JP5131204B2 - Power module substrate manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a power module substrate used in a semiconductor device that controls a large current and a high voltage.

In general, a power module for supplying power among semiconductor elements has a relatively high calorific value. As this power module substrate, for example, as shown in Patent Document 1, AlN, Al ₂ O ₃ , Si ₃ N _4. A metal plate such as an aluminum plate joined to a ceramic substrate made of SiC or the like via a brazing material such as an Al-Si type is used. This metal plate becomes a circuit layer by forming a circuit having a desired pattern by an etching process in a later step. After etching, an electronic component (power element such as a semiconductor chip) is mounted on the surface of the circuit layer via a solder material to form a power module.

  In addition, as shown in Patent Document 2, for example, this metal plate is a molten brazing material by interposing a foil-like brazing material between the ceramic substrate and the metal plate and pressing in the stacking direction in a high temperature state. To be bonded to the ceramic substrate.

JP 2004-356502 A JP 2007-53349 A

When the ceramic substrate and the metal plate are bonded as described above, if the amount of the brazing material is insufficient, a portion where the brazing material is insufficient between the metal plate and the ceramic substrate is generated, or the bonded portion is caused by warping of the ceramic substrate. There is a possibility that problems such as peeling off and peeling off of a circuit layer formed in a subsequent process may occur. Further, the brazing material does not adhere to the entire surface of the metal plate, and there is a possibility that the metal plate cannot be reliably bonded to the ceramic substrate. Furthermore, if bonding is not sufficient, peeling may occur under temperature cycle conditions that repeat temperature changes.
On the other hand, when a sufficient amount of brazing material is used, as shown in Patent Document 2, surplus of the molten brazing material adheres to the surface of the metal plate via the ceramic substrate and the side surface of the metal plate, and this surface There is a problem that the adhesion of the bonding wire of the electronic component to be fixed thereafter is impaired. In addition, the ceramic substrate may be damaged when the excess brazing material is removed.

  The present invention has been made in view of such circumstances. The metal plate and the ceramic substrate can be reliably bonded to each other, and adhesion of the brazing material to the circuit surface is prevented. It aims at providing the manufacturing method of the board | substrate for power modules which can remove a brazing material.

  The present invention is a method for manufacturing a power module substrate having a bonding step of bonding a metal plate having a smaller area than the ceramic substrate to the surface of the ceramic substrate, the bonding step including the brazing material A laminate in which a ceramic substrate and the metal plate are laminated is pressed in the thickness direction while being heated between two pressure plates having a larger area than the ceramic substrate and covering the entire surface of the ceramic substrate and the metal plate. In the joining step, the ceramic substrate and the metal plate are arranged so that the end portions of the corners of the metal plate substantially coincide with the sides of the ceramic substrate.

  According to this manufacturing method, a space sandwiched between each surface of each pressure plate is formed in a portion where the side of the ceramic substrate constituting the laminate and the tip of the corner of the metal plate substantially coincide. The The corners of the metal plate are arranged in this space, and the brazing material that is heated and melted in the joining process and pushed out between the pressed ceramic substrate and the metal plate easily flows into the space. Can be a wax pool. Note that the sides of the ceramic substrate can be linear, curved, or the like.

  Further, the present invention is a method for manufacturing a power module substrate, comprising a bonding step of bonding a metal plate having a smaller area than the ceramic substrate to the surface of the ceramic substrate, wherein the metal plate has a substantially rectangular shape. The ceramic substrate has a substantially rectangular shape having a notch formed by cutting off one corner and a diagonal opposite to the notch, and the joining step is performed with a brazing material interposed therebetween. A laminate in which a ceramic substrate and the metal plate are laminated is pressed in the thickness direction while being heated between two pressure plates having a larger area than the ceramic substrate and covering the entire surface of the ceramic substrate and the metal plate. In this joining step, the metal plate and the ceramic substrate are positioned by overlapping one corner of the metal plate and the diagonal portion of the ceramic substrate. Rice advance, substantially match other corners of the metal plate to the side portion of the notch portion of the ceramic substrate.

