JP2003060282A - Submount material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submount material that can be assembled easily to and removed from electronic equipment, prevents a metal circuit layer from being peeled off greatly even if thermal shock operates during an assembly process and use, and has superior heat radiation properties, durability, and reliability. SOLUTION: A submount material 4a has a silicon nitride substrate 2a, a metal circuit board 11 jointed to the surface of the silicon nitride substrate 2a, and a back metal plate 12 jointed onto the back of the silicon nitride substrate 2a. In the submount material 4a, a laser diode 6 should be mounted onto the metal circuit board 11, and the area of the back metal plate 12 is to be larger than that of the silicon nitride substrate 2a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a submount material for holding and mounting a laser diode or the like, and more particularly to a submount material having less peeling of a metal circuit layer and excellent durability and heat dissipation.

[0002]

2. Description of the Related Art Conventionally, a photodiode is mounted on a submount material composed of a ceramic substrate and a metal circuit layer to receive an optical signal on a surface and supply it to an external circuit as an electrical signal. Photodiode subassemblies are widely used as optical devices that supply light to an external circuit via a metal circuit layer. Also,
A laser diode light emitting element using a surface emitting laser diode instead of a photodiode is also widely used as a display component for home electric appliances and electronic devices.

FIG. 6 is a sectional view showing an example of the structure of a laser diode light emitting element. In the figure, a laser diode light emitting device 1 includes a ceramic substrate 2 having a thickness (t) of about 1.5 mm and a solder layer on a submount material 4 including a metal circuit layer 3 formed on the surface by, for example, a sputtering method. The laser diode 6 is integrally bonded via the element 5. The laser diode 6, the metal circuit layer 3, and an external circuit (not shown) are electrically connected to each other by a bonding wire (not shown) or the like. Further, in order to radiate the heat generated by the laser diode 6 to the outside of the system via the submount material 4, the lower part of the submount material 4 is formed of copper (Cu) or the like having good thermal conductivity. The heat sink 7 is integrally joined.

Conventionally, as the submount material 4 for the laser diode 6, an oxide film (Si
Submount materials in which a metal circuit layer is formed on a surface of a substrate having an (O ₂ film) formed thereon by using a thin film forming technique such as a sputtering method are widely used. Further, a gold (Au) plating layer is formed on the surface of the metal circuit layer in order to improve conductivity, adhesion, or bondability between the metal circuit layer and the laser diode, and Au is further formed on the upper surface of the Au plating layer.
In some cases, a solder layer made of —Sn alloy or Pb—Sn alloy is formed. In recent years, an aluminum nitride (AlN) substrate having high thermal conductivity has been widely used as a ceramic substrate that constitutes a submount material in order to cope with an increase in output of a diode and to realize higher heat radiation characteristics.

When a light emitting element substrate having a laser diode element mounted on a submount material as described above is incorporated into an electronic device, the back surface of the light emitting element substrate is soldered with a Pb-Sn alloy or an Au-Sn alloy. Brazing with
A method of adhering and fixing with a resin adhesive has been adopted.

[0006]

However, in the method of joining and fixing via the above-mentioned solder or resin, the heat resistance of the solder and the resin is large, so that there is a problem in that the heat dissipation is lowered, while the joining is done. Since the operation is complicated, there is a problem that it takes a lot of time for assembling work and detaching work. Further, in the soldering method, the joining is often performed at a high temperature, and there is a problem that the element on the submount material is easily damaged by heat. Particularly, in recent years, the influence on the environment has been highlighted, and a measure for refraining from using a solder material or a resin material containing a Pb component that adversely affects the human body and the environment is being sought.

Further, in the conventional submount material in which the aluminum nitride (AlN) substrate is used as the ceramics substrate and the metal circuit layer is formed by using the sputtering method as in the conventional example, the adhesive strength of the metal circuit layer is increased. Therefore, there is a problem that the metal circuit layer is easily peeled off by heat repeatedly applied during the assembling process of the photoelectric element or during use, and there is a problem that the durability and reliability of the photoelectric element are low.

