HK1111808A

HK1111808A - Electronic device and method of manufacturing the electronic device

Info

Publication number: HK1111808A
Application number: HK08102655.4A
Authority: HK
Inventors: 冲村克行
Original assignee: Nec照明株式会社
Priority date: 2006-06-02
Filing date: 2008-03-06
Publication date: 2008-08-15

Description

Electronic device and method of manufacturing the same

Technical Field

The present invention relates to an electronic device that scatters and radiates heat from a heating element having graphite, and a method of manufacturing the electronic device.

Background

Effective radiation of heat generated by heat-generating parts is essential to prevent failure of the parts and to ensure product life. Therefore, in general, various heat releasing materials are used in electric and electronic devices having parts accompanied by heat generation. In particular, in recent years, with progress made in reducing the size of electronic devices and improving the complexity and performance of electronic devices, graphite sheets made of graphite as a main material are used to effectively release heat generated from large-scale integrated CPUs or LEDs. The graphite sheet is thermally anisotropic and has good thermal conductivity properties in the planar direction. Therefore, when the LED is operated, the graphite sheet initially conducts locally generated heat in a planar direction and allows expansion of the surface of the graphite sheet or allows the effective heat radiation area of the heat releasing member to be bonded with the graphite, and high heat radiation efficiency can be obtained.

The heat scattering of a graphite sheet having such properties, to which the LED chip shown in fig. 1 is provided mounted thereon, will be described with reference to a schematic cross section on an electronic device comprising the graphite sheet.

The electronic device 100 has a heat generating structure 110, and the heat generating structure 110 is configured by mounting an LED chip 104 on a submount 103 on a heat releasing structure 120 composed of a metal layer 101 and a graphite layer 102. The LED chip 104 and the submount 103 are bonded with a hard solder 106a such as AuSn. The heat releasing structure 120 and the heat generating structure 110 are bonded with soft solder 106b composed of Sn or the like having a lower melting point than the hard solder 106 a. The LED chip 104 is coated with a resin, which is not shown in the drawing.

The schematic route of heat transfer in the electronic device 100 structured as described above is as follows.

Heat generated by operation of the LED chip 104 is conducted through the hard solder 106a and transferred to the submount 103. The heat transferred to the submount 103 is conducted through the soft solder 106b and transferred to the graphite layer 102. The heat thus transferred in the stacking direction is conducted in the planar direction in the graphite layers 102. Heat widely scattered in the planar direction in the graphite layer 102 is transferred to the metal layer 101 and is effectively scattered in air from the surface of the metal layer 101.

In the case where the graphite layer 102 is not present so that the heat generating structure 110 is directly bonded to the metal layer 101, the heat transferred from the sub-mount 103 to the metal layer 101 is conducted mainly in the thickness direction, not in the planar direction. Therefore, even if the region of the metal layer 101 is widened to improve the heat release property, a sufficient heat release effect cannot be obtained.

However, providing the graphite layer 102 to be interposed between the submount 103 and the metal layer 101 to improve the heat conduction property in the planar direction will widen the effective heat radiation area in the metal layer 101, thereby enabling the heat generating element such as an LED to be cooled effectively.

Further, an LED package having a high thermal conductive carbon material such as a graphite sheet containing carbon as a main material, which is expected to obtain high thermal scattering properties, is disclosed in japanese patent application laid-open No. 2006-86391.

The LED package disclosed in japanese patent application publication 2006-86391 has a basic structure similar to that shown in fig. 1. Fig. 2 illustrates a cross section of a main portion of the LED package disclosed in japanese patent laid-open No. 2006-86391.

The LED package 210 includes a frame metal base 211, an LED chip 212, and an insulating member 214 having lead members 213 connected to the LED chip 212, and the LED package 210 is configured by mounting the LED chip 212 on the metal base 211 through a solder material or an adhesive at a predetermined position such that it is in direct contact with a high thermal conductivity carbon material 216.

Metal base 211 is comprised of mortar-like sidewall assembly 218 and bottom plate assembly 219. Insulating assembly 214 forms opening 215 and provides it with an electrically conductive pattern for egress to the outside. The LED chip 212 is mounted on a high thermal conductivity carbon assembly 216, bonded directly thereto, disposed in an opening 215 in the base plate, and connected to the lead assembly 213 via electrically conductive patterning for outward lead-out by wire bonds 217. A metal-impregnated carbon Material (MICC) is used as the high thermal conductivity carbon material 216, which is specifically obtained by burning carbon powder or carbon fiber so that solidification occurs, and by injecting a metal such as Cu or Al. The heat conduction is performed by lattice vibration of a two-dimensional crystal plane of carbon, exhibiting a thermal conductivity of 150 to 300 mW/c.

