Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1998-06-01
2001-12-11
Gaffin, Jeffrey (Department: 2841)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S255000, C174S260000
Reexamination Certificate
active
06329610
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wiring board such as a printed wiring board, in particular, to a hybrid wiring board that is a combination of a rigid wiring substrate and a flexible wiring substrate.
In addition, the present invention relates to a flexible wiring substrate of which a wiring layer is disposed on insulation resin film, in particular, to a flexible wiring substrate laminated with a rigid wiring substrate.
Furthermore, the present invention relates to a semiconductor apparatus such as a semiconductor package of which a semiconductor device is mounted on a printed wiring board, in particular, to a semiconductor apparatus that mounts a semiconductor device with connection terminals disposed at a high mounting density.
Moreover, the present invention relates to a fabrication method of a printed wiring board, in particular, to a fabrication method of a hybrid wiring board that is a combination of a rigid wiring substrate and a flexible wiring substrate.
2. Description of the Related Art
The degree of integration of semiconductor devices is increasing year by year. Thus, the number of connection terminals (pads) for connecting a semiconductor device and an external circuit increases and the mounting density thereof becomes high. When the minimum machining size on a semiconductor device made of silicon or the like is around 0.2 &mgr;m, as many as 1000 connection terminals should be disposed for a semiconductor device in a square shape whose one side is 10 mm.
Moreover, in a semiconductor apparatus such as a semiconductor package of which such a semiconductor device is mounted on a wiring board, to improve the mounting density, there are strong needs for reducing the size and thickness thereof. In particular, for a portable information unit such as a note type PC (Personal Computer), a PDA, or a portable telephone unit, it is important to decrease the size and thickness of a semiconductor package.
To package a semiconductor device, it is necessary to mount a semiconductor device on a wiring board and connect terminals of the semiconductor device and the wiring board. However, to dispose around 1000 connection terminals around a semiconductor device in a square shape whose one side is around 10 mm, the mounting pitches of the connection terminals become as small as around 40 &mgr;m. To connect terminals disposed at fine pitches to terminals of a wiring board, high accuracy is required in forming a circuit pattern and aligning wires. However, conventional wire bonding technologies and TAB (Tape Automated Bonding) technologies cannot satisfy such requirements.
As a conventional terminal connecting method, connection terminals of a semiconductor device and connection terminals of a wiring board may be connected through a pillar made of a conductive substance such as solder. For example, when connection terminals of 32 lines×32 rows at pitches of 32 &mgr;m are disposed on a semiconductor device in a square shape whose one side is around 10 mm, the number of connection terminals amounts to as many as 1024.
Wires of a wiring board on which a semiconductor device is mounted are disposed at an L/S ratio (Line/Space, wiring width/wiring pitch) of as fine as around 50 &mgr;m/50 &mgr;m so as to connect the connection terminals of the semiconductor device and the external connection terminals of the semiconductor package.
As a wiring board for mounting a semiconductor device with connection terminals disposed at fine mounting pitches, for example a build-up board
900
a
shown in
FIG. 10
has been used.
FIG. 10
is a sectional view showing the structure of a build-up board. The build-up board is a wiring board that has a printed wiring substrate
901
, thin resin layers
902
, and conductor wiring patterns
903
. The printed wiring substrate
901
is a rigid board. The thin resin layers
902
are coated on both surfaces of the printed wiring substrate
901
. The conductor wiring patterns
903
are made of metal or the like and disposed on the resin layers
902
.
The printed wiring substrate
901
of the build-up board is referred to as core layer. The portions layered on both the surfaces of the core layer are referred to as build-up layers.
The insulation resin layers that structure the build-up layers are connected by a fine layer connecting means formed by photolithography technology or the like. A plurality of wiring layers are connected through the fine layer connecting means. In the example shown in
FIG. 10
, the layer connecting means of the build-up layers is accomplished by a photo via-hole
904
.
To connect the wiring layers on the build-up layers (disposed on both the surfaces of the core layer), for example a through-hole
905
may be formed. To allow a wiring substrate to be flat, a build-up board of which the through-hole is filled with resin is known.
In the technology at the time the present invention was filed, the minimum wiring width of the wiring layer
903
that structures the build-up layers is around 40 &mgr;m. The front surface of the insulation resin layer
902
is uneven due to a wiring pattern of a lower layer. Thus, it is very difficult to form a finer wiring pattern than the uneven surface.
The diameter of via-holes formed in the insulation resin layers
902
that structure the build-up layers is around 80 &mgr;m. To form finer via-holes, the thickness of the insulation resin layers
902
may be decreased. When the thickness of the insulation resin layers
902
is decreased, the influence of the uneven surface of the lower layer becomes strong. Thus, the wiring width should be increased.
In addition, the thickness of the build-up board is restricted. To prevent the build-up board from deforming and breaking in and after the fabrication process, the build-up board should have a thickness of at least 0.6 mm. The thickness of each of the insulation resin layers
902
is in the range from around 30 to 50 &mgr;m. The thickness of the conductor wiring layer
903
is in the range from around 10 to 20 &mgr;m. To dispose around 1000 connection terminals, three wiring layers are required. Thus, the thickness of the build-up board becomes as large as 0.84 to 1.02 mm.
In addition, the above-described semiconductor device is disposed on one surface of the build-up board. For example, solder balls are disposed in a two-dimensional grid shape on the other surface of the build-up board (the resultant package is referred to as BGA package).
To decrease the thickness of the BGA package, it is necessary to decrease the thickness of the above-described core layer or the build-up layers. However, when the thickness of the core layer is decreased, the reliability of the resultant semiconductor package deteriorates. In addition, it is difficult to form the build-up layers.
When the thickness of the build-up layers is decreased, it is difficult to form a wiring pattern at fine pitches. Thus, practically, it is very difficult to decrease the thickness of the build-up board to 0.8 mm or less.
To decrease the outer side of a semiconductor package, it is necessary to decrease the diameters and pitches of through-holes formed in a wiring board on which a semiconductor device is mounted.
Generally, as a material of an insulation resin layer that structures a core layer, a prepreg of which a glass cloth woven with glass fibers is impregnated with an insulation resin is used. In such a wiring board with a prepreg, the glass fibers and hardened insulation resin layer securely adhere.
However, when through-holes are formed in a wiring board by a drill or the like, the glass fibers are broken as well as the insulation resin. Moreover, in the vicinity of through-holes, the glass fibers separate from the insulation resin.
A plate layer is formed on the inner wall of a through-hole. When the plate layer is formed, if there is a portion of which the glass fibers separate from the insulation resin in the vicinity of the through-hole, a plate solution that contains metal ions permeates the portion. When the pitches of through-hole
Kojima Tomitsugu
Sato Yoshizumi
Takeda Go
Takubo Chiaki
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Gaffin Jeffrey
Kabushiki Kaisha Toshiba
Norris Jeremy
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