JP6278516B2 - Power module substrate - Google Patents

Description

  The present invention relates to a power module substrate capable of improving the bonding reliability between a ceramic substrate and a copper plate when a copper plate is bonded to each of both main surfaces of the ceramic substrate and a semiconductor element generating a large amount of heat is mounted on the copper plate. .

  Conventionally, power module substrates have been equipped with semiconductor elements such as power transistors, which are becoming faster and more highly integrated due to the generation of high heat by flowing a large current, and the heat generated from the semiconductor elements can be quickly dissipated. Therefore, it is used for consumer equipment, in-car use such as automobiles and electric cars.

  As shown in FIGS. 3A to 3C, a conventional power module substrate 50 includes a circuit pattern-like circuit copper plate 52 on one main surface of a ceramic substrate 51 and a solid solid plate on the other main surface. The copper plate 53 is joined. The power module substrate 50 includes a circuit copper plate 52 having a pattern formed in advance, a direct bonding method in which a solid copper plate 53 is directly heat-bonded using the melting point of copper, and an active metal that is heat-bonded through an active metal brazing. It is made by joining with the brazing material joining method. Alternatively, the power module substrate 50 is a circuit copper plate having a desired pattern by etching the copper plate after directly bonding the entire copper plate on which the pattern is not formed on the ceramic substrate 51 by the direct bonding method or the active metal brazing material bonding method. 52 or a solid copper plate 53.

  The power module substrate 50 makes a semiconductor element 54 mounted on a predetermined copper plate in the circuit copper plate 52 electrically connected to other copper plates in the circuit copper plate 52 through bonding wires 55, It is electrically connected to the outside through another copper plate. The power module substrate 50 transfers high heat generated by flowing a large current through the semiconductor element 54 to the solid copper plate 53 side via the ceramic substrate 51, and further allows heat to be dissipated from the solid copper plate 53. The power module substrate 50 has a thick copper plate so that a large current can flow through the circuit copper plate 52, and the copper plate is bonded to each of both main surfaces of the ceramic substrate 51. The thickness of the solid copper plate 53 is the same in order to prevent the occurrence of warpage due to the difference in thermal expansion coefficient between the ceramic substrate 51 and the copper plate.

  However, in the power module substrate 50 in which a thick copper plate is bonded to the ceramic substrate 51, a large current is passed through the semiconductor element 54, or by cutting, the heating and cooling temperature cycles are repeated. The thermal stress resulting from the difference in thermal expansion coefficient between the substrate 51 and the copper plate is generated. This thermal stress exists as a residual stress distribution of compression and tension on the ceramic substrate 51 in the vicinity of the joint, and in particular, the main stress of the residual stress acts on the portion of the ceramic substrate 51 close to the end of the copper plate. The residual stress causes a crack in the ceramic substrate 51 when the maximum stress value as a tensile component of the stress exceeds the tensile strength of the ceramic substrate 51, and further, the ceramic of the circuit copper plate 52 and the solid copper plate 53. Peeling from the substrate 51 is generated. Moreover, since the power module substrate 50 is usually bonded to the entire surface of the ceramic substrate 51 with the solid copper plate 53 provided at a predetermined distance from the end of the ceramic substrate 51, heating and cooling are performed. The shrinkage due to the temperature cycle is large, which causes cracks in the ceramic substrate 51.

  In order to cope with this, as shown in FIGS. 4A to 4C, the conventional power module substrate 50 includes a circuit copper plate 52 and / or a solid copper plate 53 bonded to the surface of the ceramic substrate 51. A U-shaped groove 56 (see FIG. 4A), a stepped step 57 (see FIG. 4B), and a through or non-through hole 58 (see FIG. 4C) are formed around the outer periphery. Some are provided to relieve shrinkage caused by heating and cooling temperature cycles.

A conventional power module substrate includes a ceramic substrate and a copper plate bonded to at least the surface of the ceramic substrate, and the outer peripheral edge of the copper plate opposite to the bonding surface with the ceramic substrate. It is proposed that a plurality of holes are formed in a straight line at predetermined intervals along the line (for example, see Patent Document 1).
According to this, even when a thermal cycle is added, cracks and strength reduction of the ceramic substrate can be effectively prevented, and the deformation of the copper plate is also achieved by mechanical processing (press processing) advantageous to the manufacturing process. It is possible to provide a power module substrate with excellent reliability that can prevent the above.

