10 ( a ) to  10 ( f ) are sectional views showing the process of fabricating a circuit board according to a fifth embodiment of the invention; and  
      FIGS.  11 ( a ) to  11 ( f ) are sectional views showing the process of fabricating a lead frame according to a sixth embodiment of the invention.  
      FIGS.  12 ( a ) to  12 ( o ) show a further embodiment of fabrication process of the lead frame, in which half-etching steps are repeated several times;  
      FIGS.  13 ( a ) to  13 ( o ) show an embodiment similar to the embodiment shown in FIGS.  12 ( a ) to  12 ( o ), but the half-etching is conducted from the respective surfaces of the metal plate;  
      FIGS.  14 ( a ) to  14 ( o ) show a further embodiment similar to the embodiment shown in FIGS.  12 ( a ) to  12 ( o ), but fabricating a circuit board; and  
      FIGS.  15 ( a ) to  15 ( p ) show an embodiment similar to the embodiment shown in FIGS.  14 ( a ) to  14 ( o ), but the removal of masking is conducted in two steps. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Embodiments of the invention are described in detail, below, with reference to the accompanying drawings.  
      FIGS.  2 ( a ) to  2 ( f ) are sectional views showing the process of fabricating a circuit board using the subtractive method according to a first embodiment of the invention.  
      In  FIG. 2 ( a ), a copper foil  2  is formed as a metal layer on a resin substrate  1  by a well-known method thereby to make up a substrate member  3 . The resin substrate  1  is generally constituted of epoxy resin or glass epoxy resin.  
      Next, in  FIG. 2 ( b ), a dry film resist (DFR) having a light-blocking characteristic is formed as a first masking  4  on the upper surface of the copper foil  2 , and exposed and developed by a well-known method thereby to form a resist pattern  4   b.    
      Next, in  FIG. 2 ( c ), the etching solution is applied toward the first masking  4  formed of the openings  4   a  and the resist pattern  4   b  thereby to conduct the half etching. This half etching melts the peripheral area of the copper foil  2  under the etching solution passed portions  4   a  of the first masking  4 . Thus, the half etching conditions (etching time, etc.) are adjusted in such a manner that each etched portion  11  of the copper foil  2  leaves a desired width at the upper part of the pattern portion  17  ( FIG. 2 ( f )).  
      In this way, as shown in the drawings, at the upper portion of the copper foil  2  in proximity with the resist of the first masking pattern  4   b,  the etched portion  11  of the copper foil  2  bites somewhat more into the copper foil  2  than the width (d) of the etching solution passed portion  4   a  of the resist pattern thereby to perform what is called the side etching. Thus, the width (e) of the etched portion  11  is larger than the resist pattern width (d), while the intermediate area between the upper portion of the copper foil  2  and the boundary surface  6  in contact with the resin substrate  1  is rounded, thereby forming a groove  11  having a substantially U-shaped cross section as a whole.  
      Next, in  FIG. 2 ( d ), the whole surface of the portion half-etched in the preceding step is coated with a positive liquid resist  12 . Under this condition, the whole surface of the portion coated with the positive liquid resist  12  is exposed to the parallel light  13 . The light  13  used for exposure is desirably parallel light rays radiated toward the first masking pattern  4   b  in the direction at right angles to the surface of the first masking  4  of the circuit board. In the case where the light rays reach deep into the positive liquid resist  12 , however, the light  13  is not necessarily parallel light.  
      In this exposure step, the portion of the positive liquid resist  12  exposed to the light includes the area  12   a  of the positive liquid resist  12  above the first masking pattern  4   b,  the opening  4   a  of the first masking pattern  4   b,  and the area  12   b  immediately under each opening  4   a.  In other words, that area  12   c  under the non-transmitted portion  4   b  of the first masking pattern which is etched by biting somewhat more into the copper foil  2  than the width (d) of the resist pattern at the time of half etching in the preceding step is left unexposed. By the way, the resist of the second masking  12  may be formed by electrodeposition of a positive resist on only the portion having a metal.  
      The first embodiment uses two photosensitive resists making up the first masking and the second masking, i.e. the dry film resist  4  and the positive liquid resist or the positive electrodeposition resist  12 . The photosensitive wavelengths of these photosensitive resists are required to be appropriately combined with the exposure wavelengths used. The wavelength of the parallel light  13  selected for exposing the positive liquid resist and the positive electrodeposition resist  12 , therefore, is required to be absorbed by the positive liquid resist or the positive electrodeposition resist  12  but not to be transmitted through the dry film resist  4 .  
