JPH0774023A - Integrated inductor and surface acoustic wave device using the same - Google Patents

Abstract

(57) [Abstract] [Purpose] The purpose of the present invention is to enable an integrated inductor with a high Q and a low loss, thereby making a modularized surface acoustic wave device compact and low loss. The purpose of this device is to reduce the size and weight of mobile communication devices and to improve their performance. [Construction] A spiral conductor pattern having a smooth surface is embedded in an insulating substrate made of a resin having a small dielectric constant and tan δ, and the conductor width becomes thicker as the conductor gets into the substrate. At the same time, the thickness of the conductor in the substrate normal direction was increased to be about 1/2 or more of the conductor width to provide an integrated inductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductor suitable for integration used in a high frequency electronic circuit or a high frequency electronic component, and particularly as a matching circuit element or a coupling element of a high frequency surface acoustic wave device, and a small surface acoustic wave device. The present invention relates to an inductor that can be reduced in size, reduced in surface mount, and reduced in loss.

[0002]

2. Description of the Related Art Conventionally, in order to integrate an inductor, a copper pattern spirally formed on a glass epoxy substrate or a silver-based or gold-based spirally formed on a ceramic substrate such as alumina, Either copper-based pattern has been used.

As such a technique, Japanese Patent Laid-Open No. 62-986 is known.
There is No. 05 publication.

[0004]

However, the above-mentioned conventional integrated inductor has the following problems. That is, the Q at a high frequency of several hundred MHz or more is low,
In other words, the electric resistance of the inductor at high frequencies is not sufficiently low, and when used in a high frequency surface acoustic wave device, the loss was increased.

In the above conventional technique, the surface of the substrate is roughened by unevenness of several μm to several tens of μm in order to secure the adhesion strength between the conductor pattern and the substrate. Not only is the surface roughened, but the opposite surface, the surface side, is also affected and roughened. As a result, the electric resistance is at least 30% at the surface portion within the skin depth within the skin depth from the surface where the current substantially flows at high frequency.
To about 60%. In addition, a gold thin film is formed on the surface of the conductor pattern for wire bonding to the conductor pattern. At that time, since a nickel film is formed to a thickness of several μm on the base of the gold thin film, a skin portion effective for high frequencies is formed. Of the nickel film is dominated by the large electric resistance of the nickel film, and further increases due to the roughening of the surface.

Due to these factors, in the conventional integrated inductor, the above-mentioned problem occurs even though the main portion of the conductor is made of a metal having a low resistance.

The object of the present invention is to solve the above problems.
(EN) It is possible to secure an adhesion strength between a conductor pattern and a substrate, sufficiently lower the electric resistance within a skin depth from a surface effective at high frequencies, and to enable an integrated inductor having a high Q and a low loss. As a result, the modularized surface acoustic wave device is downsized and has low loss, and the mobile communication device using the device is downsized and the performance is improved.

[0008]

In order to achieve the above object, in the present invention, a spiral conductor pattern is embedded in an insulating substrate with its surface being smooth, and only one main surface of the spiral is exposed. . Further, at that time, the conductor width is made thicker as it goes into the substrate, and the thickness of the conductor in the substrate normal direction is increased to be about the conductor width or more. As the insulator of the substrate, a resin in which a spiral thick conductor pattern is easily embedded, a resin having a small dielectric constant and a small tan δ is used.

[0009]

As described above, by increasing the conductor width as the conductor gets into the board, the spiral conductor becomes difficult to be detached from the board by an external force. In other words, the adhesion strength of the conductor pattern to the board is greatly increased. Increase. This allows
It is possible to avoid the roughening of the surface of the substrate, which is required to secure the adhesive strength in the conventional technique of simply forming the spiral conductor pattern on the substrate. In addition, this also makes it possible to avoid the roughening of the conductor surface, which is required when the spiral conductor pattern is simply embedded in the substrate. As a result, a spiral conductor pattern having a smooth surface can be formed, and the thickness can be increased to about the conductor width or more. That is, since the peripheral length in the cross section of the spiral conductor can be increased and the surface becomes smooth,
The electric resistance at high frequencies can be sufficiently reduced, and the Q value of the integrated inductor can be sufficiently increased.

As described above, since the surface of the conductor can be made smooth and the thickness can be increased to about the conductor width or more, the conductor width can be reduced while the high frequency electric resistance of the spiral conductor is kept low. It can be made thin, and as a result, the area occupied by the integrated inductor can be made small, that is, can be made small.

By using a resin as the substrate, the spiral conductor can be easily embedded, and by using a resin having a small dielectric constant and tan δ, the self-resonant frequency as an inductor can be sufficiently high and the loss can be reduced.
The Q at high frequency can be increased.

[0012]

1 is a schematic sectional view showing a preferred embodiment of an integrated inductor of the present invention, and FIG. 2 is a plan view of the embodiment shown in FIG.