  That is, when joining a substantially rectangular metal plate and a ceramic substrate, the metal plate and the ceramic substrate are positioned at one corner in the joining process, and the corner of the metal plate is a ceramic substrate at the diagonal portion. It almost matches the side of the notch. Excess molten brazing material is likely to leak from the corners of the metal plate, and a brazing pool having a thickness equal to the total thickness of the ceramic substrate and the metal plate is present between the pressure plates near the corner and the notch. Since it is formed, surplus brazing material can be concentrated and flow into the brazing pool. Further, in the bonding process, the metal plate is heated and thermally expanded in a state where the ceramic substrate is positioned at the corner facing the notch, so that the corner does not protrude from the notch in the unheated state, In the heated state, the corner portion can be substantially coincident with or protruded from the notch portion.

  According to the method for manufacturing a power module substrate of the present invention, when joining the metal plate and the ceramic substrate, the surplus brazing material that has melted and flowed out between the metal plate and the ceramic substrate is removed from the ceramic substrate. It can be collected in a wax reservoir formed in the vicinity of the notch. Since the surplus brazing material can be concentrated in the brazing pool, the outflow of the brazing material from other parts can be reduced, and the surplus brazing material removal operation can be reduced.

  Further, since the brazing pool is formed between the pressure plates that are in contact with the entire surface of the metal plate, adhesion of the brazing material to the surface of the metal plate can be suppressed. Furthermore, since the surplus brazing material collected in the brazing pool is sandwiched between the pressure plates, it does not protrude from the thickness of the laminate. In other words, even if the surplus brazing material solidifies in the brazing pool, the thickness is smaller than the thickness of the laminate, so that the laminate placed on the plane does not tilt, and the workability and processing accuracy in the subsequent process are improved. A decrease can be prevented.

  Therefore, by using a sufficient amount of brazing material, the metal plate can be securely bonded to the ceramic substrate, and the removal of excess brazing material can be prevented by preventing the occurrence of galling that can reduce workability and processing accuracy. It is possible to obtain a power module substrate that can prevent the ceramic substrate from being damaged during work.

It is a longitudinal cross-sectional view which shows the example of whole structure of the power module manufactured using the manufacturing method which concerns on this invention. It is a top view which shows an example of the laminated body used as the board | substrate for power modules. It is sectional drawing which follows the III-III line of FIG. It is sectional drawing which shows the other example of the laminated body used as the board | substrate for power modules.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a power module 10 in which a power module substrate according to the present invention is used. The power module 10 is bonded to the power module substrate 20 having a circuit pattern formed on the surface thereof, an electronic component 30 such as a semiconductor chip mounted on the surface of the power module substrate 20, and the back surface of the power module substrate 20. The cooler 33 is configured.

  The electronic component 30 is bonded onto the circuit pattern of the power module substrate 20 by a solder material 31 such as Sn—Ag—Cu, Zn—Al, or Pb—Sn, and the circuit terminal portion is made of aluminum. They are connected by bonding wires (not shown). A plating film 32 such as nickel plating is formed on the surface of the circuit pattern.

  The cooler 33 is formed by extrusion molding of an aluminum alloy, and a large number of flow paths 33a are formed along the length direction for circulating cooling water. The cooler 33 and the power module substrate 20 are joined by brazing, soldering, bolts or the like.

  The power module substrate 20 is formed by processing a laminated body 40 in which metal plates 43 and 44 are joined to both surfaces of a ceramic substrate 41 by a brazing material 42. That is, the power module substrate 20 is formed by forming a predetermined circuit pattern in the laminate 40 and performing processing such as dividing into pieces as needed.

The ceramic substrate 41 is formed using, for example, a nitride ceramic such as AlN (aluminum nitride) or Si ₃ N ₄ (silicon nitride) or an oxide ceramic such as Al ₂ O ₃ (alumina) as a base material.
The metal plate 43 bonded to the surface of the ceramic substrate 41 is a circuit layer metal plate that becomes a circuit pattern by an etching process, and is formed of pure aluminum or an aluminum alloy.
The metal plate 44 bonded to the back surface of the ceramic substrate 41 is a metal plate for heat dissipation layer to which the cooler 33 is bonded, and is formed of pure aluminum having a purity of 99.0 wt% or more.
The brazing material 42 is made of Al—Si, Al—Ge, Al—Cu, Al—Mg, Al—Mn, or the like.