As described above, the graphite sheet has high thermal conductivity in the planar direction, and thus is effectively used as a heat releasing material. However, the graphite sheet in which carbon is used as a main material has low solder wettability, and it is difficult to provide a solder layer to realize a sub-mount on the graphite sheet. Therefore, although it is apparent that high heat transfer efficiency can be obtained by joining the graphite sheet and the sub-mount, it is impossible to achieve joining between the graphite sheet and the sub-mount by a solder layer.

In a method for mechanically bringing a sub-mount into contact with a graphite sheet by a screw clamp or the like, an air layer which intervenes under a microscope as a large thermal resistance between the sub-mount and the graphite sheet thus reduces the heat scattering property of the graphite sheet.

It is possible to eliminate the air layer by applying a thermally conductive grease between the submount and the graphite sheet. However, the thermal conductivity of grease is less than that of solder. Thus, it is also not possible to fully exploit the advantages of the heat scattering properties of graphite sheets. Further, japanese patent application laid-open No.2006-86391 does not disclose how the LED package makes thermal contact between the high thermal conductive carbon material and the LED chip (i.e., the heat generating element). Therefore, it is hard to say that Japanese patent application laid-open No.2006-86391 takes advantage of the thermal characteristics of a high thermal conductivity carbon material.

Therefore, a significant thermal resistance will be exhibited between the heating element and the graphite sheet in an electronic device including the conventional graphite sheet. Therefore, the desired cooling characteristics cannot be obtained even if the graphite sheet is used.

Further, in the case where high thermal conductivity is obtained due to having a graphite sheet, a problem is likely to occur when a plurality of elements and the like are mounted on the same substrate. For example, assume that a connector is additionally installed after the LED is installed. In this case, heat suitable for soldering the connector will melt the solder for the already mounted LED, occasionally causing the LED to shift. Accordingly, there is a need for a manufacturing method that enables mounting of a connector in an electronic device comprising a highly thermally conductive graphite sheet without displacing the LED.

Disclosure of Invention

It is an object of the present invention to provide an electronic device capable of making full use of the heat scattering properties of graphite.

Further, another object of the present invention is to provide a method of manufacturing an electronic device capable of mounting a heat generating element and a connector onto a high heat conductive substrate.

In order to attain the above object, an electronic device according to the present invention is an electronic device including a heat generating structure mounted on a graphite layer side of a heat releasing structure, comprising:

a heat generating structure including a heat generating element, a base for mounting the heat generating element thereon, and a first connection member including metal for joining the heat generating element and the base; and

a heat releasing structure comprising a first metal layer and a graphite layer stacked on the first metal layer, wherein

On a plane of the graphite layer opposite to a plane in which the first metal layers are stacked, there is a second metal layer; and is

Bonding the second metal layer and the base with a second connection assembly such that the heat generating structure and the heat releasing structure are thereby bonded.

As described above, the electronic device of the present invention is provided with the second metal layer on the graphite layer, thereby allowing the junction between the heat generating structure and the heat releasing structure to be established by the second connecting member. That is, by providing the component with good wettability with the solder on the graphite surface, the solder layer can be formed, for example, as the second connecting component. Thus, the thermal resistance in the heat transfer path from the heating element to the graphite layer can be reduced, and the heat scattering property of the graphite layer can be sufficiently expressed.

Furthermore, the second metal layer of the electronic device of the present invention preferably comprises copper or aluminum.

Further, the surface on the side opposite to the side facing the graphite layer is subjected to rust-preventive treatment.

Further, the heat generating element of the electronic device of the present invention may be an LED, a CPU, and an IC.

Further, the first connection member and the second connection member of the present invention may be solder layers.

Further, the first connection member may be a solder bump or a gold bump.

Here, the melting point of the first connecting member is preferably higher than that of the second connecting member.

Further, the base may be composed of AIN or SiC as a main material.

An electronic device according to the present invention is an electronic device including a heating element mounted on a graphite layer side of a heating structure, comprising:

a heat generating element and a heat releasing structure comprising a first metal layer and a graphite layer stacked on the first metal layer, wherein

On a plane of the graphite layer opposite to a plane in which the first metal layer is stacked, there is a second metal layer; and is

The wiring layer formed on the second metal layer and the heating element are joined by means of solder bumps or gold bumps.

