Abstract:
The invention provides a high-density multilayer printed wiring board and a method for manufacturing a multilayer printed wiring board having high-density wiring that is formed easily. A method for manufacturing a multilayer printed wiring board formed by laminating a plurality of laminates comprises a step for forming a conduction hole on a laminate comprising an insulating board having both sides on which conductive films are formed, a step for electrically connecting between both sides of said laminate through the above-mentioned conduction hole and planarizing the surface, a step for patterning the above-mentioned conductive film desiredly and forming a projection member at a desired position of the above-mentioned conductive film, a step for laminating bonding members having a through hole to which the above-mentioned projection member is inserted, which is served for bonding between the above-mentioned laminates, and the above-mentioned laminates alternately with insertion of the above-mentioned projection member into the above-mentioned throughhole, and a step for press-molding the above-mentioned laminated laminates and bonding members with heating.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a modified multilayer printed wiring board and a modified method for manufacturing the multilayer printed wiring board, and more particularly relates to a multilayer printed wiring board having high density wiring and a method for manufacturing the multilayer printed wiring board having high density wiring. 
     2. Description of the Related Art 
     FIG. 8A to FIG. 8E show an exemplary process for manufacturing a conventional multilayer printed wiring board, and the process for manufacturing the conventional multilayer printed wiring board will be described herein under with reference to FIG. 8A to FIG.  8 E. 
     At first, as shown in FIG. 8A, copper foils are formed on both sides of an insulating board to form a plurality of laminates  1  that are not conductive between both sides. Subsequently as shown in FIG. 8B, a via hole la is formed on each laminate, and the laminate becomes conductive between both sides by, for example, plating on the via hole. 
     Subsequently as shown in FIG. 8C, a plurality of laminates  1  are laminated by use of a bonding member  2  consisting of prepreg. Then, a through hole  3  that passes through the plurality of laminates  1  is formed as shown in FIG.  8 D. To ensure electrical connection between the laminates, for example, copper foils  4  or the like is formed by plating on the surface of the laminates and the through hole  3 . Finally, the copper foils on the surfaces of the laminates are patterned desiredly to complete a multilayer printed wiring board  5 . 
     FIG. 9A to FIG. 9E show another conventional process for manufacturing a multilayer printed wiring board, a method for manufacturing a multilayer printed wiring board will be described herein under with reference to FIG. 9A to FIG.  9 E. The manufacturing method shown in FIG. 9A to FIG. 9E is a method so-called as build-up method. 
     At first, as shown in FIG. 9A, through holes  7  are formed on a laminate  6  comprising an insulating board, and the surface of the through holes  7  is plated. Then, insulating layers  8  are formed on both sides of the laminate  6  as shown in FIG.  9 B. Subsequently as shown in FIG. 9C, via holes  9  are formed on the insulating layers  8 , and the via holes  9  are plated. By repeating the processes shown in FIG. 9B to FIG. 9D, a multilayer printed wiring board  10  shown in FIG. 9D is formed. It is possible to form high density wiring because wirings are intersected each other on the same plane as described hereinabove. 
     However, the multiplayer printed wiring board and the manufacturing method thereof described hereinabove are involved in the problem as described hereafter. 
     In the method for manufacturing a multilayer printed wiring board shown in FIG. 8A to FIG. 8E, it is required to form a through hole  3  that passes through all the laminates  1  in order to render arbitrary laminates  1  conductive therebetween. As the result, it is difficult to realize a high density multilayer printed wiring board, and the less freedom of high density wiring of a multilayer printed wiring board  5  is the problem. 
     Furthermore, in the method for manufacturing a multilayer printed wiring board shown in FIG. 9A to FIG. 9E, it is required to form a plurality of insulating layers  8  and to plate, and such a long manufacturing process results in poor yield and the poor yield is the problem. 
     Recently, a method for forming a multilayer printed wiring board (B 2 it™) (Buried Bump Interconnection Technology) in which a projection member is formed with conductive paste and prepreg is penetrated, and a method for forming a multilayer printed wiring board (ALIVH™) (Any Layer IVH Structure Printed Wiring Board) in which a through hole is formed on prepreg and a projection member is inserted into the through hole are presented. 
