Semiconductor device and method of manufacturing the same

A semiconductor device 1 has a metallic base substrate 2 for heat-dissipating, a wiring board 3, a MOSFET 4 as a semiconductor element, externally leading terminals 5A, 5B, 5C, a casing 6 formed of a synthetic resin, a fixing resin 7, and a gel-like resin layer 8. On the metallic base substrate 2, the casing 6 is disposed to surround one ends of the externally leading terminals 5A, 5B, 5C and the MOSFET 4. The other ends of the externally leading terminals 5A, 5B, 5C are externally protruded from the casing 6, and terminal body portions 51A, 51B, 51C for coupling them are inserted in through hole portions 61A, 61B, 61c of the casing 6. The terminal body portions 51A, 51B, 51C and the through hole portions 61A, 61B, 61c are fixed with the fixing resin 7, and the gel-like resin layer 8 is formed at the lower part of the casing 6. A space 9 is formed between the gel-like resin layer 8 and the casing 6.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-218184, filed on Aug. 24, 2007; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device provided with a power semiconductor element and its production method.

2. Description of the Related Art

For example, a semiconductor device having a power semiconductor element such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is known to have a structure that a wiring board on which a semiconductor element is mounted is fixed to a metallic base substrate for heat-dissipating, and the periphery of the semiconductor element is covered with a frame. A gel-like resin layer is formed on a lower area within the frame, and a sealing resin layer is formed on the gel-like resin layer. One end of an externally leading terminal is connected to the wiring board, and the other end of the terminal is externally protruded through the gel-like resin layer and the sealing resin layer.

But, such a semiconductor device has a tendency that the gel-like resin layer charged into the frame is expanded with heat generated from the semiconductor element. With the expansion of the gel-like resin layer, a force of pulling upward is applied to the externally leading terminal, and a crack is easily produced in a joint portion for joining the wiring board and the externally leading terminal.

There is proposed a structure that a space is formed above the gel-like resin layer (e.g., JP-A 6-89946(KOKAI)). According to this structure, when the gel-like resin layer is thermally expanded, the expansion can be absorbed by the space, and a tensile stress applied to the externally leading terminal can be eased.

But, when the device is used with a bus bar connected to an end of the externally leading terminal which is externally protruded, vibrations transmitted from the bus bar to the externally leading terminal have a tendency to cause a crack in the joint between the wiring board and the externally leading terminal, or decreases a joint strength. As a result, the externally leading terminal is easily peeled from the wiring board, and the electrical connection between the externally leading terminal and the wiring board is degraded, resulting that the semiconductor device malfunctions.

SUMMARY OF THE INVENTION

A semiconductor device according to an aspect of the present invention comprises a metallic base substrate; a wiring board arranged on the metallic base substrate; a semiconductor element arranged on the wiring board; externally leading terminals having a first end which is arranged on the wiring board and electrically connected to the semiconductor element, a second end which is arranged outside of the wiring board, and a main body portion which couples/connects the first end and the second end; a housing which has a through portion, through which the main body portion of the externally leading terminal is inserted, and is disposed on the metallic base substrate to cover the first end of the externally leading terminal and the semiconductor element; a fixing resin for fixing the main body portion of the externally leading terminal to the through portion of the housing; and a gel-like resin layer which is formed within the housing to cover the first end of the externally leading terminal and the semiconductor element and to have a space between the gel-like resin layer and the housing.

A method of manufacturing a semiconductor device according to an aspect of the present invention comprises arranging a first end of externally leading terminal having the first end, second end and main body portion for coupling/connecting these ends, and a semiconductor element on a first main surface of a wiring board; arranging a metallic base substrate on a second main surface of the wiring board; inserting the main body portion of the externally leading terminal a through portion of a housing, arranging the housing to surround the first end of the externally leading terminal and the semiconductor element, and fixing the housing to the metallic base substrate; forming a gel-like resin layer within the housing to cover the first end of the externally leading terminal and the semiconductor element, and forming a space between the gel-like resin layer and the housing; and fixing the main body portion of the externally leading terminal to the through portion of the housing with a fixing resin.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments for implementing the present invention will be described. Note that the embodiments will be explained in the following description with reference to the drawings, which are presented for purpose of understanding but not intended to limit the present invention.

FIG. 1is a cross-sectional view schematically showing a structure of a semiconductor device according to a first embodiment of the present invention.FIG. 2is an exploded perspective view showing a structure of the semiconductor device shown inFIG. 1excluding a gel-like resin layer.FIG. 3is a cross-sectional view showing a structure that a bus bar is connected to the externally leading terminals of the semiconductor device shown inFIG. 1.