JP-A-8-250823

However, the conventional power module substrate as described above has the following problems.
(1) A U-shaped groove, stepped step or hole is provided on the outer periphery of the copper plate bonded to the surface of the ceramic substrate, or for a power module as disclosed in JP-A-8-250823. The board has a special arc-shaped rounded corner at the corner of the metal plate, which is a copper plate, and has a right angle. Therefore, when a thermal cycle is applied to the power module substrate, it remains on the ceramic substrate portion adjacent to the copper plate corner. Stress is concentrated and it is impossible to prevent cracks generated in the ceramic substrate portion adjacent to the corner of the copper plate and strength reduction.
(2) A power module substrate as disclosed in Japanese Patent Laid-Open No. 8-250823, for example, even if an arc-shaped round is provided at the corner of the copper plate, the through hole provided at the corner of the copper plate has a corner of the copper plate. Therefore, a plurality of through holes provided at a predetermined interval are away from the edge of the copper plate on the side portion where the center of the through hole provided at the corner of the copper plate is a straight line. Therefore, in the power module substrate provided with such a through hole, it becomes impossible to disperse the residual stress of the ceramic substrate portion adjacent to the edge portion of the copper plate side, and the occurrence of cracks in the side portion of the ceramic substrate or the strength reduction Can no longer prevent.
(3) Also, the power module substrate as disclosed in Japanese Patent Laid-Open No. 8-250823 is provided by machining the copper plate before joining the ceramic substrate with the through holes provided in the corners and sides of the copper plate. Therefore, it is difficult to provide the through hole close to the edge of the copper plate, and it becomes impossible to disperse the residual stress of the ceramic substrate portion adjacent to the edge of the copper plate, preventing the occurrence of cracks and strength reduction of the ceramic substrate. Can no longer do.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the board | substrate for power modules which can prevent generation | occurrence | production of the crack of a ceramic substrate, or a strength fall.

  The power module substrate according to the present invention that meets the above-mentioned object is a power module substrate in which one or a plurality of copper plates having arc-shaped rounded corners are joined to both main surfaces of a rectangular ceramic substrate, A first penetration centered on a first straight line connecting the midpoint of the rounded corner of the copper plate and the center of the arc shape, and the distance from the midpoint of the round is shorter than the distance to the center of the arc shape. It is provided on the first straight line extending from the hole, the midpoint of the rounded corner of the copper plate and the center of the first through hole, and the distance from the midpoint of the round is greater than the distance to the center of the arc shape A second through-hole centered at a long position and a second straight line adjacent to the first and second through-holes and extending in parallel with the outer edge of the straight side of the copper plate; The distance from the outer edge to the second straight line is The distance from the center of the second through hole is equal to the distance to the center of the through hole and shorter than the distance from the extending line of the outer edge of the side to the center of the first through hole. A third through-hole centered at a position equivalent to the distance between the centers of the through-holes, and one corner and the other corner of the copper plate on the second straight line extending in parallel with the outer edge of the side of the copper plate A plurality is provided between the centers of the third through holes provided in the portion, and the center is a position where the distance between the centers of the first through holes and the center of the third through holes is the distance between adjacent centers. The fourth through hole is parallel to the second straight line on the center side of the copper plate from the second straight line, and extends to a position shorter than the distance from the second straight line to the center of the second through hole. A plurality are provided on the third straight line, between the center of the third through hole and the center of the fourth through hole, and between the centers of the adjacent fourth through holes. Having a fifth through hole of around the position where the bird structure.

  Here, in the power module substrate, the diameters of the first to fifth through holes may be substantially the same.

  In the power module substrate described above, the first to fifth through holes may be holes formed by etching after bonding a copper plate to the ceramic substrate.

