The semiconductor device includes: a heat spreader; a first solder layer; a second solder layer; a semiconductor element including a first surface bonded to the heat spreader through the first solder layer, a second surface facing the first surface, a first electrode disposed on the first surface, and a second electrode disposed on the second surface; a block bonded to the second electrode through the second solder layer; a sheet including a first portion, and a second portion having insulating properties and being in contact with the heat spreader; a first lead frame welded to the heat spreader; a second lead frame welded to the block; and a sealant having insulating properties and sealing the first and second lead frames, the heat spreader, the first and second solder layers, the semiconductor element, and the block.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure relates to a semiconductor device and a method of manufacturing a semiconductor device.

Description of the Background Art

Semiconductor devices are provided as, for example, packages each including a semiconductor element sealed by an insulator. Examples of the insulator include a hard resin. The semiconductor devices provided as the packages also include a plurality of components with different linear coefficients of expansion, besides the semiconductor elements. Exposure of the semiconductor devices to environments in heating and cooling cycles expand and contract the plurality of components, and sometimes creates shearing stress on a surface at which components are bonded together (hereinafter, simply referred to as “subject components”). The higher moduli of elasticity of components to be bonded are, the higher the stress becomes. The stress deforms the components, for example, induces warpage. The deformation may induce stress in a portion other than portions with the deformation.

Solder is known as a bonding material for bonding metals. Solder also functions as a stress buffer that deforms to absorb the stress from subject components. Welding, which is a process of bonding subject components together by melting, for example, copper, hardly allows a portion at which the subject components are bonded together to absorb the stress.

An electrode formed on a surface of a semiconductor element (hereinafter also referred to as a “surface electrode”) is made of, for example, aluminum. Aluminum has a modulus of elasticity and a 0.2% proof strength closer to those of solder. The surface electrode is, for example, bonded to a lead part through a block made of a metal. When the surface electrode is bonded to the block through solder, the surface electrode is subject to damages with a higher priority than that of solder, depending on the shape or the size of the surface electrode. Here, solder has a poor function as the stress buffer, thus resulting in large stress. The large stress could conceivably split the surface electrode, and moreover, damage the semiconductor element.

In view of these, a package including a plurality of components with different linear coefficients of expansion desirably has at least any one of, for example, solder and a structure buffering stress (hereinafter also referred to as “stress buffer structure”) in bonding portions of a semiconductor element and portions near the portions. WO2020/105476 exemplifies a structure including: an insulating substrate; a conductive substrate mounted on the insulating substrate; a semiconductor element further mounted on the conductive substrate; a first block made of a metal and bonded to the semiconductor element through a bonding material; and a lead part welded to the first block.

For example, when the lead part is bonded to the first block through solder, the solder functions as a stress buffer and suppresses the stress to be applied to surface electrode.

WO2020/105476 describes a wide variety of materials that can be selected for each of the components to be used. It is desirable that a difference in linear coefficient of expansion between the components included in the package is smaller to reduce the stress to be generated. For example, a low thermal expansion material, e.g., ceramic is used as a material of the insulating substrate. For example, a composite substrate of graphite and a copper film is used as the conductive substrate. For example, invar or kovar is used as a material of the first blocks. For example, a clad material, e.g., copper/invar/copper (CIC) is used as a material of the lead part. These materials are special materials that increases the cost necessary for manufacturing semiconductor devices (hereinafter also referred to as “manufacturing cost”).

Examples of general-purpose materials to be used as much as possible for reducing the manufacturing cost include copper as a material of the conductive substrate or the leads, and sintered copper-molybdenum as a material of the first blocks. These materials are higher in linear coefficient of expansion than ceramic used as a material of a supporting substrate. Applications of these materials bring about warpage of components and the stress between the components, and moreover bring about concerns on reduction in the reliability of semiconductor devices. The reliability obtained from the technology disclosed by WO2020/105476 involves high manufacturing cost.

Japanese Patent Application Laid-Open No. 2008-305902, No. 2008-212977, and No. 2021-190505 may be related to the present disclosure.

SUMMARY

The present disclosure has an object of contributing to provision of a semiconductor device high in reliability and low in manufacturing cost.

A first aspect of the semiconductor device according to the present disclosure includes: a heat spreader made of copper or a copper alloy; a first solder layer; a second solder layer; a semiconductor element including a first surface bonded to the heat spreader through the first solder layer, a second surface facing the first surface, a first electrode disposed on the first surface, and a second electrode disposed on the second surface; a block bonded to the second electrode through the second solder layer, the block being made of copper or a copper alloy; a sheet including a first portion made of copper or a copper alloy, and a second portion having insulating properties and being in contact with the heat spreader; a first lead frame welded to the heat spreader and made of copper or a copper alloy; a second lead frame welded to the block and made of copper or a copper alloy; and a sealant having insulating properties and having a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the sealant sealing the sheet with at least a part of the first portion being exposed, sealing the first lead frame with the first lead frame being partly exposed opposite to the heat spreader, sealing the second lead frame with the second lead frame being partly exposed opposite to the block, and sealing the heat spreader, the first solder layer, the second solder layer, the semiconductor element, and the block.

A second aspect of the semiconductor device according to the present disclosure includes: a heat spreader made of copper or a copper alloy; a first solder layer; a second solder layer; a third solder layer having a melting point lower than a first melting point that is a lower one of a melting point of the first solder layer and a melting point of the second solder layer; a fourth solder layer having a melting point lower than the first melting point; a semiconductor element including a first surface bonded to the heat spreader through the first solder layer, a second surface facing the first surface, a first electrode disposed on the first surface, and a second electrode disposed on the second surface; a block bonded to the second electrode through the second solder layer, the block being made of copper or a copper alloy; a sheet including a first portion made of copper or a copper alloy, and a second portion having insulating properties and being in contact with the heat spreader; a first lead frame bonded to the heat spreader through the third solder layer and made of copper or a copper alloy; a second lead frame bonded to the block through the fourth solder layer and made of copper or a copper alloy; and a sealant having insulating properties and having a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the sealant sealing the sheet with at least a part of the first portion being exposed, sealing the first lead frame with the first lead frame being partly exposed opposite to the heat spreader, sealing the second lead frame with the second lead frame being partly exposed opposite to the block, and sealing the heat spreader, the first solder layer, the second solder layer, the semiconductor element, and the block.

