Abstract:
A method of manufacturing a wired circuit board, including: forming an insulating layer in a pattern thereby forming second through holes penetrating the insulating layer in a thickness direction thereof; and after forming the insulating layer, forming, on the insulating layer, a conductive pattern in a pattern having terminals which are continuous with an upper surface and a side surface of a side end portion of the insulating layer such that the terminals extend into the second through holes. The terminals are operative for connecting with external terminals via a molten metal. The terminals include annular, step-shaped shoulder portions aligned with the second through holes and that are recessed downward from an upper surface, and first through holes having a diameter smaller than that of the second through holes and which pass through the terminals in a thickness direction thereof.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Divisional Application of U.S. patent application Ser. No. 12/081,835, filed Apr. 22, 2008 now U.S. Pat. No. 8,015,703, which is a continuation of U.S. patent application Ser. No. 11/236,815, filed Sep. 28, 2005, now U.S. Pat. No. 7,732,900, which claims priority from Japanese Patent Application No. 2004-307265, filed Oct. 21, 2004, the contents of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a wired circuit board and, more particularly, to a wired circuit board having terminals to be connected to external terminals through molten metal. 
     2. Description of the Prior Art 
     A wired circuit board usually has terminals to be connected to external terminals as a part of a conductive pattern. 
     Molten metal, such as, for example, solder balls, is used for connecting the terminals of the wired circuit board to the external terminals. The solder balls are placed on the terminals and are melted on the surfaces of the terminals, whereby the terminals of the wired circuit board are connected to the external terminals through the solder balls. 
     When the terminals have flat surfaces, the solder balls can roll around the surfaces of the terminals. The prior art proposes an attempted solution wherein electrodes (terminals) formed on the substrate are provided, at center portions thereof, with cavities to place the solder balls on the electrodes stably (Cf. JP Laid-open (Unexamined) Patent Publication No. 11-266066 (1999), for example). 
     In this prior art of JP Laid-open (Unexamined) Patent Publication No. 11-266066 (1999), the electrodes are formed as ring-shaped electrodes and the cavities are formed at the center portions of the ring-shaped electrodes, while the substrate is exposed from lower ends of the cavities, in other words, the cavities are closed by the substrate. 
     On the other hand, when the electrodes are connected to the external terminals through the solder balls, the substrate of the wired circuit board and an external substrate must be placed to confront each other so that the solder balls can be sandwiched therebetween. However, when the substrate and the external substrate are placed to confront each other, it cannot disadvantageously be seen whether the solder balls are precisely set in the cavities in the electrodes, because the cavities are closed by the substrate, so the solder balls get behind the substrate. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to provide a wired circuit board having terminals that can provide reliable placement of molten metals on the terminals, to connect between the terminals and the external terminals with a high degree of precision. 
     The present invention provides a wired circuit board comprising an insulating layer and a conductive pattern formed on the insulating layer, wherein the conductive pattern includes terminals to be connected with external terminals through molten metal, wherein first holes to be filled with the molten metals are formed in the terminals to extend through the terminals in a thickness direction thereof, and wherein second holes to communicate with the first holes are formed in the insulating layer at portions thereof corresponding to the terminals, to extend through the insulating layer in a thickness direction thereof. 
     In the wired circuit board of the present invention, it is preferable that a metal supporting layer is provided on the other side of the insulating layer opposite one side thereof on which the conductive pattern is provided, and third holes to communicate with the second holes are formed in the metal supporting layer to extend through the metal supporting layer in a thickness direction thereof. 
     According to the wired circuit board of the present invention, the first holes to be filled with molten metals are formed in the terminals, and the second holes to communicate with the first holes are formed in the insulating layer. This can provide the result that when the terminals are connected to the external terminals, the connection between the terminals and the external terminals can be performed while confirming the placement of the molten metals or the external terminals from the first and second holes. This can provide reliable placement of molten metals on the terminals, to connect between the terminals and the external terminals with a high degree of precision. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a perspective view showing a suspension board with circuit presented as an embodiment of a wired circuit board of the present invention. 
         FIG. 2  is a process drawing showing an embodiment of a production method of the suspension board with circuit shown in  FIG. 1 , 
       (a) showing the process of preparing a supporting board, 
       (b) showing the process of forming an insulating base layer of a predetermined pattern on the supporting board, 
       (c) showing the process of forming a conductive pattern on the insulating base layer, 
       (d) showing the process of forming an insulating cover layer of a predetermined pattern on the insulating base layer, 
       (e) showing the process of forming third through holes in the supporting board, 
       (f) showing the process of forming second through holes in the insulating base layer, and 
       (g) showing the process of forming a plating layer on each magnetic head connecting terminal and each external connecting terminal, 
         FIG. 3  is a detailed process drawing of the process of forming the insulating base layer on the supporting board shown in  FIG. 2 , 
       (a) showing the process of forming a coating of precursor of photosensitive polyimide resin on the entire surface of the supporting board, 
       (b) showing the process of exposing the coating to light through a photo mask, 
       (c) showing the process of developing the coating, and 
       (d) showing the process of curing the coating to form the insulting base layer of polyimide resin, 
         FIG. 4  is a detailed process drawing of the process of forming the conductive pattern on the insulating base layer shown in  FIG. 2 , 
       (a) showing the process of forming a thin metal film on a surface of the supporting board exposed from the insulating base layer and on the entire surface of the insulating base layer, 
       (b) showing the process of forming on a surface of the thin metal film a plating resist of a reverse pattern to the conductive pattern, 
       (c) showing the process of forming the conductive pattern on the surface of the thin metal film exposed from the plating resist, 
       (d) showing the process of removing the plating resist, and 
       (e) showing the process of removing the thin metal film exposed from the conductive pattern, 
         FIG. 5  is a detailed process drawing of the process of forming the insulating cover layer with a predetermined pattern on the insulating base layer shown in  FIG. 2 , 
       (a) showing the process of forming a coating of precursor of photosensitive polyimide resin on the entire surface of the insulating base layer including the conductive pattern and of the supporting board, 
       (b) showing the process of exposing the coating to light through a photo mask, 
       (c) showing the process of developing the coating, and 
       (d) showing the process of curing the coating to form the insulting cover layer of polyimide resin, 
         FIG. 6  is a sectional view of a principal part of an illustrative embodiment of the present invention, explaining the connection between an external connecting terminal of the suspension board with circuit shown in  FIG. 1  and an external terminal of an external circuit, 
         FIG. 7  is a sectional view of a principal part of another illustrative embodiment of the present invention, explaining the connection between an external connecting terminal of the suspension board with circuit shown in  FIG. 1  and an external terminal of an external circuit (a variant of  FIG. 6  wherein the suspension board with circuit is turned upside down) 
         FIG. 8  is a sectional view of a principal part of the illustrative embodiment of the present invention, explaining the connection between the external connecting terminal of the suspension board with circuit shown in  FIG. 1  and the external terminal of the external circuit (an illustrative aspect of the solder ball to be dropped down), 
         FIG. 9  is a sectional view of a principal part of another illustrative embodiment of the present invention, explaining the connection between an external connecting terminal of the suspension board with circuit shown in  FIG. 1  and an external terminal of an external circuit (a variant of  FIG. 8  wherein the suspension board with circuit is turned upside down), 
         FIG. 10  is a process drawing showing another embodiment of a production method of the suspension board with circuit shown in  FIG. 1 , 
       (a) showing the process of preparing a supporting board, 
       (b) showing the process of forming an insulating base layer of a predetermined pattern with recesses on the supporting board, 
       (c) showing the process of forming a conductive pattern on the insulating base layer, 
       (d) showing the process of forming an insulating cover layer of a predetermined pattern on the insulating base layer, 
       (e) showing the process of forming third through holes in the supporting board, 
       (f) showing the process of forming second through holes in the insulating base layer, and 
       (g) showing the process of forming a plating layer on each magnetic head connecting terminal and each external connecting terminal, 
         FIG. 11  is a detailed process drawing of the process of forming the insulating base layer on the supporting board shown in  FIG. 10 , 