The circuit pattern of the power module 10 is formed by etching the metal plate 43 for the circuit layer. Further, the metal plate 44 for the heat dissipation layer is also formed in a required size and shape by etching. After the circuit is formed, a plating film 32 is formed on the surface of the circuit pattern.
Further, the power module 10 is manufactured by joining the cooler 33, soldering the electronic component 30, wire bonding, and the like to the power module substrate 20 on which the circuit pattern is formed.

  Here, the joining process which joins the metal plates 43 and 44 between the pressure plates 45 on the front and back surfaces of the ceramic substrate 41 will be described. In the joining step, as shown in FIG. 2, a laminated body 40 in which metal plates 43 and 44 are laminated with a brazing material 42 interposed on both surfaces of the ceramic substrate 41 is used to connect the ceramic substrate 41 and the metal plates 43 and 44. The pressure is applied in the thickness direction while heating between the two pressure plates 45 covering the entire surface.

  The metal plates 43 and 44 are rectangular plates having a thickness of 250 μm, a length of 138 mm, and a width of 107 mm. The ceramic substrate 41 is larger than the metal plates 43 and 44, and is a substantially rectangular plate having a thickness of 635 μm, a length of 140 mm, and a width of 108 mm, and a corner portion is cut into a length of 3 mm and a width of 3 mm. And a diagonal portion 41b opposite to the cutout portion 41a. The pressure plate 45 is a plate member having a larger plane than the ceramic substrate 41 and the metal plates 43 and 44, and is arranged so as to cover the entire surface of the ceramic substrate 41 and the metal plates 43 and 44 in the bonding step. Further, as shown by the chain line in FIG. 2, the corners 43b, 44b of the metal plates 43, 44 before heating are inward from the side of the notch 41a of the ceramic substrate 41 by a distance s (maximum 0.1 mm). It arrange | positions on the ceramic substrate 41 which entered. Then, when the metal plates 43 and 44 are heated and thermally expanded, the corner portions 43b and 44b substantially coincide with or slightly protrude from the side portion of the cutout portion 41a of the ceramic substrate 41.

  FIG. 3 is a partial cross-sectional view taken along line III-III in FIG. As shown in these drawings, in the joining process, the metal plates 43 and 44 and the ceramic substrate 41 are arranged so that the end portions of the corners of the metal plates 43 and 44 substantially coincide with the sides of the ceramic substrate 41. Has been.

  More specifically, the metal plates 43 and 44 and the ceramic substrate 41 are positioned by overlapping one corner 43a and 44a of the metal plates 43 and 44 with the diagonal portion 41b of the ceramic substrate 41. . In this state, the notch 41 a is provided so that the tips of the corners 43 b and 44 b facing the corners 43 a and 44 a of the metal plates 43 and 44 substantially coincide with the sides of the notch 41 a of the ceramic substrate 41. . Thereby, a space (wax pool 46) surrounded by each surface 45a of each pressure plate 45 and the end surface 41c of the cutout portion 41a of the ceramic substrate 41 is formed.

  Since the corners 43b and 44b are close to the notch 41a, the brazing material 42 leaking from the corners 43b and 44b can easily flow into the brazing reservoir 46. Therefore, it is preferable that the tips of the corners 43b and 44b of the metal plates 43 and 44 at the time of brazing substantially coincide with the end surface of the notch 41a, but they may slightly protrude from the notch 41a.

  Thus, the laminated body 40 which laminated | stacked the ceramic substrate 41 and the metal plates 43 and 44 is arrange | positioned between the pressurization plates 45, and it is thickness direction in the heat processing furnace hold | maintained in inert gas atmosphere, reducing gas atmosphere, or vacuum atmosphere. The metal plates 43 and 44 are brazed to the ceramic substrate 41 by heating in a state of being pressurized to melt the brazing material 42.

  In this joining process, since the brazing material 42 is a sufficient amount for joining, the ceramic substrate 41 and the metal plates 43 and 44 are securely joined, but the compressed ceramic substrate 41 and the metal plates 43 and 44 are joined together. Excess brazing material 42a leaks out from between the two. At this time, the surplus brazing material 42a can be leaked to the entire end faces 43c, 44c of the metal plates 43, 44. However, since the metal plates 43, 44 are rectangular, they are likely to leak from the corners. Therefore, the excess brazing material 42a can be leaked mainly from the corner portions 43a and 44a to the brazing pool 46, and leakage at other portions can be reduced.

