JP4822526B2 - Zygote - Google Patents

Description

  The present invention relates to a joined body, and more particularly, to a joined body formed by joining with a solder material containing Bi as a main component.

  When a material containing Bi as a main component is used as a solder material, the melting point of Bi alone is 270 ° C., so that a joined body having excellent heat resistance is obtained. In particular, in the case of a next-generation power semiconductor module in which the joined body is mounted with a semiconductor element such as GaN, heat resistance of 200 ° C. or higher is required so that it can withstand a large amount of heat generated from the power semiconductor element. The use of a material mainly composed of Bi as the solder material for joining the respective members of the semiconductor module is very suitable from the viewpoint of heat resistance.

In a power semiconductor module, it is common to join with solder at two places between a semiconductor element and an insulator and between an insulator and a heat sink. Up to now, in the solder bonding at two locations of the power semiconductor module, Pb-based solder material and Sn-based solder material have been used from the viewpoint of workability and melting temperature (for example, see Non-Patent Document 1).
However, since Pb has toxicity, it is in the direction of abolition of use, and development of a Pb-free solder material is desired. The melting point of the Pb-free solder material for semiconductor modules studied so far is around 220 ° C., which is lower than the melting point of the conventional Pb—Sn solder material around 300 ° C. In particular, development of a high melting point solder material is desired.

As described above, although the material containing Bi as the main component is excellent in heat resistance, the wettability to the bonded surface is low as compared with the conventionally used Pb-based and Sn-based solder materials. There is a problem that the joining between members is difficult to be uniform. Therefore, when joining with a solder material containing Bi as a main component, a method of uniformly joining by applying external pressure and sliding called so-called scrub as well as heating has been adopted.
In addition, power semiconductor modules need to be joined in a large area, but Bi is highly brittle and difficult to roll at room temperature, so it is difficult to produce a foil-like solder material. . Therefore, in joining of power semiconductor modules, higher wettability is required than in conventional solder materials.

Under such circumstances, attempts have been made to add Sn and In to the solder material in order to improve the wettability of the solder material containing Bi as a main component (see, for example, Non-Patent Document 2).
Yoichiro Baba “Efforts to Ensure HV Inverter Quality” Outline of the National Conference of the Japan Welding Society, Chapter 77 (2005-9) Satoshi Uejima et al. “Improvement of wettability and interfacial structure by addition of Sn and In in Bi-based alloys” 12th Symposium on “Microjoining and Assembly Technology in Electronics” February 2-3, 2006, Yokohama

  However, the above method of adding Sn or In to a solder material containing Bi as a main component is premised on the combined use of an organic flux. When this is applied to a joined body in which a high electric field is applied to the end portion of the element, such as a power semiconductor element for an HV inverter, for example, the presence of an organic substance such as a flux residue causes a problem such as a breakdown voltage failure or a leakage current. In addition, there was a situation where further improvement was desired for improvement of wettability.

  Therefore, an object of the present invention is to provide a bonded body in which bonded members are uniformly bonded by improving the wettability of the bonded surfaces when a solder material containing Bi as a main component is used.

According to the first aspect of the present invention, a Cu layer is provided on each bonded surface of two parts, and after a thin film containing at least one of Pd and Ni is formed on the surface of the Cu layer, the two parts between, Ri Na joined by the solder material containing 80 wt% to 100 wt% of Bi, a thin film containing at least one of Pd and Ni, the solder material containing 80 wt% to 100 wt% of Bi is in contact it is lost though that conjugates after joining the parts.

In the first aspect of the invention, at least an interface between Pd and Ni is in contact with a solder material containing 80% by mass to 100% by mass of Bi (hereinafter sometimes referred to as “ solder material containing Bi as a main component”). A thin film including one is provided. Molten Bi forms an alloy by coming into contact with a Pd or Ni thin film, and further, it is clear that Bi tends to wet and spread in search of Pd and Ni, leading to the present invention. As in the present invention, changing the “interface material” with which the solder material comes into contact directly changes the state of the interface that most affects wettability, so the “material of the solder material” is changed. Compared to the above, it is extremely effective in improving the wettability of the solder material.
Moreover, although Cu layer is provided in the invention of Claim 1, this is because an unnecessary reaction product is not produced | generated in the joining interface with Bi. For example, when a bonded portion becomes hot due to heat generated from a semiconductor element such as a semiconductor module, the reaction at the interface of the bonded portion becomes prominent, and depending on the material of the member surface that the bonded portion contacts, the reaction product may be Generate. Since this reaction product is a substance that is hard or brittle, cracks may occur starting from the position where the reaction product exists, or the reaction product may crack and cause cracks. Due to the progress of this crack, defects such as peeling at the bonding interface are likely to occur.
In the present invention, since the Cu layer is provided, the bonded body of the present invention is difficult to generate unnecessary reaction products at the bonding interface even when the temperature becomes high, and therefore, it is possible to prevent the occurrence of cracks starting from the reaction products. As a result, the occurrence of defects such as peeling at the interface can be suppressed.

The invention according to claim 1, a thin film containing at least one of the Pd and Ni, that disappeared after bonding the solder material is in contact with the portion containing 80 wt% to 100 wt% of Bi.

In the invention according to claim 1 , in the joined body after joining, the thin film containing at least one of Pd and Ni disappears in the part joined with the solder material mainly containing Bi. In other words, Pd and Ni are taken into the solder bath of the solder material containing Bi as a main component by heating at the time of bonding and do not remain in the finally obtained bonding interface, and Bi and Cu are firmly bonded at the bonding interface. It is joined. When a thin film containing at least one of Pd and Ni remains in the final product, an unnecessary reaction product may be generated on the joint surface during use of the product. Since the reaction product is harder or more brittle than the surrounding material, the presence of the reaction product may cause problems such as generation of cracks in the joining member and separation at the joining interface.
In the present invention, since the thin film containing at least one of Pd and Ni disappears in the joined body at the interface where the solder material containing Bi as a main component contacts, the generation of unnecessary reaction products is suppressed, Problems such as generation of cracks in the bonding member and peeling at the bonding interface are unlikely to occur.
In this case, when Pd or Ni remains and is exposed to a high temperature, Bi and Pd or Bi and Ni are prevented from reacting with each other. Therefore, at least of Pd and Ni is prevented. It is sufficient that the thin film including one disappears in a portion where the solder material mainly containing Bi is in contact, and a portion where the solder material mainly containing Bi is not in contact may remain.

According the invention described in claim 2, the solder material containing 80 wt% to 100 wt% of the Bi is claim 1, characterized in that at least one selected from the following (1) to (3) It is a conjugate | zygote as described in.
(1) Bi alone
(2) A material containing at least one selected from Cu, Ni, Ag, Sn, In, Zn, Sb, Ge and Ga in Bi,
(3) A material containing at least one selected from CuAlMn alloy particles, Ni or Au plated CuAlMn alloy particles, CuNiAl alloy particles, and CuZnAl alloy particles in Bi.
The invention according to claim 3 is that the solder material containing 80 mass% to 100 mass% of Bi is a simple substance of Bi, a material containing Cu in Bi, a material containing Ni in Bi, or CuAlMn alloy particles in Bi The joined body according to claim 2 , wherein the joined body is a material containing
The invention according to claim 4 is the joined body according to any one of claims 1 to 3 , wherein the thickness of the thin film before joining is 3 nm or more and 1000 nm or less.

