A high-frequency package has: a resin substrate; a high-frequency device mounted on a side of a first surface of the resin substrate; a ground surface conductor of a ground potential formed on a second surface of the resin substrate on an opposite side to the first surface; a transmission line for a high-frequency signal formed in an inner layer of the resin substrate; and a ground via of a ground potential formed within the resin substrate. A through hole is formed in the ground surface conductor. The ground via is placed between the transmission line and the through hole.

FIELD

The present invention relates to a high-frequency package for accommodating a high-frequency device.

BACKGROUND

A high-frequency device that handles a high-frequency signal of a microwave band or a millimeter-wave band has been known. In a high-frequency package that accommodates such a high-frequency device, the high-frequency device is mounted on a dielectric substrate. In some cases, a transmission line for the high-frequency signal is provided in an inner layer of the dielectric substrate (see, for example, Patent Literature 1).

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

The inventor of the present application has recognized the following problem for the first time.

Let us consider a case where a “resin substrate” is used as a dielectric substrate on which a high-frequency device is mounted. During the process for manufacturing the resin substrate, moisture originating from cleaning liquid or the like intrudes into a core material or the like. The intruded moisture is confined within the resin substrate due to plating. After that, a reflow process causes gas to be generated within the resin substrate. At this time, if there is no escape for the gas, the gas expands within the resin substrate, which is likely to cause delamination.

In order to avoid such the delamination, it is considered to provide a large number of degassing holes on a ground surface of the resin substrate. In this case, however, a high-frequency signal of a microwave band or a millimeter-wave band originating from a transmission line in an inner layer of the resin substrate is likely to leak to the outside through the degassing holes. This causes deterioration in EMI (Electro-Magnetic Interference) characteristics.

An object of the present invention is to provide a technique that can prevent deterioration in EMI characteristics of a high-frequency package using a resin substrate.

Solution to Problem

In an aspect of the present invention, a high-frequency package has: a resin substrate; a high-frequency device mounted on a side of a first surface of the resin substrate; a ground surface conductor of a ground potential formed on a second surface of the resin substrate on an opposite side to the first surface; a transmission line for a high-frequency signal formed in an inner layer of the resin substrate; and a ground via of a ground potential formed within the resin substrate. A through hole is formed in the ground surface conductor. The ground via is placed between the transmission line and the through hole.

In another aspect of the present invention, a high-frequency package has: a resin substrate; a high-frequency device mounted on a side of a first surface of the resin substrate; a ground surface conductor of a ground potential formed on a second surface of the resin substrate on an opposite side to the first surface; and a transmission line for a high-frequency signal formed in an inner layer of the resin substrate. A through hole is formed in the ground surface conductor. A diameter of the through hole is less than half of a wavelength of the high-frequency signal.

Advantageous Effects of Invention

According to the present invention, it is possible to prevent deterioration in EMI characteristics of a high-frequency package using a resin substrate.

DESCRIPTION OF EMBODIMENTS

A high-frequency package according to an embodiment of the present invention will be described with reference to the accompanying drawings.

Embodiment

FIG. 1is a top view of a resin substrate of a high-frequency package according to the present embodiment.FIG. 2is a cross-sectional view of the high-frequency package according to the present embodiment, and illustrates a cross-sectional structure along a line A-A′ inFIG. 1. It should be noted that inFIG. 1, some components formed in an inner layer of the resin substrate also are illustrated by dashed lines in order to facilitate understanding.

The high-frequency package according to the present embodiment accommodates a high-frequency device1that handles a high-frequency signal of a microwave band or a millimeter-wave band. For example, the high-frequency device1is exemplified by an MMIC (Monolithic Microwave Integrated Circuit) chip.