       (a) showing the process of forming a coating of precursor of photosensitive polyimide resin on the entire surface of the supporting board, 
       (b) showing the process of exposing the coating to light through a photo mask, 
       (c) showing the process of developing the coating, and 
       (d) showing the process of curing the coating to form the insulting base layer with the recesses of polyimide resin, 
         FIG. 12  is a detailed process drawing of the process of forming the conductive pattern on the insulating base layer shown in  FIG. 10 , 
       (a) showing the process of forming a thin metal film on a surface of the supporting board exposed from the insulating base layer and on the entire surface of the insulating base layer, 
       (b) showing the process of forming on a surface of the thin metal film a plating resist of a reverse pattern to the conductive pattern, 
       (c) showing the process of forming the conductive pattern on the surface of the thin metal film exposed from the plating resist, 
       (d) showing the process of removing the plating resist, and 
       (e) showing the process of removing the thin metal film exposed from the conductive pattern, 
         FIG. 13  is a detailed process drawing of the process of forming the insulating cover layer of a predetermined pattern on the insulating base layer shown in  FIG. 10 , 
       (a) showing the process of forming a coating of precursor of photosensitive polyimide resin on the entire surface of the insulating base layer including the conductive pattern and of the supporting board, 
       (b) showing the process of exposing the coating to light through a photo mask, 
       (c) showing the process of developing the coating, and 
       (d) showing the process of curing the coating to form the insulting cover layer of polyimide resin, 
         FIG. 14  is a sectional view of a principal part of the external connecting terminal of the suspension board with circuit shown in  FIG. 1 , 
         FIG. 15  is a process drawing showing yet another embodiment of a production method of the suspension board with circuit shown in  FIG. 1 , 
       (a) showing the process of preparing a supporting board, 
       (b) showing the process of forming an insulating base layer of a predetermined pattern with second through holes on the supporting board, 
       (c) showing the process of forming a conductive pattern on the insulating base layer and the supporting board, 
       (d) showing the process of forming an insulating cover layer of a predetermined pattern on the insulating base layer, 
       (e) showing the process of forming third through holes in the supporting board, and 
       (f) showing the process of forming a plating layer on each magnetic head connecting terminal and each external connecting terminal, 
         FIG. 16  is a detailed process drawing of the process of forming the insulating base layer on the supporting board shown in  FIG. 15 , 
       (a) showing the process of forming a coating of precursor of photosensitive polyimide resin on the entire surface of the supporting board, 
       (b) showing the process of exposing the coating to light through a photo mask, 
       (c) showing the process of developing the coating, and 
       (d) showing the process of curing the coating to form the insulting base layer with the second through holes, 
         FIG. 17  is a detailed process drawing of the process of forming the conductive pattern on the insulating base layer shown in  FIG. 15 , 
       (a) showing the process of forming a thin metal film on a surface of the supporting board exposed from the insulating base layer and on the entire surface of the insulating base layer, 
       (b) showing the process of forming on a surface of the thin metal film a plating resist of a reverse pattern to the conductive pattern, 
       (c) showing the process of forming the conductive pattern on the surface of the thin metal film exposed from the plating resist, 
       (d) showing the process of removing the plating resist, and 
       (e) showing the process of removing the thin metal film exposed from the conductive pattern, 
         FIG. 18  is a detailed process drawing of the process of forming the insulating cover layer of a predetermined pattern on the insulating base layer shown in  FIG. 15 , 
       (a) showing the process of forming a coating of precursor of photosensitive polyimide resin on the entire surface of the insulating base layer including the conductive pattern and of the supporting board, 
       (b) showing the process of exposing the coating to light through a photo mask, 
       (c) showing the process of developing the coating, and 
       (d) showing the process of curing the coating to form the insulting cover layer of polyimide resin, 
         FIG. 19  is a sectional view of a principal part of the external connecting terminal of the suspension board with circuit shown in  FIG. 1 , 
         FIG. 20  is a sectional view showing a single-sided flexible wired circuit board which is in the form of one embodiment of the wired circuit board of the present invention, 
         FIG. 21  is a process drawing showing a production method of a suspension board with circuit of Comparative Example 1, 
       (a) showing the process of preparing a supporting board, 
       (b) showing the process of forming an insulating base layer of a predetermined pattern on the supporting board, 
       (c) showing the process of forming a conductive pattern on the insulating base layer, 
       (d) showing the process of forming an insulating cover layer of a predetermined pattern on the insulating base layer, and 
       (e) showing the process of forming a plating layer on each magnetic head connecting terminal and each external connecting terminal, and 
         FIG. 22  is a process drawing showing a production method of a suspension board with circuit of Comparative Example 2, 
       (a) showing the process of preparing a supporting board, 
       (b) showing the process of forming an insulating base layer of a predetermined pattern on the supporting board, 
       (c) showing the process of forming a conductive pattern on the insulating base layer, 
       (d) showing the process of forming an insulating cover layer of a predetermined pattern on the insulating base layer, and 
       (e) showing the process of forming a plating layer on each magnetic head connecting terminal and each external connecting terminal 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a perspective view showing a suspension board with circuit presented as an embodiment of a wired circuit board of the present invention. 
     In  FIG. 1 , the suspension board with circuit  1  is designed to mount a magnetic head of a hard disc drive (not shown) thereon and hold it against an airflow generated when the magnetic head and a magnetic disk run relative to each other, while supporting the magnetic head closely spaced from the magnetic disc. A conductive pattern  4  for connecting between the magnetic head and a read-write substrate is integrally formed with the suspension board with circuit  1 . 
     This suspension board with circuit  1  comprises a supporting board  2  serving as a metal supporting layer, an insulating base layer  3  serving as an insulating layer formed on the supporting board  2 , and a conductor layer  4  formed on the insulating base layer  3 . 
     The supporting board  2  is formed by a thin plate extending longitudinally. The supporting board  2  has a gimbal  5 , formed at a front end portion thereof, for mounting the magnetic head, and a terminal arranging portion  6 , formed at a rear end portion thereof, for arranging external connecting terminals  8  mentioned later along a longitudinal direction of the supporting board  2 . The terminal arranging portion  6  is formed to protrude to one widthwise side of the supporting board  2  (orthogonal to the longitudinal direction of the supporting board  2 ). 
     The insulating base layer  3  includes a part of the supporting board  2  where the conductive pattern  4  is formed, and is formed in the form of a predetermined pattern. 
     The conductive pattern  4  comprises a number of lines of wire  4   a ,  4   b  and  4   c ,  4   d , magnetic head connecting terminals  7 , and external connecting terminals  8  serving as a terminal portion, which are formed in a unified manner. The lines of wire  4   a ,  4   b ,  4   c ,  4   d  are extended along the longitudinal direction of the supporting board  2  and are arranged in parallel at spaced intervals with respect to the widthwise direction. 
     The magnetic head connecting terminals  7  are arranged at the front end portion of the supporting board  2  to correspond to the respective lines of wire  4   a ,  4   b ,  4   c , and  4   d . The magnetic head connecting terminals  7  are integrally formed with the supporting board  2  to continuously extend from front end portions of the respective lines of wire  4   a ,  4   b ,  4   c ,  4   d  and are spaced apart from each other along the widthwise direction of the supporting board  2 . The magnetic head (not shown) is mounted on the magnetic head connecting terminals  7 . 
     The external connecting terminals  8  are arranged in the terminal arranging portion  6  at the rear end portion of the supporting board  2  to correspond to the lines of wire  4   a ,  4   b ,  4   c , and  4   d , respectively. The external connecting terminals  8  are integrally formed with the supporting board  2  to continuously extend from rear end portions of the respective lines of wire  4   a ,  4   b ,  4   c ,  4   d  and are spaced apart from each other along the longitudinal direction of the supporting board  2 . The connection with the external connecting terminals  8  is performed using connecting terminals of a read/write board (not shown) serving as the external terminals and solder balls  21  (Cf.  FIG. 6 ) serving as molten metal. 
     Each of the external connecting terminals  8  is formed in generally square form as viewed from top, and first through holes  9  are formed in the form of first holes for molten solder balls  21  to be filled in. The first through holes  9  are formed to extend through the external connecting terminals  8  in the thickness direction thereof, respectively (Cf.  FIG. 6 ). 
     Also, second through holes  19  which are in the form of second holes to communicate with the first through holes  9 , respectively, are formed in the insulating base layer  3  at regions thereof corresponding to the external connecting terminals  8 . The second through holes  19  are formed in generally circular form as viewed from top larger than the first through holes  9 , extending through the insulating base layer  3  in the thickness direction. 
