Method of manufacturing double-sided circuit board

A method for manufacturing a double-sided circuit board from a board material having a first electric conductor layer and a first electrically insulating layer, including the steps of: making conduction holes in the board material so as to penetrate only the first electrically insulating layer or both the first electrically insulating layer and the first electric conductor layer; forming an electrically conductive thin-film layer on a surface of the first electrically insulating layer and wall surfaces of the conduction holes; forming a second electrically insulating layer on the electrically conductive thin-film layer; forming a first electric conductor wiring by electroplating on predetermined portions of the electrically conductive thin-film layer; covering the first electric conductor wiring with a chemical-resistant film; forming a second electric conductor wiring by chemically dissolving a predetermined portion of another surface of the first electric conductor layer; and removing the second electrically insulating layer and the film.

The present application is based on Japanese Patent Application No. 2002-29643, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a double-sided circuit board having electric conductor wiring formed on opposite surfaces of an electrically insulating layer, and particularly to a manufacturing method suitable for manufacturing a flexible circuit board.

2. Related Art

A double-sided circuit board according to the related art is generally manufactured by a method shown inFIGS. 6Ato6G. That is, as shown inFIG. 6A, there is used a printed board material6which has an electrically insulating layer61such as a layer of polyimide, and electric conductor layers62such as layers of copper foil formed on opposite surfaces of the electrically insulating layer61. As shown inFIG. 6B, conduction holes63are formed in the material6by drilling using a laser, a mold, or the like, by chemical dissolution or by a method using both drilling and chemical dissolution in combination. Then, as shown inFIG. 6C, an electrically conductive thin-film layer64is formed on wall surfaces of the conduction holes63by a method such as chemical treatment, vapor deposition or sputtering. Then, as shown inFIG. 6D, an electric conductor layer65such as a layer of copper is formed by electroplating on all the front and rear surfaces of the board material6inclusive of all the surface of the thin-film layer64. Then, as shown inFIG. 6E, the electric conductor layer65is covered with photosensitive films66. Then, as shown inFIG. 6F, after portions of the photosensitive films66corresponding to predetermined electric conductor wiring patterns are exposed and developed to thereby form chemical-resistant films67, portions of the electric conductor layers65and62which are not covered with the chemical-resistant films67are chemically dissolved in chemicals. Finally, as shown inFIG. 6G, the chemical-resistant films67are removed. Thus, a double-sided circuit board60is manufactured.

That is, a so-called subtractive method in which portions unnecessary for electric conductor wiring patterns are removed from the electric conductor layers62formed on opposite surfaces of the electrically insulating layer61is used in the method for manufacturing a double-sided circuit board60according to the related art.

The requirements of higher-density and finer wiring in the double-sided circuit board have been elevated in recent years. Wiring formation by the subtractive method used heretofore, however, has a tendency to hardly meet the requirements. More specifically, in the case of the subtractive method, as described above, while the chemical-resistant films67obtained by exposing and developing portions corresponding to predetermined electric conductor wiring patterns are used as masks, the electric conductor layers65and62are dissolved in chemicals to thereby form electric conductor wiring. When fine wiring or high-density wiring is formed by this method, the dissolution chemicals spread so slowly that the velocity of dissolution varies largely in accordance with the wiring width or the gap width. Hence, there is a problem that uniform wiring can be hardly formed. In addition, there is another problem that the difference between the wiring width in surfaces of the electric conductor layers65and62and the wiring width in bottoms thereof is apt to become large.

On the other hand, an additive method in which an electric conductor wiring is formed on an electrically insulating board by electroplating is known as another method than the subtractive method. Particularly in the case of a flexible circuit board, stress generated inevitably in the electrically insulating board material due to carrying tension in a continuous carrying (sheeting) process is too large to be neglected because the electrically insulating board material is shaped like a flexible film. As a result, there is a problem that dimensional stability is lowered or the flexible circuit board is apt to be curled. In addition, when an electric conductor wiring is formed by electroplating, flexing characteristic such as bending characteristic of the flexible circuit board deteriorates because the electric conductor wiring is made of an electrolytically deposited metal. As a result, there is a further problem that the additive method is not suitable for the method of manufacturing a double-sided circuit board requiring sufficient flexing characteristic.

SUMMARY OF THE INVENTION

The invention is developed for solving the problems inherent in the related art, and an object of the invention is to provide a method for manufacturing a double-sided circuit board, which can meet the requirement of high-density fine wiring and by which a double-sided circuit board having high dimensional stability, hardly curled and adapted for a flex purpose can be obtained when the method is used for manufacturing a flexible circuit board.

In order to solve the problems, the invention provides a method of manufacturing a double-sided circuit board from a board material constituted by a first electric conductor layer and a first electrically insulating layer formed on one surface of the first electric conductor layer, including: the first step of making conduction holes in the board material so that the conduction holes penetrate only the first electrically insulating layer or both the first electrically insulating layer and the first electric conductor layer from predetermined portions of the first electrically insulating layer; the second step of forming an electrically conductive thin-film layer both on a surface of the first electrically insulating layer and on wall surfaces of the conduction holes; the third step of forming a second electrically insulating layer on at least one predetermined portion of the electrically conductive thin-film layer; the fourth step of forming a first electric conductor wiring by plating on a portion of the electrically conductive thin-film layer where the second electrically insulating layer is not formed; the fifth step of covering the first electric conductor wiring with a: chemical-resistant film; the sixth step of forming a second electric conductor wiring by chemically dissolving at least one predetermined portion of the other surface of the first electric conductor layer in chemicals; and the seventh step of removing the second electrically insulating layer and the chemical-resistant film.

