JP6375086B1 - Insulated heat dissipation board - Google Patents

Abstract

Provided is an insulating heat dissipation substrate that enhances durability against a cooling cycle and contributes to miniaturization of a semiconductor module. An insulating heat dissipation substrate having a ceramic substrate and a conductor layer bonded on at least one main surface of the ceramic substrate, wherein the conductor layer has an upper surface, a lower surface, and a side surface 1 connecting the upper surface and the lower surface. And the ceramic substrate has a lowest part, a side face 2 connecting the lowest part and the side face 1 of the conductor layer, and a joint surface that is positioned higher than the lowest part and is joined to the lower face of the conductor layer. When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer in plan view, the elevation angle α of the side surface 1 with respect to the lower surface at the height of the lower surface; The absolute value of the difference in elevation angle β of the side surface 2 with respect to the joint surface at the height of the joint surface is 20 ° or less on average, and the side surface 1 is a method for the tangent of the planar view contour of the conductor layer rather than the end of the upper surface. Receding in the line direction Insulated radiating substrate having portions were.

Description

  The present invention relates to an insulating heat dissipation substrate, and more particularly to an insulating heat dissipation substrate on which a power semiconductor is mounted.

  Power semiconductor modules are used for power control of HEV / EV and trains. The power semiconductor module includes, for example, a power semiconductor such as a switching element, IGBT, and MOSFET, an insulating heat dissipation substrate provided with a conductor layer, a cooling member, and a housing. The power semiconductor module generates high heat because it performs high power control, and is used in a cold cycle environment. Therefore, the insulating heat dissipation board on which the power semiconductor is mounted is required to have reliability (durability) with respect to the thermal cycle in addition to the bonding strength, electrical insulation, and heat dissipation.

  A DCB (Direct Copper Bond) substrate in which a thin copper plate is directly bonded to a ceramic substrate such as an alumina substrate, an aluminum nitride substrate, or a silicon nitride substrate is widely known as an insulating heat dissipation substrate that meets such requirements. In addition, an AMB (AMB) formed by bonding a ceramic substrate such as an alumina substrate, an aluminum nitride substrate, or a silicon nitride substrate and a thin copper plate through a bonding layer formed using a brazing material (bonding material) containing an active metal. Active metal bonding) substrates are also widely known as insulating heat dissipation substrates. With regard to such an insulating heat dissipation substrate, research and development has been continued day and night in order to further improve the performance.

  For example, according to Japanese Patent No. 4051164 (Patent Document 1), by controlling the surface roughness Rmax and thickness of an insulating substrate between circuit layers, adhesion of a wiring circuit layer such as a metal foil or a metal plate to the insulating substrate. Strength can be increased, and even when electroless plating is applied to the surface, adhesion of plating due to residual active liquid on the substrate surface can be prevented, and defects due to short-circuiting between wirings can be eliminated, and low thermal resistance can be achieved. It is said that a circuit board can be obtained.

  According to Japanese Patent No. 4688380 (Patent Document 2), by controlling the surface roughness Rmax of the insulating substrate having silicon nitride as the main crystal phase, the bonding strength between the metal plate and the insulating substrate can be increased, Further, it is said that no problems occur even after the plating process, and a low-cost circuit board can be obtained.

  Japanese Patent No. 5038565 (Patent Document 3) reveals that the anisotropy of the surface roughness of the ceramic substrate constituting the circuit board has a great influence on the bending strength, and further the surface roughness of the ceramic substrate. By reducing the anisotropy of the ceramic substrate to a predetermined value or less, the bending strength of the ceramic substrate can be improved. By using the ceramic substrate, a circuit with less generation of cracks and high withstand voltage and reliability is provided. It is described that a substrate is realized.

  Japanese Patent No. 54988839 (Patent Document 4) discloses an insulating heat dissipation substrate including an insulating film made of a ceramic material, a bonding layer made of a brazing material, and a circuit board made of metal. ing. This document describes that by setting the thickness of the insulating film to 100 μm or less, the heat transfer resistance by the insulating film can be reduced and the thermal conductivity from the circuit board to the heat conductive substrate can be improved. Further, it is described that the bonding strength between the insulating film and the circuit board is improved by providing a plurality of convex portions on the bonding layer side of the insulating film. Further, it is also described that since the convex portion has a curved surface curved in a convex manner, the occurrence of cracks in the bonding layer made of the brazing material is suppressed, and the reliability is improved.

