Semiconductor module and method for manufacturing the same

A semiconductor module includes: one or more semiconductor elements; a wiring substrate having a first surface on which the one or more semiconductor elements are mounted, the wiring substrate being electrically connected to the one or more semiconductor elements; a heat sink on which the wiring substrate is mounted, the heat sink facing a second surface of the wiring substrate on a reverse side of the first surface; a binder which is formed in a die pad area on the heat sink so as to be present between the wiring substrate and the heat sink, and bonds the wiring substrate and the heat sink; and a support which is formed in a peripheral part of the die pad area on the heat sink, and fixes the wiring substrate to the heat sink by being in contact with a peripheral part of the second surface of the wiring substrate.

BACKGROUND

1. Technical Field

The present disclosure relates to a semiconductor module and a method for manufacturing the semiconductor module.

2. Description of the Related Art

In recent years, light emitting diodes (LEDs) have become widely popular as optical elements which save power consumption and replace incandescent lamps and fluorescent lamps. Semiconductor packages having such semiconductor elements are being replaced with modules having not only semiconductor elements or semiconductor packages but also peripheral components because of demands for reducing the sizes of casing sets having the semiconductor elements or semiconductor packages housed therein and ease in creating electrical or optical designs of semiconductor elements or semiconductor packages.

In these circumstances, it is increasingly important for semiconductor modules to achieve high heat dissipation that supports high output by the semiconductor elements. Thus, semiconductor modules having a binder which provides a high thermal conductivity and a wiring substrate and a metal substrate which provide high heat dissipation have been developed (for example, see Japanese Unexamined Patent Application Publication No. 2012-109521 (PTL 1) and Japanese Unexamined Patent Application Publication No. 2013-105929 (PTL 2).

SUMMARY

However, with the above-described configuration, it is difficult to secure mounting accuracy on the X-Y plane and control the height along the Z axis when mounting and bonding a wiring substrate or a sub-mount having the semiconductor elements mounted thereon. In order to achieve the mounting accuracy (a height, a tilt, a swing, a position on the X-Y plane, etc.) required for optical elements etc., a mounting head tool needs to hold the sub-mount long time, which makes it difficult to mount the sub-mount in a short time.

In view of the above problem, the present disclosure has an object to provide a semiconductor module for mounting a wiring substrate or a sub-mount having one or more semiconductor elements mounted thereon onto a heat sink with high accuracy in a short time, and provide a method for manufacturing the semiconductor module.

In order to solve the above problems, a semiconductor module according to an aspect of the present disclosure is a semiconductor module including: one or more semiconductor elements; a wiring substrate having a first surface on which the one or more semiconductor elements are mounted, the wiring substrate being electrically connected to the one or more semiconductor elements; a heat sink on which the wiring substrate is mounted, the heat sink facing a second surface of the wiring substrate on a reverse side of the first surface; a binder which is formed in a die pad area on the heat sink so as to be present between the wiring substrate and the heat sink, and bonds the wiring substrate and the heat sink; and a support which is formed in a peripheral part of the die pad area on the heat sink, and fixes the wiring substrate to the heat sink by being in contact with a peripheral part of the second surface of the wiring substrate; wherein the binder and the support are formed apart from each other.

In addition, a semiconductor module manufacturing method according to an aspect of the present disclosure is a semiconductor module manufacturing method including: forming at least three supports independently on a heat sink; forming a binder on the heat sink so that the binder does not touch the at least three supports; disposing a wiring substrate on which one or more semiconductor elements are mounted so that the binder is present between the wiring substrate and the heat sink and across the at least three supports, and fixing the wiring substrate to the at least three supports; and heating and melting the binder to bond the wiring substrate and the heat sink, wherein, in the forming of a binder, the binder is disposed to be surrounded by the at least three supports in a plan view.

The semiconductor module and the method for manufacturing the semiconductor module according to the present disclosure make it possible to mount the wiring substrate or the sub-mount having the one or more semiconductor elements mounted thereon onto the heat sink with high accuracy in a short time.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 12illustrates a first exemplary semiconductor module according to a conventional technique. Semiconductor module200illustrated inFIG. 12includes LED package substrate201on which LED chip202is mounted. Furthermore, LED package203is mounted on wiring substrate204. Part immediately below LED package203is bonded to heat sink206by soldering or with binder205having a high thermal conductivity.

FIG. 13illustrates a second exemplary semiconductor module according to a conventional technique. In semiconductor module300illustrated inFIG. 13, each of LED elements323are electrically connected to positive electrode land324aand negative electrode land324bof heat sink321via sub-mount322which is a mount structure including a mounted wiring substrate, and sub-mount322is mounted on the upper surface of heat sink321.

However, the above configuration makes it difficult to secure mounting accuracy on the X-Y plane and control the height along the Z axis when mounting or bonding the wiring substrate or the sub-mount having LED elements323mounted thereon onto heat sink321. This is explained below in detail.

