Radio frequency module with thermally and electrically...

Details Radio frequency module with thermally and electrically... Radio frequency module with thermally and electrically...

1997-06-11

2001-10-09

Gaffin, Jeffrey (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S728000, C361S736000, C361S746000, C361S760000, C361S762000, C361S767000, C361S783000, C361S807000, C257S676000, C257S684000, C257S690000, C257S698000, C257S704000, C257S787000, C257S773000, C257S774000, C174S050510, C174S050510

Reexamination Certificate

active

06301122

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio frequency module operating at a frequency of several hundred MHz or higher and a method for fabricating the same. More particularly, the present invention relates to a radio frequency module including active elements (such as transmission power transistors) mounted on a printed circuit board and a method for fabricating the same.
2. Description of the Related Art
A typical “radio frequency module” implements a compact radio frequency circuit by mounting principally various chip components at a high density on a printed circuit board of a small size. Specifically, a radio frequency module includes various active elements such as transmission power transistors and various kinds of small-sized passive elements or chip components such as resistors, capacitors and inductors. Both the active elements and the passive elements are mounted on a printed circuit board on which transmission lines such as microstrip lines have been formed. A radio frequency module operates at a frequency of several hundred MHz or higher and is typically used as a transmission section for various kinds of mobile communication units such as transceivers, cellular phone units and the like.
A radio frequency module used as a transmission section generally implements a two-stage or three-stage radio frequency power amplifier circuit including a plurality of field effect transistors (hereinafter, simply referred to as “FETs”). The impedance of a radio frequency module viewed from an external circuit at the terminal thereof for inputting/outputting a radio frequency signal therethrough is adjusted to be 50 &OHgr; and a direct current bias circuit is incorporated therein.
A prior art metal base substrate for a radio frequency module is described, for example, in Japanese Laid-Open Patent Publication No. 3-272189. The metal base substrate described in this patent publication includes an insulating film, and a metal plate and a sheet of conductive metal foil which are adhered to both surfaces of the insulating film.
Also, a prior art radio frequency module is described, for example, in Japanese Laid-Open Patent Publication No. 5-95236.
FIG. 13
is a schematic cross-sectional view of the radio frequency module described in this patent publication. The radio frequency module shown in
FIG. 13
includes a circuit board
1310
and a semiconductor device
1320
which have been mounted on a radiator plate
1300
by means of soldering. The circuit board
1310
has a multi-layer structure of a metal film
1312
, a resin substrate
1314
and another metal film
1316
. A solder layer
1330
connects the circuit board
1310
and the semiconductor device
1320
to the radiator plate
1300
, respectively.
The semiconductor device
1320
includes: an FET chip
1322
; a package metal base
1323
; a ceramic frame
1324
; electrodes
1325
; a source wire
1326
; a gate wire
1327
; a drain wire
1328
; and lead terminals
1329
.
The heat generated from the FET chip
1322
is passed through the package metal base
1323
and the solder layer
1330
to be transmitted into the radiator plate
1300
.
In order to fabricate the radio frequency module shown in
FIG. 13
, the circuit board
1310
and the semiconductor device
1320
must be individually soldered to the radiator plate
1300
. Thus, the radio frequency module shown in
FIG. 13
has a problem in that the number of required process steps is increased. Also, the lead terminals
1329
must be connected to the circuit board
1310
of an individual module.
Furthermore, the radio frequency module shown in
FIG. 13
cannot be tested until the radiator plate
1300
has been mounted. This is because the characteristics of the FET chip
1322
in an operation state are required to be tested under the same conditions as the conditions where the radio frequency module is actually used or the state where the radiator plate
1300
has already been mounted. However, in order to mount the radiator plate
1300
onto the radio frequency module, the circuit board
1310
having a small area corresponding to an individual radio frequency module must be cut out from a circuit board having a larger area corresponding to a plurality of radio frequency modules. Consequently, a prior art radio frequency module cannot be tested before the circuit board
1310
for an individual radio frequency module is cut out from the larger sized circuit board. Thus, the radio frequency module can be tested only after the individual radio frequency module is completed. Therefore, in accordance with the conventional technologies, multiple radio frequency modules on an identical large-sized circuit board
1310
cannot be tested simultaneously.
As described above, since the conventional radio frequency module cannot reduce the number of necessary components and the number of necessary process steps, the reduction in size and cost of a single module and the automatic fabrication of the modules cannot be realized.
SUMMARY OF THE INVENTION
The radio frequency module of the present invention includes an insulating substrate having a first metal film on a first principal surface thereof and a second metal film on a second principal surface thereof opposed to the first principal surface and a semiconductor device. In the radio frequency module, the semiconductor device is thermally and electrically coupled to the second metal film, and a thickness of the second metal film is larger than that of the first metal film.
In one embodiment, the radio frequency module further includes an opening extending through the first metal film and the insulating substrate, and the semiconductor device is thermally and electrically coupled to the second metal film located inside the opening.
In another embodiment, the radio frequency module further includes a via hole for thermally and electrically coupling the first metal film to the second metal film, and the semiconductor device is thermally and electrically coupled to the second metal film through the via hole.
In still another embodiment, the thickness of the first metal film is from about 10 &mgr;m to about 100 &mgr;m, both inclusive, and the thickness of the second metal film is from about 100 &mgr;m to about 1000 &mgr;m, both inclusive.
In still another embodiment, the thickness of the first metal film is from about 30 &mgr;m to about 50 &mgr;m, both inclusive, and the thickness of the second metal film is from about 200 &mgr;m to about 300 &mgr;m, both inclusive.
In still another embodiment, the first metal film or the second metal film includes a multi-layer structure of copper
ickel/gold layers or a multi-layer structure of copper/titanium/gold layers. The copper
ickel/gold layers and the copper/titanium/gold layers are stacked such that distances from a center in a thickness direction of the second metal film to the copper
ickel/gold layers and the copper/titanium/gold layers increase in this order.
In still another embodiment, the semiconductor device is sealed inside a package.
In still another embodiment, the semiconductor device is a bare chip.
In still another embodiment, the semiconductor device is mounted on a metal block.
In still another embodiment, the semiconductor device is coupled to the second metal film thermally at a heat resistance of about 3° C./W or less and electrically at an electrical resistance of about 1 &OHgr; or less.
In still another embodiment, the second metal film is patterned.
In still another embodiment, at least a part of the patterned second metal film is electrically coupled to the first metal film through a via hole.
According to another aspect of the present invention, a method for fabricating a radio frequency module is provided. The method includes the steps of providing an opening through an insulating substrate and a first metal film, the insulating substrate having the first metal film formed on a first principal surface thereof and a second metal film formed on a second principal surface thereof opposed to the first principal surface, a thicknes

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