According to the invention, the first electric conductor wiring can meet the requirement of high-density fine wiring because the first electric conductor wiring is formed by plating. That is, the first electric conductor wiring can be formed uniformly without being influenced by the wiring width or the gap width, and the difference between the wiring width in the surface and the wiring width in the bottom can be reduced extremely. Incidentally, the second electric conductor wiring per se can hardly meet the requirement of high-density fine wiring because the second electric conductor wiring is formed by the so-called subtractive method, that is, by chemically dissolving the predetermined portion of the other surface of the first electric conductor layer in chemicals to remove the predetermined portion. The double-sided circuit board manufactured, however, can meet the requirement of high-density fine wiring as a whole because wiring can be drawn from the second electric conductor wiring to the first electric conductor wiring through the conduction holes.

Further, even in the case where the manufacturing method according to the invention is used for manufacturing a flexible circuit board, influence of carrying tension in a continuous carrying (sheeting) process can be reduced greatly because the first electric conductor layer has been already formed on the first electrically insulating layer (flexible film-like electrically insulating layer in this case) in the fourth step of forming the first electric conductor wiring by plating. As a result, a double-sided circuit board having high dimensional stability and hardly curled can be obtained. That is, because the electrical conductor layer is generally more elastic than the electrically insulating layer, stress generated in the board material is dispersed or relaxed by the presence of the first electric conductor layer so that the influence of carrying tension can be reduced greatly.

Moreover, the second electrically insulating layer is formed on portions requiring flexing characteristic such as bending characteristic so that the first electric conductor wiring can be prevented from being formed on the portions by plating (in addition, portions of the other surface of the first electric conductor layer where the first electric conductor wiring is not formed are chemically dissolved as occasion demands). Thus, sufficient flexing characteristic can be obtained.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described below with reference to the accompanying drawings.

First Embodiment

FIGS. 1Ato1I are views for explaining a method of manufacturing a double-sided circuit board according to a first embodiment of the invention. As shown inFIG. 1A, a board material1having a first electric conductor layer11, and a first electrically insulating layer12formed on one surface of the first electric-conductor layer11is used in the manufacturing method according to this embodiment. In this embodiment, a layer of a metal or metal foil capable of being treated with chemicals, such as copper foil, copper alloy, stainless steel, or nickel is preferably used as the first electric conductor layer11. The thickness of the first electric conductor layer11is generally selected to be in a range of from 1 μm to 100 μm, preferably in a range of from 3 μm to 30 μm. On the other hand, a resin excellent in chemical resistance, heat resistance and high dimensional stability, such as a polyimide-based resin, is preferably used as the first electrically insulating layer12. The thickness of the first electrically insulating layer12is generally selected to be in a range of from 3 μm to 200 μm, preferably in a range of from 5 μm to 100 μm.

Then, as shown inFIG. 1B, conduction holes13are formed in the board material1so that the conduction holes13penetrate both the first electrically insulating layer12and the first electric conductor layer11from predetermined portions of the first electrically insulating layer12. Incidentally, as the method for forming the conduction holes13, there may be used a known method such as drilling using a laser, a mold or the like, dissolution using chemicals, or use of a photosensitive resin. The diameter of each of the conduction holes13is generally selected to be in a range of from 10 μm to 500 μm, preferably in a range of from 30 μm to 30 μm.

Then, as shown inFIG. 1C, an electrically conductive thin-film layer14is formed both on the surface of the first electrically insulating layer12and on wall surfaces of the conduction holes13. Incidentally, Ni, Cr, Cu, Ni/Cr alloy, Cu/Ni alloy, Ti or an alloy of these metals is preferably used as the material of the electrically conductive thin-film layer14. Especially, Cr-based metal such as Cr or Ni/Cr alloy is preferably used as the material of the electrically conductive thin-film layer14. The thickness of the electrically conductive thin-film layer14is generally selected to be in a range of from 3 Å to 3000 Å, preferably in range of from 5 Å to 2000 Å. In addition, the electrically conductive thin-film layer14is not limited to a single layer but may be provided as a laminate of a plurality of layers in accordance with necessity.

Then, as shown inFIG. 1D, a second electrically insulating layer15is formed on predetermined portions of the electrically conductive thin-film layer14. Incidentally, a material having resistance to electrolytic plating solution is used as the material of the second electrically insulating layer15. The thickness of the second electrically insulating layer15is preferably selected to be larger than the plating thickness of a first electric conductor wiring16which will be described later. When, for example, the plating thickness of the first electric conductor wiring16is 10 μm, the second electrically insulating layer15is formed as a 15 μm-thick layer. In addition, in order to process the second electrically insulating layer15into a shape corresponding to a pattern of the first electric conductor wiring16which will be described later, a photosensitive electrically insulating material may be used as an example of the material of the second electrically insulating layer15so that portions of the electrically insulating material corresponding to the pattern of the electric conductor wiring are exposed and developed and then non-developed portions of the electrically insulating material are dissolved.