The invention according to claim 5 is the joined body according to any one of claims 1 to 3 , wherein the thickness of the thin film before joining is 10 nm or more and 200 nm or less.

As described in the invention described in claim 1, conjugates of the invention, in a portion which is in contact with solder material mainly composed of Bi, the thin film containing at least one of Pd and Ni has disappeared after bonding Is desirable. Conditions under which the thin film disappears can be adjusted by the heating temperature and heating time during bonding, but the thickness of the thin film is preferably 3 nm or more and 1000 nm or less, more preferably 10 nm or more and 200 nm or less. It is.

The invention according to claim 6, wherein the two parts, the power semiconductor element and the insulating substrate, and, claims 1 to 5, wherein the insulating substrate and the heat sink, at least one combination of the It is a joined body of any one of these.

  In the joined body in which the power semiconductor element and the insulating substrate are joined, or in the joined body in which the insulating substrate and the heat sink are joined, that is, in the power semiconductor module, by applying the joined body having the configuration of the present invention, By improving the heat resistance at the joining portion of the power semiconductor module and improving the wettability of the joining portion, it is possible to obtain a power semiconductor module in which inconveniences such as the members being inclined and joined are suppressed.

The invention according to claim 7, wherein the power semiconductor element is a conjugate according to claim 6, characterized in that is formed using a GaN or SiC.

When the power semiconductor element is formed using the next generation GaN or SiC, the amount of heat generated from the power semiconductor element becomes extremely large and may reach about 200 ° C.
However, since the bonded body of the present invention is bonded with a solder material mainly composed of Bi, the heat resistance of the bonded portion is secured at about 270 ° C., and the wettability of the interface where the solder material is in contact is improved. Therefore, since uniform joining is possible, problems such as the member being inclined and joined are suppressed.
Furthermore, in the present invention, since the material between the contacting members is selected, unnecessary products are generated at the bonding interface even under severe thermal cycle conditions due to the power semiconductor formed of the next generation GaN or SiC. It is possible to obtain a power semiconductor module that is difficult to generate and is less likely to cause defects such as cracks in the bonding member and peeling at the bonding interface.

The invention according to claim 8, wherein the insulating substrate is a AlN layer, according to claim 6 or claim 7, characterized by comprising a conductive layer formed of Cu on both surfaces of the AlN layer It is a joined body.

  When an AlN layer is used as an insulating substrate, the insulation is improved, and when there are conductive layers formed of Cu on both surfaces of the AlN layer, even if a solder material containing Bi as a main component is in contact, it is unnecessary for the bonding interface. The reaction product is not generated, and it is difficult to cause problems such as cracking of the joining member and peeling at the joining interface.

The invention according to claim 9 is a laminate of Cu layer / Mo layer / Cu layer in which the two parts include a combination of an insulating substrate and a heat sink, and the heat sink has a Cu layer on both sides of the Mo layer. It is a joined body according to any one of claims 6 to 8 .

  When a Mo layer is used as the heat radiating plate, the thermal conductivity is high and excellent heat dissipation is exhibited. In addition, when Cu layers are provided on both surfaces of the Mo layer, even if a solder material containing Bi as a main component comes into contact, an unnecessary reaction product is not generated at the bonding interface, and cracks in the bonding member or at the bonding interface occur. It is difficult to cause defects such as peeling. Furthermore, the laminated body of Cu layer / Mo layer / Cu layer is suitable from the viewpoint of adjusting the thermal conductivity and the thermal expansion coefficient.

The invention according to claim 10, the ratio of the thickness of the Cu layer / Mo layer / Cu layer in the heat sink, to claim 9, characterized in that a 1/5 / 1-1 / 12/1 It is a joined body of description.

  Among laminates of Cu layer / Mo layer / Cu layer, when the ratio of the thickness of each layer is 1/5/1 to 1/12/1, the balance between thermal conductivity and thermal expansion coefficient becomes good. It effectively demonstrates its function as a heat sink.

  ADVANTAGE OF THE INVENTION According to this invention, the to-be-joined body by which the to-be-joined member was joined uniformly can be provided by the improvement of the wettability when using the solder material which has Bi as a main component.

The joined body of the present invention includes a Cu layer on each surface to be joined of two parts, and a thin film containing at least one of Pd and Ni is formed on the surface of the Cu layer, and then the gap between the two parts. , A bonded body formed by bonding with a solder material (solder material containing Bi as a main component) containing 80% by mass to 100% by mass of Bi. The thin film containing at least one of Pd and Ni disappears after bonding at a portion where a solder material containing 80% by mass to 100% by mass of Bi contacts. In this joined body, it is sufficient that at least one place is joined with a solder material containing Bi as a main component. Therefore, two or more places may be joined with a solder material containing Bi as a main component.

  There are no particular restrictions on the type of the two parts that are the objects to be joined, and various parts can be applied. Therefore, a joined body in which the two components are a power semiconductor element and an insulating substrate, or an insulating substrate and a heat sink, that is, the joined body may be a power semiconductor module. By applying the configuration of the present invention to the power semiconductor module, the heat resistance at the joined portion of the power semiconductor module is improved, and the wettability of the joined portion is improved, so that the members to be joined are inclined and joined. The occurrence of defects can be suppressed.

  Therefore, in the following, the case where the joined body is a power semiconductor module will be described in detail. However, as described above, the joined body of the present invention is not limited to the power semiconductor module, and includes a joined body in which various members are joined. Include.

<Power semiconductor module>
In FIG. 1, the principal part sectional drawing of the power semiconductor module 10 which is an example of the conjugate | zygote of this invention is typically shown.
The power semiconductor module 10 includes at least a power semiconductor element 20, an insulating unit 30, and a heat sink 40. The power semiconductor element 20 and the insulating part 30 are joined by the first joining part 50. The insulating part 30 and the heat sink 40 are joined by the second joining part 60.

  The power semiconductor module 10 is used for an in-vehicle inverter or the like. Since an internal combustion engine (not shown) is provided around the power semiconductor module 10, the environment in which the power semiconductor module 10 is placed is considerably high. Further, when next-generation GaN or SiC is used as the power semiconductor element, heat generated from the power semiconductor element 20 is large, and the temperature of the power semiconductor module 10 rises.

  A cooling pipe (not shown) through which cooling water flows is provided so as to prevent the power semiconductor element from being destroyed by the heat generated by the power semiconductor element or the high-temperature ambient environment, and between the cooling pipe and the power semiconductor element. A heat sink 40 is provided between them.

