JP2021044468A - Submount - Google Patents

Abstract

To provide a submount that can stabilize a composition of a solder film and stably generate a eutectic structure of the solder film.SOLUTION: A submount 10 for placing electronic components on a support substrate includes a substrate 11, a first metal film 12b formed on at least one side of the substrate 11, and a solder film 14b formed on the first metal film 12b. On the side surface of the first metal film 12b, there is a second metal film 15a with a surface that has better wettability for the solder film 14b than that of the first metal film 12b.SELECTED DRAWING: Figure 1

Description

The present invention relates to a submount for mounting an electronic component such as a laser element and arranging the electronic component on a support substrate such as a stem or a housing.

A laser element is a semiconductor element that converts a current into light, but since the conversion efficiency of light is not perfect, there is always a current loss, and the loss is converted into heat. The submount on which the laser element is mounted has the role of electrode wiring and the role of quickly transferring the heat generated from the element to the housing.

The laser submount includes a solder film for mounting the laser on a substrate made of AlN or the like having high thermal conductivity, and a solder film for arranging the submount on the support substrate. AuSn solder films are widely used as these solder films, and the AuSn solder films are formed on a metallized thin film formed on a substrate (for example, a Ti / Pt / Au laminated film from the substrate side). Is common.

Further, in order to further increase the thermal conductivity of the laser submount, a submount in which a thick metal film made of copper plating or the like having good thermal conductivity is arranged on the front and back of the substrate has been developed (see, for example, Patent Document 1). .). FIG. 4 is a schematic view of a conventional submount. The submount 100 includes copper plating 102a and 102b on the front and back surfaces of the substrate 101 made of AlN. An AuSn solder film 103 for mounting a laser element is provided on the upper surface of the copper plating 102a formed on one surface of the submount 100, and the copper submount 100 is provided on the entire upper surface of the copper plating 102b on the other surface. An AuSn solder film 104 for attaching to a support substrate (not shown) is provided. Ti / Pt / Au metallization (not shown) is formed between the solder film 103 and the copper plating 102a and between the solder film 104 and the copper plating 102b from the surface side of the copper plating 102a and 102b. The thickness of the copper platings 102a and 102b is generally 20 μm or more, and may exceed 100 μm. The higher the ratio of the copper plating 102a and 102b to the total volume of the submount 100, the higher the thermal conductivity of the submount 100, and the higher the laser output than the submount without the copper plating 102a and 102b. And power saving can be expected.

Japanese Unexamined Patent Publication No. 5--13820

In the conventional submount, the side surfaces of the metal film (copper plating 102a, 102b in the conventional example) formed of the thick film are exposed. When this metal film is copper-plated and the solder film is formed of AuSn solder, when the solder film is melted and bonded to a bonding partner member (for example, a supporting substrate such as a laser element or a stem), the Sn component constituting the solder film is formed. Diffuses into the metal film. In addition, due to the diffusion of the solder film, the wettability of the solder film is reduced due to the change in the physical condition between the side surface of the metal film and the interface between the solder film, and the wettability of the solder film to the metal film side is insufficient. It may get wet and spread unnecessarily. In such a case, the composition of the solder film becomes unstable, and the original eutectic structure of the solder film cannot be obtained.

If the eutectic structure of the solder film cannot be obtained and it becomes subeutectic or hypereutectic, the joint strength becomes weak, and cracks are likely to occur at the joint due to thermal expansion and contraction, especially in a heat cycle test, which is remarkable. Bond strength decreases.

The present invention has been made to solve the above problems, and provides a submount capable of stabilizing the composition of a solder film and stably forming a eutectic structure of the solder film.

A submount for arranging electronic components on a support substrate, the substrate, a first metal film formed on at least one surface of the substrate, and a solder film formed on the first metal film. A submanto having a second metal film having a surface on the side surface of the first metal film, which has a better wettability of the solder film than the first metal film.
Further, it may be a submount which is on the upper surface of the first metal film and further has the second metal film between the first metal film and the solder film.
Further, the second metal film is a surface metal layer having better wettability of the solder film than the first metal film, a barrier layer for the solder film located below the surface metal layer, and a lower layer of the barrier layer. It may be a submount provided with an adhesion layer that adheres to the first metal film.
Further, the second metal film formed on the side surface of the first metal film and the second metal film formed on the upper surface of the first metal film may be a submount made of different materials. ..
Further, the second metal film is formed by vapor deposition or sputtering, and is formed by a plating method under the second metal layer, and the wettability of the solder film from the first metal film to the first metal film. It may be a submount having a third metal film having a good surface.
Furthermore, the side surface of the first metal film may be a submount having an inclined surface extending from the surface of the first metal film toward the substrate.