A third aspect of the semiconductor device according to the present disclosure includes: a first lead frame; a second lead frame; a housing being tubular and having insulating properties and burying a center of the first lead frame and a center of the second lead frame; a sheet including a circuit pattern made of copper or a copper alloy and bonded to the first lead frame, a first portion made of copper or a copper alloy, and a second portion having insulating properties and sandwiched between the circuit pattern and the first portion, the sheet being housed in the housing with at least a part of the first portion being exposed; a first solder layer housed in the housing; a second solder layer housed in the housing; a semiconductor element including a first surface, a second surface facing the first surface, a first electrode disposed on the first surface and bonded to the circuit pattern through the first solder layer, and a second electrode disposed on the second surface, the semiconductor element being housed in the housing; a block bonded to the second electrode through the second solder layer and bonded to the second lead frame, the block being made of copper or a copper alloy and being housed in the housing; and a sealant having insulating properties and having a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the sealant sealing the sheet with at least a part of the first portion being exposed, sealing the first lead frame with the first lead frame being partly exposed opposite to the circuit pattern, sealing the second lead frame with the second lead frame being partly exposed opposite to the block, and sealing the circuit pattern, the first solder layer, the second solder layer, the semiconductor element, and the block.

The present disclosure can provide a semiconductor device high in reliability and low in manufacturing cost.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.1is a cross-sectional view exemplifying a structure of a semiconductor device1A according to Embodiment 1 of the present disclosure. The semiconductor device1A includes a semiconductor element14, a heat spreader15, and a block17made of a metal, all of which are sealed by a sealant16.

FIG.2is a plan view exemplifying the structure of the semiconductor device1A. An alternate long and short dashed line ofFIG.2indicates only a position of the sealant16in the plan view to provide better viewability of the structure of the semiconductor device1A.FIG.1is a cross-sectional arrow view taken along the line AA inFIG.2.

The semiconductor element14has a first surface14aand a second surface14bthat face each other. The semiconductor element14has the first surface14afarther from the block17, and the second surface14bcloser to the block17.

The semiconductor element14includes a first electrode144disposed on the first surface14a. For example, the first surface14ais metalized and functions as the first electrode144. In the drawings, the first surface14aappears as the first electrode144, and thus has a reference numeral “14a(144)”. The first surface14ais bonded to the heat spreader15through a first solder layer131. The heat spreader15is made of copper or a copper alloy (a composite of copper and at least one other metal; the same holds true for the following description).

For example, a rolled material made of copper or a copper alloy and 2 to 4 mm thick is adopted as the heat spreader15. For example, a basis material of the rolled material is used as it is as a portion of the heat spreader15to which the first surface14ais bonded.

The semiconductor element14includes a second electrode145(illustration omitted inFIG.1) disposed on the second surface14b. For example, the second surface14bis partly metalized, and formed as the second electrode145. The block17is disposed without extending beyond the second electrode145in a plan view.FIG.2exemplifies that an outline of the block17matches that of the second electrode145in the plan view. The block17is made of copper or a copper alloy. The second surface14bis bonded to the block17through a second solder layer132. The illustration of the first solder layer131and the second solder layer132is omitted inFIG.2.

The semiconductor device1A further includes a sheet11A. The sheet11A includes a first portion111and a second portion112. The first portion111is made of copper or a copper alloy. The second portion112has insulating properties, and is made of, for example, a resin. The heat spreader15is in contact with, for example, adheres to the second portion112opposite to the semiconductor element14.

The semiconductor device1A further includes a first lead frame104and a second lead frame105. The first lead frame104is partially welded and bonded to the heat spreader15by laser irradiation from the opposite side of the sheet11A. A portion (hereinafter also referred to as a “welded portion”)183in which the first lead frame104is welded to the heat spreader15is at a position advanced in a direction of arrows with respect to the line AA. Thus,FIG.1illustrates an outline of the welded portion183using broken lines that are hidden lines.

The second lead frame105is partially welded and bonded to the block17on a side opposite to the semiconductor element14. For example, the second lead frame105is partially welded and bonded to the block17at welded portions181and182by laser irradiation from the opposite side of the semiconductor element14. The welding by laser irradiation contributes to improvement on the productivity.

Each of the block17, the heat spreader15, the first lead frame104, and the second lead frame105is made of copper or a copper alloy. Since the laser light melts copper or a copper alloy material in the welding, a range to be heated is limited, and other portions are hardly thermally damaged.

When an insulated gate bipolar transistor (hereinafter abbreviated as an “IGBT”) is used as the semiconductor element14, the first electrode144functions as a collector electrode, and the second electrode145functions as an emitter electrode.

The first lead frame104becomes conductive with the first electrode144through the heat spreader15, and functions as a collector terminal of the IGBT functioning as the semiconductor element14. The second lead frame105becomes conductive with the second electrode145through the block17, and functions as an emitter terminal of the IGBT. When the IGBT operates, a collector current flows through the first lead frame104, and an emitter current flows through the second lead frame105.

The semiconductor element14further includes an electrode group140(illustration omitted inFIG.1) disposed on the second surface14b. The electrode group140includes third electrodes141,142, and143. For example, the third electrode141is a gate electrode of the IGBT functioning as the semiconductor element14, and receives a gate signal for controlling ON and OFF of the IGBT. For example, the third electrode142receives a signal for detecting an emitter voltage of the IGBT. For example, the third electrode143receives a signal for protecting the IGBT, for example, a signal with information on a temperature or information on a current value.