In FIGS. 1 and 2, 1 is a conductor, one surface of which is substantially flush with the surface of the insulating substrate 2,
A rectangular spiral coil is formed. Also, FIG.
As shown in, the conductor 1 has a substantially rectangular cross section,
In most of the places, the width is so thick that it enters the substrate 2. Moreover, the surface of the conductor 1 is smooth.
Further, as shown in FIG. 2, bonding pads 3, 3'are provided on both ends of the spiral. In this embodiment, the outer diameter of the spiral is 1.4 mm, the conductor width w and the interval s are all 80 μm, the number of turns of the spiral is 1.5 times, the thickness of the conductor is 40 μm, and the material of the conductor is electroplated with copper. The substrate is a BT resin with good high frequency characteristics and contains glass fibers. The dielectric constant at 1 GHz is 3.45, tan δ = 0.0.
027 and FR4, which is a commonly used glass epoxy, have smaller permittivity and tan δ and better high frequency characteristics.

A method of manufacturing the integrated inductor of the above embodiment will be described with reference to the process flow chart of FIG. A metal plate a having a smooth surface is prepared, and a photoresist film b having a thickness of 40 μm or more is formed on one surface of the metal plate a, and a photomask, an ultraviolet light source,
Is used for exposure and development to remove the photoresist in a predetermined conductor pattern portion to expose the metal plate surface in that portion. At this time, the sidewalls of the photoresist pattern are inclined so that they are not overhanging or upright. afterwards,
The metal plate on which the photoresist pattern is formed is immersed in a copper plating bath, and electroplating is performed to form a copper conductor pattern 1 on the exposed portion of the metal plate to a thickness substantially equal to that of the photoresist b, and the photoresist is peeled off. At this time, a 40 μm thick copper conductor pattern 1 having an overhang on the side wall is formed on the metal plate. Then, on the side of the metal plate on which the copper conductor pattern 1 is formed, a semi-cured BT containing glass fiber
The resin is pressure-bonded and heat-cured. At this time, the copper conductor 1 is embedded in the BT resin substrate 2, and the conductor 1 becomes thicker as it goes into the substrate. Then, the metal plate is peeled off and removed to complete the spiral conductor pattern 1 embedded in the substrate 2 of BT resin. At this time,
Since the conductor 1 becomes thicker as it enters the substrate, the conductor 1 does not stick to the metal plate a and fall off the substrate 2 when the metal plate is peeled off. Therefore, the surface of the conductor 1 can be made smooth.

After this, the bonding pad portions 3, 3 '
Except for the above, the substrate 1 is covered with the plating resist 4, and only the bonding pads 3 and 3 ′ are plated with Ni and then with gold to complete the integrated inductor.

Table 1 shows the inductance value L, the high frequency resistance values R, and Q values of the integrated inductor of this embodiment produced by the above method shown in FIG. Table 1 also shows the values of L, R and Q in the conventional example having the same plane size for comparison.
In this conventional example, an alumina ceramic having a dielectric constant of 9.4 is used for the substrate 2 ', and the conductor pattern 1'is formed on the substrate by a so-called subtract method in the order of copper, Ni, and gold by electroless plating. After that, the one formed by removing the unnecessary portion by photoetching is used. The thickness of the conductor is 10 μm. FIG. 4 shows a cross-sectional view of the conductor portion in the conventional example. The surface of the alumina ceramic substrate has a roughened surface with a roughness of about 10 μm. Has become. This roughening is not only caused by the material itself, but also has the meaning of ensuring adhesive strength. Further, since the conductor pattern is produced by the subtract method, the conductor width becomes thin due to undercutting during the wet etching, and the reduction amount becomes approximately the conductor thickness or twice the conductor thickness. Therefore, and as the thickness of the conductor becomes thicker, the conductor is easily separated from the substrate. Therefore, the thickness of the conductor is suppressed to about 10 μm.

[0017]

[Table 1]

As shown in Table 1 above, L, R, and Q at a frequency of 1 GHz in this embodiment are L = 5.4n, respectively.
H, R = 0.25Ω, Q = 120, L = 6.
Compared with 2 nH, R = 1.14Ω, and Q = 31, the effect that the resistance R of the high frequency is small, that is, ¼ or less, and Q is increased to about 4 times is obtained. The influence of the bonding wire during the measurement is corrected. Such a large Q improving effect in the present embodiment makes the conductor surface sufficiently smooth,
Moreover, by increasing the thickness of the conductor, the cross-sectional area of the skin portion of the conductor (the area from the surface to the skin depth in the cross-sectional area of the conductor)
And the fact that a metal film having a large specific resistance, such as Ni, is not provided near the surface of the conductor.
δ is because a resin having a small value is used to avoid a decrease in the self-resonant frequency.

Further, the conductor surface is smoothed as described above,
Moreover, the reason why the conductor can be made thicker is that the conductor width is made thicker as it gets into the substrate and embedded in the substrate, so that the adhesion strength between the conductor and the substrate is enhanced.