      Next, in  FIG. 2 ( e ), the exposed portions  12   a,    12   b  of the positive liquid resist  12  are developed thereby to etch only the light-exposed portions  12   a,    12   b  of the positive liquid resist  12 . In this way, it becomes possible to remove the etched portions  12   a,    12   b  of the positive liquid resist  12 . Each unetched portion  12   c  of the positive liquid resist  12  remains as it is, while each substantially U-shaped groove  11  described above forms a groove  14  having parallel inner walls on the two sides thereof, and each unetched portion  12   c  of the positive liquid resist  12  is used as a mask pattern (second masking) in the next step.  
      Then, the secondary etching is performed using, as a mask pattern, the dry film resist (first masking)  4  on the surface of the remaining copper foil  2  and the remaining portion  12   c  (second masking) of the positive liquid resist. As a result, the copper foil portion  15  under the parallel-wall groove  14  is etched, and the etched portion reaches the boundary surface  6  where the copper foil  2  and the resin substrate  1  are in contact with each other.  
      Next, the dry film resist  4  and the remaining positive liquid resist  12   c  are separated.  
      As a result, as shown in  FIG. 2 ( f ), a Dharma doll-shaped groove  16  is formed with a narrow central portion and round-expanded upper and lower portions along the depth. Specifically, the difference between the width (g) of the narrowest portion and the width (h) of the widest portion of the cross section of the conductor pattern  17  is much smaller than the width difference (b−a) of the trapezoidal cross section of the conventional conductor pattern shown in  FIG. 1 . As a result, the pitch (c) between adjacent pattern portions can be reduced thereby to achieve a finer circuit board.  
      FIGS.  3 ( a ) to  3 ( f ) are cross sectional views of the circuit board in the fabrication process according to the second embodiment using the subtractive method. Unlike in the first embodiment requiring a light-blocking resist (i.e. a resist through which the parallel light  13  is not passed), the first resist  4  according to the second embodiment requires no light-blocking characteristic. Only the points in which the second embodiment is different from the first embodiment are explained below.  
      First, according to the second embodiment, as shown in  FIG. 3 ( a ), a thin second metal layer  20  is formed on the copper foil  2  of a substrate member  3  including a resin substrate  1  formed with a copper foil  2  constituting a first metal layer. The thin second metal layer  20  may be a silver plating as described later.  
      Next, as shown in  FIG. 3 ( b ), as in the first embodiment, a dry film resist (DFR) is formed as a first resist  4  on the upper surface of the second metal layer  20 , and exposed and developed by a well-known method thereby to form a resist pattern  4   b.    
      In  FIG. 3 ( c ), only the thin second metal layer  20  is selectively removed by the quick etching process through each opening  4   a  of the patterned first resist  4  formed on the upper surface of the second metal layer  20 . As a result, only the portion of the second metal layer  20  corresponding to each opening  4   a  of the first resist  4  is removed. In the case where silver is used for the second metal layer  20 , for example, the parting solution as described in JP-A 2-175825, and capable of separating the silver without damaging the undercoating copper or copper alloy disclosed in JP-A 62-115891 material, may be used.  
      With the first resist  4  and the second metal layer  20  as a first masking, the etching solution is applied thereby to half-etch the copper foil  2  constituting the first metal layer  2 . As the result of the half-etching, the peripheral area of the copper foil  2  under each etching solution passed opening  4   a  of the first masking  4  of the copper foil  2  is etched. The conditions for this half-etching process are similar to those in the first embodiment.  
      In  FIG. 3 ( d ), as in the first embodiment, the whole surface including the portion half-etched in the preceding step is coated with the second resist  12  of positive liquid type and exposed. In this case, the first resist  4  has no light-blocking characteristic but the second metal layer  20  has a light-blocking characteristic. Therefore, the masking function can be sufficiently exhibited at the time of exposure by using the first resist  4  and the second metal layer  20  combined as a second masking.  
      In  FIG. 3 ( e ), the exposed portions  12   a,    12   b  of the second resist  12  are developed thereby to etch only the light-exposed portions  12   a,    12   b  of the second resist  12 . The unetched portion  12   c  of the second resist  12  can be used as a mask pattern (second masking) in the next step.  
      Next, as in the first embodiment, the secondary etching process is executed using a mask pattern including the first resist  4 , the second metal layer  20  (first masking) and the remaining portion  12   c  of the second resist of positive liquid type (second masking) remained on the surface of the copper foil  2 .  
      Then, the dry film resist (first resist  4 ) and the remaining positive liquid resist (second resist)  12   c  are separated. Further, the second metal layer  20  is removed by the quick etching process, etc. as required. In the case where the second metal layer  20  formed on the copper pattern  17  is used as a part of the conductor pattern, the process of separating the second resist  12   c  is followed by removing only the exposed portion of the second metal layer  20  by the quick etching process, etc. after which the first resist  4  is separated.  