     Further, third through holes  20  which are in the form of third holes to communicate with the second through holes  19 , respectively, are formed in the supporting board  2  at regions thereof corresponding to the second through holes  19 . The third through holes  20  are formed in generally circular form as viewed from top larger than the second through holes  19 , extending through the supporting board  2  in the thickness direction. 
     Though not shown in  FIG. 1 , an insulating cover layer  10  formed in a predetermined pattern (Cf.  FIG. 2(   d )) is formed on the insulating base layer  3  to cover the conductive pattern  4 . 
     Next, a production method of this suspension board with circuit  1  will be described with reference to  FIGS. 2-5 . It should be noted that  FIGS. 2-5  each shows a sectional view of the terminal arranging portion  6  of the supporting board  2  taken along the longitudinal direction of the supporting board  2 . 
     In this method, the supporting board  2  is prepared, first, as shown in  FIG. 2(   a ). A metal foil or a thin metal sheet is used as the supporting board  2 . For example, stainless steel, 42-alloy, aluminum, copper-beryllium, phosphor bronze, etc. are used as the metal used for the supporting board  2 . Preferably, stainless foil is used in terms of rigidity, corrosion resistance and easiness in workability. The supporting board  2  has a thickness of e.g. 10-100 μm, or preferably 18-30 μm and a width of e.g. 50-500 mm, or preferably 125-300 mm. 
     Then, the insulating base layer  3  is formed in a predetermined pattern on the supporting board  2 , as shown in  FIG. 2(   b ). 
     No particular limitation is imposed on the insulating materials used for forming the insulating base layer  3 . For example, synthetic resins, such as polyimide resin, polyamide imide resin, acrylic resin, polyether nitrile resin, polyether sulfonic resin, polyethylene terephthalate resin, polyethylene naphthalate resin, and polyvinyl chloride resin. Of these synthetic resins, polyimide resin is preferably used in terms of heat resistance and chemical resistance. In addition, photosensitive synthetic resin is preferably used in terms of easiness in fine processing of the pattern. Further preferably, photosensitive polyimide resin is used. 
     For example when photosensitive polyimide resin is used to form the insulating base layer  3  of the predetermined pattern on the supporting board  2 , a solution of precursor of the photosensitive polyimide resin (photosensitive polyamic acid resin) is coated over the entire surface of the supporting board  2 , as shown in  FIG. 3(   a ). Then, it is heated at e.g. 60-150° C., or preferably at 80-120° C., to form a coating  11  of the precursor of the photosensitive polyimide resin. 
     Then, the coating  11  is exposed to light through a photo mask  12 , as shown in  FIG. 3(   b ). The photo mask  12  has a predetermined pattern comprising light shielding portions  12   a  and a total-light-transmitting portion  12   b.    
     The photo mask  12  is disposed opposite the coating  11  so that the light shielding portions  12   a  confront portions of the coating  11  where the insulating base layer  3  is not to be formed on the supporting board  2  and the total-light-transmitting portions  12   b  confront portions of the coating  11  where the insulating base layer  3  is to be formed on the supporting board  2 . 
     Preferably, light irradiated through the photo mask  12  (irradiated radiation) has an exposure wavelength of e.g. 300-450 nm, or preferably 350-420 nm. An integrated quantity of exposure light is preferably in the range of e.g. 100-2,000 mJ/cm 2 . 
     Then, the coating  11  exposed to light is developed, after heated to a predetermined temperature, if necessary, as shown in  FIG. 3(   c ). When the exposed-to-light portion of the coating  11  irradiated is heated at a temperature in the range of between e.g. 130° C. or more and less than 150° C., it is solubilized (positive type) in the next developing process. On the other hand, when heated at a temperature in the range of between e.g. 150° C. or more and 200° C. or less, it is insolubilized (negative type) in the next developing process. 
     The development can be performed by any known method, such as a dipping process and a spraying process, using a known developing solution such as alkaline developer. In this method, it is preferable that the negative pattern is formed. Illustrated in  FIG. 3  is an embodiment using the process steps for forming the negative pattern. 
     In this developing process, the coating  11  is melted at marginal portions thereof confronting the light shielding portions  12   a  of the photo mask  12 , so that it is formed in such a predetermined pattern that the marginal portions of the supporting board  2  are exposed. 
     Then, the coating  11  formed in the predetermined pattern is heated finally to e.g. 250° C. or more to be cured (imidized). As a result, the insulating base layer  3  of polyimide resin is formed in such a predetermined pattern that the marginal portions of the supporting board  2  are exposed, as shown in  FIG. 3(   d ). 
     As an alternative to using the photosensitive synthetic resin, for example the synthetic resin may be coated to form said pattern, or a dry film previously processed to have said pattern may be adhesively bonded to the supporting board  2  through an adhesive layer, if necessary. 
     The insulating base layer  3  thus formed has a thickness of e.g. 5-20 μm, or preferably 7-15 μm. 
     Then, the conductive pattern  4  is formed, as shown in  FIG. 2(   c ). No particular limitation is imposed on the conductive materials used for the conductive pattern  4 . For example, copper, nickel, gold, solder, or alloys thereof may be used. Copper is preferably used in terms of electrical conductivity, cost efficiency, and easiness in workability. 
     The conductive pattern  4  can be formed by a known patterning process, such as a subtractive process and an additive process. When the conductive pattern  4  is formed at fine pitch using the fine pitch technology, the additive process is preferably used. 
     In the additive process, a thin metal film  14  is formed as a seed film on a surface of the supporting board  2  exposed from the insulating base layer  3  and the entire surface of the insulating base layer  3 , as shown in  FIG. 4(   a ). The metal materials that may be used for the thin metal film  14  include, for example, chromium, nickel, copper, and alloys thereof. No particular limitation is imposed on the formation of the thin metal film  14 . For example, the thin metal film  14  can be formed by a vacuum deposition process such as a sputtering process. Preferably, the thin metal film  14  has thickness of e.g. 100-2,000 Å. The thin metal film  14  may be formed in multilayer, for example, by forming a thin chromium film and a thin copper film sequentially by the sputtering process. 
     Then, a plating resist  15  having a reverse pattern to the conductive pattern  4  is formed on the thin metal film  14 , as shown in  FIG. 4(   b ). To be more specific, the plating resist  15  is formed on the surface of the thin metal film  14  so that the thin metal film  14  can be exposed at potions thereof corresponding to the lines of wire  4   a ,  4   b ,  4   c ,  4   d , the magnetic head connecting terminals  7  and the external connecting terminals  8 . 
     The plating resist  15  is formed to have the reverse pattern to the conductive pattern  4  by a known process using a dry film photoresist, for example. 
     Then, the conductive pattern  4  is formed on the surface of the thin metal film  14  exposed from the plating resist  15 , as shown in  FIG. 4(   c ). No particular limitation is imposed on the formation of the conductive pattern  4 . For example, the conductive pattern  4  can be formed thereon by electrolytic plating, or preferably electrolytic copper plating. 
     Thereafter, the plating resist  15  is removed, as shown in  FIG. 4(   d ). The plating resist  15  is removed, for example, by a known etching process, such as a chemical etching (wet etching), or by stripping. 
     Then, the thin metal film  14  exposed from the conductive pattern  4  is removed, as shown in  FIG. 4(   e ). The thin metal film  14  is removed, for example, by the chemical etching (wet etching). 
     After the processes mentioned above, the conductive pattern  4  including the lines of wire  4   a ,  4   b ,  4   c , and  4   d , the respective magnetic head connecting terminals  7  and the respective external connecting terminals  8 , all of which are integrally formed, as shown in  FIG. 1 . In  FIG. 1 , the thin metal film  14  shown in  FIG. 4  is omitted. 
     The conductive pattern  4  has a thickness of e.g. 5-20 μm, or preferably 7-15 μm, and the lines of wire  4   a ,  4   b ,  4   c , and  4   d  have each a width of e.g. 5-500 μm, or preferably 10-200 μm. The interval between adjacent lines of wire  4   a ,  4   b ,  4   c , and  4   d  is for example in the range of e.g. 5-500 μm, or preferably 10-200 μm. 