     However, the so-called B 2 it™ is involved in a problem that the thickness of a printed wiring board is restricted because the projection member is formed of conductive paste. In detail, it is required to use a large projection member to render the insulating layer thick and the large projection member is disadvantageous for high density wiring. On the other hand, it is required to render the insulating layer thin if the bump is small. 
     ALIVH™ is also involved in a problem that the resistance value in the through hole is large because conductive paste connects between layers. Both in B 2 it™ and ALIVH™, conductive paste that migrates along fibers that form the insulating layer is also a problem. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished to solve the above-mention problems, and provides a multilayer printed wiring board having high density wiring to be formed easily and a manufacturing method thereof. 
     According to one aspect of the present invention, the above-mentioned object is achieved by applying a method for manufacturing a multilayer printed wiring board formed by laminating a plurality of laminates comprising a step for forming a conduction hole on a laminate comprising an insulating board having both sides on which conductive films are formed, a step for electrically connecting between both sides of the above-mentioned laminate through the above-mentioned conduction hole and planarizing the surface, a step for patterning the above-mentioned conductive film desiredly and forming a projection member at a desired position of the above-mentioned conductive film, a step for laminating bonding members having a through hole to which the above-mentioned projection member is inserted, which is served for bonding between the above-mentioned laminates, and the above-mentioned laminates alternately with insertion of the above-mentioned projection member into the above-mentioned through hole, and a step for press-molding the above-mentioned laminated laminates and bonding members with heating. 
     According to the structure of the above aspect, a multilayer printed wiring board is manufactured by applying a process comprising a step for alternately laminating laminates having conductive films in the form of desired pattern on which a projection member is formed and bonding members on which a through hole is formed, and a step for press-heat-molding a plurality of laminates and bonding members that have been laminated alternately. Electrical connection between arbitrary laminates is formed by connecting a projection member consisting of metal to a conductive film. 
     Laminates are laminated not in one after another fashion, but a laminate and a projection member are laminated previously and heat-press-molded in one step to manufacture a multilayer printed wiring board. Furthermore, laminates to be used for a multilayer printed wiring board are manufactured separately and then laminated. Thereby, only non-defective laminates are used for manufacturing. Because the projection member consists of metal, the length can be adjusted arbitrarily, and the resistance value between laminates is small when the projection member is connected to the conductive film consisting of metal. 
     According to another aspect of the present invention, the above-mentioned object is achieved by applying a multilayer printed wiring board formed by means of a laminating process comprising a step for forming a conduction hole on a laminate comprising an insulating board having both sides on which conductive films are formed, a step for electrically connecting between both sides of the above-mentioned laminate through the above-mentioned conduction hole and planarizing the surface, a step for patterning the above-mentioned conductive film desiredly and forming a projection member at a desired position of the above-mentioned conductive film, a step for laminating bonding members having a through hole to which the above-mentioned projection member is inserted, which is served for bonding between the above-mentioned laminates, and the above-mentioned laminates alternately with insertion of the above-mentioned projection member into the above-mentioned through hole, and a step for press-molding the above-mentioned laminated laminates and bonding members with heating. 
     According to the structure of the above aspect, laminates, each of which has a conductive film having a predetermined pattern on which projection members are formed, and bonding members, each of which has through holes, are laminated alternately and a plurality of laminated laminates are subjected to press-heat, molding. A metal projection member is electrically connected to a conductive film to electrically connect between arbitrary laminates. A multiplayer printed wiring board is formed not by laminating laminates one after another but by molding laminates and projection members at a time in the present invention. 
     Because the projection member consists of metal, the length of the projection member can be adjusted arbitrarily, and the resistance value between laminates is reduced when the conductive film consisting of metal is connected to the projection member. As the result, the freedom of wiring is improved and the high-density wiring is realized by applying the multilayer printed wiring board of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A to FIG. 1I are schematic process diagrams for illustrating a preferred embodiment of a method for manufacturing a multilayer printed wiring board of the present invention. 
     FIG. 2A to FIG. 2E are schematic process diagrams for illustrating a preferred embodiment of a method for manufacturing a multilayer printed wiring board of the present invention. 
     FIG. 3A to FIG. 3C are process diagrams for illustrating the second embodiment of a method for manufacturing a laminate having both sides that are conductive each other in the method for manufacturing a multilayer printed wiring board of the present invention. 