      As a result, as in the first embodiment, a conductor pattern  17  can be obtained whereby a circuit board of a finer structure can be produced as shown in  FIG. 3 ( f ). Also, according to the second embodiment, a resist having no light-blocking characteristic can also be used as the first resist  4  as described above.  
      FIGS.  4 ( a ) to  4 ( f ) show a modification of the second embodiment shown in  FIG. 3 , in which a part of the second metal layer  20  is intended to be used for an electrode requiring the plating of a precious metal such as a wire bonding pad or a flip chip pad. In the step shown in  FIG. 4 ( a ), a part of the second metal layer  20  is formed with a greater thickness using a plating mask or the like. In the step of  FIG. 4 ( b ), as in the step of  FIG. 3 ( b ), the first resist  4  is formed on the upper surface of the second metal layer  20  and patterned, exposed and developed. Only the second metal layer  20  is selectively subjected to the quick etching process through the opening  4   a  of the patterned first resist  4  formed on the upper surface of the second metal layer  20 . In this way, only the portion  20   a  of the second metal layer  20  corresponding to the opening  4   a  of the first resist  4  is removed. Next, the first metal layer  2  is subjected to the half-etching process as designated by numeral  11 . As shown in  FIG. 4 ( c ), a thick portion  21  of the second metal layer  20  is left in the same thickness.  
      The steps shown in FIGS.  4 ( d ),  4 ( e ) are similar to those shown in FIGS.  3 ( d ),  3 ( e ) except for the fact that the portion  21  of the second metal layer  20  is formed as a thick layer. At the time of separating the second metal layer  20  by quick etching or a like process, as required, however, the thin other portion of the second metal layer  20  is separated substantially entirely, while the surface of the portion of the second metal layer  21  is etched off only partly. Thus, as shown in  FIG. 4 ( f ), the metal of the thick portion of the second metal layer  21  partly remains unetched. This remaining portion  21   a  can be used as an electrode such as a wire bonding pad or a flip chip pad.  
      FIGS.  5 ( a ) to  5 ( f ) are sectional views of a lead frame in fabrication process by the subtractive method according to a third embodiment of the invention. The third embodiment is basically similar to the second embodiment except that the third embodiment is applicable to the lead frame. Only the different points of the third embodiment from the second embodiment are described below.  
      First, in  FIG. 5 ( a ), a copper plate  2  making up a substrate of the lead frame is prepared, and the two surfaces of the copper plate  2  are each formed with a thin second metal layer  20  capable of being partly plated.  
      Next, in  FIG. 5 ( b ), as in the first embodiment, a dry film resist (DFR) is formed, as a first resist  4 , on each of the second metal layers  20 , and is patterned, exposed and developed by a well-known method thereby to form a resist patterns  4   b.  The thin second metal layers  20  are selectively subjected to the quick etching process through the openings  4   a  of the patterned first resists  4  formed on the surface of the second metal layers  20 . As a result, only the portions  20   a  of the second metal layers  20  corresponding to the openings  4   a  of the first resist  4  are removed. In the case where the second metal layers  20  are formed of silver, for example, the silver can be separated without adversely affecting the undercoating copper or copper alloy material as described in JP-A No. 62-115891 by suitably using the separation agent as described in JP-A 2-175825.  
      In  FIG. 5 ( c ), the etching solution is applied to half etch the copper plate  2  from the two surfaces thereof with the first resists  4  and the second metal layers  20  as a first masking. As the result of this half etching process, the peripheral area  11  of the copper foil  2  under the etching solution passed portions  4   a,    20   a  of the first masking  4  of the copper plate  2  is etched. The half etching depth is appropriately set in such a manner as to secure the desired width of the conductor pattern.  
      Next, as shown in  FIG. 5 ( d ), as in the first embodiment, the whole surface including the portion  11  half etched in the preceding step is coated with the second resist  12  of a positive liquid type and exposed. In this case, the first resists  4  have no light-blocking characteristics. As the second metal layers  20  have a light-blocking ability, however, the first resists  4  and the second metal layers  20 , combined, exhibit a masking function sufficiently at the time of exposure.  
      In  FIG. 5 ( e ), the exposed portions  12   a,    12   b  of the second resist  12  are developed thereby to etch only the photosensitized portions  12   a,    12   b  of the second resist. Each unetched portion  12   c  of the second resist  12  can be used as a mask pattern (second masking) in the next step.  
      As shown in  FIG. 5 ( f ), as in the first embodiment, the secondary etching is carried out using a mask pattern including the remaining part of each first resist  4  on the surface of the copper plate  2 , the second metal layers  20  (first masking) and the remaining portion  12   c  (second masking) of the second resist of positive liquid type.  
      Next, though not shown, the dry film resist (first resist  4 ) and the remaining positive liquid resist (second resist)  12   c  are separated. Further, the second metal layers  20  are separated by the quick etching or the like process as required. In the case where each second metal layer  20  formed on the copper pattern is used directly as a part of the conductor pattern, the second metal layers  20  are not necessarily separated.  