Then, as shown inFIG. 1E, the first electric conductor wiring16is formed by electroplating on the portions of the electrically conductive thin-film layer14where the second electrically insulating layer15is not formed. In this embodiment, an electric conductor layer16′ is formed by electroplating on the other surface of the first electric conductor layer11where the electrically conductive thin film layer14is Not formed. Incidentally, for example, the electroplating is performed by immersing the board material1in an electrolytic plating solution of copper sulfate and applying electricity to the electrolytic plating solution.

Then, as shown inFIG. 1F, the first electric conductor wiring16is covered with a film17, for example, having chemical resistance to acid such as ferric chloride or cupric chloride. For example, a photosensitive electrically insulating material is used as the material of the film17. When the whole surface of the electrically insulating material is exposed and developed, the film17having such chemical resistance is formed. Incidentally, in this embodiment, a film17′ similar to the film17is formed on the electric conductor layer16′. The film17′ is however different from the film17in that only portions of the film17′ corresponding to a pattern of a second electric conductor wiring18which will be described later are exposed and developed so as to have chemical resistance whereas the whole surface of the film17is exposed and developed. In addition, the film17′ is different from the second electrically insulating layer15in that the film17′ functions as a protective film when the second electric conductor wiring18which will be described later is formed by a subtractive method. Hence, from the point of view of reducing the difference between the wiring width in the surface and the wiring width in the bottom, it is preferable that the thickness of the film17′ is as small as possible (.e.g., 15 μm or smaller) For example, the film17′ is formed by use of a liquid resist.

Then, as shown inFIG. 1G, a second electric conductor wiring18is formed by chemically dissolving predetermined portions of the other surface of the first: electric conductor layer11(inclusive of predetermined portions of the film17′ and the electric conductor layer16′ in this embodiment) in chemicals. That is, the second electric conductor wiring18is formed by a subtractive method. Incidentally, acid (such as ferric chloride or cupric chloride) is used in dissolution of the electric conductor layer in this embodiment.

Then, as shown inFIG. 1H, the films17and17′ and the second electrically insulating layer15are removed. Incidentally, for example, the films17and17′ and the second electrically insulating layer15can be separated and removed by alkaline chemicals.

Finally, as shown inFIG. 1I, the electrically conductive thin-film layer14remaining on the first electrically insulating layer12is removed. Thus, a double-sided circuit board10having the first electric conductor wiring16and the second electric conductor wiring18is completed. Incidentally, for example, the electrically conductive thin-film layer14can be separated and removed by acidic chemicals.

Incidentally, the first and second electric conductor wirings16and18by electroplating are not formed on the predetermined portion19of the double-sided circuit board10manufactured by the method according to this embodiment but the predetermined portion19is constituted by only the first electrically insulating layer12. Hence, when, for example, the first electrically insulating layer12is made of a flexible film-like material, sufficient flexing characteristic can be obtained in this portion19.

Second Embodiment

FIGS. 2Ato2I are views for explaining a method of manufacturing a double-sided circuit board according to a second embodiment of the invention. As shown inFIG. 2A, a board material2having a first electric conductor layer21, and a first electrically insulating layer22formed on one surface of the first electric conductor layer21is used in the manufacturing method according to this embodiment, like the first embodiment. The preferred materials for forming the first electric conductor layer21and the first electrically insulating layer22and the preferred thicknesses of the materials are the same as those in the first embodiment.

Then, as shown inFIG. 2B, conduction holes23are formed in the board material2so that the conduction holes23penetrate both the first electrically insulating layer22and the first electric conductor layer21from predetermined portions of the first electrically insulating layer22. Incidentally, the preferred method for forming the conduction holes23and the preferred diameter of each of the conduction holes23are the same as those in the first embodiment.

Then, as shown inFIG. 2C, an electrically conductive thin-film layer24is formed both on the surface of the first electrically insulating layer22and on wall surfaces of the conduction holes23. Incidentally, the preferred material of the electrically conductive thin-film layer24and the preferred thickness of the electrically conductive thin-film layer24are the same as those in the first embodiment.

Then, as shown inFIG. 2D, a second electrically insulating layer25is formed on predetermined portions of the electrically conductive thin-film layer24. In this embodiment, an electrically insulating layer25′ is also formed on a predetermined portion of the other surface of the first electric conductor layer21. Incidentally, the preferred materials of the second electrically insulating layer25and the electrically insulating layer25′ and the preferred thicknesses thereof are the same as those of the second electrically insulating layer15in the first embodiment.

Then, as shown inFIG. 2E, a first electric conductor wiring26is formed by electroplating on the portions of the electrically conductive thin-film layer24where the second electrically insulating layer25is not formed. In this embodiment, an electric conductor layer26′ is also formed by electroplating on portions where the electrically insulating layer25′ is not formed, among portions of the other surface of the first electric conductor layer21where the electrically conductive thin film layer24is not formed. Incidentally, for example, the electroplating is performed by immersing the board material2in an electrolytic plating solution of copper sulfate and applying electricity to the electrolytic plating solution in the same manner as in the first embodiment.