     FIG. 4A to FIG. 4E are process diagrams for illustrating the third embodiment of a method for manufacturing a laminate having both sides that are conductive each other in the method for manufacturing a multilayer printed wiring board of the present invention. 
     FIG. 5A to FIG. 5E are process diagrams for illustrating an embodiment of a method for forming a projection member in the method for manufacturing a multilayer printed wiring board of the present invention. 
     FIG.  6 A and FIG. 6B are process diagrams for illustrating the second embodiment of a method for forming a projection member in the method for manufacturing a multilayer printed wiring board of the present invention. 
     FIG.  7 A and FIG. 7B are process diagrams for illustrating the third embodiment of a method for forming a projection member in the method for manufacturing a multilayer printed wiring board of the present invention. 
     FIG. 8A to FIG. 8E are process diagrams for illustrating an exemplary conventional method for manufacturing a multilayer printed wiring board. 
     FIG. 9A to FIG. 9E are process diagrams for illustrating an exemplary conventional method for manufacturing a multilayer printed wiring board. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described in detail hereinafter with reference to the attached drawings. 
     The embodiments described hereinafter involve various technically preferable restrictions because the embodiments are detailed preferred examples of the present invention, but the scope of the present invention is by no means limited by any of these embodiments unless otherwise the present invention is specified to be limited. 
     FIG. 1A to FIG.  1 I and FIG. 2A to FIG. 2E are schematic process diagrams for illustrating a preferred embodiment of a method for manufacturing a multilayer printed wiring board of the present invention, and the method for manufacturing a multilayer printed wiring board will be described with reference to FIG. 1A to FIG.  1 I and FIG. 2A to FIG.  2 E. 
     At first, as shown in FIG. 1A, a laminate  100  having conductive films  101  comprising copper foils on both side of an insulating board is prepared. As shown in FIG. 1B, for example, via holes  102  that are conductive holes are formed from both sides of the laminate  100 . Each via hole  102  is formed so as to be wider at the surface side of the laminate  100  than at the middle  102   a  of the via hole  102 . Because the area that is available for electrical connection to the via hole  102  is wide, it is easy to fill up the conduction hole and planarize the surface. 
     Exemplary methods for forming a through hole  102  include a method in which a drill is used for drilling, a method in which a punch having a sharp tip is used with tapping, and a method in which a laser beam is converged. At that time, by forming a via hole  102  by means of carbon dioxide gas laser after a copper foil on the one side of the laminate  100  has been removed previously by means of etching or the like, a conical via hole  102  having copper foil on the other side is formed. 
     Next, as shown in FIG. 1C, a sufficient plated metal layer  102 b is formed on the inside of the via hole by means of low current plating or pulse plating on the laminate  100 . Thereby, the laminate  100  becomes conductive between both sides. At that time, if metal plated layer  102   b  is formed so as to fill the via hole  102 , a process for filling up the via hole  102  can be eliminated. 
     Then, as shown in FIG. 1D, both sides of the laminate  100  are polished and planarized, and a desired pattern is formed on the conductive film  101  by means of photolithography technique. 
     Thereafter as shown in FIG. 1E, projection members  103  consisting of metal are formed on the desired location on the laminate  100 . The height H of the projection member  103  is adjusted desirably because metal is used for forming the projection member  103  differently from the case in which conductive paste is used for forming the projection member  103 . In the case of metal, it is not required to widen the projection member  103  horizontally in spite of thick interlayer, and thus the high density wiring is realized. Furthermore, because the projection member  103  consists of metal, the resistance value of the projection member  103  is reduced. 
     On the other hand, a prepreg  110  that is to be used as a binding member as shown in FIG. 1F is prepared separately from the laminate  100 , and through holes  111  are formed at the desired position of the prepreg  110  as shown in FIG.  1 G. The prepreg  110  is a material formed by partially hardening epoxy resin or the like impregnated in glass cloth. 