Japanese Patent No. 4051164 Japanese Patent No. 4688380 Japanese Patent No. 5038565 Japanese Patent No. 5498839

  In recent years, power semiconductor modules have been required to have improved output density and downsizing. In response to such demands, it has been studied to increase the thickness of the copper plate for the purpose of achieving both heat dissipation and downsizing of the insulating heat dissipation substrate used in the power semiconductor module. However, when a thick copper plate is used, the thermal stress generated at the bonding interface between the copper plate and the ceramic substrate increases due to the difference in thermal expansion between copper and ceramics, which is generated by heat treatment when bonding the ceramic substrate and the copper plate. Due to the residual thermal stress and the repeated thermal stress caused by the temperature change at the time of actual use, a problem that a crack occurs in the ceramic substrate is likely to occur.

  In this regard, the conventional technology cannot be said to be sufficient to prevent the occurrence of cracks in a cold cycle environment, and further improvement in durability is desired. This invention is made | formed in view of such a problem, and makes it one subject to provide the insulated heat dissipation board which improves durability with respect to a thermal cycle, and contributes to size reduction of a semiconductor module.

  Cracks in the ceramic substrate that occur due to repeated cooling and heating cycles are likely to occur in the vicinity of the junction end between the conductor layer (synonymous with the circuit layer) and the ceramic substrate. As a result of pursuing the cause, the present inventor has revealed by thermal stress analysis that a large thermal stress is applied due to a sudden angle change at the joint end of the ceramic substrate and the conductor layer. And this inventor discovered that a thermal stress fell by smoothing the said junction edge part, and cooling-heat cycle durability improved significantly. Moreover, it discovered that a mounting area could be expanded by devising the side surface shape of a conductor layer. The present invention has been completed based on the above findings.

In one aspect of the present invention,
An insulating heat dissipation substrate having a ceramic substrate and a conductor layer bonded on at least one main surface of the ceramic substrate,
The conductor layer has an upper surface, a lower surface, and a side surface 1 connecting the upper surface and the lower surface,
The ceramic substrate has a lowest part, a side face 2 that connects the lowest part and the side face 1 of the conductor layer, and a joint surface that is at a position higher than the lowest part and is joined to the lower face of the conductor layer,
When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer in plan view, the elevation angle α of the side surface 1 with respect to the lower surface at the height of the lower surface, and the bonding The absolute value of the difference in the elevation angle β with respect to the joint surface of the side surface 2 at the height of the surface is 20 ° or less on average,
When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar outline of the conductor layer, the side surface 1 is tangent to the planar outline of the conductor layer rather than the end of the upper surface. It is an insulated heat dissipation board | substrate which has the location reverse | retreated in the normal line direction with respect to.

  In one embodiment, the insulated heat dissipation substrate according to the present invention is characterized in that the elevation angle of the side surface 1 when the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar outline of the conductor layer. α is 20 ° to 60 ° on average.

  In another embodiment of the insulated heat dissipation substrate according to the present invention, the distance H in the thickness direction between the lowest portion of the ceramic substrate and the end of the joining surface is 0 μm to 30 μm on average.

  In another embodiment of the insulated heat dissipation substrate according to the present invention, when the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the outline of the conductor layer in plan view, the side surface 1 and The contours of the side surfaces 2 are both curved lines that are recessed inward.

  In still another embodiment, the insulated heat dissipation substrate according to the present invention is the lowest part when the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the outline of the conductor layer in plan view. The distance L in the normal direction with respect to the tangent of the contour in plan view of the conductor from the joint surface to the joint end of the joint surface is 5 μm to 30 μm on average.

  In yet another embodiment of the insulated heat dissipation board according to the present invention, the most receded portion of the receded portion of the side surface 1 is normal to the tangent line of the contour of the conductor layer in plan view rather than the end portion of the upper surface. Retreats on average in the direction below 200 μm.

  In yet another embodiment of the insulated heat dissipation board according to the present invention, the most receded portion of the receded portion of the side surface 1 is normal to the tangent line of the contour of the conductor layer in plan view rather than the end portion of the upper surface. Retreats in the direction from 20 μm to 100 μm on average.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to improve the durability with respect to the thermal cycle of an insulated heat dissipation board | substrate, and a mounting area is expanded. For this reason, the present invention can be advantageously applied to an insulating heat dissipation board obtained by thickening a copper plate in order to achieve both heat dissipation and downsizing, and particularly contributes to improvement in output density and downsizing of a power semiconductor module. be able to.