A semiconductor device1of the first embodiment has a metallic base substrate2for heat-dissipating, a wiring board3, a MOSFET4as a semiconductor element, externally leading terminals5A,5B,5C, a casing6of a synthetic resin, a fixing resin7, and a gel-like resin layer8. A semiconductor device having a vertical power MOSFET as an example of a semiconductor element is described in this embodiment. The MOSFET4has a gate electrode4A and a source electrode4C on its front surface and a drain electrode4B on its back surface.

The metallic base substrate2is comprised of a metallic material (e.g., Al, Cu or the like) having good thermal conductivity and used as a plate for heat-dissipation of heat generated from the MOSFET4. A wiring board3is joined to the metallic base substrate2with a conductive bonding material10. As the conductive bonding material10, a solder is used in this embodiment, and a thermosetting resin (e.g., an epoxy resin or a silicone resin) containing silver powder can also be used. The conductive bonding material10interposed between the metallic base substrate2and the wiring board3preferably has a thickness in a range of 10 to 100 μm.

The wiring board3has a structure that a wiring pattern32comprised of Cu or the like is formed on a first main surface (top surface inFIG. 1,FIG. 3) of an insulating substrate such as a ceramic substrate31. And, a metallic film33(e.g., Cu or the like) is formed on a second main surface (the bottom surface inFIG. 1,FIG. 3) of the wiring board3to efficiently conduct heat generated from the MOSFET4toward the metallic base substrate2.

As shown inFIG. 2, the wiring pattern32is composed of a gate wiring pattern32A corresponding to the gate electrode4A of the MOSFET4, a drain wiring pattern32B corresponding to the drain electrode4B, and a source wiring pattern32C corresponding to the source electrode4C. The drain electrode4B of the MOSFET4is disposed on the drain wiring pattern32B of the wiring board3, and the drain electrode4B and the drain wiring pattern32B are bonded with the conductive bonding material10. The gate electrode4A formed on the surface of the MOSFET4is connected (wire bonded) to the gate wiring pattern32A through a bonding wire, and the source electrode4C of the MOSFET4is wire bonded to the source wiring pattern32C.

One end (first end) of each of the externally leading terminals5A,5B,5C for gate, drain and source is arranged on the wiring pattern32and joined with a conductive bonding material (a solder in this embodiment). These joints (joints between the wiring pattern32and the first ends of the externally leading terminals5A,5B,5C) comprised of the conductive bonding material are denoted by reference numeral11. In other words, the first end of the externally leading terminal5A for gate is arranged on the gate wiring pattern32A and joined by the joint11comprised of the conductive bonding material, and the first end of the externally leading terminal5B for drain is arranged on the drain wiring pattern32B and joined by the joint11comprised of the conductive bonding material. The first end of the externally leading terminal5C for source is arranged on the source wiring pattern32C and joined by the joint11comprised of the conductive bonding material. Thus, the first end of the externally leading terminal5A for gate is electrically connected with the gate electrode4A of the MOSFET4, and the first end of the externally leading terminal5B for drain is electrically connected with the drain electrode4B of the MOSFET4. And, the first end of the externally leading terminal5C for source is electrically connected with the source electrode4C of the MOSFET4.

The other end (second end) of each of the externally leading terminals5A,5B,5C for gate, drain and source is positioned outside of the wiring board3and arranged to protrude externally from the casing6. And, terminal body portions51A,51B,51C connecting the first end and the second end are disposed through hole portions61A,61B,61C for gate, drain and source formed in the casing6. The terminal body portion51C of the externally leading terminal5C for source is not shown inFIG. 1andFIG. 3but has the same structure as that of the terminal body portion51A of the externally leading terminal5A for gate and the terminal body portion51B of the externally leading terminal5B for drain.

The second ends of the externally leading terminals5A,5B,5C for gate, drain and source externally protruded from the casing6are connected to a bus bar13when the semiconductor device1is used. The fixing resin7is provided between the through hole portions61A,61B,61C for gate, drain and source of the casing6and the terminal body portions51A,51B,51C of the externally leading terminals5A,5B,5C for gate, drain and source.

