Abstract:
Priorly, semiconductor devices wherein a flexible sheet with a conductive pattern was employed as a supporting substrate, a semiconductor element was mounted thereon, and the ensemble was molded have been developed. In this case, problems occur that a multilayer wiring structure cannot be formed and warping of the insulating resin sheet in the manufacturing process is prominent. In order to solve these problems, a laminated plate  10  in which a first conductive film  11  and a second conductive film  12  have been laminated via a third conductive film  13  is used. After forming a conductive pattern layer  11 A by etching the first conductive film  11 , anchor portions  15  are formed by overetching the third conductive film  13  by use of the conductive pattern layer  11 A as a mask, and a sealing resin layer  22  is made to bite into the anchor portions  15  so as to strengthen bonding of the sealing resin layer  22  with the conductive pattern layer  11 A.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method for manufacturing circuit devices, and particularly, to a method for forming a low-profile circuit device using two conductive films laminated via a third conductive film to serve as a barrier layer in an etching step. 
   2. Description of the Related Art 
   In recent years, IC packages have increasingly been used in portable equipment and small-sized high-density mounting equipment, and conventional IC packages and mounting concepts have undergone drastic changes. This has been mentioned in, for example, Japanese Unexamined Patent Publication No. 2000-133678, which is a technique related to a semiconductor device employing a polyimide resin sheet of a flexible sheet as an example of its insulating resin sheet. 
   In FIG.  15  through  FIG. 17 , a flexible sheet  50  is employed as an interposer substrate. Herein, drawings shown in the upper part of the respective drawings are plan views, drawings shown in the lower part are sectional views along a line A—A. 
   First, on the flexible sheet  50  shown in  FIG. 15 , a copper foil pattern  51  is prepared by being adhered via an adhesive. This copper foil pattern  51  is different in its pattern depending on whether a semiconductor element to be mounted is a transistor or an IC, and in general, bonding pads  51 A and an island  51 B are formed. In addition, a symbol  52  shows an opening portion to lead out an electrode from the rear surface of the flexible sheet  50 , and the copper foil pattern  51  is exposed therethrough. 
   Next, this flexible sheet  50  is transferred to a die bonder, and as shown in  FIG. 16 , semiconductor elements  53  are mounted. Thereafter, this flexible sheet  50  is transferred to a wire die bonder, and the bonding pads  51 A and pads of the semiconductor elements  53  are electrically connected by metal wires  54 . 
   Lastly, as in  FIG. 17A , a sealing resin  55  is provided on the front surface of the flexible sheet  50  for sealing. Herein, transfer molding is performed so as to cover the bonding pads  51 A, island  51 B, semiconductor element  53 , and metal wires  54 . 
   Thereafter, as shown in  FIG. 17B , connecting means  56  such as solder or solder balls are provided, and as a result of passing through a solder reflow furnace, spherical solder  56  fusion-bonded with the bonding pads  51 A via the opening portions  52  are formed. In addition, since the semiconductor elements  53  are formed in a matrix shape on the flexible sheet  50 , dicing is performed as in  FIG. 16  to separate the semiconductor elements individually. 
   In addition, in the sectional view shown in  FIG. 17C ,  51 A and  51 D are formed as electrodes on both surfaces of the flexible sheet  50 . In general, this flexible sheet  50  is supplied after patterning of both surfaces by a manufacturer. 
   A semiconductor device using the above-described flexible sheet  50  uses no widely-known metal frame and, therefore, has an advantage such that an extremely small-sized low-profile package can be realized, however, substantially, wiring is carried out by only one-layer copper pattern  51  provided on the front surface of the flexible sheet  50 . Therein exists a problem such that, since the flexible sheet is flexible, distortion occurs before and after a pattern formation of a conductive film, and this is not suitable for a multilayer wiring structure since displacement between laminated layers is great. 
   In order to improve supporting strength to suppress the sheet distortion, it is necessary to sufficiently thicken the flexible sheet  50  to approximately 200 μm, and this goes against a reduction in thickness. 
   Furthermore, in terms of a manufacturing method, in the aforementioned manufacturing devices, for example, in the die bonder, wire bonder, transfer molding device, reflow furnace, etc., the flexible sheet  50  is transferred and attached to a part called a stage or a table. 