     Each external connecting terminal  8  has a width W 1  of e.g. 100-1,100 μm, or preferably 140-540 μm, (a width of a portion thereof exposed from the insulating cover layer  10  with respect to a direction extending along the longitudinal direction of the supporting board  2 ) (Cf.  FIG. 6 ). The interval W 2  between adjacent external connecting terminals  8  (Cf.  FIG. 6 ) is for example in the range of 50-1,500 μm, or preferably 200-800 μm. 
     Also, the each external connecting terminal  8  has an outer shape of a generally square form as viewed from top and has, at a center portion thereof, the first through hole  9  of a circular shape as viewed from top, as mentioned above. The first through holes  9  have a diameter D 1  (Cf.  FIG. 6 ) of e.g. 50-1,000 μm, or preferably 100-500 μm. 
     It is preferable that a nickel plating layer (not shown) is formed on the surface of the conductive pattern  4  by electroless nickel plating in a sequential process, to protect the conductive pattern  4 . 
     Then, the insulating cover layer  10  is formed on the insulating base layer  3  to form a predetermined pattern that can allow the lines of wire  4   a ,  4   b ,  4   c ,  4   d  of the conductive pattern  4  to be covered and can allow the magnetic head connecting terminals  7  and the external connecting terminals  8  to be exposed, as shown in  FIG. 2(   d ). 
     The same insulating material as that for the insulating base layer  3  is used for forming the insulating cover layer  10 . Preferably, photosensitive polyimide resin is used for the insulating cover layer  10 . 
     When the insulating cover layer  10  is formed in a predetermined pattern using e.g. the photosensitive polyimide resin, a solution of precursor of the photosensitive polyimide resin (photosensitive polyamic acid resin) is coated over the entire surface of the insulating base layer  3  including the conductive pattern  4  and the entire surface of the supporting board  2 , as shown in  FIG. 5(   a ), and then is heated at e.g. 60-150° C., or preferably at 80-120° C., to form a coating  16  of the precursor of the photosensitive polyimide resin. 
     Then, the coating  16  is exposed to light through a photo mask  17 , as shown in  FIG. 5(   b ). The photo mask  17  has a predetermined pattern comprising light shielding portions  17   a  and total-light-transmitting portions  17   b.    
     The photo mask  17  is disposed opposite the coating  16  so that the light shielding portions  17   a  confront portions of the coating  16  where the insulating base layer  3  is not to be formed on the supporting board  2  and portions of the coating  16  corresponding to the magnetic head connecting terminals  7  and the external connecting terminals  8 , and the total-light-transmitting portions  17   b  confront portions of the coating  16  where the insulating cover layer  10  is to be formed on the insulating base layer  3  including the lines of wire  4   a ,  4   b ,  4   c ,  4   d . Then, the coating  16  is exposed to light in the same manner as the coating  11  is. 
     Then, the coating  16  thus exposed to light is developed in the same manner as the coating  11  is, as shown in  FIG. 5(   c ). Illustrated in  FIG. 5  is an embodiment using the process steps for forming the negative pattern. 
     In this developing process, the coating  16  is melted at portions thereof confronting the light shielding portions  17   a  of the photo mask  17  where the insulating base layer  3  is not formed on the supporting board  2  and corresponding to the respective magnetic head connecting terminals  7  and the respective external connecting terminals  8 . As a result, the coating  16  is formed in such a predetermined pattern that the marginal portions of the supporting board  2 , the magnetic head connecting terminals  7 , and the external connecting terminals  8  are exposed. 
     Then, the coating  16  formed in the predetermined pattern is heated finally to e.g. 250° C. or more to be cured (imidized). As a result, the insulating cover layer  10  of polyimide resin is formed in the predetermined pattern wherein the respective lines of wire  4   a ,  4   b ,  4   c ,  4   d  are covered and also the respective magnetic head connecting terminals  7  and the respective magnetic head connecting terminals  8  are exposed, as shown in  FIG. 5(   d ). 
     As an alternative to using the photosensitive synthetic resin, for example the synthetic resin may be coated to form said pattern, or a dry film previously processed to have said pattern may be adhesively bonded to the insulating base layer  3  through an adhesive layer, if necessary. 
     The insulating cover layer  10  has a thickness of e.g. 1-30 μm, or preferably 2-20 μm. 
     Thereafter, third through holes  20  corresponding to the first through holes  9  respectively (each having a common center axis with the first through hole  9 ) are formed in the supporting board  2  at portions thereof corresponding to the external connecting terminals  8 , to extend through the supporting board  2  in the thickness direction thereof, as shown in  FIG. 2(   e ). No particular limitation is imposed on the formation of the third through holes  20 . For example, the third through holes  20  can be formed by the chemical etching, the drilling, the laser processing, and so on. Preferably, the chemical etching is used for forming them. The third through holes  20  have a diameter D 3  of e.g. 150-1,200 μm, or preferably 180-600 μm (Cf.  FIG. 6) . As an alternative to forming the third through holes  20  to correspond to the first through holes  9 , respectively, openings may be formed to include the first through holes  9 . 
     Further, second through holes  19  corresponding to the first through holes  9  respectively (each having a common center axis with the first through hole  9 ) are formed in the insulating base layer  3  at portions thereof exposed from the respective third through holes  20  and corresponding to the external connecting terminals  8 , to extend through the insulating base layer  3  in the thickness direction thereof, as shown in  FIG. 2(   f ). No particular limitation is imposed on the formation of the second through holes  19 . For example, the second through holes  19  can be formed by the chemical etching, the drilling, the laser processing, and so on. Preferably, the chemical etching is used for forming them. The second through holes  19  have a diameter D 2  of e.g. 100-1,100 μm, or preferably 140-540 μm (Cf.  FIG. 6) . 
     Thereafter, a plating layer  18  is formed on the magnetic head connecting terminals  7  and the external connecting terminals  8  to cover their surfaces so as to protect those surfaces, as shown in  FIG. 2(   g ). No particular limitation is imposed on plating material used for forming the plating layer  18 . For example, nickel and gold are used for the plating layer  18 . 
     The plating layer  18  is formed using the electrolytic plating, or electroless plating, for example. The plating layer  18  may be formed in multilayer, using nickel plating and gold plating in a sequential order. In this plating layer  18 , the nickel plating layer has a thickness of e.g. 0.5-5 μm and the gold plating layer has a thickness of e.g. 0.05-3 μm. 
     Then, the supporting board  2  is cut out into a gimbal  5  by a known process such as the chemical etching. After trimmed, it is rinsed and dried. The suspension board with circuit  1  shown in  FIG. 1  is produced by the processes mentioned above. The trimming of the supporting board  2  may be performed before the plating layer  18  is formed. 
     In the suspension board with circuit  1  thus produced, the first through holes  9  are formed in the external connecting terminals  8 ; the second through holes  19  are formed in the insulating base layer  3 , to communicate with and be larger than the first through holes  9 ; and the third through holes  20  are formed in the supporting board  2 , to communicate with and be larger than the second through holes  19 , as shown in  FIG. 6 . 
     This constitution can provide the result that when the solder balls  21  are placed on the external terminals  23  and then the suspension board with circuit  1  is placed from above to connect the external connecting terminals  8  to the external terminals  23  of the external circuit  22  via the solder balls  21 , the solder balls  21  can be seen from above the suspension board with circuit  1  from the first through holes  9 , the second through holes  19 , and the third through holes  20 . 
     This can provide the advantage that the connection between the external connecting terminals  8  and the external terminals  23  can be carried out while confirming whether the solder balls  21  are placed precisely from the first through holes  9 , the second through holes  19 , and the third through holes  20 . This can ensure the reliable placement of the solder balls  21  on the external connecting terminals  8 , for the connection between the external connecting terminals  8  and the external terminals  23  with a high degree of precision. 
     No particular limitation is imposed on the connection using the solder balls  21 . For example, the solder balls  21  may be melted by reflow soldering with carriage or by the melting using laser thermo and the like. 
     In the connection method shown in  FIG. 6 , the solder balls  21  are placed on the external terminals  23  and then the suspension board with circuit  1  is placed in the state in which the supporting board  2  is located below and the insulating cover layer  10  is located above, to sandwich the solder balls  21  between the external connecting terminals  8  and the external terminals  23 . An alternative connection method shown in  FIG. 7  for example may be adopted wherein the solder balls  21  are placed on the external terminals  23  and then the suspension board with circuit  1  is placed in the state in which the insulating cover layer  10  is located below and the supporting board  2  is located above, to sandwich the solder balls  21  between the external connecting terminals  8  and the external terminals  23 . 