Further, since no consideration has been given to the thickness of the ceramic substrate which constitutes the conventional submount material, the thermal resistance becomes large even when an AlN substrate having a high thermal conductivity is used, and the heat dissipation is improved. There was also a problem that was insufficient.

The present invention has been made to solve the above problems, and is particularly easy to assemble and remove from electronic equipment, and even when a thermal shock is applied during the assembly process or during use, a metal circuit is provided. It is an object of the present invention to provide a submount material which has little peeling of layers and has excellent heat dissipation, durability and reliability.

[0010]

In order to achieve the above object, the inventors of the present invention have various metal circuit boards and back metal plates on the front and back surfaces of a silicon nitride substrate having various dimensions, thermal conductivity and surface roughness. Submount materials were prepared by bonding with each other, and the effects of the specifications of each submount material on the assemblability, thermal shock resistance, peeling resistance, etc. were compared and examined. As a result, in particular, the area relationship between the silicon nitride substrate and the back metal plate that form the submount material is adjusted to a certain range, the volume ratio between the metal circuit board and the back metal plate, or the surface roughness of the silicon nitride substrate. The heat dissipation of the submount material can be improved when the thickness is regulated within a certain range, and the separation of the metal circuit board and the back metal plate can be effectively prevented, and the submount has excellent heat dissipation and durability. We have obtained the knowledge that wood can be obtained for the first time. The present invention has been completed based on the above findings.

That is, the submount material according to the present invention comprises a silicon nitride substrate, a metal circuit board bonded to the front surface of the silicon nitride substrate, and a back metal plate bonded to the back surface of the silicon nitride substrate. In the submount material for mounting the laser diode on the metal circuit board, the area of the back metal plate is larger than the area of the silicon nitride substrate.

Further, in the submount material, it is preferable that at least a part of the outer peripheral edge of the back metal plate is projected to a width of 2.5 mm or more from the outer peripheral edge of the silicon nitride substrate. Further, in the submount material, it is preferable that a mounting hole for inserting a fixing screw is formed in the projecting portion of the back metal plate.

In the submount material, it is preferable that the Vb / Va ratio is 5 or more when the volume of the metal circuit board is Va and the volume of the back metal is Vb. Further, the surface roughness of the silicon nitride substrate is preferably 0.1 to 0.5 μm on the basis of arithmetic average roughness (Ra). Further, it is preferable that the silicon nitride substrate has a plate thickness of 0.8 mm or less, and further that each of the vertical and horizontal lengths of the silicon nitride substrate is 1 mm or more. Further, it is also possible to form a groove at the joint end portion of the back metal plate with the silicon nitride substrate.

The silicon nitride substrate constituting the submount material according to the present invention is excellent in thermal shock resistance, heat dissipation and structural strength, especially for mounting a large capacity and high power laser diode element, and a metal plate. It is preferable to use a silicon nitride substrate made of a silicon nitride sintered body that can obtain high bonding strength when bonded to.

Specifically, as described in Japanese Patent Application Laid-Open No. 2000-34172, which is a prior application filed by the present applicant, it has a high thermal conductivity of 70 W / m · K or more and has a grain boundary phase. It is preferable to use a silicon nitride substrate made of a silicon nitride sintered body having at least a part thereof crystallized.

In the above silicon nitride sintered body, the rare earth element is converted into an oxide in an amount of 2.0 to 17.5% by weight, the Mg is converted into an oxide in an amount of 0.3 to 3.0% by weight, and an impurity positive electrode is added. Al, Li, Na, K, Fe, Ba, Mn, B as ionic elements
Of 0.3% by weight or less in total, which is composed of a silicon nitride crystal and a grain boundary phase, and the ratio of the crystal compound phase in the grain boundary phase to the entire grain boundary phase is 20% or more. It is a conductive silicon nitride sintered body. Such a silicon nitride sintered body not only has a high thermal conductivity of 70 W / mK or more, but also has a three-point bending strength (room temperature) of 600 MP.
Excellent as a or higher.