   However, when the thickness of an insulating resin to serve as a base of the flexible sheet  50  is reduced to approximately 50 μm, if the thickness of the copper foil pattern  51  formed on the front surface is also thin such as 9-35 μm, transferring characteristics are considerably inferior due to warping as shown in  FIG. 18 , and attaching characteristics to the aforementioned stage, or table are inferior, therein exists a drawback. This is considered to be warping owing to that the insulating resin itself is considerably thin and warping owing to a difference in the thermal expansion coefficient between the copper foil pattern  51  and insulating resin. 
   In addition, since the part of the opening portions  52  is pressured from the upside during molding, a force to warp the circumferences of the bonding pads  51 A upward may act to deteriorate the bonding pads  51 A in adhesive properties. 
   In addition, if the resin material itself to form a flexible sheet  50  lacks flexibility or if a filler is mixed to enhance thermal conductivity, the flexible sheet  50  becomes rigid. In this condition, when bonding is performed by a wire bonder, the bonding part may crack. In addition, during transfer molding, the part where the metal mold is brought into contact may crack. This appears more prominently if warping exists as shown in FIG.  18 . 
   Although the flexible sheet  50  described above is a flexible sheet on whose rear surface no electrode is formed, an electrode  51 D may be formed, as shown in  FIG. 17C , on the rear surface of the flexible sheet  50 , as well. In this case, since the electrode  51 D is brought into contact with the manufacturing devices or is brought into contact with the transferring surfaces of the transferring means between the manufacturing devices, there exists a problem such that damage occurs to the rear surface of the electrode  51 D. Since the electrode is formed with this damage included, there also exist problems, such that the electrode  51 D itself cracks afterward by a heat application and solder wettability declines in a solder connection to a motherboard. 
   In addition, during transfer molding, a problem also occurs such that a sufficient sealing structure cannot be realized because of weak adhesive properties between the flexible sheet  50 , copper foil pattern  51  and the insulating resin. 
   SUMMARY OF THE INVENTION 
   In order to solve such problems, the present inventors have proposed using a laminated plate formed by laminating a thin, first conductive film and a thick second conductive film via a third conductive film. 
   First, the preferred embodiments include that a method for manufacturing circuit devices comprises: a step for preparing a laminated plate by laminating a first conductive film and a second conductive film via a third conductive film; a step for forming a conductive pattern layer by etching the first conductive film into a desirable pattern; a step for removing the third conductive film by use of the conductive pattern layer as a mask and thus forming anchor portions where the third conductive film is depressed further inside than the conductive pattern layer; a step for fixedly fitting semiconductor elements on the conductive pattern layer; a step for electrically connecting electrodes of the semiconductor elements with predetermined parts of the conductive pattern layer; a step for covering the semiconductor elements with a sealing resin layer and filling the sealing resin layer into the anchor portions; and a step for exposing the sealing resin layer and the third conductive film on the rear surface by removing the second conductive film. In particular, the preferred embodiments have a feature in forming anchor portions by removing the third conductive film by use of the conductive pattern layer as a mask and thus providing an anchoring effect by a sealing resin layer. 
   Second, the preferred embodiments include that the third conductive film is used as an etching stopper when the first conductive film is etched. 
   Third, the preferred embodiments include that a solution containing ferric chloride or cupric chloride is used as a solution to perform the etching. 
   Fourth, the preferred embodiments include that the anchor portions are formed by overetching the third conductive film by use of the conductive pattern layer as a mask. 
   Fifth, the preferred embodiments include that the etching solution is an iodine-based solution. 
   Sixth, the preferred embodiements include that the third conductive film is peeled off by electrolysis by use of the conductive pattern layer as a mask, and the anchor portions are formed by over-peeling. 
   Seventh, the preferred embodiments include that the third conductive film and the sealing resin layer in the anchor portions remaining after entirely etching the second conductive film are exposed. 
   Eighth, the preferred embodiments include that ball-like external electrodes are formed on the rear surface by adhering a brazing filler material to the remaining third conductive film. 
   Ninth, the preferred embodiments include that a method for manufacturing circuit devices comprises: a step for preparing a laminated plate by laminating a first conductive film and a second conductive film via a third conductive film; a step for selectively forming pads of a fourth conductive film on the first conductive film; a step for forming a conductive pattern layer by etching the first conductive film into a desirable pattern; a step for removing the third conductive film by use of the conductive pattern layer as a mask and thus forming anchor portions where the third conductive film is depressed further inside than the conductive pattern layer; a step for fixedly fitting semiconductor elements on the conductive pattern layer; a step for electrically connecting electrodes of the semiconductor elements with the pads on predetermined parts of the conductive pattern layer; a step for covering the semiconductor elements with a sealing resin layer and filling the sealing resin layer into the anchor portions; and a step for exposing the sealing resin layer and the third conductive film on the rear surface by removing the second conductive film. In particular, the preferred embodiments have a feature in selectively providing pads and external electrodes on the conductive pattern layer. 