     Further, since this suspension board with circuit  1  has the first through holes  9 , the second through holes  19 , and the third through holes  20  which are formed at the respective external connecting terminals  8  to extend through the suspension board with circuit  1  in the thickness direction, another alternative connection method shown in  FIG. 8  may be adopted wherein the external connecting terminals  8  are disposed opposite the external terminals  23  in the state in which the supporting board  2  is located below and the insulating cover layer  10  is located above, and then the solder balls  21  are melted and dropped from above the external connecting terminals  8 , whereby the external connecting terminals  8  and the external terminals  23  are connected with each other via the solder balls  21 . 
     In these alternatives as well, the connection between the external connecting terminals  8  and the external terminals  23  can be carried out while confirming whether the external terminals  23  are precisely placed from the first through holes  9 , the second through holes  19 , and the third through holes  20 . This can ensure the reliable placement of the solder balls  21  on the external connecting terminals  8 , for the connection between the external connecting terminals  8  and the external terminals  23  with a high degree of precision. 
     A further alternative connection method shown in  FIG. 9  may be adopted wherein the external connecting terminals  8  are disposed opposite the external terminals  23  in the state in which the insulating cover layer  10  is located below and the supporting board  2  is located above, and then the solder balls  21  are melted and dropped from above the external connecting terminals  8 . 
     As an alternative to the producing method described above, the producing method shown in  FIGS. 10-13  may be adopted wherein the insulating base layer  3  is formed to have reduced thickness at portions thereof where the second through holes  19  are to be formed. This method can provide improved producing efficiency. In  FIGS. 10-13 , terminal placing portions  6  of the supporting board  2  are shown in section taken along the longitudinal direction of the supporting board  2 . 
     In this method, after the supporting board  2  is prepared, first, as shown in  FIG. 10(   a ), the insulating base layer  3  is formed on the supporting board  2  in a predetermined pattern wherein concave portions  13  are formed in the insulating base layer  3  at portions thereof corresponding to portions of the external connecting terminals  8  where the second through holes  19  are to be formed, as shown in  FIG. 10(   b ). 
     Then, for example when photosensitive polyimide resin is used to form the insulating base layer  3  in the predetermined pattern on the supporting board  2 , the coating  11  is formed from the solution of precursor of the photosensitive polyimide resin (photosensitive polyamic acid resin) in the same manner as above, as shown in  FIG. 11(   a ). Then, the coating  11  is exposed to light through a photo mask  27 , as shown in  FIG. 11(   b ). The photo mask  27  has a predetermined pattern comprising light shielding portions  27   a , total-light-transmitting portions  27   b , and semi-light-transmitting portions  27   c . The semi-light-transmitting portions  27   c  permit light to transmit in a light transmission ratio selected from the range falling within 10-90%, or preferably 30-60%, of the total transmission of 100%. 
     The photo mask  27  is disposed opposite the coating  11  so that that the light shielding portions  27   a  confront portions of the coating  11  where the insulating base layer  3  is not to be formed on the supporting board  2 ; the total-light-transmitting portions  27   b  confront portions of the coating  11  where the insulating base layer  3  is to be formed on the supporting board  2 ; and the semi-light-transmitting portions  27   c  confront portions of the coating  11  where the concave portions  13  are to be formed. Then, the coating  11  is exposed to light in the same manner as above. 
     Then, the coating  11  thus exposed to light is developed in the same manner as above, as shown in  FIG. 11(   c ). In this developing process, the coating  11  is melted at marginal portions thereof confronting the light shielding portions  27   a  of the photo mask  27 , so that the marginal portions of the supporting board  2  are exposed. Also, it is partly melted at the portions thereof confronting the semi-light-transmitting portions  27   c  of the photo mask  27  where the concave portions  13  are to be formed. Accordingly, the coating  11  is formed in such a predetermined pattern that the portions confronting the semi-light-transmitting portions  27   c  have a thickness smaller than the portions confronting the total-light-transmitting portions  27   b.    
     Then, the coating  11  formed in the predetermined pattern is heated finally to e.g. 250° C. or more to be cured (imidized). As a result, the insulating base layer  3  of polyimide resin is formed in a predetermined pattern wherein the marginal portions of the supporting board  2  are exposed and also the concave portions  13  are formed in the insulating base layer  3  at portions thereof where the second through holes  19  of the external connecting terminals  8  are to be formed, to have a thickness smaller than the remaining portions, as shown in  FIG. 11(   d ). To be more specific, the concave portions  13  are formed in generally circular form as viewed from top, having a thickness equal to 10-50% of that of the remaining portion of the insulating base layer  3 . 
     Then, the conductive pattern  4  is formed in the same manner as above, as shown in  FIG. 2(   c ). For example, in the additive process, a thin film  14  is formed as a seed film on a surface of the supporting board  2  exposed from the insulating base layer  3  and the entire surface of the insulating base layer  3 , as shown in  FIG. 12(   a ). Then, the plating resist  15  having a reverse pattern to the conductive pattern  4  is formed on the surface of the thin metal film  14 , as shown in  FIG. 12(   b ). Then, the conductive pattern  4  is formed on the surface of the thin metal film  14  exposed form the plating resist  15  in the same manner as above, as shown in  FIG. 12(   c ). Thereafter, the plating resist  15  is removed, as shown in  FIG. 12(   d ). Then, the thin metal film  14  exposed from the conductive pattern  4  is removed, as shown in  FIG. 12(   e ). 
     After the processes mentioned above, the conductive pattern  4  including the lines of wire  4   a ,  4   b ,  4   c , and  4   d , the respective magnetic head connecting terminals  7  and the respective external connecting terminals  8 , all of which are integrally formed, as shown in  FIG. 1 . In  FIG. 1 , the thin metal film  14  shown in  FIG. 12  is omitted. 
     The external connecting terminals  8  have annular shoulder portions  26  at opening portions of the first through holes  9  corresponding to the concave portions  13  of the insulating base layer  3 , 
     Then, the insulating cover layer  10  is formed on the insulating base layer  3  to form a predetermined pattern that can allow the lines of wire  4   a ,  4   b ,  4   c ,  4   d  of the conductive pattern  4  to be covered and can allow the magnetic head connecting terminals  7  and the external connecting terminals  8  to be exposed, as shown in  FIG. 10(   d ). The same insulating material as above is used for the insulating cover layer  10 . 
     For example, when the insulating cover layer  10  is formed on the insulating base layer  3  to have a predetermined pattern by using e.g. the photosensitive polyimide resin, the coating  16  is formed from the solution of precursor of the photosensitive polyimide resin (photosensitive polyamic acid resin) in the same manner as above, as shown in  FIG. 13(   a ). Then, the coating  16  is exposed to light through the photo mask  17 , as shown in  FIG. 13(   b ). Then, the coating  16  thus exposed to light is developed in the same manner as the coating  11  is, as shown in  FIG. 13(   c ). Then, the coating  16  formed in the predetermined pattern is cured (imidized) in the same manner as above, as shown in  FIG. 13(   d ). As a result, the insulating cover layer  10  of polyimide resin is formed in a predetermined pattern wherein the respective lines of wire  4   a ,  4   b ,  4   c ,  4   d  are covered and also the respective magnetic head connecting terminals  7  and the respective external connecting terminals  8  are exposed. 
     Thereafter, the third through holes  20  are formed in the supporting board  2  at portions thereof corresponding to the external connecting terminals  8  in the same manner as above, as shown in  FIG. 10(   e ). Then, the concave portions  13  corresponding to the external connecting terminals  8  are removed from the insulating base layer  3  exposed from the third through holes  20 , to form second through holes  19 , as shown in  FIG. 10(   f ). In the formation of the second through holes  19 , since the concave portions  13  are thinner in thickness than the remaining portions of the insulating base layer  3 , the time required for the removal (e.g. etching time) can be shortened to that extent. Hence, the suspension board with circuit  1  can be produced with efficiency. 
