Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-07-06
2004-04-06
Zarneke, David A. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S258000, C174S261000, C174S266000, C361S803000
Reexamination Certificate
active
06717070
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-207322, filed Jul. 7, 2000, 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 printed wiring board having a via for electrically connecting a plurality of wiring layers and a method of manufacturing printed wiring board.
2. Description of the Related Art
For example, a semiconductor package used for electronic apparatus such as a portable computer or the like is mounted on a printed wiring board. This printed wiring board has an insulating layer made of synthetic resin and a plurality of wiring layers. The insulating layer has a first surface and a second surface located on the opposite side of this first surface. The wiring layers are laminated on the first and second surfaces of the insulating layer, respectively. The wiring layers are formed so as to correspond to the predetermined circuit pattern, signal pins used for inputting and outputting for a semiconductor package and power source pins are electrically connected to these wiring layers.
Recently, as for a semiconductor package, the number of signal pins is much increased along with the higher packing density and higher performance, and there is increasing tendency to density of the signal pins. Therefore, for example, a wiring layer of a printed wiring board connected to a signal pin has to be arranged between pins arranged in a high density. As a result, a pattern width of a wiring layer itself becomes extremely narrow as well as a pitch of the wiring layer is finely divided.
On the other hand, this kind of printed wiring board has a via for electrically connecting a plurality of wiring layers which are separated by an insulating layer being interposed therebetween. This via is formed on the insulating layer in the steps of manufacturing a printed wiring board.
A conventional printed wiring board is manufactured according to the following procedure. First, a copper clad laminate is prepared. The copper clad laminate is a laminated layer in which copper foils are laminated on the first and second surfaces of the insulating layer, respectively. After this copper clad laminate is cut into a predetermined shape, a via is formed at a predetermined position of the copper clad laminate. A via is formed by applying a void processing to the insulating layer of the copper clad laminate, and has one end opened on the first surface of this insulating layer and the other end closed by the wiring layer on the second surface of the insulating layer.
When the via is formed on the copper clad laminate, electroless plating is applied to this copper clad laminate. By doing so, a first plating layer which is a groundwork for the conductivity is formed on the copper foil covering the first and second surfaces of the insulating layer and the inner surface of the via. Subsequently, an electrolytic plating is applied to the copper clad laminate, and a second plating layer is laminated on the first plating layer.
Next, the copper clad laminate is covered with an etching resist, and an etching processing is applied to this copper clad laminate. By doing so, the copper foil doubly covered with the first and second plating layers is selectively etched so that the copper foil is to be a fine circuit pattern. When the etching is completed, the etching resist is removed. By doing so, the wiring layers are formed on the first and second surfaces of the insulating layer, respectively. These wiring layers are maintained in a state where these are electrically connected through the first and second plating layers within the via.
However, according to a conventional method of manufacturing a printed wiring board, the first plating layer and the second plating layer are doubly adhered on the copper foil which is to be a wiring layer. Therefore, the thickness of the copper foil is exceeded by the portion of thickness of the first and second plating layers, and the thickness thereof may exceed the thickness limitation of the etching.
Specifically, a pattern width of a wiring layer obtained by etching relates to the thickness of this wiring layer, and usually, the minimum pattern width is made on the order of 10 to 20-fold of the thickness of the wiring layer. Therefore, as making a pitch and a pattern width of the wiring layer finer is pursued, as to the printed wiring board obtained by the above method of manufacture, the wiring layer itself becomes too thick with respect to the pattern width of the wiring layer. As a result, the etching becomes incomplete, the wiring layers adjacent to each other may develop a short circuit, and to make the wiring layer finer cannot be corresponded.
Moreover, a flexible printed wiring board in which a resin film of thermoplasticity is made as an insulating layer is often repeatedly bended or is mounted on electronic apparatus in a state of being bended in a U shape. Therefore, if the plating layers are doubly adhered on the copper foil positioned on the surface which is to be an internal side of the bending out of the flexible printed wiring board, particularly when the flexible printed wiring board is repeatedly bended, the plating layers may be released or a crack may be occurred. This released plating layer may interpose between the adjacent wiring layers and develop a short circuit in these wiring layers. Moreover, the missing of the plating layer causes the wiring layers themselves easily to be broken. Therefore, the reliability of the printed wiring board having the conventional fine wiring layers is low in the viewpoint of an electrical connection.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to obtain a printed wiring board in which a wiring layer can be formed to be as thin as possible and can correspond to the tendency of making this wiring layer finer in an affordable way and a method of manufacturing the printed wiring board.
In order to achieve the object, a printed wiring board according to a first aspect of the present invention comprises an insulating layer having a first surface and a second surface located on the opposite side of the first surface; a plurality of wiring layers which are formed so as to correspond to a predetermined circuit pattern and formed by etching metal foils laminated on the first surface and the second surface of the insulating layer, respectively; a via which is formed on the insulating layer and has one end opened on the first surface of the insulating layer and the other end closed by the wiring layer on the second surface of the insulating layer; a first plating layer which continuously covers the inner surface of the via and the wiring layer on the second surface exposed within the via and that portion of the wiring layer which is formed on the first surface and which faces one end of the via; and a second plating layer which is laminated on the first plating layer and electrically connects the wiring layer located on the first surface and the wiring layer located on the second layer by cooperating with this first plating layer.
Moreover, in order to achieve the object, a printed wiring board according to a second aspect of the present invention comprises a laminate which includes an insulating layer having a first surface and a second surface located on the opposite side of the first surface, and a plurality of wiring layers laminated on the first surface and the second surface of the insulating layer and inside of the insulating layer, these wiring layer being formed so as to correspond to a predetermined circuit pattern; a via which is formed on the laminate and has one end opened on the first surface of the insulating layer and the other end closed by the wiring layer inside of the insulating layer; a first plating layer which continuously covers the inner surface of the via and the wiring layer inside of the insulating layer exposed within the via and that portion of the wiring layer w
Kabushiki Kaisha Toshiba
Patel I B
Zarneke David A.
LandOfFree
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