SEMICONDUCTOR DEVICE AND MANUFACTURING METHOD THEREOF

A semiconductor device according to the present invention includes a die pad, a semiconductor element joined to an upper surface of the die pad, and a resin sheet making close contact with a lower surface of the die pad, wherein the semiconductor element is resin-sealed together with the die pad and the resin sheet, wherein a recess is formed in the lower surface of the die pad, and a part of the resin sheet is filled into the recess bring the resin sheet into close contact with the lower surface of the die pad including an inside of the recess.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

Structure

FIG. 1shows a perspective view of a semiconductor device100according to this preferred embodiment.FIG. 2shows a bottom view and a side view of the semiconductor device100according to this preferred embodiment. A package of the semiconductor device100is resin-sealed by a sealing resin2, and a lead frame1projects from side surfaces thereof. At the bottom surface of the semiconductor device100, a metal plate3made of copper foil, for example, has its one principal plane exposed. The metal plate3may be made of a material having a higher heat conductivity than the sealing resin2, and may be made of aluminum, for example. As described later, a resin sheet makes close contact with the other principal plane of the metal plate3. The sealing resin is an epoxy resin, for example.

FIG. 3shows a top view and a cross-sectional view taken along lines AB and CD of the semiconductor device100. The semiconductor device100includes a plurality of lead frames1. As shown in the cross-sectional view taken along line CD, the left lead frame1is integral with a die pad5. That is, the left lead frame1includes an outer lead1awhich is not resin-sealed by the sealing resin2, an inner lead1bwhich is resin-sealed by the sealing resin2, the die pad5, and a step1cconnecting the die pad5and the inner lead. The inner lead1band the die pad5are not necessarily required to be connected via the step1c.

A semiconductor element7is joined to an upper surface of the die pad5by a joining portion6with solder or silver paste. Further, the semiconductor element7joined to the upper surface of the die pad5is, for example, a semiconductor element for electric power, and is FWD (Free Wheeling Diode), IGBT (Insulated Gate Bipolar Transistor), MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and SBD (Schottky Barrier Diode). In this preferred embodiment, as the semiconductor element7, IGBT and FWD as a SiC semiconductor element which is a preferred application example of the present invention are joined in parallel to the upper surface of the die pad5.

In the lead frame1which is not directly connected to the die pad5, an IC (integrated circuit) semiconductor element10is joined to an upper surface of the inner lead1bvia the joining portion6. The IC semiconductor element10is, for example, a logic chip. The IC semiconductor element10controls an operation of the semiconductor element7.

The semiconductor elements7or the semiconductor element7and the inner lead1bare connected by a thick bonding wire8amade of, for example, gold or aluminum. The thick bonding wire8ais made of aluminum, copper, or an alloy thereof. In addition, the IC semiconductor element10and the inner lead1bare connected by a thin bonding wire8bmade of gold, copper, or an alloy thereof having a smaller wire diameter than the thick bonding wire8a.

Note that a plurality of semiconductor elements7and IC semiconductor elements10may be provided according to the function of the semiconductor device100.

A surface of the package of the semiconductor device100is covered by the sealing resin2. That is, the semiconductor element7and the IC semiconductor element10are resin-sealed by the sealing resin2together with the die pad5and a resin sheet4. In addition, the metal plate3is exposed from a back side of the semiconductor device100. Since the metal plate3protects the resin sheet4from damage, the resin sheet4can maintain high insulation properties. This damage is considered to be caused, for example, when the semiconductor device100is screwed into an external heat sink (not shown) while a foreign substance is caught between the semiconductor device100and the external heat sink.

When the above damage is unlikely to be caused, the metal plate3may not be provided. In this case, the resin sheet4is exposed from the back side of the semiconductor device100.

In this preferred embodiment, the metal plate3is made of copper foil having a thickness of 0.1 mm. However, as described later, when the metal plate3onto which the resin sheet4is bonded is resin-sealed, the metal plate3may only have strength to the extent that its structure is not deformed when conveyed into a die cavity, and have a thickness of 0.075 mm or more. For example, the copper foil having a thickness below 0.05 mm is torn or deformed.

A lower surface of the die pad5makes close contact with an upper surface of the resin sheet4. An area of the resin sheet4is larger than an area of the die pad5. A thickness of the resin sheet4is, e.g., 0.1 mm.