     Subsequently, as shown in FIG. 1H, laminates  100  and prepregs  110  are laminated alternately with insertion of projection members  103  into through holes  111 . Then, the laminated laminates  100  and prepregs  110  are press-molded with heating to manufacture a multilayer printed wiring board  200 . At that time, electrical connection between the projection members  103  and conductive films  101  is secured by coating of conductive paste, by forming plated gold layer, or by coating of reducing agent such as formalin or glyoxylic acid on the top end of the projection members  103  or portion of the conductive films  101  to be connected to the projection members  103 . Thereby the conductive films  101  are rendered surely conductive to the projection members  103 . Finally, as shown in FIG. 1I, solder resist is coated and apparent finishing work is applied, and thus a multilayer printed wiring board  200  is completed. Subsequently, the multilayer printed wiring board  200  is subjected to inspection. 
     According to the present embodiment, electrical connection between laminates  100  can be secured in one forming process when a multilayer printed wiring plate  200  is manufactured. Thereby, the manufacturing process can be simplified and the manufacturing time can be shortened. Furthermore, because electrical connection can be formed at arbitrary portions on the laminates  100 , the freedom of wiring is improved and high density wiring is realized. Furthermore, because a multilayer printed wiring board  200  is formed not by laminating insulating layers one on another differently from the conventional method, as the result the yield can be improved. In detail, when a multilayer printed wiring board  200  is manufactured by means of a lamination method, the yield is represented by the product of the number of layers. On the other hand, according to the method for manufacturing a multilayer printed wiring board  100  shown in FIG. 1A to FIG. 11, because each laminate  100  is inspected individually and only the non-defective laminate is used for lamination, as the result the yield is improved. Furthermore, because a projection member  103  is surrounded by only resin that has migrated from a prepreg  110 , as a result the migration that is caused by migration of metal ions along glass cloth is suppressed. 
     FIG. 2A to FIG. 2E are process diagrams for illustrating another embodiment of a method for manufacturing a laminate  100  having both sides that are electrically connected to each other in the method for manufacturing a multilayer printed wiring board shown in FIG. 1A to FIG.  1 I. At first, a laminate  100  comprising an insulating board having conductive films  101  on both sides as shown in FIG. 2A is prepared, and a cylindrical via hole  122  is formed by, for example, drilling as shown in FIG.  2 B. 
     Next, as shown in FIG. 2C, for example, copper sulfate plated layer  123  is formed on the surface of the via hole  122  and the conductive films  101 . Subsequently, as shown in FIG. 2D, for example, UV ink or conductive paste layer  124  is filled in the via hole  122 . Then, plated layers  125  are formed on both sides, particularly in the case that the portion on the via hole  122  is rendered conductive, and the plated layer  125  is formed also on the portion on the via hole  122  and planarized by polishing. As described hereinabove, a laminate  100  having both sides that are conductive to each other may be formed by means of the method in which a cylindrical via hole  122  is formed for conduction between the both sides and conductive paste is filled in the via hole  122 . 
     FIG. 3A to FIG. 3C are process diagrams for illustrating the third embodiment of the multilayer printed wiring board of the present invention, and a method for manufacturing a multilayer printed wiring board will be described with reference to FIG. 3A to FIG.  3 C. 
     At first, in FIG. 3A, a laminate  100  comprising an insulating board having both sides on which conductive films  101  consisting of copper, aluminum or the like are formed is prepared. Subsequently, as shown in FIG. 3B, a conical via hole  132  is formed by, for example, laser convergence. At that time, the via hole  132  is formed from the one surface side. 
     Subsequently, as shown in FIG. 3C, the conductive films  101  are subjected to plating, and the via hole  132  is filled up with conductive material. At that time, for example, a current density of 1 (a/dm 3 ) or lower is preferably applied in an electrolytic plating process or a PR electrolytic plating process so that the via hole  132  is easily filled up with the plated layer  133 . Then, the surface of the plated layer  133  is polished to complete the planar laminate  100 . 
     FIG. 4A to FIG. 4E are process diagrams for illustrating a method for forming a projection member in the method for manufacturing a multilayer printed wiring board of the present invention, and the method for forming a projection member will be described with reference to FIG. 4A to FIG.  4 E. 
     At first, as shown in FIG. 4A, films consisting of an etching-selective metal such as tin are formed by plating on the planar surface of a laminate  100  having both sides that are connected electrically to each other as shown in FIG.  4 B. Furthermore, projection forming films  141   a  comprising copper foil having a thickness equivalent to that of the projection member  141  is formed by plating on the films. 