Therefore, as a performance generally required for a power semiconductor module, firstly, with respect to a cooling cycle that occurs in an atmospheric temperature when the entire assembly is not driven and a high temperature state during driving, cracks in the semiconductor and the insulating substrate, It does not cause defects such as cracks in the joining member and peeling that occurs from the joining interface, and secondly, it is to ensure insulation by the insulating substrate, and thirdly radiates heat generated from the power semiconductor element. It is to convey as little as possible to the board.
In order to prevent the above cracks, cracks, peeling, etc. from occurring in the thermal cycle, members such as semiconductor elements, insulating substrates, heat sinks and joining members must be durable against temperature changes. In the cooling and heating cycle, it is important that unnecessary reaction products are not generated at the bonding interface or that the reaction products do not grow greatly. Such a reaction product is a brittle substance or, on the other hand, a substance that is too hard, and easily causes cracks in the joining member, separation from the joining interface, etc. starting from the site where the reaction product is generated. Moreover, it is important for the thermal expansion coefficient of each member to be a close value to suppress the occurrence of the cracks, cracks, peeling, and the like due to the thermal cycle. When members having completely different thermal expansion coefficients are joined, the above-described cracks, cracks, peeling, and the like are likely to occur due to the volume change of the member repeatedly caused by the cooling and heating cycle.

  The performance required for the joined portion of the power semiconductor module is as follows: first, the joining is performed uniformly, the members are not inclined and joined, and second, the cracks and joining of the semiconductor and the insulating substrate against the thermal cycle This is to prevent the occurrence of defects such as the occurrence of cracks in the member and peeling that occurs from the bonding interface.

  In the power semiconductor module that is the joined body of the present invention, the first joined portion 50 or the second joined portion 60 is joined using a solder material mainly composed of Bi, so that the heat resistance of the joined portion is increased. ing. Further, since the thin film containing at least one of Pd and Ni is provided at the interface where the solder material containing Bi as the main component contacts, the wettability of the solder material containing Bi as the main component is improved. As a result, since the joining is performed uniformly, it is possible to prevent problems such as the members being joined at an inclination, and to prevent the heat conduction from being hindered.

  In addition, since a Cu layer is provided in the present invention, unnecessary reaction products are not generated at the interface with Bi, and the occurrence of reaction products causes the occurrence of cracks in the bonding member and peeling at the bonding interface. Can be suppressed.

Furthermore, in the power semiconductor module after bonding, the solder material is in contact with the portion composed mainly of Bi, and Pd or Ni is incorporated in the solder bath, that have thin film containing at least one of Pd and Ni disappeared .
If Ni or Pd remains in contact with Bi, it is not necessary because Bi and Pd or Bi and Ni react with heat generated from the semiconductor element while the power semiconductor module is used as a product. Reaction products may be produced. Bi and Cu are unnecessary reaction products if Pd and Ni are taken into the solder bath at the portion where the solder material containing Bi as the main component is in contact and the thin film containing at least one of Pd and Ni disappears. It joins firmly, without producing. As a result, the occurrence of defects such as cracks and peeling due to the generation of reaction products is suppressed.
In this case, the reaction between Bi and Pd or Bi and Ni occurs instantaneously, and the thin film containing at least one of Pd and Ni in the thin film may be taken into the Bi bath and disappear, and Bi is the main component. The portion that is not in contact with the soldering material may remain.

In the power semiconductor module of FIG. 1, the thin films 24, 38, 39, and 48 containing at least one of Pd and Ni are illustrated. However, after bonding, these thin films are in contact with the solder material mainly composed of Bi. It is desirable to disappear.
2 to 4 also show thin films containing at least one of Pd and Ni. However, after bonding, these thin films may disappear in the portion where the solder material containing Bi as a main component contacts. desirable.

<Joint part>
The power semiconductor element 20 has at least two joint portions, and the first joint portion 50 and the second joint portion 60 exist. The first joint portion 50 in the present invention is provided to join the power semiconductor element 20 and the insulating portion 30, and the second joint portion 60 in the present invention is between the insulating portion 30 and the heat sink 40. Provided for joining.

The solder material containing Bi as the main component according to the present invention may be applied to either the first joint 50 or the second joint 60, but at least one of the solder materials containing Bi as the main component. Is used.
The solder material containing Bi as the main component may be Bi alone or may contain other components. Examples of other components added to Bi include metals such as Cu, Ni, Ag, Sn, In, Zn, Sb, Ge, and Ga, CuAlMn alloy particles, Ni or Au plated CuAlMn alloy particles, and CuNiAl alloys. Examples thereof include particles and CuZnAl alloy particles. Thus, when other components are contained in Bi, the strength of Bi is improved, and it becomes a material in which cracking of the joining member and separation at the joining interface hardly occur.

  In addition, in this invention, "the solder material which has Bi as a main component" means that 80 mass%-100 mass% of Bi is contained in solder material, and the more preferable Bi content rate is other materials to add. Although it varies depending on the material, it is preferably contained in an amount of 82 mass% to 99.9 mass%, more preferably 85 mass% to 99.8 mass%. If the Bi content is lower than 80% by mass, it is difficult to exhibit the soldering characteristics of Bi.

Here, Bi—CuAlMn in which CuAlMn alloy particles are dispersed in Bi will be described.
Since Bi has a melting point near 270 ° C., it is suitable as a solder material for the joint. However, since Bi has a weak shear stress and is brittle, when it is subjected to a thermal cycle, it will cause cracks and peeling. However, the strength can be increased by dispersing CuAlMn alloy particles in Bi. This function will be described in more detail.

  Furthermore, the CuAlMn alloy has martensitic transformation properties. The alloy phase of the metal having martensitic transformation properties takes either a martensitic phase or a parent phase based on temperature and stress. When the alloy phase of the metal is a martensite phase, the metal is extremely flexible and can be easily changed in shape based on an external force. For this reason, the stress based on an external force is relieved. Furthermore, even if the cooling and heating cycle is repeated, the shape can be changed flexibly, so that accumulation of fatigue based on stress is suppressed. In addition, when the metal alloy phase is the parent phase, the metal undergoes phase transfer to the martensite phase based on the external force and elastically deforms, so that when the external force is unloaded, the original shape is restored. Can do. For this reason, the stress applied to the metal is relieved and the accumulation of the stress is suppressed.

  Therefore, by adding a CuAlMn alloy having a martensitic transformation property to Bi which is a bulk metal, stress from an external force can be relieved and the accumulation of the stress can be controlled. As a result, it is possible to provide a solder that locally relaxes the thermal stress of a solder material containing Bi as a main component.

  CuAlMn alloy has little toxicity and little influence on the melting point of the bulk metal to be added. Further, since the CuAlMn alloy has a small electric resistance, it can be suitably used even under a situation where a current flows through the CuAlMn alloy.