According to the submount of the present invention, the composition of the solder film that joins the submount and the joining member to be joined to the submount can be stabilized, and the eutectic structure of the solder film can be stably generated.

It is sectional drawing of the submount which concerns on this invention. It is sectional drawing of the submount which concerns on this invention, and is the figure which shows after the laser element and the stem are bonded to the submount. It is sectional drawing of the submount which concerns on this invention. It is a perspective view of the conventional submount.

The submount according to the present invention will be described below with reference to the drawings. However, the technical scope of the present invention is not limited to those embodiments, but extends to the inventions described in the claims and their equivalents.

FIG. 1 is a cross-sectional view of the first embodiment of the submount according to the present invention.

The submount 10 is formed on the surface of the AlN substrate 11, the copper plating 12a formed on one surface of the AlN substrate 11, the copper plating 12b formed on the other surface, and the copper plating 12a. A laminated film 13a in which Ti / Pt / Au films are laminated in order from the surface side of the copper plating 12a, and a Ti / Pt / Au film formed on the surface of the copper plating 12b in order from the surface side of the copper plating 12b. It includes a laminated laminated film 13b. The copper platings 12a and 12b are formed smaller than the outer shape of the AlN substrate 11, and the laminated film 13a is also formed on one surface of the AlN substrate 11 on which the copper plating 12a is not formed. Is also formed on the other surface of the AlN substrate 11 on which the copper plating 12b and the Ni plating film 15a described later are not formed. Further, the submount 10 is formed on the surface of the laminated film 13a and is formed on the surface of the AuSn solder film 14a for mounting electronic components and the laminated film 13b, and the submount 10 is mounted on a support substrate such as a stem. It is provided with an AuSn solder film 14b for mounting. Furthermore, the submount 10 includes a Ni plating film 15a formed on the side surface of the copper plating 12b from the surface of the copper plating 12b to the surface of the AlN substrate 11.

AlN substrate 11, for example, a _Y 2 _{O 3} can be used the added AlN sintered body as a binder. It is desirable that the submount 10 has a high thermal conductivity, and from this viewpoint, a SiC substrate or other ceramics can also be used. The surface of the AlN substrate 11 is preferably polished, but a ground surface or a surface as it is after sintering may be used.

The copper platings 12a and 12b are metal films for improving the thermal conductivity of the submount 10, and can be formed by electroplating. The copper platings 12a and 12b have the highest thermal conductivity among the members constituting the submanto 10, and contribute to the improvement of the thermal conductivity of the submount 10. When the copper platings 12a and 12b are formed by electroplating, a Ti / Cu or TiW / Cu laminated film is formed as a thin film on the surface of the AlN substrate 11 in advance as a seed metal film for plating growth. (Not shown). The Ti or TiW film in the seed metal film is an adhesive film that adheres the AlN substrate 11 and the Cu of the seed metal film, but Cr, Ni, or the like can also be used depending on the base material of the submount 10. In addition to electroplating, a similar structure can be obtained by bonding a copper foil to the AlN substrate 11 (DBC: Direct bonding copper). When the copper foil is bonded to the AlN substrate 11, the surface of the AlN substrate 11 or the copper foil may be oxidized or a metal film may be formed on the surface in order to improve the adhesion between the two. The copper platings 12a and 12b are not limited to copper plating as long as they are materials having good thermal conductivity, and may be a metal film made of another material. The larger the thickness, the better the thermal conductivity.

The copper platings 12a and 12b have a smaller outer shape than the AlN substrate 11, and any pattern shape can be produced by etching (subtractive method). As a method of forming an arbitrary pattern shape, a method of directly forming a desired copper pattern shape by copper plating on the resist opening (additive method) may be used. Further, the side surfaces of the copper platings 12a and 12b are inclined surfaces that spread toward the AlN substrate 11.

The Ti / Pt / Au laminated films 13a and 13b are typically formed so that the thickness is about Ti = 0.06 μm, Pt = 0.2 μm, Au = 0.5 μm, and vacuum deposition or sputtering is performed. Can be used. Ti is an adhesion layer, Pt is a barrier layer that prevents diffusion when the AuSn solder films 14a and 14b are melted, Au is diffused into the AuSn solder films 14a and 14b when the AuSn solder films 14a and 14b are melted, and the composition of the entire AuSn varies. It is a layer for adjusting the amount. As the barrier layer, Ni, Pd, Co and the like can be used in addition to Pt. However, the thickness is not limited to the above.