The semiconductor device1A further includes a lead frame group10and a wire group12. The lead frame group10includes third lead frames101,102, and103. The third lead frames101,102, and103contain copper or a copper alloy. The wire group12includes wires121,122, and123. The wires121,122, and123contain, for example, aluminum or an aluminum alloy. The third lead frame101is connected to the third electrode141through the wire121. The third lead frame102is connected to the third electrode142through the wire122. The third lead frame103is connected to the third electrode143through the wire123.

The sealant16seals the first lead frame104, the second lead frame105, the heat spreader15, the lead frame group10, the first solder layer131, the second solder layer132, the semiconductor element14, and the block17. The sealant16exposes at least a part of the first portion111(a surface of the first portion111opposite to the second portion112), partly exposes the first lead frame104opposite to the heat spreader15, partly exposes the second lead frame105opposite to the block17, and partly exposes the lead frame group10opposite to the electrode group140.

For example, resin transfer molding is adopted as the sealing using the sealant16. Before the transfer molding, the first lead frame104, the second lead frame105, and the lead frame group10form a linked portion having a thickness of 0.5 mm to 1.0 mm and made of copper or a copper alloy. After the transfer molding, the first lead frame104, the second lead frame105, and the lead frame group10are separated, for example, by cutting. For example, the lead frame group10is bent into the exemplified shape as necessary.

For example, copper foil approximately 0.1 mm thick is used as the first portion111of the sheet11A. For example, an insulating resin approximately 0.1 to 0.3 mm thick is used as the second portion112. The second portion112is evenly applied to the first portion111and is heat pressed up to what is called a B-stage (a semi-cured state) to prepare the sheet11A. The second portion112in this state receives the pressure from the sealant16by the transfer molding, and is exposed to a temperature of a mold to be adopted in the transfer molding to transition to what is called a C-stage (a completely cured state). In this manner, the second portion112adheres to the sealant16and the heat spreader15.

For example, the basis material of the rolled material is used as it is as a portion of the heat spreader15in contact with the second portion112.

A portion of the heat spreader15in contact with the sealant16is, for example, dimpled by pressing it. Dimples obtained from this pressing easily fit the sealant16, and suppress peels of the sealant16. Suppressing the peels prevents moisture ingress from outside of the sealant16into the constituent elements sealed by the sealant16. Suppressing the peels also prevents the constituent elements sealed by the sealant16from moving. This contributes to maintaining the reliability of bonding the first solder layer131and the second solder layer132and the reliability of connection between the lead frame group10and the electrode group140through the wire group12for a long period of time.

The sealant16is made of an insulating material with a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K. The sealant16is, for example, a thermosetting hard resin obtained by mixing fillers into a resin made of an epoxy system or a polyimide system as a main component. The linear coefficient of expansion of the sealant16may widely range approximately from 7 to 40 ppm/K. Controlling, for example, a compounding ratio of the fillers to the resin, or the size or the shape of the fillers leads to a linear coefficient of expansion ranging from 11 to 21 ppm/K.

Linear coefficients of expansions of general copper or copper alloys fall within the range of 11 to 21 ppm/K. Thus, a difference in linear coefficient of expansion between the sealant16and each of the block17, the heat spreader15, the first lead frame104, and the second lead frame105is small. The small differences reduce the stress in the cooling/heating cycles, and moreover contribute to enhancement of the reliability of semiconductor devices. Application of the block17, the heat spreader15, the first lead frame104, and the second lead frame105each made of copper or a copper alloy contributes to reduced material cost and processing cost and even to reduced manufacturing cost.

FIG.3is a flowchart exemplifying, as a first manufacturing method, steps of manufacturing the semiconductor device1A (also referred to as “manufacturing steps” in this disclosure with steps of manufacturing semiconductor devices1B to1G to be described later). The first manufacturing method includes Steps S1, S2, S3, and S4. In Step S1, a first step is executed. In Step S2, a second step is executed. In Step S3, a third step is executed. In Step S4, a fourth step is executed.

In the first step, the heat spreader15and the block17are bonded to the semiconductor element14.FIG.4is a cross-sectional view exemplifying the structure after the first step. The location of the cross-section ofFIG.1is used inFIG.4. In the first step, the first surface14aof the semiconductor element14is bonded to the heat spreader15through the first solder layer131. For example, known soldered joint is adopted to the bonding. The block17is bonded to the second surface14bof the semiconductor element14, specifically, the second electrode145(illustration omitted inFIGS.4to7; seeFIG.2) through the second solder layer132. For example, known soldered joint is adopted to the bonding.

In the second step, the first lead frame104is welded to the heat spreader15, and the second lead frame105is welded to the block17.FIG.5is a cross-sectional view exemplifying the structure after the second step. The location of the cross-section ofFIG.1is used inFIG.5. In executing the second step, the first lead frame104, the second lead frame105, and the lead frame group10are prepared as one linked component.FIGS.5to7omit the structure illustrating such a link.

The first lead frame104is welded to the heat spreader15by laser irradiation from the first lead frame104side to form the welded portion183. The second lead frame105is welded to the block17by laser irradiation from the second lead frame105side to form the welded portions181and182.

In the third step, the lead frame group10and the electrode group140are connected through the wire group12.FIG.6is a cross-sectional view exemplifying the structure after the third step. Specifically, the third lead frame101is connected to the third electrode141through the wire121, the third lead frame102is connected to the third electrode142through the wire122, and the third lead frame103is connected to the third electrode143through the wire123(illustration omitted inFIGS.4to7; seeFIG.2). For example, a known wire bonding technology is adopted to the connections. The location of the cross-section ofFIG.1is used inFIG.6. Thus,FIG.6does not illustrate the third lead frames101and103and the wires121and123.

In the fourth step, the sheet11A is disposed on the heat spreader15opposite to the semiconductor element14. The sealant16seals the first lead frame104, the second lead frame105, the heat spreader15, the lead frame group10, the first solder layer131, the second solder layer132, the semiconductor element14, and the block17while exposing the various portions as described above. Thus, the fourth step is a sealing step for forming the sealant16.