In a semiconductor module including; a plurality of semiconductor elements; a wiring substrate or a sub-mount on which the plurality of semiconductor elements are mounted; a heat sink on which the wiring substrate is mounted, optical centers are determined with respect to the optical positions of the respective semiconductor elements. The semiconductor module is mounted on a casing using reference holes in the heat sink as references. Accordingly, mounting components onto the semiconductor module requires high mounting accuracy with respect to the optical centers and the positions of the reference holes in the heat sink. As a result, bonding with the wiring substrate or the heat sink of the sub-mount requires a highly-accurate positioning between them.

In the above configuration, for example in the sub-mount mounting method disclosed in Patent Literature 2 (PTL 2), heat sink321is heated first, and then a binder (die bond material) is placed on heat sink321and is heated to be melted. Sub-mount322is then picked up by a mounting head tool and is mounted on the binder. At this time, in order to secure the mounting accuracy on the X-Y plane and the height along the Z axis, the mounting head tool keeps holding sub-mount322until sub-mount322is disposed at a predetermined location. In sequence, sub-mount322is bonded with the binder, held, and cooled down to be solidified. Here, if sub-mount322is dissipated from the mounting head tool, it is impossible to control mounting accuracy such as height variation.

The generally-used heat sinks made of metal such as Cu take long time to be heated or cooled down to a desired temperature because of its high thermal capacity, which lengthens manufacturing cycle time. In addition, it is impossible to achieve the mounting accuracy (a height, a tilt, a swing, a position on the X-Y plane, etc. required for optical elements etc. without securing long time for a mounting head tool to hold a sub-mount. In other words, it is difficult to achieve the mounting accuracy while reducing the manufacturing cycle time.

Furthermore, if a metal binder having a high melting point is used, the metal binder itself needs to be heated to a high temperature to be melted. Thus, a long time is required for heating from and cooling down to a normal temperature, which lengthens the manufacturing cycle time. These problems are noticeable.

In view of this, descriptions are given of a semiconductor module for mounting a wiring substrate or a sub-mount having semiconductor elements mounted thereon onto a heat sink with high accuracy in a short time and a method for manufacturing the semiconductor module.

Hereinafter, embodiments and modifications and variations thereof are described in detail with reference to the drawings. It is to be noted that substantially the same constituent elements are given the same numerical references and descriptions thereof may be omitted in the embodiments etc. below. Each of the embodiments etc. below describes a specific example. The numerical values, shapes, materials, constituent elements, the arrangement and connection of the constituent elements, steps, the processing order of the steps etc. indicated in the following exemplary embodiments etc. are mere examples, and therefore do not limit the scope of the present disclosure. Among the constituent elements in the following embodiments etc., constituent elements not recited in any one of the independent claims are described as arbitrary constituent elements. It is to be noted that unnecessarily detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and overlapping descriptions of substantially the same constituent elements may be omitted. This omission is made to prevent the following descriptions from being unnecessarily redundant and help the person skilled in the art appreciate the present disclosure.

It is to be noted that the attached drawings and the descriptions below are provided to help the person skilled in the art fully appreciate the present disclosure, and thus are not intended to limit the scope of the claims.

Each of cross-sectional views described in the embodiments below is a cross-sectional view along a straight line passing through two opposing supports arranged in the semiconductor module in each embodiment.

Hereinafter, Embodiment 1 is described with reference toFIG. 1.

InFIG. 1, (a) is a schematic diagram (cross-sectional view) of a configuration of semiconductor module100according to this embodiment. InFIG. 1, (b) is a schematic diagram (perspective view) of a configuration of semiconductor module100according to this embodiment. It is to be noted that semiconductor elements1, phosphors6, and electrodes8illustrated in (a) ofFIG. 1are not illustrated in (b) ofFIG. 1.

Semiconductor module100illustrated in (a) and (b) ofFIG. 1includes: a plurality of semiconductor elements1; wiring substrate2which has a first surface on which semiconductor elements1are mounted and which is electrically connected to semiconductor elements1; heat sink3on which wiring substrate2is mounted so as to face a second surface opposite to the first surface of wiring substrate2; binder4which bonds wiring substrate2and heat sink3; and a plurality of supports5which fix wiring substrate2on heat sink3. Binder4is located to cover the projection surfaces of semiconductor elements1and has supports5around binder4.

Semiconductor elements1are, for example, optical elements. Light-emitting elements such as LEDs and lasers are used as semiconductor elements1. Semiconductor elements1are mounted on and electrically connected to wiring substrate2. Wiring substrate2on which semiconductor elements1are mounted may be referred to as a sub-mount.

In order to secure optical characteristics, phosphors6cover the surfaces of semiconductor elements1. Light from semiconductor elements1is emitted outward through phosphors6.

Wiring substrate2has a plurality of semiconductor elements1mounted thereon. Another element for controlling light-emitting modes and brightness of the plurality of semiconductor elements1may also be mounted thereon.

