BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a state in which a metal foil is laminated on each surface of a supporting substrate;
FIG. 2 illustrates an example of a structure in which metal foil layers are detachably laminated on a supporting substrate;
FIG. 3 illustrates a state in which a multilayer interconnection pattern is formed by means of a buildup method on each metal foil layer shown in FIG. 2;
FIG. 4 illustrates a state in which laminates formed in a step shown in FIG. 3 are detached from the supporting substrate;
FIG. 5 illustrates a state in which a resist pattern is formed on the metal foil layer on the laminate;
FIG. 6 illustrates a state in which the metal foil layer is etched using the resist pattern as a mask to form an interconnection pattern;
FIG. 7 illustrates a state in which a solder resist pattern is formed on the laminate;
FIG. 8 illustrates a state in which protective plating films are formed on the exposed interconnection pattern;
FIG. 9 illustrates a state in which solder bumps are formed on the exposed interconnection pattern to complete a circuit board;
FIGS. 10A to 10D illustrate first four steps in a known method for producing a circuit board; and
FIGS. 11A to 11F illustrate last six steps in the known method for producing the circuit board.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be described in detail with reference to the drawings.
FIGS. 1 to 9 each illustrate a process for producing a circuit board according to the present invention.
As shown in FIG. 1, metal foil layers 62 are detachably laminated on the front surface and the back surface of a supporting substrate 60.
The metal foil layers 62 are each composed of copper foil and each have a thickness of about 18 to 7 μm.
The supporting substrate 60 is composed of a material having sufficient stiffness so as to have good handleability in forming work (laminate) including formation of an insulating layer, a plating layer, and the like, and in transportation thereof, and having sufficient strength to prevent deformation, such as shrinkage and warpage, of the work. In this embodiment, the supporting substrate 60 is an epoxy resin substrate having a thickness of 0.3 to 0.4 mm and containing a glass cloth. The supporting substrate 60 may be formed of only a resin substrate such as the epoxy resin substrate containing a glass cloth or may be formed of only a metal plate, as long as a predetermined strength is ensured.
A structure shown in FIG. 2 is preferred in order to detachably laminate each metal foil layers 62 on the supporting substrate 60.
That is, dummy metal layers 68 are bonded to the front surface and the back surface of the supporting substrate 60 with adhesive layers 67. Each metal foil layer 62 that is larger than the corresponding dummy metal layer 68 is bonded on a surface of the supporting substrate at the periphery of the metal foil layer 62 with an adhesive layer 67 to cover the dummy metal layer 68.
A thick line A shown in FIG. 2 indicates a portion in which the dummy metal layer 68 and the metal foil layer 62 are bonded to the adhesive layer 67. Furthermore, a dashed line B indicates a portion in which the metal foil layer 62 is only in contact with the dummy metal layer 68. Thus, it is possible to detach the metal foil layer 62 from the dummy metal layer 68 by cutting the metal foil layer 62, the dummy metal layer 68, and the supporting substrate 60 along a line C that is located at a position inside the periphery of the dummy metal layer 68. To prevent the inclusion of air at the portion indicated by the dashed line B, these lamination step are preferably performed using a vacuum apparatus.
As shown in FIG. 3, a laminate 76 in which interconnection patterns 74 are laminated with insulating layers 73 provided therebetween and are electrically connected to each other using vias 75 is formed on each metal foil layer 62.
Next, the resulting laminates are cut along line C shown in FIG. 2 to detach the laminates 76 from the supporting substrate 60 as shown in FIG. 4.
As shown in FIG. 5, the metal foil layer 62 on the resulting laminate 76 is processed by a series of photolithographic steps, for example, by forming a resist pattern 77, etching the metal foil layer 62 using the resist pattern 77 as a mask, and removing the resist pattern 77, thereby forming an interconnection pattern 78.
As shown in FIG. 7, solder resist layers 80 are formed on the front and back surfaces of the laminate 76 in such a manner that predetermined portions of interconnection patterns 74 and 78 disposed at the front and back surfaces of the laminate 76 are exposed. As shown in FIG. 8, the exposed portions of interconnection patterns 74 and 78 are plated with nickel and then gold to form protective plating films 82. Furthermore, solder bumps 84 for connection with the exterior are formed on the predetermined portions of the interconnection pattern 78 to complete a circuit board 86.
With respect to the circuit board 86, generally, a plurality of circuit boards are integrally formed. Then, the resulting integrated boards are separated into target circuit boards.
In the above-described embodiment, the laminates 76 are formed on the front surface and the back surface of the supporting substrate 60. However, the laminate 76 may be formed on only one surface of the supporting substrate 60.
Patent Application
20070289704