The high thermal conductivity silicon nitride sintered body is manufactured, for example, by the following manufacturing method.

That is, oxygen of 1.7% by weight or less, Al, Li, Na, K, Fe as impurity cation elements,
A total of 0.3% by weight or less of Ba, Mn, and B, 90% by weight or more of α-phase silicon nitride, and a silicon nitride powder having an average particle size of 1.0 μm or less, and rare earth elements are converted to oxides. 2.0 to 17.5% by weight, and Mg in the form of an oxide of 0.
A raw material mixture added with 3 to 3.0% by weight is molded to prepare a molded body, and the obtained molded body is degreased and then the temperature is set to 1700 to 1
Sinter at 900 ° C., and gradually cool the sintered body from the above sintering temperature to a temperature at which the liquid phase formed by sintering the above rare earth element and MgO solidifies at 100 ° C. or less per hour. It can be manufactured.

The components of the metal circuit board and the back metal plate, which are integrally bonded to the front and back surfaces of the silicon nitride substrate made of the silicon nitride sintered body having high thermal conductivity, are mainly current-carrying capacity,
From the viewpoint of electrical resistance (conductivity) and heat dissipation, copper (Cu),
Aluminum (Al) is preferred.

The method of joining the silicon nitride substrate to the metal circuit board or the back metal plate is not particularly limited, but the thickness is considered from the viewpoint of the holding property of the diode chip in the submount material and the thermal resistance. Considering that a thick metal plate of 0.2 mm or more is often joined, the active metal method or the direct joining method (D
Bonding is preferably performed by the BC method).

Here, the active metal method is based on Ti, Zr, H
This is a method of integrally joining a metal plate and a ceramics substrate through an Ag-Cu-based brazing filler metal containing an active metal such as f. The above-mentioned direct joining method is a state in which the metal plate and the ceramics substrate are in contact with each other. This is a method of directly joining both members by a eutectic compound of a metal plate component and oxygen or a substrate component generated when heated. Further, in the case of the direct bonding method, there is also a method in which an oxide film is provided on the ceramics substrate and then a metal plate is brought into contact with the ceramics substrate to integrally bond them.

In the submount material of the present invention, the area of the back metal plate is larger than the area of the silicon nitride substrate, so that the heat transfer area through the back metal plate is large, and the predetermined bonding is performed. Since the amount of solder or resin adhesive used to obtain strength is reduced, heat dissipation is greatly improved. Even when deformation occurs when the back metal plate is joined to the electronic device, the stress due to the deformation is
Since it is absorbed in the back metal plate having a large area, the stress is less likely to reach the silicon nitride substrate and the metal circuit board, and a submount material having excellent durability can be obtained.

When a thick back metal plate or a metal circuit board is bonded to a silicon nitride substrate, a large stress acts on the silicon nitride substrate, but compared with a fragile ceramic such as aluminum nitride (AlN). Since a silicon nitride substrate with high structural strength is used, it is unlikely to be damaged by stress.

Further, in a preferred aspect of the present invention, at least a part of an outer peripheral edge of the back metal plate is formed so as to project at a width of 2.5 mm or more from an outer peripheral edge of the silicon nitride substrate, so that the heat dissipation can be improved. In addition to making it possible to more reliably improve the effect of improving the durability, absorbing the deformation stress, and improving the durability, it becomes possible to provide a mounting hole for screwing as described later, and the submount material It becomes possible to drastically improve the mounting structure.

Even if the amount of protrusion of the back metal plate from the silicon nitride substrate exceeds 5 mm, the above-mentioned improvement effect cannot be expected to further increase, and it becomes difficult to secure a mounting space. The range of 0.5-5 mm is preferable. A more preferable range is 3 to 4 mm.