The fixing resin7firmly fixes the terminal body portions51A,51B,51C of the externally leading terminals5A,5B,5C for gate, drain and source and the through hole portions61A,61B,61C for gate, drain and source of the casing6. When the bus bar13is connected to the second ends of the externally leading terminals5A,5B,5C for gate, drain and source as shown inFIG. 3, even if the externally leading terminals5A,5B,5C for gate, drain and source are vibrated, a crack doesn't occur in the joints11between the first ends of the externally leading terminals5A,5B,5C and the wiring board3, and the joint strength can be prevented from lowering. The fixing resin7is not limited to a particular type of synthetic resin if it can firmly fix the terminal body portions51A,51B,51C of the externally leading terminals5A,5B,5C to the through hole portions61A,61B,61C of the casing6. For example, a thermosetting resin such as an epoxy resin, a silicone resin or the like can be used, and the epoxy resin is more preferably used.

The casing6is a housing whose bottom is not closed and disposed to surround the joints11between the wiring board3and the first ends of the externally leading terminals5A,5B,5C, and the MOSFET4. The lower end of the casing6is disposed on the metallic base substrate2by, for example, fixing. The casing6has a square rod shape in this embodiment and its shape is not limited to a particular one and may have a cylindrical shape or a dome shape. The casing6is formed to have a desired shape by injection molding of a synthetic resin. On the top surface of the casing6are formed the through hole portions61A,61B,61C in which the terminal body portions51A,51B,51C of the externally leading terminals5A,5B,5C for gate, drain and source are inserted and held. The individual through hole portions61A,61B,61C have cylindrical protruded portions62A,62B,62C which are open downwardly. The cylindrical protruded portion62C is not shown inFIG. 1andFIG. 3but has the same structure as the protruded portions62A,62B.

A gel-like resin layer8(e.g., a gel-like silicone resin layer) is formed on a lower section within the casing6so as to cover the joints11between the wiring board3and the first ends of the externally leading terminals5A,5B,5C for gate, drain and source and the MOSFET4. In this embodiment, the top surface of the gel-like resin layer8is contacted to the fixing resin7, but the top surface of the gel-like resin layer8cannot be contacted to the fixing resin7as shown inFIG. 4. In addition, a space9is formed between the gel-like resin layer8and the inner top surface of the casing6. The provision of the space9allows absorption of the thermal expansion of the gel-like resin layer8, which is caused by heat generated from the MOSFET4, by the space9, and a tensile stress applied to the externally leading terminals5A,5B,5C can be eased.

For example, the above-described semiconductor device1of the first embodiment can be produced as follows.FIG. 5is a flow chart showing a manufacturing process of the semiconductor device1according to the first embodiment.

First, the wiring board3having the wiring pattern32, which is comprised of the gate wiring pattern32A, the drain wiring pattern32B and the source wiring pattern32C, formed on the front surface of the ceramic substrate31and the metallic film33formed on the back surface is prepared. Then, the MOSFET4is arranged on the wiring board3, and the drain electrode4B of the MOSFET4is joined (bonded) to the drain wiring pattern32B with the conductive bonding material10(step1). The first end of the externally leading terminal5A for gate is bonded to the gate wiring pattern32A with the conductive bonding material. Similarly, the first end of the externally leading terminal5B for drain is bonded to the drain wiring pattern32B with the conductive bonding material, and the first end of the externally leading terminal5C for source is bonded to the source wiring pattern32C with the conductive bonding material. There are formed the joints11, which are formed of the conductive bonding material, to join the first ends of the externally leading terminals5A,5B,5C for gate, drain and source and the respective wiring patterns32A,32B,32C for gate, drain and source.

The metallic base substrate2formed of a metallic material having good thermal conductivity is arranged on the metallic film33, which is formed on the back surface of the wiring board3, via the conductive bonding material10(e.g., a solder). And, the conductive bonding material10is fused by heating in a reflow furnace to fix the metallic base substrate2with the metallic film33of the wiring board3(step2).

The gate wiring pattern32A of the wiring board3and the gate electrode4A of the MOSFET4are connected (wire bonded) through the bonding wire. The source wiring pattern32C of the wiring board3and the source electrode4C of the MOSFET4are also wire bonded in the same manner (step3).

The casing6is placed to cover the wiring board3from above, and the terminal body portions51A,51B,51C of the externally leading terminals5A,5B,5C for gate, drain and source are inserted through the corresponding through hole portions61A,61B,61C of the casing6. And, the lower end of the casing6is fixed to the metallic base substrate2with an adhesive agent (step4).

A gel-like resin (e.g., a gel-like silicone resin) is dispensed through a filling hole (not shown) formed in the casing6by a dispenser to fill the casing6(step5). It is preferable to adjust the hardness (penetration) of the gel-like resin to a dispensable level. The filling hole is formed to fill the gel-like resin into the casing6, and its arranged position, the number of holes and the size are not limited.

