Method for producing semiconductor device and semiconductor device

The method of producing a semiconductor device in which chips are resin-molded, including steps of: preparing frames having front and back surfaces and die pads; preparing an insulation resin sheet having a first and a second surfaces; preparing a resin-sealing metal mold having cap pins; mounting the resin sheet inside the resin-sealing metal mold in such a manner that the second surface of the resin sheet contacts an inner bottom surface of the resin-sealing metal mold; mounting power chips on the surfaces of the die pads; positioning the frames on the first surface of the resin sheet in such a manner that the back surfaces of the die pads contact the first surface of the resin sheet; pressing the die pads toward the resin sheet using the cap pins and fixing the die pads; injecting a sealing resin in the resin-sealing metal mold and hardening the sealing resin; and removing the semiconductor device in which the power chips are molded with the sealing resin out from the resin-sealing metal mold. The resin sheet may include a metal foil which is disposed to the second surface.

CROSS-REFERENCE TO RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2003-358815 filed on Oct. 20, 2003 including specification, drawings and claims is incorporated herein by reference in its entirety

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method of producing a semiconductor device, and more particularly, a method of producing a power semiconductor device including a power chip.

2. Description of the Related Art

In a power semiconductor device having a conventional structure, a power chip, an IC chip and the like are each die-bonded on a frame and these chips are sealed with a resin. Since a power chip has large heat dissipation, a cooling fin is attached to the back surface of the semiconductor device for instance to thereby enhance a heat dissipation efficiency. The frames seating the power chips are coated with a resin and insulated from the cooling fin which is attached to the back surface (JP 2000-138343, A).

SUMMARY OF THE INVENTION

While it is necessary for improvement in heat dissipation property that the resin covering the frames seating the power chips, namely, the resin between the back surfaces of the frames seating the power chips and the back surface of the semiconductor device is thin in such a semiconductor device, there is a problem that reduction in thickness of the resin disposed in these portions deteriorates an insulating property.

Noting this, the inventors found that with an insulation resin sheet having a high thermal conductivity fixed to the back surfaces of frames seating power chips in contact with the back surfaces of the frames, it was possible to obtain a semiconductor device exhibiting an enhanced heat dissipation property and an excellent insulating property, thus completing the present invention regarding a method of producing such a semiconductor device.

In short, an object of the present invention is to provide a method of producing a semiconductor device which exhibits an enhanced heat dissipation property and an excellent insulating property.

The present invention is directed to a method of producing a semiconductor device in which chips are resin-molded, including steps of: preparing frames having front and back surfaces and die pads; preparing an insulation resin sheet having a first and a second surfaces; preparing a resin-sealing metal mold having cap pins; mounting the resin sheet inside the resin-sealing metal mold in such a manner that the second surface of the resin sheet contacts an inner bottom surface of the resin-sealing metal mold; mounting power chips on the surfaces of the die pads; positioning the frames on the first surface of the resin sheet in such a manner that the back surfaces of the die pads contact the first surface of the resin sheet; pressing the die pads toward the resin sheet using the cap pins and fixing the die pads; injecting a sealing resin in the resin-sealing metal mold and hardening the sealing resin; and removing the semiconductor device in which the power chips are molded with the sealing resin out from the resin-sealing metal mold. The resin sheet may include a metal foil which is disposed to the second surface.

Using the semiconductor device producing method according to the present invention, it is possible to provide a semiconductor device in which a resin sheet and frames are fixed in a favorable fashion and which therefore exhibits an enhanced heat dissipation property and an excellent insulating property.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a perspective view of a semiconductor device according to this embodiment of the present invention generally denoted at100.FIG. 2is a cross sectional view of the semiconductor device along lines I—I inFIG. 1.

As shown inFIG. 1, the semiconductor device100has a resin-molded package structure and includes a mold resin2on the both sides of which a plurality of metal frames1are disposed. The mold resin2is preferably of an epoxy resin.

As shown inFIG. 2, the semiconductor device100includes the plurality of frames1. One frame1seats an IC chip7such as a logic chip. The other frame1includes a die pad portion1aand a step portion1b, and the die pad portion1aseats power chips5such as an IGBT and an FW Diode. The power chips5, the IC chip7and the frames1are connected with each other by bonding wires6and8of gold, aluminum and the like, allowing the IC chip7control operations of the power chips5. One or more power chips5, IC chip7and the like may be disposed depending upon the functions of the semiconductor device100.

The mold resin2includes an insulation resin sheet3whose back surface seats a metal foil4of copper for instance, and the metal foil4is exposed in the back surface of the mold resin2. The insulation resin sheet3is preferably formed by an epoxy resin containing fillers. The fillers are made of one or more materials selected from group of SiO2, Al2O3, AlN, Si3N4and BN. The thermal conductivity of the insulation resin sheet3is larger than that of the mold resin2. The insulation resin sheet3alone as it is without the metal foil4may be used.