   Tenth, the preferred embodiments include that the third conductive film is used as an etching stopper when the first conductive film is etched. 
   Eleventh, the preferred embodiments include that a solution containing ferric chloride or cupric chloride is used as a solution to perform the etching. 
   Twelfth, the preferred embodiments include that the anchor portions are formed by overetching the third conductive film by use of the conductive pattern layer as a mask. 
   Thirteenth, the preferred embodiments include that the etching solution is an iodine-based solution. 
   Fourteenth, the preferred embodiments include that the third conductive film is peeled off by electrolysis by use of the conductive pattern layer as a mask, and the anchor portions are formed by over-peeling. 
   Fifteenth, the preferred embodiments include that the third conductive film and the sealing resin layer in the anchor portions remaining after entirely etching the second conductive film are exposed. 
   Sixteenth, the preferred embodiments include that ball-like external electrodes are formed on the rear surface by adhering a brazing filler material to the remaining third conductive film. 
   According to the preferred embodiments, in the step for forming a conductive pattern layer, the first conductive film can be fully etched by providing the third conductive film  13  as a barrier layer, therefore, an advantage is provided such that etching for a conductive pattern layer can be easily performed and unnecessary etching of other conductive films is prevented. 
   In addition, anchor portions can be formed in self-alignment by the third conductive film depressed around the conductive pattern layer by overetching or over-peeling the third conductive film by use of the conductive pattern layer as a mask, and these anchor portions are filled when the semiconductor elements are covered with the sealing resin layer later, therefore, an advantage is provided such that biting between the sealing resin layer and conductive pattern layer is strengthened to realize a satisfactory sealing condition. 
   Furthermore, when the second conductive film is entirely removed, the third conductive film functions as a barrier layer to etching with the sealing resin layer, therefore, an advantage is provided such that removal of the second conductive film without a mask can be made possible. 
   Furthermore, since the third conductive film forms a flat rear surface along with the sealing resin layer, either the land grid array structure or ball grid array structure can be employed, therefore, an advantage is provided such that the remaining third conductive film itself can construct the whole or part of the external electrodes. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 2  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 3  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 4  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 5  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 6  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 7  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 8  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 9  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 10  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 11  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 12  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 13  is a sectional view for explaining a method for manufacturing circuit devices of the preferred embodiments; 
       FIG. 14  is a sectional view for explaining a circuit device manufactured according to the preferred embodiments; 
       FIG. 15  is a view for explaining a conventional method for manufacturing semiconductor devices; 
       FIG. 16  is a view for explaining a conventional method for manufacturing semiconductor devices; 
       FIG. 17  is a view for explaining a conventional method for manufacturing semiconductor devices; 
       FIG. 18  is a view for explaining a conventional flexible sheet. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A method for manufacturing circuit devices of the preferred embodiments will be described in detail with reference to FIG.  1  through FIG.  14 . 
   A method for manufacturing circuit devices of the preferred embodiments comprise a step for preparing a laminated plate  10  by laminating a first conductive film  11  and a second conductive film  12  via a third conductive film  13 ; a step for selectively forming pads  14 A of a fourth conductive film  14  on the first conductive film  11 ; a step for forming a conductive pattern layer  11 A by etching the first conductive film,  11  into a desirable pattern; a step for removing the third conductive film  13  by use of the conductive pattern layer  11 A as a mask and thus forming anchor portions  15  where the third conductive film  13  is depressed further inside than the conductive pattern layer  11 A; a step for fixedly fitting semiconductor elements  19  on the conductive pattern layer  11 A and electrically connecting electrodes of the semiconductor elements  19  with the predetermined pad  14 A of the conductive pattern layer  11 A; a step for covering the semiconductor elements  19  with a sealing resin layer  22  and filling the sealing resin layer  22  into the anchor portions  15 ; and a step for exposing the sealing resin layer  22  and the third conductive film  13  on the rear surface by removing the second conductive film  12 . Such respective steps will be described in the following. 
   The first step of the preferred embodiments is, as shown in  FIG. 1 , for preparing a laminated plate  10  by laminating a first conductive film  11  and a second conductive film  12  via a third conductive film  13 . 