As shown inFIG. 4A, a recess5ahaving a V-shaped cross section is formed in the lower surface of the die pad5, that is, in a surface making contact with the resin sheet4. A part of the resin sheet4is filled into the recess5a,and makes close contact with the die pad5inside the recess5a.In this way, the recess5aincreases a contact area of the lower surface of the die pad5with the resin sheet4. The die pad5and the resin sheet4thus make close contact with each other.

A heat dissipation filler may be mixed into the resin sheet4. In the resin sheet4, a density of the filler in the portion filled into the recess5athat is provided in the lower surface of the die pad may be lower than a density of the filler in a portion not filled into the recess5a.

As shown inFIG. 4B, a cross-sectional shape of the recess5amay be rectangular. In addition, as shown inFIG. 4C, the cross-sectional shape of the recess5amay be semicircular. As described later, the recess5amay have any cross-sectional shape as long as the resin sheet4can enter the recess5a.

The recess5aonly needs to have a depth in which the die pad5provided with the recess5ais not easily deformed. When the thinnest portion of the die pad5is 0.1 mm or more, the depth of the recess5ais not limited. For example, when a plate thickness of the die pad5is 0.4 mm, the depth of the recess5amay be 0.3 mm or less.

More preferably, for a shape of the recess5a,a width of an inside of the recess5ais larger than a width of an opening of the recess5a.Such a shape allows the resin sheet4filled into the recess5ato be hard to be separated from the recess5a.The die pad5and the resin sheet4can thus make close contact with each other more strongly.

A composition of the resin sheet4will be described below. The resin sheet4is made by kneading an epoxy resin component and the heat dissipation filler that increases the heat dissipation properties of the resin sheet. The epoxy resin component is a base material, and serves as a binder with the filler and an adhesive of the die pad5and the metal plate3(hereinafter, referred to as an insulating resin). The thickness of the resin sheet4is 0.1 mm. As described later, the thickness of the resin sheet4is changed according to heat resistance required for the semiconductor device100, but is desirably in the range of 0.05 mm to 0.5 mm. The filler contained in the resin sheet4will be described in detail. The filler is selected from the group consisting of SiO2, Al2O3, AlN, Si3N4, and BN, and is scale-shaped or spherical-shaped. In addition, a particle diameter of the coagulated filler can be from 0.05 mm to about 0.1 mm, but filler particles which have a particle diameter smaller than that are used. In the present invention, the filler is a mixture of the scale-shaped filler and fine particles of about several tens of nanometers. However, a combination of the filler material and the particle diameter is not specified thereto, and a plurality of materials may be combined according to heat resistance required for the semiconductor device100. In addition, in this preferred embodiment, to increase a heat conductivity of the resin sheet4, the filler has a volume content of 80%, and a heat conductivity of about 10 W/mK. The filler may have any volume content when it can satisfy heat resistance required for the semiconductor device100and heat conductivity required for the resin sheet4, and actually has a volume content of 50% to 90%. A heat conduction mechanism of the resin sheet4will be described. A heat conductivity of the insulating resin alone of the resin sheet4is about 0.5 W/mK, and the heat conductivity of the filler is about 80 W/mK. In the resin sheet4, a contact path of the heat dissipation fillers preferentially and selectively becomes a heat conduction path.

Manufacturing Method

A method of manufacturing the semiconductor device100according to this preferred embodiment will be described. First, a process for manufacturing the lead frame1including the die pad5, the inner lead1b,the outer lead1a,and the step1cwill be described. A copper plate cut into a suitable size is subjected to pressing one or a plurality of times to form the lead frame1including the die pad5, the inner lead1b,the outer lead1a,and the step1c.Here, the copper plate may be of an alloy mainly containing copper having a composition of Cu-0.03P-0.1Fe or an alloy having a composition of Cu-0.15Sn. In addition, the copper plate may be of an alloy mainly containing Al like an A5052 material or pure copper. Further, although a thickness of the lead frame1is 0.4 mm in the present invention, the lead frame1only needs to have a thickness in which pressing is enabled and which is not easily deformed after press forming. For example, the thickness of the lead frame1is desirably in the range of 0.1 to 1.5 mm. To improve the soldering ability of the semiconductor element7, the upper surface of the die pad5may be subjected to silver plating or palladium plating.

Next, a process for forming the recess5ain a lower surface of the die pad5will be described.FIGS. 5A,5B,5C and5D show a procedure for forming the recess5ahaving a V-shaped cross section and in which the width of the inside of the recess5ais larger than the width of the opening of the recess5a.