Wiring substrate2is required to have a high heat dissipation to dissipate heat from semiconductor elements1. Wiring substrate2is also required to have a linear expansion coefficient that is comparatively closer to that of semiconductor elements1in order to mount semiconductor elements1with high accuracy and secure reliability. Wiring substrate2is formed using an aluminum nitride or the like. Here, an organic substrate made of a ceramic material or a resin material other than the aluminum nitride can be used instead as long as the requirements in heat dissipation and linear expansion coefficient are satisfied.

In addition to the electrodes for connection with semiconductors1, electrodes8for electrical connection with heat sink3are also formed on wiring substrate2.

Heat sink3is generally formed using a metal material such as copper and aluminum. Heat sink3has a surface with die pad area9for connection with the second surface of wiring substrate2and electrodes10for electrical connection with electrodes8on wiring substrate2. In addition, a finished product of semiconductor module100has reference holes11to be used as references when semiconductor module100is mounted onto an optical device. In general, reference holes11are aligned with reference holes in an optical device, and semiconductor module100is screw-fixed to the optical device.

Supports5and binder4are present between heat sink3and wiring substrate2and fix or bond heat sink3and wiring substrate2. Supports5are preferably made of a resin or metal material such as an epoxy resin material. Supports5may be made of a metal material, specifically may be formed with metal bumps.

Supports5are provided for the purpose of provisionally fixing heat sink3in the process of mounting wiring substrate2onto heat sink3in order to maintain mounting accuracy. At least three supports5are formed separately on a surface of heat sink3so as to surround binder4. Binder4is generally a die bond material having a high heat dissipation. A SnAgCu or AuSn soldering material or a material having a high metal filling rate such as Ag nano paste is used for binder4. It is desirable for binder4to have a heat expansion which is between those of wiring substrate2and heat sink3in order to absorb the difference in heat expansion between wiring substrate2and heat sink3and secure reliability in bonding wiring substrate2and heat sink3. For example, when wiring substrate2is made of an aluminum nitride and heat sink3is made of Cu, binder4having a line expansion of 7 to 14 ppm/k is desirable because the line expansion of the aluminum nitride is 4 to 5 ppm/k and the line expansion of Cu is 16 to 18 ppm/k.

In addition, it is desirable that binder4has a height of 20 to 70 μm after bonding wiring substrate2and heat sink3in terms of the balance between reliability and heat dissipation. A desired height is easy to maintain even after melting if a metal pellet is used as a material for binder4. In addition, binder4is located immediately below semiconductor elements1, and thus increases efficiency in heat dissipation to heat sink3.

It is to be noted that heat sink3and wiring substrate2may be electrically connected by directly bonding electrodes8on wiring substrate2and electrodes10on heat sink3using a metal wire made of aluminum, Au, Cu, or the like, instead of using binder4.

Subsequently, not-shown connectors, thermistors, chips, etc. are mounted on heat sink3, and general solder mounting such as reflow heating is performed to manufacture a semiconductor module.

Semiconductor module100according to this embodiment is configured to allow supports to keep holding wiring substrate2and heat sink3in a provisionally fixed manner until wiring substrate2and heat sink3are bonded by binder4. In this way, it is possible to prevent wiring substrate2and heat sink3from being misaligned and displaced toward the Z direction caused due to the difference in line expansion rate between the materials thereof. Furthermore, the configuration obviates the need to cause a mounting head tool to hold wiring substrate2long time from mounting to cooling down as in the conventional technique, which reduces the manufacturing cycle time.

In addition, as illustrated in the left part of (b) inFIG. 1, four supports5are arranged separately on a surface of heat sink3to surround binder4. The number of supports5here is four but may be at least three. Here, as illustrated in the right part of (b) inFIG. 1, wiring substrate2is mounted on supports5. At this time, it is possible to provisionally fix wiring substrate2and heat sink3.

With the configuration, wiring substrate2is stably fixed on the surface of heat sink3via supports5. Thus, it is possible to reduce tilt, displacement on the X-Y plane, etc of semiconductor elements1and wiring substrate2with respect to heat sink3.

When supports5are made of a resin material in the case of (a) and (b) ofFIG. 1, insulation from supports5made of a conductive material can be secured. Thus, it is possible to fix wiring substrate2and heat sink3under comparatively few restrictions in the positions of supports5between wiring substrate2and heat sink3.

Modification 1 of Embodiment 1

FIG. 2is a schematic cross-sectional view of a configuration of Modification 1 of semiconductor module100according to Embodiment 1.

Semiconductor module100aaccording to Modification 1 is characterized by being configured to include supports5made of a metal material having a melting point different from that of binder4.

With this configuration, since both of binder4and supports5are made of a metal material, heat can be dissipated from wiring substrate2to heat sink3via supports5. Accordingly, it is possible to increase heat dissipation from semiconductor elements1. Furthermore, by configuring binder4and supports5using different materials having different melting points, it is possible to selectively heat and melt one of the materials having the lower one of the melting points. For example, supports5may be made of a material having a melting point higher than that of the material of supports5. In this way, it is possible to prevent supports5from re-melting when heating binder4.

Modification 2 of Embodiment 1

FIG. 3shows cross-sectional views of configurations of Modification 2 of semiconductor module100according to Embodiment 1 and a variation of Modification 2.

