Radio frequency semiconductor device package and method for manufacturing same, and radio frequency semiconductor device

A radio frequency semiconductor device package includes a metal base plate, a first metal wall, a second metal wall, and feed-through parts. The first metal wall is provided with first and second openings and connected onto the metal base plate. The openings are set back from a lower surface side and do not reach an upper surface. The second metal wall is connected to the upper surface of the first metal wall. Thickness of the second metal wall is larger than thickness of the first metal wall. The feed-through parts include insulators and line patterns insulated from the first and second metal walls and are joined to inner walls of the openings and the metal base plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No.2014-049335, filed on Mar. 12, 2014; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally a radio frequency semiconductor device package and a method for manufacturing same, and a radio frequency semiconductor device.

BACKGROUND

Radio frequency semiconductor devices operated at 1 GHz or more are required to have high reliability while keeping their radio frequency characteristics.

The radio frequency characteristics can be kept at high level by reducing parasitic capacitance in the input line pattern and the output line pattern. However, the metal wall constituting the radio frequency semiconductor device package around the input line pattern and the output line pattern needs to be thinned in order to reduce the parasitic capacitance of the input line pattern and the output line pattern.

On the other hand, if the metal wall constituting the radio frequency semiconductor device package is thinned, a leakage path is likely to occur between the metal wall and the lid part soldered to the metal wall upper surface. Furthermore, the workability for soldering the lid part to the metal wall upper surface is deteriorated. As a result, a leakage path is likely to occur between the metal wall and the lid part. In order to improve airtightness and workability, the metal wall of the radio frequency semiconductor device package needs to be thickened.

DETAILED DESCRIPTION

In general, according to one embodiment, a radio frequency semiconductor device package includes a metal base plate, a first metal wall, a second metal wall, a first feed-through part and a second feed-through part. The first metal wall is provided with first and second openings and connected onto the metal base plate. The first and second openings are set back from a lower surface side of the firs metal wall and do not reach an upper surface of the first metal wall. The second metal wall is connected to the upper surface of the first metal wall. The second metal wall is thicker than the first metal wall. The first feed-through part includes a first insulator and a first line pattern insulated from the first and second metal walls and is joined to an inner wall of the first opening and the metal base plate. The second feed-through part includes a second insulator and a second line pattern insulated form the first and second metal walls and is joined to an inner wall of the second opening and the metal base plate.

FIG. 1Ais a schematic perspective view of a radio frequency semiconductor device package according to a first embodiment.FIG. 1Bis a schematic perspective view describing the step of forming a metal wall among the members thereof.

The radio frequency semiconductor device package5includes a metal base plate30, a first metal wall10, a second metal wall20, a first feed-through part50and a second feed-through part50. Radio frequency can include microwave frequency in this specification.

The first metal wall10includes first and second openings10a.The first metal wall10is joined onto the metal base plate30. The first metal wall10has a uniform thickness T1. The first metal wall10is shaped like a ring. The openings10aare set back from the lower surface10bof the first metal wall10and do not reach the upper surface10c.

The second metal wall20is joined to the upper surface10cof the first metal wall10. The second metal wall20has a uniform thickness T2thicker than the thickness T1of the first metal wall10. The second metal wall20is shaped like a ring. The first and second metal walls10,20can be made of a conductive metal such as Fe—Ni—Co, copper, aluminum, molybdenum, copper-tungsten alloy, copper-molybdenum laminate, and copper-molybdenum alloy.

The metal base plate30can be made of a conductive metal such as copper, copper-tungsten alloy, molybdenum and copper-molybdenum alloy. Furthermore, the surface of the metal base plate30may be a plating layer of e.g. gold, nickel, silver, silver-platinum alloy, or silver-palladium alloy.

The feed-through part50includes an insulator layer made of e.g. ceramic. The feed-through part50is joined to the inner wall of the opening10aand the metal base plate30. The feed-through part50includes a line pattern on the surface of the insulator layer.