For example, the resin transfer molding is adopted as the sealing using a mold that is not illustrated. As described above, a state of the second portion112transitions from the B-stage (semi-cured state) to the C-stage (completely cured state) in the sealing.FIG.7is a cross-sectional view exemplifying the structure after the fourth step. The location of the cross-section ofFIG.1is used inFIG.7.

In the fourth step, the first lead frame104, the second lead frame105, and the lead frame group10are separated and bent into desired shapes to obtain the structure illustrated inFIG.1.

FIG.8is a cross-sectional view exemplifying a structure of a semiconductor device1B according to Embodiment 2 of the present disclosure. A hole105ais opened in the second lead frame105included in the semiconductor device1B. The hole105ais adjacent to portions bonded to the block17, for example, the welded portions181and182. The block17included in the semiconductor device1B according to Embodiment 2 includes a protrusion171. The protrusion171protrudes opposite to the semiconductor element14, and is inside the hole105a. The other constituent elements and the relationship between the constituent elements are identical to those of the semiconductor device1A.

FIG.9is a plan view exemplifying the structure of the semiconductor device1B. An alternate long and short dashed line ofFIG.9indicates only a position of the sealant16in the plan view to provide better viewability of the structure of the semiconductor device1B.FIG.8is a cross-sectional arrow view taken along the line DD inFIG.9.FIG.9exemplifies a case where the hole105aand the protrusion171are sandwiched between the welded portions181and182. The illustration of the first solder layer131and the second solder layer132is omitted inFIG.9.

In Embodiment 2, the semiconductor device1B is also fabricated by, for example, the first to fourth steps described in Embodiment 1. In the second step, engaging the protrusion171into the hole105aeasily determines the position of the second lead frame105with respect to the block17. In executing the second step, the first lead frame104, the second lead frame105, and the lead frame group10are prepared as one linked component. Easily determining the position of the second lead frame105with respect to the block17also easily determines the position of the first lead frame104with respect to the heat spreader15and also the position of the lead frame group10with respect to the electrode group140.

The hole105aand the protrusion171contribute not only to positioning of the second lead frame105with respect to the block17when they are welded, but also to positioning of the first lead frame104with respect to the heat spreader15when they are welded and moreover to facilitating execution of the second step.

The hole105aand the protrusion171also contribute not only to positioning of the lead frame group10with respect to the electrode group140when they are connected through the wire group12, but also to facilitating execution of the third step.

FIG.10is a cross-sectional view exemplifying a structure of a semiconductor device1C according to Embodiment 3 of the present disclosure. The location of the cross-section ofFIG.1is used inFIG.10.

The block17included in the semiconductor device1C includes a surface172. The surface172is closer to the third lead frames101,102, and103. A distance between the surface172and each of the third lead frames101,102, and103increases with distance away from the second surface14b. The other constituent elements and the relationship between the constituent elements are identical to those of the semiconductor device1A.

In Embodiment 3, the semiconductor device1C is also fabricated by, for example, the first to fourth steps described in Embodiment 1.FIGS.11to14are cross-sectional views exemplifying the progress of the third step in steps of manufacturing the semiconductor device1C. The location of the cross-section ofFIG.10is used inFIGS.11to14.

An aluminum wire120is supplied from the side of a bonding tool9.FIG.11exemplifies a state where an apex of the bonding tool9closer to the heat spreader15(hereinafter simply referred to as an “apex”) connects the aluminum wire120to the third electrode142(not illustrated; seeFIG.2).

FIG.12exemplifies a halfway state of the bonding tool9, after the connection, which is moving toward the third lead frame102while supplying the aluminum wire120.FIG.13exemplifies a state where the apex of the bonding tool9connects the aluminum wire120to the third lead frame102.FIG.14exemplifies a state after the apex of the bonding tool9separates the aluminum wire120from the third lead frame102to form the wire122.

Typically, the bonding tool9has a widespread shape in an extension direction of the second surface14bwhen seen from the apex. When the aluminum wire120is connected to the third electrode142, the apex comes in proximity to the semiconductor element14. The proximity causes interference between the position of the bonding tool9and that of the block17.

The distance between the surface172and each of the third lead frames101,102, and103increases with distance away from the second surface14b. This facilitates avoiding the interference between the position of the bonding tool9and that of the block17.

The wires121,122, and123are easily formed in the semiconductor device1C. In the semiconductor device1C, extension of the second electrode145closer to the third electrodes141,142, and143is easily designed. The wider second electrode145contributes to reduced ON resistance of the semiconductor element14.

FIG.15is a cross-sectional view exemplifying a structure of a semiconductor device1Da according to Embodiment 4 of the present disclosure. The location of the cross-section ofFIG.1is used inFIG.15.

FIGS.16and17are enlarged cross-sectional views of the heat spreader15and the block17, each illustrating, in the semiconductor device1Da, the heat spreader15in contact with the first surface14a, the block17in contact with the second surface14b, and the first surface14a, and the second surface14b.FIG.18is a partial enlarged plan view illustrating the block17, and the semiconductor element14and the heat spreader15in the vicinity of the block17. The illustration of the first solder layer131and the second solder layer132is omitted inFIG.18.FIG.16is a cross-sectional view taken along the line BB inFIG.18.FIG.17is a cross-sectional view taken along the line CC inFIG.18.

The block17includes protrusions173protruding toward the semiconductor element14. The protrusions173are in contact with the second surface14b. The block17includes, for example, three or more of the protrusions173. The heat spreader15includes protrusions151protruding toward the semiconductor element14. The protrusions151are in contact with the first surface14a. The heat spreader15includes, for example, three or more of the protrusions151. The other constituent elements and the relationship between the constituent elements are identical to those of the semiconductor device1A.