Semiconductor module100baccording to Modification 2 and semiconductor module100caccording to the variation of Modification 2 are characterized by being configured to have groove13between supports5and binder4in the surface facing wiring substrate2of heat sink3. Although binder4is partly in groove13in semiconductor module100billustrated in (a) ofFIG. 3, this configuration is not essential.

With this configuration, even when binder4is melted and spread when heat sink3and wiring substrate2are bonded, an extra portion is housed in groove13and is prevented from further spreading. Thus, it is possible to reduce contact between binder4and supports5.

Here, as in the case of semiconductor module100cillustrated in (b) ofFIG. 3, it is also possible to form groove13and binder4apart from each other when binder4is significantly shrunk due to cooling down after the extra portion of binder4is housed in groove13. In this case, it is possible to set presence/absence of contact of binder4with groove13as a reference for determining success or failure of separation between binder4and supports5. This makes it possible to check the success or failure easily with X-rays or a transmission electron microscope.

Modification 3 of Embodiment 1

FIG. 4shows cross-sectional views of configurations of Modification 3 of semiconductor module100according to Embodiment 1 and a variation of Modification 2.

Semiconductor module100daccording to Modification 3 and semiconductor module100eaccording to the variation of Modification 3 are characterized by being configured to have heat sink3whose thickness is different from part to part.

More specifically, in the case of semiconductor module100dillustrated in (a) ofFIG. 4, heat sink3is formed to be thicker at the part immediately below binder4than at the parts on which supports5are arranged.

In semiconductor module100d, a large amount of heat is generated at the part immediately below the area in which a plurality of semiconductor elements1are mounted. By forming binder4to be partly thinner in this way, it is possible to increase heat dissipation to heat sink3. In particular, heat dissipation is further increased by forming binder4to be thinner only at the part immediately below electrodes8of semiconductor elements1or to be thinner at the parts corresponding to the positions to electrodes8.

In addition, the plating thickness of heat sink3etc. in semiconductor module100dmay be adjusted by changing only the thickness of die pad area9of heat sink3, or only die pad area9may be plated. In any case, it is easier to make modifications and minor adjustments after designing semiconductor module100dcompared to change the thickness of heat sink3.

In contrast to the case of semiconductor module100dillustrated in (a) ofFIG. 4, in semiconductor module100eillustrated in (b) ofFIG. 4, heat sink3is formed to be thinner at the part immediately below binder4than at the parts on which supports5are mounted. In this way, binder4itself is formed to be relatively thicker.

With this configuration, thick binder4absorbs the difference in line expansion between wiring substrate2and heat sink3, and thereby reducing stress due to the difference in line expansion between wiring substrate2and heat sink3. Accordingly, reliability in connecting wiring substrate2and heat sink3is increased.

Modification 4 of Embodiment 1

FIG. 5is a schematic cross-sectional view of a configuration of Modification 4 of semiconductor module100according to this embodiment.

Semiconductor module100faccording to Modification 4 is characterized in that electrodes8on wiring substrate2on which semiconductor elements1are mounted and electrodes10on heat sink3are electrically connected by ribbon bonding or the like using a metal wire made of Cu, Au, Al, or the like, and that binder4is not electrically connected to any of semiconductor elements1and wiring substrate2.

With this configuration, even when binder4is insulated from semiconductor elements1and wiring substrate2, in semiconductor module100f, semiconductor elements1and wiring substrate2are electrically connected to electrodes8and electrodes10, respectively. In this way, semiconductor module100fmaintains electrical characteristics required as a semiconductor module irrespective of a bonding state of supports5and binder4.

Here, it is desirable that supports5be arranged so that the positions of the centers of supports5are located immediately below electrodes8of wiring substrate2. With this arrangement, supports5are located immediately below electrodes8of wiring substrate2when electrodes8of wiring substrate2and electrodes10of heat sink3are electrically connected using metal wire12after heat sink3is mounted on wiring substrate2. This prevents wiring substrate2from deflecting in semiconductor module100f, which stabilizes bonding therein.

Modification 5 of Embodiment 1

FIG. 6is a schematic cross-sectional view of a configuration of Modification 5 of semiconductor module100according to Embodiment 1.

Semiconductor module100gaccording to Modification 5 is characterized in that the top ends of supports5are located at positions higher than a first surface of wiring substrate2when seen from heat sink3. More specifically, as illustrated inFIG. 6, supports5partly cover the lower surface, side surfaces, and corners of wiring substrate2, or extend upward to partly cover the upper surface of wiring substrate2.

With this configuration, in semiconductor module100g, supports5fix wiring substrate2by extending upward to cover the side surfaces and further partly cover the upper surface of wiring substrate2. This particularly makes it possible to minimize displacement and movement of heat sink3and wiring substrate2in the bonding thereof. This also reduces a risk that wiring substrate2is moved on heat sink3due to external force. Furthermore, by forming supports5so that the upper surfaces of supports5are substantially flush with the upper surfaces of semiconductor elements1including phosphors6, an effect of preventing external light from entering semiconductor elements1is also provided.