Further, in a preferred aspect of the present invention, a mounting hole for inserting a fixing screw is formed in the projecting portion of the back metal plate without using solder or resin adhesive having high heat resistance. It becomes possible to easily and quickly assemble and fix the submount material directly to an electronic device or the like by using a fixing screw such as a screw. Moreover, it is extremely easy to remove.
Further, since no solder or resin is used, the thermal resistance of the submount material can be reduced, and it is particularly suitable as a submount material for mounting a high-power laser diode element that requires heat dissipation.

The mounting hole may be a mere through hole, and is not particularly limited to a mode in which a screw groove is provided. Therefore, the fixing method of the screw when fixing the submount material of the present invention is not limited to the method of fixing only with the screw or the method of fixing with the bolt and the nut, and after inserting the fixing pin into the mounting hole, the tip of the pin There is no particular limitation on the method of bending, fixing by soldering or the like.

In a preferred embodiment of the present invention, when the volume of the metal circuit board is Va and the volume of the back metal board is Vb, the back metal is defined by setting the Vb / Va ratio to 5 or more. Since the plate has a heat dissipation function as a heat sink, the heat dissipation of the submount material is greatly improved.

When a metal plate having a volume difference of 5 times or more is joined to the front and back surfaces of an ordinary ceramic substrate,
A large difference in thermal expansion between the front and back surfaces of the ceramic substrate easily causes cracks and the like on the substrate, but since a silicon nitride (Si ₃ N ₄ ) substrate having high toughness and high strength is used as in the above embodiment, However, there are few problems of fatigue peeling and cracking due to the difference in thermal expansion.

Further, the surface roughness of the ceramic substrate constituting the submount material of the present invention is regulated in the range of 0.1 to 0.5 μm on the basis of arithmetic average roughness (Ra), whereby the metal circuit board and the back metal are The bonding strength of the board can be improved by an appropriate anchor effect, and as a result, even when an excessive thermal shock acts when soldering the diode chip to the submount material, silicon nitride such as metal circuit board Peeling from the substrate can be effectively prevented.

Further, in order to ensure the heat dissipation of the submount material, the thermal conductivity K of the silicon nitride substrate constituting the submount material is 70 W / mK or more, more preferably 90 W.
/ M · K or more is desirable.

The high thermal conductivity silicon nitride sintered body disclosed in Japanese Patent Application Laid-Open No. 2000-34172, which is a prior application by the present applicant, satisfies the high thermal conductivity defined as described above. Since the surface roughness (Ra) in the as-sintered state is 0.4 μm or less, it is particularly suitable as a constituent material of the silicon nitride substrate used in the present invention. In other words, it goes without saying that the silicon nitride sintered body according to the present invention is not necessarily limited to the one described in JP-A-2000-34172.

Further, in a preferred aspect of the present invention, by setting the plate thickness of the silicon nitride substrate to be 0.8 mm or less, it becomes possible to increase the amount of bending of the silicon nitride substrate, and to use the submount material. Even when assembled by being fixed by screwing to an electronic device or the like, tightening cracks are less likely to occur, and the manufacturing yield can be greatly improved.

Furthermore, by setting the length and width of the silicon nitride substrate to be 1 mm or more, it is particularly suitable as a submount material for mounting a large-capacity laser diode element for optical fibers. To support higher output, the vertical and horizontal lengths of the silicon nitride substrate are 2 each.
It is preferably at least mm, more preferably at least 5 mm.

In a preferred aspect of the present invention, the stress generated after the back metal plate and the silicon nitride substrate are joined by forming a groove at the joint end of the back metal plate with the silicon nitride substrate. Is absorbed and relaxed by the groove, so that the durability of the submount material can be significantly improved. This is particularly effective when mounting a high-power laser diode element. The width of the groove is preferably about 0.1 to 0.5 mm. If it is less than 0.1 mm, the effect of providing the groove is small, and if it exceeds 0.5 mm, no further improvement is observed.

