Submount and method of manufacturing the same

Abstract

To provide a submount having high thermal conductivity.SOLUTION: A submount 1 includes: an insulating first insulating member 10 having a first mounting surface 11 and a first bonding surface 12 which is a surface opposite to the first mounting surface 11; a heat conductive member 30 bonded to the first bonding surface 12; and a second insulating member 50 having a second mounting surface 51 and a second bonding surface 52 which is a surface opposite to the second mounting surface 51, and in which the second bonding surface 52 is bonded to a surface opposite to a surface to which the first bonding surface 12 of the heat conductive member 30 is bonded. The thickness of the heat conducting member 30 is thicker than the thickness of any of the first insulating member 10 and the second insulating member 50.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a submount and a method for manufacturing the same. [Background technology]

[0002] Various techniques are known for improving the characteristics of submounts that mount electronic elements, including semiconductor elements such as laser diodes, piezoelectric elements, pyroelectric elements, electronic cooling elements, and optical elements. For example, Patent Document 1 describes a submount in which a 30 μm-thick Al-Si alloy, an alloy of aluminum (Al) and silicon (Si), is disposed between a pair of 0.38 mm-thick alumina (Al2O3) substrates. Patent Document 2 also describes a submount in which a 1-6 μm-thick In solder layer is disposed between a 0.2 mm-thick silicon carbide (SiC) submount and a 0.2 mm-thick diamond submount. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-23145 [Patent Document 2] Japanese Patent Application Publication No. 11-307875 Summary of the Invention [Problem to be solved by the invention]

[0004] In a submount for mounting an electronic element, it is desirable to improve the thermal conductivity of the submount so that heat generated by the electronic element mounted on the submount can be dissipated to the substrate on which the submount is mounted.

[0005] The present invention is intended to solve such problems, and has an object to provide a submount with high thermal conductivity. [Means for solving the problem]

[0006] The submount of the present invention comprises an insulating first insulating member having a first mounting surface and a first bonding surface opposite the first mounting surface, a heat conduction member bonded to the first bonding surface, and a second insulating member having a second mounting surface and a second bonding surface opposite the second mounting surface, the second bonding surface being bonded to the surface opposite to the surface to which the first bonding surface of the heat conduction member is bonded, wherein the thickness of the heat conduction member is greater than the thickness of either the first insulating member or the second insulating member.

[0007] Furthermore, in the submount according to the present invention, the thermal conductivity is preferably 260 W / m·K or more.

[0008] Furthermore, it is preferable that the first insulating member and the second insulating member are made of aluminum nitride, and the heat conducting member is made of copper.

[0009] Furthermore, in the submount according to the present invention, the thickness of the first insulating member and the second insulating member is preferably not less than 1 μm and less than 500 μm.

[0010] Furthermore, in the submount according to the present invention, the thickness of the heat conducting member is preferably not less than 2 μm and less than 1000 μm.

[0011] Furthermore, in the submount according to the present invention, it is preferable that the first mounting surface and the second mounting surface are mirror-finished, and the first bonding surface and the second bonding surface are non-mirror-finished.

[0012] In addition, the method for manufacturing a submount according to the present invention includes a preparation step of placing a thermally conductive base material including a base material of a thermally conductive member between a first insulating base material and a second insulating base material; a joining step of applying joining pressure between the first insulating base material and the second insulating base material to join the thermally conductive member to the first insulating member and the second insulating member; a first polishing step of polishing the surface of the first insulating base material opposite to the surface to which the thermally conductive base material is joined; and a second polishing step of polishing the surface of the second insulating base material opposite to the surface to which the thermally conductive base material is joined, wherein the thickness of the thermally conductive base material is thicker than the thickness of either the polished first insulating base material or the polished second insulating base material.

[0013] The method may further include a cutting step of cutting the first insulating member, the thermally conductive member, and the second insulating member to form a plurality of submounts.

[0014] Furthermore, in the method for manufacturing a submount according to the present invention, the bonding pressure is preferably 10 MPa or more. [Effects of the Invention]

[0015] The submount according to the present invention can have high thermal conductivity. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 2 is a cross-sectional view of a submount according to an embodiment. [Figure 2] 2 is a flowchart showing the manufacturing process of the submount shown in FIG. [Figure 3] 2A to 2E are diagrams showing the manufacturing process of the submount shown in FIG. 1, where (a) shows the preparation process, (b) shows the bonding process, (c) shows the first polishing process, (d) shows the second polishing process, and (e) shows the cutting process. DETAILED DESCRIPTION OF THE INVENTION

[0017] A submount and a manufacturing method thereof according to the present invention will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0018] (Configuration and Function of Submount According to the Embodiment) FIG. 1 is a cross-sectional view of a submount according to an embodiment.