In each of Embodiment 1, Modifications 1 to 5 of Embodiment 1, and the variations of Modifications 1 to 5, the plurality of supports5are formed to have an approximately equal height from the interface with heat sink3. In this way, wiring substrate2mounted on heat sink3while being fixed by heat sink3and supports5is stably disposed substantially in parallel with heat sink3.

Hereinafter, Embodiment 2 is described with reference toFIG. 7.

This embodiment describes a method for manufacturing semiconductor module100according to Embodiment 1 explained with reference to (a) ofFIG. 1.

First, as illustrated in (a) ofFIG. 7, supports5are mounted above predetermined areas at a peripheral part of heat sink3. Here, supports5may be made of, for example, a resin material. A liquid resin material may be applied to heat sink3using dispenser20.

Next, as illustrated in (b) ofFIG. 7, heat sink3is heated on a not-shown stage. Subsequently, a metal pellet as binder4is mounted on die pad area9, and is heated at a temperature below the melting point thereof for provisional bonding. In the case of an AuSn pellet for example, provisional bonding is performed at 250 degrees Celsius that is below the melting point thereof. Here, the metal pellet having a thickness of approximately 50 μm is used. During the provisional bonding, the metal pellet that is binder4maintains its initial height on heat sink3. At this time, it is desirable that supports5be prevented from touching wiring substrate2.

Next, as illustrated in (c) ofFIG. 7, on the stage, wiring substrate2having semiconductor elements1mounted thereon is disposed by not-shown mounting head tool above heat sink3having binder4and supports5mounted thereon. Subsequently, wiring substrate2having semiconductor elements1mounted thereon is pressed in contact and bonded with heat sink3having binder4and supports5mounted thereon. Here, it is only necessary that supports5be transformed to be flush with the metal pellet that is binder4. In other words, it is desirable that supports5be higher than binder4before wiring substrate2and heat sink3are bonded.

Next, as illustrated in (d) ofFIG. 7, supports5and wiring substrate2are bonded in a heating process so that wiring substrate2can be provisionally fixed in alignment with the positions of supports5. Here, the heating temperature is lower than a temperature at which the metal pellet that is binder4is provisionally bonded, and may be, for example, 230 degrees Celsius that is lower than 250 degrees Celsius in the case of the AuSu pellet. After the provisional fixing, the mounting head tool releases wiring substrate2.

Subsequently, the pellet that is binder4is heated to the melting point or above to be melted, and then is cooled down to bond wiring substrate2and heat sink3. For example, the AuSn pellet is heated at 300 degrees Celsius or above. In this way, semiconductor module100illustrated in (a) ofFIG. 1is completed.

Since supports5are used in this embodiment, supports5and wiring substrate2are bonded first in the heating process, and then wiring substrate2is provisionally fixed in alignment with the positions of supports5. As a result, wiring substrate2and binder4can be bonded by performing the heating process which is a general heating process such as reflow heating. Thus, it is also possible to collectively bond a large number of such components using equipment exclusive for reflow heating. This increases process performance.

Modification 1 of Embodiment 2

Hereinafter, Modification 1 of Embodiment 2 is described with reference toFIG. 8.

Modification 1 describes a method for manufacturing semiconductor module100aaccording to Modification 1 of Embodiment 1, explained with reference toFIG. 2.

First, as illustrated in (a) ofFIG. 8, metal bumps which become supports5are bonded to electrodes10(not illustrated inFIG. 8) on heat sink3by ultrasonic bonding or heat-melting bonding. In ultrasonic bonding, bonding is accelerated by metal adhesion due to ultrasonic rather than temperature, and thus is possible at a low temperature. In the case of inter-Au bonding for example, Au and Au are fixed at 200 degrees Celsius or below.

Next, as illustrated in (b) ofFIG. 8, binder4made of a metal pellet different from the metal pellet used to form supports5is mounted and heated on die pad area9of heat sink3in such a manner that binder4is prevented from touching supports5. Here, binder4and heat sink3are bonded at a temperature below the melting point of binder4, and are provisionally fixed in a semi-melted state. Materials for use as a material for binder4include not only metal pellets but also paste materials. The pellet materials are more suitable for the present manufacturing method because they shrink less after heating and cooling down.

In the case of using a paste material, flux is applied to the upper surface of the paste material after the paste material is mounted. A paste including metal balls having a diameter corresponding to a target height after bonding may be used. In this case, the height of the metal balls accurately determine the height of wiring substrate2with respect to heat sink3in the process in which weights are applied to binder4as described later, which makes it easier to control the height.

Next, as illustrated in (c) ofFIG. 8, wiring substrate2having semiconductor elements1mounted thereon is made contact with supports5so that wiring substrate2presses supports5by using its weight to flatten supports5. Here, binder4is heated at a temperature below the melting point thereof so as not to be melted.

Next, as illustrated in (d) ofFIG. 8, semiconductor module100ais completed by heating binder4to the melting point or above and then cooling down binder4.

