JP6287216B2 - Manufacturing method of power module substrate with heat sink - Google Patents

Description

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

  As a power module substrate with a heat sink, a circuit layer such as an aluminum plate is bonded to one surface of a ceramic substrate serving as an insulating layer, and an aluminum-based material is connected to the other surface of the ceramic substrate via a heat dissipation layer such as an aluminum plate. The thing of the structure where the heat sink was joined is known.

This type of power module substrate is manufactured by joining a circuit layer or the like to a ceramic substrate by brazing, but at this time, there is a problem that warpage occurs due to a difference in thermal expansion and contraction of each member.
Therefore, in Patent Document 1, in order to reduce the amount of warpage of the power module substrate, a laminated body in which each member is laminated via a brazing material is formed, and the laminated body is made up of metal plates for circuit layers or heat dissipation. It has been proposed that a plurality of layer metal plates are stacked so as to be adjacent to each other via a cushion sheet, and brazing and joining is performed by heating while pressing in the stacking direction in that state. In this case, it is described that the direction of stress causing warping is reversed between adjacent laminates, and the stresses in the opposite direction are partially offset by mutual interference, thereby reducing the amount of warping. .

JP 2012-49437 A

  When the heat sink is joined to the power module substrate described in Patent Document 1 by brazing, the resulting power module substrate with a heat sink is warped because it is joined at a high temperature.

On the other hand, in order to improve the heat dissipation performance, a power module substrate with a heat sink in which a ceramic substrate and a heat sink are directly bonded without using a heat dissipation layer having a buffering effect has been used.
In a power module substrate with a heat sink in which this ceramic substrate is directly bonded to the heat sink, since the buffering effect by the heat dissipation layer cannot be obtained, the warping at the time of bonding tends to be large, resulting in cracks in the ceramic substrate. there were. Further, in the configuration in which the ceramic substrate and the heat sink are directly bonded, it is impossible to completely prevent the ceramic substrate from cracking even if a method as described in Patent Document 1 is used.

  The present invention has been made in view of such circumstances, and a power module substrate with a heat sink that can reduce warpage that occurs during the manufacture of a power module substrate with a heat sink and can prevent the occurrence of cracks in the ceramic substrate. The purpose is to provide.

The present invention is a method of manufacturing a power module substrate with a heat sink, wherein a heat sink having a larger area than the ceramic substrate is disposed on one surface of the ceramic substrate, and a circuit layer is disposed on the other surface, Al—Si, Al—Ge, Al—Cu, Al—Mg, and Al—Mn brazing materials (excluding Al—Cu—Mg) are interposed on both sides of the ceramic substrate. A laminated body formed by laminating a circuit layer and a heat sink is formed, and the ceramic substrate, the circuit layer, and the heat sink are brazed by heating while pressing in the laminating direction in a state where a plurality of the laminated bodies are stacked. has a brazing step of attaching, in the brazing step, the laminate surfaces on each of the circuit layers are stacked so as to face said Hitoshi The back of the click, the reinforcing plate having a higher flexural rigidity than the heat sink, characterized in that the pressurized while being stacked.

In a power module substrate with a heat sink having a structure in which a ceramic substrate is directly bonded on a heat sink, the plane area of the heat sink is larger than that of the ceramic substrate. Since the circuit layer disposed on the ceramic substrate is formed of a material having a small thickness and low bending rigidity such as pure aluminum, the circuit layer follows the warp of the heat sink and the ceramic substrate.
For this reason, in the brazing process, if the ceramic substrate and the heat sink are cooled in a joined state, warpage is likely to occur with the circuit layer side being convex due to the difference in thermal expansion and contraction. Further, since the heat sink has a larger flat area than the ceramic substrate and the heat sink protrudes beyond the peripheral edge of the ceramic substrate, stress tends to concentrate on the peripheral portion of the ceramic substrate, and the ceramic substrate is likely to crack at the peripheral portion.