[0019] The submount 1 has a first insulating member 10, a first bonding layer 20, a thermally conductive member 30, a second bonding layer 40, and a second insulating member 50, and is mounted on a mounting substrate 100, and an electronic element 101 is mounted thereon.

[0020] The first insulating member 10 is an insulating substrate made of aluminum nitride and has a rectangular planar shape. The first insulating member 10 has a first mounting surface 11 and a first bonding surface 12, which is the surface opposite to the first mounting surface 11. The first mounting surface 11 is a mirror surface formed by mirror polishing and is soldered to a mounting substrate 100 on which the submount 1 is mounted. The first bonding surface 12 is not a mirror surface formed by mirror polishing but a non-mirror surface with fine irregularities formed thereon. Note that the first mounting surface 11 may not be a mirror surface formed by mirror polishing but may be a non-mirror surface with fine irregularities formed thereon, and the first bonding surface 12 may be a mirror surface formed by mirror polishing.

[0021] The thickness of the first insulating member 10 is preferably 1 μm or more and less than 500 μm, and is 50 μm in one example. If the thickness of the first insulating member 10 is less than 1 μm, cracks may occur in the first insulating member 10. If the thickness of the first insulating member 10 is 500 μm or more, the height of the submount 1 increases, making it difficult to miniaturize the submount 1. The first insulating member 10 is made of aluminum nitride, but in the submount according to the embodiment, the first insulating member may be made of ceramics such as silicon carbide and alumina, and insulating materials containing silicon (Si) other than aluminum nitride.

[0022] The first bonding layer 20 is made of titanium (Ti), is disposed so as to cover the entire first bonding surface 12 of the first insulating member 10, and is a bonding layer that bonds the first insulating member 10 to the thermal conduction member 30. The thickness of the first bonding layer 20 is, for example, 0.1 μm.

[0023] The heat conduction member 30 is a metal foil made of copper and having a rectangular planar shape with the same area as the first insulating member 10. One surface of the heat conduction member 30 is disposed so as to face the first bonding surface 12 of the first insulating member 10 via a first bonding layer 20, and the other surface of the heat conduction member 30 is disposed so as to face the second bonding surface 52 of the second insulating member 50 via a second bonding layer 40. The thermal conductivity of the heat conduction member 30 is higher than the thermal conductivity of both the first insulating member 10 and the second insulating member 50. Although the heat conduction member 30 is formed of a metal foil, it may also be formed of a metal material such as a metal thin film.

[0024] The thickness of the heat conducting member 30 is thicker than both the first insulating member 10 and the second insulating member 50, and is preferably 2 μm or more and less than 1000 μm, and is 100 μm in one example. If the thickness of the heat conducting member 30 is 1000 μm or more, the height of the submount 1 increases, making it difficult to miniaturize the submount 1. In the submount according to the embodiment, the heat conducting member only needs to have a higher thermal conductivity than the insulating member, and may be formed of a high thermal conductive material other than copper, including silver (Ag), Cu-Diamond, which is a composite material of copper and diamond, and Ag-Diamond, which is a composite material of silver and diamond.

[0025] The second bonding layer 40 is made of titanium, similar to the first bonding layer 20, and is disposed so as to cover the entire second bonding surface 52 of the second insulating member 50, and is a bonding layer that bonds the second insulating member 50 to the thermal conduction member 30. The thickness of the second bonding layer 40 is the same as the thickness of the first bonding layer 20, and is, for example, 0.1 μm.

[0026] Like the first insulating member 10, the second insulating member 50 is made of aluminum nitride and has a rectangular planar shape. The second insulating member 50 has a second mounting surface 51 and a second bonding surface 52, which is the surface opposite the second mounting surface 51. Like the first mounting surface 11, the second mounting surface 51 is a mirror surface formed by mirror polishing, and the electronic element 101 is mounted thereon by soldering or bonding with an adhesive. Like the first bonding surface 12, the second bonding surface 52 is not a mirror surface formed by mirror polishing, but a non-mirror surface with fine irregularities formed thereon. Note that the second mounting surface 51 may be a non-mirror surface with fine irregularities formed thereon instead of a mirror surface formed by mirror polishing, and the second bonding surface 52 may be a mirror surface formed by mirror polishing.