     Then, as shown in FIG. 4C, etching resists  142  are formed on the portions of the projection forming films  143   a  where projection members  143  are to be formed. The projection forming films  143   a  and the films are etched with, for example, ammonium alkali etchant. 
     Subsequently, as shown in FIG. 4D, to pattern electrode films  101  and plated layers  133  desiredly, positive type electrodeposition resist layer  144  is coated on both sides of the laminate  100 , and the resist layer is patterned in the desired pattern by means of a projection type parallel exposing apparatus. Then, the laminate  100  is etched with cupric chloride to remove the resist, and thus the laminate  100  having projection members  143  is completed. 
     FIG. 5A to FIG. 5E are process diagrams for illustrating another exemplary method for forming the projection member in the method for manufacturing a multilayer printed wiring board of the present invention. 
     At first, as shown in FIG. 5A, a planar laminate  100  having conductive films  101  on both sides that are connected electrically to each other is prepared, and pattern resist layer is formed on plated layers  133  as shown in FIG.  5 B. Subsequently, the conductive films  101  and plated layers  133  are etched to form a desired pattern. 
     Next, as shown in FIG. 5C, resist layer  151  is formed on the entire surface (both sides) of the laminate  100 , and openings  152  are formed on portions of the resist layer  151  where projection members  153  are to be formed. Then, as shown in FIG. 5D, catalyst is applied on the entire surface and electric plating is applied to form the projection members  153 . Otherwise, the surface of copper is replaced with palladium, and the projection members  153  are formed by means of electroless plating. Subsequently, as shown in FIG. 5E, the resist layer  151  is removed to complete the laminate  100  having projection members  153 . 
     FIG.  6 A and FIG. 6B are process diagrams for illustrating another exemplary method for forming the projection member in the method for manufacturing a multilayer printed wiring board of the present invention, and the method for forming the projection member will be described with reference to FIG.  6 A and FIG.  6 B. 
     At first, a planar laminate  100  having conductive films  101  on both sides that are connected electrically each other is formed as shown in FIG.  6 A. Then, pattern resist is coated on plated layers  133 , and the conductive films  101  and the plated layers  133  are etched to form a desired pattern. 
     Subsequently, as shown in FIG. 6B, bumps  163   a  are disposed on portions where the projection members  163  on the plated layers  133  are to be formed by stud bump bonder. A plurality of bumps  163   a  are stacked so that the projection members  163  are positioned at a desired height. By repeating the above-mentioned process, the projection members  163  are formed. 
     FIG.  7 A and FIG. 7B are process diagrams for illustrating another exemplary method for forming the projection member in the method for manufacturing a multilayer printed wiring board of the present invention. 
     At first, a planar laminate  100  having conductive films  101  on both sides that are connected electrically to each other as shown in FIG. 7A is formed. Then, pattern resist is coated on plated layers  133 , and the conductive films  101  and plated layers  133  are etched to form a desired pattern. 
     Subsequently, as shown in FIG. 6B, metal wires  173   a  are disposed on portions where projection members  173  are to be formed on the conductive films  101 . A high current is applied between a metal wire  173   a  and a conductive film  102  (plated layer  133 ) by means of a high current generator  171 . At that time, the metal wire  173   a  melts to form a projection member  173 . 
     The embodiment of the present invention is by no means limited by the above-mentioned embodiments. For example, when printed wiring boards and prepregs are laminated, printed wiring boards on which parts such as IC are mounted and prepregs on which recesses are formed are laminated to manufacture a parts-built-in board easily. 
     In the methods for manufacturing the projection member shown in FIGS. 4A to  4 E to FIGS. 7A and 7B, a planar laminate  100  having both sides that are electrically connected to each other shown in FIG. 3A to FIG. 3C is used for the purpose of description, a laminate  100  manufactured by mans of the methods shown in FIG. 1A to FIG.  1 I and FIG. 2A to FIG. 2E may be used. 
     As described hereinabove, according to the present invention, when a multilayer printed wiring board is manufactured, electrical connection between laminates is formed in one forming process to thereby realize simplified manufacturing process and shortened manufacturing time, and electrical connection is formed at arbitrary portions on respective laminates to thereby realize improved freedom of wiring and high density wiring.