Since supports5are used in semiconductor module100aaccording to this modification, supports5and wiring substrate2are bonded first in the heating process, and then wiring substrate2is provisionally fixed in alignment with the positions of supports5. As a result, wiring substrate2and binder4can be bonded by performing the heating process which is a general heating process such as reflow heating. Thus, it is also possible to collectively bond a large number of such components using equipment exclusive for reflow heating. This increases process performance.

Modification 2 of Embodiment 2

Hereinafter, Modification 2 of Embodiment 2 is described with reference toFIG. 9.

Modification 2 describes a method for manufacturing semiconductor module100baccording to Modification 2 of Embodiment 1, explained with reference toFIG. 3.

The method for manufacturing semiconductor module100baccording to Modification 2 is similar to the manufacturing method described in Modification 1 with reference toFIG. 8, and thus only the differences from Modification 1 are described.

The manufacturing method illustrated in (a) and (b) ofFIG. 9is similar to the manufacturing method illustrated in (a) and (b) ofFIG. 8. As illustrated in (a) ofFIG. 9, groove13is formed in heat sink3at parts between the area with supports formed therein and an area on which binder4is to be disposed in the process for forming supports5and the subsequent processes.

Next, as illustrated in (b) ofFIG. 9, binder4made of a metal pellet different from the metal pellet used to form supports5is mounted and heated on die pad area9(not shown inFIG. 9) of heat sink3in such a manner that binder4is prevented from touching supports5. Here, binder4and heat sink3are bonded at a temperature below the melting point of binder4, and are provisionally fixed in a semi-melted state. Materials for use as a material for binder4include not only metal pellets but also paste materials. The pellet materials are more suitable for the present manufacturing method because they shrink less after heating and cooling down.

In the case of using a paste material, flux is applied to the upper surface of the paste material after the paste material is mounted. A paste including metal balls having a diameter corresponding to a target height after bonding may be used. In this case, the height of the metal balls accurately determine the height of wiring substrate2with respect to heat sink3in the process in which weights are applied to binder4as described later, which makes it easier to control the height.

Next, as illustrated in (c) ofFIG. 9, wiring substrate2having semiconductor elements1mounted thereon is made contact with supports5so that wiring substrate2presses supports5by using its weight to flatten supports5. Here, binder4is heated at a temperature corresponding to the melting point or above. In this case, even after binder4is melted, the extra portion of binder4is housed in groove13in the melting process and does not spread beyond groove13. Thus, it is possible to prevent binder4from touching supports5.

Since supports5are used in this modification, supports5and wiring substrate2are bonded first in the heating process, and then wiring substrate2is provisionally fixed in alignment with the positions of supports5. As a result, wiring substrate2and binder4can be bonded by performing the heating process which is a general heating process such as reflow heating. Thus, it is also possible to collectively bond a large number of such components using equipment exclusive for reflow heating. This increases process performance.

Modification 3 of Embodiment 2

Hereinafter, Modification 3 of Embodiment 2 is described with reference toFIG. 10.

Modification 3 is a method for manufacturing semiconductor module100hsimilar to semiconductor module100gdescribed in Modification 5 of Embodiment 1, with reference toFIG. 6.

A finished product of semiconductor module100hmanufactured according to Modification 3 differs from a finished product of semiconductor module100gdescribed with reference toFIG. 6in that supports5partly cover the side surfaces of wiring substrate2but do not extend upward to partly cover the upper surface of wiring substrate2.

Next, as illustrated in (b) ofFIG. 10, a metal pellet as binder4is mounted on die pad area9on heat sink3, and is heated at a temperature below the melting point thereof for provisional bonding. In the case of an AuSn pellet for example, provisional bonding is performed at approximately 250 degrees Celsius that is the melting point thereof or below. The AuSn pellet may have a thickness of approximately 50 pm. During the provisional bonding, the metal pellet that is binder4maintains its initial height on heat sink3.

Next, as illustrated in (c) ofFIG. 10, supports5are mounted at peripheral parts of heat sink3. In (c) ofFIG. 10, supports5are made of a resin material. A liquid resin material is applied to heat sink3using dispenser20. At this time, supports5are formed to cover only the peripheral parts of the side surfaces and the upper surface of binder4. In this way, it is possible to prevent supports5from entering space between wiring substrate2and binder4and wet-spreading in the process for forming supports5and the subsequent processes.

Next, as illustrated in (d) ofFIG. 10, on the stage, wiring substrate2having semiconductor elements1mounted thereon is disposed by not-shown mounting head tool above heat sink3having binder4and supports5mounted thereon.

Next, as illustrated in (e) ofFIG. 10, wiring substrate2having semiconductor elements1mounted thereon is pressed in contact and bonded with heat sink3having binder4and supports5mounted thereon. At this time, in the heating process, the parts of supports5above the peripheral parts of the upper surface of binder4are bonded with wiring substrate2, and are provisionally fixed in alignment with supports5. Here, the heating temperature is lower than a temperature at which the metal pellet that is binder4is provisionally bonded, and may be, for example, 230 degrees Celsius that is lower than 250 degrees Celsius in the case of the AuSu pellet. After the provisional fixing, the mounting head tool releases wiring substrate2.