It is a schematic diagram when the insulated heat dissipation board which concerns on one Embodiment of this invention is partially observed in the cross section parallel to both the normal line direction and thickness direction with respect to the tangent of the planar view outline of a conductor layer and a ceramic substrate. . An insulating heat dissipation substrate according to an embodiment of the present invention, a conductor layer and a ceramic substrate when partially observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the outline of the conductor layer in plan view, It is a schematic diagram near the joining end of a ceramic substrate. An insulating heat dissipation substrate according to an embodiment of the present invention, a conductor layer and a ceramic substrate when partially observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the outline of the conductor layer in plan view, It is a SEM image near the joining end of a ceramic substrate. When a conventional insulating heat dissipation substrate is partially observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the conductor layer and the ceramic substrate in a plan view, the vicinity of the junction end of the conductor layer and the ceramic substrate It is a SEM image of. It is a plane schematic diagram of the insulation heat dissipation board produced in the Example.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. The present invention is not limited to the following embodiments, and appropriate modifications and improvements are added to the following embodiments on the basis of ordinary knowledge of those skilled in the art without departing from the spirit of the present invention. It should be understood that what has been described also falls within the scope of the invention.

<1. Insulated heat dissipation board>
FIG. 1 shows an insulating heat dissipation substrate 100 according to an embodiment of the present invention when a conductor layer and a ceramic substrate are partially observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the conductor layer in plan view. FIG. In this specification, the plan view means a method of observing the insulated heat dissipation substrate from the direction in which the projected area is maximum, and the thickness direction means a direction parallel to the observation direction. Insulating heat dissipation substrate 100 includes a ceramic substrate 110 and a conductor layer 120 bonded onto at least one main surface of ceramic substrate 110. The conductor layer 120 may be bonded on one main surface of the ceramic substrate 110, or may be bonded on both main surfaces. An example of a plan view of the insulating heat dissipation substrate 100 is shown in FIG. The conductor layer 120 can be formed in an arbitrary pattern for forming an electric circuit.

The conductor layer 120 has an upper surface 121, a lower surface 122, and a side surface 1 (123) that connects the upper surface 121 and the lower surface 122. The ceramic substrate 110 is located at a position higher than the lowest portion 111, the side surface 2 (112) connecting the lowest portion 111 and the side surface 1 (123) of the conductor layer 120, and the lowest portion 111, and is bonded to the lower surface 122 of the conductor layer 120. And a joining surface 113 to be connected. In the present specification, the lowest part 111 of the ceramic substrate is parallel to both the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer 120 in the plan view of the conductor layer 120 by SEM with a magnification of 1000 times. The portion of the ceramic substrate surface from the end portion (joining end) of the joining surface (113) to the location 50 μm away from the joining surface (113) when observed in a cross section has the longest distance from the joining end in the thickness direction. Point to. When there are a plurality of locations where the distance from the joining end in the thickness direction is the longest or continuous, the location where the distance from the joining end in the normal direction is the shortest is the lowest part. Examples of normal lines with respect to the tangent of the planar outline of the conductor layer 120 are shown by dotted lines N ₁ -N ₁ ′ and dotted lines N ₂ -N ₂ ′ in FIG.

  The insulating heat dissipation substrate 100 can be used as a substrate on which the power semiconductor is mounted in a power semiconductor module including a power semiconductor (not shown) such as a switching element, IGBT, MOSFET, or the like. The conductor layer 120 can form an electric circuit pattern, and a power semiconductor can be mounted on the electric circuit pattern.

Examples of the ceramic substrate 110 include an alumina (Al ₂ O ₃ ) substrate in addition to a nitride ceramic substrate such as a silicon nitride (Si ₃ N ₄ ) substrate or an aluminum nitride (AlN) substrate. In realizing the present invention, the planar shape and size of the ceramic substrate 110 are not particularly limited. However, from the viewpoint of reducing the size of the power semiconductor module, one side is about 20 mm to 70 mm and the thickness is 0.1 mm. A ceramic substrate 100 having a rectangular shape in plan view of ˜1.0 mm is illustrated.

  The conductor layer 120 can be formed of a metal such as copper (Cu), a copper alloy, aluminum (Al), or an aluminum alloy. The conductor layer 120 can also be formed of a metallized layer made of a refractory metal such as tungsten (W) or molybdenum (Mo) or silver (Ag). In addition, nickel, iron, titanium, and molybdenum can also be used. The thickness of the conductor layer 120 (the difference in height between the upper surface 121 and the lower surface 122 of the conductor layer 120 (distance in the thickness direction)) is 0.3 mm to 2.0 mm from the viewpoint of reducing the size of the power semiconductor module. It is preferable that it is 0.5 mm-1.5 mm.

