Bonding substrate and method for manufacturing bonding substrate

Abstract

The present invention provides a bonding substrate that improves the bonding strength between a silicon nitride ceramic substrate and a bonding layer, has high cold and heat durability but does not produce migration. The bonding substrate comprises a silicon nitride ceramic substrate, a copper plate, a bonding layer and an entry area. The copper plate and the bonding layer are patterned into a given shape and arranged on the main surface of the silicon nitride ceramic substrate. The bonding layer bonds the copper plate to the main surface of the silicon nitride ceramic substrate. The entry area is composed of one or more entry portions that are continuous from the main surface of the substrate and enter the interior of the silicon nitride ceramic substrate to a depth of more than 3μm and less than 20μm, and contains silver, and every 1mm of the main surface of the substrate 2 There are at least 1 and no more than 30 entry areas.

Description

Technical Field

[0001] The present invention relates to a bonding substrate and a method for manufacturing the bonding substrate. Background Art

[0002] Silicon nitride ceramics have high thermal conductivity and high insulation properties. Therefore, a bonded substrate consisting of a copper plate bonded to a silicon nitride ceramic substrate via a bonding layer is suitable for use as an insulating and heat-dissipating substrate for mounting power semiconductor devices.

[0003] This bonded substrate is often manufactured by producing an intermediate product having a brazing material layer between a copper plate and a silicon nitride ceramic substrate, and heat-treating the produced intermediate product to form a bonding layer between the copper plate and the silicon nitride ceramic plate.

[0004] The brazing material layer often contains titanium hydride powder and powder containing silver and copper. The joining layer often contains titanium nitride as a main component, which is a reaction product of titanium derived from the titanium hydride powder and nitrogen derived from the silicon nitride ceramic substrate.

[0005] For example, in the technology described in Patent Document 1, a copper metal plate is joined to a silicon nitride substrate by brazing (paragraph 0016). As the brazing filler metal, an Ag-Cu alloy containing an active metal such as Ti, Zr, or Hf is used (paragraph 0016). In the technology described in Patent Document 1, TiN particles are sufficiently precipitated at the brazing filler metal layer / silicon nitride interface to achieve strong bonding strength (paragraph 0018).

[0006] Furthermore, Patent Document 2 discloses a technique for addressing the problem that, when a ceramic substrate having few white spots (voids generated at the grain boundaries) is bonded to a metal plate, the amount of metal components invading the white spots is small, resulting in a lack of anchoring effect and consequently a lack of bonding strength (paragraph 0007). The technique discloses a technique for reducing the number of white spots to 1 / mm per 1 mm of the main surface. 2 The number of the plurality of bonding elements is 50 to 200, thereby achieving both bonding strength and high insulation strength (paragraph 0022).

[0007] However, in this case, there is a problem in that ion migration is likely to occur in the bonding substrate when a voltage is applied to the patterned metal plate.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-201076

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2015-164184 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] Conventional technologies may not be able to sufficiently increase the adhesion strength between the silicon nitride ceramic substrate and the bonding layer. As a result, a bonded substrate having high thermal durability may not be obtained.

[0014] The present invention has been made in view of this problem. The problem to be solved by the present invention is to improve the adhesion strength between the silicon nitride ceramic substrate and the bonding layer and to obtain a bonding substrate having high thermal durability.

[0015] Means for solving problems

[0016] The present invention is directed to bonding substrates.

[0017] The bonding substrate comprises a silicon nitride ceramic substrate, a copper plate, a bonding layer, and an entry region. The copper plate and the bonding layer are patterned into a given shape and arranged on the main surface of the silicon nitride ceramic substrate. The bonding layer bonds the copper plate to the main surface of the silicon nitride ceramic substrate. The entry region is composed of one or more entry portions that extend continuously from the main surface of the silicon nitride ceramic substrate and penetrate into the interior of the silicon nitride ceramic substrate to a depth of 3 μm or more and 20 μm or less. 2 There are more than 1 and less than 30 entry areas.

[0018] The present invention is also directed to a method for manufacturing a bonded substrate.

[0019] In the manufacturing method of the bonding substrate, a silicon nitride ceramic substrate is prepared. In addition, a brazing material layer is formed on the main surface of the silicon nitride ceramic substrate. In addition, a copper plate is arranged on the brazing material layer. Thus, an intermediate product having a silicon nitride ceramic substrate, a brazing material layer and a copper plate is obtained. In addition, the intermediate product is heat-treated to generate a bonding layer and a plurality of entry areas, wherein the bonding layer bonds the copper plate to the main surface of the silicon nitride ceramic substrate, and the plurality of entry areas have one or more entry portions that are continuous from the bonding layer and enter the interior of the silicon nitride ceramic substrate to a depth of more than 3 μm and less than 20 μm from the main surface. The entry area contains silver and is per 1 mm of the main surface of the silicon nitride ceramic substrate. 2 The copper plate and the bonding layer after the heat treatment are patterned into a predetermined shape.

[0020] Effects of the Invention

[0021] According to the present invention, the delamination of the bonding layer from the silicon nitride ceramic substrate is hindered by the silver-containing access area. Consequently, the bond strength between the silicon nitride ceramic substrate and the bonding layer is improved. Furthermore, the reduction in insulation resistance caused by silver migration between patterns is suppressed. This results in a bonding substrate with high thermal durability and guaranteed insulation resistance between patterns. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic cross-sectional view of the bonding substrate 1 .

[0023] Figure 2 This is a diagram for explaining a bonding state between the silicon nitride ceramic substrate 11 and the bonding layer 13 in the bonding substrate 1 .