      FIGS.  6 ( a ) to  6 ( f ) show a modification of the second embodiment of the invention shown in FIGS.  3 ( a ) to  3 ( f ). According to the second embodiment, the second resist  12  of positive liquid type is used, whereas according to this modification, a positive photosensitive permanent resist  24  is used. The positive photosensitive permanent resist  24  is left as a part of the circuit pattern without being removed in the subsequent process of removing the first resist. Only the points different from the second embodiment are described below. A polyimide resin high in chemical resistance is used for the positive photosensitive permanent resist  24 .  
      As shown in  FIG. 6 ( a ), a thin second metal layer  20  is formed on the copper foil  2  of the substrate material  3  in the same way as in  FIG. 3 ( a ). In  FIG. 6 ( b ), a dry film resist (DFR) is formed as a first resist  4  on the upper surface of the second metal layer  20 , and is patterned, exposed and developed to thereby form a resist pattern  4   b  in the same manner as in  FIG. 3 ( b ). In  FIG. 6 ( c ), the copper foil  2  making up the second metal layer  2  is half etched with the openings  4   a  of the first resist  4  and the openings  20   a  of the thin second metal layer  20  as a first masking in the same manner as in  FIG. 3 ( c ).  
      In  FIG. 6 ( d ), this modification uses a positive photosensitive permanent resist  24  in place of a normal positive liquid resist  12  used in the second embodiment. The positive photosensitive permanent resist  24  is coated over the entire surface including the portions half etched in the preceding step. Even though the first resist  4  may have no light-blocking ability, as in the second embodiment, the second metal layer  20  has it. By using the first resist  4  and the second metal layer  20  combined as a second masking, therefore, the masking function can be sufficiently exhibited at the time of exposure. Under these conditions, the whole surface of the portion coated with the positive photosensitive permanent resist  24  is exposed by the parallel light  13 .  
      In  FIG. 6 ( e ), only the exposed portions  24   a,    24   b  of the second resist  24  providing a positive photosensitive permanent resist are developed, so that only the photosensitized portions  24   a,    24   b  of the second resist are etched. The portion  24   c  not etched can be used as a mask pattern (second masking) in the next step. The secondary etching process is carried out as in the aforementioned embodiments using a mask pattern including the first resist  4 , the second metal layer  20  (first masking) and the remaining portion  24   c  (second masking) of the positive photosensitive permanent resist  24  left on the surface of the copper foil  2 .  
      In  FIG. 6 ( f ), only the dry film resist (first resist  4 ) is separated using a strong alkali solution such as sodium hydroxide aqueous solution. The remaining portion  24   c  of the positive photosensitive permanent resist which is high in chemical resistance is not removed, and it is left as it is to form a part of the circuit pattern.  
      Next, the thin second metal layer  20  formed on the copper circuit pattern  17  is removed by the quick etching process or the like as required.  
      FIGS.  7 ( a ) to  7 ( f ) show a modification corresponding to that shown in  FIG. 4 ( a ) to  4 ( f ), in which a part of the second metal layer  20  is intended to be used for an electrode requiring the plating of a precious metal such as a wire bonding pad or a flip chip pad. Also, the positive photosensitive permanent resist  24  is used as a second resist. This positive photosensitive permanent resist  24  remains unremoved and is left as a part of the circuit pattern in the subsequent step of removing the first resist. Only the points different from the embodiment shown in FIGS.  4 ( a ) to  4 ( f ) are described below.  
      The steps shown in FIGS.  7 ( a ),  7 ( b ) and  7 ( c ) are similar to those shown in FIGS.  4 ( a ),  4 ( b ) and  4 ( c ), respectively.  
      In  FIG. 7 ( d ), as in  FIG. 6 ( d ), the positive photosensitive permanent resist  24  is used in place of the ordinary positive liquid resist  12 . This positive photosensitive permanent resist  24  is coated and exposed over the entire surface of the portion subjected to the half etching process in the preceding step.  
      In  FIG. 7 ( e ), as in  FIG. 6 ( e ), the exposed portions  24   a,    24   b  of the second resist  24  making up a positive photosensitive permanent resist are developed thereby to etch only the photosensitized second resist portions  24   a,    24   b.  The secondary etching is carried out using a mask pattern including the first resist  4 , the second metal layer  20  (first masking) and the remaining portion  24   c  (second masking) of the positive photosensitive permanent resist  24  left on the surface of the copper foil  2 .  