As shown inFIG. 5A, the lower surface of the die pad5is subjected to coining by a die15with a projection16having a V-shaped cross section. In this case, projections17are formed near the opening of the recess5aformed by coining (FIGS. 5B and 5C). The projections17formed near the opening of the recess5aare then subjected to coining again by a flat die18to be collapsed (FIG. 5D). As a result, a pawl19is formed in the opening of the recess5ato reduce the width of the opening. By performing coining twice, the recess5ain which the width of the inside of the recess5ais larger than the width of the opening of the recess5ais formed in the lower surface of the die pad5. The width of the opening of the recess5ais formed into, e.g., 0.05 mm.

When the width of the inside of the recess5ais not required to be larger than the width of the opening of the recess5a,coining by the flat die18is omitted.

In addition, the forming of the recess5ahaving a rectangular cross section will be described. First, a rectangular recess is formed by half etching. Next, the recess is subjected to coining by a die in which the projection16of the die15has a rectangular cross section, thereby forming a deeper rectangular recess. At the same time, projections are formed near the opening of the recess. Further, the projections are subjected to coining with the flat die to be collapsed, thereby forming a pawl in the opening.

The semiconductor element7is joined to the upper surface of the die pad5via the joining portion6with solder, for example. In this case, the joining portion6is solder. The IC semiconductor element10is joined to the upper surface of another lead frame1.

Next, a contacting process for causing the lower surface of the die pad5to make close contact with the resin sheet4and a sealing process using the sealing resin2will be described. The contacting process and the sealing process are performed at the same time using a mold (not shown).

First, the half-cured resin sheet4is arranged in the mold. The mold is held at a high temperature above a melting temperature of the sealing resin2, e.g., at a temperature above 180° or more. When providing the metal plate3, the metal plate3is arranged between the mold and the resin sheet4so as to make contact with a lower surface of the resin sheet4.

The die pad5is arranged on the upper surface of the resin sheet4so that the lower surface of the die pad5makes contact with the upper surface of the resin sheet4. At this time, the half-cured resin sheet4receives heat from the mold held at high temperature to be melted. Another lead frame1which is not connected to the die pad5is arranged in a predetermined position of the mold.

The sealing resin2is injected into the mold. The sealing pressure of the melted sealing resin2presses the die pad5onto the resin sheet4. At this time, the melted resin sheet4has suitable flowability, but the filler included in the resin sheet4is not melted. Therefore, the melted insulating resin preferentially enters the recess5ain the lower surface of the die pad5. Since the opening width of the recess5ais 0.05 mm, the coagulated filler hardly enters the recess5a.The density of the filler in the resin sheet4is thus relatively increased to increase its heat conductivity.

As described above, a part of the resin sheet4is filled into the recess5aso that the resin sheet4makes close contact with the lower surface of the die pad5including the inside of the recess. Simultaneously with the contact of the die pad5and the resin sheet4with each other, the semiconductor element7is resin-sealed by the sealing resin2together with the die pad5and the resin sheet4. When the metal plate3is arranged between the mold and the resin sheet4, one principal plane of the metal plate3is adhered onto the lower surface of the resin sheet4, and the other principal plane of the metal plate3is exposed from the bottom surface of the semiconductor device100. By the above manufacturing process, the semiconductor device100according to this preferred embodiment is manufactured.

Effect

The semiconductor device100according to this preferred embodiment includes the die pad5, the semiconductor element7arranged on the upper surface of the die pad5, and the resin sheet4making close contact with the lower surface of the die pad5. The semiconductor element7is resin-sealed together with the die pad5and the resin sheet4. The recess5ais formed in the lower surface of the die pad5. A part of the resin sheet4is filled into the recess5aso that the resin sheet4makes close contact with the lower surface of the die pad5including the inside of the recess5a.

Since the recess5ais provided in the lower surface of the die pad5, the contact area of the die pad5with the resin sheet4can be larger as compared to the structure in which the recess is not provided in the lower surface of the die pad5. The contactivity between the die pad5and the resin sheet4can thus be improved. In addition, the larger contact area can efficiently conduct heat from the semiconductor element7joined onto the die pad5to the resin sheet4via the die pad5. That is, the improved heat dissipation properties can hold the semiconductor element7in operation at a suitable temperature. For example, when the semiconductor element7is a switching semiconductor element, switching loss can be prevented. Further, the improved contactivity between the die pad5and the resin sheet4can prevent the separation of the resin sheet4. The reliability of the semiconductor device100can thus be improved.