[0024] Figure 3 This is a schematic cross-sectional view showing the inlet portion 14 x and its vicinity inside the silicon nitride ceramic substrate 11 in more detail.

[0025] Figure 4 1 is a flowchart illustrating a manufacturing flow of the bonding substrate 1 .

[0026] Figure 5 It is a cross-sectional view schematically showing an intermediate product obtained in the process of manufacturing the bonding substrate 1 .

[0027] Figure 6 It is a cross-sectional view schematically showing an intermediate product obtained in the process of manufacturing the bonding substrate 1 .

[0028] Figure 7 It is a cross-sectional view schematically showing an intermediate product obtained in the process of manufacturing the bonding substrate 1 .

[0029] Figure 8 This is a diagram showing a second example of a temperature profile and a surface pressure profile when hot pressing is performed in the process of manufacturing the bonded substrate 1 .

[0030] Figure 9 This is an electron microscope (SEM) image of a cross section of the bonded substrate 1 .

[0031] Figure 10 These are an SEM image and an element distribution image of the cross section of the bonded substrate 1 .

[0032] Figure 11 It is a graph showing the time change of the insulation resistance during the migration test on some bonded substrates 1 . DETAILED DESCRIPTION

[0033] 1 Bonding substrate

[0034] Figure 1 It is a schematic cross-sectional view of the bonding substrate 1 according to the present embodiment.

[0035] Figure 1 The bonding substrate 1 shown includes a silicon nitride ceramic substrate 11, a copper plate 12, and a bonding layer 13. The bonding substrate 1 may include elements other than these elements.

[0036] The silicon nitride ceramic substrate 11 is a sintered body of many columnar or plate-shaped silicon nitride crystal grains. The copper plate 12 is bonded to the silicon nitride ceramic substrate 11 via a bonding layer 13 .

[0037] The bonding layer 13 is a layer generated by a brazing material layer used to bond the copper plate 12 to the silicon nitride ceramic substrate 11. The bonding layer 13 is configured to contain an active metal contained in the brazing material layer. Here, the so-called active metal is at least one metal selected from the group consisting of titanium and zirconium. However, in addition to containing at least silver as a metal other than the active metal, the bonding layer 13 may also contain at least one metal selected from the group consisting of copper, indium and tin. In addition, the bonding layer 13 may also contain nitrogen and / or silicon supplied from the silicon nitride ceramic substrate 11 during bonding. In this case, the supplied nitrogen and / or silicon may also form a compound with the active metal. In addition, the bonding layer 13 may also contain copper supplied from the copper plate 12 during bonding.

[0038] The copper plate 12 and the bonding layer 13 are arranged on at least one of the two main surfaces 11s (11s1, 11s2) of the silicon nitride ceramic substrate 11. Figure 1 , the copper plate 12 and the bonding layer 13 are arranged on both main surfaces 11 s. The bonding layer 13 bonds the copper plate 12 to the main surface 11 s of the silicon nitride ceramic substrate 11 .

[0039] The copper plate 12 is patterned into a given shape corresponding to a desired wiring pattern. Hereinafter, the patterned portion of the copper plate 12 constituting a portion of the wiring pattern is also referred to as a pattern portion. Figure 1 , the case where the first pattern portion 12a and the second pattern portion 12b are arranged at intervals from each other on one main surface 11s1, and the third pattern portion 12c and the fourth pattern portion 12d are arranged at intervals from each other on the other main surface 11s2 is exemplified.

[0040] In addition, the bonding layer 13 is also patterned according to the shape of the copper plate 12. Hereinafter, the patterned portion of the bonding layer 13 is also referred to as a pattern bonding portion or simply a bonding portion. Figure 1 In the case shown, the first pattern portion 12a and the second pattern portion 12b of the copper plate 12 are respectively bonded to the main surface 11s1 through the first bonding portion 13a and the second bonding portion 13b, and the third pattern portion 12c and the fourth pattern portion 12d of the copper plate 12 are respectively bonded to the main surface 11s2 through the third bonding portion 13c and the fourth bonding portion 13d.

[0041] Hereinafter, a laminated portion of the pattern portion of the copper plate 12 and a joint portion of the bonding layer 13 bonding the pattern portion to the silicon nitride ceramic substrate 11 will also be referred to as a pattern laminated portion.

[0042] Since the copper plate 12 and the bonding layer 13 have the above structure, Figure 1 In the bonding substrate 1 shown, a portion of the principal surface 11 s 1 serves as an exposed portion 11 e exposed to the outside.

[0043] More specifically, the exposed portion 11e includes an inter-pattern exposed portion 11e1 located between spaced-apart pattern stacked portions on the same main surface 11s1 and a non-inter-pattern exposed portion 11e2 located outside the inter-pattern exposed portion 11e1.

[0044] The pattern stacking parts are usually provided with a gap of about 0.5 mm to 1.5 mm between each other.

[0045] The bonding substrate 1 can be used arbitrarily, and can be used as an insulating heat dissipation substrate for mounting a power semiconductor element, for example.

[0046] 2Joint structure

[0047] Figure 2 This is a diagram for explaining a bonding state between the silicon nitride ceramic substrate 11 and the bonding layer 13 in the bonding substrate 1 .

[0048] like Figure 2 As shown, the bonding substrate 1 includes a plurality of entry regions 14 ( 14 a , 14 b , 14 c , and 14 d ). Each entry region 14 has an entry portion 14 x extending inward from the main surface 11 s of the silicon nitride ceramic substrate 11 .