[0027] The thickness of the second insulating member 50, like the first insulating member 10, is preferably 1 μm or more and less than 500 μm, and is 50 μm in one example. If the thickness of the second insulating member 50 is less than 1 μm, cracks may occur in the second insulating member 50. If the thickness of the second insulating member 50 is 500 μm or more, the height of the submount 1 increases, making it difficult to miniaturize the submount 1. The second insulating member 50 is formed of aluminum nitride, but in the submount according to the embodiment, the second insulating member may be formed of ceramics such as silicon carbide and alumina, or an insulating material other than aluminum nitride that contains silicon (Si). In the embodiment, the first insulating member 10 and the second insulating member 50 have the same thickness, but the thicknesses of the first insulating member 10 and the second insulating member 50 may be different.

[0028] (Method of manufacturing a submount according to an embodiment) Fig. 2 is a flowchart showing the manufacturing process of the submount 1. Fig. 3 is a diagram showing the manufacturing process of the submount 1, where Fig. 3(a) shows the preparation step, Fig. 3(b) shows the bonding step, Fig. 3(c) shows the first polishing step, Fig. 3(d) shows the second polishing step, and Fig. 3(e) shows the cutting step.

[0029] First, in a preparation step, a thermally conductive base material 130 including a base material of the thermally conductive member 30 is placed between a first base material 110 including a base material of the first insulating member 10 and a second base material 150 including a base material of the second insulating member 50 (S101). The first base material 110 has a first insulating base material 111 which is the base material of the first insulating member 10, and a first bonding layer base material 112 which is arranged to cover the first insulating base material 111. The first bonding layer base material 112 is the base material of the first bonding layer 20, and is formed on the surface of the first insulating base material 111 by a vapor deposition process. The second base material 150 has a second insulating base material 151 which is the base material of the second insulating member 50, and a second bonding layer base material 152 which is arranged to cover the second insulating base material 151. The second bonding layer base material 152 is the base material of the second bonding layer 40, and is formed on the surface of the second insulating base material 151 by a vapor deposition process.

[0030] Next, in the bonding process, bonding pressure is applied between the first base material 110 and the second base material 150 to bond the thermally conductive base material 130 to the first base material 110 and the second base material 150 (S102). In the bonding process, the bonding pressure is set so that the thermal conductivity of the submount 1 to be manufactured, i.e., the thermal conductivity between the first mounting surface 11 of the first insulating member 10 and the second mounting surface 51 of the second insulating member 50, is 260 W / m K or higher. The bonding pressure is preferably 10 MPa or higher.

[0031] Next, in a first polishing step, the surface of the first base material 110 opposite to the surface to which the thermally conductive base material 130 is bonded is polished (S103). The amount of polishing of the first base material 110 in the first polishing step is set so that the thickness of the first insulating base material 111 matches the target thickness of the first insulating member 10. For example, when the target thickness of the first insulating member 10 is 50 μm, the amount of polishing in the first polishing step is set so that the thickness of the first insulating base material 111 becomes 50 μm. The surface of the first insulating base material 111 polished in the first polishing step becomes a mirror finish.

[0032] Next, in a second polishing step, the surface of the second base material 150 opposite to the surface to which the thermally conductive base material 130 is bonded is polished (S104). The amount of polishing of the second base material 150 in the second polishing step is set so that the thickness of the second insulating base material 151 matches the target thickness of the second insulating member 50. For example, when the target thickness of the second insulating member 50 is 50 μm, the amount of polishing in the second polishing step is set so that the thickness of the second insulating base material 151 becomes 50 μm. The surface of the second insulating base material 151 polished in the second polishing step becomes a mirror finish.

[0033] Then, in the cutting step, the first base material 110, the thermally conductive base material 130, and the second base material 150 are cut to form a plurality of submounts 1 (S105). Note that in the method for manufacturing a submount according to the embodiment, the cutting step (S105) is performed after the second polishing step (S104), but if an electrode film is to be formed on the first mounting surface 11 and the second mounting surface 51 of the submount 1, a step of forming an electrode film may be performed after the second polishing step and before the cutting step.

[0034] (Actions and Effects of the Submount According to the Embodiment) The thickness of the heat conduction member 30, which has a higher thermal conductivity than the first insulating member 10 and the second insulating member 50, is greater than the thickness of either the first insulating member 10 or the second insulating member 50, so the submount 1 can have high thermal conductivity. The thickness of the heat conduction member 30 is preferably 1.5 times or more and less than 3.0 times that of the first insulating member 10 and the second insulating member 50, and more preferably 2 times or more and less than 2.5 times.

[0035] Specifically, the thermal conductivity of the submount 1 is 260 W / m·K or more, and the heat radiated from the electronic element 101 mounted on the submount 1 can be efficiently dissipated to the mounting substrate 100 on which the submount 1 is mounted.