In the semiconductor device100according to this preferred embodiment, the cross section of the recess5ais V-shaped.

Since the cross section of the recess5ais V-shaped, the forming of the recess5abecomes easy. Cost reduction can thus be expected in the manufacturing process.

In the semiconductor device100according to this preferred embodiment, the width of the inside of the recess5ais larger than the width of the opening of the recess5a.

The pawl19formed in the opening of the recess5aallows the resin sheet4filled into the recess5ato be hard to detach from the recess5a.The contactivity between the die pad5and the resin sheet4can thus be improved.

In the semiconductor device100according to this preferred embodiment, the heat dissipation filler is mixed into the resin sheet4, and the density of the filler in the portion of the resin sheet4filled into the recess5ais lower than the density of the filler in the rest portion of the resin sheet4.

Since the density of the filler in the portion of the resin sheet4filled into the recess5ais lower than the density of the filler in the rest portion of the resin sheet4, the adhesion between the resin sheet4and the recess5abecomes stronger. On the other hand, since the density of the filler in the portion of the resin sheet4not filled into the recess5ais higher than the density of the filler in the portion of the resin sheet4filled into the recess5a,the heat conductivity is excellent for efficiently performing heat release. In addition, since the density of the filler is higher as compared with the case where the recess5ais not provided, when about the same heat dissipation properties as the case where the recess5ais not provided is required, the thickness of the resin sheet4can be relatively reduced.

In the semiconductor device100according to this preferred embodiment, the semiconductor element7is a SiC semiconductor element. The SiC semiconductor element which can be operated at a higher temperature than the Si semiconductor element is assumed to produce particularly much heat (e.g., 200° C. or more). By improving the contactivity between the die pad5and the resin sheet4in the present invention, even when the semiconductor element7becomes hot, the separation of the resin sheet4from the die pad5due to a difference in linear expansion coefficient can be prevented. The reliability of the semiconductor device100can thus be improved.

In the method of manufacturing the semiconductor device100according to this preferred embodiment includes the steps of: (a) forming the recess5ain the lower surface of the die pad5; (b) after the step (a), joining the semiconductor element7to the upper surface of the die pad5; (c) after the step (b), arranging the resin sheet4in the mold held at a temperature at which the sealing resin2can be melted to arrange the die pad5on the upper surface of the resin sheet4; and (d) after the step (c), injecting the sealing resin2into the mold and pressing the lower surface of the die pad5onto the resin sheet4by a pressure of the sealing resin2injected into the mold to fill a part of the resin sheet4into the recess5aso that the resin sheet4makes close contact with the lower surface of the die pad5including the inside of the recess5a,and simultaneously, resin-sealing the semiconductor element7by the sealing resin2together with the die pad5and the resin sheet4.

The contact between the die pad5and the resin sheet4, and the resin sealing are simultaneously performed in one step. Therefore, the semiconductor device100according to this preferred embodiment can be manufactured without adding the sealing step as in the conventional technique. The number of times to handle the lead frame1on which the semiconductor element7or the like is mounted can be reduced to improve the yield.

In the method of manufacturing the semiconductor device100according to this preferred embodiment, coining is performed a plurality of times in the step of forming the recess5ain the lower surface of the die pad5so that the width of the inside of the recess5ais formed to be larger than the width of the opening of the recess5a.

Since the width of the inside of the recess5ais formed to be larger than the width of the opening of the recess5a,the pawl19formed in the opening allows the resin sheet4filled into the recess5ato be hard to detach from the recess5a.Thus, the contactivity between the lower surface of the die pad5and the resin sheet4can be improved.

Second Preferred Embodiment

Structure

The semiconductor device100according to this preferred embodiment is different from the semiconductor device100according to the first preferred embodiment in the structure of the recess5aformed in the lower surface of the die pad5. Other structure is the same as the first preferred embodiment, and the description thereof is omitted.

FIG. 6shows a plan view of the lower surface of the die pad5and a side view of the die pad5of the semiconductor device100according to this preferred embodiment. The semiconductor element7is joined to the upper surface of the die pad5via the joining portion6. The lower surface of the die pad5is a surface making close contact with the resin sheet4.