  In the embodiment shown in FIG. 1, when the conductor layer 120 and the ceramic substrate 110 are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the contour of the conductor layer 120 in plan view, the side surface 1 (123) is The conductive layer 120 has a portion that is recessed in the normal direction with respect to the tangent to the outline of the conductor layer 120 from the end of the upper surface 121. In other words, the side surface 1 (123) is configured such that the upper surface 121 protrudes. As a result, in addition to the bonding area where the semiconductor chip can be mounted, it is possible to increase the mounting area such as a mounting area where the semiconductor chip is mounted by soldering, an area for connecting terminals (eg, ultrasonic connection), etc. I understand. For this reason, according to the present invention, if the mounting amount of the semiconductor chip is the same, the area of the insulating heat dissipation substrate can be reduced. In other words, the semiconductor module can be reduced in size.

  From the viewpoint of increasing the mounting area, the most retracted portion of the side surface 1 (123) is in a direction normal to the tangent to the contour of the conductor layer 120 from the end of the upper surface 121. The average is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more. However, if the side surface 1 (123) is retracted too much, the tip of the upper surface 121 becomes an acute angle and the strength tends to decrease, and further, the tip tends to hang down. Such a part is not suitable as a mounting area. For this reason, it is preferable that the most receded portion of the receded portion of the side surface 1 is receded by 200 μm or less on average in the normal direction with respect to the tangent to the outline of the conductor layer in plan view from the end portion of the upper surface. It is more preferable to recede by 150 μm or less, and it is even more preferable to recede by 100 μm or less.

  FIG. 2 shows the insulating heat dissipation board according to the embodiment of the present invention, in which the conductor layer 120 and the ceramic substrate 110 are partially cross-sectionally parallel to both the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer 120 in plan view. A schematic view of the vicinity of the joining end of the conductor layer 120 and the ceramic substrate 110 when observed is shown. In the cross-sectional observation, the absolute value of the difference between the elevation angle α with respect to the lower surface 122 of the side surface 1 (123) at the height of the lower surface 122 and the elevation angle β with respect to the bonding surface 113 of the side surface 2 (112) at the height of the bonding surface (113). Small is important for enhancing the heat cycle durability.

  In the conventional insulated heat dissipation substrate, as shown in FIG. 4, the joint end of the ceramic substrate and the conductor layer has a pin angle (a corner with a sharp tip), and there is a sudden angle change. A large thermal stress is applied to such a pin angle. This means that if a pin angle exists in the vicinity of the joining end of the conductor layer and the ceramic substrate, cracks are likely to occur from the starting point due to repeated cooling and heating cycles.

  Therefore, the present inventor made a hypothesis that cracks can be suppressed by the absence of a pin angle in the vicinity of the joint end of the conductor layer and the ceramic substrate, and repeated various experiments and examinations. The elevation angle α (0 ° ≦ α ≦ 90 °) of the side surface 1 (123) at the height with respect to the lower surface 122 and the elevation angle β (0 ° ≦ 0 °) of the side surface 2 (112) at the height of the bonding surface (113). It has been found that when the absolute value (| α−β |) of the difference in β ≦ 90 ° is 20 ° or less on average, the thermal cycle durability is significantly improved. The average of | α−β | is preferably 8 ° or less, more preferably 5 ° or less, for example, 1 ° to 20 °. The average value is obtained by observing cross sections of any five or more locations of the insulating heat dissipation substrate to be measured (the same applies to the average values of the following parameters).

  The elevation angle α itself of the side surface 1 (123) is not particularly limited. However, if it is less than 20 ° or less than 60 °, the selection of etching conditions and wet blasting conditions for shape formation becomes complicated, so α is The average is generally 20 ° to 60 °, and preferably 20 ° to 30 °.

  In FIG. 3, when the insulated heat dissipation board which concerns on one Embodiment of this invention is partially observed in the cross section parallel to both the normal line direction and thickness direction with respect to the tangent of the planar view outline of a conductor layer and a ceramics board | substrate. The SEM image of the joining edge vicinity of a conductor layer and a ceramic substrate is shown. It can be understood that the joining ends of the ceramic substrate and the conductor layer are smoothly connected.