Then, as shown inFIG. 2F, the first electric conductor wiring26is covered with a film27, for example, having chemical resistance to acid such as ferric chloride or cupric chloride. Incidentally, also in this embodiment, a film27′ similar to the film27is also formed on the electric conductor layer26′ in the same manner as in the first embodiment. The preferred materials of the films27and27′ and the preferred thicknesses of the films27and27′ are the same as those of the films17and17′ in the first embodiment.

Then, as shown inFIG. 2G, a second electric conductor wiring28is formed by chemically dissolving predetermined portions of the other surface of the first electric conductor layer21(inclusive of predetermined portions of the film27′ and the electric conductor layer26′ in this embodiment) in chemicals. Incidentally, the dissolution method is the same as in the first embodiment.

Then, as shown inFIG. 2H, the films27and27′, the second electrically insulating layer25and the electrically insulating layer25′ are removed. Incidentally, the method for removing these films and layers is the same as in the first embodiment.

Finally, as shown inFIG. 2I, the electrically conductive, thin-film layer24remaining on the first electrically insulating layer22is removed. Thus, a double-sided circuit board20having the first electric conductor wiring26and the second electric conductor wiring28is completed. Incidentally, the method for removing the electrically conductive thin-film film24is the same as in the first embodiment.

Incidentally, the first electric conductor wiring26by electroplating is not formed on a predetermined portion29of the double-sided circuit board20manufactured by the method according to this embodiment but the predetermined portion29is constituted by the first electrically insulating layer22and the first electric conductor layer21. Hence, when, for example, the first electrically insulating layer22is made of a flexible film-like material and the first electric conductor layer21is made of a rolled sheet of copper foil or the like, sufficient flexing characteristic can be obtained in this portion29.

Third Embodiment

FIGS. 3Ato3I are views for explaining a method of manufacturing a double-sided circuit board according to a third embodiment of the invention. As shown inFIG. 3A, a board material3having a first electric conductor layer31, and a first electrically insulating layer32formed on one surface of the first electric conductor layer31is used in the manufacturing method according to this embodiment, like the first embodiment. The preferred materials for forming the first electric conductor layer31and the first electrically insulating layer32and the preferred thicknesses of the first electric conductor layer31and the first electrically insulating layer32are the same as those in the first embodiment.

Then, as shown inFIG. 3B, conduction holes33are formed in the board material3so that the conduction holes33penetrate both the first electrically insulating layer32and the first electric conductor layer31from predetermined portions of the first electrically insulating layer32. Incidentally, the preferred method for forming the conduction holes33and the preferred diameter of each of the conduction holes33are the same as those in the first embodiment.

Then, as shown inFIG. 3C, an electrically conductive thin-film layer34is formed both on the surface of the first electrically insulating layer32and on wall surfaces of the conduction holes33. Incidentally, the preferred material of the electrically conductive thin-film layer34and the preferred-thickness thereof are the same as those in the first embodiment.

Then, as shown inFIG. 3D, a second electrically insulating layer35is formed on predetermined portions of the electrically conductive thin-film layer34. Incidentally, in this embodiment, an electrically insulating layer35′ is also formed on the whole of the other surface of the first electric conductor layer31. Incidentally, the preferred materials of the second electrically insulating layer35and the electrically insulating layer35′ and the preferred thicknesses thereof are the same as those of the second electrically insulating layer15in the first embodiment.

Then, as shown inFIG. 3E, a first electric conductor wiring36is formed by electroplating on the portions of the electrically conductive thin-film layer34where the second electrically insulating layer35is not formed. In this embodiment, an electric conductor layer is not formed by electroplating on the other surface of the first electric conductor layer31because the electrically insulating layer35′ is formed on the whole of the other surface of the first electric conductor layer31. Incidentally, for example, the electroplating is performed by immersing the board material3in an electrolytic plating solution of copper sulfate in the same manner as in the first embodiment.

Then, as shown inFIG. 3F, the first electric conductor wiring36is covered with a film37, for example, having chemical resistance to acid such as ferric chloride or cupric chloride. Incidentally, also in the embodiment, a film37′ similar to the film37is formed on the electrically insulating layer35in the same manner as in the first embodiment. The preferred materials of the films37and37′ and the preferred thicknesses thereof are the same as those of the films17and17′ in the first embodiment.

Then, as shown inFIG. 3G, a second electric conductor wiring38is formed by chemically dissolving a predetermined portion of the other surface of the first electric conductor layer31(inclusive of predetermined portions of the film37′ and the electrically insulating layer35′ in this embodiment) in chemicals. Incidentally, the dissolution method is the same as in the first embodiment.

Then, as shown inFIG. 3H, the films37and37′, the second electrically insulating layer35and the electrically insulating layer35′ are removed. Incidentally, the method for removing these films and layers is the same as in the first embodiment.

Finally, as shown inFIG. 3I, the electrically conductive thin-film layer34remaining on the first electrically insulating layer32is removed. Thus, a double-sided circuit board30having the first electric conductor wiring36and the second electric conductor wiring38is completed. Incidentally, the method for removing the electrically conductive thin-film layer34is the same as in the first embodiment.