According to the submount material having the above structure,
Since the area of the back metal plate is configured to be larger than the area of the silicon nitride substrate, the heat transfer area through the back metal plate is large, and by providing the back metal plate with mounting holes for screwing, Since the amount of solder or resin adhesive (coating thickness) required for attaching the submount material is reduced, heat dissipation is greatly improved. Even when deformation occurs when the back metal plate is bonded to an electronic device, the stress due to the deformation is absorbed in the back metal plate having a large area, and therefore the stress is applied to the silicon nitride substrate or the metal. A submount material that does not extend to the circuit board and has excellent durability can be obtained.

When a thick back metal plate or a metal circuit board is bonded to a silicon nitride substrate, a large stress acts on the silicon nitride substrate, but compared with a fragile ceramic such as aluminum nitride (AlN). Since a silicon nitride substrate with high structural strength is used, it is unlikely to be damaged by stress. Therefore, by bonding a diode element to this submount material, it becomes possible to mass-produce a highly reliable photoelectric element with a high production yield.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the embodiments of the present invention will be described more specifically based on the following examples and reference examples.

Example 1 and Reference Examples 1 and 2 The thermal conductivity was 90 W / m · K, the three-point bending strength (room temperature) was 700 MPa, the surface roughness (Ra) was 0.3 μm, and the length was 3 mm × A silicon nitride (Si ₃ N ₄ ) substrate having a width of 5 mm and a thickness of 0.635 mm is prepared, while a length of 2.5 m
m × width 4.5 mm × thickness 0.5 mm copper (Cu) circuit board (metal circuit board) and length 3.5 mm × width 11 mm × thickness 0.
A 5 mm back copper plate (back metal plate) was prepared.

On the other hand, since it contains Ti as an active metal,
The composition is 70% Ag-27% Cu-3% Ti in terms of quantity ratio.
The brazing material having the above Si_ThreeN_Four25μ thick on both sides of the substrate
After coating with m, contact the copper circuit board and back copper plate
1.33 × 10 when placed ^-4Warm in a vacuum below Pa
The temperature was maintained at 850 ° C. for 10 minutes to obtain a joined body. Further back copper
Two mounting holes are drilled in the overhanging part of the board, and further copper circuit board
Laser diode chip is soldered after circuit is formed on
Then, the submount material according to Example 1 was prepared.

As shown in FIGS. 1 and 2, the submount material 4a according to Example 1 has a copper circuit board serving as the metal circuit board 11 joined to the front surface side of the Si ₃ N ₄ substrate 2a, while the back surface side thereof. A back copper plate serving as a back metal plate 12 is integrally joined to the above, and a laser diode (LD) element 6 is soldered to a predetermined position of a copper circuit plate 11 on which a circuit is formed.
It has a structure in which mounting holes 13 for inserting fixing screws are formed in two overhanging portions (two places). In Example 1, the width W of the overhanging portion is 3 mm.

On the other hand, a submount material according to the reference example was prepared in the same manner as in Example 1 except that a mounting hole for inserting a fixing screw was not formed. Then, a fixing screw was inserted into and tightened in the mounting hole 13 of the submount material 4a according to the first embodiment to directly fix the submount material 4a on the heat dissipation plate. On the other hand, the submount material of the reference example was fixed on the heat dissipation plate via Pb-Sn solder to obtain the joint structure according to the reference example 1. Further, the submount material of the reference example was fixed on the heat dissipation plate via the epoxy resin adhesive to obtain the joint structure according to the reference example 2. The Pb-Sn solder layer of Reference Example 1 and the resin adhesive layer of Reference Example 2 each had a thickness of 0.2 m.
unified to m.

Then, the thermal resistance between the surface of the copper circuit board and the surface of the heat sink of the submount material having each joint structure was measured. As a result, with the thermal resistance value of the submount material according to Example 1 in which the submount material was directly fixed on the heat dissipation plate by the fixing screw as a reference (100%), the average thermal resistance value in the reference example 1 by soldering was 122. On the other hand, in Reference Example 2 in which resin adhesion was used, the average was 153%.