The content of the CuAlMn alloy in Bi—CuAlMn is preferably 0.5 to 20% by mass, and more preferably 1 to 15% by mass. When the content of the CuAlMn alloy is less than 0.5% by mass, it is difficult to obtain the above effect by adding a material having martensitic transformation properties. When the content is more than 20% by mass, the content of molten Bi is low. Therefore, the bonding strength with the object to be bonded cannot be obtained.
Even when the volume fraction of Bi and CuAlMn is changed from 90:10 to 45:55, the melting point of Bi-CuAlMn is 271 ° C.

  In the CuAlMn alloy, it is preferable that the Mn content is 0.01 to 20% by mass, the Al content is 3 to 13% by mass, and the balance is Cu. By adjusting to this composition ratio, the property of martensitic transformation appears remarkably, and it is possible to suppress the breakage of the joint formed by solder.

Moreover, when Ag, Ni, Au, Sn, P, Zn, Co, Fe, B, Sb, and Ge are added to the CuAlMn alloy, there is an effect of improving the consistency with Bi and stabilizing the martensite phase. Therefore, an embodiment in which these additional elements are added is also preferable.
The content of the additive element in the CuAlMn alloy is preferably 0.001 to 10% by mass. When the additive element is less than 0.001% by mass, it is difficult to obtain the above effect of adding the additive element. If there are more additive elements than 10% by mass, the CuAlMn alloy cannot exhibit a martensite phase.

  By adjusting the particle diameter of the CuAlMn alloy particles, the stress relaxation ability of Bi—CuAlMn can be adjusted. Specifically, the particle diameter of the CuAlMn alloy particles is preferably 0.01 to 100 μm, and more preferably 0.01 to 20 μm.

The method for preparing CuAlMn alloy particles is not particularly limited, and a known method for preparing alloy particles can be appropriately applied. An example of the adjustment method is shown below, but is not limited thereto.
First, Cu, Al, and Mn are melted in a high-frequency melting furnace in an Ar atmosphere to prepare a CuAlMn alloy ingot as a precursor. You may add the said additional element to an ingot as needed. Next, the obtained ingot is pulverized using a powder production technique such as an atomizing method to obtain CuAlMn alloy particles. The powdered CuAlMn alloy particles are plated with Ni or Au on the particle surface using a dropping method or the like. By adjusting the film thickness of the plating layer on the particle surface, the dispersibility of CuAlMn particles in Bi-CuAlMn can be improved. A preferable film thickness of the plating layer is 0.01 to 3 μm.

  When joining members to be joined by Bi—CuAlMn, joining at a temperature several tens of degrees higher than the melting point of Bi—CuAlMn (270 ° C.) is a viewpoint of uniformly melting the joint and obtaining sufficient fluidity. It is preferable to join at about 300 to 350 ° C.

  Next, Bi added with Cu will be described. When Cu is added to Bi, the strength of Bi increases. This is believed to be due to dispersion strengthening due to fine dispersion of Cu in the Bi matrix.

As Cu is added to Bi, the liquidus temperature increases as the Cu content increases. The liquidus temperature is a temperature at which the whole melts and becomes a liquid. On the other hand, even when the Cu content is increased, the solidus temperature is about 270 ° C., which is almost constant. The solidus temperature is a temperature at which at least a part starts to dissolve.
That is, as the Cu content increases, the difference between the temperature at which melting begins and the temperature at which the entire melting ends increases. When such a solid-liquid coexistence region temperature difference arises, it becomes difficult to perform uniform joining during the joining operation, and it is easy to cause problems such as joining the members to be joined tilted. Further, when the semiconductor element is bonded under a high temperature condition due to an increase in the liquidus temperature, the semiconductor element may be destroyed.

  Therefore, considering the liquidus temperature and the solidus temperature, the Cu content in Bi is preferably 0.01% by mass to 5% by mass, and 0.3% by mass to 4% by mass. More preferably.

The method for preparing Bi to which Cu is added is not particularly limited, and known preparation methods can be applied as appropriate. An example of the adjustment method is shown below, but is not limited thereto.
Cu and Bi are melted by a high-frequency melting furnace in an Ar atmosphere to produce a Bi—Cu alloy ingot as a precursor. The obtained ingot is hot-rolled at 250 ° C. to form a plate material and cut out as a solder piece.
When other metals are added to Bi, they can be prepared in the same manner as in the case of Cu.

Bi added with Ni will be described. When Ni is added to Bi, the strength of Bi increases as in the case of adding Cu. It is presumed that this cause is the same as in the case of Cu. Note that when Ni is added to Bi, Ni forms a reaction product Bi ₃ Ni in Bi and is uniformly dispersed in the Bi matrix.

  In consideration of the liquidus temperature and the solidus temperature, the Ni content in Bi is preferably 0.01% by mass to 5% by mass, and 0.01% by mass to 3% by mass. Is more preferable.

When a reaction product is generated in a harsh cooling cycle such as a semiconductor module, a crack is generated starting from the position where the reaction product exists, or in the case of a fragile reaction product, the reaction product is cracked. Cause cracks. As a result, it becomes easy to generate cracks in the bonding member and peeling at the bonding interface.
Therefore, a Cu layer is provided on the surfaces to be joined of the members to be joined. In other words, when a solder material containing Bi as a main component is applied to the first joint portion 50, a Cu layer is provided on each joint surface of the power semiconductor element 20 and the insulating portion 30, and Bi is mainly used in the second joint portion 60. When the solder material as a component is applied, a Cu layer is provided on each of the surfaces to be joined of the insulating portion 30 and the heat sink 40. By providing the Cu layer, it is possible to suppress generation of unnecessary reaction products at the interface with Bi.

Bi is a substance with low wettability and is difficult to wet and spread with respect to Cu. If the solder material does not wet and spread during the heating of the bonding, bonding cannot be performed uniformly, and problems may occur such as bonding with the members to be bonded tilted.
In order to solve such a problem, in the conventional method, the members to be joined are rubbed while applying external pressure during the heating of joining, and the members to be joined are joined so as not to tilt. If such a method is adopted, even if the solder material is mainly composed of Bi, the members to be joined can be uniformly joined. However, applying external pressure while heating is a complicated operation. In addition, there is a risk of protruding to the periphery and causing electrical problems.

  Therefore, in the present invention, a thin film containing at least one of Pd and Ni is formed on the surface of the Cu layer to improve the wettability of Bi. Below, reaction of Pd or Ni and Bi is demonstrated.

  It has been clarified in the course of the present invention that Pd and Ni easily react with molten Bi to form an alloy. In other words, in the heating at the time of joining, when the solder material containing Bi as a main component melts exceeding the melting point, it expands by itself while causing an alloy formation reaction. In the present invention, by utilizing the ease with which this alloy is formed, a thin film containing at least one of Pd and Ni is formed on the surface in contact with the solder material containing Bi as a main component, thereby improving the wettability of Bi. I am letting.

In addition, in heating at the time of joining, it has been found that Pd and Bi currently produce two types of alloys, and Ni and Bi produce an alloy called Bi ₃ Ni. In the present invention, the invention is not limited to the type of alloy to be produced, and any thin film containing at least one of Pd and Ni may be included in the present invention as long as the thin film containing at least one of Pd and Ni is formed on the surface in contact with the solder material mainly composed of Bi. .