  The power module substrate is provided on a first straight line connecting the midpoint of the rounded corner of the copper plate and the center of the arc shape, and the distance from the midpoint of the radius is shorter than the distance to the center of the arc shape. Is provided on the first straight line extending from the center of the first through hole, the center of the corner of the copper plate corner and the center of the first through hole, and the distance from the center of the corner is A second through hole centered at a position longer than the distance to the center of the arc shape, and a second adjacent to the first and second through holes and extending in parallel with the outer edge of the straight side of the copper plate Provided on a straight line, the distance from the outer edge of the side to the second straight line is equal to the distance from the center of the radius to the center of the first through hole, and from the extended line of the outer edge of the side It is shorter than the distance to the center of the through hole, and the distance from the center of the second through hole is the distance between the centers of the first and second through holes. A third through-hole centered at the same position and a third through-hole provided at one corner and the other corner of the copper plate on the second straight line extending in parallel with the outer edge of the side of the copper plate A fourth through-hole centered at a position where the distance between the center of the first through-hole and the distance between the centers of the first and third through-holes is a distance between adjacent centers A plurality of third straight lines extending parallel to the second straight line on the center side of the copper plate from the second straight line and extending to a position shorter than the distance from the second straight line to the center of the second through hole. Is provided, and has a fifth through-hole centered at a position having a staggered structure between the center of the third through-hole and the center of the fourth through-hole, and between the centers of the adjacent fourth through-holes. An arc-shaped radius is formed at the corner of the copper plate, and through holes are provided at equal distances from the outer edge and at substantially equal intervals between the outer edges of the outer periphery of the copper plate. It is possible to prevent the residual stress generated in the ceramic substrate adjacent to the copper plate that is concentrated when the thermal cycle is added to the power module substrate, and to prevent the generation of cracks in the ceramic substrate and the decrease in strength. it can.

  In particular, since the power module substrate has substantially the same diameter of the first to fifth through holes, the outer peripheral portion of the copper plate that is concentrated when the cooling cycle is applied to the power module substrate. Residual stress generated in the ceramic substrate portions to be joined can be effectively prevented.

  In particular, in the power module substrate described above, the first to fifth through holes are holes formed by etching after bonding the copper plate to the ceramic substrate, and therefore close to the outer periphery of each copper plate. It is possible to provide a power module substrate in which first to fifth through holes are easily provided at desired positions.

(A)-(C) are the top views of one main surface of the board | substrate for power modules which concerns on one embodiment of this invention, the top view of the other main surface, and the A-A 'line longitudinal cross-sectional view, respectively. It is expansion explanatory drawing of the corner | angular part of the board | substrate for power modules. (A)-(C) is the top view of one main surface of the board | substrate for conventional power modules, the top view of the other main surface, and an A-A 'line longitudinal cross-sectional view, respectively. (A)-(C) is an enlarged explanatory view of the corner | angular part of the board | substrate for power modules, respectively.

Next, with reference to the accompanying drawings, embodiments for embodying the present invention will be described for understanding of the present invention.
As shown in FIGS. 1A to 1C, a power module substrate 10 according to an embodiment of the present invention includes alumina (Al ₂ O ₃ ), aluminum nitride (AlN), zirconia-containing alumina, and the like. A rectangular ceramic substrate 11 made of the above ceramic is provided. In addition, the power module substrate 10 has one or a plurality of copper plates 13 having various shapes with arc-shaped rounds 12 at the corners bonded to both main surfaces of the ceramic substrate 11. Yes. The power module substrate 10 has a circuit pattern formed by a plurality of copper plates 13 on one main surface of the ceramic substrate 11, and a solid copper plate 13 bonded to the other main surface of the ceramic substrate 11. ing. In this power module substrate 10, the entire copper plate on which no pattern is formed on both main surfaces of the ceramic substrate 11 is usually heat bonded by a direct bonding method or an active metal brazing material bonding method, and then the entire copper plate on both main surfaces. These are etched to form a desired circuit pattern having arc-shaped rounds 12 at the corners or a solid copper plate 13.

The direct bonding method of the entire copper plate is a method in which a copper plate whose surface has been oxidized in advance is brought into contact with the oxidizable ceramic substrate 11 and fired in a nitrogen atmosphere to raise the temperature to the vicinity of the melting point of copper oxide (1083 ° C.). In this method, a Cu—O eutectic liquid phase generated by the reaction between copper and a small amount of oxygen is directly bonded to the ceramic substrate 11 as a binder. In the direct bonding method, when the ceramic substrate 11 is made of AlN, there is no oxide film on the surface of AlN, so an oxide film is formed on the surface of the ceramic substrate 11, that is, the surface of AlN is made Al ₂ O _3. It is necessary to keep.