[0049] like Figure 2 As shown, each entry portion 14x is a linear portion extending from the main surface 11s of the silicon nitride ceramic substrate 11 toward the inside. Figure 2 In the figure, for ease of illustration, the entry portion 14x is illustrated as a line (typically a broken line or a curve) that exists only within the plane formed by the paper surface, but the actual entry portion 14x is formed into a linear shape while randomly bending, curving or branching in three dimensions, and enters the interior of the silicon nitride ceramic substrate 11.

[0050] Each entry area 14 is a single entry portion 14x or a collection (aggregation) of a plurality of entry portions 14x that are close to each other. Figure 2 In the illustrated example, entry region 14a is formed by a single entry portion 14x. Furthermore, entry region 14b is formed by two different entry portions 14x three-dimensionally intertwined. Furthermore, entry region 14c is formed by branches from a single entry portion 14x, with different entry portions 14x close to each other. Meanwhile, entry region 14d is formed by two entry portions 14x extending from exposed portion 11e, distinct from the other entry regions 14 (14a, 14b, 14c).

[0051] Furthermore, assuming that the entry portion 14x enters linearly from the starting point of the main surface 11s, the area occupied by the entry region 14 on the main surface is the same as the area occupied within the main surface. However, in the bonding substrate 1 according to this embodiment, since the entry portion 14x and the entry region 14 are provided in the above-described configuration, the area occupied by the entry region 14 within the silicon nitride ceramic substrate 11 on a surface parallel to the main surface 11s—in other words, the projected area obtained by virtually projecting the range of the entry region 14 within the silicon nitride ceramic substrate 11 onto the main surface 11s, except in cases where the entry region 14 is excessively present—tends to be larger than the area of the entry region 14 actually present on the main surface 11s serving as the starting point. This suggests that even when the entry region 14 is not excessive, the bonding strength between the silicon nitride ceramic substrate 11 and the copper plate 12 in the bonding substrate 1 can be appropriately maintained.

[0052] Figure 3 This is a schematic cross-sectional view showing in more detail the appearance (microstructure) of entry portion 14x and its vicinity within silicon nitride ceramic substrate 11. Silicon nitride ceramic substrate 11 is a sintered body of numerous silicon nitride particles (crystal grains) 21. Between silicon nitride particles 21, there exists a secondary phase 22 composed of oxides or glass, containing elements such as magnesium and yttrium derived from the sintering aid used in manufacturing silicon nitride ceramic substrate 11. Some of the spaces between silicon nitride particles 21 form voids 23.

[0053] Figure 3 The shown intrusion portion 14x enters into the interior of the silicon nitride ceramic substrate 11 from the main surface 11s of the silicon nitride ceramic substrate 11 forming an interface with the bonding layer 13. The intrusion portion 14x enters into a portion that was originally the void 23.

[0054] In addition, although Figure 3 The illustration shows a continuous entry portion 14x, but as mentioned above, the actual entry portion 14x is randomly bent, curved, or branched in three dimensions, and therefore may appear discontinuous in any cross-sectional image (e.g., a cross-sectional SEM image) along the thickness direction (perpendicular to the main surface 11s) of the silicon nitride ceramic substrate 11. Figure 3 In order to illustrate such an apparently discontinuous state, a state is shown in which one entry portion 14x is apparently divided into at least six parts 14x1 to 14x6 in a cross section along the paper surface.

[0055] Furthermore, the fact that a single entry portion 14x appears to be divided into multiple parts in any given cross-section also means that in a cross-sectional image of a portion where multiple entry portions 14x are close together, it is difficult to distinguish and identify each entry portion 14x. Therefore, in this embodiment, particularly in a cross-sectional image, a single entry portion 14x and a collection of multiple close entry portions 14x are not distinguished and are considered the entry region 14.

[0056] In more detail, Figure 3 The entry portion 14x shown is continuous from the lower end of the bonding layer 13 in contact with the main surface 11s. The entry portion 14x is generated by the brazing material layer for bonding the copper plate 12 to the silicon nitride ceramic substrate 11, similarly to the bonding layer 13. That is, Figure 3 The intrusion portion 14x shown is formed when a portion of the brazing material layer penetrates into the silicon nitride ceramic substrate 11 when forming the bonding layer 13. The intrusion portion 14x contains metal (mainly silver) other than the active metal in the metal contained in the brazing material layer.

[0057] In addition, some of the intrusions 14x start from the exposed portion 11e of the silicon nitride ceramic substrate 11 and are not continuous with the bonding layer 13. Figure 2 In this case, the entry portion 14x constituting the entry region 14d corresponds to this. However, this entry portion 14x is also originally continuous with the bonding layer 13. After the formation of the entry portion 14x, the bonding layer 13 is removed, and the exposed portion 11e becomes the starting point. Therefore, this entry portion 14x also contains metal other than the active metal in the metal contained in the brazing filler metal layer.

[0058] exist Figure 3 In the bonding substrate 1 shown, which includes a plurality of intrusion regions 14 including intrusion portions 14x extending continuously from the bonding layer 13, the presence of the intrusion portions 14x hinders the separation of the bonding layer 13 from the silicon nitride ceramic substrate 11. As a result, in the bonding substrate 1, the adhesion strength between the silicon nitride ceramic substrate 11 and the bonding layer 13 is improved. As a result, the bonding substrate 1 according to this embodiment can achieve high thermal durability.

[0059] Furthermore, in the bonded substrate 1, at least a portion of the voids 23 present in the silicon nitride ceramic substrate 11 before bonding is filled by the intrusions 14x. Specifically, the voids 23 in the silicon nitride ceramic substrate 11 after bonding are reduced compared to before bonding, thereby preventing the voids 23 from becoming the starting point of cracks or other damage. Consequently, the bonded substrate 1 has high flexural strength.