  Here, if the thin film formed to ensure wettability remains after solder bonding, an unnecessary reaction product may be generated at the bonding interface by the thermal cycle when the power semiconductor module is used as a product. . Such an unnecessary reaction product is usually a brittle substance or a hard substance, so that a crack is generated starting from the position where the unnecessary reaction product exists. It is easy to generate defects such as cracks and peeling that occurs from the bonding interface.

  Therefore, it is desirable that the thin film containing at least one of Pd and Ni has a film thickness that is taken into the Bi solder bath and does not remain at the bonding interface after the solder material wets and spreads. Since such a film thickness varies depending on the heating temperature and heating time at the time of soldering, and the type of solder material (the type of other material contained in Bi), etc., it cannot be determined in general and is suitably suitable. Although it is desirable to adopt a film thickness, it is generally preferably 3 nm or more and 1000 nm or less, and more preferably 10 nm or more and 200 nm or less. If the film thickness is too thin, the bonded portion may be island-shaped and cannot be bonded uniformly. However, as a matter of course, the joining portion may have an island shape as long as uniform joining is possible. On the other hand, when it is thicker than 1000 nm, not all is taken into the Bi solder bath, and a thin film containing at least one of Pd and Ni may remain.

  A thin film containing at least one of Pd and Ni can be formed by sputtering, plating, vapor deposition, or the like.

  Note that, as shown in FIG. 2, the bonding portion bonded with the solder material containing Bi as a main component has a larger area of the insulating substrate 32 than the semiconductor device 20 in the case of bonding the semiconductor element 20 and the insulating substrate 32. The appearance of the solder welded portion (first joint portion) 50 on the insulating substrate 32 can be observed. At this time, the substrate having the Ni or Pd thin film 38 which is precursor to the entire insulating substrate 32, and the ferret portion (see the first bonding portion 50 in FIG. 2B) in which those thin films are taken into the solder. The semiconductor element 20 can be confirmed. Similarly, when solder containing Bi as a main component is used for the insulating substrate 32 and the heat radiating plate 40, the area of the heat radiating plate 40 is larger than that of the insulating substrate 32. The thin film 48, the ferret, and the insulating substrate 32 can be observed.

  A specific joining method will be described later.

<Power semiconductor element>
As the power semiconductor element 20, it can apply suitably according to a use without a restriction | limiting in particular, A general Si substrate etc. can also be applied.
In the present invention, even when a GaN substrate or SiC substrate is used as the next generation device, the melting point of Bi used for the junction is about 270 ° C., and thus exceeds 200 ° C. that is dissipated by repeated use of the semiconductor device. A highly reliable power semiconductor module that does not cause defects such as cracks and peeling even at high temperatures.

When applying the solder material which has Bi as a main component to the 1st junction part 50, the power semiconductor element 20 provides the Cu layer 22 on the surface by the side of the 1st junction part 50 as above-mentioned. When the Cu layer 22 is provided on the surface on the first joint 50 side, an unnecessary reaction product due to the cooling / heating cycle is not generated at the interface between the first joint 50 and the Cu layer 22. Resistance is also high.
The thickness of the Cu layer 22 is preferably 0.1 μm to 10 μm, and more preferably 0.5 μm to 7 μm. If it is thinner than 0.1 μm, it may be dissolved in the solder material during bonding, and if it is thicker than 10 μm, the thermal expansion coefficient of the entire power semiconductor module will be affected and thermal stress will be generated. Absent.
The Cu layer 22 can be formed by sputtering, plating, vapor deposition, or the like.

  Furthermore, as described above, when a solder material mainly composed of Bi is applied as the bonding material of the first bonding portion 50, the thin film 24 containing at least one of Pd and Ni is formed on the surface of the Cu layer 22. Is done.

<Insulation part>
The insulating substrate 32 in the insulating portion 30 can be applied without particular limitation as long as it can ensure insulation, but preferably has a thermal expansion coefficient of the semiconductor element so as not to cause significant thermal stress during the cooling cycle. It has a thermal expansion coefficient comparable to the above.

Specific examples of suitable insulating substrate 32 include those formed of AlN, Si ₃ N ₄ , Al ₂ O _3, etc. Among them, AlN is preferable from the viewpoint of thermal conductivity and thermal expansion coefficient. is there.

  Further, a conductive layer 34 is provided on the surface of AlN in order to conduct electricity from the surface of the insulating substrate 32 on the power semiconductor element side to the semiconductor element. In order to suppress warping against temperature changes, it is preferable to provide the conductive layer 36 also on the heat radiating plate 40 side. Examples of such conductive layers 34 and 36 include Al, Cu, Mo, and Ni. Among these, Cu is preferable. When a Cu layer is provided on the surface of AlN, it can be thinned because of its high conductivity, and in addition to relieving thermal stress, solder containing Bi as a main component in the first joint 50 or the second joint 60 When the material is applied, it can also function as a Cu layer provided so as not to generate unnecessary reaction products at the interface with the joint.

  The thickness of the conductive layers 34 and 36 provided on the surface of AlN is preferably 0.01 mm to 1 mm, and more preferably 0.05 mm to 0.5 mm. If the thickness of the conductive layer is less than 0.01 mm, the loss and heat generation due to the current in the lateral direction cannot be ignored, and if it exceeds 1 mm, the thermal expansion coefficient of the entire power semiconductor module is affected, and the heat This is not preferable because stress is generated.

  The method for attaching the conductive layers 34 and 36 to both surfaces of AlN is not particularly limited, and a known method such as brazing can be appropriately employed.

  Furthermore, as described above, when a solder material mainly composed of Bi is applied as the bonding material of the first bonding portion 50, the surface of the conductive layer (Cu layer) 34 includes at least one of Pd and Ni. In the case where a thin film 38 is formed and a solder material mainly composed of Bi is applied as a bonding material for the second bonding portion 60, the surface of the conductive layer (Cu layer) 36 includes at least one of Pd and Ni. A thin film 39 is formed.

When one of the first joint portion 50 and the second joint portion 60 is joined with a material other than the solder material containing Bi as a main component, another layer is provided on the surface side in contact with this material. Also good.
For example, in the case of joining with a zinc-based alloy, a Ni layer that can slow down the growth rate of unnecessary reaction products due to the thermal cycle may be provided on the surface side to be joined with the zinc-based alloy. Further, a thin Au layer may be provided on the surface of the Ni layer in order to prevent oxidation and secure touch. The Au layer preferably has a film thickness that dissolves in the solder bath during bonding and hardly remains in the final power semiconductor module.

<Heat sink>
The heat sink 40 can be applied without particular limitation as long as it has heat dissipation properties, but it has a sufficiently high thermal conductivity and an excellent function as a heat sink and is close to the thermal expansion coefficient of the semiconductor element. It is preferable to use it from the viewpoint of relaxing stress applied to the joint and preventing peeling.