As described above, in the submount material 4a according to the first embodiment, which is directly fixed to the heat sink by screwing without using solder or resin having a high heat resistance value, the heat resistance value should be significantly reduced. It has been found that it is particularly suitable as a submount material for mounting a high-power LD element.

In the above embodiment, an example using a rectangular silicon nitride substrate and a metal plate is shown.
Alternatively, the silicon nitride substrate 2b and the back metal plate 12b having a substantially square shape may be used as shown in FIG.

In the above embodiment, the rectangular back metal plate 12 is provided with the mounting hole 13 having a circular cross section, but as shown in FIGS. 4 (a) and 4 (b). By using the back metal plates 12b and 12c having the notched hole-shaped mounting hole 13a having one end opened, it is possible to absorb an error from the screw hole provided in the heat dissipation plate. Further, as shown in FIGS. 4B and 4C, by using the back metal plates 12c and 12d in which four corners are formed in a curved shape, a submount material with less distortion can be obtained.

Examples 2 to 6 and Comparative Example 1 In the submount materials according to Example 1, the size of the back metal plate (back copper plate), that is, the width of the overhanging portion was adjusted so as to be the values shown in Table 1. Thus, the submount materials according to Examples 2 to 6 were prepared. Then, in order to evaluate the durability and reliability of each submount material, a thermal shock test (heat cycle test: TCT) as described below was performed to perform Si ₃ N ₄
The rate at which cracks were generated on the substrate was measured.

The above heat cycle test was conducted at -40 ° C. for 3 hours.
Hold for 0 minutes, then heat up and hold at room temperature (25 ° C) for 10 minutes, then heat and hold at 125 ° C for 30 minutes, then return to room temperature and hold for 10 minutes as one cycle Temperature rising / falling temperature Repeat 1000 cycles, 10
The rate at which cracks occurred after the completion of 00 cycles was measured. In the heat cycle test, 100 submount materials according to each of the examples were prepared, and the ratio of cracks generated was investigated. Further, as a measurement of the “peeling rate (%) of the back metal plate when fixed by screwing”, 1000 or more submount materials according to each example are prepared, and the back metal plate peels off when screwed. investigated.

As Comparative Example 1, a submount material having the same shape as in Example 3 was used except that the silicon nitride substrate was replaced with an aluminum nitride substrate (heat conductivity 160 W / mK, three-point bending strength (room temperature) 300 MPa). It prepared, and the same measurement was performed. The measurement results are shown in Table 1 below.

[0050]

[Table 1]

As is clear from the results shown in Table 1 above,
The width of the protruding portion of the back metal plate with respect to the Si ₃ N ₄ substrate is 1 m
It was found that in the submount material according to Example 2 having a small m, the stress caused by the deformation of the back metal plate due to screwing was not sufficiently relaxed, and thus cracks were likely to occur.

In each of Examples 3 to 6, the amount of cracks in the silicon nitride substrate after the TCT test was zero, so that the overhang width W of the back metal plate with respect to the Si ₃ N ₄ substrate was 2. It has been found that it is preferably 5 mm or more. Further, in Examples 4 to 6 in which the width W of the protruding portion of the back metal plate is 5.0 or more, it is clear that the effect of reducing the peeling rate of the back metal plate is almost saturated. Therefore, when the mounting space of the submount material is also taken into consideration, the width W of the overhanging portion of the back metal plate is most preferably in the range of 2.5 to 5 mm.

On the other hand, in the submount material using the AlN substrate of Comparative Example 1, the "peeling rate of the back metal plate at the time of screwing and fixing" was about 7%, but the "generation rate of cracks after TCT test". Was over 50%. This indicates that the AlN substrate with weak strength cannot obtain sufficient reliability under the severe TCT test condition of 1000 cycles.