FIGS.15to18exemplify that the semiconductor device1Da includes the three protrusions151and the three protrusions173.FIGS.15to18exemplify that the two protrusions173and the one protrusion151form one row, the other one protrusion173and the other two protrusions151form another row, and the two rows are approximately parallel to each other in a plan view.

In Embodiment 4, the semiconductor device1Da is also fabricated by, for example, the first to fourth steps described in Embodiment 1.

The semiconductor element14is thinner in view of reducing the losses, and is, for example, several tens of micrometers thick. When the semiconductor element14is curved by the weight of the block17in the first step, the second solder layer132being melted easily extends beyond the second surface14b. The protrusions173prevent the extension.

When the semiconductor element14is curved by the weight of the block17, the first solder layer131being melted easily extends beyond the first surface14a. The protrusions151prevent the extension.

FIG.19is a partial enlarged cross-sectional view illustrating the protrusion151, and the semiconductor element14and the heat spreader15in the vicinity of the protrusion151. The protrusion151is formed by, for example, press working using a die with annular protrusions when the heat spreader15is manufactured. This formation forms an annular groove152around the protrusion151. The protrusion151and the groove152contribute to enhancement of the reliability of bonding the heat spreader15to the semiconductor element14through the first solder layer131.

FIG.20is a cross-sectional view exemplifying a structure of another semiconductor device1Db according to Embodiment 4. The location of the cross-section ofFIG.1is used inFIG.20.

FIGS.21and22are enlarged cross-sectional views of the heat spreader15and the block17, each illustrating, in the semiconductor device1Db, the heat spreader15in contact with the first surface14a, the block17in contact with the second surface14b, and the first surface14a, and the second surface14b.FIG.23is a partial plan view illustrating the block17, and the semiconductor element14and the heat spreader15in the vicinity of the block17. The illustration of the first solder layer131and the second solder layer132is omitted inFIG.23.FIG.21is a cross-sectional view taken along the line GG inFIG.23.FIG.22is a cross-sectional view taken along the line HH inFIG.23.

The block17includes the aforementioned protrusions173. The semiconductor device1Db includes, between the heat spreader15and the first surface14a, bumps125made of a metal. The bumps125are in contact with the first surface14aand the heat spreader15. The semiconductor device1Db includes, for example, three or more of the bumps125. The bumps125are formed by, for example, a known wire bonding technology.

FIGS.20to23exemplify that the semiconductor device1Db includes the three protrusions173and the three bumps125.FIGS.20to23exemplify that the two protrusions173and the one bump125form one row, the other one protrusion173and the other two bumps125form another row, and the two rows are approximately parallel to each other in a plan view.

The bumps125prevent the first solder layer131being melted from extending beyond the first surface14a, similarly to the protrusions151.

The protrusions151and173and the bumps125are not exclusively adopted. For example, both of the protrusions151and the bumps125are adopted. In this case, the total number of the protrusions151and the bumps125is, for example, three or more.

The three or more protrusions173contribute to stably disposing the block17on the semiconductor element14. The three or more of the protrusions151and the bumps125in total (including a case where the semiconductor device1Db does not include the protrusions151or the bumps125) contribute to stably disposing the semiconductor element14on the heat spreader15.

FIG.24is a cross-sectional view exemplifying a structure of a semiconductor device1E according to Embodiment 5 of the present disclosure. The location of the cross-section ofFIG.1is used inFIG.24.

The first lead frame104is bonded to the heat spreader15through a third solder layer133in Embodiment 5, unlike Embodiments 1 to 4. The second lead frame105is bonded to the block17through a fourth solder layer134in Embodiment 5, unlike Embodiments 1 to 4. The other constituent elements and the relationship between the constituent elements are identical to those of the semiconductor device1A.

In Embodiment 5, the semiconductor device1E is also fabricated by, for example, the first to fourth steps described in Embodiment 1. In the second step according to Embodiment 5, a solder alloy is disposed each between the heat spreader15and the first lead frame104and between the block17and the second lead frame105. Melting these solder alloys produces the third solder layer133and the fourth solder layer134.

For example, the solder alloy between the heat spreader15and the first lead frame104is locally heated by laser irradiation through the first lead frame104, and is melted into the third solder layer133. The solder alloy between the block17and the second lead frame105is locally heated by laser irradiation through the second lead frame105, and is melted into the fourth solder layer134.

It is preferred to melt the solder alloys to form the third solder layer133and the fourth solder layer134, without melting the first solder layer131and the second solder layer132. This is because melting the first solder layer131and the second solder layer132may lead to elution of metals (for example, nickel) from the first electrode144and the second electrode145, respectively, and avoidance of such elution is desirable.

Taking into account that the heat spreader15and the block17contain copper or a copper alloy and have high thermal conductivity, it is preferred that each of a melting point of the third solder layer133and a melting point of the fourth solder layer134is lower than a first melting point that is a lower one of a melting point of the first solder layer131and a melting point of the second solder layer132.

In the laser irradiation, for example, the heat spreader15, the semiconductor element14, and the block17are heated lower than the first melting point. The heating contributes to easy formation of the third solder layer133and the fourth solder layer134by laser irradiation while avoiding melting the first solder layer131and the second solder layer132.

The third solder layer133functions as a stress buffer, and contributes to enhancement of the reliability of bonding the first lead frame104to the heat spreader15at low cost and moreover enhancement of the reliability of the semiconductor device1E at low cost. The fourth solder layer134functions as a stress buffer, and contributes to enhancement of the reliability of bonding the second lead frame105to the block17at low cost and moreover enhancement of the reliability of the semiconductor device1E at low cost.

FIG.25is a cross-sectional view exemplifying a structure of a semiconductor device1F according to Embodiment 6 of the present disclosure. The location of the cross-section ofFIG.1is used inFIG.25.