  Referring to FIG. 2 again, not only the location of the bonding interface but also the side surface 2 (112) is less susceptible to thermal stress if there is no sudden change in the angle as a whole, leading to an improvement in the cooling cycle durability. From this viewpoint, when the conductor layer 120 and the ceramic substrate 110 are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer 120, the elevation angle β of the side surface 2 (112), The absolute value (| β−γ |) of the difference in elevation angle γ of the side surface 2 (112) with respect to the bonding surface 113 at a point 10 μm away from the bonding end of the bonding surface 113 in the normal direction to the tangent to the contour of the conductor layer 120 in plan view. Is preferably smaller. Specifically, it is preferable that | β−γ | is 30 ° or less on average. On the other hand, if | β−γ | is too small, the ceramic substrate 110 is greatly scraped to reduce the thickness and easily deteriorate the insulation performance. Therefore, | β−γ | may be 5 ° or more on average. preferable. However, the difference in characteristics caused by the change of | β−γ | is slight.

  From the viewpoint of preventing the ceramic substrate 110 from being greatly shaved and reducing the insulation performance, the conductor layer 120 and the ceramic substrate 110 are parallel to both the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer 120 in plan view. When observed in a simple cross section, the distance H in the thickness direction between the lowest portion 111 of the ceramic substrate 110 and the end portion (joining end) of the joining surface 113 is preferably 30 μm or less, more preferably 20 μm or less. Preferably, it is still more preferably 10 μm or less. The lower limit of H is not particularly set and may be 0. However, since it is easy to make | α−β | smaller when H is larger, H is preferably 2 μm or more on average.

  Further, from the viewpoint of preventing the ceramic substrate 110 from being greatly shaved and deteriorating the insulation performance, the conductor layer 120 and the ceramic substrate 110 are both in the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer 110 in plan view. The distance L in the normal direction from the lowest portion 111 to the joining end of the joining surface 113 with respect to the tangent of the planar view contour of the conductor 120 is preferably 5 μm or more on average. It is more preferable that However, if the distance L becomes too long, it is necessary to increase the distance (space) between the conductors, and the distance L is 30 μm or less on average from the viewpoint that the effect of suppressing the decrease in insulation performance is saturated. Is preferable, and it is more preferable that it is 20 micrometers or less.

  In the present invention, the elevation angles α and β are measured according to the following procedure by observing the above-described cross section with an SEM having a magnification of 1000 times. An approximate straight line A having a length of 30 μm corresponding to the contour shape of the side surface 1 (123) is drawn from the joining end of the conductor layer 120 and the ceramic substrate 110. An approximate straight line B having a length that is half the distance H in the thickness direction between the lowest end 111 corresponding to the contour shape of the side surface 2 (112) and the bonded end is drawn from the bonded end of the conductor layer 120 and the ceramic substrate 110. An approximate straight line C having a length of 30 μm corresponding to the contour shape of the joint surface 113 (lower surface 122) is drawn from the joint end of the conductor layer 120 and the ceramic substrate 110. The elevation angle α is determined from the angle formed by the approximate line A and the approximate line C, and the elevation angle β is determined from the angle formed by the approximate line B and the approximate line C.

  Illustratively, in the SEM image of FIG. 3, an image of the approximate straight line A having a length of 30 μm corresponding to the contour shape of the side surface 1 (123) from the joining end of the conductor layer 120 and the ceramic substrate 110 is shown. When the contour points of the side surface 1 from the joint end are uniformly plotted on the orthogonal coordinate system ((x, y) coordinates) in the range where the length of the approximate straight line is 30 μm, approximation of the form y = ax + b by the least square method The formula is obtained. A straight line corresponding to this approximate expression is an approximate straight line A. At that time, the inclination of the approximate straight line A can be uniquely determined. The inclinations of the approximate line B and the approximate line C can be determined by the same method. From these inclinations, the elevation angle α and the elevation angle β can be obtained.

  In the present invention, the elevation angle γ is measured according to the following procedure by observing the above-described cross-section with an SEM having a magnification of 1000 times. An approximate straight line D having a length of 5 μm corresponding to the contour shape of the side surface 2 (112) at a point 10 μm away from the joining end of the conductor layer 120 and the ceramic substrate 110 in the normal direction to the tangent to the contour of the conductor 120 in plan view. From above (in the thickness direction, the direction approaching the joint end). The elevation angle γ is obtained from the angle formed by the approximate line D and the approximate line C.

<2. Manufacturing method>
The insulating heat dissipation board according to the present invention is a method in which a ceramic substrate and a metal plate or metal foil are joined to produce a joined substrate, and then an electric circuit pattern is formed using a lithography technique and an etching technique, and further smoothed. Can be manufactured.