The first metal wall10, the second metal wall20, and the feed-through part50are stacked on the metal base plate30and joined together to constitute the structure ofFIG. 1A. The radio frequency semiconductor device package5can further include a lid part40. The lid part40can be a metal plate or a ceramic plate. In the case of the metal plate, the lid part40can be made of a conductive metal such as Fe—Ni—Co, copper, molybdenum and copper-molybdenum alloy. In the case of the ceramic plate, the lid part40can be made of e.g. alumina or aluminum nitride.

FIG. 2is a schematic perspective view of the feed-through part.

The feed-through part50includes an insulator52, and a line pattern54. The insulator52includes a lower insulator layer52aand an upper insulator layer52b.The upper insulator layer52bis provided on the upper surface of the lower insulator layer52aon which the line pattern54is provided. The lower insulator layer52aand the upper insulator layer52bare made of e.g. ceramic. The lower insulator layer52aand the upper insulator layer52bsandwiches a conductive region (such as a conductive film or paste) constituting the line pattern. The lower insulator layer52aand the upper insulator layer52bcan be formed by e.g. a firing process.

The material of the ceramic can be e.g. alumina or aluminum nitride.

The line pattern54exposed at the surface can be provided with e.g. a plating layer of e.g. gold, nickel, silver, silver-platinum alloy, or silver-palladium alloy. A conductive region made of e.g. a conductive film may be provided on e.g. the side surface52c,the bottom surface52e,and the upper surface52fof the feed-through part50. This facilitates joining to the metal base plate30and the first metal wall10.

FIG. 3is a radio frequency equivalent circuit diagram of the feed-through part.

Parasitic capacitance C1occurs between the line pattern54and grounded parts which are the metal base plate30or the metal wall10across the conductive region constituting the line pattern54. The parasitic capacitance C1increases with the increase of the thickness of the metal wall.

The radio frequency semiconductor element installed in the package5is connected to e.g. an input-side line pattern50or output-side line pattern50through an input circuit (not shown) or output circuit (not shown). In this case, the parasitic capacitance C1is added in each case.

FIG. 4Ais a schematic front view describing the step of forming a metal wall.FIG. 4Bis a schematic sectional view describing the step of forming a metal wall.FIG. 4Cis a schematic plan view of the first metal wall.FIG. 4Dis a schematic plan view of the second metal wall.

Here,FIG. 4Bis a schematic sectional view taken along line A-A. First, a first metal wall10shaped like a ring is cut out from a first metal pipe having a uniform thickness T1. Furthermore, an opening10ais formed. The opening10ais set back from the lower surface10bof the first metal wall10and does not reach the upper surface10c.

Next, a second metal wall20shaped like a ring is cut out from a second metal pipe having a uniform thickness T2which is thicker than the thickness T1of the first metal wall10. A lid part40is joined after a radio frequency semiconductor element is bonded to the inside thereof and subjected to e.g. wire bonding.

On the other hand, as shown inFIG. 2, a feed-through part50including a line pattern54is formed. Here, the order of the step of cutting out a metal wall from a metal pipe and the step of forming a feed-through part50may be arbitrary.

The feed-through part50is fitted in the opening10a.Furthermore, the metal base plate30is joined to the lower surface10bof the first metal wall10. The upper surface10cof the first metal wall10is joined to the lower surface20aof the second metal wall20. The metal base plate30is joined to the bottom surface52eof the feed-through part50. The upper surface52fand the side surface52cof the feed-through part50are joined to the inner wall10dof the opening10a.This joining step can be performed by stacking these members in a die and using e.g. a brazing material such as silver brazing alloy.

FIG. 5Ais a schematic perspective view of a radio frequency semiconductor device package according to a comparative example.FIG. 5Bis a schematic perspective view describing the step of forming a metal wall among the members thereof.

A lid part140is joined after a radio frequency semiconductor element is bonded to the inside thereof and subjected to e.g. wire bonding. The comparative example includes only one metal wall110.

The metal wall110near the opening110ain which the feed-through part150is to be fitted is shaved more thinly than the other part to suppress the occurrence of parasitic capacitance.