[0060] Each entry portion 14x preferably enters the silicon nitride ceramic substrate 11 to a depth of 3 μm to 30 μm from the main surface 11s, and more preferably enters the silicon nitride ceramic substrate 11 to a depth of 3 μm to 20 μm. In this case, a bonding substrate 1 with high thermal durability and high insulation can be achieved. When the entry depth of the entry portion 14x is shallower than the lower limit of these ranges, it is difficult to prevent the bonding layer 13 from peeling off from the silicon nitride ceramic substrate 11, and there is a tendency that it is difficult to ensure high thermal durability in the bonding substrate 1. In addition, when the entry depth of the entry portion 14x is deeper than the upper limit of these ranges, due to the concentration of the electric field on the entry portion 14x, there is a tendency that it is difficult to ensure high insulation in the bonding substrate 1.

[0061] Furthermore, the inlet region 14 is preferably formed every 1 mm of the main surface 11s. 2 The number of intrusion regions 14 is preferably 1 or more and 30 or less, more preferably 1 or more and 10 or less. If the number of intrusion regions 14 is less than the lower limit of this range, the effect of inhibiting the separation of the bonding layer 13 from the silicon nitride ceramic substrate 11 cannot be sufficiently achieved. As a result, it tends to be difficult to ensure high thermal durability in the bonding substrate 1.

[0062] On the other hand, when the number of the inlet regions 14 is greater than the upper limit of the range, between the pattern portions of the copper plates 12 provided in the adjacent pattern laminated portions (for example, between the pattern portions 12 and the pattern laminated portions 14), the inlet regions 14 are larger than the upper limit of the range. Figure 1 In the case where a voltage is applied between the first pattern portion 12a and the second pattern portion 12b, and between the third pattern portion 12c and the fourth pattern portion 12d), migration of the metal (typically silver) present in the entry region 14 occurs significantly, and the insulation resistance between the pattern stacking portions decreases, so it is not preferred.

[0063] 3. Method for manufacturing a bonded substrate

[0064] Figure 4 1 is a flowchart showing a production flow of the bonding substrate 1 . Figure 5 、 Figure 6 as well as Figure 7 It is a cross-sectional view schematically showing an intermediate product obtained in the process of manufacturing the bonding substrate 1 .

[0065] In the manufacture of the bonding substrate 1, the following steps are performed: Figure 4 Steps S101 to S105 are shown.

[0066] In step S101 , a silicon nitride ceramic substrate 11 is prepared. As described above, the prepared silicon nitride ceramic substrate 11 is a sintered body of many silicon nitride particles (crystal grains) 21 , has a primary surface 11 s , and has secondary phases 22 and voids 23 between the silicon nitride particles 21 .

[0067] In step S102, Figure 5 As shown, a brazing material layer 13 i is formed on the main surface 11 s of the silicon nitride ceramic substrate 11 .

[0068] When forming the solder layer 13i, a paste (solder paste) comprising an active metal solder, an adhesive and a solvent is modulated. The solder paste may also include a dispersant, a defoamer, etc. Then, the modulated solder paste is screen-printed on the main surface 11s of the silicon nitride ceramic substrate 11, and a screen-printed film of the solder paste is formed on the main surface 11s of the silicon nitride ceramic substrate 11. Then, the solvent contained in the formed screen-printed film is volatilized. Thus, the screen-printed film is changed into a solder layer 13i comprising an active metal solder and an adhesive. The solder layer 13i may also be formed by a method different from this method.

[0069] The active metal brazing filler metal includes a hydrogenation active metal powder and a metal powder other than the active metal. The hydrogenation active metal powder includes a hydride of at least one active metal selected from the group consisting of titanium and zirconium. The metal powder other than the active metal includes at least silver and may also include at least one metal selected from the group consisting of copper, indium, and tin. When the active metal brazing filler metal includes at least one metal selected from the group consisting of copper, indium, and tin in addition to silver, the melting point of the active metal brazing filler metal is lower than that of silver.

[0070] The active metal brazing filler metal preferably contains 40 wt % or more and 80 wt % or less of silver.

[0071] The active metal brazing filler metal is preferably composed of a powder having an average particle size of 0.1 μm or more and 10 μm or less. The average particle size can be determined by measuring the particle size distribution using a commercially available laser diffraction particle size distribution analyzer and calculating the D50 (median particle size) based on the measured particle size distribution. When the active metal brazing filler metal is composed of a powder having such a small average particle size, the brazing filler metal layer 13i can be formed thinner.

[0072] The brazing material layer 13i preferably has a thickness of 0.1 μm or more and 10 μm or less, and more preferably has a thickness of 0.1 μm or more and 5 μm or less.

[0073] In step S103, Figure 6 As shown in FIG. 1 , a copper plate 12i is placed on the brazing material layer 13i thus formed. Thus, an intermediate product 1i including the silicon nitride ceramic substrate 11, the copper plate 12i, and the brazing material layer 13i is obtained.

[0074] In step S104, the obtained intermediate product 1i is heat-treated. Due to the heat treatment, a portion of the brazing material layer 13i moves into the gap 23 of the silicon nitride ceramic substrate 11. As a result, a plurality of entry portions 14x containing metals (mainly silver) other than the active metal contained in the brazing material layer 13i are formed. That is, the brazing material layer 13i changes to Figure 7 The illustrated bonding layer 13j includes an active metal, and a plurality of intrusions 14x that are continuous from the bonding layer 13j and include a metal other than the active metal.