  Any known technique may be used as a method of manufacturing a bonded substrate by bonding a ceramic substrate and a metal plate or metal foil. Typically, a ceramic substrate and a metal plate or metal foil are directly bonded to form a DCB substrate, and the ceramic substrate and the metal plate or metal foil are bonded using a brazing material (bonding material) containing an active metal. There is a method of manufacturing an AMB substrate by bonding through a bonding layer to be formed. Among these, from the viewpoint of increasing the bonding strength, a method of heat-pressure bonding (hot pressing) using a brazing material containing Ag and Ti is preferable. Since the brazing material is a conductor, in the present invention, the bonding layer is also handled as a part of the conductor layer.

  When hot-pressing using a brazing material, the bonding atmosphere must be a vacuum or an inert atmosphere (Ar atmosphere or the like) because Ti cannot be bonded in the first place when Ti, which is an active metal, is oxidized. From the viewpoint of increasing the bonding strength, the bonding pressure is desirably 5 MPa or more. However, if the bonding pressure is too high, the ceramic substrate may be destroyed during bonding, so the bonding pressure is preferably 25 MPa or less. The bonding temperature may be adjusted as appropriate depending on the type of brazing material to be used. However, when a brazing material containing Ag and Ti is used, it is preferable that the bonding temperature be about 800 ° C to 1000 ° C.

  In addition, as the brazing material, one in which one or more of Cu, Sn, In and the like are added to Ag for lowering the melting point, or one in which Ti is added to those alloy powders may be used. it can. For example, examples of the Ag-Cu-Ti brazing material include those containing Ag, Cu, and Ti in a range of 30 to 70%, 0 to 40%, and 0.1 to 20% in terms of composition weight ratio, respectively. Commercially available products satisfying these composition ranges can also be used.

  Although any known method may be employed for the lithography technique and the etching technique after producing the bonded substrate, wet etching is particularly suitable as the etching method. Since the elevation angle α of the side surface 1 of the conductor layer is significantly affected by the etching conditions, it is necessary to pay attention to the etching conditions. In general, the elevation angle α tends to increase as the etching time increases.

  It is important to perform a smoothing process after forming the electric circuit pattern to smooth the joint end of the conductor layer and the ceramic substrate and the periphery thereof. Examples of the smoothing method include wet blasting, dry blasting, cutting, laser processing, and other mechanical processing, but asymptotically approach the reference surface (plane) of the ceramic substrate from the bonding surface with the metal layer of the ceramic substrate. It is easy to make a smooth curved surface shape, and wet blasting is preferred because stress concentration can be prevented by using such a curved surface shape. When wet blasting is employed, the state of the smoothing process varies depending on the spraying pressure and spraying time, the type of abrasive used for wet blasting, and the particle size, so it is desirable to select appropriate conditions as appropriate. In general, the elevation angle β of the ceramic substrate tends to increase as the injection time increases. In order to reduce the value of | α−β |, it is necessary to adjust the injection time according to the shape of the side surface 1 of the conductor layer using fine abrasive grains.

  As examples of suitable conditions for wet blasting, the injection pressure is 0.01 to 0.5 MPa, the type of abrasive is abrasive ceramics (SiC, alumina, zirconia, etc.), and the particle size of the abrasive is about 1 to 100 μm. can do.

An insulating heat dissipation board manufactured by performing smoothing treatment by wet blasting can typically have any one or more of the following structural features, more typically two or more. And even more typically can have all three. Any of the following features is advantageous in that it leads to cost reduction of wet etching, improvement of productivity, and improvement of controllability of the angle α.
(1) The end portion 124 on the upper surface of the conductor layer 120 is set back from the end portion 125 on the lower surface of the conductor layer 120 in a direction normal to the tangent line of the contour of the conductor layer 120 in plan view (see FIG. 1).
(2) When the conductor layer 120 and the ceramic substrate 110 are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar view outline of the conductor layer 120, the side surface 1 (123) and the side surface 2 (112) Both contours are curved lines that are recessed inward (see FIG. 1).
(3) When the conductor layer 120 and the ceramic substrate 110 are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar view outline of the conductor layer 120, the side surface 1 (123) is the upper surface of the conductor layer 120. It has a location that recedes in a direction normal to the tangent to the contour of the conductor layer 120 from the end portion 124 (see FIG. 1).