FIG. 6Ais a schematic front view describing the step of forming a metal wall of the comparative example.FIG. 6Bis a schematic sectional view describing the forming step.FIG. 6Cis a schematic plan view of the metal wall.

The lid part is joined by e.g. AuSb solder. Here,FIG. 6Bis a schematic sectional view taken along line A-A. If the thickness TT3of the region near the opening110aformed by shaving the metal wall110is so thin, the solder material or the like for joining the lid part to the metal wall110may trickle downward. Furthermore, airtight sealing may be difficult. In the comparative example, the thickness TT3of the shaved region is set to 0.7 mm or more. Because the thickness TT3of the cut region cannot be set to less than 0.7 mm, the parasitic capacitance of the line pattern154increases. Thus, the impedance of the line pattern decreases with the increase of frequency. Accordingly, for instance, impedance matching is difficult at a frequency higher than 5 GHz. This degrades the radio frequency characteristics.

In contrast, in the radio frequency semiconductor device package according to the first embodiment, the thickness of the metal wall around the line pattern54can be thinner than 0.7 mm. Thus, the parasitic capacitance C1can be reduced. This can suppress the decrease of the impedance of the line pattern54. Thus, the degradation of radio frequency characteristics can be suppressed even at a frequency of 5 GHz or more. Furthermore, the lid part40can be reliably jointed with e.g. a solder material to the upper surface of the second metal wall20having a large thickness T2. As a result, airtightness is achieved. This can improve reliability.

The first and second metal walls10,20can be cut out from a metal pipe having a simple shape. This enables a radio frequency semiconductor device package superior in volume productivity. Thus, the cost of the radio frequency semiconductor device can be reduced.

FIG. 7Ais a schematic perspective view of a radio frequency semiconductor device package according to a variation of the first embodiment.FIG. 7Bis a schematic perspective view describing the step of forming a metal wall among the members thereof.

FIG. 8Ais a schematic front view describing the step of forming a metal wall of the variation.FIG. 8Bis a schematic sectional view describing the forming step.FIG. 8Cis a schematic plan view of the first metal wall.FIG. 8Dis a schematic plan view of the second metal wall.

The first metal wall210near the opening210ain which the feed-through part250is to be fitted is shaved to a thickness T4thinner than the other part. Thus, the thickness T4is made comparable to the thickness in the first embodiment. The second metal wall220stacked thereon has a thickness (T2) at which a leakage path is less likely to occur when the lid part240is soldered.

FIG. 9is a schematic plan view of the inside of the radio frequency semiconductor device based on the radio frequency semiconductor device package according to the first embodiment (the lid part being omitted).

The radio frequency semiconductor device includes a package5and a radio frequency semiconductor element60. The radio frequency semiconductor element60can be e.g. a field effect transistor, including HEMT (high electron mobility transistor), made of e.g. AlGaAs/GaAs or InAlGaN/GaN. The radio frequency semiconductor device can further include an input circuit62and an output circuit64.

The line pattern54of the feed-through part50constitutes micro-strip line structure. On the other hand, the first and second metal walls10,20are fallen to the ground potential. Thus, the line pattern54of the feed-through part50is surrounded with the first and second metal walls10,20and constitutes a strip line structure. The impedance of the strip line is lower than the impedance of the microstrip line. The impedance of the line pattern54surrounded with the first and the second metal walls10,20is smaller than the impedance of the other parts of the line pattern54. This discontinuity of the impedance of the line pattern54can cause the degradation of radio frequency characteristics even at 5 GHz or more.

In the radio frequency semiconductor device of this embodiment, the thickness T1of the first metal wall10is reduced. Thus, the length of the line pattern54surrounded with the first and the second metal walls10,20can be decreased. Accordingly, the parasitic capacitance C1of the line pattern54is reduced. This can suppress the degradation of radio frequency characteristics even at 5 GHz or more. Such radio frequency semiconductor devices can be used for radar devices and microwave amplifiers.