In the above embodiment, the conductor is embedded in the substrate leaving one surface, but it may be partially embedded. Furthermore, in the above-described embodiment, as shown in FIG. 1, the width of the conductor 1 is thicker so that the conductor 1 is almost entirely inside the substrate. I just have to.

Although copper is used for the conductor in the above embodiment, the present invention is not limited to this, and gold or silver may be plated and used. If the conductor is gold, the price is a little high,
It is not necessary to wear Ni or gold on the bonding pad,
No plating resist is required.

Further, in the above embodiment, the conductor width and interval are set to 80 μm, but they can be set to 40 to 50 μm, and by increasing the number of spiral turns, the external dimension is 1 m.
An integrated inductor having an L value similar to that of the above embodiment and a Q value of about 100 can be realized at m or less.

FIG. 5 is a schematic perspective view showing an embodiment of a surface acoustic wave device (SAW device) using the integrated inductor according to the present invention. In this figure, a small-sized SAW demultiplexer used in a cellular radio terminal is configured, and a chip 1 is mounted by embedding various integrated inductors for matching for coupling between a chip 11 of a SAW filter on the transmission side and its element electrodes.
2, and a chip 14 in which various inductors for matching for coupling between the SAW chip 13 on the receiving side and its element electrodes are embedded and mounted is a lead-less chip of ceramic.
It is mounted on a carrier (LCC) type surface mount package (SMP) 15. The metal cap of the package is omitted in this figure. The short sides of chips 12 and 14 loaded with various inductors are 1.6 mm.
Since it is pressed down to about 1 mm, S of 800MHz band
Even with the AW duplexer, the outer dimensions of SMP are 13.6 mm x 6.6.
mm × 1.6 mm, occupied area 0.9 cm ² , volume 0.1
It is possible to maintain the advantages of miniaturization of about 1 / 2.5 in occupied area and about 1/5 in volume compared to a duplexer using a dielectric resonator of 5 cm ³ . In terms of weight, the weight can be reduced to 0.5 g, which is 1/5 or less of that of a duplexer using a dielectric resonator. Also,
Along with a design that minimizes the length of the bonding wire, the advantages of the high Q integrated inductor can be fully utilized and the loss of each of the transmitting and receiving filters can be suppressed to the minimum.

[0024]

According to the present invention, a spiral conductor pattern having a smooth and thick surface and a relatively narrow width can be formed without fear of peeling from the substrate.
Mass production of small integrated inductors. Therefore, the high-performance electronic circuit can be improved in performance and miniaturized. In particular, it becomes easy to improve the performance of the surface acoustic wave device, reduce its size and weight, and modularize it. As a result, the mobile wireless terminal can be made compact and lightweight by using the SAW duplexer module.

[Brief description of drawings]

1 is a cross-sectional view of an integrated inductor according to the present invention.

FIG. 2 is a plan view of an integrated inductor according to the present invention.

FIG. 3 is a process flow chart showing a method for manufacturing an integrated inductor according to the present invention.

FIG. 4 is a sectional view of a conductor portion of an integrated inductor according to a conventional example.

FIG. 5 is a schematic perspective view showing an embodiment of a surface acoustic wave device using an integrated inductor according to the present invention.

[Explanation of symbols]

1 ... Conductor, 2 ... Insulator substrate, 3, 3 '... Bonding pad, 4 ... Plating resist, 1' ... Conductor (conventional example), 2 '... Insulator substrate (conventional example), 11 ... Transmit side SAW filter Chips, 12 ... Chips embedded with various integrated inductors on the transmitting side, 13 ... Chips of SAW filter on the receiving side, 14 ... Chips embedded with various integrated inductors on the receiving side, 15 ... Surface mount package of LCC type , A ... Metal plate, b ... Photoresist film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiichi Ogawa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stock company Hitachi Ltd. AV equipment division

Claims (7)

[Claims] 1. An integrated circuit characterized in that a conductor inductor is embedded in a substrate made of an insulator, and the conductor inductor is thicker in at least a part of its cross section such that its width becomes closer to the inside of the insulator. Inductor. 2. The integrated inductor according to claim 1, wherein a conductor having a smooth surface is used for a main part. 3. The integrated inductor according to claim 2, wherein the thickness of the conductor is about ½ or more of the width. 4. A wire bonding metal film is added only to the bonding pad portion.
The integrated inductor according to 2 or 3. 5. The integrated inductor according to claim 1, wherein the conductor portion exposed from the substrate is covered with a resin film except for the bonding pad portion. 6. The integrated inductor according to claim 1, wherein a resin having a low dielectric constant and tan δ at a high frequency is mainly used as the substrate made of an insulating material. 7. A surface acoustic wave device using the integrated inductor according to claim 1, 2, 3, 4, 5 or 6 as a matching element or a coupling element.