As various kinds of electronic instrument become smaller in size and higher in performance, a demand for higher electronic component packaging density is increasing. As for wiring boards, multi-layered wiring boards in which insulating layers and wiring layers are stacked alternately are widely used reflecting the demand. The multi-layered wiring boards respond to the demand for higher density and higher performance due to the multi-layered wiring structure. In the multi-layered wiring boards, the connection among wiring pattern layers is performed through via-connection or the like.
FIG. 28 is a cross sectional view showing an example of a cross section structure of an existing ordinary multi-layered wiring board. In this figure, a multi-layered wiring board 901, wiring circuits formed over five layers are connected by via-holes. Each of a first wiring circuit 901, a second wiring circuit 902, a third wiring circuit 903, a fourth wiring circuit 904 and a fifth wiring circuit 905 is formed respectively by patterning a conductor layer. Each wiring circuit of the respective layers is insulated each other by an insulating layer 906.
An existing ordinary method for manufacturing the multi-layered wiring boards as illustrated in FIG. 28 will be described. First, in order to perform interlayer connection between a double-sided laminate board prepared by adhering conductor layers such as copper foils on both surfaces of an insulating layer, through-hole 907 will be formed at a portion where the double-sided laminate is electrically connected. An inner wall surface of the through-hole 907 is plated by chemical plating, further, plating by electrical plating is given to enhance reliability of the interlayer connection by thickening the conductor layer 907b of the inner wall surface of the through-hole.
Next, the conductor layers on both surfaces are patterned with prescribed circuits using, for example, photo-etching etching method or the like.
Then, the patterned conductor layers are laminated thereon by insulating layers such as, for example, prepreg cloth or the like, further by conductor layer such as copper foil. Thereafter, they are heated and pressed to integrate into one body. The processes from the formation of the through-hole to the patterning of the circuit are repeated to obtain multi-layered structure.
The multi-layered wiring boards in which interlayer connection between wiring layers is made by using via-hole, have a problem that the multi-layered wiring boards are difficult to cope with high density packaging.
For example, in an ordinary way, in a region where a through-hole is disposed, wiring cannot be formed, and an electronic component cannot be disposed. Accordingly, attaining higher wiring density and higher packaging density are restricted. Further, as the packaging density of the electronic component goes up, the wiring density of the wiring board becomes higher in recent years. If diameters of the through-holes are made small to meet with such finer wiring patterns, there occurs a problem that reliability of the interlayer connection becomes difficult to secure.
In addition, the formation of connection between wiring layers by a through-hole involves through-hole formation process, plating process or the like, accordingly the manufacturing processes are redundant and are unfavorable from the viewpoint of productivity.
For example, the through-hole formation process is carried out by boring the through-holes one by one with a drill or the like. Accordingly, it takes long time for boring operation. Further, after boring a through-hole, polishing step is necessary for removing burrs. In addition, the through-holes are required to be formed with high positioning accuracy, and compatibility with plating has to be considered for the inner wall surface of the through-hole. Therefore, the accuracy of through-hole formation and management of formation condition become troublesome.
In addition, the plating process for obtaining electrical connection among plural wiring layers by through-holes requires a sophisticated process control such as concentration and temperature control of chemicals, or the like. Further, both the through-hole forming process and the plating process require large scale apparatus.
Such interlayer connection of a multi-layered wiring board by through-holes lowers productivity of printed wiring boards (PWB), accordingly, it is difficult to meet with the demand for cost reduction or the like.
To simplify the electrical connection between wiring layers of a multi-layered wiring board, a method is proposed in which the connection between wiring layers are made by conductive bumps. In this method, conductive bumps are formed at via-lands placed on the wiring circuits and formed for interlayer connections. By putting the conductive bumps through an interlayer insulating layer in the thickness direction, connection between via-lands formed on the opposing wiring layer is established.
FIG. 29A and FIG. 29B show an example of a method for manufacturing a multi-layered wiring board in which wiring layers are connected by conductive bumps described above.