  Specific examples of the suitable heat sink 40 include those formed of Mo, Cu—Mo alloy, Al—SiC, Cu, Al, etc. Among them, high thermal conductivity and heat close to power semiconductor elements. Mo is preferable because it has an expansion coefficient.

  When Mo is used for the heat sink, it is preferable to provide other metal layers on both sides of Mo from the viewpoint of enabling joining by soldering. Examples of such metal layers include Cu and Ni. Among these, Cu is preferable. In particular, it is preferable that the heat dissipation plate 40 is a laminate of a Cu layer 44 / Mo layer 42 / Cu layer 46 in which a Cu layer is provided on the surface of Mo from the viewpoint of adjusting the thermal conductivity and the thermal expansion coefficient. It is.

  Thus, when the heat sink 40 is a laminated body composed of the Cu layer 44 / Mo layer 42 / Cu layer 46, the thickness ratio of each layer is 1/5/1 to 1/12/1. It is preferable that it is 1/7/1 to 1/9/1. If the Mo layer is thinner than 1/5/1, it is not preferable because it has a thermal expansion coefficient far from that of the power semiconductor element. If the Mo layer is thicker than 1/12/1, the heat dissipation function as a heat sink is not sufficiently exhibited, which is not preferable.

  As a specific layer thickness, the Cu layers 44 and 46 are preferably 0.05 mm to 1 mm, and more preferably 0.2 mm to 0.5 mm. The thickness of the Mo layer 42 is preferably 1 mm to 7 mm, and more preferably 2 mm to 4 mm.

  In order that the laminated body constituted by the Cu layer 44 / Mo layer 42 / Cu layer 46 sufficiently exhibits the heat dissipation function, the total thickness is preferably 1 mm to 8 mm, more preferably 2 mm to 5 mm. preferable.

  As described above, the solder material containing Bi as a main component does not generate unnecessary products due to the thermal cycle at the interface with the Cu layer, so that the Cu layer 44 / Mo layer 42 / Cu is used as a heat sink. A power semiconductor module having a laminate composed of the layers 46 has high resistance to temperature changes.

  When a solder material mainly composed of Bi is applied as the bonding material for the second bonding portion 60, a thin film 48 containing at least one of Pd and Ni is formed on the surface of the Cu layer 44.

Here, in the power semiconductor module 10 of FIG. 1, when a solder material mainly composed of Bi is applied to the first joint portion 50 and the second joint portion 60, the surface in contact with the first joint portion 50 is Pd. Although the thin films 24 and 38 including at least one of Ni and Ni are illustrated to include the thin films 39 and 48 including at least one of Pd and Ni on the surface in contact with the first bonding portion 60, In the case where a solder material mainly composed of Bi is not applied to any one of the joint portions 60, a thin film containing at least one of Pd and Ni may not be formed on the joint surface.
Moreover, when joining the 1st junction part 50 or the 2nd junction part 60 with materials other than the solder material which has Bi as a main component, you may form the thin film suitable for the solder material.

<Power semiconductor module manufacturing method>
If the power semiconductor module concerning this invention has the said structure, it will not restrict | limit in particular about a manufacturing method, A well-known method can be applied suitably.
The manufacturing procedure is as follows: (1) First, the power semiconductor element 20 and the insulating part 30 are joined by the first joining part 50, and then the insulating part 30 provided with the power semiconductor element 20 and the radiator plate 40 are joined to the second part. (2) First, the insulating portion 30 and the heat radiating plate 40 are bonded together by the second bonding portion 60, and then the power semiconductor element 20 and the heat radiating plate 40 are insulated. The part 30 may be joined by the first joining part 50.

  Specifically, for example, as a method of joining the power semiconductor element 20 and the insulating part 30 by applying a solder material mainly composed of Bi to the first joint part 50, the power semiconductor element 20 / Bi is mainly used. In a state where the solder material (first joint portion) 50 / insulating portion 30 as components are laminated in this order, the solder material is joined in an inert gas or reducing gas atmosphere using a reflow method or the like. At this time, a thin film of Pd or Ni is provided on the surfaces of the power semiconductor element 20 and the insulating part 30 on the surface side in contact with the first bonding part 50, and a Cu layer is further provided on the inside thereof.

  The bonding temperature is preferably 30 to 60 ° C. higher than the melting point of the solder material containing Bi as a main component. Specifically, a bonding temperature of 270 ° C. to 600 ° C. is preferable from the viewpoint of surely bonding and preventing destruction of the semiconductor element, and more preferably a bonding temperature of 300 ° C. to 450 ° C. .

It is desirable that Pd and Ni are taken into the solder bath by heating the bonding. In this case, no thin film of Pd or Ni remains after the bonding.
The thickness of the layer of the first joint portion 50 after joining is preferably 5 to 500 μm and more preferably 10 to 200 μm from the viewpoint of thermal conduction and thermal stress.
In addition, since an oxide film is produced when the solder material containing Bi as a main component is cut out from an ingot-shaped ingot, it is preferable to remove the oxide film using polishing and acid cleaning.

Here, the state of Bi spreading out will be described.
As shown in FIG. 2A, when a solder material mainly composed of Bi is applied to the first joint portion 50 to join the power semiconductor element 20 and the insulating portion 30, in the present invention, Bi is wetted. Since the property is improved, as shown in FIG. 2B, the solder material is uniformly spread by the heating of bonding. At this time, since the bonding surface of the insulating substrate is usually larger than the bonding surface of the power semiconductor element, the solder material has a flared shape called a fillet. Even if it is such a joining shape, there is no problem as long as it is uniformly joined, but the following method can be exemplified as a method for suppressing the spread of the fillet.

For example, as shown in FIGS. 3A and 3B, there is a method of making the area of the Pd or Ni thin film 38 provided on the insulating substrate smaller than the bonding surface of the insulating substrate. In this method, a thin film of Pd or Ni can be formed only in the mask opening by attaching a masking sheet or the like on the insulating substrate and plating, or by attaching and sputtering a mask member having an opening. The area where the solder material spreads out can be controlled by a simple method. Thus, in the present invention, since the interface state that most affects wettability is directly changed, it is also easy to control the range in which the solder material spreads.
On the other hand, in the conventional method, in order to improve the wettability of the solder material itself, by adding another substance to the solder material, not only the interface that directly affects the wettability but also the entire solder material is modified. Therefore, it is difficult to control the range in which the solder material spreads out compared to the present invention.

  However, even in the conventional method, as shown in FIGS. 4A and 4B, the wetting and spreading of the solder material can be controlled by patterning the resist 70 or the like in a portion that suppresses the spreading of the solder material. can do. Unnecessary resist can be removed after bonding, and in the case of a resist having high heat resistance, it may be left as it is. This method can also be applied to the method for manufacturing a joined body of the present invention.