  In addition, the active metal brazing material joining method for the entire copper plate is an active metal brazing material in which a so-called active metal such as titanium, zirconium, beryllium or the like is added to an Ag-Cu brazing filler metal. In this method, the ceramic substrate 11 and the copper plate are joined together. In this bonding, a paste made of an active metal brazing material is applied to the surface of the ceramic substrate 11 and brought into contact with a copper plate whose surface has been oxidized in advance, and heated at about 750 ° C. to 850 ° C. for oxygen such as titanium. It is directly bonded to the ceramic substrate 11 using the strength of the affinity. In the active metal brazing method, when the ceramic substrate 11 is made of zirconia-based alumina, the Ag—Cu-based brazing contains, for example, at least one of zirconium, titanium, hydrogen fluoride, and niobium. A material can be used, and by increasing the affinity for the ceramic substrate 11, the bonding reaction strength can be increased and a strong bonding can be achieved.

  Further, in the above etching, first, an etching resist film to be a desired circuit pattern shape or a solid copper plate 13 is formed on the entire copper plate by screen printing or a photoresist method. The etching resist film also includes a pattern for providing the arc-shaped rounds 12 at the corners of the copper plate 13 described above, a pattern for providing through holes in the outer peripheral portion of the desired copper plate 13 to be described later, and the like.

  Next, on the entire copper plate provided with the etching resist film, an etching solution made of an aqueous solution containing 30 to 40% by weight of ferric chloride is sprayed to remove the copper plate portion which is not covered with the etching resist film. ing. Further, the etching resist film is peeled off from the copper plate 13, thereby producing the power module substrate 10 provided with a desired circuit pattern or solid copper plate 13 bonded to the ceramic substrate 11.

  As shown in FIG. 2, the power module substrate 10 has a 45 ° angle by connecting the midpoint 14 of the arc-shaped round 12 and the center 15 of the round-shaped arc 12 to the corner of the desired copper plate 13. A center 15a of the first through hole 17 is provided on a first straight line 16 extending at an angle. The center 15a of the first through-hole 17 has a distance A shorter than the distance R from the midpoint 14 of the radius 12 to the arcuate center 15 having the radius of the radius 12 from the midpoint 14 of the radius 12. The position is <R). Further, the distance A from the midpoint 14 of the center 12a of the center 15a of the first through-hole 17 varies depending on the hole diameter size of the first through-hole 17, the etching accuracy, and the like. The distance is set such that the midpoint 14 of 12 becomes a position where the strength of the copper plate 13 can be kept close while maintaining the strength.

  The power module substrate 10 is a straight line that extends from the corner portion of the copper plate 13 by connecting the midpoint 14 of the corner radius 12 and the center 15a of the first through-hole 17. The center 15 b of the second through hole 18 is provided on one straight line 16. The center 15b of the second through-hole 18 is longer than the distance R from the midpoint 14 of the radius 12 to the arc-shaped center 15 that is the radius of the radius 12, and the hole diameter of the first through-hole 17 intersects with the hole diameter. In addition, the copper plate 13 is positioned at a distance B from the center 15a of the first through-hole 17 that can maintain and maintain the strength of the copper plate 13. That is, the center 15b of the second through hole 18 is located at a distance (A + B) from the midpoint 14 of the radius 12.

  This power module substrate 10 is adjacent to the first and second through-holes 17 and 18 and is third on a second straight line 19 extending in parallel with the outer edge of the straight side of the copper plate 13. The through-hole 20 has a center 15c. The distance from the outer edge of the second straight line 19 is equal to the distance A from the midpoint 14 of the corner radius 12 to the center 15a of the first through hole 17, and from the extended line of the outer edge of the side. The distance is shorter than the distance A ′ to the center 15 a of the first through hole 17 (A <A ′). The center 15 c of the third through-hole 20 is a distance from the center 15 b of the first through-hole 17 to the center 15 b of the second through-hole 18 from the center 15 b of the second through-hole 18. It is the position of distance B. The distance A from the outer edge of the side of the second straight line 19 varies depending on the hole diameter size, etching accuracy, and the like of the third through-hole 20 as in the case of the first through-hole 17, but the third through-hole 20 And a distance between the outer edges of the copper plate 13 so as to be close to each other while maintaining the strength.