  Various surface treatments can be further performed after the smoothing treatment. Examples of the surface treatment include, but are not limited to, acid treatment, alkali treatment, washing, plating, rust prevention treatment, and the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(1. Production of insulated heat dissipation substrate)
A silicon nitride (Si ₃ N ₄ ) substrate having a thickness of 0.3 mm and a rectangular shape (width 21 mm × length 21 mm) in plan view was prepared as a ceramic substrate. A copper (Cu) plate having a thickness of 0.5 mm in plan view (width 21 mm × length 21 mm) is bonded to one side of the silicon nitride substrate by hot pressing using a brazing material, and a bonded substrate of the ceramic substrate and the copper plate is bonded. Obtained. As the brazing material, one having a composition weight ratio of Ag: 51 mass%, Cu: 24 mass%, In: 11 mass%, and Ti: 14 mass% was used. Hot pressing was performed under a vacuum of 850 ° C. and a bonding pressure of 20 MPa.

  A conductive pattern as shown in FIG. 5 was formed from the bonded substrate obtained by the above procedure through pattern formation by photolithography and wet etching. An aqueous solution (pH = 1 to 3) containing cupric chloride and ferric chloride was used as an etching solution. Wet etching was performed under two conditions (Cu etching condition 1 and Cu etching condition 2) with different etching times according to the test number. In Cu etching condition 1, the target value of angle α of side surface 1 of the conductor layer was set to 50 °, and in Cu etching condition 2, the target value of angle α of side surface 1 of the conductor layer was set to 25 °, and the etching time was adjusted. Specifically, Cu etching condition 1 was an etching time of 1 hour, and Cu etching condition 2 was an etching time of 0.5 hour.

  After forming the conductive pattern, wet blasting was performed on the conductive pattern forming surface of the bonded substrate for the purpose of smoothing the periphery of the bonded end of the conductive layer and the ceramic substrate. The wet blasting was performed by using a wet blasting apparatus and injecting slurry of water and an abrasive (SiC particles having a particle diameter of about 10 to 20 μm) from a direction perpendicular to the conductor pattern forming surface. At this time, the shape of the side surface 2 of the ceramic substrate was changed by changing the injection pressure to 0.15 MPa, the nozzle moving speed to 100 mm / sec, and changing the number of passes. In one pass, the slit-shaped nozzle is moved from one side of the bonding substrate toward the side opposite to the bonding substrate, whereby the entire surface is wet-blasted once. The pass count represents the number of repetitions of this operation.

(2. Shape evaluation)
For the insulated heat dissipation substrate of each test example obtained through the above steps, the conductor layer and the ceramic substrate were cut so that the cross-section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar outline of the conductor layer was exposed. Then, after embedding the resin, the exposed cross section was polished, SEM observation was performed at 1000 times, and the following evaluation was performed. The results are shown in Table 1.
(1) Evaluation 1
It was evaluated whether or not the end portion of the upper surface of the conductor layer was retracted in the normal direction with respect to the tangent to the contour in plan view of the conductor layer from the end portion of the lower surface of the conductor layer. The evaluation result was made for any five cross-sections, and when all the five cross-sections satisfied the above conditions, it was set to YES, and otherwise it was set to NO.
(2) Evaluation 2
It was evaluated whether or not the contours of the side surface 1 and the side surface 2 were curved lines recessed inward. The evaluation result was made for any five cross-sections, and when all the five cross-sections satisfied the above conditions, it was set to YES, and otherwise it was set to NO.
(3) Evaluation 3
It was evaluated whether or not the side surface 1 had a portion that was receded in the normal direction with respect to the tangent to the contour of the conductor layer from the end of the upper surface of the conductor layer. The evaluation result was made for any five cross-sections, and when all the five cross-sections satisfied the above conditions, it was set to YES, and otherwise it was set to NO. Further, in the case of YES, the distance where the most receded portion of the receded location of the side surface 1 is receded in the normal direction with respect to the tangent to the contour of the conductor layer in plan view from the end of the upper surface of the conductor layer Was calculated from the cross-sections at the five locations.
(4) Evaluation 4
Elevation angle α, elevation angle β, elevation angle γ, α-β, and β-γ were measured for arbitrary five cross sections, and the average value of each was determined.
(5) Evaluation 5
For any five cross-sections, the distance H in the thickness direction between the lowest portion and the joining end of the ceramic substrate was measured, and the average value was obtained.
(6) Evaluation 6
For any five cross-sections, the distance L in the normal direction from the lowest part of the ceramic substrate to the bonding end of the bonding surface of the ceramic substrate with respect to the tangent of the planar outline of the conductor layer was measured, and the average value was obtained.