Fourth Embodiment

FIGS. 4Ato4I are views for explaining a method of manufacturing a double-sided circuit board according to a fourth embodiment of the invention. As shown inFIG. 4A, a board material4having a first electric conductor layer41, and a first electrically insulating layer42formed on one surface of the first electric conductor layer41is used in the manufacturing method according to this embodiment, like the first embodiment. The preferred materials for forming the first electric conductor layer41and the first electrically insulating layer42and the preferred thicknesses thereof are the same as those in the first embodiment.

Then, as shown inFIG. 4B, conduction holes43are formed in the board material4so that the conduction holes penetrate only the first electrically insulating layer42from predetermined portions of the first electrically insulating layer42. Incidentally, the preferred method for forming the conduction holes43and the preferred diameter of each of the conduction holes43are the same as those in the first embodiment.

Then, as shown inFIG. 4C, in this embodiment, an electrically conductive thin-film layer44is formed on bottoms of the conduction holes43, that is, on exposed surfaces of the first electric conductor layer41as well as the electrically conductive thin-film layer44is formed both on the surface of the first electrically insulating layer42and on wall surfaces of the conduction holes43. Incidentally, the preferred material of the electrically conductive thin-film layer44and the preferred thickness thereof are the same as those in the first embodiment.

Then, as shown inFIG. 4D, a second electrically insulating layer45is formed on predetermined portions of the electrically conductive thin-film layer44. Incidentally, in this embodiment, an electrically insulating layer45′ is also formed on the whole of the other surface of the first electric conductor layer41. Incidentally, the preferred materials of the second electrically insulating layer45and the electrically insulating layer45′ and the preferred thicknesses thereof are the same as those of the second electrically insulating layer15in the first embodiment.

Then, as shown inFIG. 4E, a first electric conductor wiring46is formed by electroplating on the portions of the electrically conductive thin-film layer44where the second electrically insulating layer45is not formed. In this embodiment, the electric conductor layer by electroplating is not formed on the other surface of the first electric conductor layer41because the electrically insulating layer45′ is formed on the whole of the other surface of the first electric conductor layer41. Incidentally, for example, the electroplating is performed by immersing the board material4in an electrolytic plating solution of copper sulfate in the same manner as in the first embodiment.

Then, as shown inFIG. 4F, the first electric conductor, wiring46is covered with a film47, for example, having chemical resistance to acid such as ferric chloride or cupric chloride. Incidentally, also in this embodiment, a film47′ similar to the film47is formed on the electrically insulating layer45′ in the same manner as in the first embodiment. The preferred materials of the films47and47′ and the preferred thicknesses thereof are the same as those of the films17and17′ in the first embodiment.

Then, as shown inFIG. 4G, a second electric conductor wiring48is formed by chemically dissolving predetermined portions of the other surface of the first electric conductor layer41(inclusive of predetermined portions of the film47′ and the electrically insulating layer45′ in this embodiment) in chemicals. Incidentally, the dissolution method is the same as in the first embodiment.

Then, as shown inFIG. 4H, the films47and47′, the second electrically insulating layer45and the electrically insulating layer45′ are removed. Incidentally, the method for removing these films and layers is the same as in the first embodiment.

Finally, as shown inFIG. 4I, the electrically conductive thin-film layer44remaining on the first electrically insulating layer42is removed. Thus, a double-sided circuit board40having the first electric conductor wiring46and the second electric conductor wiring48is completed. Incidentally, the method for removing the electrically conductive thin-film layer44is the same as in the first embodiment.

Fifth Embodiment

FIGS. 5Ato5I are views for explaining a method of manufacturing a double-sided circuit board according to a fifth embodiment of the invention. As shown inFIG. 5A, a board material5having a first electric conductor layer51, and a first electrically insulating layer52formed on one surface of the first electric conductor layer51is used in the manufacturing method according to this embodiment, like the first embodiment. The preferred materials for forming the first electric conductor layer51and the first electrically insulating layer52and the preferred thicknesses thereof are the same as those in the first embodiment.

Then, as shown inFIG. 5B, conduction holes53are formed in the board material5so that the conduction holes53penetrate only the first electrically insulating layer52from predetermined portions of the first electrically insulating layer52. Incidentally, the preferred method for forming the conduction holes53and the preferred diameter of each of the conduction holes53are the same as those in the first embodiment.

Then, as shown inFIG. 5C, an electrically conductive thin-film layer54is formed on the surface of the first electrically insulating layer52, wall surfaces of the conduction holes53, and bottoms of the conduction holes53. Incidentally, the preferred material of the electrically conductive thin-film layer54and the preferred thickness thereof are the same as those in the first embodiment.

Then, as shown inFIG. 5D, a second electrically insulating layer55is formed on a predetermined portion of the electrically conductive thin-film layer54. Incidentally, in this embodiment, an electrically insulating layer55′ is also formed on the whole of the other surface of the first electric conductor layer51. Incidentally, the preferred materials of the second electrically insulating layer55and the electrically insulating layer55′ and the preferred thicknesses thereof are the same as those of the second electrically insulating layer15in the first embodiment.