Examples 7 to 11 and Reference Examples 3 to 5 In the submount materials according to Example 1, the thickness of the Si ₃ N ₄ substrate, the thermal conductivity, the material and thickness of the metal circuit board and the back metal plate, The submount materials according to each Example and Reference Example were processed in the same manner as in Example 1 except that the volume (Va, Vb), the Vb / Va ratio, and the joining method of the metal plates were changed as shown in Table 2. Prepared. The three-point bending strength of each Si ₃ N ₄ substrate was 600 MPa or more at room temperature.

In the joining process using the active metal method,
Contains Ti as an active metal and has a weight ratio of 70% Ag-2.
After applying an Ag—Cu based brazing material having a composition of 7% Cu-3% Ti to both sides of a Si ₃ N ₄ substrate with a thickness of 25 μm, a metal circuit board or a back metal plate is placed in contact, and then a temperature of 850 is set in vacuum. Bonding was performed by holding at 10 ° C. for 10 minutes.

On the other hand, in the joining process using the direct joining method,
An oxide film (SiO ₂ film) having a thickness of 1 μm is provided on the surface by heating the Si ₃ N ₄ substrate in advance, and then the metal circuit board and the back metal plate are pressed against the Si ₃ N ₄ substrate. Were joined by heating at a temperature of 1070 ° C. for 10 minutes.

A heat cycle test (TCT) was carried out on each of the prepared submount materials under the same conditions as in Examples 2 to 6, and the incidence of peeling of the metal circuit board after the TCT test was measured. The measurement results are shown in Table 2 below.

[0058]

[Table 2]

As is clear from the results shown in Table 2 above,
In the submount materials according to Examples 7 to 11 in which the ratio (Vb / Va) of the volume Vb of the back metal plate to the volume Va of the metal circuit board constituting the submount material was adjusted to a predetermined range, The peeling rate was 0%, and it was confirmed that the metal circuit board could be effectively prevented from peeling from the Si ₃ N ₄ substrate even when a thermal shock was applied, and that it had excellent thermal shock resistance. It was also found that the volume ratio (Vb / Va) of the back metal plate to the metal circuit plate is preferably in the range of 5-10.

[0060] On the other hand, as the submount member according to the reference example 3, when thick as _Si 3 _{N 4} thickness of the substrate is more than 0.8mm, since _Si 3 _{N 4} strength of the substrate is high, It was confirmed that the amount of flexure became small and the difference in thermal expansion between the metal circuit board and the Si ₃ N ₄ substrate became remarkable, so that peeling of the metal circuit board occurred.

Also, as in Reference Example 4, the Vb / Va ratio was set to 2
Even if it is set to 0, no further peeling prevention effect can be obtained. Further, as in Reference Example 5, Si ₃ N having a low thermal conductivity is used.
_In the case of using _four substrates, it is considered that since the heat dissipation property is lowered, the difference in thermal expansion between the metal circuit board and the Si ₃ N ₄ substrate becomes remarkable, and the peeling rate of the metal circuit board increases.

Examples 12 to 14 Sub-mount materials according to Example 1 were treated in the same manner as in Example 1 except that the surface roughness (Ra) of the Si ₃ N ₄ substrate was changed as shown in Table 3. Then, a submount material according to each example was prepared.

A heat cycle test (TCT) was carried out on each of the prepared submount materials under the same conditions as in Examples 2 to 6, and the incidence of peeling of the metal circuit board after the TCT test was measured. The results are shown in Table 3 below. I got the result.

[0064]

[Table 3]

As is clear from the results shown in Table 3 above,
The surface roughness (Ra) of the Si ₃ N ₄ substrate is 0.1 to 0.5 μm.
It was confirmed that the peeling of the metal circuit board can be effectively prevented and the reliability of the LD element can be improved by adjusting the thickness within the range of m.

Embodiments 15 to 19 In the submount materials according to Embodiment 2, as shown in FIG. 5, at the joint end portion of the back metal plate 12b with the silicon nitride substrate 2a, as shown in Table 4, the width 0 A groove 14 having a depth of 0.2 mm and a diameter of 0.02 mm to 0.8 mm is further formed, and the groove of Example 15 to
Submount material 4b according to No. 19 was prepared.