     Thereafter, the plating layer  18  is formed on the magnetic head connecting terminals  7  and the external connecting terminals  8  to cover their surfaces so as to protect those surfaces in the same manner as above, as shown in  FIG. 10(   g ). Then, the supporting board  2  is cut out into a shape of the gimbal  5  by a known process such as the chemical etching. After trimmed, it is rinsed and dried. The suspension board with circuit  1  shown in  FIG. 1  is produced by the processes mentioned above. A sectional view of the principal part of the external connecting terminals  8  is shown in  FIG. 14 . 
     As an alternative to the producing method described above, the producing method shown in  FIGS. 15-18  may be adopted wherein the conductive pattern  4  is formed on the stainless supporting board  2 . This can provide the result of eliminating the need to etch the insulating base layer  3  and thus curtailing the producing processes. In  FIGS. 15-18 , terminal arranging portions  6  of the supporting board  2  are shown in section taken along the longitudinal direction of the supporting board  2 . 
     In this method, after the supporting board  2  is prepared, first, as shown in  FIG. 15(   a ), the insulating base layer  3  is formed on the supporting board  2  in a predetermined pattern wherein the second through holes  19  are formed in the insulating base layer  3 , as shown in  FIG. 15(   b ). 
     The same as those mentioned above is used as the supporting board  2  and the insulating base layer  3 . 
     For example when photosensitive polyimide resin is used to form the insulating base layer  3  in the predetermined pattern on the supporting board  2 , the coating  11  is formed from the solution of precursor of the photosensitive polyimide resin (photosensitive polyamic acid resin) in the same manner as above, first, as shown in  FIG. 16(   a ). Then, the coating  11  is exposed to light through a photo mask  28 , as shown in  FIG. 16(   b ). The photo mask  28  has a pattern comprising light shielding portions  28   a , and total-light-transmitting portions  28   b . The photo mask  28  is disposed opposite the coating  11  so that the light shielding portions  28   a  confront portions of the coating  11  where the insulating base layer  3  is not to be formed on the supporting board  2  (the marginal portion of the supporting board  2  and the second-through-hole- 19 -forming portions of the external connecting terminals  8 ) and the total-light-transmitting portions  28   b  confront portions of the coating  11  where the insulating base layer  3  is to be formed on the supporting board  2 . 
     Then, the coating  11  thus exposed to light is developed in the same manner as above, as shown in  FIG. 16(   c ). In this developing process, the coating  11  is melted at its marginal portions and at its second-through-hole- 19 -forming portions in the external connecting terminals  8 , both confronting the light shielding portions  28   a  of the photo mask  28 , to form such a predetermined pattern that the marginal portions of the supporting board  2  and the second through holes  19  of the supporting board  2  are exposed. 
     Then, the coating  11  formed in the predetermined pattern is heated finally to e.g. 250° C. or more to be cured (imidized). As a result, the insulating base layer  3  of polyimide resin is formed in a predetermined pattern wherein the marginal portions of the supporting board  2  are exposed and also the second through holes  19  of the supporting board  2  are exposed, as shown in  FIG. 16(   d ). 
     Then, the conductive pattern  4  is formed in the same manner as above, as shown in  FIG. 15(   c ). For example, in the additive process, the thin film  14  is formed as the seed film on the surface of the supporting board  2  exposed from the insulating base layer  3  and the entire surface of the insulating base layer  3 , as shown in  FIG. 17(   a ). Then, the plating resist  15  having a reverse pattern to the conductive pattern  4  is formed on the surface of the thin metal film  14 , as shown in  FIG. 17(   b ). Then, the conductive pattern  4  is formed on the surface of the thin metal film  14  exposed from the plating resist  15  in the same manner as above, as shown in  FIG. 17(   c ). Thereafter, the plating resist  15  is removed, as shown in  FIG. 17(   d ). Then, the thin metal film  14  exposed from the conductive pattern  4  is removed, as shown in  FIG. 17(   e ). 
     After the processes mentioned above, the conductive pattern  4  including the lines of wire  4   a ,  4   b ,  4   c , and  4   d , the respective magnetic head connecting terminals  7  and the respective external connecting terminals  8 , all of which are integrally formed, as shown in  FIG. 1 . In  FIG. 1 , the thin metal film  14  shown in  FIG. 17  is omitted. 
     The external connecting terminals  8  have annular shoulder portions  26  formed at opening portions of the first through holes  9  corresponding to portions thereof where the insulating base layer  3  is not formed. 
     Then, the insulating cover layer  10  is formed on the insulating base layer  3  to form a predetermined pattern that can allow the lines of wire  4   a ,  4   b ,  4   c ,  4   d  of the conductive pattern  4  to be covered and can allow the magnetic head connecting terminals  7  and the external connecting terminals  8  to be exposed, as shown in  FIG. 15(   d ). The same insulating material as above is used for the insulating cover layer  10 . 
     For example, when the insulating cover layer  10  is formed on the insulating base layer  3  to have a predetermined pattern by using the photosensitive polyimide resin, the coating  16  is formed from the solution of precursor of the photosensitive polyimide resin (photosensitive polyamic acid resin) in the same manner as above, as shown in  FIG. 18(   a ). Then, the coating  16  is exposed to light through the photo mask  17 , as shown in  FIG. 18(   b ). Then, the coating  16  thus exposed to light is developed in the same manner as the coating  11  is, as shown in  FIG. 18(   c ). Then, the coating  16  formed in the predetermined pattern is cured (imidized) in the same manner as above, as shown in  FIG. 18(   d ). As a result, the insulating cover layer  10  of polyimide resin is formed in a predetermined pattern wherein the respective lines of wire  4   a ,  4   b ,  4   c ,  4   d  are covered and also the respective magnetic head connecting terminals  7  and the respective external connecting terminals  8  are exposed. 
     Thereafter, the third through holes  20  are formed in the supporting board  2  at portions thereof corresponding to the external connecting terminals  8  in the same manner as above, as shown in  FIG. 15(   e ). 
     Then, after the plating layer  18  is formed on the magnetic head connecting terminals  7  and the external connecting terminals  8  to cover their surfaces so as to protect those surfaces in the same manner as above, as shown in  FIG. 15(   f ). Thereafter, the supporting board  2  is cut out into a shape of the gimbal  5  by a known process such as the chemical etching. After trimmed, it is rinsed and dried. The suspension board with circuit  1  shown in  FIG. 1  is produced by the processes mentioned above. A sectional view of the principal part of the external connecting terminals  8  is shown in  FIG. 19 . 
     Although the illustrative embodiment wherein the external connecting terminals  8  are formed in generally square form as viewed from top and the first through holes  9 , the second through holes  19 , and the third through holes  20  are formed in generally circular form as viewed from top has been illustrated above, the shape of the external connecting terminals  8  and the shape of the first, second, and third through holes  9 ,  19 ,  20  may be properly selected for intended purposes and applications, without any particular limitation being imposed thereon. For example, the first through holes  9 , the second through holes  19 , and the third through holes  20  may be formed in generally rectangular form as viewed from top. In this variant, one side of the first rectangular through holes  9 , one side of the second rectangular through hole  19 , and one side of the third rectangular through hole  20  are set to be equal to diameters of the first through holes  9 , second through holes  19 , and third through holes  20 , respectively. 
     Although the suspension board with circuit  1  is presented as an example of the wired circuit board of the present invention, the wired circuit board of the present invention includes a single sided flexible wired circuit board, a double sided flexible wired circuit board, and a multilayer flexible wired circuit board. 
     For example, such a single sided flexible wired circuit board  31  is shown in  FIG. 20  for illustrative purposes. 
     The single sided flexible wired circuit board  31  shown in  FIG. 20  comprises the insulating base layer  32 , a number of terminals  33  formed on the insulating base layer  32  to be integral with the conductive pattern, and the insulating cover layer  34  formed on the insulating base layer  32  in such a manner that the conductive pattern is covered and the respective terminals  33  are exposed 
     In this single sided flexible wired circuit board  31 , the first through holes  35  are formed in the terminals  33  to extend therethrough in the thickness direction, and the second through holes  36  are formed in the insulating base layer  32  to extend therethrough in the thickness direction so as to communicate with the first through holes  35 . Also, the plating layers  37  are formed on the terminals  33 . 
     The suspension board with circuit  1  illustrated above can be industrially produced by a known process such as, for example, a roll-to-roll process. 