In Embodiment 6, a hole104bis opened in the first lead frame104, and a hole105bis opened in the second lead frame105. The third solder layer133is inside the hole104b, and bonds the first lead frame104to the heat spreader15. The fourth solder layer134is inside the hole105b, and bonds the second lead frame105to the block17. The other constituent elements and the relationship between the constituent elements are identical to those of the semiconductor device1E.

In Embodiment 6, the semiconductor device1F is also fabricated by, for example, the first to fourth steps described in Embodiment 1.

FIGS.26and27are cross-sectional views illustrating a part of steps of manufacturing the semiconductor device1F.FIG.28is a flowchart exemplifying the second step in Embodiment 6.

The second step in Embodiment 6 includes Steps S21, S22, S23, S24, S25and S26. A process of Step S21is to bring the surrounding of the hole104bin contact with the heat spreader15. After Step S21, Step S22is executed. A process of Step S22is to dispose a first solder alloy133bat a position inside the hole104b(seeFIG.26).

A process of Step S23is to bring the surrounding of the hole105bin contact with the block17. After Step S23, Step S24is executed. A process of Step S24is to dispose a second solder alloy134bat a position inside the hole105b(seeFIG.26). For example, Steps S21and S23are simultaneously executed. For example, Steps S22and S24are simultaneously executed.

After Steps S21, S22, S23, and S24, Steps S25and S26are executed. A process of Step S25is to melt the first solder alloy133bto form the third solder layer133. A process of Step S26is to melt the second solder alloy134bto form the fourth solder layer134(seeFIG.27). For example, Steps S25and Step S26are simultaneously executed.

After Steps S25and S26, the manufacturing steps return to the third step (Step S3; seeFIG.3).

For example, the first solder alloy133bis locally heated by laser irradiation into a region inside the hole104b, and is melted into the third solder layer133. The second solder alloy134bis locally heated by laser irradiation into a region inside the hole105b, and is melted into the fourth solder layer134.FIGS.25and27exemplify that the third solder layer133and the fourth solder layer134are recessed opposite to the heat spreader15.

As described in Embodiment 5, it is preferred that each of the melting point of the third solder layer133and the melting point of the fourth solder layer134is lower than the first melting point that is a lower one of the melting point of the first solder layer131and the melting point of the second solder layer132. Here, the first solder alloy133bin Step S25and the second solder alloy134bin Step S26are melted at a temperature lower than the first melting point.

The semiconductor device1F has the same advantages as those of the semiconductor device1E in forming the third solder layer133and the fourth solder layer134. The laser irradiation into the first solder alloy133bdoes not involve the first lead frame104. The laser irradiation into the second solder alloy134bdoes not involve the second lead frame105.

The semiconductor device1F has an advantage of enabling visual inspection of bonding of the third solder layer133and the fourth solder layer134prior to the fourth step. This advantage contributes to enhancement of the reliability of bonding the first lead frame104to the heat spreader15, the reliability of bonding the second lead frame105to the block17, and moreover the reliability of the semiconductor device1F.

FIG.29is a cross-sectional view exemplifying a structure of a semiconductor device1G according to Embodiment 7 of the present disclosure. The location of the cross-section ofFIG.1is used inFIG.29.

The semiconductor device1G includes the first lead frame104, the second lead frame105, and a housing16B.

The housing16B is tubular and has insulating properties. The housing16B buries the center of the first lead frame104, and the center of the second lead frame105.

The semiconductor device1G further includes a sheet11B, the first solder layer131, the second solder layer132, the semiconductor element14, and the block17all of which are housed in the housing16B.

The sheet11B includes a circuit pattern115, a first portion113, and a second portion114. Both of the circuit pattern115and the first portion113contain copper or a copper alloy. The second portion114has insulating properties, and is sandwiched between the circuit pattern115and the first portion113. The sheet11B is bonded to the housing16B while at least a part of the first portion113(a surface of the first portion113opposite to the second portion114) is exposed.

The semiconductor element14includes the first surface14a, the second surface14b, the first electrode144, and the second electrode145(illustration omitted inFIG.29; seeFIG.2), similarly to that in the semiconductor device1A. The first surface14ais bonded to the circuit pattern115through the first solder layer131.

The block17is bonded to the second electrode145through the second solder layer132, similarly to that in the semiconductor device1A.

The first lead frame104is welded and bonded to the circuit pattern115through the welded portion183. The second lead frame105is welded and bonded to the block17through the welded portions181and182.

A sealant16A has insulating properties, and has a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K. The sealant16A seals the first lead frame104, the second lead frame105, the sheet11B, the lead frame group10, the circuit pattern115, the first solder layer131, the second solder layer132, the semiconductor element14, and the block17. The sealant16A exposes the aforementioned part of the first portion113, partly exposes the first lead frame104opposite to the circuit pattern115, partly exposes the second lead frame105opposite to the block17, and partly exposes the lead frame group10opposite to the electrode group140.

The semiconductor device1G further includes the wire group12(the wire122inFIG.29; seeFIG.2) and the electrode group140(illustration omitted inFIG.29; seeFIG.2), similarly to the semiconductor device1A. The sealant16A also seals the wire group12and the electrode group140.

The sealant16A in the semiconductor device1G is formed by potting an insulator, for example, a resin into the space surrounded by the housing16B. The sealant16A is made of a material identical to that of the sealant16according to Embodiment 1.

Since the sealant16A in the semiconductor device1G has the linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the semiconductor device1G less expensive and high in reliability can be obtained, similarly to that in Embodiment 1. The housing16B with the linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K contributes to enhancement of the reliability. The housing16B is made of, for example, a material identical to that of the sealant16according to Embodiment 1.

For example, the laser irradiation is adopted to welding the first lead frame104to the circuit pattern115and welding the second lead frame105to the block17.

FIGS.30to32are cross-sectional views illustrating steps of manufacturing the semiconductor device1G. The location of the cross-section ofFIG.1is used in FIGS.30to32.FIG.33is a flowchart exemplifying the manufacturing steps as a second manufacturing method.