The frames1are buried and fixed by the mold resin2such that the back surfaces of the die pads1aare in direct contact with the top surface of the insulation resin sheet3. In the semiconductor device100, since the die pads1aand the insulation resin sheet3contact directly each other without the mold resin2and the like intermediate between the back surfaces of the die pads1aand the top surface of the insulation resin sheet3, the thermal conductivity from the die pads1ato the insulation resin sheet3improves. This improves the heat dissipation property of the power chip5which are attached to the top surfaces of the die pads1a.

Further, there are dents9in the top surface of the mold resin2. The dents9are created when cap pins23are pulled out at a producing step. The dents9will be described in detail when describing the producing steps. Considering the design of a resin-sealing metal mold, it is difficult to pull out the cap pins without creating the dents9at all.

A method of producing the semiconductor device100will now be described with reference toFIGS. 3A–3G. This producing method includes the following steps1through7.FIGS. 3A–3Gare cross sectional views taken along the same direction as the direction I—I shown inFIG. 1.

Step 1: As shown inFIG. 3A, the frames1of copper for instance are prepared. This is followed by fixing of the IC chip7on one frame1and the power chips5on the die pad1aof the other frame1, each using solder, silver paste, etc.

Step 2: As shown inFIG. 3B, using the bonding wires6of aluminum, the power chips5are connected with each other, the power chips5and the frames1are connected with each other, and the frames1are connected with each other (aluminum wire bonding step). As the bonding wires6, alloy mainly containing aluminum, or other metal may be used.

Step 3: As shown inFIG. 3C, using the bonding wires8of gold, the IC chip7and the frames1are connected with each other (gold wire bonding step). As the bonding wires8, alloy mainly containing gold, or other metal may be used.

While the foregoing has described that the IC chip7and the power chips5are connected through the frames1, they may be connected directly. Alternatively, they may be connected by metal plates instead of bonding wires6and8.

Step 4: As shown inFIG. 3D, a metal mold20for resin-sealing is prepared. The metal mold20can be separated into an upper metal mold21and a lower metal mold22. The upper metal mold21includes the cap pins23. The cap pins23are attached such that they can be pulled out from the upper metal mold21.

Following this, the insulation resin sheet3whose back surface seats the metal foil4is prepared and located at a predetermined position inside the metal mold20. The insulation resin sheet3is positioned so that the back surface of the metal foil4included in the insulation resin sheet3contacts an inner bottom surface of the lower metal mold22.

Step 5: As shown inFIG. 3E, the frames1seating the power chips5and the like are located at predetermined positions inside the metal mold20. The frames1are positioned so that the back surfaces of the die pads1aof the other frames1contact the top surface of the resin sheet3.

While the foregoing has described that the resin sheet3is positioned on the lower metal mold22first and the frames1mounting the power chips5and the like are disposed on the resin sheet3, the frames1mounting the power chips5and the like may be temporarily fixed on the resin sheet3in advance and the resin sheet3may then be positioned on the lower metal mold22.

Step 6: As shown inFIG. 3F, the upper metal mold21is attached and fixed to the lower metal mold22. In consequence, the cap pins32press at their tips the die pads1aof the other frames1against the top surface of the resin sheet3.

Further, with the cap pins23pressing the die pads1a, a pressurized sealing resin12is injected and held in the resin-sealing metal mold20. The die pads1aand the resin sheet3are fixed during this.

FIG. 4is a schematic view of the frames1which are arranged inside the metal mold20. The portions denoted at19are the positions at which the frames1are pressed by the tips of the cap pins23. As the area around the die pads1aseating the power chips5are pressed at one or more locations, the die pads1aand the resin sheet3are brought into perfect contact each other.

InFIG. 4, the die pads1aseating the power chips5include pin pressing sections1cwhich are local projections of the die pads1a. The pin pressing sections1cprotrude between the adjacent die pads1a, while avoiding mutual contact. By means of the pin pressing sections1c, the die pads1aare pressed against the resin sheet3securely.

Other than for fixing the die pads1aat the resin sealing step, the pin pressing sections1cmay be used to fix the frames1at the power chip mounting step, the wire bonding steps or the like.

Between the adjacent die pads1a, there are two cap pins23which press the different die pads1a(i.e., different along the vertical direction inFIG. 4). While the diameter of the cap pins23is usually smaller than the gaps between the adjacent die pads1a, the diameter may be enlarged to the extent not touching the adjacent die pads1aas shown inFIG. 4.

Since electric potentials are generally different between the adjacent die pads1a, it is necessary to ensure a certain distance for insulation between the adjacent die pads1a. InFIG. 4, utilizing the distance for insulation, the cap pins23press the die pads1awith the die pads1apartially sticking out.

For such an arrangement of the cap pins23, the cap pins23having a large diameter, i.e., strong cap pins23which have long lifetime may be used, which does not increase the size of the semiconductor device100.

The frames1are fixed at their ends to the metal mold as shown inFIG. 3F, with the die pads1apressed each by the two cap pins23as shown inFIG. 4. The die pads1aare thus pressed stably on the resin sheet3, whereby the resin sheet3and the die pads1aare fixed in a favorable fashion.