      In  FIG. 7 ( f ), as in the case of  FIG. 6 ( f ), only the dry film resist (first resist  4 ) is separated. The remaining positive photosensitive permanent resist portion  24   c  is not removed, and it is left as it is to form a part of the circuit pattern  17 . Whenever required, the thin second metal layer  20  formed on the copper circuit pattern  17  is removed by the quick etching or the like process.  
       FIG. 8  shows a case in which the positive photosensitive permanent resist  24  is coated as a second resist along the upper and side surfaces of the dry film resist (first resist  4 ), the side etching portion  11   a  of the copper foil  2  and the half etching portion  11 . Also in this case, only the unexposed portion of the positive photosensitive permanent resist  24  under the first resist  4  is held.  
      The first to third embodiments are explained above with reference to a case in which the first metal layer  2  is formed of copper as a material to be etched. Nevertheless, a material such as a copper alloy, iron-nickel alloy/alloy  42 , SUS or the like can be used with equal effect. Also, a silver plating (1 to 5 μm thick, for example) is used for the second metal layer  20 , of which a copper strike plating (plating as thin as 0.1 to 0.3 μm) is applied as an undercoating layer. Nickel plating is another choice. As another alternative, the second metal layer  20  may be a thin film of iron, nickel or chrome formed by sputtering.  
      The resist (dry film resist or liquid-type positive resist) can be separated using an alkali aqueous solution such as sodium hydroxide. Also, the use of an alkali potassium ferricyanide solution makes it possible to separate the resist while at the same time removing the chrome selectively.  
      As described above, according to the first to third embodiments, the pitches of the conductor pattern or the lead of the circuit board or the lead frame can be reduced. Also, the width of the upper portion of the conductor pattern or the lead can be secured, thereby reducing the difference between the width of the upper pattern (lead) and the width of the lower pattern (lead). Further, the circuit board having a thick conductor pattern or the lead frame having a thick lead can be processed using an inexpensive, simple subtractive method or patterning and etching techniques. Further, the plating can be formed accurately on the surfaces of the conductor pattern and the lead at the same time.  
      FIGS.  9 ( a ) to  9 ( f ) are sectional views showing the fabrication process of a circuit board according to a fourth embodiment of the invention using the subtractive method.  
       FIG. 9 ( a ) shows a state in which a copper foil  102  is formed on a resin substrate  101  by a well-known method to make up a substrate member  103 . The resin substrate  101  is generally formed of epoxy resin or glass-epoxy resin.  
      Next, in  FIG. 9 ( b ), a dry film resist (DFR) is formed as a first masking  104  on the upper surface of the copper foil, and exposed and developed by a well-known method thereby to form a resist pattern  104   b.    
      Next, in  FIG. 9 ( c ), the etching solution is applied toward the first masking  104  of the resist pattern thereby to conduct the half etching. This half etching melts the peripheral area of the copper foil  102  under the etching solution passed portion  104   a  of the first masking  104 . The half etching conditions (etching time, etc.) are adjusted so that the etched portion  111  of the copper foil  102  leaves a desired width at the upper portion of the pattern  117  ( FIG. 9 ( f )).  
      In this way, as shown in the drawings, at the upper portion of the copper foil  102  in proximity to the resist of the first masking pattern  104   b,  the etched portion  111  of the copper foil  102  bites somewhat more inward of the copper foil  102  than the width (d) of the etching solution passed portion  104   a  of the resist pattern. Thus, the width (e) of the etched portion  111  is larger than the resist pattern width (d), while the intermediate area between the upper portion of the copper foil  102  and the boundary surface  106  in contact with the resin substrate  101  is rounded and forms a groove  111  having a substantially U-shaped cross section.  
      Next, in  FIG. 9 ( d ), the whole surface of the portion half-etched in the preceding step is coated with a positive liquid resist  112 . Under this condition, the whole surface of the portion coated with the positive liquid resist  112  is exposed to the parallel light  113 . The light  113  used for this exposure is desirably parallel light rays radiated toward the first masking pattern  104   b  in the direction orthogonal to the surface of the first masking  104  of the circuit board. In the case where the light rays reach deep into the positive liquid resist  112 , however, the light  113  is not necessarily parallel light.  
      In this exposure step, the portion of the positive liquid resist  112  exposed to the light includes the area  112   a  of the positive liquid resist  112  above the first masking pattern  104   b  and the area  112   b  of the first masking pattern  104   b  immediately below the etching solution passed portion  104   a.  In other words, that the part of the area  112   c  under the non-transmitted portion  104   b  of the first masking pattern, which was etched somewhat widely to an extent more into the copper foil  102  than the width (d) of the resist pattern at the time of half etching in the preceding step, is left unexposed. By the way, the resist of the second masking  112  may be formed by electrodeposition whereby the resist is deposited only on the portion having a metal.  