Subsequently, the pellet that is binder4is heated to the melting point or above to be melted, and then is cooled down to bond wireless substrate2and heat sink3. For example, the AuSn pellet is heated at 300 degrees Celsius or above. At this time, the parts of supports5in the vicinity of the side surfaces of wiring substrate2surround the side surfaces of wiring substrate2and solidify thereon. As a result, wiring substrate2is fully fixed by integrated support5surrounding the peripheral parts. In this way, semiconductor module100his completed.

Since supports5are used in this modification, supports5and wiring substrate2are bonded first in the heating process, and then wiring substrate2is provisionally fixed in alignment with the positions of supports5. As a result, wiring substrate2and binder4can be bonded by performing the heating process which is a general heating process such as reflow heating. Thus, it is also possible to collectively bond a large number of such components using equipment exclusive for reflow heating. This increases process performance.

In Embodiment 2 and modifications thereof, binders4and supports5are formed in different orders. There is no problem if the formation order of binders4and supports5is changed as long as their arrangement relationship is maintained.

Hereinafter, common characteristics of Embodiment 1 and Embodiment 2 are described in comparison with conventional techniques.

FIG. 11illustrates a method for manufacturing semiconductor module150according to a conventional technique.

Semiconductor module150according to the conventional technique is manufactured by: mounting binder154on heat sink153as illustrated in (a) ofFIG. 11; melting binder154, and causing a not-shown mounting head tool to dispose wiring substrate152having semiconductor elements151mounted thereon above heat sink153with binder154as illustrated in (b) ofFIG. 11; and pressing wiring substrate152having semiconductor elements151mounted thereon in contact with heat sink153with binder154so as to bond wiring substrate152to heat sink153. Semiconductor module150is completed by cooling down binder154next as illustrated in (c) ofFIG. 11.

In the conventional technique, it is necessary to dispose wiring substrate152having semiconductor elements151mounted thereon above heat sink153with binder154, press wiring substrate152having semiconductor elements151mounted thereon in contact with heat sink153with binder154so as to bond wiring substrate152to heat sink153, and cause the mounting head tool to hold wiring substrate152having semiconductor elements151mounted thereon until binder154is sufficiently cooled down.

In this embodiment, since supports5are used, supports5and wiring substrate2are bonded first in the heating process, and then wiring substrate2is provisionally fixed in alignment with the positions of supports5. This provisional fixing makes it possible to perform highly-accurate control on the mounting accuracy (a height, a tilt, a swing, a position on the X-Y plane, etc. of wiring substrate2and semiconductor elements1with respect to heat sink3.

In addition, there is no need to cause the mounting head tool to hold wiring substrate2after the provisional fixing. As a result, wiring substrate2and binder4can be bonded by performing the heating process which is a general heating process such as reflow heating. Thus, it is also possible to collectively bond a large number of such components using equipment exclusive for reflow heating. This increases process performance.

A semiconductor module according to an aspect of the present disclosure includes: one or more semiconductor elements; a wiring substrate having a first surface on which the one or more semiconductor elements are mounted, the wiring substrate being electrically connected to the one or more semiconductor elements; a heat sink on which the wiring substrate is mounted, the heat sink facing a second surface of the wiring substrate on a reverse side of the first surface; a binder which is formed in a die pad area on the heat sink so as to be present between the wiring substrate and the heat sink, and bonds the wiring substrate and the heat sink; and a support which is formed in a peripheral part of the die pad area on the heat sink, and fixes the wiring substrate to the heat sink by being in contact with a peripheral part of the second surface of the wiring substrate.

With this configuration, the semiconductor module is capable of maintaining the state in which the wiring substrate and the heat sink are provisionally fixed by the support when the wiring substrate and the heat sink are bonded by the binder. In this way, it is possible to prevent the wiring substrate and the heat sink from being misaligned and displaced toward the Z direction caused due to the difference in line expansion rate between the materials thereof. Furthermore, the configuration obviates the need to cause a mounting head tool to hold the wiring substrate long time from mounting to cooling down as in the conventional technique, which reduces the manufacturing cycle time.

In addition, in the semiconductor module according to the aspect of the present disclosure, the support may comprise at least three supports formed independently, the at least three supports may have substantially the same height from the interface between the at least three supports and the heat sink, and the binder may be disposed to be surrounded by the at least three supports in a plan view.

With this configuration, the wiring substrate is stably fixed on the surface of the heat sink via the at least three supports. Thus, it is possible to reduce tilt and displacement on the X-Y plane of the one or more semiconductor elements and the wiring substrate with respect to the heat sink.

In addition, in the semiconductor module according to the aspect of the present disclosure, the binder may not be electrically connected to any of the one or more semiconductor elements and the wiring substrate.

With this configuration, even when the binder is insulated from the one or more semiconductor elements and the wiring substrate, the one or more semiconductor elements and the wiring substrate are electrically connected to electrodes (8) and electrodes (10), respectively. In this way, the semiconductor module is capable of maintaining electrical characteristics required as a semiconductor module irrespective of a bonding state of the support and the binder.