FIG.30is a cross-sectional view illustrating a positional relationship between the first lead frame104, the second lead frame105, and the housing16B. A part of the first lead frame104surrounded by the housing16B is bonded to the circuit pattern115(for example, by laser irradiation). A part of the second lead frame105surrounded by the housing16B is bonded to the block17(for example, by laser irradiation).

The housing16B that buries the center of the first lead frame104and the center of the second lead frame105is manufactured by a known molding technology. Hereinafter, the housing16B with the first lead frame104and the second lead frame105as described above will be provisionally referred to as a first component301, and a step of manufacturing the first component301will be provisionally referred to as a first component manufacturing step for convenience. In the first component301, the center of the lead frame group10(only the third lead frame102inFIG.30) is also buried in the housing16B.

FIG.31is a cross-sectional view illustrating a positional relationship between the sheet11B, the first solder layer131, the second solder layer132, the semiconductor element14, and the block17. The circuit pattern115is bonded to the semiconductor element14through the first solder layer131. The semiconductor element14is bonded to the block17through the second solder layer132. The aforementioned bonding produces a laminated structure of the sheet11B, the first solder layer131, the semiconductor element14, the second solder layer132, and the block17. Hereinafter, this laminated structure will be provisionally referred to as a second component302, and a step of manufacturing the second component302will be provisionally referred to as a second component manufacturing step for convenience.

The first component manufacturing step and the second component manufacturing step are independently executed. The order of executing the first component manufacturing step and executing the second component manufacturing step may be any.

The second manufacturing method includes Steps S5, S6, S7, S8, and S9. In Step S5, a step of manufacturing components is executed. The first component manufacturing step and the second component manufacturing step are executed in the step of manufacturing components.

After Step S5, Step S6is executed. In Step S6, a housing step is executed. In the housing step, the second component302is housed in the first component301, specifically, the housing16B. Here, the sheet11B is bonded to the housing16B while at least a part of the first portion113is exposed.

After Step S6, Step S7is executed. In Step S7, a welding step is executed. In the welding step, the first lead frame104is welded to the circuit pattern115, and the second lead frame105is welded to the block17.

After Step S7, Step S8is executed. In Step S8, a wiring step is executed. In the wiring step, the lead frame group10and the electrode group140(illustration omitted; seeFIG.2) are connected through the wire group12(only the wire122inFIG.32).

FIG.32is a cross-sectional view illustrating an end state of the wiring step. In this state, the circuit pattern115, the semiconductor element14, the block17, the first solder layer131, the second solder layer132, and the wire group12are exposed. In this state, portions of the lead frame group10that are connected to the wire group12, a portion of the first lead frame104that is bonded to the circuit pattern115, and a portion of the second lead frame105that is bonded to the block17are also exposed.

After Step S8, Step S9is executed. In Step S9, a sealing step is executed. The sealing step is sealing the sheet11B with at least a part of the first portion113being exposed, sealing the first lead frame104with the first lead frame104being partly exposed opposite to the circuit pattern115, sealing the second lead frame105with the second lead frame105being partly exposed opposite to the block17, and sealing the circuit pattern115, the first solder layer131, the second solder layer132, the semiconductor element14, and the block17. The sealing step applies, for example, potting a resin.

The end of the sealing step ends the second manufacturing method to produce the semiconductor device1G (seeFIG.29).

The second manufacturing method contributes to manufacturing the semiconductor device1G.

Adopting, to the semiconductor devices1A to1F, a structure in which a hole is opened in the first lead frame104and a protrusion engaged into this hole protrudes opposite to the sheet11A from the heat spreader15leads to the contribution similarly to Embodiment 2. Adopting, to the semiconductor device1G, a structure in which a hole is opened in the first lead frame104and a protrusion engaged into this hole protrudes opposite to the sheet11B from the circuit pattern115leads to the contribution similarly to Embodiment 2.

These structures contribute not only to facilitating positioning of the first lead frame104and the heat spreader15(or the circuit pattern115) when they are welded and positioning of the second lead frame105and the block17when they are welded, but also to facilitating execution of the second step. These structures also contribute not only to facilitating positioning of the lead frame group10and the electrode group140when they are connected through the wire group12, but also to facilitating execution of the third step.

Without the protrusions173, the protrusions151or the bumps125in Embodiment 4 prevent the first solder layer131being melted from extending beyond the first surface14awhen the semiconductor element14is curved by the weight of the block17in the first step.

Without the protrusions151and the bumps125, the protrusions173in Embodiment 4 prevent the second solder layer132being melted from extending beyond the second surface14bdue to the curved semiconductor element14.

Embodiments can be freely combined, and appropriately modified or omitted. For example, the protrusion171described in Embodiment 2 is applicable to any one of the semiconductor devices1A,1C,1Da,1Db,1E,1F, and1G. For example, the surface172described in Embodiment 3 is applicable to any one of the semiconductor devices1A,1B,1Da,1Db,1E,1F, and1G. For example, any one or more of the protrusions151, the protrusions173, and the bumps125described in Embodiment 4 are applicable to any one of the semiconductor devices1A,1B,1C,1E,1F, and1G.

The following will describe a summary of various aspects of the present disclosure as appendixes.