  The power module substrate 10 is provided at one corner of the copper plate 13 on the second straight line 19 extending in parallel with the outer edge of the side of the copper plate 13 and at each other corner. Centers 15 d of the plurality of fourth through holes 21 are provided between the distances X between the centers 15 c of the third through holes 20. The center 15d of the fourth through-hole 21 is an inter-pitch distance at which an integer number is obtained with a distance closest to the distance between the center 15a of the first through-hole 17 and the center 15c of the third through-hole 20. Z position. The center 15d of the fourth through hole 21 is the position of the pitch distance Z in each direction when the outer dimensions of the copper plate 13 are different in the vertical direction and the horizontal direction. Further, the fourth through hole 21 differs from the fourth through hole 21 and the side of the copper plate 13, although it differs depending on the hole size and etching accuracy of the fourth through hole 21 as in the case of the third through hole 20. The distance between the outer edges of the part is such that the copper plate 13 can be brought close to the position while maintaining the strength. Also,

  The distance X between the centers 15c of the third through holes 20 provided at one corner of the copper plate 13 on the second straight line 19 and the other corner is when the outer dimension of the copper plate 13 is W. Further, it can be obtained by the following formula 1.

  Further, the power module substrate 10 is parallel to the second straight line 19 on the center side of the copper plate 13 with respect to the second straight line 19 and from the second straight line 19 to the center 15b of the second through hole 18. A center 15d of a plurality of fifth through holes 23 is provided on a third straight line 22 extending to a position shorter than the distance. The center 15d of the fifth through hole 23 is located between the center 15c of the third through hole 20 and the center 15d of the fourth through hole 21 and between the centers 15d of the adjacent fourth through holes 21. However, it has a staggered position between them. Note that the distance between the second straight line 19 and the third straight line 22 is such that the hole diameter of the fifth through hole 23 does not intersect the hole diameter of the third through hole 20 or the fourth through hole 21. The copper plate 13 is provided at a position where the strength can be kept close.

  The first, second, and third straight lines 16, 19, and 22 described above are not lines that are actually drawn on the copper plate 13, but the first to fifth through holes 17, 18, 20, and 21. , 23 imaginary lines for specifying the positions of the centers 15a to 15e. Similarly, the center point 14 of the arc-shaped round 12, the arc-shaped center 15 of the round 12, and the centers 15 a to 15 e of the first to fifth through holes 17, 18, 20, 21, 23 are actually copper plates. 13 is not a point written on 13 but a virtual point for specifying each position.

  The power module substrate 10 can be provided with large arc-shaped rounded corners 12 at the corners of the copper plate 13, and the corners of the ceramic substrate 11 close to the corners of the copper plate 13 by applying a cooling cycle to the power module substrate 10. Even if the thermal stress concentrates on the portion, the residual stress at the joint portion of the copper plate 13 can be dispersed, and cracks occurring at the ceramic substrate 11 portion adjacent to the corner portion of the copper plate 13 and strength reduction can be prevented. be able to. Further, the power module substrate 10 is provided with arc-shaped rounds 12 at the corners of the copper plate 13, and the first through holes 17 and the second through holes 18 provided at the corners of the copper plate 13 from the corners of the copper plate 13. Even if it becomes the center side, the copper plate 13 includes the third and fourth through holes 20 and 21 provided at predetermined intervals in the side portion of the copper plate 13 and the fifth through hole 23 provided in a staggered shape therebetween. Since the residual stress of the ceramic substrate 11 portion adjacent to the edge of the copper plate 13 side can be dispersed, cracks generated in the side portion of the ceramic substrate 11 and strength are provided. Decline can be prevented.

  The diameters of the first to fifth through holes 17, 18, 20, 21, and 23 of the power module substrate 10 are not particularly limited in size, and also depend on the etching processing accuracy. However, all should be substantially the same size. The through-holes provided in the copper plate 13 are processed using an etching mask having the same hole diameter, so that a hole diameter with high processing accuracy can be efficiently produced, and when a thermal cycle is added to the power module substrate Residual stress generated in the ceramic substrate portion joined to the outer peripheral portion of the concentrated copper plate 13 can be effectively prevented over the entire circumference by the same hole diameter provided in the outer peripheral portion of the copper plate 13.