An electronic device according to the present invention is an electronic device including a heat-generating electronic element mounted on a side of a graphite layer of a heat releasing structure, comprising:

a heat-generating electronic component having a wiring extracting portion; and

On a plane of the graphite layer opposite to a plane in which the first metal layers are stacked, there is a second metal layer;

the heat-generating electronic component has a first plane in which the wiring extracting portion is provided and a second plane in which the wiring extracting portion is not provided;

the second metal layer is bonded to the second plane of the heat-generating electronic component.

As described above, the heat-generating electronic component of the electronic device of the present invention is not provided with the wiring extracting portion on the second plane, and therefore can be directly mounted on the second metal layer without intervention of an insulator or the like. Therefore, the thermal resistance between the heating electronic element and the heat release structure can be reduced, and the heat scattering property of the graphite layer is fully exerted.

Further, the heat generating electronic element of the electronic device of the present invention is a semiconductor device, and the wiring extracting portion may be a P pole and an N pole in which wires for wiring are electrically connected. In this case, the semiconductor device may be an LED.

Furthermore, the second metal layer and the second plane may be joined by means of a solder layer.

The method for manufacturing an electronic device of the present invention is a method for manufacturing an electronic device including: a heat generating structure including a heat generating element, a base for mounting the heat generating element thereon, and a first connection member including metal for joining the heat generating element and the base; and a heat releasing structure including a first metal layer and a graphite layer stacked on the first metal layer, wherein the heat generating structure and a connector are mounted on a side of the graphite layer of the heat releasing structure, the method comprising:

forming a second metal layer on a plane of the graphite layer opposite to a plane in which the first metal layers are stacked, and joining the second metal layer and a base with a second connection member containing metal; and

on the base on which the second metal layer and the second connection member are joined, the heat generating element is joined by the first connection member, while the connector is joined to the heat releasing structure by a third connection member containing a metal.

According to the method for manufacturing the electronic device of the present invention as described above, the heat generating element and the connector are joined simultaneously. Therefore, even in the case where the solder layer is used as each connecting component, the heat applied at the time of mounting the connector will not melt the solder layer fixing the heat generating element to cause displacement.

forming a second metal layer on a plane of the graphite layer opposite to a plane in which the first metal layers are stacked, and joining the second metal layer and a base with a second connection member containing metal;

forming an insulating layer on the heat releasing structure;

forming a wiring layer on the insulating layer;

bonding the connector to the wiring layer through the third connection member containing metal;

applying heat from the first metal layer side after the connector is bonded to the insulating layer by the third connecting member, thereby melting the first connecting member so that the heat generating element is bonded to the base; and

stopping the application of heat from the first metal layer side before the third connection assembly melts due to the heat applied from the first metal layer side.

Comparing the amount of time required for bonding the heating element to the mount by melting the first connection member by heat applied from the first metal layer side with the amount of time required for bonding the connector by melting the third connection member through the wiring layer, the latter amount of time will become longer due to the intervention of the insulating layer, thereby causing a time difference between times to rise. The method for manufacturing the electronic device of the present invention as described above utilizes this time difference to stop applying heat before the third connecting member melts. Thus, the heat generating element can be mounted on the base without melting the third connecting member for engaging the connector.

According to the present invention, the second metal layer is formed on the graphite layer. Therefore, the mount of the heat generating element and the heat releasing structure can be joined by the solder layer. Therefore, the heat transferred from the heat generating element to the graphite layer will be appropriate, and it enables the graphite layer to sufficiently apply the heat conductive property in the planar direction and achieve heat scattering.

Further, according to the method for manufacturing an electronic device of the present invention, it is possible to mount the heat generating element and the connector onto a substrate having high thermal conductivity without causing any displacement.

The above and other objects, features and advantages of the present invention will become apparent from the following description, which illustrates examples of the present invention, taken in conjunction with the accompanying drawings.

Drawings

FIG. 1 is a schematic cross-section of an electronic device comprising a graphite sheet;

fig. 2 is a cross section of a main portion of an example of an LED package including a conventional high thermal conductivity carbon material;

fig. 3 is a schematic cross section illustrating the configuration of an electronic device of the first embodiment of the present invention;

fig. 4 is a schematic cross section illustrating another configuration of the electronic device of the first embodiment of the present invention;

fig. 5 is a schematic cross section illustrating still another configuration of the electronic device of the first embodiment of the present invention;

fig. 6 is a schematic cross section illustrating the configuration of an electronic device of a second embodiment of the present invention; and

fig. 7 is a diagram for describing a method for manufacturing an electronic device in the third embodiment of the present invention.