  The brazing material 42 (excess brazing material 42a) leaked into the brazing pool 46 is held between the pressure plates 45 outside the notch 41a as shown in FIG. Therefore, as shown in FIG. 3, the thickness of the surplus brazing material 42a in the brazing pool 46 is regulated by each pressure plate 45, so that it does not have a hump shape, and the laminated body 40 includes the surplus brazing material 42a. Formed. Since the flat laminated body 40 can be stably placed on a flat surface, a subsequent process (for example, etching or printing for forming a circuit pattern) is performed on the laminated body 40 without removing the excess brazing material 42a. Etc.).

  If the leaked and solidified brazing material 42 adheres to the outer surfaces of the metal plates 43 and 44, when the brazing material 42 is removed, bending stress is generated in the metal plates 43 and 44, and the ceramic substrate 41 is cracked. Although there is a possibility of causing damage, since the metal plates 43 and 44 are held between the pressure plates 45 in the laminating process of the present embodiment, the surplus brazing material 42 a does not adhere to the outer surfaces of the metal plates 43 and 44. . Therefore, it is possible to easily remove the surplus brazing material 42a without applying a strong load to the metal plates 43 and 44 and suppressing the breakage of the ceramic substrate 41.

  As described above, according to the method for manufacturing a power module substrate of the present invention, surplus brazing material can be collected in the brazing pool, so that leakage of brazing material in other parts can be reduced, and surplus brazing material The removal work can be facilitated, and the generation of a thick bump is suppressed, and the ceramic substrate can be prevented from being damaged when the excess brazing material is removed.

In addition, this invention is not limited to the thing of the structure of the said embodiment, In a detailed structure, it is possible to add a various change in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the metal plates 43 and 44 are bonded to both surfaces of the ceramic substrate 41. However, the metal plate 43 may be bonded only to one surface of the ceramic substrate 41 as shown in FIG.
Further, since the cutout portion of the ceramic substrate only needs to be configured so that the corner portion of the metal plate substantially coincides with the side portion thereof, it may be formed in, for example, a curved shape, a bent line shape, etc. It is not limited to linear form like.

DESCRIPTION OF SYMBOLS 10 Power module 20 Power module board | substrate 30 Electronic component 31 Solder material 32 Plating film 33 Cooler 33a Flow path 40 Laminate body 41 Ceramic substrate 41a Notch part 41b Diagonal part 41c End surface 42 Brazing material 42a Excess brazing material 43, 44 Metal plate 43a, 44a Corners 43b, 44b Corners 43c, 44c End face 45 Pressure plate 45a Surface 46 Brazing pool

Claims (2)

A method for manufacturing a power module substrate, comprising a bonding step of bonding a metal plate having a smaller area than the ceramic substrate to the surface of the ceramic substrate,
In the joining step, a laminate obtained by laminating the ceramic substrate and the metal plate with a brazing material interposed between them is added two sheets of a larger area than the ceramic substrate and covering the entire surface of the ceramic substrate and the metal plate. It is a process of pressurizing in the thickness direction while heating between pressure plates,
In the bonding step, the ceramic substrate and the metal plate are arranged so that the end portions of the corners of the metal plate substantially coincide with the side portions of the ceramic substrate. Production method. A method for manufacturing a power module substrate, comprising a bonding step of bonding a metal plate having a smaller area than the ceramic substrate to the surface of the ceramic substrate,
The metal plate has a substantially rectangular shape;
The ceramic substrate has a substantially rectangular shape having a notch formed by cutting off one corner and a diagonal facing the notch,
In the joining step, a laminate obtained by laminating the ceramic substrate and the metal plate with a brazing material interposed between them is added two sheets of a larger area than the ceramic substrate and covering the entire surface of the ceramic substrate and the metal plate. It is a process of pressurizing in the thickness direction while heating between pressure plates,
In the joining step, the metal plate and the ceramic substrate are positioned by overlapping one corner portion of the metal plate and the diagonal portion of the ceramic substrate, and the notch portion of the ceramic substrate is positioned. A method for manufacturing a power module substrate, characterized in that the other corners of the metal plate substantially coincide with the sides.

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