First, a double-sided wiring board 913 in which wiring circuits 912 consisting of copper are formed on both surfaces of an insulating resin base material 911 consisting of, for example, paper-phenol system is prepared as an inner layer core. The wiring circuits 912 formed on both surfaces of the insulating resin base material 911 have via-lands 912a for interlayer connection. On these via-lands 912a, conductive bumps 914 formed by printing conductive paste, for example, are formed.
Next, an insulating resin sheet 915 of B stage (semi-cured state) and a copper foil 916 are laminated, and on both sides of the double-sided wiring board 913, the wiring circuits 912 and copper foil 916 are disposed facing oppositely through the insulating resin sheet 915 (FIG. 29A).
Thereafter, this laminate is pressed and heated. Thereby, the insulating resin sheets 915 of B stage are cured to form a board having all layers in one body. At this time, by pressing, the conductive bumps 914 is put through the insulating resin sheets 915 of B stage (semi-cured) and is connected with the copper foil 916 in a body while deforming plastically. Thus, connection between conductive layers by the conductive bump is formed.
Then, through-holes 917 are formed at prescribed positions, conductive material, for example, silver paste 918 is filled in this through-hole 917, or the conductive material such as, for example, silver paste is coated on the inner wall of the through-holes 917. Thereby, conductor layers on the external surfaces of the board are connected. The copper foils 916 of the external surfaces are patterned by, for example, a photo-etching method or the like to form prescribed wiring circuit 916b including via-lands 916a. Thereby, a multi-layered wiring board in which the conductive bumps and the through-holes are combined to form interlayer connection between the wiring circuits is formed (FIG. 29B).
FIG. 30A and FIG. 30B are diagrams showing another example of the method for manufacturing multi-layered wiring boards that are connected between the wiring layers by conductive bumps.
First, a double-sided wiring board 923 in which wiring circuits 922 are formed by laminating copper foils, curing and patterning on both surfaces of base material 921, for example, a glass cloth and an epoxy resin, is prepared as an inner layer core. The wiring circuits 922 formed on both surfaces of the double-sided wiring board 923 have via-lands 922a for interlayer connection.
On the other hand, copper foils 925 thereon conductive bumps 924 are formed, and prepregs 926 of epoxy resin system are prepared, respectively. The conductive bumps 924 are formed at the positions corresponding to the via-lands 922a when the copper foil 925 is laminated with the double-sided wiring board 923. Next, as shown in FIG. 30A, the copper foils 925, after being disposed on both sides of the double-sided wiring board 923 through the prepregs 926, pressed and heated to integrate all the layers. At this time, due to the pressing, the conductive bumps at the two sides are disposed oppositely. At this time, as a result of the pressing, the conductive bumps 924 are put through the prepregs 926 of B stage (semi-cured state), and are integrated and connected with the via-lands 922a while being formed plastically. Thus, connection between conductor layers by the conductive bumps is formed.
Next, through-holes 927 are formed at prescribed positions. To these through-holes 927, conductor layers 928 such as copper or the like, for example, are plated to connect between respective conductor layers.
Thereafter, the copper foils 925 of the external layers are patterned by, for example, photo-etching method or the like into prescribed wiring circuits 925b including via-lands 925a. Thereby, a multi-layered wiring board in which the conductive bumps and plated through-holes are combined to connect the interlayer of the wiring board is formed (FIG. 30B).
The interlayer wiring circuit connection adopting the conductive bumps mentioned above has advantages of simplicity in construction, high productivity due to small number of processing steps, and ability of replying demands for higher density packaging, or the like.
Now, in manufacturing the multi-layered wiring board described above, we must prepare base materials consisting of a laminate of a wiring layer (or a Cu foil) and an insulating resin layer. Accordingly, upon laminating a plurality of base materials, securing accuracy of their relative positions is an important technical point.