      This embodiment uses two photosensitive resists making up the first masking and the second masking, i.e. the dry film resist  104  and the positive liquid resist or the positive electrodeposition resist  112 . The photosensitive wavelength of these photosensitive resists are required to be appropriately combined with the exposure waveform used. The wavelength of the parallel light  113  selected for exposing the positive liquid resist and the positive electrodeposition resist  112 , therefore, is required be absorbed by the positive liquid resist or the positive electrodeposition resist  112  but must not be transmitted through the dry film resist  104 .  
      Next, in  FIG. 9 ( e ), the exposed portions  112   a,    112   b  of the positive liquid resist  112  are developed thereby to etch only the light-exposed portions  112   a,    112   b  of the positive liquid resist. In this way, it becomes possible to remove the etched portions  112   a,    112   b  of the positive liquid resist  112 . The unetched portion  112   c  of the positive liquid resist  112  remains as it is, while the substantially U-shaped groove  111  described above becomes a groove  114  having parallel inner side walls, and the unetched portion  112   c  of the positive liquid resist  112  can be used as a mask pattern (second masking) in the next step.  
      Then, the secondary etching is performed using as a mask pattern including the dry film resist (first masking)  104  remaining on the surface of the copper foil  102  and the remaining portion  112   c  (second masking) of the positive liquid resist. As a result, the copper foil portion  115  under each parallel-wall groove  114  is etched, and the etched portion reaches the boundary surface  106  where the copper foil  102  and the resin substrate  101  are in contact with each other.  
      Next, the dry film resist  104  and the remaining positive liquid resist  112   c  are separated.  
      As a result, as shown in  FIG. 9 ( f ), a Dharma doll-shaped groove  116  having a narrow central portion and roundly expanded upper and lower portions is formed along the depth. Specifically, the difference (h−g) between the width (g) of the narrowest portion and the width (h) of the widest portion of the cross section of the conductor pattern  117  is much smaller than the width difference (b−a) for the conventional conductor pattern having a trapezoidal cross section shown in  FIG. 1 ( d ). As a result, the pitch (c) between adjacent pattern portions can be reduced thereby to achieve a finer circuit board.  
      FIGS.  10 ( a ) to  10 ( f ) are cross sectional views of the circuit board in fabrication process according to a fifth embodiment using the subtractive method. Unlike in the fourth embodiment, requiring the use of a light-blocking material, the first resist  104  of the fifth embodiment requires no light-blocking characteristic only the points in which the fifth embodiment is different from the fourth embodiment are explained below.  
      First, as shown in  FIG. 10 ( a ), a dry film resist (DFR) is formed as a first masking  104  on a copper foil  102  of the substrate member  103  on a resin substrate  101 , and exposed and developed by a well-known method to thereby form a resist pattern  104   b.  The resin substrate  101  is generally formed of epoxy resin or glass epoxy resin.  
      Next, as shown in  FIG. 10 ( b ), a light-blocking film  130  is formed on the portion  104   b  of the first masking  104  providing a the resist pattern. The light-blocking film  130  is formed only on the pattern portion  104   b  except for each opening  104   a  of the resist  104  by coating or transfer.  
      As shown in  FIG. 10 ( c ), the etching solution is applied on the copper foil  102  thereby to carry out the half etching process with the resist pattern  104  and the light-blocking film  130  as a first masking. As the result of this half etching process, as in the fourth embodiment, the peripheral area  111  of the copper foil  102  under the etching solution passed portion of the first masking is etched. The light-blocking film  130  may be formed after conducting the half etching process with the resist pattern  104  as a first masking.  
      Next, as shown in  FIG. 10 ( d ), as in the fourth embodiment, the whole surface including the portion half-etched in the preceding step is coated with the second resist  112  of positive liquid type and exposed. In this case, even though the first resist  104  has no light-blocking ability, the fact that the light-blocking film  130  is formed on the upper surface of the first resist  104  makes it possible to exhibit the light-blocking function sufficiently, at the time of exposure, by use of the first resist  104  and the light-blocking film  130  combined as a second masking.  
      As shown in  FIG. 10 ( e ), the exposed portions  112   a,    112   b  of the second resist  112  are developed to thereby etch only the photosensitized potions  112   a,    112   b  of the second resist  112 . The unetched portion  112   c  of the second resist  112  can be used as a mask pattern (second masking) in the next step.  
      Next, the secondary etching process is executed, as in the fourth embodiment, using a mask pattern including the first resist  104  and the light-blocking film  130  (first masking) remaining on the surface of the copper foil  102  and the remaining portion  112   c  (second masking) of the positive liquid type.  
      Then, the light-blocking film  130 , the dry film resist (first resist  104 ) and the remaining positive liquid resist (second resist)  112   c  are separated.  