As shown inFIG. 6, the recess5aextends from one side to the other side of the lower surface of the die pad5. A plurality of recesses5aare formed in a lattice shape. InFIG. 6, a path in which each recess5aextends is straight, but may be curved. The recess5ais not required to be formed in the lattice shape, and the number of the recess5amay be one. In this preferred embodiment, the cross-sectional shape of the recess5ais V-shaped, but may be rectangular or semicircular.

In the process for manufacturing the semiconductor device100, when the resin sheet4is arranged in the mold to arrange the die pad5on an upper portion of the resin sheet4and the sealing resin2is injected into the heated mold for sealing, the solvent in the resin sheet4may be volatilized by heating to cause gas.

With the die pad5having the structure of this preferred embodiment, the gas passes through the path in which the recess5aprovided in the lower surface of the die pad5extends, and is discharged outside of a contact surface between the die pad5and the resin sheet4. That is, the staying of the gas on the contact surface between the die pad5and the resin sheet4to cause a gap in the contact surface can be prevented.

Effect

In the semiconductor device100according to this preferred embodiment, the recess5aextends from one side to the other side of the lower surface of the die pad5.

Therefore, when the semiconductor device100is manufactured, the gas generated from the resin sheet4passes through the path in which the recess5aextends, and is discharged from the contact surface between the die pad5and the resin sheet4. That is, the staying of the gas on the contact surface between the die pad5and the resin sheet4to cause a gap in the contact surface can be prevented. Accordingly, the lowering of the heat conductivity due to the gap caused in the contact surface between the die pad5and the resin sheet4can be prevented.

Third Preferred Embodiment

In the semiconductor device100according to this preferred embodiment, the structure of the recess5ain the lower surface of the die pad5according to the second preferred embodiment (FIG. 6) is replaced with the structure shown inFIG. 7. Other structure is the same as the first preferred embodiment, and the description thereof is omitted.

InFIG. 7, the recess5ais provided radially from a region overlapped with the semiconductor element7in plan view. The recess5aextends from one side to the other side of the lower surface of the die pad5.

When manufacturing the semiconductor device100, if the semiconductor element7is joined to the upper surface of the die pad5by solder, for example, the die pad5can be convexly warped about the joining portion of the semiconductor element7due to a difference in linear thermal expansion coefficient between the semiconductor element7and the die pad5.

With the die pad5having the structure of this preferred embodiment (FIG. 7), compression stress onto the warped die pad5can be reduced. In addition, when the sealing resin2is injected into the mold to press and contact the die pad5onto the resin sheet4by the pressure of the sealing resin2, the warp of the die pad5can be corrected to be returned to the flat state.

The external heat sink is typically brought into contact with the bottom surface of the semiconductor device100. However, when the semiconductor element7produces heat during operation, the die pad5can be convexly warped due to the difference in linear thermal expansion coefficient. When the die pad5is convexly warped, the resin sheet4making close contact with the lower surface of the die pad5and the metal plate3are also convexly warped. Consequently, a gap is caused between the bottom surface of the semiconductor device100and the external heat sink to deteriorate heat dissipation properties.

With the die pad5having the structure of this preferred embodiment (FIG. 7), compression stress onto the warped die pad5can be reduced. The warp of the die pad5can be reduced to prevent a gap from being caused in a contact surface between the bottom surface of the semiconductor device100and the external heat sink.

Effect

In the semiconductor device100according to this preferred embodiment, the recess5ais provided radially from a region overlapped with the semiconductor element7in plan view.

Since the recess5aformed in the lower surface of the die pad5is provided radially from a region overlapped with the semiconductor element7in plan view, stress on the die pad5when the semiconductor element7is joined to the die pad5can be reduced to improve the reliability of the joining portion6. In addition, since the stress on the die pad5can be reduced to prevent the warp of the die pad5, the pressure is uniformly applied onto the resin sheet4when the die pad5and the resin sheet4are brought into close contact with each other. Thus, the thickness of the resin sheet4which is in close contact with the die pad5can be uniform. Further, since the warp of the die pad5is prevented, the warp of the bottom surface of the semiconductor device100can be prevented. A gap can thus be prevented from being caused in the contact surface between the bottom surface of the semiconductor device100and the external heat sink.

The preferred embodiments can be freely combined, and can be modified and omitted, as needed, in the scope of the present invention.