Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-12-14
2001-04-10
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S210000, C174S250000, C174S258000, C174S262000
Reexamination Certificate
active
06214445
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printed wiring board having a core substrate, and insulating resin layers and wiring layers laminated on opposite sides of the core substrate. More particularly, the invention relates to a printed wiring board having a capacitor incorporated therein.
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. 17
shows a printed wiring board
300
including a core substrate
310
, three insulating resin layers
320
,
340
, and
360
formed on the front side (upper side in
FIG. 17
) of the core substrate
310
, three insulating resin layers
330
,
350
, and
370
formed on the back side (lower side in
FIG. 17
) 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 (lower side in
FIG. 17
)
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 (upper side in
FIG. 17
)
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.
17
), 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 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 comprising a composite dielectric layer that contains resin and a high-permittivity powder; and a plurality of metal layers disposed to sandwich the composite dielectric layer therebetween to thereby form a laminated capacitor.
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.
Preferably, in order to permit access, on a surface of the core substrate, to an electrical potential of metal layers serving as electrodes of the laminated capacitor, a through-hole conductor connected electrically to selected metal layers is formed in the core substrate. In other words, the through-hole conductor is preferably electrically connected to predetermined ones of the above-mentioned plurality of metal layers other than a metal layer located on the surface of the core substrate to thereby permit access, on the surface of the core substrate, to an electrical potential of the predetermined interior metal layers. A manner of connecting the through-hole conductor and the predetermined metal layers may be determined according to other circuit lines formed on the printed wiring board such as signal circuit lines and the required type and number of power supply and ground lines.
Circuit lines extending from the metal layers of the laminated capacitor to the surface of the printed wiring board on which electronic components are mounted may include a stacked via. The reason for this is that the shorter and the thicker the circuit lines extending between an electronic component, such as an IC chip, and the electrodes (metal layers) of the capacitor, the lower the inductance of the circuit lines, thereby suppressing noise entry into the lines.
The resin to be contained in the composite dielectric layer may be selected in view of permittivity, heat resistance, and other properties. Examples of usable resins include epoxy resin, polyimide resin and BT resin. The high-permittivity powder to be contained in the composite dielectric layer may be of a substance having high permittivity; for example, a high-permittivity ceramic, such as BaTiO
3
, PbTiO
3
, PbZrO
3
, Pb(Ti,Zr)O
3
(so-called PZT), Pb(Mn,Nb)O
3
, SrTiO
3
, CaTiO
3
, or MgTiO
3
. Further, the addition of a metal powder of, for example, Ag, Au, Cu, Ag—Pd, Ni, W, or Mo, may increase the permittivity of the composite dielectric layer.
The present invention further provides a core substrate which is used to fabricate a printed wiring board through lamination of one or more insulating resin layers and wiring layers on at least one side of the core substrate. The core substrate comprises at least one composite dielectric layer that contains resin and high-permittivity powder; and a plurality of metal layers disposed to sandwich the composite dielectric layer therebetween to thereby form a laminated capacitor.
A capacitor is likely to suffer a defect, such as a short circuit. According to the present invention, the capacitor is incorporated in the core substrate, thereby enabling the laminated capacitor to be inspected for capacitance and any defect, such as a short circuit, upon completion of the core substrate. Therefore, only those core substrates that conform to pre
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