[0075] By performing heat treatment, an intermediate product 1j is obtained, which includes a silicon nitride ceramic substrate 11, a copper plate 12j, and a bonding layer 13j. The bonding layer 13j bonds the copper plate 12j to the main surface 11s of the silicon nitride ceramic substrate 11. A plurality of intrusion regions 14 are formed on the silicon nitride ceramic substrate 11. Each intrusion region 14 has an intrusion portion 14x extending from the bonding layer 13j and extending into the voids 23 of the silicon nitride ceramic substrate 11.

[0076] The heat treatment is preferably performed by heating the intermediate product 1i according to a temperature profile having a maximum temperature of 800°C to 860°C. This forms a plurality of penetration portions 14x that penetrate into the silicon nitride ceramic substrate 11 to a depth of 3 μm to 20 μm from the main surface 11s.

[0077] However, when the maximum temperature is lower than 800°C, the penetration depth of the penetration portion 14x tends to be shallower than 3 μm. In this case, it is difficult to prevent the bonding layer 13 from peeling off from the silicon nitride ceramic substrate 11 in the final bonding substrate 1. As a result, it tends to be difficult to ensure high thermal durability in the bonding substrate 1.

[0078] Furthermore, when the maximum temperature exceeds 860°C, the penetration depth of the penetration portion 14x tends to exceed 20 μm. In this case, partial discharge tends to occur starting from the penetration portion 14x, resulting in difficulty in ensuring high insulation properties in the bonding substrate 1.

[0079] As a heat treatment for the intermediate product 1i, hot pressing is preferably performed. Hot pressing of the intermediate product 1i is preferably performed as follows: while the intermediate product 1i is heated in a vacuum or in an inert gas according to a temperature curve having a maximum temperature TMAX of 800°C to 900°C, the silicon nitride ceramic substrate 11 is pressurized along its thickness direction according to a surface pressure curve having a maximum surface pressure PMAX of 5 MPa to 30 MPa (the copper plate 12i is pressurized). In this case, even when the brazing material layer 13i has a relatively thin thickness of 0.1 μm to 10 μm, the copper plate 12i can be bonded to the silicon nitride ceramic substrate 11 through the bonding layer 13j without forming voids in the bonding layer 13j.

[0080] Figure 8 It is a diagram showing an example of a temperature profile and a surface pressure profile when hot pressing is performed in the process of manufacturing the bonded substrate 1 .

[0081] In accordance with Figure 8 When hot pressing is performed according to the temperature and surface pressure profile shown, the temperature of the intermediate product 1i is first raised from room temperature to the binder removal temperature TB. Thereafter, the temperature of the intermediate product 1i is maintained at the binder removal temperature TB for a predetermined period of time. This completes the binder removal process in the brazing filler metal layer 13i. Next, the temperature of the intermediate product 1i is raised from the binder removal temperature TB to the maximum temperature TMAX. Thereafter, the temperature of the intermediate product 1i is maintained at the maximum temperature TMAX for a predetermined period of time. Finally, the temperature of the intermediate product 1i is lowered from the maximum temperature TMAX to room temperature.

[0082] At this time, until the temperature of the intermediate product 1i reaches the binder removal temperature TB and the binder removal is completed, the intermediate product 1i is subjected to only low-pressure pressurization for preventing movement with the copper plate 12i as the target, and no pressurization for bonding is performed.

[0083] The pressure applied to prevent movement is performed as follows: the copper plate 12i is pressed at a lower surface pressure (movement-preventing surface pressure) than the surface pressure applied during bonding, but sufficient to prevent movement of the intermediate product 1i. For example, a lower surface pressure of approximately 0.1 to 0.3 MPa is applied to the copper plate 12i. This movement-preventing surface pressure is lower than the surface pressure applied to the intermediate product 1i during bonding. Therefore, even if pressure is applied during the debonding process to prevent movement, it is possible to appropriately prevent debonding from being hindered, and it is also possible to prevent the formation of carbon residue in the bonding layer 13 of the resulting bonded substrate 1.

[0084] After binder removal is complete and the temperature of the intermediate product 1i rises from the binder removal temperature TB to the maximum temperature TMAX, during this process, pressure is applied to the copper plate 12i for bonding the intermediate product 1i, and the surface pressure applied to the copper plate 12i is increased to the maximum surface pressure PMAX. In other words, the application of pressure to the copper plate 12i for bonding begins after the temperature of the copper plate 12i rises, making it easier for the copper plate 12i to deform plastically. Thereafter, the surface pressure applied to the copper plate 12i is increased to the maximum surface pressure PMAX.

[0085] exist Figure 8 In the example shown, the copper plate 12i, which expands thermally with increasing temperature, is restrained by the strong pressure applied during bonding only after the adhesive is removed. Therefore, the restraint on the copper plate 12i is restraining, thereby preventing residual stress from remaining within the copper plate 12 after the bonding substrate 1 is manufactured. As a result, deformation or damage to the bonding substrate 1 caused by residual stress within the copper plate 12 can be prevented. For example, undulations and cracks can be prevented from occurring in the bonding substrate 1.

[0086] exist Figure 8 In the example shown, the surface pressure applied to the intermediate product 1i for bonding is increased in two stages from the movement-blocking surface pressure to the maximum surface pressure PMAX. More specifically, when the temperature of the intermediate product 1i begins to rise again after maintaining the adhesive removal temperature TB, the surface pressure applied to the intermediate product 1i (specifically, the copper plate 12i) is first increased from the movement-blocking surface pressure to the first surface pressure P1 and then maintained at the first surface pressure P1 for a set period of time.