By a transfer mold method, the sealing resin12formed by an epoxy resin for example is thereafter injected in the metal mold20.

FIG. 5is a schematic view which shows a step of injecting the sealing resin12to the direction of the arrow15from below in the fixed state shown inFIG. 4. The sealing resin12is injected at a plurality of resin injection inlets into the metal mold20. Since the cap pins23serve as obstacles against the flow of the sealing resin12during this, the sealing resin12flows dominantly onto the power chips5which are free from the cap pins23. In consequence, pressure acts upon the area of the die pads1awhere the power chips5are mounted, and the die pads1aare pressed against and tightly adhered to the resin sheet3.

With the cap pins23arranged in the gaps between the power chips5on the die pads1a, it is possible to fix the portions of the die pads1amounting the power chips to the resin sheet3in a favorable manner. Hence, even when the pressing of the die pads1aby the cap pins23is insufficient, the die pads1aand the resin sheet3are fixed favorably. In other words, it is possible to increase the process margin and enhance the stability of producing. This effect becomes more significant as the diameter of the cap pins23becomes larger.

Although one cap pin23may be assigned to one die pad1a, one die pad1amay be pressed with a plurality of (two inFIG. 4) cap pins23as shown inFIG. 5. This increases the stability of the pressing. In addition, since a plurality of cap pins23are arranged utilizing the dead spaces which are present between the die pads1ain the arrangement shown inFIG. 4, the size of the semiconductor device does not increase even when more cap pins23are used.

Next, before the sealing resin12hardens, the cap pins23are pulled out from the upper metal mold21until the tips of the cap pins23are positioned slightly below the top surface of the mold resin2, and the cap pins23are held in this condition. In this case, while the holes left by the cap pins23are closed by the sealing resin12, the dents9are created in the top surface of the mold resin2. It is difficult to pull out the cap pins without creating the dents9at all, owing to the structure of the metal mold20.

Step 7: As shown inFIG. 3G, after releasing from the metal mold20, post cure for completely hardening the mold resin, cutting of excessive frame portions such as tie bars, and the like are executed. The frames (external terminals)1are further molded, thereby completing the semiconductor device100shown inFIG. 1.

FIG. 6is a cross sectional view of a semiconductor device according to this embodiment of the present invention generally denoted at200, taken along the same direction as the direction I—I inFIG. 1. InFIG. 6, the same reference symbols as those inFIGS. 1 and 2denote the same or corresponding portions.

In the semiconductor device200, projections29are formed instead of the dents9, at the same positions as those of the dents9of the semiconductor device100. The projections29are formed as the cap pins23are pulled out from the upper metal mold21until the tips of the cap pins23are positioned slightly above the top surface of the mold resin2and the cap pins23are held as such at the step6of the producing method of the semiconductor device100described above with the sealing resin12hardened to a certain extent.

Since the semiconductor device200includes such projections29, the strength of the mold resin2, especially the bending strength, improves.

FIG. 7is a cross sectional view of a semiconductor device according to this embodiment of the present invention generally denoted at300, taken along the same direction as the direction I—I inFIG. 1. InFIG. 7, the same reference symbols as those inFIGS. 1 and 2denote the same or corresponding portions.

The semiconductor device300has a structure that the dents9of the semiconductor device100are buried with a resin30. The semiconductor device300is otherwise the same in structure as the semiconductor device100. Burying with the resin3is accomplished using a potting method for instance.

As compared with a structure that the dents9are not buried, the strength and especially the bending strength improves in the semiconductor device300.

FIG. 8is a cross sectional view of a semiconductor device according to this embodiment of the present invention generally denoted at400, taken along the same direction as the direction I—I inFIG. 1. InFIG. 8, the same reference symbols as those inFIGS. 1 and 2denote the same or corresponding portions.

The semiconductor device400is produced using the metal mold20in which the cap pins23are fixed to the upper metal mold21, e.g., a metal mold in which the cap pins23and the upper metal mold21are integrated with each other. Hence, as the sealing resin12hardens with the cap pins23pressing the die pads1aand the upper metal mold21is removed at the step6(FIG. 3F) described above, hole portions31are created in the mold resin2.

In the semiconductor device400, the hole portions31are filled with a resin32. Filling with the resin32is accomplished using a potting method for instance.

The frames1exposed at the bottom of the hole portions31are covered with an injected resin32, thus preventing corrosion and the like of the frames1.

As the semiconductor device400is produced using the metal mold20in which the cap pins23are fixed to the upper metal mold21, the producing steps are simplified and a producing cost is reduced.

FIG. 9is a schematic view similar toFIG. 4, showing the frames1which are arranged inside the metal mold20for resin-sealing. InFIG. 9, the pin pressing sections1care disposed on the both sides of the respective die pads1a. The cross sectional shape of the cap pins23is oval.

Owing to these shapes of the pin pressing sections1cand the cap pins23, the die pads1aare pressed stably on the resin sheet3. The resin sheet3and the die pads1aare thus fixed in a favorable fashion.