Detailed Description

(first embodiment)

Fig. 3 illustrates a schematic cross section showing the configuration of the electronic device 1 of the present embodiment.

The electronic device 1 has a heat generating structure 10, and the heat generating structure 10 is configured by mounting the LED chip 2 on the submount 3 on a heat releasing structure 20 including the first metal layer 6 and the graphite layer 5. The second metal layer 7 is provided on the graphite layer 5. The heat generating structure 10 and the heat releasing structure 20 are joined by the second solder layer 4 b. That is, the submount 3 of the heat generating structure 10 and the second metal layer 7 of the heat releasing structure 20 are bonded by the second solder layer 4 b.

The heat releasing structure 20 is for scattering heat from the LED chip 2 to the outside air, and includes a first metal layer 6 made of a metal having good thermal conductivity and a graphite layer 5 having good thermal conductivity in a plane direction. The graphite layer 5 is provided by being stacked on the plane of the side of the first metal layer 6 on which the LED chip 2 is mounted.

In the heat generating structure 10, the LED chip 2 and the submount 3 are bonded with a first solder layer 4a made of AuSn or the like. The heat generating structure 10 is arranged in the opening 40 formed in the insulating layer 32 and the wiring layer 31, wherein the insulating layer 32 and the wiring layer 31 are stacked on the heat releasing structure 20. The wiring layer 31 and the submount 3 are connected by a wire 33. The heat releasing structure 20 and the heat generating structure 10 join the second solder layer 4b having a melting point lower than that of the first solder layer 4 a. The LED chip 2 is coated with resin, which is not shown in the drawing.

Next, the respective layers in the heat generating structure 10 will be described.

The submount 3 is a base in which the LED chip 2 is mounted. In order not to cause pressure, distortion, or the like due to a difference in thermal scattering coefficient, an insulating substrate is used as the sub-mount 3, and ceramics having good thermal conductivity such as AIN, SiC, or the like is used as a material of the sub-mount 3, which is relatively similar to the substrate material of the LED chip 2 in terms of thermal scattering coefficient.

The LED chip 2 is bonded to the submount 3 by the first solder layer 4 a. As the first solder layer 4a, it is preferable that a solder having Au as a main material is made of AuSn. In the case of using AuSn as a main material, the melting point is about 280 ℃.

As the second solder layer 4b, Sn-based solder having a melting point lower than that of the first solder layer 4a is preferable as the second solder layer 4 b.

Next, the respective layers of the heat releasing structure 20 will be described.

A material such as copper, aluminum, etc. is used for the first metal layer 6. Here, the thermal conductivity of copper is 390 (W/m.K), and the thermal expansion coefficient thereof is 1.0 to 1.4 (cm)²In s). On the other hand, the thermal conductivity of aluminum is 230 (W/m.K), and the thermal expansion coefficient thereof is 0.9 (cm)²/s)。

The graphite layer 5 is a graphite sheet having graphite as its main material, and uses, for example, "super λ GS (®): produced by Taica corporation. In the case of the super λ GS (®), the thermal conductivity in the in-plane direction is 400 (W/m.K), and the thermal expansion coefficient thereof is 3.0 to 3.2 (cm. K)²/s)。

It is desirable that the second metal layer 7 reduces the thermal resistance between the heat generating structure 10 and the heat releasing structure 20 to sufficiently achieve the thermal expansion property of the graphite layer 5. For the second metal layer 7, a metal film made of a metal having good thermal conductivity such as copper is preferably used. Even if the graphite layer 5 and the submount 3 are bonded by means of solder layers, both solders have poor wettability. Therefore, it is extremely difficult to directly join both by welding. Thus, in the present embodiment, the second metal layer 7 is provided on the graphite layer 5. Thereby, wettability of the solder is improved. That is, in the electronic device 1 of the present embodiment, the presence of the second metal layer 7 enables bonding between the heat generating structure 10 and the heat releasing structure 20 by using the second solder layer 4 b.

The thermal conductivity of the second metal layer 7 and the second solder layer 4b is generally higher than that of the thermally conductive grease, and therefore, it is possible to efficiently transfer heat from the heat generating structure 10 to the heat releasing structure 20. Further, it is preferable that the second metal layer 7 is a thin film formed as thin as possible to the extent that the usability is ensured when stacking onto the graphite layer 5 and bonding to the heat generating structure 10. Also, in the case of using a material such as copper that is easily oxidized for the second metal layer 7, it is preferable to perform a rust prevention treatment such as gold plating in order to maintain the heat transfer property. Here, in the case of using aluminum for the second metal layer 7, the heat conduction property is good, but solder wettability is not good. Therefore, it is necessary to perform plating treatment on the surface to improve solder wettability.