[0087] When the maintenance of the first surface pressure P1 is completed, the surface pressure applied to the intermediate product 1i is increased from the first surface pressure P1 to a higher second surface pressure (maximum surface pressure) PMAX, and is maintained at the second surface pressure PMAX for a set time. This increase in surface pressure occurs while the temperature of the intermediate product 1i is increased from the debonding temperature TB to the maximum temperature TMAX. In other words, it is performed after the temperature of the copper plate 12i rises and the copper plate 12i becomes easily plastic. In addition, since the first surface pressure P1 applied previously is relatively weak, even if the first surface pressure P1 is applied before the copper plate 12i becomes easily plastically deformed, the cracking of the silicon nitride ceramic substrate 11 can be suppressed.

[0088] More specifically, the first surface pressure P1 is set to a value at which the copper plate 12i is flattened and contacts the previously existing brazing material layer 13i in a non-contact area after the intermediate product 1i is pressed for bonding, and is preferably set to 1.0 MPa or higher. The effect of this example is particularly evident when the active metal brazing material contains silver and no copper. This is because, in this case, when the intermediate product 1i is hot-pressed, copper diffuses from the copper plate 12i into the titanium particles contained in the brazing material layer 13i, thereby forming a titanium-copper compound in the brazing material layer 13i, thereby suppressing the formation of a silver-titanium compound that would otherwise hinder bonding.

[0089] Pressurization of the intermediate product 1i for joining is preferably started when the temperature of the intermediate product 1i is 500°C to 700°C. This is because the binder removal temperature TB is approximately 500°C and the temperature at which the titanium-copper compound begins to form is approximately 700°C.

[0090] Furthermore, the first surface pressure P1 is preferably 5 MPa or less. When the first surface pressure P1 exceeds 5 MPa, the copper plate 12i is strongly pressed against the silicon nitride ceramic substrate 11, which tends to easily crack the silicon nitride ceramic substrate 11. The second surface pressure PMAX is preferably 5 MPa or more and 30 MPa or less. When the second surface pressure PMAX is less than 5 MPa, the bonding properties of the copper plate 12i to the silicon nitride ceramic substrate 11 tend to decrease. When the second surface pressure PMAX exceeds 30 MPa, the copper plate 12i is strongly pressed against the silicon nitride ceramic substrate 11, which tends to easily crack the silicon nitride ceramic substrate 11.

[0091] During the heat treatment of the intermediate product 1i, all or part of the metal components, such as silver, contained in the brazing filler metal layer 13i may be diffused into the silicon nitride ceramic substrate 11 and / or the copper plate 12i. Furthermore, nitrogen and / or silicon contained in the silicon nitride ceramic substrate 11 may be diffused into the brazing filler metal layer 13i. Furthermore, copper contained in the copper plate 11i may be diffused into the brazing filler metal layer 13i.

[0092] In step S105, the copper plate 12j and the bonding layer 13j are patterned by etching or the like. As a result, the copper plate 12j is transformed into Figure 1 The copper plate 12 after the pattern is formed as shown. In addition, the bonding layer 13j is changed to Figure 1 The bonding layer 13 after patterning is shown.

[0093] 4. Influence of the maximum temperature of heat treatment

[0094] Seven types of bonding substrates 1 were manufactured according to the above-mentioned manufacturing method. Specifically, the bonding substrates 1 were manufactured under seven conditions (conditions 1 to 7) with different maximum temperatures in the temperature profile of hot pressing performed as the heat treatment.

[0095] Titanium was used as the active metal contained in the active metal brazing filler metal, and silver was used as the metal other than the active metal contained in the active metal brazing filler metal.

[0096] During the heat treatment of the intermediate product 1i, the aforementioned hot pressing was performed. However, the surface pressure curve was set to a maximum surface pressure of 20 MPa. While the intermediate product 1i (specifically, the copper plate 12i) was pressed in the thickness direction of the silicon nitride ceramic substrate 11 according to this surface pressure curve, the intermediate product 1i was heated according to each of the seven temperature profiles having the maximum temperature shown in Table 1.

[0097] Furthermore, a cross section of the manufactured bonded substrate 1 was observed with a scanning electron microscope (SEM) to obtain a SEM image. Based on the obtained SEM image, the average value of the penetration depth of the penetration region 14 from the main surface 11 s was determined.

[0098] The adhesion strength and insulation properties of the silicon nitride ceramic substrate 11 and the copper plate 12 in the manufactured bonding substrate 1 were evaluated. The adhesion strength was evaluated by performing a peel test on the copper plate 12 to measure the peel strength of the copper plate 12 in the bonding substrate 1. The insulation properties were evaluated by performing a withstand voltage test on the bonding substrate 1 and recording the breakdown voltage at which the bonding substrate 1 broke down. The voltage ramp rate during the withstand voltage test was set to 0.1 kV / s.

[0099] Table 1 lists the maximum temperature of the temperature profiles under conditions 1 to 7, the penetration depth into the region 14 , and the results of the peel test and the pressure test.

[0100] also, Figure 9 These are cross-sectional SEM images of the bonded substrate 1 produced under different conditions. Figure 9 (a)~ Figure 9 (d) is an SEM image of the bonded substrate 1 produced by sequentially applying conditions 2 to 5. Figure 9 (e) is Figure 9 (d) is an enlarged image of the image.

[0101] [Table 1]

[0102]

[0103] As shown in Table 1, for the bonded substrate 1 produced under condition 1 where the maximum temperature in the temperature profile is lower than 800° C., the average penetration depth of the penetration region 14 is 1 μm, the peel strength is 17 kN / m, and the voltage at which dielectric breakdown occurs is 10 kV.