Then, as shown inFIG. 5E, a first electric conductor wiring56is formed by electroplating on the portion of the electrically conductive thin-film layer54where the second electrically insulating layer55is not formed. In this embodiment, an electric conductor layer by electroplating is not formed on the other surface of the first electric conductor layer51because the electrically insulating layer55′ is formed on the whole of the other surface of the first electric conductor layer51. Incidentally, the electroplating is performed by immersing the board material5in an electrolytic plating solution of copper sulfate and applying electricity to the electrolytic plating solution in the same manner as in the first embodiment.

Then, as shown inFIG. 5F, the first electric conductor wiring56is covered with a film57, for example, having chemical resistance to acid such as ferric chloride or cupric chloride. Incidentally, also in this embodiment, a film57′ similar to the film57is formed on the electrically insulating layer55′ in the same manner as in the first embodiment. The preferred materials of the films57and57′ and the preferred thicknesses thereof are the same as those of the films17and17′ in the first embodiment.

Then, as shown inFIG. 5G, a second electric conductor wiring58is formed by chemically dissolving predetermined portions of the other surface of the first electric conductor layer51(inclusive of predetermined portions of the film57′ and the electrically insulating layer55′ in this embodiment) in chemicals. Incidentally, the dissolution method is the same as in the first embodiment. In this embodiment, a predetermine portion of the first electric conductor wiring56is also dissolved so that a predetermined pattern of the first electric conductor wiring56is formed.

Then, as shown inFIG. 5H, the films57and57′, the second electrically insulating layer55and the electrically insulating layer55′are removed. Incidentally, the method for removing these films and layers is the same as in the first embodiment.

Finally, as shown inFIG. 5I, the electrically conductive thin-film layer54remaining on the first electrically insulating layer52is removed. Thus, a double-sided, circuit board50having the first electric conductor wiring56and the second electric conductor wiring58is completed. Incidentally, the method for removing the electrically conductive thin-film layer54is the same as in the first embodiment.

Incidentally, in the double-sided circuit board manufactured by the manufacturing method according to each of the first to fifth embodiments described above, an electrically insulating layer (cover layer) may be formed on the first electric conductor wiring and the second electric conductor wiring in accordance with necessity, and surface treatment such as gold plating may be further applied to the electrically insulating layer in accordance with necessity.

EXAMPLES

Description will be made on the following examples so that the characteristic of the invention will be made clearer.

In this example, a double-sided circuit board was manufactured by the manufacturing method according to the first embodiment shown inFIGS. 1Ato1I. First, as a board material1, there was used a copper-clad laminate (e.g., ESPANEX made by Nippon Steel Chemical Co., Ltd. or NEOFLEX made by Mitsui Chemicals Inc.) in which a first electrically insulating layer12made of a polyimide resin with a thickness of 25 μm was formed directly on one surface of a first electric conductor layer11made of copper foil with a thickness of 12 μm. Then, conduction holes13each having a diameter of 75 μm were formed by a YAG laser. Then, an electrically conductive thin-film layer14made of an Ni/Cr alloy with a thickness of 500 Å was formed by sputtering. Then, as a second electrically insulating layer15, a photosensitive electrically insulating film (e.g., SPG152 made by Asahi Kasei Corp.) having a thickness of 15 μm was laminated on the resulting laminate. After the second electrically insulating layer15was irradiated with ultraviolet light while predetermined positions were covered with glass masks capable of shielding the light, the second electrically insulating layer15was developed in an alkaline solution. Then, the board material1was immersed in an electrolytic plating solution of copper sulfate and plated at the rate of 2.5 A/dm2for about 18 minutes to thereby form a first electric conductor wiring16made of a copper plating with a thickness of 8 μm. Further, an electric conductor layer16′ made of a copper plating with a thickness of 8 μm was formed on the whole of the other surface of the first electric conductor; layer11. Thus, a copper layer having a total thickness of 20 μm was formed as a combination of the first electric conductor layer11and the electric conductor layer16′. Then, as each of films17and17′, a photosensitive electrically insulating film (e.g., SFG102 made by Asahi Kasei Corp.) having a thickness of 10 μm was laminated on the resulting laminate. After the film17′ was exposed and developed in accordance with a desired wiring pattern, the 20 μm-thick copper layer was dissolved in ferric chloride to thereby form a second electric conductor wiring18. Further, the films17and17′, the second electrically insulating layer15and the electrically conductive thin-film layer14were removed. Thus, a double-sided circuit board10was obtained. It was confirmed that the first electric conductor wiring16was formed uniformly and the difference between the wiring width in the surface and the wiring width in the bottom was reduced extremely in the double-sided circuit board10manufactured according to this example. In addition, the double-sided circuit board10was produced as a board having high dimensional stability, hardly curled and having sufficient flexing characteristic.