The AuSn solder films 14a and 14b are layers in which the composition ratio of Au and Sn is adjusted to be a eutectic point, and vacuum deposition or sputtering can be used. Preferably, the two-way simultaneous vapor deposition method in which Au and Sn are evaporated from different evaporation sources to obtain a desired composition is good because the film quality and composition are uniform. Alternatively, Au and Sn may be laminated to form a structure.

For AuSn solder films 14 and 14b, a composition ratio of Au and Sn of about 71:29 (atomic%) is often used from the viewpoint of reliability and bonding strength, but a composition ratio of 6.3: 93.7 is also used. Can be done. This composition ratio is often set to this composition ratio after bonding, and is mixed with Au contained in the Ti / Pt / Au laminated films 13a and 13b and Au contained in the bonding partner (electronic component or supporting substrate) in advance. , AuSn solder films 14a and 14b should be set to hypereutectic in anticipation of this.

The AuSn solder film 14a has a thickness of about 1 to 3 μm, is a layer for joining with an electronic component such as a laser element, and is patterned by a photolithography or the like. On the other hand, the AuSn solder film 14b has a thickness of about 3 to 7 μm, and is a layer for joining to a support substrate such as a housing or a stem.

The Ni plating film 15a is a layer formed on the side surface of the copper plating 12b, and is used on the AuSn solder film 14b, Au contained in the AuSn solder film 14b and the Ti / Pt / Au laminated film 13b, and the bonding partner (support substrate). It is made of a material having better wettability than copper plating 12b with respect to the formed solder film mixed with Au for mounting the submount 10. The Ni plating film 15a is a submount 10 formed on the AuSn solder film 14b when the AuSn solder film 14b is melted, Au contained in the AuSn solder film 14b and the Ti / Pt / Au laminated film 13b, and a bonding partner (support substrate). The solder film mixed with Au for mounting is a layer for making the side surface of the copper plating 12b wet and spread well, and further, for suppressing the Sn of the AuSn solder film 14b from diffusing into the copper plating 12b. It also functions as a barrier layer for soldering. The Ni plating film 15a can be formed not only with Ni but also with Pd, Co, etc. if it is made of a material having good wettability with respect to the solder film, but Ni is particularly preferable. The reason why Ni is good is that it has good wettability with respect to AuSn solder, and the melting rate to AuSn solder is slow (high barrier property) next to Pt. A seed metal film disposed between the copper platings 12a and 12b and the AlN substrate 11 may extend between the Ni plating film 15a and the AlN substrate 11. In this case, between the Ni plating film 15a and the AlN substrate 11, the seed metal film functions as an adhesion film that adheres the Ni plating film 15a and the AlN substrate 11. Further, the seed metal film may extend between the Ti / Pt / Au laminated films 13a and 13b and the AlN substrate 11. However, when the adhesion layer of the seed metal film with the AlN substrate 11 is TiW, it is compared with the Ti which is the adhesion layer with the AlN substrate 11 of the Ti / Pt / Au laminated films 13a and 13b with the AlN substrate 11. Since the adhesion is small, there is a risk of peeling at the interface with the AlN substrate 11 due to stress when the AuSn solder film 14b is melt-solidified. In this case, the Ti / Pt / Au laminated films 13a, 13b and AlN may occur. It is preferable not to extend the seed metal film between the substrate 11 and the substrate 11. That is, when the adhesion between the seed metal film and the AlN substrate 11 is smaller than the adhesion between the Ti / Pt / Au laminated films 13a and 13b and the AlN substrate 11, the Ti / Pt / Au laminated films 13a and 13b and AlN It is preferable not to dispose the seed metal film between the substrate 11 and the adhesion between the seed metal film and the AlN substrate 11 is larger than the adhesion between the Ti / Pt / Au laminated films 13a and 13b and the AlN substrate 11. In this case, the seed metal film may be arranged between the Ti / Pt / Au laminated films 13a and 13b and the AlN substrate 11.

The Ni plating film 15a can be formed by electroplating or electroless plating, and the thickness may be 1 μm or more as long as the above-mentioned functions are exhibited. Although it is possible to use vacuum deposition or sputtering, it is difficult to form a film on the side surface of the copper plating 12b by this method, and the surface of the side surface of the copper plating 12b may be exposed. Therefore, it is preferable to form the film by electroplating or the like. .. By making the side surface of the Ni plating film 15a an inclined surface as in this embodiment, the Ni plating film 15a can be more reliably formed on the side surface of the copper plating 12b regardless of the method of forming the Ni plating film 15a. Can be done. Further, in the present embodiment shown in FIG. 1, the Ni plating film 15a is formed only on the side surface of the copper plating 12b, but in addition to the side surface of the copper plating 12b, the copper plating 12b and the Ti / Pt / Au laminated film 13b are formed. There is no problem even if the configuration is provided with the Ni plating film 15a between the two.