     EXAMPLE 
     While in the following, the present invention will be described in further detail with reference to Examples, the present invention is not limited thereto. 
     Example 1 
     The supporting board  2  of a stainless foil (SUS304) of 300 mm wide and 25 μm thick was prepared (Cf.  FIG. 2(   a )). 
     Then, after solution of precursor of photosensitive polyimide resin (photosensitive polyamic acid resin) was coated over the entire surface of the supporting board  2 , the coated resin was heated for two minutes at 120° C., to form a coating  11  of the precursor of the photosensitive polyimide resin (Cf.  FIG. 3(   a )). 
     Thereafter, the photo mask  12  was disposed opposite the coating  11  so that the light shielding portions  12   a  confronted portions of the coating  11  where the insulating base layer  3  was not to be formed on the supporting board  2  and the total-light-transmitting portions  12   b  confronted portions of the coating  11  where the insulating base layer  3  was to be formed on the supporting board  2 . Then, the coating  11  was exposed to ultraviolet light (an integrated quantity of exposure light of 720 mJ/cm 2 ) (Cf.  FIG. 3(   b )). 
     Then, after heated (for three minutes at 160° C.), the coating  11  exposed to light was developed using alkaline developer, so that the coating  11  was formed in such a predetermined pattern that could allow the marginal portions of the supporting board  2  to be exposed (Cf.  FIG. 3(   c )). Thereafter, the coating  11  was heated at  420 ° C. to thereby form the insulating base layer  3  of polyimide resin having a thickness of 10 μm (Cf.  FIG. 3(   d )). 
     Then, a thin chromium film and a thin copper film were sequentially formed on the surface of the supporting board  2  exposed from the insulating base layer  3  and on the entire surface of the insulating base layer  3  by the sputtering process to form the thin metal film  14  having thickness of 300-1,000 Å (Cf.  FIG. 4(   a )). Then, after laminated on the surface of the thin metal film  14 , the dry film photoresist was exposed to ultraviolet light (an integrated quantity of exposure light of 235 mJ/cm 2 ) and then developed by alkaline developer to form the plating resist  15  having the reverse pattern to the conductive pattern  4  on the thin metal film  14  (Cf.  FIG. 4(   b )). 
     Then, the conductive pattern  4  having thickness of 10 μm was formed on the surface of the thin metal film  14  exposed from the plating resist  15  by electrolytic copper plating (Cf.  FIG. 4(   c )). Thereafter, the plating resist  15  was stripped (Cf.  FIG. 4(   d )) and then the thin metal film  14  exposed from the conductive pattern  4  was removed by chemical etching (Cf.  FIG. 4(   e )). 
     As a result of these processes, the conductive pattern  4  wherein the lines of wire  4   a ,  4   b ,  4   c ,  4   d , the magnetic head connecting terminals  7 , and the external connecting terminals  8  were integrally formed was formed. The width of the each external connecting terminal  8  was 450 μm, and the interval between adjacent external connecting terminals  8  was 300 μm. Also, the first through holes  9  were formed in the external connecting terminals  8 . The diameter of the each first through hole  9  was 150 μm. 
     Then, after the surface of the conductive pattern  4  was activated by palladium solution, the nickel plating layer having thickness of 0.05 μm was formed on the surface thus activated by electrolytic nickel plating. Thereafter, solution of precursor of photosensitive polyimide resin was coated over the entire surface of the nickel plating layer and the insulating base layer  3  and then was heated for two minutes at 120° C., to thereby form the coating  16  of precursor of the photosensitive polyimide resin (Cf.  FIG. 5(   a )). 
     Thereafter, the photo mask  17  was disposed opposite the coating  16  so that the light shielding portions  17   a  confronted portions of the coating  16  where the insulating base layer  3  was not to be formed on the supporting board  2  and portions of the coating  16  corresponding to the magnetic head connecting terminals  7  and the external connecting terminals  8 , and the total-light-transmitting portions  17   b  confronted portions of the coating  16  where the insulating cover layer  10  was to be formed on the insulating base layer  3  including the lines of wire  4   a ,  4   b ,  4   c ,  4   d . Then, the coating  16  was exposed to ultraviolet light (an integrated quantity of exposure light of 720 mJ/cm 2 ) (Cf.  FIG. 5(   b )). 
     Then, after exposed to light and then heated (for three minutes at 160° C.), the coating  16  exposed to light was developed using alkaline developer, so that the coating  16  was formed in such a predetermined pattern that could allow the lines of wire  4   a ,  4   b ,  4   c ,  4   d  to be covered with the coating  16  and could allow the magnetic head connecting terminals  7  and the external connecting terminals  8  to be exposed therefrom (Cf.  FIG. 5(   c )). Thereafter, the coating  16  was heated at 420° C. to thereby form the insulating cover layer  10  of polyimide resin having a thickness of 4 μm (Cf.  FIG. 5(   d )). 
     Then, after laminated, the dry film photoresist was exposed to ultraviolet light (an integrated quantity of exposure light of 105 mJ/cm 2 ) and then developed by alkaline developer. After the entire area of the suspension board with circuit  1 , except the portions of the supporting board  2  where the third through holes  20  were to be formed, was covered with the dry film photoresist, the portions of the supporting board  2  where the third through holes  20  were to be formed were chemically etched to form the third through holes  20  (Cf.  FIG. 2(   e )). 
     Further, the portions of the insulating base layer  3  where the second through holes  19  were to be formed were chemically etched to form the second through holes  19  (Cf.  FIG. 2(   f )). 
     Then, after the nickel plating layer on the surface of the magnetic head connecting terminals  7  and on the surface of the external connecting terminals  8  was removed by chemical etching, the dry film photoresist was laminated thereon. Then, the lamination was exposed to ultraviolet light (an integrated quantity of exposure light of 105 mJ/cm 2 ) and then developed using alkaline developer. After the supporting board  2  was covered with the dry film photoresist to cover the outer shape of the suspension board with circuit  1 , the supporting board  2  thus covered was etched using ferric chloride solution to cut out to form the gimbal  5  and trimmed along the outer shape of the suspension board with circuit  1 . 
     Thereafter, the plating layer  18  of 3 μm thick comprising the nickel plating layer and the gold plating layer was formed on the respective magnetic head connecting terminals  7  and on the respective external connecting terminals  8  by electroless nickel plating and by electroless gold plating (Cf.  FIG. 2(   g )). 
     Example 2 
     The supporting board  2  of a stainless foil (SUS304) of 300 mm wide and 25 μm thick was prepared (Cf.  FIG. 10(   a )). 
     Then, after solution of precursor of photosensitive polyimide resin (photosensitive polyamic acid resin) was coated over the entire surface of the supporting board  2 , the coated resin was heated for two minutes at 120° C., to form the coating  11  of the precursor of the photosensitive polyimide resin (Cf.  FIG. 11(   a )). 
     Thereafter, the photo mask  27  was disposed opposite the coating  11  so that the light shielding portions  27   a  confronted portions of the coating  11  where the insulating base layer  3  was not to be formed on the supporting board  2 ; the total-light-transmitting portions  27   b  confronted portions of the coating  11  where the insulating base layer  3  was to be formed on the supporting board  2 ; and the semi-light-transmitting portions  27   c  confronted portions of the coating  11  where the second through holes  19  were to be formed in the external connecting terminals  8 . Then, the coating  11  was exposed to ultraviolet light (an integrated quantity of exposure light of 720 mJ/cm 2 ) (Cf.  FIG. 11(   b )). 
     Then, after exposed to light and then heated (for three minutes at 160° C.), the coating  11  exposed to light was developed using alkaline developer, so that the coating  11  was formed in such a predetermined pattern that could allow the marginal portions of the supporting board  2  to be exposed and could allow the second-through-hole- 19 -forming portions to be smaller in thickness than the remaining portions (Cf.  FIG. 11(   c )). Thereafter, the coating  11  was heated at 420° C. to thereby form the insulating base layer  3  of polyimide resin having a thickness of 10 μm (Cf.  FIG. 11(   d )). 