   On the front surface of the laminated plate  10 , the first conductive film  11  is formed substantially throughout the whole area, and the second conductive film  12  is formed substantially throughout the whole area of the rear surface via the third conductive film  13 , as well. The first conductive film  11  and second conductive film  12  are, preferably, made of Cu as a main material or are made of a widely-known lead frame material. The first conductive film  11 , second conductive film  12 , and third conductive film  13  can be formed by a plating method, an evaporation method, or a sputtering method, or a metal foil formed by a rolling method or a plating method can be adhered to the same. Moreover, as the first conductive film  11  and second conductive film  12 , Al, Fe, Fe—Ni, a widely-known lead frame material and the like can be employed. 
   As the material of the third conductive film  13 , a material is employed which is not etched by an etchant used when the first conductive film  11  and second conductive film  12  are removed. In addition, since external electrodes  24  of solder or the like are formed on the rear surface of the third conductive film  13 , adhesion of the external electrodes  24  is also considered. Concretely, a conductive film composed of gold, silver, and palladium can be employed as a material of the third conductive film  13 . 
   The first conductive film is formed thin in thickness for forming a fine pattern, and the thickness is approximately 5-35 μm, while for forming a normal pattern, the thickness is approximately 35 μm-100 μm. The second conductive pattern is formed thick to mechanically support the ensemble, and the thickness is approximately 35-150 μm. The third conductive film  13  functions as a barrier layer when the first conductive film  11  and second conductive film  12  are etched, and is formed with a thickness of approximately 2-20 μm. 
   Accordingly, by forming the second conductive film  12  thick, flatness of the laminated plate  10  can be maintained, whereby, workability in the following steps can be improved. 
   Furthermore, the second conductive film  12  is damaged through various steps. However, the thick second conductive film  12  is to be removed in a later step, so that damage is prevented from remaining in a circuit device of a finished product. In addition, since the sealing resin can be hardened while flatness is maintained, the rear surface of a package can also be flattened, and the external electrodes formed on the rear surface of the laminated plate  10  can also be arranged flat. Therefore, electrodes on a mounting substrate can be brought into contact with the electrodes on the rear surface of the laminated plate  10 , whereby a soldering failure can be prevented. 
   Next, a concrete manufacturing method for the aforementioned laminated plate  10  will be described. A laminated plate  10  can be manufactured by lamination by electroplating or by rolling and joining. When a laminated plate  10  is manufactured by electroplating, first, a second conductive film  12  is prepared. Then, electrodes are provided on the rear surface of the second conductive film  12 , and a third conductive film is laminated by an electrolytic plating method. Thereafter, similarly by an electrolytic plating method, a first conductive film is laminated on the third conductive film. When a laminated plate  10  is manufactured by rolling, a first conductive film  11 , a second conductive film  12 , and a third conductive film  13  which have been prepared in a plate shape are joined under pressure by a roll or the like. 
   The second step of the preferred embodiments is, as shown in FIG.  2  through  FIG. 4 , for selectively forming pads  14 A formed of a fourth conductive film  14  on the first conductive film  11 . 
   In this step, as shown in  FIG. 2 , a fourth conductive film  14  is formed on the whole surface of the first conductive film  11  by electroplating. As the fourth conductive film, silver plating is suitable for the first conductive film  11  and for providing etching with selectivity, and pads to which bonding wires are fixedly fitted will be formed later on. Furthermore, preappointed pad regions on the fourth conductive film  14  are covered with a photoresist PR. 
   Next, as shown in  FIG. 3 , pads  14 A are formed by etching, with an iodine-based solution, the fourth conductive film  14  exposed through the photoresist PR as a mask. At this time, the first conductive film  11  is not etched by the iodine-based solution since this has been formed of copper. 
   Furthermore, as shown in  FIG. 4 , the photoresist PR is removed to expose the pads  14 A. 
   Herein, the method for forming pads  14 A can be a method for selectively forming pads with gold plating on preappointed pad regions while exposing the preappointed pad regions and covering the rest with a photoresist. 
   The third step of the preferred embodiments is, as shown in FIG.  5  and  FIG. 6 , for forming a conductive pattern layer  11 A by etching the first conductive film  11  into a desirable pattern. 
   The first conductive film  11  is covered with a photoresist PR of a desirable pattern, and a conductive pattern layer  11 A to form wiring is formed by chemical etching. Since the first conductive film  11  is made of Cu as a main material, ferric chloride or cupric chloride is sufficient as an etchant. As a result of etching of the first conductive film  11 , the third conductive film  13  also comes into contact with the etchant, however, since the material for the third conductive film  13  is not etched by ferric chloride or cupric chloride, etching stops on the front surface of the third conductive film  13 . Thus, since the first conductive film  11  has been formed with a thickness of approximately 5-35 μm, the conductive pattern layer  11 A can be formed as a fine pattern of 50 μm or less. Moreover, the rear surface of the second conductive film  12  is covered with a photoresist PR or a cover film and is thus protected from the etchant during chemical etching for the conductive pattern layer  11 A. 