Next, a state in which the laser element is mounted on the submount according to the present invention and joined to the stem will be described. FIG. 2 is a cross-sectional view of the submount according to the present invention, which is a view after the laser element and the stem are joined to the submount.

The submount 10 mounts the laser element 21 with the AuSn solder film 14a as the bonding film, and mounts the AuSn solder film 14b on the stem 22 as the bonding film. Although not shown, metallized films for joining with the submount 10 are formed in advance on the surfaces of the laser element 21 and the stem 22, respectively, and the AuSn solder films 14a and 14b are formed when the AuSn solder films 14a and 14b are melted. It functions as a bonding film with 14b. Specifically, the AuSn solder film 14a and the metallized film on the surface of the laser element 21 are bonded, and the AuSn solder film 14b and the metallized film on the surface of the stem 22 are bonded. As the metallized film of the laser element 21 and the stem 22, for example, a laminated film in which Ti / Pt / Au is laminated from the surface side of the laser element 21 and the stem 22, or a laminated film in which Ni / Au is laminated is used.

Junction in the sub-mount 10 and the laser element 21 and the stem 22, AuSn solder film 14a, 14b of the eutectic temperature (Au:: Sn = 7 In 3at% 278 ° C.) or higher temperatures, in a vacuum or in _{N 2} atmosphere It is generally joined.

After joining, Au of the Ti / Pt / Au laminated films 13a and 13b of the submount 10 diffuses into the AuSn solder films 14a and 14b, respectively, and becomes Ti / Pt films 23a and 23b, and the AuSn solder films 13a and 13b are respectively. AuSn eutectic 24a and 24b. Although not shown, an intermetallic compound (IMC) composed of Au, Sn and Pt is formed between the Ti / Pt films 23a and 23b and the AuSn eutectic 24a and 24b. The thickness and composition ratio of this intermetallic compound differ depending on the bonding conditions.

Further, when the submount 10 and the stem 22 are joined, the submount 10 applies a load from the upper surface (the side on which the stem 22 is mounted on the submount 10 and the opposite side sandwiching the AlN substrate 11), so that the molten AuSn solder film is formed. The 14b (hereinafter referred to as AuSn solder) is extruded from the AuSn solder film 14b forming region on the submount 10, and a part of the AuSn solder protrudes around the AuSn solder film 14b forming region. The protruding AuSn solder is appropriately wetted and spread on the side surface of the copper plating 12b by the Ni plating film 15a formed on the side surface of the copper plating 12b, so that the AuSn eutectic 24b is appropriately formed around the submount 10. If the Ni plating film 15a is not provided, the AuSn solder cannot sufficiently wet and spread on the side surface of the copper plating 12b, and will wet and spread on the surface of the stem 22. In such a case, the amount of AuSn solder that wets and spreads between the submount 10 and the stem 22 and on the side surface of the copper plating 12b, that is, the amount of AuSn solder that contributes to bonding is insufficient, and the AuSn solder tends to become subeutectic. AuSn eutectic 24b may not be produced.

Further, the Ni plating film 15a prevents a large amount of Sn component in the AuSn solder from diffusing into the copper plating 12b, and the AuSn solder is not biased toward the Au-rich composition, resulting in the formation of a stable AuSn eutectic structure. Contribute. Therefore, the submount 10 and the stem 22 can be stably and firmly joined to each other.

Next, a second embodiment of the submount according to the present invention will be described. FIG. 3 is a cross-sectional view showing a second embodiment of the submount of the present invention. In the present embodiment, the same reference numerals are used for the configurations common to the submounts of the first embodiment, and the same configurations and functions as those of the first embodiment are used unless the common configurations are particularly mentioned. Is.