Next, a method of manufacturing the electronic device 1 will be schematically described.

The electronic device 1 of the present embodiment is manufactured by separately producing the thermal structure 10 and the heat releasing structure 20 in advance, and then finally by joining them.

The method of producing the heat generating structure 10 is as follows. A first solder layer 4a made of AuSn is formed on the submount 3 in advance. Subsequently, the first solder layer 4a is melted in advance. In this state, the LED chip 2 is placed on the first solder layer 4 a. The first solder layer 4a is cooled and solidified. Thereby mounting the LED chip 2 on the submount 3 to complete the heat generating structure 10.

The method of producing the heat releasing structure 20 is as follows.

First, the graphite layer 5 is stacked on the first metal layer 6. Subsequently, the second metal layer 7 is stacked onto the graphite layer 5 on the plane opposite to the plane in which the first metal layer 6 is stacked to complete the heat releasing structure 20.

Next, the insulating layer 32 and the wiring layer 31, which form the openings 40, are sequentially stacked onto the second metal layer 7 of the heat releasing structure 20 including the second metal layer 7.

Next, a second solder layer 4b made of Sn as a main material is formed on the second metal layer 7 of the opening 40. Since the second metal layer 7 has good wettability with solder, the second solder layer 4b is formed in a good state on the second metal layer 7.

The heat generating structure 10 is placed on the second solder layer 4b formed as described above so that the submount 3 faces the second solder layer 4 b. Heat is then applied until the melting point of the second solder layer 4b is reached. Here, since the melting point of the first solder layer 4a is higher than that of the second solder layer 4b, melting does not occur when heat is applied.

Incidentally, the melting point of the second metal layer 4b is not limited to be lower than that of the first solder layer 4a, but any layer having the same melting point may be used. Even if solders with the same melting point are used, the first solder layer 4a will not melt due to the associated application of heat. The reason for this is as follows.

A gold pattern (not shown) is formed on the submount 3. Heat for melting the second solder layer 4b is transmitted through the sub-mount 3 to melt the gold pattern. When the gold pattern melts, it melts into the first solder layer 4 a. Whereby the gold content of the first solder layer 4a will be increased. The increase in the gold content will raise the melting point of the first solder layer 4 a. Thereby, the melting point of first solder layer 4a will become higher than the melting point of second solder layer 4b, and therefore, when heat is applied to melt second solder layer 4b, first solder layer 4a will not melt.

Finally, the submount 3 and the wiring layer 31 are connected with a wire 33 for wiring to complete the electronic device 1.

Next, a schematic route of transfer of heat generated by the LED chip 2 in the electronic device 1 of the present embodiment will be described.

Heat generated by the operation of the LED chip 2 is first transferred through the first solder layer 4a and then transferred to the submount 3.

The heat transferred to submount 3 is conducted through second solder layer 4b, transferred to second metal layer 7, and then transferred to graphite layer 5. In this way, heat transfer from submount 3 to graphite layer 5 is accomplished by conduction through second solder layer 4b and second metal layer 7. In the case of the present embodiment, the second metal layer 7 is provided on the graphite layer 5. Thereby, a joint between the heat generating structure 10 and the heat releasing structure 20 having good thermal conductivity using the second solder layer 4b can be created. Therefore, this allows the thermal resistance between the heat generating structure 10 and the heat releasing structure 20 to be reduced as much as possible. Therefore, heat generated in the LED chip 2 can be efficiently transferred to the graphite layer 5.

The heat transferred from the LED chip 2 to the graphite layer 5 in the stacking direction is conducted in the plane direction having the graphite layer 5. The heat widely scattered in the plane direction having the graphite layer 5 is transferred to the first metal layer 6 and is effectively scattered from the surface of the first metal layer 6 into the air. Here, in the case of mounting the electronic device 1 into another apparatus, the relevant apparatus is made to function as a heat releasing member to widen the heat radiation region. For example, consider the case where the electronics are attached to a luminaire body that includes a metal periphery. In case the first metal layer 6 side is attached to the body of the lamp, heat will be transferred from the first metal layer 6 to the body of the lamp, radiating from the surface of the body of the lamp into the air. Here, similarly, there is also a case where the first metal layer 6 is attached to a radiation fin (fin) or to a heat generation tube to improve heat radiation efficiency.