   This step includes that etching is stopped at the third conductive film  13  when the first conductive film  11  is etched. Since etching of the first conductive film  11  can be thereby carried out as full etching, an advantage is provided in that stable etching can be realized. In this step, the first conductive film  11  to be etched is formed mainly of Cu, and ferric chloride or cupric chloride is used as an etchant to selectively remove the Cu. In contrast thereto, since the third conductive film  13  is formed of a conductive material which is not etched by ferric chloride or cupric chloride, etching stops at the front surface of the conductive film  13 . As the material for the third conductive film  13 , gold, silver, and palladium can be employed. 
   The fourth step of the preferred embodiments is, as shown in FIG.  7  and  FIG. 8 , for removing the third conductive film  13  by use of the conductive pattern layer  11 A as a mask and thus forming anchor portions  15  where the third conductive film  13  is depressed further inside than the conductive pattern layer  11 A. 
   The third conductive film  13  is selectively removed by use of the conductive pattern layer  11 A formed of the first conductive film  11  in the previous step. Two methods can be employed for selectively removing the third conductive film  13 . A first method thereof is an etching method by use of a solution to remove only the third conductive film  13 . A second method thereof is a method for removing only the third conductive film  13  by electrolytic peeling. 
   As the first method, a method for partially removing the third conductive film  13  by etching will be described. As an etchant used in this method, an etchant is employed which etches the third conductive film  13  and does not etch the first conductive pattern  11 A or second conductive film  12 . For example, in a case where the conductive pattern  11 A and second conductive film  12  are formed of a material mainly of Cu and the third conductive film  13  is an Ag film, only the third conductive film  13  can be removed by using an iodine-based etchant. As a result of etching of the third conductive film  13 , the second conductive film  12  comes into contact with the iodine-based etchant, however, the second conductive film  12  made of, for example, Cu is not etched by the iodine-based etchant. Accordingly, etching herein performed stops at the front surface of the second conductive film  12 . By performing overetching in this etching, the third conductive film  13  is overetched, thus anchor portions  15  where the third conductive film  13  is depressed further inside than the peripheral ends of the conductive pattern layer  11 A are formed. 
   As the second method, a method for removing only the third conductive film  13  by electrolytic peeling will be described. First, a solution containing metal ions is brought into contact with the third conductive film  13 . Then, a positive electrode is provided in the solution, a negative electrode is provided on the laminated plate  10 , and a direct current is applied. Thereby, only the third conductive film  13  is removed based on a principle reverse to that of plating film formation by an electrolytic method. The solution herein used is a solution used when the material composing the third conductive film  13  is plated. Accordingly, in this method, only the third conductive film  13  is peeled. By performing over-peeling in this electrolytic peeling, the third conductive film  13  is over-peeled, thus anchor portions  15  where the third conductive film  13  is depressed further inside than the peripheral ends of the conductive pattern layer  11 A are formed. 
   This step includes forming the anchor portions  15  intentionally by overetching or over-peeling. In addition, since the anchor portions  15  are formed by using the conductive pattern layer  11 A as a mask, owing to a self-alignment effect, the anchor portions  15  are formed around the conductive pattern layer  11 A with uniform concavity. 
   The fifth step of the preferred embodiments is, as shown in  FIG. 9 , for fixedly fitting semiconductor elements  19  on the conductive pattern layer  11 A and electrically connecting electrodes of the semiconductor elements  19  with the pads  14 A on predetermined parts of conductive pattern layers  11 A. 
   The semiconductor elements  19  are, in the state of bare chips, die-bonded onto the conductive pattern layer  11 A with a conductive or insulating adhesive resin. Heat generated from the semiconductor elements  19  is released outside from the underlying conductive pattern layer  11 A. 
   In addition, the respective electrode pads of the semiconductor element  19  are connected to the pads  14 A provided at predetermined positions of the surrounding conductive pattern layer  11 A via bonding wires  20 . The semiconductor element  19  can be mounted face-down. In this case, solder balls or bumps are provided on the front surfaces of the respective electrode pads of the semiconductor element  19 , while on the front surface of the laminated plate  10 , electrodes similar to the bonding pads formed of the conductive pattern layer  11 A are provided at parts corresponding to the solder ball positions. 