The submount 30 is formed on the surface of the AlN substrate 11, the copper plating 12a formed on one surface of the AlN substrate 11, the copper plating 12b formed on the other surface, and the copper plating 12a. A laminated film 13a in which Ti / Pt / Au films are laminated in order from the surface side of the copper plating 12a, a Ni plating film 15b formed on the surface and side surfaces of the copper plating 12b, and the surface and side surfaces of the Ni plating film. A laminated film 13c in which Ti / Pt / Au films are laminated in order from the surface of the Ni plating film 15b is provided. The copper platings 12a and 12b are formed smaller than the outer shape of the AlN substrate 11, and the laminated film 13a is also formed on one surface of the AlN substrate 11 on which the copper plating 12a is not formed. Is also formed on the other surface of the AlN substrate 11 on which the copper plating 12b and the Ni plating film 15b are not formed. Further, the submount 30 is formed on the surface of the laminated film 13a on the copper plating 12a, and is formed on the surface of the AuSn solder film 14a for mounting electronic components and the laminated film 13c, and is a support substrate such as a stem. Is provided with an AuSn solder film 14b for mounting the submount 30.

The difference between the sub-mount 10 of the first embodiment and the sub-mount 30 of the present embodiment is that the Ni plating film 15b is provided not only on the side surface of the copper plating 12b but also on the surface thereof, and the Ni plating film 15b is provided. The laminated film 13c is provided on the side surface of the above. In the present embodiment, by providing the laminated film 13c on the side surface of the Ni plating film 15b, an appropriate wet spread on the side surface side of the copper plating 12b at the time of melting the AuSn solder film 14b of the submount is ensured, and the AuSn solder film 14b is provided. The Sn component of the above is improved in function as a barrier layer for suppressing diffusion into the copper plating 12b.

The submount 30 includes a laminated film 13c on the Ni plating film 15b, but since the Au layer, which is the outermost layer of the laminated film 13c, has good wettability with respect to the AuSn solder film 14b, appropriate wetting on the side surface side of the copper plating 12b The spread can be secured. Further, since the structure is such that the laminated film 13c is provided on the Ni plating film 15b, and a plurality of layers having good wettability of the AuSn solder film 14b are laminated by the Ni plating film 15b and the Au layer in the laminated film 13c. Even if the film formation on the surface side of the submount 30 is insufficient on the side surface of the copper plating 12b where film formation is difficult (when the underlying layer is exposed), the risk of impairing wettability is small. can do. Needless to say, it is preferable to set the side surface of the Ni plating film 15b as an inclined surface in order to perform the film formation more reliably.

Further, of the Ni plating film 15b and the Pt forming the barrier layer in the laminated film 13c, the Pt has a greater effect of suppressing the diffusion of the Sn component in the AuSn solder film 14b. Therefore, a high effect as a barrier layer on the AuSn solder film 14b can be expected, and further, since the structure is such that the laminated film 13b is provided on the Ni plating film 15b, the Ni plating film 15b and the laminated film also have characteristics as a barrier layer. A plurality of barrier layers are laminated together with the barrier layer (specifically, the Pt layer) in 13c, and the risk of impairing the barrier function can be reduced as in the case of wettability. In this embodiment, the Ni plating film 15b is formed on the side surface of the copper plating 12b and between the copper plating 12b and the laminated film 13c, but it is formed between the copper plating 12b and the laminated film 13c. There is no problem even if it is formed only on the side surface of the copper plating 12b without it.

10, 30 Submount 11 AlN Substrate 12a, 12b Copper Plating 13a, 13b, 13c Laminated Film 14a, 14b AuSn Solder Film 15a, 15b Ni Plating Film 21 Laser Element 22 Stem 23a, 23b Ti / Pt Film 24a, 24b AuSn Co-crystal 100 Submount 101 Substrate 102a, 102b Copper plating 103 Solder film 104 Solder film

Claims (6)

A sub-mount for arranging electronic components on a support board.
With the board
A first metal film formed on at least one surface of the substrate and
A solder film formed on the first metal film is provided.
A submanto having a second metal film having a surface on the side surface of the first metal film, which has a better wettability of the solder film than the first metal film. The submount according to claim 1, wherein the submount is on the upper surface of the first metal film and further has the second metal film between the first metal film and the solder film. The second metal film is a surface metal layer having better wettability of the solder film than the first metal film, a barrier layer for the solder film located below the surface metal layer, and a lower layer of the barrier layer. 1 The submount according to claim 1 or 2, further comprising an adhesion layer that adheres to a metal film. A claim characterized in that the second metal film formed on the side surface of the first metal film and the second metal film formed on the upper surface of the first metal film are made of different materials. Item 2. The submount described in Item 2. The second metal film is formed by vapor deposition or sputtering, and is formed by a plating method in the lower layer of the second metal layer, and the solder film has better wettability than the first metal film than the first metal film. The submount according to any one of claims 1 to 4, wherein the submount has a third metal film provided with a surface. The submount according to any one of claims 1 to 5, wherein the side surface of the first metal film is an inclined surface extending from the surface of the first metal film toward the substrate.

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