In this example, a double-sided circuit board was manufactured by the manufacturing method according to the second embodiment shown inFIGS. 2Ato2I. First, as a board material2there was used a copper-clad laminate (e.g., ESPANEX made by Nippon Steel Chemical Co., Ltd. or NEOFLEX made by Mitsui Chemicals Inc.) in which a first electrically insulating layer22made of a polyimide resin with a thickness of 12 μm was formed directly on one surface of a first electric conductor layer21made of copper foil with a thickness of 12 μm. Then, conduction holes23each having a diameter of 100 μm were formed by a YAG laser. Then, an electrically conductive thin-film layer24made of an Ni/Cu alloy with a thickness of 300 Å was formed by sputtering. Then, as each of a second electrically insulating layer25and an electrically insulating layer25′, a photosensitive electrically insulating film (e.g., SPG152 made by Asahi Kasei Corp.) having a thickness of 15 μm was laminated on the resulting laminate. After the second electrically insulating layer25and the electrically insulating layer25′ were irradiated with ultraviolet light while predetermined positions were covered with glass masks capable of shielding the light, the second electrically insulating layer25and the electrically insulating layer25′ were developed in an alkaline solution. Then, the board material2was immersed in an electrolytic plating solution of copper sulfate and plated at the rate of 2.5 A/dm2for about 20 minutes to thereby form a first electric conductor wiring26made of a copper plating with a thickness of 10 μm. Further, an electric conductor layer26′ made of a copper plating with a thickness of 10 μm was formed on portions which were on the other surface of the first electric conductor layer21and on which the electrically insulating layer25′ was not formed. Thus, a copper layer having a total thickness of 22 μm was formed as a combination of the first electric conductor layer21and the electric conductor layer26′. Then, as each of films27and27′, a photosensitive electrically insulating film (e.g., RY3206 made by Hitachi Chemical Co., Ltd.) having a thickness of 6 μm was laminated on the resulting laminate. After the film27′ was exposed and developed in accordance with a desired wiring pattern, the 22 μm-thick copper layer was dissolved in ferric chloride to thereby form a second electric conductor wiring28. Further, the films27and27′, the second electrically insulating layer25, the electrically insulating layer25′ and the electrically conductive thin-film layer24were removed. Thus, a double-sided circuit board20was obtained. It was confirmed that the first electric conductor wiring26was formed uniformly and the difference between the wiring width in the surface and the wiring width in the bottom was reduced extremely in the double-sided circuit board20manufactured according to this example. In addition, the double-sided circuit board20was produced as a board having high dimensional stability, hardly curled and having sufficient flexing characteristic.

In this example, a double-sided circuit board was manufactured by the manufacturing method according to the third embodiment shown inFIGS. 3Ato3I. First, as a board material3, there was used a copper-clad laminate (e.g., ESPANEX made by Nippon Steel Chemical Co., Ltd. or NEOFLEX made by Mitsui Chemicals Inc.) in which a first electrically insulating layer32made of a polyimide resin with a thickness of 12 μm was formed directly on one surface of a first electric conductor layer31made of copper foil with a thickness of 18 μm. Then, conduction holes33each having a diameter of 150 μm were formed by punching. Then, an electrically conductive thin-film layer34made of Cr with a thickness of 400 Å was formed by sputtering. Then, as each of a second electrically insulating layer35and an electrically insulating layer35′, a photosensitive electrically insulating film (e.g., SPG252 made by Asahi Kasei Corp.) having a thickness of 25 μm was laminated on the resulting laminate. After the second electrically insulating layer35and the electrically insulating layer35were irradiated with ultraviolet light while predetermined positions were covered with glass masks capable of shielding the light, the second electrically insulating layer35and the electrically insulating layer35′ were developed in an alkaline solution. Then, the board material3was immersed in an electrolytic plating solution of copper sulfate and plated at the rate of 2.5 A/dm2for about 36 minutes to thereby form a first electric conductor wiring36made of a copper plating with a thickness of 18 μm. Then, as each of films37, and37′, a photosensitive electrically insulating film (e.g., RY3206 made by Hitachi Chemical Co. Ltd.) having a thickness of 6 μm was laminated on the resulting laminate. After the film37′ was exposed and developed in accordance with a desired wiring pattern, the 18 μm-thick first electric conductor layer31was dissolved in ferric chloride to thereby form a second electric conductor wiring38. Further, the films37and37′, the second electrically insulating layer35, the electrically insulating layer35′ and the electrically conductive thin-film layer34were removed. Thus, a double-sided circuit board30was obtained. It was confirmed that the first electric conductor wiring36was formed uniformly and the difference between the wiring width in the surface and the wiring width in the bottom was reduced extremely in the double-sided circuit board30manufactured according to this example. In addition, the double-sided circuit board30was produced as a board having high dimensional stability, hardly curled and having sufficient flexing characteristic.