In the high-frequency package according to the present embodiment, two substrates facing each other are used. More specifically, as illustrated inFIG. 2, a mother substrate10on a lower side and a resin substrate20on an upper side are arranged to face each other. Further, inter-substrate connection conductors15connecting the mother substrate10and the resin substrate20are so arranged as to be sandwiched between the mother substrate10and the resin substrate20. The high-frequency device1is placed in a space surrounded by the mother substrate10, the resin substrate20, and the inter-substrate connection conductors15. More specifically, the high-frequency device1is mounted on the resin substrate20.

The resin substrate20has a first surface21and a second surface22. The first surface21is a surface (a device surface) on which side the high-frequency device1is mounted and that faces the mother substrate10. The second substrate22is a surface on an opposite side to to the first surface21, and is used for forming a ground surface as will be described later.

The high-frequency device1is mounted on the side of the first surface21of the resin substrate20. More specifically, a surface-layer transmission line30and a ground wiring (not illustrated) are formed on the first surface21of the resin substrate20. The high-frequency device1is flip-chip connected to the surface-layer transmission line30and the ground wire through bumps31.

On the other hand, a ground surface conductor40is formed on the second surface22of the resin substrate20. A potential of the ground surface conductor40is a ground potential. By this ground surface conductor40, a ground surface is formed on the side of the second surface22of the resin substrate20.

In an inner layer of the resin substrate20, an inner-layer transmission line50as a transmission line for the high-frequency signal is formed. The inner-layer transmission line50is connected to the above-mentioned surface-layer transmission line30through a via51. For example, the inner-layer transmission line50constitutes a tri-plate line. In this case, the above-mentioned ground surface conductor40on the second surface22also is a constituent element of the tri-plate line.

Furthermore, an inner-layer ground conductor60also is formed in an inner layer of the resin substrate20. A potential of the inner-layer ground conductor60is the ground potential.

In the case where the resin substrate20is used, a reflow process causes gas to be generated within the resin substrate20, as described above. At this time, if there is no escape for the gas, the gas expands within the resin substrate20, which is likely to cause delamination. According to the present embodiment, in order to avoid such the delamination, a large number of through holes70for degassing are formed in the ground surface conductor40on the second surface22(seeFIG. 1). However, the high-frequency signal of a microwave band or a millimeter-wave band originating from the inner-layer transmission line50is likely to leak to the outside through the through holes70. This causes deterioration in EMI characteristics.

Therefore, according to the present embodiment, a diameter D of the through hole70is designed to be less than half of a wavelength λ of the high-frequency signal (D<λ/2). By decreasing the diameter of the through hole70in this manner, a cutoff frequency regarding the through hole70becomes equal to or higher than the frequency band used by the high-frequency device1. As a result, leakage of the high-frequency signal from the through holes70is reduced.

Furthermore, according to the present embodiment, a ground via80formed within the resin substrate20is effectively utilized. A potential of the ground via80is the ground potential. For example, the ground via80is so formed within the resin substrate20as to connect between the ground surface conductor40and the inner-layer ground conductor60. As illustrated inFIGS. 1 and 2, such the ground via80is placed between the inner-layer transmission line50and the through hole70. That is, the ground via80of the ground potential is placed on the leakage path from the inner-layer transmission line50to the through hole70. As a result of shielding effect by the ground via80, the leakage of the high-frequency signal from the through hole70is reduced.

It is preferable that a large number of ground vias80are placed along the inner-layer transmission line50, as illustrated inFIG. 1. It is further preferable that a large number of ground vias80are so placed as to surround the inner-layer transmission line50. Due to these configurations, the shielding effect by the ground vias80becomes prominent, and thus the leakage of the high-frequency signal from the through holes70is greatly reduced.

According to the present embodiment, as described above, it is possible to prevent the delamination and to prevent deterioration in the EMI characteristics, even in the case where the resin substrate20is used.

The embodiment of the present invention has been described above with reference to the accompanying drawings. Note that the present invention is not limited to the above-described embodiment and can be modified as appropriate by persons skilled in the art without departing from the scope of the invention.

REFERENCE SIGNS LIST