In addition, in the semiconductor module according to the aspect of the present disclosure, the heat sink may have a surface which faces the second surface of the wiring substrate, and the surface may have a groove formed between the support and the binder in a plan view, and in the groove, the binder is partly disposed.

With this configuration, even when the boding material is melted and spread when the heat sink and the wiring substrate are bonded, an extra portion is housed in the groove and is prevented from further spreading. Thus, it is possible to reduce contact between the binder and the support.

In addition, in the semiconductor module according to the aspect of the present disclosure, the binder may be made of a material containing a metal, the support may be made of a material containing a metal different from the metal contained in the material of the binder, and the support may have a melting point higher than a melting point of the binder.

With this configuration, since the binder and the support are each made of a metal material, heat can be dissipated from the wiring substrate to the heat sink via the support. In this way, it is possible to prevent the support from re-melting when heating the binder.

In addition, in the semiconductor module according to the aspect of the present disclosure, the support may be made of a resin material.

With this configuration, the heat sink and the wiring substrate can be insulated from each other.

In addition, in the semiconductor module according to the aspect of the present disclosure, the support may cover at least part of a side surface of the wiring substrate.

With this configuration, in the manufacturing process after the formation of the support, it is possible to prevent the support from entering space between the wiring substrate and the binder and wet-spreading.

In addition, in the semiconductor module according to the aspect of the present disclosure, an uppermost end of the support may be located higher than the first surface of the wiring substrate when seen from the heat sink.

With this configuration, the support fixes the wiring substrate by extending upward to cover the side surfaces and further partly cover the upper surface of the wiring substrate. This particularly makes it possible to minimize displacement and movement of the heat sink and the wiring substrate in the bonding thereof. This also reduces a risk that the wiring substrate is moved on the heat sink due to external force. Furthermore, by forming the support so that the upper surface of the support is substantially flush with the upper surfaces of the one or more semiconductor elements including phosphors, an effect of preventing external light from entering the one or more semiconductor elements is provided.

In addition, in the semiconductor module according to the aspect of the present disclosure, the binder may have a linear expansion coefficient which is between a linear expansion coefficient of the wiring substrate and a linear expansion coefficient of the heat sink.

With this configuration, the binder absorbs the difference in heat expansion rate between the wiring substrate and the heat sink, and thereby maintaining the reliability in the bonding of the wiring substrate and the heat sink.

In addition, a semiconductor module manufacturing method according to an aspect of the present disclosure is a semiconductor module manufacturing method including: forming at least three supports independently on a heat sink; forming a binder on the heat sink so that the binder does not touch the at least three supports; disposing a wiring substrate on which one or more semiconductor elements are mounted so that the binder is present between the wiring substrate and the heat sink and across the at least three supports, and fixing the wiring substrate to the at least three supports; and heating and melting the binder to bond the wiring substrate and the heat sink, wherein, in the forming of a binder, the binder is disposed to be surrounded by the at least three supports in a plan view.

With this configuration, since the at least three supports are used, the at least three supports and the wiring substrate are bonded first in the heating process, and then the wiring substrate is provisionally fixed in alignment with the positions of the at least three supports. This provisional fixing makes it possible to perform highly-accurate control on the mounting accuracy (a height, a tilt, a swing, a position on the X-Y plane, etc. of the wiring substrate and the one or more semiconductor elements with respect to the heat sink.

In addition, in the semiconductor module manufacturing method according to the aspect of the present disclosure, the binder may be made of a material containing a metal, and in the forming of a binder, the binder may be formed by heating and melting the material containing the metal.

With this configuration, heat can be dissipated from the wiring substrate to the heat sink via the binder.

In addition, in the semiconductor module manufacturing method according to the aspect of the present disclosure, the support may be made of a resin material.

With this configuration, the heat sink and the wiring substrate can be insulated from each other.

In addition, in the semiconductor module manufacturing method according to the aspect of the present disclosure, in the disposing and fixing of a wiring substrate, the resin material may be formed to cover at least a part of a side surface of the wiring substrate.

With this configuration, in the manufacturing process after the formation of the support, it is possible to prevent the support from entering space between the wiring substrate and the binder and wet-spreading.

In addition, in the semiconductor module manufacturing method according to the aspect of the present disclosure, the support may be made of a material containing a metal different from the metal contained in the material of the binder, and the support may have a melting point higher than a melting point of the binder.

Although the semiconductor modules and the methods for manufacturing the semiconductor modules according to aspects of the present disclosure have been described above based on the embodiments, modifications, and variations, the present disclosure is not limited to the embodiments, modifications, and variations. Embodiments etc. that a person skilled in the art may arrive at by adding various kinds of modifications to the above embodiments etc. or by arbitrarily combining some of the constituent elements in the embodiments etc. may be included in the aspects of the present disclosure without deviating from the scope of the present disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure is useful for head lamps with LEDs and luminaires which provide high optical accuracy.