Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-04-25
2001-12-25
Lam, Cathy (Department: 1775)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S306300, C361S315000, C361S794000, C361S795000, C174S262000, C174S266000
Reexamination Certificate
active
06333857
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a core substrate, to a printed wiring board having a core substrate, and insulating resin layers and wiring layers laminated on opposite sides of the core substrate, and to a method of fabricating the core substrate. More particularly, the invention relates to a printed wiring board having a capacitor incorporated therein, a core substrate used therein, and a method of fabricating the core substrate.
2. Description of the Related Art
Conventionally, a decoupling capacitor is disposed between a ground line and a power supply line for an IC chip in order to eliminate noise. For example, a chip capacitor is mounted on either side of a printed wiring board.
FIG. 22
shows a printed wiring board
300
including a core substrate
310
, three insulating resin layers
320
,
340
, and
360
formed on the front side (the upper side in
FIG. 22
) of the core substrate
310
, three insulating resin layers
330
,
350
, and
370
formed on the back side (the lower side in
FIG. 22
) of the core substrate
310
, and wiring layers
315
,
325
,
345
,
335
, and
355
sandwiched between the core substrate
310
and the insulating resin layers and between the insulating resin layers. By means of solder SL, a chip capacitor CC is mounted on the wiring layer (pads)
355
located on a back side (the lower side in
FIG. 22
)
300
B of the printed wiring board
300
. Two electrodes CCA and CCB of the chip capacitor CC are connected to the wiring layer (pads)
345
located on a front side (the upper side in
FIG. 22
)
300
A of the printed wiring board
300
through through-hole conductors
316
and the wiring layers
315
,
325
,
335
, and
355
.
However, many manhours are required to mount such a chip capacitor on a printed wiring board and connect the same to the printed wiring board. Further, since the chip capacitor is disposed on the back side of the printed wiring board or around an IC chip, the distance between the IC chip and the chip capacitor becomes relatively large, permitting entry of noise into a circuit line extending therebetween.
In order to solve the above problem, a capacitor may be incorporated into a printed wiring board and in the vicinity of an IC chip. The capacitor may be formed within the printed wiring board while a portion of an insulating resin layer is used as a dielectric layer therefor.
When a capacitor including a thin dielectric layer sandwiched between electrode layers having a wide area is formed by an insulating resin layer and wiring layers (for example, the insulating resin layer
320
and the wiring layers
315
and
325
in the printed wiring board of FIG.
22
), the capacitor is likely to suffer a short circuit, among other problems, causing a significant decrease in the yield of printed wiring boards. When the capacitor is found to be defective, the insulating resin layers and wiring layers that constitute the capacitor must be disposed of together with the core substrate, and this represents a substantial loss.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a printed wiring board that has a built-in capacitor in the vicinity of an IC chip to be mounted thereon, that can be easily fabricated at high yield, and that can minimize loss due to occurrence of a defective capacitor in the fabrication process.
Another object of the present invention is to provide a core substrate for use in the printed wiring board.
Still another object of the present invention is to provide a method for fabricating the core substrate easily and at low cost.
To achieve the above objects, the present invention provides a printed wiring board comprising a core substrate, at least one insulating resin layer laminated on each of front and back surfaces on at least one side of the core substrate, and a wiring layer formed at least between the core substrate and the insulating resin layer or between the insulating resin layers. The core substrate comprises a plurality of composite dielectric layers each containing resin and a high-permittivity powder and a plurality of metal layers stacked alternately with the composite dielectric layers such that the metal layers are disposed between the composite dielectric layers, on a lower surface of the lowermost composite dielectric layer, and on an upper surface of the uppermost composite dielectric layer so as to provide a sandwich of the composite dielectric layers forming a laminated capacitor. The core substrate further comprises a plurality of through-holes conductors each of which is formed in a through-hole extending through or penetrating the plurality of composite dielectric layers and the plurality of the metal layers, and which extends between said front and back surfaces of the core substrate. The through-hole conductors include: a plurality of first through-hole conductors directly connected to first interior metal layers which comprise first alternate interior metal layers formed between the composite dielectric layers; a plurality of second through-hole conductors directly connected to second interior metal layers which comprise second alternate interior metal layers different from the first alternate interior metal layers and unconnected to the first through-hole conductors; and a plurality of third through-hole conductors unconnected to any of the interior metal layers.
According to the printed wiring board of the present invention, the core substrate includes a laminated capacitor formed of the composite dielectric layer and the metal layers. Thus, the capacitor having a large capacitance can be disposed in the vicinity of an electronic component, such as an IC chip, thereby effectively eliminating noise. Since the laminated capacitor is incorporated in the core substrate, the core substrate may be inspected for the characteristics of, and any defect (such as a short circuit) in, the laminated capacitor. Only those core substrates that have passed the inspection may be sent to a step of fabricating printed wiring boards; in other words, insulating resin layers and wiring layers may be formed on an accepted core substrate to thereby yield a printed wiring board. Thus, printed wiring boards can be fabricated at high yield. When the built-in capacitor is found defective due to, for example, a short circuit, only the bare core substrate is disposed of, before the insulating resin layers and wiring layers are formed thereon, thereby minimizing loss. Therefore, the corresponding printed wiring boards can be fabricated at low cost.
In addition, in order to permit access to the electric potentials of metal layers serving as electrodes of the laminated capacitor not only on the front surface of the core substrate but also on the back surface of the core substrate, through-hole conductors connected electrically to selected metal layers are formed in the core substrate. Specifically, the core substrate comprises first and second through-hole conductors which connect, to the front and back surfaces of the core substrate, the electric potentials of the metal layers other than metal layers located on the front and back surfaces of the core substrate (i.e., provide an electrical connection between interior metal layers formed between the composite dielectric layers). The core substrate further comprises third through-hole conductors which are not connected to the interior metal layers.
In the printed wiring board, since the three types of through-hole conductors extend between the front and back surfaces of the core substrate, a wiring layer formed on the back surface side of the core substrate can be easily connected, by means of the through-hole conductors, to a wiring layer formed on the front surface side of the core substrate. Accordingly, when the wiring layer formed on the back surface side of the core substrate is connected to another printed wiring board, such as a motherboard, and the wiring layer formed on the front surface side of the core substrate is connected to an electronic component
Kanbe Rokuro
Kimura Yukihiro
Ogawa Kouki
Lam Cathy
Larson & Taylor PLC
NGK Spark Plug Co. Ltd.
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