The graphite layer 5 is interposed between the sub-mount 3 and the first metal layer 6 to improve the heat conduction property in the plane direction. This will thereby allow the effective heat radiation area of the first metal layer 6 to be widened, and thus effective cooling of the heat generating element such as an LED or the like is made possible. However, since a significant thermal resistance is left by interposing between the heat generating structure 10 and the heat releasing structure 20, as described in the above prior examples and the like, the advantage of the property of graphite cannot be utilized.

In contrast, in the patent application of the present invention, the second metal layer having high wettability with solder is formed on the graphite layer 5. Thereby, the joining between the heat generating structure 10 and the heat releasing structure 20 is achieved by the second solder layer 4 b. Thereafter, a low thermal resistance between the heat generating structure 10 and the heat releasing structure 20 can be maintained. Further, by employing a metal film having high thermal conductivity for the second metal layer 7, the thermal resistance is kept low.

Here, another configuration of the present embodiment is illustrated in fig. 4.

In the configuration shown in fig. 3, the LED chip 2 and the submount 3 are bonded to the first solder layer 4 a. In contrast, in the configuration of the electronic device 1b shown in fig. 4, the LED chip 2 and the submount 3 are flip-chip bonded by bumps (bump)4 d. The bumps 4d may be solder bumps or gold bumps. Here, the configuration shown in fig. 3 is similar to that shown in fig. 4 except that the first solder layer 4a is replaced with bumps 4d, and corresponding portions are indicated by the same reference numerals used in fig. 3. Also, in the present configuration, heat from the LED chip 2 is transferred to the submount 3 through the bump 4 d. Thereafter, the heat propagates along the route as described above and is well radiated.

Further, still another configuration of the present embodiment is illustrated in fig. 5.

Each of the electronic devices 1 in fig. 3 and 1b in fig. 4 has an LED chip 2. In contrast, the electronic device 1c shown in fig. 5 includes a CPU 2 a. That is, the present invention is applicable not only to an electronic device including an LED chip mounted on a wiring layer through a submount, but also to an electronic device including a CPU, an IC, and the like directly flip-chip bonded on a wiring layer through bumps without intervention of a submount.

As described above, according to the present embodiment, it is possible to fully utilize the advantage of the high heat scattering property of graphite in the planar direction. Thus, the required cooling properties can be achieved in the electronic device.

(second embodiment)

A schematic cross section showing the configuration of the electronic device 51 of the present embodiment is illustrated in fig. 6.

The LED chip 52 of the electronic device 51 of the present embodiment is configured by the P pole 52a and the N pole 52b provided on the upper plane, and is directly mounted on the second metal layer 7 without interposing a submount. Since the other basic configurations are the same as those of the first embodiment described above, a detailed description will be omitted.

On the lower plane of the LED chip 52 in which the P pole 52a and the N pole 52b are not provided, a plating layer (e.g., gold plating layer) is formed so that it can have good solder wettability. The LED chip 52 has a plane facing the second metal layer 7 and is bonded by means of the solder layer 4 c. The P-pole 52a is electrically connected to the first wiring layer 31a through the first wiring line 33 a. Further, the N-pole 52b is electrically connected to the second wiring layer 31b through the second wiring layer 33 b.

The first embodiment is exemplified by a configuration of the LED chip 2 suitable for mounting, in which the LED chip 2 includes a P pole (or N pole) on an upper plane and an N pole (or P pole) on a lower plane. In the case of the LED chip 2 in which P and N poles are arranged on the upper and lower planes, it is necessary to insulate the second metal layer 7 on the heat releasing structure 20. Thus, the LED chip 2 mounted on the submount 3 is mounted on the second metal layer 7. Therefore, the heat generated by the LED chip 2 will be transferred to the second metal layer 7 via the first solder layer 4a, the submount 3, and the second solder layer 4 b.

In contrast, in the case of the present embodiment, as described above, the P pole 52a and the N pole 52b in the LED chip 52 are formed on the upper plane of the LED chip 52, not on the lower plane. Therefore, no sub-mount isolation is required. Also, in the first embodiment, sufficiently good heat radiation properties can be obtained. However, in the case of the present embodiment, the LED chip 52 is directly mounted on the second metal layer 7, so that the submount and the first solder layer 4a can be omitted. Therefore, in the case of the present embodiment, the thermal resistance from the LED chip 52 to the graphite layer 5 can be reduced. Therefore, it is possible to fully utilize the high heat scattering property of graphite in the planar direction, and at the same time, better heat radiation can be obtained.

