Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-07-30
2004-10-26
Pert, Evan (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S261000, C174S262000, C361S760000, C361S761000, C361S763000, C029S832000
Reexamination Certificate
active
06809268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printed wiring substrate having electronic components embedded in a core substrate, and to a method for manufacturing the same.
2. Description of the Related Art
In response to recent requirements for high densification and high performance of a printed wiring substrate, a printed wiring substrate having electronic components embedded in a core substrate has been proposed.
For example, a printed wiring substrate
40
shown in
FIG. 6
is configured such that dielectric layers
43
are formed on the corresponding front and back surfaces of a dielectric layer
41
via unillustrated wiring layers. An electronic component
45
is mounted on the first main surface of the printed wiring substrate
40
. By means of a prepreg adhesive layer
47
, an electronic component
44
is embedded in a through-hole
42
formed in the dielectric layer
41
, the dielectric layer
41
being located at the center of the printed wiring substrate
40
in the thickness direction, and chip capacitors (electronic components)
46
are embedded in corresponding recesses
42
a
formed in the dielectric layer
41
and extending from the interior of the dielectric layer
41
to the front surface of the dielectric layer
41
.
3. Problems Solved by the Invention
In the printed wiring substrate
40
, the chip capacitors
46
are embedded in the corresponding recesses
42
a
by the thin prepreg adhesive layer
47
. Thus, a crack is likely to be generated in the prepreg adhesive layer
47
in the vicinity of an electrode of the chip capacitor
46
, which extends through the prepreg adhesive layer
47
. Such a crack impairs dielectric capability and hermetic capability in a region peripheral to the crack, and the characteristics of the chip capacitor
46
may become unstable.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to solve the above-mentioned problems of a conventional printed wiring substrate and to provide a printed wiring substrate having an electronic component embedded in a core substrate in a condition unlikely to generate cracks, as well as to provide a method for manufacturing the same.
To achieve the above object, the present inventors investigated the addition of an inorganic filler to a resin which is used to embed an electronic component, as well the particle size of the organic filler relative to an electrode of the electronic component, to thereby achieve the present invention.
Specifically, in a first embodiment, the printed wiring substrate of the present invention comprises a core substrate having a front surface and a back surface; and an electronic component embedded via a resin in a through-hole extending through the core substrate between the front surface and the back surface of the core substrate. The printed wiring substrate is characterized in that the electronic component has an electrode projecting from at least either an upper end or a lower end thereof and the resin contains an inorganic filler.
In a second embodiment, the printed wiring substrate of the present invention comprises a core substrate having a front surface and a back surface; and an electronic component embedded via a resin in a recess formed in the core substrate and extending from interior of the core substrate to the front surface or the back surface of the core substrate. The printed wiring substrate is characterized in that the electronic component has an electrode projecting from at least either an upper end or a lower end thereof and the resin contains an inorganic filler.
According to the present invention, the inorganic filler reinforces the resin and lowers the coefficient of thermal expansion of the resin. Thus, no cracks are generated in the resin used to embed an electronic component. Particularly, cracking or separation is unlikely to occur at a thin resin portion adjacent to the upper or lower end of an electronic component from which an electrode projects. Thus, an electronic component can be embedded in a through-hole or a recess formed in the core substrate such that good dielectric performance and good hermetic performance are maintained. Accordingly, the electronic component can reliably function as expected, and electrical continuity can be stably established via the electrode between the electronic component and a wiring layer formed in the printed wiring substrate.
In a third embodiment, the printed wiring substrate of the present invention comprises a core substrate having a front surface and a back surface; and an electronic component embedded in the core substrate. The printed wiring substrate is characterized in that the electronic component has an electrode projecting from at least either an upper end or a lower end thereof and the core substrate contains an inorganic filler. Since the core substrate, in which an electronic component is embedded, contains a reinforcing inorganic filler, no cracks are generated in a portion of the core substrate around the electronic component. Particularly, cracking or separation becomes unlikely to occur at a thin portion of the core substrate adjacent the upper or lower end of the electronic component from which the electrode projects. Thus, the electronic component can be embedded in the core substrate such that good dielectric performance and good hermetic performance are maintained. Accordingly, the electronic component can reliably function as expected, and electrical continuity can be stably established via the electrode between the electronic component and a wiring layer formed in the printed wiring substrate.
Examples of the above-mentioned electronic component include passive components, such as capacitors, inductors, filters, and resistors; active components, such as low noise amplifiers (LNAs), transistors, semiconductor devices, and FETs; as well as SAW filters, LC filters, antenna switch modules, couplers, and diplexers. Also included are these electronic components in the form of chips, and electronic component units each composed of a plurality of these electronic components in the form of chips. Among these electronic components, electronic components of different types may be embedded in the same through-hole or recess.
Examples of the inorganic filler include crystalline silica, fused silica, alumina, and silicon nitride. However, the present invention is not limited thereto. The inorganic filler is generally added in an amount of 35-65 vol. %, preferably from 40 to 60 vol. %, and more preferably from 40 to 50 vol. %. These amounts are for the content of the inorganic filler in both the resin and core substrate.
Through addition of the above-mentioned inorganic filler to the resin, the resin can assume a coefficient of thermal expansion of not greater than 40 ppm/° C. (zero is not included), preferably not greater than 30 ppm/° C. (zero is not included), more preferably not greater than 25 ppm/° C. (zero is not included), further preferably not greater than 20 ppm/° C. (zero is not included). Thus, stress concentration derived from the difference in coefficient of thermal expansion between the resin and an embedded electronic component can be reduced. In the above ranges of coefficient of thermal expansion, the lower limit is preferably not less than 10 ppm/° C.
In yet a fourth embodiment, the present invention provides a printed wiring substrate wherein the particle size of the inorganic filler is not greater than one-half the height of the electrode (zero is not included).
Employing the above mentioned particle size reinforces a thin resin portion or a thin portion of the core substrate adjacent to the upper or lower end of an electronic component from which an electrode projects, thereby preventing cracking or separation of the thin portion which would otherwise result from thermal expansion or contraction. Usually, an inorganic filler is unlikely to reach a thin portion of resin or core substrate adjacent to the upper or lower end of an electronic component from which an electrode projects. However, according to t
Hayashi Teruhisa
Hotta Yasutake
Ogawa Kouki
NGK Spark Plug Co. Ltd.
Patel I B
Pert Evan
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