Although the joining method of the 1st junction part 50 was demonstrated in detail above, it can join also about the 2nd junction part 60 with the same method.
Specifically, in the bonding by the second bonding portion 60, in a state where the insulating portion 30 bonded to the power semiconductor element 20 by the first bonding portion 50 / the solder material of the second bonding portion 60 / the heat radiation plate 40 are stacked in this order. Similar to the joining by the first joining portion 50, the joining is performed using the reflow method or the like in an inert gas or reducing gas atmosphere. The bonding temperature is preferably 30 to 60 ° C. higher than the melting point of the second bonding portion 60 material.

Here, when a solder material mainly composed of Bi is applied to the second joint portion 60, Pd or Ni is formed on the surfaces of the insulating portion 30 and the heat radiating plate 40 on the surface side in contact with the second joint portion 60. Thin films 39 and 48 are respectively provided, and Cu layers 36 and 44 are provided on the outer sides thereof.
The thickness of the second bonding portion 60 is preferably 5 to 400 μm and more preferably 10 to 300 μm from the viewpoint of thermal conduction and thermal stress.

When joining two places of the 1st junction part 50 and the 2nd junction part 60 with solder, the 1st junction part 50 may be joined first, and the 2nd junction part 60 may be joined next, and the 2nd junction part The first joint 50 may be joined after joining 60 first, but in any case, if the temperature of the second soldering is higher than the melting point of the solder material used for the first time, 2 When soldering for the first time, the first soldered portion melts, causing problems such as misalignment or tilting.
In order to avoid this problem, the solder material is generally selected so that the melting point of the solder material used for the first time is higher than the melting point of the solder material used for the second time. Preferably, the melting point of the solder material used for the second bonding is desirably 50 ° C. lower than the melting point of the solder material used for the first bonding.

That is, when a solder material containing Bi as the main component is applied to the first bonding, the melting temperature of the solder material containing Bi as the main component is around 270 ° C., so the solder material used for the second bonding is Bi. It is preferable that the soldering material containing as a main component has a temperature at which the solder material does not melt and a melting temperature of about 220 ° C. or less. However, considering the heat generation from the power semiconductor, it is desirable that the melting temperature of the solder material used for the second bonding is 200 ° C. or higher.
On the other hand, when a solder material mainly composed of Bi is applied to the second bonding, it is preferable that the solder material used for the first bonding has a melting temperature of about 320 ° C. or higher.

<Other joints>
In the above, the power semiconductor module has been described as an example of the joined body of the present invention, but the member to be joined is not limited to each component of the power semiconductor module, solder mounting performed using a reflow furnace, When welding using a flow furnace, it is possible to apply various parts such as solder mounting that uses a thin film of Ni or Pd on the surface of the Cu film to be joined.

In the case of a power semiconductor module, since it is exposed to a severe cooling / heating cycle, the Pd layer or Ni layer provided for improving the wettability is taken into consideration that an unnecessary reaction product is generated by this cooling / heating cycle. However, in the case of a joined body that is not exposed to such a thermal cycle, an unnecessary reaction product may not be generated, so that the Pd layer or the Ni layer may not be formed after joining. It may not be lost.
That is, even in a joined body other than the power semiconductor module, it is desirable that the Pd layer or the Ni layer disappear after joining, but the Pd layer or the Ni layer does not necessarily disappear after joining.

  Moreover, even if it is a joined body other than a power semiconductor module, the joining part joined by the solder material which has Bi as a main component may be only one place, and may be two or more places.

  The following examples illustrate the invention. Hereinafter, in the embodiments, a part of the power semiconductor module, specifically, an example of a manufacturing method of a joined body in which the power semiconductor element and the insulating portion are joined will be described, and the present invention is limited to these embodiments. is not.

[Example 1]
FIG. 5A shows the structure of each member for producing the joined body of Example 1. FIG.

<Preparation of power semiconductor element>
A power semiconductor element 20 (area of about 1 cm ² ) using GaN was prepared, and a Cu layer 22 was formed on the outermost surface by sputtering. A 50 nm thick Pd layer 80 was formed on the surface of the Cu layer 22 by sputtering.

<Preparation of insulation part>
On the other hand, Cu layers 34 and 36 were attached to both surfaces of AlN as the insulating substrate 32 by brazing to produce a laminate of Cu layer 34 / AlN layer 32 / Cu layer 36. Further, a Pd layer 81 was formed on the surface of the Cu layer 34 on the power semiconductor element side of this laminate by plating to produce an insulating portion 30 (area of about 3 cm ² ). The film thickness of the Pd layer 81 was 50 nm. During plating, the non-plated surface was protected with a masking sheet or the like.

<Preparation of Bi-CuAlMn>
First, a CuAlMn alloy was prepared.
Cu, Al, and Mn adjusted to a predetermined weight% were melted in a Ar atmosphere using a high-frequency melting furnace to obtain a CuAlMn ingot as a precursor. The obtained ingot was pulverized using an atomizing method.
The finely divided CuAlMn was plated with Ni on the powder surface using a dropping method.

  Next, CuAlMn powder with Ni plating on the surface and Bi were vacuum-sealed in a transparent quartz tube, and held at a temperature of 400 ° C., which is higher than the melting point of Bi, for 5 minutes. Thereby, Bi became a molten state and CuAlMn powder was disperse | distributed uniformly. Bi-CuAlMn which is a solder material was obtained by cooling and solidifying the dispersed sample.

  An ingot Bi-CuAlMn was cut into a size of about 4 mm square by using an electric discharge machining method to obtain a tablet-like Bi-CuAlMn52. The oxide film covering the surface of the cut Bi-CuAlMn layer was removed using polishing and acid cleaning.

<Join the first joint>
The prepared Pd layer 80 of the power semiconductor element 20 and the Pd layer 81 of the insulating part 30 are arranged so as to face each other, and a tablet-like Bi—CuAlMn 52 is sandwiched therebetween, and 5% H ₂ / N ₂ Using a reflow method in a reducing gas atmosphere, bonding was performed at a bonding temperature of 400 ° C. to obtain a bonded body 1 of the present invention.

[Example 2]
FIG. 5B shows the configuration of each member for producing the joined body of Example 2.

<Preparation of power semiconductor element>
In the preparation of the power semiconductor element of Example 1, the 50 nm-thickness Pd layer 80 was formed on the surface of the Cu layer 22 by sputtering, except that a 50 nm-thickness Ni layer 82 was formed by electron beam evaporation. Thus, a power semiconductor element was prepared.

<Preparation of insulation part>
In the preparation of the insulating portion of Example 1, the Pd layer 81 having a thickness of 50 nm was formed on the surface of the Cu layer 34 by plating, and the same procedure was performed except that the Ni layer 83 having a thickness of 50 nm was formed by plating. Prepared the department.

<Join the first joint>
The prepared power semiconductor element and the insulating part were joined by the same method as in Example 1 to produce a joined body-2 of the present invention.

[Comparative Example 1]
FIG. 6A shows the structure of each member for producing the joined body of Comparative Example 1.

<Preparation of power semiconductor element>
In the preparation of the power semiconductor element of Example 1, a 50 nm thick Pd layer 80 was formed on the surface of the Cu layer 22 by sputtering, except that a 50 nm thick Au layer 84 was formed by sputtering. A power semiconductor element was prepared.