[0104] In addition, for the bonding substrate 1 produced under conditions 2 to 6 in which the highest temperature in the temperature curve is above 800°C and below 860°C, the average penetration depth into the region 14 becomes 3μm to 20μm, the peel strength of the bonding substrate 1 becomes 25kN / m to 39kN / m, and the voltage at which insulation breakdown occurs in the bonding substrate 1 becomes 8.6kV-9.7kV.

[0105] That is, the dielectric breakdown voltage is slightly lower than that of the bonding substrate 1 produced under Condition 1, but the peel strength is significantly higher than that of the bonding substrate 1 produced under Condition 1.

[0106] in addition, Figure 9 (d) and Figure 9 The image of the entry portion 14x shown in (e) is a typical example of a case where the projected area when the existence range of the entry region 14 inside the silicon nitride ceramic substrate 11 is virtually projected onto the main surface 11s is larger than the area where the entry region 14 actually exists on the main surface 11s as the starting point.

[0107] In addition, for the bonding substrate 1 produced under condition 7 where the maximum temperature in the temperature curve is higher than 860°C, the average penetration depth into the region 14 is 25 μm, the peel strength of the bonding substrate 1 is 37 kN / m, and the voltage at which insulation breakdown occurs in the bonding substrate 1 is 7.2 kV.

[0108] That is, the peel strength is about the same as that of the bonding substrate 1 produced under Conditions 2 to 6, but the dielectric breakdown voltage is further reduced compared to the bonding substrate 1 produced under Condition 1.

[0109] These results show that by setting the maximum temperature in the temperature profile to 800°C or higher and 860°C or lower, a plurality of penetration regions 14 can be formed that penetrate into the silicon nitride ceramic substrate 11 to a depth of 3 μm or higher and 20 μm or lower. As a result, a bonded substrate 1 having a balanced high adhesion strength and high insulation properties can be obtained.

[0110] also, Figure 10 These are an SEM image of the bonded substrate 1 produced under application condition 5 and an element distribution image of the imaging field in the SEM image. Figure 10 (a) is Figure 9 (e) SEM image, Figure 10 (b)~ Figure 10(i) are element distribution images of magnesium (Mg), titanium (Ti), yttrium (Y), silver (Ag), boron (B), nitrogen (N), silicon (Si), and copper (Cu). From these element distribution images, it can be understood that the entry portion 14x is mainly composed of silver.

[0111] 5. Migration evaluation

[0112] To evaluate the relationship between the distribution of the intrusion regions 14 in the bonding substrate 1 and silver migration, six types of bonding substrates 1 were prepared, each with a different number of intrusion regions 14 per unit area. Migration tests were conducted between adjacent pattern stacks for each type. Peel tests and withstand voltage tests were also conducted in the same manner as in the case where the values shown in Table 1 were obtained.

[0113] The bonded substrate 1 is produced by preparing a plurality of silicon nitride ceramic substrates 11, each categorized into different levels based on the distribution of voids 23 (number per unit area). A copper plate 12i is bonded to each silicon nitride ceramic substrate using hot pressing as a heat treatment, and then patterning is performed by etching. By varying the temperature profile and surface pressure profile employed, the number of voids per unit area and the average penetration depth of the penetration region 14 are varied.

[0114] The obtained bonded substrates were classified and selected based on the distribution state (number per unit area) and (average value) of the penetration depths of the penetration regions 14 .

[0115] Specifically, the exposed portion 11e of the silicon nitride ceramic substrate 11 constituting the bonding substrate 1 has a thickness of 1 mm. 2 The number of entry areas existing in the (count value converted to an integer by rounding off) is classified into 6 levels: 0, 1, 2-3, 4-10, 11-30, and 31-50. At this time, only the bonding substrates 1 whose (average value of) entry depth satisfies the range of 5μm to 10μm are selected. In addition, for the sake of convenience in the following text, the maximum value of the number in each level is used as the representative value of the level, and each count value range is distinguished (called) by the representative value. In addition, in the actual bonding substrate 1, there may also be 100% penetration depth per 1mm. 2 There are bonding substrates with more than 50 entry regions in the present embodiment, but such bonding substrates 1 were not confirmed in the above classification. Therefore, the upper limit was set to 50 when setting the above level.

[0116] The migration test is carried out as follows: a bonding substrate 1 is arranged in a high temperature and high humidity atmosphere of 85°C and 85% humidity, and a DC voltage of 1.5 kV / mm is continuously applied for 1000 hours between the pattern portions of the copper plates 12 belonging to adjacent pattern stacking portions. At this time, the insulation resistance between the portions is continuously measured. When the measured value continuously decreases by more than one digit from the initial value during the measurement of the insulation resistance, it is judged that a significant decrease in the insulation resistance has occurred, which is problematic. In addition, for the bonding substrate 1 that has produced such a significant decrease in insulation resistance at the time point of applying the DC voltage for 500 to 1000 hours, the insulation resistance is re-measured after drying at 100°C.

[0117] Figure 11 Graph showing the time variation of insulation resistance during a migration test on a portion of the bonded substrate 1. Specifically, for each 1 mm of the intrusion area 14, 2 The graph shows representative values of the number of bonding substrates 1, 10, and 50, respectively, and 2, 2, and 1, respectively.

[0118] from Figure 11 It can be seen that for every 1 mm of the entry area 14 2 The representative values of the number of bonding substrates 1 are 1 and 10, respectively. The insulation resistance at the start of the test is almost maintained. On the other hand, for every 1 mm of the penetration area 14, 2 The representative number of the number of bonding substrates 1 is 50, and the insulation resistance drops significantly to about four digits during the test. The latter is considered to be a result of migration, which leads to a significant drop in insulation resistance.