   Now, an advantage of using the laminated plate  10  in wire bonding will be described. In general, when wire bonding is carried out with Au wires, this is heated at 200° C.-300° C. At this time, if the second conductive film  12  is thin, the laminated plate  10  warps, and in this condition, if the laminated plate  10  is pressurized via a bonding head, there is a possibility that damage occurs to the laminated plate  10 . However, these problems can be solved by forming the second conductive film  12  itself thick. 
   The sixth step of the preferred embodiments is, as shown in  FIG. 10 , for covering the semiconductor elements  19  with a sealing resin layer  22  and filling the sealing resin layer  22  into the anchor portions  15 . 
   The laminated plate  10  is set in a molding device for resin molding. As a molding method, transfer molding, injection molding, coating, dipping and the like can be carried out. However, considering productivity, transfer molding and injection molding are suitable. 
   In this step, when performing molding with the sealing resin layer  22 , the sealing resin layer  22  is filled into the anchor portions  15  formed by a concavity in the third conductive film  13  formed on the front surface of the second conductive film  12 , therein exists an advantage such that bonding between the sealing resin layer  22  and conductive pattern layer  11 A is strengthened by an anchoring effect. 
   In addition, in this step, it is necessary that the laminated plate  10  is brought into contact flatly with a lower metal mold of a mold cavity, and the thick second conductive film  12  performs this function. Moreover, even after removal from the mold cavity, flatness of the package is maintained by the second conductive film  12  until contraction of the sealing resin layer  22  is completely finished. Namely, a role is played of mechanically supporting the laminated plate  10  until this step is assumed by the second conductive film  12 . 
   The seventh step of the preferred embodiments is, as shown in  FIG. 11 , for exposing the sealing resin layer  22  and the third conductive film  13  on the rear surface by removing the second conductive layer  12 . 
   In this step, the second conductive film  12  is etched without masking so that the whole surface is removed. In this etching, chemical etching by use of ferric chloride or cupric chloride is sufficient, and the second conductive film  12  is entirely removed. By thus entirely removing the second conductive film  12 , the third conductive film  13  is exposed through the insulating layer  22 . As described above, since the third conductive film  13  is formed of a material which is not etched by a solution to etch the second conductive film  12 , the third conductive film  13  is not etched in this step. 
   This step include that when the second conductive layer  12  is removed by etching, the third conductive film  13  functions as a barrier layer even without using a mask, therefore, a rear surface composed of the sealing resin layer  22  and third conductive film  13  is formed flat. Since the second conductive film  12  is entirely removed by etching, the third conductive film  13  also comes into contact with the etchant in the final stage of etching. As described above, the third conductive film  13  is formed of a material which is not etched by ferric chloride or cupric chloride that etch the second conductive film  12  made of Cu. Accordingly, since etching stops at the lower surface of the third conductive film  13 , the third conductive film  13  functions as an etching barrier layer. Moreover, in and after this step, the ensemble is mechanically supported by the sealing resin layer  22 . 
   The last step of the preferred embodiments is, as shown in FIG.  12  through  FIG. 14 , for forming a land grid array structure or a ball grid array structure. 
   For a land grid array structure, in the previous step where the second conductive film  12  has been entirely removed, the third conductive film  13  excluding parts to become external electrodes  24  is covered with an overcoat resin  23 , and next, as shown in  FIG. 12 , the sealing resin layer  22  and overcoat resin  23  are diced to separate these into individual circuit devices. 
   Furthermore, for use in an environment where Ag migration is considered to be a problem, it is preferable to remove the third conductive film  13  by selective etching before covering the conductive film  13  with an overcoat resin. 
   For a ball grid array structure, the third conductive film  13  is, for the most part, covered with an overcoat resin  23  by screen-printing with an epoxy resin and the like dissolved in a solvent while exposing parts to form external electrodes  24 . Next, as shown in  FIG. 13 , by screen-printing with a solder cream and by solder reflow, external electrodes  24  are formed in these exposed parts. Subsequently, as shown in  FIG. 14 , since a large number of circuit devices are formed on the laminated plate  10  in a matrix fashion, these are separated into individual circuit devices by dicing the sealing resin layer  22  and overcoat resin  23 . 
   In this step, since the circuit devices can be separated into individual circuit devices by dicing the sealing resin layer  22  and overcoat resin  23 , frictional wear of a dicer to perform dicing can be reduced.