A filling amount of the gel-like resin is sufficient if it could cover the joints11between the first ends of the externally leading terminals5A,5B,5C for gate, drain and source and the wiring board3and the MOSFET4and also form the space9between the gel-like resin and the inside top surface of the casing6. Preferably, as shown inFIG. 1andFIG. 3, it is an amount to contact the gel-like resin to the open lower ends of the cylindrical protruded portions62A,62B,62C formed on the through hole portions61A,61B,61C of the casing6. When the filling amount is determined as described above, the open ends of the cylindrical protruded portions62A,62B,62C of the casing6are closed by the top surface of the gel-like resin layer8. Therefore, after the gel-like resin is thermally cured, the fixing resin7is contacted to the top surface of the gel-like resin layer8and accumulated in the cylindrical protruded portions62A,62B,62C in a step (described later) of injecting the fixing resin7into the through hole portions61A,61B,61C of the casing6. Thus, the fixing resin7is prevented from sagging, and workability becomes good as a result. Besides, the contact between the fixing resin7and the gel-like resin layer8can effectively suppress vibrations from being transmitted from the bus bar13to the externally leading terminals5A,5B,5C when the bus bar13is connected to the second ends of the externally leading terminals5A,5B,5C for gate, drain and source. Therefore, a crack can be prevented more reliably from being produced in the joints11between the first ends of the externally leading terminals5A,5B,5C for gate, drain and source and the wiring board3.

After the gel-like resin is dispensed to fill, the gel-like resin is cured by heating (e.g., at 150 degrees C. for one hour) to form the gel-like resin layer8.

Then, the fixing resin7(e.g., a thermosetting resin such as an epoxy resin, a silicone resin or the like) is injected into the through hole portions61A,61B,61C for gate, drain and source of the casing6and cured by heating. When the fixing resin7is cooled to room temperature, there may be clearance (gap) between the fixing resin7and the gel-like resin layer8. Thus, the terminal body portions51A,51B,51C of the externally leading terminals5A,5B,5C for gate, drain and source are respectively fixed to the through hole portions61A,61B,61C of the casing6(step6). As a result, the semiconductor device1of the first embodiment is obtained.

As described above, the terminal body portions51A,51B,51C of the externally leading terminals5A,5B,5C for gate, drain and source and the through hole portions61A,61B,61C for gate, drain and source of the casing6are fixed with the fixing resin7in this embodiment. According to the above configuration, when the bus bar13is connected to the second ends of the externally leading terminals5A,5B,5C for gate, drain and source which are externally protruded from the casing6at the time of using the semiconductor device1, a crack doesn't occur easily in the joints11between the first ends of the externally leading terminals5A,5B,5C and the wiring board3by vibrations transmitted from the bus bar13to the individual externally leading terminals5A,5B,5C. Specifically, the fixing resin7is used to fix the externally leading terminals5A,5B,5C and the through hole portions61A,61B,61C of the casing6as described above, so that the service life of the semiconductor device1can be extended to about three times, namely to about 10 to 15 years. And, the electrical connection between the externally leading terminals5A,5B,5C and the wiring board3is not inhibited, and the highly reliable semiconductor device1can be provided.

Besides, the gel-like resin layer8is formed to contact its top surface to the lower ends of the cylindrical protruded portions62A,62B,62C of the through hole portions61A,61B,61C of the casing6, so that the fixing resin7can be formed at a prescribed position with good workability. In other words, when the liquid fixing resin7is injected through the through hole portions61A,61B,61C of the casing6, the fixing resin7is stopped from flowing down when it comes into contact with the top surface of the gel-like resin layer8, and sagging is prevented. Thus, good workability can be obtained.

In this embodiment, the wiring board3and the metallic base substrate2are joined with the conductive bonding material10but may be joined by screwing. In this case, it can be configured to join the metallic base substrate2by forming threaded screw holes in the wiring board3, cutting threads in the metallic base substrate2, and joining them.

As an example of the semiconductor element, the structure using the vertical power MOSFET was described in this embodiment, but an IGBT (insulation gate bipolar transistor), a diode or a composite element combining such elements can also be used. The structure, shape, size and disposed relationships described in the embodiment are merely described roughly, and the numerals and the compositions (materials) of the individual structures are mere examples. Therefore, the present invention is not limited to the embodiment described above, and it is to be understood that modifications and variations of the embodiment can be made without departing from the spirit and scope of the invention.