  The first to fifth through-holes 17, 18, 20, 21, and 23 of the power module substrate 10 are formed by directly bonding a whole-surface copper plate in which no pattern is formed on both main surfaces of the ceramic substrate 11, After heat-bonding by the metal brazing material bonding method, it is preferable that the holes are formed by etching each of the entire copper plates on both main surfaces. The entire copper plate bonded to both main surfaces of the ceramic substrate 11 is provided with the above first to fifth through holes 17, 18, 20, 21, 23 at the time of etching, and has an arc-shaped round shape 12 at the corner. A desired circuit pattern or a solid copper plate 13 is provided. The power module substrate 10 can be easily provided with first to fifth through holes 17, 18, 20, 21, 23 at desired positions close to the outer periphery of the desired copper plate 13. Residual stress generated in the ceramic substrate 11 portion close to the outer periphery can be prevented over the entire circumference.

  In the power module substrate 10 described above, a semiconductor element mounted on a predetermined copper plate 13 in a circuit pattern is electrically connected to another predetermined copper plate 13 through a bonding wire, and the other copper plate 13 is further electrically connected. It is in electrical continuity with the outside via. The power module substrate 10 can transmit high heat generated by flowing a large current to the semiconductor element to the solid copper plate 13 on the back surface through the ceramic substrate 11, and further radiate heat from the solid copper plate 13. I have to. In the power module substrate 10, the thickness of the copper plate 13 is increased in order to allow a large current to flow through the copper plate 13, and the copper plate 13 is joined to each of the two main surfaces of the ceramic substrate 11. In order to prevent the occurrence of warping due to the difference in thermal expansion coefficient between the ceramic substrate 11 and the copper plate 13, the thickness of the solid copper plate 13 on the back surface is the same.

  The power module substrate of the present invention is mounted with a semiconductor element that generates a large amount of heat through which a high-voltage current flows. For example, the power module substrate can be used as a power module substrate for use in an inverter, an automobile part, or the like. Can do.

  10: Power module substrate, 11: Ceramic substrate, 12: Earl, 13: Copper plate, 14: Midpoint, 15, 15a, 15b, 15c, 15d, 15e: Center, 16: First straight line, 17: First Through hole, 18: second through hole, 19: second straight hole, 20: third through hole, 21: fourth through hole, 22: third straight hole, 23: fifth through hole

Claims (3)

In each of the main surfaces of the quadrangular ceramic substrate, in the power module substrate that joins one or more copper plates having arc-shaped rounded corners,
Centered on a first straight line connecting the midpoint of the rounded corner of the copper plate corner and the center of the arc shape, the distance from the midpoint of the round is shorter than the distance to the center of the arc shape A first through hole to be
Provided on the first straight line extending from the center of the radius of the corner of the copper plate and the center of the first through-hole, the distance from the center of the radius to the center of the arc shape A second through hole centered at a position longer than the distance of
Provided on a second straight line adjacent to the first and second through-holes and extending in parallel with a straight side outer edge of the copper plate, from the side outer edge to the second straight line; The distance is equal to the distance from the center of the radius to the center of the first through hole, and is shorter than the distance from the extending line of the outer edge of the side portion to the center of the first through hole. A third through hole centered at a position where the distance from the center of the two through holes is the same as the distance between the centers of the first and second through holes;
A plurality are provided between the center of the third through hole provided at one corner of the copper plate on the second straight line extending in parallel with the outer edge of the side of the copper plate and the other corner. A fourth through hole centered at a position where the distance between the center of the first through hole and the distance between the centers of the third through holes is a distance between adjacent centers;
A third straight line extending parallel to the second straight line on the center side of the copper plate from the second straight line and extending to a position shorter than the distance from the second straight line to the center of the second through hole. A plurality of elements are provided on the top and centered on a position where a staggered structure is formed between the center of the third through hole and the center of the fourth through hole and between the centers of the adjacent fourth through holes. 5. A power module substrate having 5 through holes.   The power module substrate according to claim 1, wherein the first to fifth through holes have substantially the same diameter.   3. The power module substrate according to claim 1, wherein the first to fifth through holes are holes formed by etching after joining the copper plate to the ceramic substrate. Power module substrate.

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