     Then, the thin chromium film and the thin copper film were sequentially formed on the surface of the supporting board  2  exposed from the insulating base layer  3  and on the entire surface of the insulating base layer  3  by the sputtering process to form the thin metal film  14  having thickness of 300-1,000 Å (Cf.  FIG. 12(   a )). Then, after laminated on the surface of the thin metal film  14 , the dry film photoresist was exposed to ultraviolet light (an integrated quantity of exposure light of 235 mJ/cm 2 ) and then developed by alkaline developer to form the plating resist  15  having the reverse pattern to the conductive pattern  4  on the thin metal film  14  (Cf.  FIG. 12(   b )). 
     Then, the conductive pattern  4  having thickness of 10 μm was formed on the surface of the thin metal film  14  exposed from the plating resist  15  by electrolytic copper plating (Cf.  FIG. 12(   c )). Thereafter, the plating resist  15  was stripped (Cf.  FIG. 12(   d )) and then the thin metal film  14  exposed from the conductive pattern  4  was removed by chemical etching (Cf.  FIG. 12(   e )). 
     As a result of these processes, the conductive pattern  4  wherein the lines of wire  4   a ,  4   b ,  4   c ,  4   d , the magnetic head connecting terminals  7 , and the external connecting terminals  8  were integrally formed was formed. The width of the each external connecting terminal  8  was 450 μm, and the interval between adjacent external connecting terminals  8  was 300 μm. Also, the first through holes  9  and the shouldered portions  26  were formed in the external connecting terminals  8 . The diameter of the each first through hole was 150 μm. 
     Then, after the surface of the conductive pattern  4  was activated by palladium solution, the nickel plating layer having thickness of 0.05 μm was formed on the surface thus activated by electrolytic nickel plating. Thereafter, solution of precursor of photosensitive polyimide resin was coated over the entire surface of the nickel plating layer and the insulating base layer  3  and then was heated for two minutes at 120° C., to thereby form the coating  16  of precursor of the photosensitive polyimide resin (Cf.  FIG. 13(   a )). 
     Thereafter, the photo mask  17  was disposed opposite the coating  16  so that the light shielding portions  17   a  confronted portions of the coating  16  where the insulating base layer  3  was not to be formed on the supporting board  2  and portions of the coating  16  corresponding to the magnetic head connecting terminals  7  and the external connecting terminals  8 , and the total-light-transmitting portions  17   b  confronted portions of the coating  16  where the insulating cover layer  10  was to be formed on the insulating base layer  3  including the lines of wire  4   a ,  4   b ,  4   c ,  4   d . Then, the coating  16  was exposed to ultraviolet light (an integrated quantity of exposure light of 720 mJ/cm 2 ) (Cf.  FIG. 13(   b )). 
     Then, after exposed to light and then heated (for three minutes at 160° C.), the coating  16  exposed to light was developed using alkaline developer, so that the coating  16  was formed in such a predetermined pattern that could allow the lines of wire  4   a ,  4   b ,  4   c ,  4   d  to be covered with the coating  16  and could allow the magnetic head connecting terminals  7  and the external connecting terminals  8  to be exposed therefrom (Cf.  FIG. 13(   c )). Thereafter, the coating  16  was heated at 420° C. to thereby form the insulating cover layer  10  of polyimide resin having a thickness of 4 μm (Cf.  FIG. 13(   d )). 
     Then, after laminated, the dry film photoresist was exposed to ultraviolet light (an integrated quantity of exposure light of 105 mJ/cm 2 ) and then developed by alkaline developer. After the entire area of the suspension board with circuit  1 , except the portions of the supporting board  2  where the third through holes  20  were to be formed, was covered with the dry film photoresist, the portions of the supporting board  2  where the third through holes  20  were to be formed were chemically etched to form the third through holes  20  (Cf.  FIG. 10(   e )). 
     Further, the portions of the insulating base layer  3  where the second through holes  19  were to be formed were also chemically etched to form the second through holes  19  (Cf.  FIG. 10(   f )). 
     Then, after the nickel plating layer on the surface of the magnetic head connecting terminals  7  and on the surface of the external connecting terminals  8  was removed by chemical etching, the dry film photoresist was laminated thereon. Then, the lamination was exposed to ultraviolet light (an integrated quantity of exposure light of 105 mJ/cm 2 ) and then developed using alkaline developer. After the supporting board  2  was covered with the dry film photoresist to cover the outer shape of the suspension board with circuit  1 , the supporting board  2  thus covered was etched using ferric chloride solution to cut out to form the gimbal  5  and trimmed along the outer shape of the suspension board with circuit  1 . 
     Thereafter, the plating layer  18  of 3 μm thick comprising the nickel plating layer and the gold plating layer was formed on the respective magnetic head connection terminals  7  and on the respective external connecting terminals  8  by electroless nickel plating and by electroless gold plating (Cf.  FIG. 10(   g )). 
     Comparative Example 1 
     The supporting board  2  of a stainless foil (SUS304) of 300 mm wide and 25 μm thick was prepared (Cf.  FIG. 21(   a )). 
     Then, the insulating base layer  3  of polyimide resin was formed by the same processes as in Example 1 (Cf.  FIG. 21(   b )). 
     Then, the conductive pattern  4  wherein the lines of wire  4   a ,  4   b ,  4   c ,  4   d , the magnetic head connecting terminals  7 , and the external connecting terminals  8  were integrally formed on the insulating base layer  3  was formed by the same processes as in Example 1 (Cf.  FIG. 21(   c )). The first through holes  19  were formed in the external connecting terminals  8 , as is the case with Example 1. 
     Then, after the nickel plating layer of 0.05 μm thick was formed on the surface of the conductive pattern  4  by the same processes as in Example  1 , the insulating cover layer  10  of polyimide resin, with which the lines of wire  4   a ,  4   b ,  4   c ,  4   d  were covered and from which the magnetic head connecting terminals  7  and the external connecting terminals  8  were exposed, was formed on the insulating base layer  3  (Cf.  FIG. 21(   d )). 
     Then, after the nickel plating layer on the surface of the magnetic head connecting terminals  7  and on the surface of the external connecting terminals  8  was removed by the same process as in Example 1, the suspension board with circuit  1  was cut out to form the gimbal  5  and trimmed along the outer shape thereof. Thereafter, the plating layer  18  comprising the nickel plating layer and the gold plating layer was formed (Cf.  FIG. 21(   e )). 
     Comparative Example 2 
     The supporting board  2  of a stainless foil (SUS304) of 300 mm wide and 25 μm thick was prepared (Cf.  FIG. 22(   a )). 
     Then, the insulating base layer  3  of polyimide resin was formed by the same processes as in Example 1 (Cf.  FIG. 22(   b )). 
     Then, the conductive pattern  4  wherein the lines of wire  4   a ,  4   b ,  4   c ,  4   d , the magnetic head connecting terminals  7 , and the external connecting terminals  8  were integrally formed on the insulating base layer  3  was formed by the same processes as in Example 1 (Cf.  FIG. 22(   c )). The external connecting terminals  8  were formed to have uniform thickness without forming the first through holes  9 . 
     Then, after the nickel plating layer of 0.05 μm thick was formed on the surface of the conductive pattern  4  by the same processes as in Example 1, the insulating cover layer of polyimide resin, with which the lines of wire  4   a ,  4   b ,  4   c ,  4   d  were covered and from which the magnetic head connecting terminals  7  and the external connecting terminals  8  were exposed, was formed on the insulating base layer  3  (Cf.  FIG. 22(   d )). 
     Then, after the nickel plating layer on the surface of the magnetic head connecting terminals  7  and on the surface of the external connecting terminals  8  was removed by the same process as in Example 1, the suspension board with circuit I was cut out to form the gimbal  5  and trimmed along the outer shape thereof. Thereafter, the plating layer  18  comprising the nickel plating layer and the gold plating layer was formed (Cf.  FIG. 22(   e )). 
     Evaluation 
     The external connecting terminals  8  of the suspension boards with circuits obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were connected with the connecting terminals of the read/write substrate via the solder balls  21 . The suspension board with circuit of each of Examples 1 and 2 was able to be connected with the read/write substrate reliably. However, in the suspension board with circuit of Comparative Example 1, electrical conductive failure occurred, and in the suspension board with circuit of Comparative Example 2, the solder balls  21  were rolled down, thus producing reduced working efficiency in the connecting process. 
     While the illustrative embodiments of the present invention are provided in the above description, such is for illustrative purpose only and it is not to be construed restrictively. Modification and variation of the present invention that will be obvious to those skilled in the art is to be covered by the following claims.