[0119] Table 2 shows at a glance the values of the penetration area 14 per 1 mm for all the bonded substrates 1 classified. 2The number of counts (count value range and representative value) and the results of the migration evaluation are shown. In addition, in the migration evaluation, the bonding substrate 1 that did not show a significant decrease in insulation resistance that would be problematic even after a DC voltage of 1.5 kV / mm was continuously applied for 1000 hours was evaluated as "good" and marked with "○" (circle mark) in the "Migration Evaluation" column of Table 2. In addition, for the bonding substrate 1 in which the insulation resistance was significantly reduced at the time point when the DC voltage was continuously applied for 500 to 1000 hours, but the insulation resistance was reduced to within a single digit from the initial value after drying at 100°C, it was evaluated as "suitable" and marked with "△" (triangle mark) in the "Migration Evaluation" column of Table 2. On the other hand, bonding substrates 1 in which the insulation resistance significantly decreased before the continuous application time of the DC voltage reached 500 hours, or in which the insulation resistance significantly decreased after the continuous application time of 500 to 1000 hours, and in which the insulation resistance remeasured after drying at 100°C decreased by more than a single digit from the initial value were evaluated as "unsuitable" and marked with "×" (cross mark) in the "Migration Evaluation" column of Table 2.

[0120] [Table 2]

[0121]

[0122] As shown in Table 2, the migration evaluation of the bonding substrate 1 in which the number of substrates entering the region 14 was zero was good. However, the bonding strength between the silicon nitride ceramic substrate 11 and the bonding layer 13 evaluated in the peel test was insufficient in this bonding substrate 1 .

[0123] Furthermore, the migration evaluation was also good for the bonding substrate 1 having 1 or more and 10 or less regions 14. Furthermore, similarly to the bonding substrate 1 shown in Table 1, high adhesion strength and high insulation properties were achieved in a balanced manner.

[0124] In contrast, the bonding substrate 1 having 11 or more and 30 or less intrusion regions 14 achieved high adhesion strength, but had a slightly low migration evaluation and not very high insulation properties.

[0125] Furthermore, for the bonded substrate 1 having 31 or more and 50 or less intrusion regions 14 , although high adhesion strength was confirmed, migration with a significant change in insulation resistance was confirmed. Therefore, the migration evaluation was poor.

[0126] The above results are the same even when the penetration depth (average value) is made shallower (changed to about 3 μm) or deeper (changed to about 20 μm). 2The bonding substrate 1 is manufactured in a manner in which the representative value of the number is more than 1 and less than 30, preferably more than 1 and less than 10, and the penetration depth satisfies the range of more than 3 μm and less than 20 μm. It can achieve high adhesion strength and high insulation in a balanced manner, and will not produce a decrease in insulation resistance due to the migration of silver from the penetration area.

Claims

1. A bonding substrate, characterized in that: have: Silicon nitride ceramic substrate; a copper plate disposed on the main surface of the silicon nitride ceramic substrate and patterned into a predetermined shape; a bonding layer arranged on the main surface in a shape formed by the pattern of the copper plate and bonding the copper plate to the main surface; as well as The plurality of entry regions are composed of one or more entry portions that extend continuously from the main surface and enter at least a portion of the voids of the silicon nitride ceramic substrate to a depth of 3 μm to 20 μm. The entry area contains silver, and every 1 mm of the main surface 2 There are more than 1 and less than 30 of the said entry areas.

2. The bonding substrate according to claim 1, wherein The one or more inlet portions are continuous from the bonding layer in a portion not exposed on the main surface.

3. The bonding substrate according to claim 1 or 2, wherein: The bonding layer contains at least one active metal selected from the group consisting of titanium and zirconium, The entry portion further includes at least one metal selected from the group consisting of copper, indium, and tin.

4. The bonding substrate according to claim 1 or 2, wherein: A projected area obtained when the range of the entry region inside the silicon nitride ceramic substrate is virtually projected onto the main surface is larger than an area on the main surface where the entry region actually exists.

5. The bonding substrate according to claim 1 or 2, wherein: The interval between the stacked portions of the patterned portion of the copper plate and the patterned portion of the bonding layer is 0.5 mm to 1.5 mm.

6. A method for manufacturing a bonded substrate, characterized in that: have: Step a), preparing a silicon nitride ceramic substrate; Step b), forming a brazing material layer on the main surface of the silicon nitride ceramic substrate; Step c) disposing a copper plate on the brazing material layer to obtain an intermediate product comprising the silicon nitride ceramic substrate, the brazing material layer, and the copper plate; step d) heat-treating the intermediate product to form a bonding layer and a plurality of intrusion regions, the bonding layer bonding the copper plate to the main surface, the plurality of intrusion regions including one or more intrusion portions extending from at least a portion of a void inside the silicon nitride ceramic substrate and extending to a depth of 3 μm to 20 μm from the main surface and containing silver; and Step e), patterning the copper plate and the bonding layer into a given shape, In the step d), the main surface is 2 The presence ratio of 1 or more and 30 or less forms the entry area, The heat treatment is performed by heating the intermediate product according to a temperature profile having a maximum temperature of 800° C. or higher and 860° C. or lower. The brazing material layer includes at least one active metal hydride selected from the group consisting of titanium and zirconium, and at least one metal selected from the group consisting of silver, copper, indium, and tin. In the step d), the metal containing at least silver is moved into the gaps in the silicon nitride ceramic substrate by the heat treatment to form the entry region. The heat treatment is performed by pressurizing the intermediate product according to a surface pressure curve having a maximum surface pressure of 5 MPa to 30 MPa.

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