      As a result, as in the case of the fourth embodiment, a conductor pattern  117  capable of miniaturizing the circuit board is obtained, as shown in  FIG. 9 ( f ). Also, according to this fifth embodiment, the first resist  104  has no light-blocking ability.  
      FIGS.  11 ( a ) to  11 ( f ) are sectional views showing the fabrication process of the lead frame using the subtractive method according to a sixth embodiment of the invention. This embodiment is basically similar to the fifth embodiment except that the etching process is executed from the two surfaces of the copper plate  102  for application to the lead frame. Only the points different from the fifth embodiment are described below.  
      First, in  FIG. 11 ( a ), the copper plate  102  providing a substrate of the lead frame is prepared, and the two surfaces of the copper plate  102  are each formed with a dry film resist (DFR) as a first masking, and exposed and developed by a well-known method thereby to form resist patterns  104   b.    
      Next, in  FIG. 11 ( b ), a light-blocking film  130  is formed on each portion  104   b  of the first masking  104  formed with the resist pattern on the two surfaces of the copper plate  102 . In  FIG. 11 ( c ), the half-etching is carried out by applying the etching solution from the two surfaces of the copper plate  102  with the resist patterns  104  and the light-blocking films  130  as a first masking. This half-etching process is carried to an appropriate depth smaller than one half of the thickness of the copper plate  102 . In  FIG. 11 ( d ), the whole surface including the half-etched portion on the each surface of the copper plate  102  is coated with a second resist  112  of positive liquid type and exposed. In  FIG. 11 ( e ), the two surfaces of the copper plate  102  are each formed with a mask pattern (second masking) by developing the second resist  112 . Next, in  FIG. 11 ( f ), the secondary etching process is executed using a mask pattern including the first resists  104  and the light-blocking films  130  (first masking) remaining on each surface of the copper plate  102  and the remaining portion  112   c  (second masking) of the second resist of positive liquid type.  
      The light-blocking films  130 , the dry film resists (first resists  104 ) and the remaining positive liquid resists (second resists)  112   c  are separated.  
      As a result, a lead frame having a very small lead width and a lead interval is obtained.  
      FIGS.  12 ( a ) to  12 ( o ) and FIGS.  13 ( a ) to  13 ( o ) show embodiments of fabrication process of the lead frame, similar to the sixth embodiment shown in FIGS.  11 ( a ) to  11 ( f ), but half-etching steps are repeated several times.  
      In the embodiment shown in FIGS.  12 ( a ) to  12 ( o ), the lead frame is fabricated by etching from one of the surfaces of the copper plate  2  and, on the other hand, in the embodiment shown in FIGS.  13 ( a ) to  13 ( p ), the lead frame is fabricated by etching from the respective surfaces of the copper plate  2 .  
      Therefore, in FIGS.  12 ( a ), a copper plate  2  providing a substrate of the lead frame is prepared. In FIGS.  12 ( b ), a dry film resist (DFR)  4  is laminated on one of the surfaces of the copper plate  2 . Then, in FIGS.  12 ( c ), the dry film resist  4  is patterned as  4   a.    
      Then, in FIGS.  12 ( d ), a light-blocking film  30  is coated on the formed on the patterned resist. Then, in FIGS.  12 ( e ), a half-etching is carried out by applying the etching solution from one of the surfaces of the copper plate  2  with the patterned dry film  4  and the light-blocking film  30  as a first masking.  
      Then, in FIGS.  12 ( f ), the whole surface including the half-etched portion on one surface of the copper plate  2  is coated with a positive liquid type resist  12  and exposed with the parallel ultra-violet light in  FIG. 12 ( g ). In  FIG. 12 ( h ), the positive liquid type resist  12  is developed in such a manner that unexposed positive liquid resist  12  located under the first masking is protected and exposed, uncured liquid resist is removed.  
      In  FIG. 12 ( i ), the metal plate  2  is again half-etched from one of the surface thereof by means of second masking composed of the first masking (light-blocking film  30 ) and the protected positive liquid resist  12   c.  In  FIG. 12 ( j ), the whole surface on one surface of the copper plate  2  is coated again with a positive liquid type resist  12  and exposed with the parallel ultra-violet light in  FIG. 12 ( k ). In  FIG. 12 ( l ), the positive liquid type resist  12  is developed again in such a manner that unexposed positive liquid resist  12  is further protected and exposed, uncured liquid resist is removed. In  FIG. 12 ( m ), the metal plate  2  is again half-etched from one of the surface thereof.  
      Thus, according to this embodiment, as shown in  FIG. 12 ( n ), the steps shown in FIGS.  12 ( j ) to  12 ( m ) are repeated for several times. Then, finally, in  FIG. 12 ( o ), the first masking (light-blocking film  30 ) and the second or subsequent masking of the unexposed positive liquid resist  12   c  are simultaneously removed from the metal plate  2  to obtain a lead frame.  