Even when the interlayer connection is performed by conductive pillars for example, and also when the interlayer connection is performed by through-holes or the like, the interlayer connection cannot be performed appropriately unless the accuracy of respective wiring layer positions is secured.
So far, upon laminating and positioning base materials constituting such a multi-layered wiring board, pin insertion mounting method and eyelet mounting method are generally used.
In the pin insertion mounting method, holes (guide holes) for positioning are disposed in advance at prescribed positions of base materials to be laminated. Stacking and laminating of base materials obtaining proper positioning of base materials are carried out by putting pins disposed on a stainless-steel plate mold (normally approximately 8 mm thick) through the holes of the base materials. Then, in a state in which each of the stacked plural base materials is kept its proper positioning, they are integrated to a laminate by pressing while heating through a mirror plate, for example. In the eyelet mounting method, the base materials are laminated by pressing while heating in a state in which the base materials are tentatively fixed by eyelets and holes for positioning described above.
However, manufacturing of the multi-layered wiring boards employing existing laminating method have following inconveniences.
First, in the pin insertion mounting method, the respective base material must be provided with guide holes. The providing with guide halls increases the processing step and lowers productivity. In addition, another problem of this method is that the resin such as prepreg or the like permeates into the guide holes formed for positioning. As the resin permeates, the base material tends to deform. Further, the pins for positioning and the guide holes are stuck solidly by the permeated resin to tend to induce displacement and surface damage. Further, another problem of this method has a difficulty in making the laminating step automatic.
On the other hand, the eyelet mounting method have a problem that the pressing cannot be uniform due to projected eyelet portions at a step of integrating base materials to a laminate by heating/pressing.
Further, the base materials (for example, prepreg or the like) constituting a multi-layered wiring board tend to cause displacement of positions upon boring guide holes, or tend to cause displacement of positions and deformation after pulling out the pins from positioning holes after carrying out integrating lamination, since the base materials usually tends to induce dimension variation due to heating/pressing. That is to say, when the base materials are constrained by the pins for positioning, free dimension variation in the surrounding is restricted, and the base materials cause distortion and non-uniform dimension variation due to stress of the base material caused by the pins. The dimension variation and distortion are likely to occur also when the pins are pulled out and the stress is released. Such distortion and dimension variation of the base materials as described above induce non-uniformity of the insulating resin layers constituting the interlayer insulating layers of the multi-layered wiring board, resulting in deterioration of reliability of the interlayer insulation.
The distortion or dimension variation of the base materials means change in pitch or deformation of the guide holes formed on the base material. When lamination of the base material is required to perform in plural steps, different guide holes are required for every step of lamination. Accordingly there is a problem that the manufacturing productivity of the multi-layered wiring boards is remarkably lowered. Metallic molds and pressing plates are necessary to prepare in plural kinds for manufacturing a definite multi-layered wiring boards, giving rise to an increase of manufacturing cost and a reduction of effective area for formation of wiring pattern due to an increase of area for the guide holes.
As described above, the conventional technology has a problem that there is a difficulty in laminating plural base materials with high accuracy and high productivity in producing multi-layered wiring boards. The problem becomes remarkable as the scale down of wiring pattern is advanced, number of laminating is increased, or total thickness is reduced. Particularly in recent years the scale down of wiring pattern is remarkable since wiring boards are required to reply to the demand for higher integration of electronic components and various kinds of electronic instruments. Accordingly, establishment of a technology that enables manufacturing wiring boards of high accuracy with high productivity is demanded. Here, the accuracy of laminating plural base materials and the accuracy of interlayer connections are directly related to the reliability of the wiring board.
The present invention is carried out to solve the problem described above.
That is, an object of the present invention is to provide a method and an apparatus for manufacturing multi-layered wiring boards that enables to manufacture multi-layered wiring boards of high accuracy with high productivity.
Another object of the present invention is to provide multi-layered wiring boards having a structure that enables to perform the interlayer connection of high accuracy. Still another object of the present invention is to provide multi-layered wiring boards having a structure that enables to manufacture them with high productivity.