[Appendix 1] A semiconductor device, comprising:a heat spreader made of copper or a copper alloy;a first solder layer;a second solder layer;a semiconductor element including a first surface bonded to the heat spreader through the first solder layer, a second surface facing the first surface, a first electrode disposed on the first surface, and a second electrode disposed on the second surface;a block bonded to the second electrode through the second solder layer, the block being made of copper or a copper alloy;a sheet including a first portion made of copper or a copper alloy, and a second portion having insulating properties and being in contact with the heat spreader;a first lead frame welded to the heat spreader and made of copper or a copper alloy;a second lead frame welded to the block and made of copper or a copper alloy; anda sealant having insulating properties and having a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the sealant sealing the sheet with at least a part of the first portion being exposed, sealing the first lead frame with the first lead frame being partly exposed opposite to the heat spreader, sealing the second lead frame with the second lead frame being partly exposed opposite to the block, and sealing the heat spreader, the first solder layer, the second solder layer, the semiconductor element, and the block.
[Appendix 2] A semiconductor device, comprising:a heat spreader made of copper or a copper alloy;a first solder layer;a second solder layer;a third solder layer having a melting point lower than a first melting point that is a lower one of a melting point of the first solder layer and a melting point of the second solder layer;a fourth solder layer having a melting point lower than the first melting point;a semiconductor element including a first surface bonded to the heat spreader through the first solder layer, a second surface facing the first surface, a first electrode disposed on the first surface, and a second electrode disposed on the second surface;a block bonded to the second electrode through the second solder layer, the block being made of copper or a copper alloy;a sheet including a first portion made of copper or a copper alloy, and a second portion having insulating properties and being in contact with the heat spreader;a first lead frame bonded to the heat spreader through the third solder layer and made of copper or a copper alloy;a second lead frame bonded to the block through the fourth solder layer and made of copper or a copper alloy; anda sealant having insulating properties and having a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the sealant sealing the sheet with at least a part of the first portion being exposed, sealing the first lead frame with the first lead frame being partly exposed opposite to the heat spreader, sealing the second lead frame with the second lead frame being partly exposed opposite to the block, and sealing the heat spreader, the first solder layer, the second solder layer, the semiconductor element, and the block.
[Appendix 3] The semiconductor device according to appendix 2,wherein a first hole is opened, inside which the third solder layer is, in the first lead frame, and a second hole is opened, inside which the fourth solder layer is, in the second lead frame.
[Appendix 4] The semiconductor device according to any one of appendixes 1 to 3,wherein the second lead frame includes a hole adjacent to portions bonded to the block, andthe block incudes a protrusion protruding opposite to the semiconductor element and being inside the hole.
[Appendix 5] The semiconductor device according to any one of appendixes 1 to 4, further comprising:a third lead frame; anda wire connected to the third lead frame,wherein the semiconductor element further includes a third electrode disposed on the second surface and connected to the third lead frame through the wire, andthe block includes a surface closer to the third lead frame, the surface having an increasing distance from the third lead frame with distance away from the second surface.
[Appendix 6] The semiconductor device according to any one of appendixes 1 to 5,wherein the block includes three or more protrusions protruding toward the semiconductor element.
[Appendix 7] The semiconductor device according to any one of appendixes 1 to 6,wherein the heat spreader includes three or more protrusions protruding toward the semiconductor element.
[Appendix 8] The semiconductor device according to any one of appendixes 1 to 7, further comprisinga bump between the first surface and the heat spreader, the bump being made of a metal.
[Appendix 9] A method of manufacturing the semiconductor device according to appendix 2 or 3, the method comprising:bonding the semiconductor element to the heat spreader through the first solder layer, and the semiconductor element to the block through the second solder layer;melting a first solder alloy at a temperature lower than the first melting point to form the third solder layer, and a second solder alloy at a temperature lower than the first melting point to form the fourth solder layer, the melting being executed after the bonding; andforming the sealant, the forming being executed after the melting.
[Appendix 10] The method according to appendix 9,wherein the melting includes performing laser irradiation to melt the first solder alloy and the second solder alloy.
[Appendix 11] A semiconductor device, comprising:a first lead frame;a second lead frame;a housing being tubular and having insulating properties and burying a center of the first lead frame and a center of the second lead frame;a sheet including a circuit pattern made of copper or a copper alloy and bonded to the first lead frame, a first portion made of copper or a copper alloy, and a second portion having insulating properties and sandwiched between the circuit pattern and the first portion, the sheet being housed in the housing with at least a part of the first portion being exposed;a first solder layer housed in the housing;a second solder layer housed in the housing;a semiconductor element including a first surface, a second surface facing the first surface, a first electrode disposed on the first surface and bonded to the circuit pattern through the first solder layer, and a second electrode disposed on the second surface, the semiconductor element being housed in the housing;a block bonded to the second electrode through the second solder layer and bonded to the second lead frame, the block being made of copper or a copper alloy and being housed in the housing; anda sealant having insulating properties and having a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the sealant sealing the sheet with at least a part of the first portion being exposed, sealing the first lead frame with the first lead frame being partly exposed opposite to the circuit pattern, sealing the second lead frame with the second lead frame being partly exposed opposite to the block, and sealing the circuit pattern, the first solder layer, the second solder layer, the semiconductor element, and the block.
[Appendix 12] A method of manufacturing a semiconductor device, the method comprising:manufacturing a first component and a second component,the first component including:a housing being tubular and having insulating properties;a first lead frame including a center buried in the housing; anda second lead frame including a center buried in the housing; andthe second component including:a sheet including a circuit pattern made of copper or a copper alloy, a first portion made of copper or a copper alloy, and a second portion having insulating properties and sandwiched between the circuit pattern and the first portion;a first solder layer;a second solder layer;a semiconductor element including a first surface bonded to the circuit pattern through the first solder layer, a second surface facing the first surface, a first electrode disposed on the first surface, and a second electrode disposed on the second surface; anda block bonded to the second electrode through the second solder layer, the block being made of copper or a copper alloy;bonding the sheet to the housing with at least a part of the first portion being exposed, and housing the second component in the first component;welding the first lead frame to the circuit pattern and welding the second lead frame to the block, the welding being executed after the bonding and the housing; andsealing, using a sealant having insulating properties and having a linear coefficient of expansion more than or equal to 11 ppm/K and less than or equal to 21 ppm/K, the sheet with at least the part of the first portion being exposed, the first lead frame with the first lead frame being partly exposed opposite to the circuit pattern, the second lead frame with the second lead frame being partly exposed opposite to the block, and the circuit pattern, the first solder layer, the second solder layer, the semiconductor element, and the block, the scaling being executed after the welding.