Further, in the case of the first embodiment, a step for manufacturing the heat generating structure 10 including the LED chip 2 bonded to the first solder layer 4a and the submount 3 is required. That is, steps for supplying the first solder layer 4a to the submount 3, bringing the first solder layer 4a into a molten state, and integrating the submount 3 and the LED chip 52 by cooling and solidifying the first solder layer 4a after mounting the LED chip 52 on the first solder layer 4a in the molten state are required.

In contrast, the LED chip 52 of the present embodiment does not require a submount and a first solder layer. Therefore, a heat generating structure does not need to be generated. Thus, the manufacturing steps can be simplified, and the number of parts in the device can be reduced.

Further, in the case of a heat generating structure including a submount, it is necessary to extract a wiring line from the submount. Therefore, in order to protect the region for connection of the wiring line, it is necessary to make the area of the submount larger than that of the LED chip. This allows the size of the device to be larger. It is necessary to make the area of the submount larger than the area of the LED chip, resulting in a larger size of the portion.

In contrast, the chip 52 of the present embodiment requires only a mounting area for a portion of the LED chip. Therefore, it is possible to make the apparatus smaller.

As described above, according to the present embodiment, it is possible to sufficiently utilize the high heat scattering property of graphite in the planar direction. Thus, it will be possible to obtain the required cooling properties in the electronic device.

Here, it is preferable to configure the configuration of the present embodiment by isolating the P-pole and the N-pole on the plane of the heat generating structure other than the plane in which the LED chip contacts the second metal layer 7 to serve as the wiring extracting portion. For example, the P and N poles may be formed on the side plane in addition to the case where the P and N poles appear on the upper plane.

Further, the present embodiment is exemplified by bonding an LED chip including a gold plating layer formed on the lower plane with the second metal layer 7 by means of the solder layer 4 c. However, in the case where the gold plating pattern is not formed, the bonding may be achieved by using an adhesive.

(third embodiment)

For this embodiment, the electronic device includes a graphite layer and a second metal layer to achieve high thermal conductivity. A method for manufacturing an electronic device comprising in particular a connector will be described. Here, in the following description, the electronic device 1 shown in the first embodiment will be used as an example.

In the case of the idea of establishing electrical connection of another device to the electronic device 1, it may be considered to link the wiring layer 31 of the electronic device 1 to the other device using an electric wiring. In such a case, the electric wiring will be soldered to the wiring layer 31. However, as described above, the electronic device 1 is highly thermally conductive. Thus, the heat of the soldering iron will be absorbed by the electronic device 1 and will fail during the process of creating sufficient alloy layer, resulting in a mechanically incomplete soldering. That is, a method of performing soldering on the wiring layer 31 becomes considerably difficult.

Therefore, as shown in fig. 7, a method of using the third solder layer 4e to intervene and insert a plug into the connector 34 thereof to establish electrical connection to other devices to mount the connector 34 on the wiring layer 31 can be considered. However, when the device includes the LED chip 2 already mounted thereon, any attempt to subject the connector 34 to reflow soldering onto the electronic device 1 will melt not only the third solder layer 4e to be melted but also the first solder layer 4 a. Subsequently, a displacement of the LED chip 2 that has undergone positioning will occur, so that an unsustainable force will be applied to the wired wires 33.

Therefore, in the case of mounting the connector to the electronic device of the present invention including the graphite layer and the second metal layer, the connector is preferably mounted by the following method.

First, a first solder layer 4a is formed on the submount 3. Further, a third solder layer 4e is formed on the wiring layer 31 in advance. Thus, after the first solder layer 4a and the third solder layer 4e are formed in advance, the LED chip 2 is placed on the first solder layer 4a, and the connector 34 is placed on the third solder layer 4 e. Subsequently, the first solder layer 4a and the third solder layer 4e are heated simultaneously. Thereby, the LEP chip is soldered to the submount 3 using the first solder layer 4 a. At the same time, the connector 34 is soldered to the wiring layer 31 using the third solder layer 4 e. Thereby, simultaneously soldering the LED chip 2 and the connector 34 can prevent the previously placed LED chip 2 from being displaced due to the soldering to the connector 34.

Further, the following method may be employed.