In this example, a double-sided circuit board was manufactured by the manufacturing method according to the fourth embodiment shown inFIGS. 4Ato4I. First, as a board material4, there was used a copper-clad laminate (e.g., ESPANEX made by Nippon Steel Chemical Co., Ltd. or NEOFLEX made by Mitsui Chemicals Inc.) in which a first electrically insulating layer41made of a polyimide resin with a thickness of 12 μm was formed directly on one surface of a first electric conductor layer41made of copper foil with a thickness of 18 μm. Then, conduction holes43each having a diameter of 80 μm were formed by chemicals. Then, an electrically conductive thin-film layer44made of an Ni/Cr alloy with a thickness of 400 Å was formed by sputtering. Further, an electrically conductive thin-film layer made of Cu was formed on the electrically conductive thin-film layer44by sputtering. Then, as each of a second electrically insulating layer45and an electrically insulating layer45′, a photosensitive electrically insulating film (e.g., SPG252 made by Asahi Kasei Corp.) having a thickness of 25 μm was laminated on the resulting laminate. After the second electrically insulating layer45and the electrically insulating layer45′ were irradiated with ultraviolet light while predetermined positions were covered with glass masks capable of shielding the light, the second electrically insulating layer45and the electrically insulating layer45′ were developed in an alkaline solution. Then, the board material4was immersed in an electrolytic plating solution of copper sulfate and plated at the rate of 2.5 A/dm2for about 18 minutes to thereby form a first electric conductor wiring46made of a copper plating with a thickness of 8 μm. Then, as each of films47and47′, photosensitive electrically insulating film (for example, RY3206 made by Hitachi Chemical Co., Ltd.) having a thickness of 6 μm was laminated on the resulting laminate. After the film47′ was exposed and developed in accordance with a desired wiring pattern, the 18 μm-thick first electric conductor layer41was dissolved in ferric chloride to thereby form a second electric conductor wiring48. Further, the films47and47′, the second electrically insulating layer45, the electrically insulating layer45′ and the electrically conductive thin-film layer44were removed. Thus, a double-sided circuit board40was obtained. It was confirmed that the first electric conductor wiring46was formed uniformly and the difference between the wiring width in the surface and the wiring width in the bottom was reduced extremely in the double-sided circuit board40manufactured according to this example. In addition, the double-sided circuit board40was produced as a board having high dimensional stability, hardly curled and having sufficient flexing characteristic.

In this example, a double-sided circuit board was manufactured by the manufacturing method according to the fifth embodiment shown inFIGS. 5Ato5I. First, as a board material5, there was used a copper-clad laminate in which a first electrically insulating layer52made of a photosensitive polyimide resin with a thickness of 12 μm was formed directly on one surface of a first electric conductor layer51made of copper foil with a thickness of 18 μm. Then, conduction holes53each having a diameter of 80 μm were formed by chemicals. Then, an electrically conductive thin-film layer54made of An Ni/Cr alloy with a thickness of 400 Å was formed by sputtering. Then, as each of a second electrically insulating layer55and an electrically insulating layer55′, a photosensitive electrically insulating film (e.g., SPG252 made by Asahi Kasei Corp.) having a thickness of 25 μm was laminated on the resulting laminate. After the second electrically insulating layer55and the electrically insulating layer55′ were irradiated with ultraviolet light while predetermined positions were covered with glass masks capable of shielding the light, the second electrically insulating layer55and the electrically insulating layer55′ were developed in an alkaline solution. Then, the board material5was immersed in an electrolytic plating solution of copper sulfate and plated at the rate of 2.5 A/dm2for about 36 minutes to thereby form a first electric conductor wiring56made of a copper plating with a thickness of 18 μm. Then, as each of films57and57′, a photosensitive electrically insulating film (e.g., RY3206 made by Hitachi Chemical Co., Ltd.) having a thickness of 6 μm was laminated on the resulting laminate. After the film57and57′ were exposed and developed in accordance with a desired wiring pattern, the 18 μm-thick first electric conductor layer51was dissolved in ferric chloride to thereby form a second electric conductor wiring58. Also a predetermined portion of the first electric conductor wiring36was dissolved so that a predetermined wiring patter of the first electric conductor wiring36was formed. Further, the films57and57′, the second electrically insulating layer55, the electrically insulating layer55′ and the electrically conductive thin-film layer54were removed. Thus, a double-sided circuit board50was obtained. It was confirmed that the first electric conductor wiring56was formed uniformly and the difference between the wiring width in the surface and the wiring width in the bottom was reduced extremely in the double-sided circuit board50manufactured according to this example. In addition, the double-sided circuit board50was produced as a board having high dimensional stability, hardly curled and having sufficient flexing characteristic.

In the method for manufacturing a double-sided circuit board according to the invention as described above, since a first electric conductor wiring is formed by electroplating, a semiconductor device or the like can be mounted on the first electric conductor wiring side to meet the requirement of high density fine wiring. That is, the first electric conductor wiring can be formed uniformly without being influenced by the wiring width or the gap width, and the difference, between the wiring width in the surface and the wiring width in the bottom can be reduced extremely. In addition, even in the case where the manufacturing method according to the invention is used for manufacturing a flexible circuit board, the influence of carrying tension in a continuous carrying (sheeting) process can be reduced greatly because the first electric conductor layer has been already formed on the first electrically insulating layer in the step of forming the first electric conductor wiring by electroplating. As a result, a double-sided circuit board having high dimensional stability and hardly curled can be obtained.

Further, a second electrically insulating layer is formed on portions requiring flexing characteristic such as bending characteristic so that so that the first electric conductor wiring can be prevented from being formed on the portions by plating (in addition, portions of the other surface of the first electric conductor layer where the first electric conductor wiring is not formed are dissolved chemically as occasion demands). Accordingly, sufficient flexing characteristic can be obtained.