[0036] In the manufacturing method of the submount 1, the first base material 110 and the second base material 150 are bonded to the thermally conductive base material 130, and then the surfaces of the first base material 110 and the second base material 150 are polished to form the first insulating member 10 and the second insulating member 50. If the first base material 110 and the second base material 150 are polished individually to an excessively thin thickness, they may crack during handling due to their low rigidity. In the manufacturing method of the submount 1, the first base material 110 and the second base material 150 bonded to the thermally conductive base material 130 are polished, so the thickness can be made thinner than if the first base material 110 and the second base material 150 were polished individually. In the manufacturing method of the submount 1, by reducing the thickness of the first base material 110 and the second base material 150, the thickness of the first insulating member 10 and the second insulating member 50 of the submount 1 can be reduced, thereby improving the thermal conductivity of the submount.

[0037] In the submount 1, the first mounting surface 11 of the first insulating member 10 is a mirrored surface, which allows for high mounting accuracy when mounting the submount 1 on the mounting substrate 100. For example, when a laser diode is mounted on the submount 1, the mounting position of the laser diode can be determined with high accuracy by making the first mounting surface 11 of the first insulating member 10 a mirrored surface. Furthermore, in the submount 1, the second mounting surface 51 of the second insulating member 50 is a mirrored surface, which allows for even higher mounting accuracy when mounting the electronic element 101.

[0038] In the submount 1, the first bonding surface 12 of the first insulating member 10 and the second bonding surface 52 of the second insulating member 50 are non-mirror-finished, which increases the surface area of the interface with the heat conductive member 30 and improves the bonding strength between the first bonding surface 12 of the first insulating member 10 and the heat conductive member 30, and between the second bonding surface 52 of the second insulating member 50 and the heat conductive member 30. If the first bonding surface 12 of the first insulating member 10 and the second bonding surface 52 of the second insulating member 50 are mirror-finished, bonding can be performed without gaps between the first bonding surface 12 of the first insulating member 10 and the second bonding surface 52 of the second insulating member 50 and the heat conductive member 30, thereby improving the thermal conductivity of the submount 1. [Example]

[0039] (Method for measuring thermal conductivity) The thermal conductivity of the samples according to the examples and comparative examples was measured by the following procedure. 1. Calculate the density of the sample from its dimensions and mass. 2. A blackbody treatment is performed on the surface of the sample by spraying carbon powder onto the surface of the sample to make it black. 3. In accordance with JIS standard R1611, pulsed light is irradiated onto a sample that has been subjected to blackbody treatment, and the thermal conductivity is calculated.

[0040] (Method of manufacturing the sample according to Example 1) A pair of aluminum nitride substrates each having a titanium vapor deposition film formed on both sides thereof, with copper foil placed between them, were mounted in a vacuum hot press apparatus, and hot press processing was performed to produce a sample according to Example 1. In the sample according to Example 1, the pair of aluminum nitride substrates had a thickness of 1.0 mm, and the copper foil had a thickness of 2.0 mm. The heating temperature in the hot press processing was 1000°C, and the temperature was increased from room temperature at a rate of 10°C / min, and a pressure of 10 MPa was applied to the sample according to Example 1 placed in the hot press apparatus for 1 hour.

[0041] (Manufacturing method of sample according to Comparative Example 1) The manufacturing method of the sample according to Comparative Example 1 differs from the manufacturing method of the sample according to Example 1 only in the pressure applied. In the manufacturing method of the sample according to Comparative Example 1, a pressure of 10 MPa was applied, whereas in the manufacturing method of the sample according to Comparative Example 1, a pressure of 5 MPa was applied to the sample according to Comparative Example 1 placed in a hot press device.

[0042] Table 1 shows a comparison between the sample according to Example 1 and the sample according to Comparative Example 1.

[0043] [Table 1]

[0044] In Table 1, the "Crack Occurrence" column indicates the results of visually inspecting the prepared sample to see whether or not cracks occurred. If no cracks were observed, the "Crack Occurrence" column is marked with a "Yes." If cracks were observed, the "Crack Occurrence" column is marked with an "X." The "Misalignment Occurrence" column indicates the results of visually inspecting the prepared sample to see whether or not misalignment occurred between the pair of aluminum nitride substrates and the copper foil. If no misalignment was observed, the "Misalignment Occurrence" column is marked with a "Yes." If misalignment was observed, the "Misalignment Occurrence" column is marked with an "X." The "Bonding Strength" column indicates the results of applying a load to the prepared sample and checking whether or not delamination occurred between the pair of aluminum nitride substrates and the copper foil. If no delamination was observed, the "Bonding Strength" column is marked with a "Yes." If delamination was observed, the "Bonding Strength" column is marked with an "X." The "Thermal Conductivity [W / m·K]" column indicates the calculated thermal conductivity. The "Evaluation" column shows the evaluation results based on the presence or absence of cracks and misalignment, bond strength, and calculated thermal conductivity. If "O" is marked in the "Crack Occurrence", "Misalignment Occurrence", and "Bonding Strength" columns, and the value recorded in the "Thermal Conductivity [W / m·K]" column is 260 or greater, the "Evaluation" column is marked with "O". If "X" is marked in either the "Crack Occurrence", "Misalignment Occurrence", or "Bonding Strength" columns, or if the value recorded in the "Thermal Conductivity [W / m·K]" column is less than 260, the "Evaluation" column is marked with "X".