First, the connector 34 is soldered to the wiring layer 31 with the intervention of the third solder layer 4e in advance. Next, the LED chip 2 is placed on the first solder layer 4 a. In this state, heat is applied from the rear plane (plane where graphite layer 5 is not formed) side of first metal layer 6. Then, heat is transferred to first solder layer 4a via graphite layer 5, second metal layer 7, second solder layer 4b, and submount 3 to melt first solder layer 4a, thereby bonding LED chip 2 and submount 3. The heat from the rear plane side for heating the first metal layer 6 will naturally also be transferred to the third solder layer 4 e. However, an insulating layer 32, which functions to provide a significant thermal resistance, is present between the first metal layer 6 and the third solder layer 4 e. Therefore, the time required for the third solder layer 4e to start melting will become longer than the time required for the first solder layer 4a to start melting, and a time difference will occur between the two times. That is, when this time difference is used, the rear plane of the first metal layer 6 is heated to melt the first solder layer 4a, and the heating is stopped before the third solder layer 4e starts to melt. Thus, the LED chip 2 can be mounted without melting the third solder layer 4e to which the connector is bonded.

Further, the metal layer in each of the above embodiments may be a thin plate or a plated layer. In particular, in the case of an electroplating layer, a nickel layer may be formed in advance so that a gold plating layer is formed thereon.

Although preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.

Claims

1. An electronic device, comprising:

a heat releasing structure comprising the first metal layer and a graphite layer stacked on the first metal layer, wherein

The second metal layer and the base are joined by a second joining member so that the heat generating structure and the heat releasing structure are joined thereby, and the heat generating structure is mounted on the graphite layer side of the heat releasing structure.

2. The electronic device of claim 1, wherein the second metal layer comprises copper or aluminum.

3. The electronic device according to claim 1, wherein a surface on a side opposite to a side facing the graphite layer is subjected to an antirust treatment.

4. The electronic device of claim 1, wherein the heat generating element is an LED.

5. The electronic device according to claim 1, wherein the heat generating element is a CPU or an IC.

6. The electronic device of claim 1, wherein the first and second connection components are solder layers.

7. The electronic device of claim 1, wherein the first connection component is a solder bump or a gold bump.

8. The electronic device of claim 1, wherein a melting point of the first connection component is higher than a melting point of the second connection component.

9. The electronic device according to claim 1, wherein the mount is made of AIN or SiC as a main material.

10. An electronic device, comprising:

a heating element; and

The wiring layer formed on the second metal layer and the heat generating element are joined by means of solder bumps or gold bumps, and the heat generating element is mounted on the graphite layer side of the heat releasing structure.

11. The electronic device according to claim 10, wherein the heat generating element is a CPU or an IC.

12. An electronic device, comprising:

a heat-generating electronic component having a wiring extracting portion; and

On a plane of the graphite layer opposite to a plane in which the first metal layer is stacked, there is a second metal layer;

the second metal layer is bonded to the second plane of the heat-generating electronic component, and

the heat generating electronic component is mounted on the graphite layer side of the heat releasing structure.

13. The electronic device according to claim 12, wherein the heat-generating electronic element is a semiconductor device, and the wiring extracting portion is a P pole and an N pole in which wires for wiring are electrically connected.

14. The electronic device of claim 13, wherein the semiconductor device is an LED.

15. The electronic device of claim 12, wherein the second metal layer and the second plane are joined by means of a solder layer.

16. A method for manufacturing an electronic device, the electronic device comprising: a heat generating structure including a heat generating element, a base for mounting the heat generating element thereon, and a first connection member including metal for joining the heat generating element and the base; and a heat releasing structure including a first metal layer and a graphite layer stacked on the first metal layer, wherein the heat generating structure and a connector are mounted on a side of the graphite layer of the heat releasing structure, the method comprising:

on the base on which the second metal layer and the second connection member are joined, the heat generating element is joined by the first connection member, while the connector is joined to the heat releasing structure by a third connection member containing metal.

17. A method for manufacturing an electronic device, the electronic device comprising: a heat generating structure including a heat generating element, a base for mounting the heat generating element thereon, and a first connection member including metal for joining the heat generating element and the base; and a heat releasing structure including a first metal layer and a graphite layer stacked on the first metal layer, wherein the heat generating structure and a connector are mounted on a side of the graphite layer of the heat releasing structure, the method comprising:

forming an insulating layer on the heat releasing structure;

forming a wiring layer on the insulating layer;

bonding the connector to the wiring layer by the third connection member containing metal;

applying heat from a side of the first metal layer after the connector is bonded to the insulating layer by the third connecting member, thereby melting the first connecting member so that the heat generating element is bonded to the base; and