A heat cycle test (TCT) was carried out on the submount material 4b under the same conditions as in Example 2, and the rate of crack generation in the Si ₃ N ₄ substrate 2a after the TCT test was measured. As shown in FIG. 5, the occurrence rate was 0 to 6%, and it was found that the durability was improved as compared with the case of Example 2. This is because the deformation generated in the joint portion is mitigated by the groove 14.

[0068]

[Table 4]

[0069]

As described above, according to the submount material of the present invention, since the area of the back metal plate is larger than the area of the silicon nitride substrate, the heat transfer through the back metal plate is performed. Since the area is increased and the amount of solder or resin adhesive used to obtain a predetermined bonding strength is reduced, heat dissipation is greatly improved. Even when deformation occurs when the back metal plate is bonded to an electronic device, the stress due to the deformation is absorbed in the back metal plate having a large area, and therefore the stress is applied to the silicon nitride substrate or the metal. A submount material that does not extend to the circuit board and has excellent durability can be obtained.

Further, when a thick back metal plate or a metal circuit board is bonded to a silicon nitride substrate, a large stress acts on the silicon nitride substrate, but compared with fragile ceramics such as aluminum nitride (AlN). Since a silicon nitride substrate with high structural strength is used, it is unlikely to be damaged by stress. Therefore, by bonding a diode element to this submount material, it becomes possible to mass-produce a highly reliable photoelectric element with a high production yield.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a submount material according to the present invention.

FIG. 2 is a sectional view of the submount material shown in FIG.

FIG. 3 is a plan view showing a shape example of a silicon nitride substrate and a back metal plate.

4A, 4B, and 4C are plan views showing examples of the shapes of a back metal plate and a mounting hole, respectively.

FIG. 5 is a cross-sectional view showing an embodiment of a submount material in which a groove is formed at a joining end portion of a back metal plate with a silicon nitride substrate.

FIG. 6 is a cross-sectional view showing a configuration example of a photoelectric device in which a diode is mounted on a submount material.

[Explanation of symbols]

1 Laser diode light emitting element 2, 2a, 2b Ceramic substrate (AlN substrate, Si
₃ N ₄ substrate) 3 metal circuit layers 4, 4a, 4b submount material 5 solder layer 6 laser diode 7 heat sink 8 Ti film 9 Pt film 10 Au film 11 metal circuit board (copper circuit board) 12, 12a, 12b back metal Plate (back copper plate) 13, 13a Mounting hole 14 Groove

Claims (8)

[Claims] 1. A silicon nitride substrate, a metal circuit board bonded to the front surface of the silicon nitride substrate, and a back metal plate bonded to the back surface of the silicon nitride substrate, and a laser on the metal circuit board. A submount material for mounting a diode, wherein the area of the back metal plate is larger than the area of the silicon nitride substrate. 2. The submount material according to claim 1, wherein at least a part of an outer peripheral edge of the back metal plate is projected to a width of 2.5 mm or more from an outer peripheral edge of the silicon nitride substrate. 3. The submount material according to claim 2, wherein a mounting hole for inserting a fixing screw is bored in the projecting portion of the back metal plate. 4. When the volume of the metal circuit board is Va and the volume of the back metal is Vb, Vb / Va
The submount material according to claim 1, wherein the ratio is 5 or more. 5. The submount material according to claim 1, wherein the surface roughness of the silicon nitride substrate is 0.1 to 0.5 μm on the basis of arithmetic average roughness (Ra). 6. The thickness of the silicon nitride substrate is 0.8 mm.
The submount material according to claim 1, wherein: 7. The vertical and horizontal lengths of the silicon nitride substrate are each 1 mm or more.
The listed submount material. 8. The submount material according to claim 1, wherein a groove is formed at a joint end portion of the back metal plate with the silicon nitride substrate.