<Preparation of insulation part>
In the preparation of the insulating portion of Example 1, the Pd layer 81 having a film thickness of 50 nm was formed on the surface of the Cu layer 34 by plating, and the insulation was similarly performed except that the Au layer 85 having a film thickness of 50 nm was formed by plating. Prepared the department.

<Join the first joint>
The prepared power semiconductor element and the insulating part were joined by the same method as in Example 1 to produce a comparative joined body-1.

[Comparative Example 2]
FIG. 6B shows the structure of each member for producing the joined body of Comparative Example 2.

<Preparation of power semiconductor element>
In the preparation of the power semiconductor device of Example 1, a 50 nm-thickness Pd layer was formed on the surface of the Cu layer 22 by sputtering, but nothing was performed on the surface of the Cu layer 22 without forming anything. A power semiconductor element was prepared in the same manner as in Example 1.

<Preparation of insulation part>
In the preparation of the insulating part of Example 1, the Pd layer 81 having a film thickness of 50 nm was formed on the surface of the Cu layer 34 by plating, but nothing was formed on the surface of the Cu layer 34. In the same manner as in 1, an insulating part was prepared.

<Join the first joint>
The prepared power semiconductor element and the insulating part were joined by the same method as in Example 1 to produce a comparative joined body-2.

[Example 3]
<Preparation of Bi containing Cu>
1% by mass of Cu with respect to Bi was melted in a high-frequency melting furnace in an Ar atmosphere to prepare a Bi—Cu alloy ingot as a precursor. The obtained ingot was hot-rolled at 250 ° C. to obtain a plate material and cut out as a solder piece. The oxide film covering the surface of the cut Bi-Cu layer was removed using polishing and acid cleaning.

<Preparation of joined body>
A joined body-3 of the present invention was produced in the same manner as in Example 1 except that Bi-CuAlMn52 was used as the solder material and was changed to Bi-Cu prepared as described above.
Similarly, in Example 2, a joined body-4 of the present invention was produced in the same manner except that Bi-CuAlMn was used as the solder material and changed to Bi-Cu.

[Comparative Example 3]
A comparative joined body-3 was produced in the same manner as in Comparative Example 1, except that Bi-CuAlMn was used as the solder material and the Bi-Cu prepared in Example 3 was changed.

  The composition of the manufactured joined body is summarized in Table 1 below.

<Evaluation of wet spread>
The obtained bonded bodies -1 to 4 of the present invention and comparative bonded bodies -1 to 3 were cut and polished, and the cross section was observed with an electron microscope.

As a result, regarding the joined bodies 1 and 3 of the present invention in which the Pd layer was formed on the surface of the Cu layer and the joined bodies 2 and 4 in which the Ni layer was formed, the size of the solder material before melting was about 4 mm square. Regardless, it spreads over 10 mm square and was densely bonded.
Furthermore, in the joined bodies -1 to 4 of the present invention, Pd or Ni does not remain at the interface between the Cu layer and the solder material containing Bi as a main component, and it is presumed that it was taken into the solder bath. A state like this was observed.
Note that the results were almost the same when Bi—CuAlMn was used as the solder material and when Bi—Cu was used.

  On the other hand, as for the comparative bonded bodies 1 and 3 in which the Au layer is formed on the surface of the Cu layer and the comparative bonded body 2 in which nothing is formed on the surface of the Cu layer, a solder material containing Bi as a main component Was melted and joined, but only a few mm square part near the center of the sample was joined, and the peripheral part was not joined at all.

It is a figure which shows the structure of the power semiconductor module 10 which is an example of the conjugate | zygote of this invention. It is a figure explaining the manufacturing method of the power semiconductor module which is an example of the conjugate | zygote of this invention. It is a figure which shows an example of the control method of wetting spread about the solder material which has Bi as a main component, (A) is a figure explaining the state before joining, (B) is a figure explaining the state after joining It is. It is a figure which shows another example of the control method of wetting spread about the solder material which has Bi as a main component, (A) is a figure explaining the state before joining, (B) explains the state after joining. It is a figure to do. FIG. 5A shows members constituting the joined body of Example 1, and FIG. 5B shows members constituting the joined body of Example 2. FIG. 6A shows members constituting the joined body of Comparative Example 1, and FIG. 6B shows members constituting the joined body of Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Power semiconductor module 20 Power semiconductor element 22 Cu layer 24 Pd layer or Ni layer 30 Insulating part 32 Insulating substrate 34, 36 Conductive layer 38 Pd layer or Ni layer 39 Pd layer or Ni layer 40 Heat sink 42 Mo layers 44, 46 Cu Layer 50 First junction 52 Bi-CuAlMn
60 Second joint 80, 81 Pd layer 82, 83 Ni layer 85 Au layer

Claims (10)

A Cu layer is provided on each bonded surface of the two parts,
After a thin film containing at least one of Pd and Ni is formed on the surface of the Cu layer, the between the two parts, Ri Na joined by the solder material containing 80 wt% to 100 wt% of Bi, the thin film containing at least one of Pd and Ni, the conjugate in the solder material is in contact with the portion containing 80 wt% to 100 wt% of Bi that disappeared after bonding. 2. The joined body according to claim 1, wherein the solder material containing 80 mass% to 100 mass% of Bi is at least one selected from the following (1) to (3).
(1) Bi alone
(2) A material containing at least one selected from Cu, Ni, Ag, Sn, In, Zn, Sb, Ge and Ga in Bi,
(3) A material containing at least one selected from CuAlMn alloy particles, Ni or Au plated CuAlMn alloy particles, CuNiAl alloy particles, and CuZnAl alloy particles in Bi. The solder material containing 80% by mass to 100% by mass of Bi is Bi alone, a material containing Cu in Bi, a material containing Ni in Bi, or a material containing CuAlMn alloy particles in Bi The joined body according to claim 2 . The joined body according to any one of claims 1 to 3 , wherein a thickness of the thin film before joining is 3 nm or more and 1000 nm or less. The joined body according to any one of claims 1 to 3 , wherein the thickness of the thin film before joining is 10 nm or more and 200 nm or less. The joining according to any one of claims 1 to 5 , wherein the two parts are a combination of at least one of a power semiconductor element and an insulating substrate, and an insulating substrate and a heat sink. body. The joined body according to claim 6 , wherein the power semiconductor element is formed using GaN or SiC. The joined body according to claim 6 or 7 , wherein the insulating substrate is an AlN layer, and has conductive layers formed of Cu on both surfaces of the AlN layer. Claim 6, wherein the two parts comprises a combination of the heat sink and the insulating substrate, the heat radiating plate, characterized in that it is a laminate of Cu layer / Mo layer / Cu layer having a Cu layer on both surfaces of the Mo layer The joined body according to any one of claims 8 to 9 . 10. The joined body according to claim 9 , wherein a ratio of a thickness of Cu layer / Mo layer / Cu layer in the heat radiating plate is 1/5/1 to 1/12/1.

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