(3. Thermal cycle test)
A thermal cycle test was performed on the insulating heat-radiating substrate of each test example obtained through the above steps. The cold cycle test was a test in which a cold cycle of −55 ° C. (15 minutes) / 175 ° C. (15 minutes) was applied at 1000 cyc (cycle). About every 100 cyc in the middle (that is, 10 times in total), the presence of peeling of the bonded portion and the presence or absence of cracks in the ceramic substrate (hereinafter collectively referred to as “defects”) by external appearance confirmation and ultrasonic flaw detection using a stereomicroscope The number of cycles in which the cooling / heating cycle test was able to be conducted without any problems was confirmed.

  The results are shown in Table 1. For example, “100” indicates that no defect occurred until the first 100 cyc, but a defect occurred during observation after the end of 200 cyc. Further, “1000” indicates that no malfunction occurred before the execution of 1000 cyc.

(4. Dielectric breakdown voltage)
The dielectric breakdown voltage was measured for the insulating heat dissipation substrate of each test example obtained through the above steps. In the insulating oil, the top surface of the largest conductor layer in the middle of the three conductor layers shown in FIG. 5 and the non-joint surface of the ceramic substrate (the surface opposite to the surface where the conductor layer is joined) are measured. In the meantime, an AC voltage (effective value 6 kV, frequency 60 Hz) was applied for 10 seconds. The evaluation was “OK” when no short circuit occurred and “NG” when short circuit occurred. Table 1 shows the results.

(5. Discussion)
From the above results, in comparison with Comparative Example 1-1 and Comparative Example 2-1, in which the average absolute value of α-β exceeds 20 °, Example 1 in which the average absolute value of α-β is 20 ° or less. It can be understood that the heat cycle durability was significantly improved in 1-1-7 and Examples 2-1 through 2-5. In addition, it is thought that when the grinding amount is large as in Example 1-5, the thickness of the substrate becomes thin and the dielectric breakdown characteristics are affected.

100 Insulating heat dissipation substrate 110 Ceramic substrate 111 Minimum portion 112 of ceramic substrate Side surface 2 of ceramic substrate
113 Bonded surface 120 of ceramic substrate Conductor layer 121 Upper surface of conductor layer 122 Lower surface of conductor layer 123 Side surface of conductor layer 1
124 End of upper surface of conductor layer 125 End of lower surface of conductor layer

Claims (7)

An insulating heat dissipation substrate having a ceramic substrate and a conductor layer bonded on at least one main surface of the ceramic substrate,
The conductor layer has an upper surface, a lower surface, and a side surface 1 connecting the upper surface and the lower surface,
The ceramic substrate has a lowest part, a side face 2 that connects the lowest part and the side face 1 of the conductor layer, and a joint surface that is at a position higher than the lowest part and is joined to the lower face of the conductor layer,
When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the contour of the conductor layer in plan view, the elevation angle α of the side surface 1 with respect to the lower surface at the height of the lower surface, and the bonding The absolute value of the difference in the elevation angle β with respect to the joint surface of the side surface 2 at the height of the surface is 20 ° or less on average,
When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar outline of the conductor layer, the side surface 1 is tangent to the planar outline of the conductor layer rather than the end of the upper surface. An insulating heat dissipating board having a portion that is retracted in the normal direction to.   When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent to the outline of the conductor layer in plan view, the elevation angle α of the side surface 1 is 20 ° to 60 ° on average. The insulated heat dissipation board | substrate of 1.   The insulating heat dissipation substrate according to any one of claims 1 and 2, wherein a distance H in a thickness direction between the lowest portion of the ceramic substrate and an end portion of the bonding surface is 0 µm to 30 µm on average.   When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar outline of the conductor layer, the contours of the side surface 1 and the side surface 2 are both curved lines that are recessed inward. The insulated heat dissipation board | substrate as described in any one of Claims 1-3.   When the conductor layer and the ceramic substrate are observed in a cross section parallel to both the normal direction and the thickness direction with respect to the tangent of the planar outline of the conductor layer, the planar outline of the conductor from the lowest part to the joint end of the joint surface is observed. The insulation heat dissipation substrate according to any one of claims 1 to 4, wherein a distance L in a normal direction to the tangent line is 5 m to 30 m on average.   The most retracted portion of the receded portion of the side surface 1 is receded by 200 μm or less on average in the normal direction to the tangent to the contour of the conductor layer in plan view from the end of the upper surface. The insulated heat dissipation board | substrate as described in any one.   7. The most receded portion of the side surface 1 that has receded from the end portion of the upper surface has receded in an average direction of 20 μm or more and 100 μm or less in the normal direction to the tangent to the contour of the conductor layer in plan view. The insulation heat dissipation board of description.

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