      The steps of shown in FIGS.  13 ( a ) to  13 ( o ) are the same as the steps of FIGS.  12 ( a ) to  12 ( o ), respectively, except that in the steps of shown in FIGS.  13 ( a ) to  13 ( o ), the half-etching steps are carried out from the respective surfaces of the copper plate  2  to obtain a lead frame.  
      FIGS.  14 ( a ) to  14 ( o ) show an embodiment of fabrication process of a circuit board, similar to the fourth embodiment shown in FIGS.  9 ( a ) to  9 ( f ), but half-etching steps are repeated several times in the same manner as the previous embodiments.  
      In FIGS.  14 ( a ), a resin substrate  1  having a copper foil  2  formed on one of the surfaces thereof is prepared. In FIGS.  14 ( b ), a dry film resist (DFR)  4  is laminated on one of the surfaces of the copper foil  2 . Then, in FIGS.  14 ( c ), the dry film resist  4  is patterned as  4   a.    
      Then, in  FIG. 14 ( d ), a light-blocking film  30  is coated on the formed on the patterned resist. Then, in  FIG. 14 ( e ), a half-etching is carried out by applying the etching solution from one of the surfaces of the copper foil  2  with the patterned dry film  4  and the light-blocking film  30  as a first masking.  
      Then, in  FIG. 14 ( f ), the whole surface including the half-etched portion on one surface of the copper foil  2  is coated with a positive liquid type resist  12  and exposed with the parallel ultra-violet light in  FIG. 14 ( g ). In  FIG. 14 ( h ), the positive liquid type resist  12  is developed in such a manner that unexposed positive liquid resist  12  located under the first masking is protected and exposed, uncured liquid resist is removed.  
      In  FIG. 14 ( i ), the metal foil  2  is again half-etched from one of the surface thereof by means of second masking composed of the first masking (light-blocking film  30 ) and the protected positive liquid resist  12   c.  In  FIG. 14 ( j ), the whole surface on one surface of the copper plate  2  is coated again with a positive liquid type resist  12  and exposed with the parallel ultra-violet light in  FIG. 14 ( k ). In  FIG. 14 ( l ), the positive liquid type resist  12  is developed again in such a manner that unexposed positive liquid resist  12  is further protected and exposed, uncured liquid resist is removed. In FIG.  14 ( m ), the metal foil  2  is again half-etched from one of the surface thereof.  
      Thus, according to this embodiment, as shown in  FIG. 14 ( n ), the steps shown in FIGS.  14 ( j ) to  14 ( m ) are repeated for several times. Then, finally, in  FIG. 14 ( o ), the first masking (light-blocking film  30 ) and the second or subsequent masking of the unexposed positive liquid resist  12   c  are simultaneously removed to obtain a circuit board having a conductor pattern  2 .  
      The embodiment shown in FIGS.  15 ( a ) to  15 ( o ) are the same as the steps of FIGS.  14 ( a ) to  14 ( o ), respectively, except that, in the latter embodiment, the light-blocking film  30  is first, separately removed from the metal foil  2  as shown in  FIG. 15 ( o ) prior to the dry film resist  4  and positive liquid type resist  12 , which are then finally removed in the step shown in  FIG. 15 ( p ).  
      The embodiments of the invention are described above with reference to the accompanying drawings. This invention, however, is not limited to the embodiments described above, but can be modified or changed in various ways without departing from the spirit and scope of the invention.  
      In the aforementioned embodiment referring to a case in which a conductor pattern is formed on the surface of the resin substrate  1 , for example, a TAB tape can be fabricated by use of a flexible resin substrate according to the present invention. In this way, the invention is applicable to all circuit frame or lead frame products fabricated by the subtractive method.  
      Further, this invention is applicable to a metal plate formed with a fine pattern by etching. In this case, the metal plate is etched from one or two surfaces thereof in accordance with the condition of all the patterns formed.  
      In the embodiments described above, copper is used for the first metal layers  102  as a member to be etched. Nevertheless, a copper alloy, iron, an iron-nickel alloy/alloy  42 , SUS, etc. may alternatively be used with equal effect.  
      Also, an etching solution may be an aqueous solution of ferric chloride or aqueous solution of cupric chloride normally used. Further, the positive liquid resist may be coated by any of the method using a bar coater and a method of a dip type. The resist (the dry film resist or the positive liquid resist) may be separated using an alkali potassium ferricyanide solution.  
      It will thus be understood from the foregoing description that, according to this invention, the pitches of the conductor pattern portions can be reduced in the circuit board. Also, the width of the upper portion of the conductor pattern can be secured and a difference can be reduced between the pattern width at the upper portion and the pattern width at the lower portion. Further, the subtractive method can be used for a circuit board having a thick conductor pattern.