[0045] No cracks were observed in either the sample according to Example 1 or the sample according to Comparative Example 1, and the "Occurrence of cracks" column is marked with "O." No displacement was observed in either the sample according to Example 1 or the sample according to Comparative Example 1, and the "Occurrence of displacement" column is marked with "O." No cracks or displacement occurred in the sample according to Example 1, and the pressure of 10 MPa applied during the preparation of the sample according to Example 1 is considered to be within an appropriate range.

[0046] In the sample of Example 1 and the sample of Comparative Example 1, no peeling was observed between the pair of aluminum nitride substrates and the copper foil when a load was applied, and the "Bonding strength" column is marked with "◯." No peeling was observed even in the sample of Comparative Example 1, which was fabricated using a low pressure, and the pressure of 5 MPa applied during fabrication of the sample of Comparative Example 1 is considered to be within an appropriate range.

[0047] The thermal conductivity of the sample according to Example 1 was 281.9 W / m·K, which was equal to or greater than the target thermal conductivity of 260 W / m·K. On the other hand, the thermal conductivity of the sample according to Comparative Example 1 was 256.5 W / m·K, which was less than the target thermal conductivity of 260 W / m·K. Because the pressure applied during fabrication was low for the sample according to Comparative Example 1, more voids were formed at the bonding interface between the pair of aluminum nitride substrates and the copper foil than for the sample according to Example 1, which was fabricated under high pressure. It is believed that the sample according to Comparative Example 1 has lower thermal conductivity because more voids were formed at the bonding interface between the pair of aluminum nitride substrates and the copper foil than for the sample according to Example 1. [Explanation of symbols]

[0048] 1 Submount 10 First insulating member 11 First mounting surface 12 1st joint surface 20 1st bonding layer 30 Thermal Conduction Material 40 Second bonding layer 50 Second insulating member 51 Second mounting surface 52 Second joint surface

Claims

1. a first insulating member having a first mounting surface and a first bonding surface opposite to the first mounting surface; a heat conduction member joined to the first joining surface; a second insulating member having a second mounting surface and a second bonding surface that is an opposite surface to the second mounting surface, the second bonding surface being bonded to a surface of the thermal conduction member opposite to a surface to which the first bonding surface is bonded; The thickness of the thermally conductive member is greater than the thickness of either the first insulating member or the second insulating member.

2. The submount of claim 1 , wherein the thermal conductivity is 260 W / m·K or more.

3. 3. The submount according to claim 2, wherein the first insulating member and the second insulating member are made of aluminum nitride, and the thermally conductive member is made of copper.

4. The submount according to claim 1 , wherein the first insulating member and the second insulating member have a thickness of 1 μm or more and less than 500 μm.

5. The submount according to claim 1 , wherein the thickness of the thermally conductive member is equal to or greater than 2 μm and less than 1000 μm.

6. The submount of claim 1 , wherein the first mounting surface and the second mounting surface are specular and the first bonding surface and the second bonding surface are non-specular.

7. a preparation step of disposing a thermally conductive base material including a base material of a thermally conductive member between a first insulating base material and a second insulating base material; a joining step of joining the thermally conductive member to the first insulating member and the second insulating member by applying a joining pressure between the first insulating base material and the second insulating base material; a first polishing step of polishing a surface of the first insulating base material opposite to a surface to which the thermally conductive base material is joined; a second polishing step of polishing a surface of the second insulating base material opposite to the surface to which the thermally conductive base material is joined, A method for manufacturing a submount, wherein the thickness of the thermally conductive base material is greater than the thickness of either the polished first insulating base material or the polished second insulating base material.

8. The method for manufacturing a submount according to claim 7, further comprising a cutting step of cutting the first insulating member, the thermally conductive member, and the second insulating member to form a plurality of submounts.

9. The method for manufacturing a submount according to claim 6 , wherein the bonding pressure is 10 MPa or more.

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