Therefore, as one method for reducing warpage and preventing cracking of the ceramic substrate, a method of joining a plurality of laminated bodies in a stacked state (in a normal lamination) can be considered. However, when joining by forward lamination, the heat sink of the other laminate is stacked on the circuit layer of one laminate, so that the heat sink is pressed in the lamination direction by a circuit layer with a small plane area. The load concentrates on the surface, further promoting warpage. For this reason, it was easy to produce a crack in the ceramic substrate whose toughness is smaller than a heat sink.
Therefore, in the present invention, the back surface of the heat sink is reinforced by a reinforcing plate having a bending rigidity equal to or higher than that of the heat sink, so that the load is uniformly pressed against the entire back surface of the heat sink. Thereby, the curvature which arises in the board | substrate for power modules with a heat sink can be reduced, and the crack of a ceramic substrate can be prevented reliably.

  ADVANTAGE OF THE INVENTION According to this invention, the curvature which arises at the time of manufacture of the board | substrate for power modules with a heat sink can be suppressed, and generation | occurrence | production of the crack of a ceramic substrate can be prevented.

It is sectional drawing which shows the power module using the board | substrate for power modules with a heat sink. It is a side view explaining 1st Embodiment (circuit layer alignment) of the manufacturing method of the board | substrate for power modules with a heat sink which concerns on this invention. It is a side view explaining 2nd Embodiment (heat sink matching) of the manufacturing method of the board | substrate for power modules with a heat sink which concerns on this invention. It is a side view explaining the manufacturing method (forward lamination) of the conventional substrate for power modules with a heat sink. It is sectional drawing explaining the curvature of the board | substrate for power modules with a heat sink.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A power module substrate 1 with a heat sink manufactured by the method for manufacturing a power module substrate with a heat sink according to the present invention is disposed on a ceramic substrate 2 and one surface of the ceramic substrate 2 as shown in FIG. A heat sink 3 and a circuit layer 4 disposed on the other surface of the ceramic substrate 2 are provided, and an electronic component 5 such as a semiconductor chip is mounted on the surface of the circuit layer 4 of the power module substrate 1 with a heat sink. Thus, the power module 11 is manufactured.

The ceramic substrate 2 is formed of oxide ceramics such as Al ₂ O ₃ (alumina) or nitride ceramics such as AlN (aluminum nitride) or Si ₃ N ₄ (silicon nitride). And the thickness of the ceramic substrate 2 is set in the range of 0.2 mm-1.5 mm. In the present embodiment, Al ₂ O ₃ is used and the thickness is set to 0.38 mm.
The circuit layer 4 is made of aluminum having a purity of 99% by mass or more, and in the JIS standard, aluminum in the 1000s, particularly 1N90 (purity 99.9% by mass or more: so-called 3N aluminum) or 1N99 (purity 99.99% by mass). Above: so-called 4N aluminum) can be used, and its thickness is set to 0.2 mm to 3.0 mm. In addition to aluminum, aluminum alloy, copper, or copper alloy can also be used. In this embodiment, the circuit layer 4 is an aluminum plate made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more, and its thickness is 0.9 mm.

  The heat sink 3 is formed of an aluminum alloy. For example, a material having a Young's modulus (longitudinal elastic modulus) of 70 MPa or more, such as an A1050, A3003, A5052, A6063, or A7075 alloy, can be used. The plane area is set larger than that of the ceramic substrate 2. Here, the heat sink 3 is a metal part intended to lower the temperature by heat dissipation, such as a plate-like heat sink, a cooler in which refrigerant flows, an air-cooled heat sink with fins formed therein, a heat pipe, etc. Is included. In the present embodiment, the heat sink 3 is a cooler formed of an aluminum alloy of A1050, and the top plate portion of the cooler is joined to the ceramic substrate 2 to constitute the power module substrate 1 with a heat sink. Yes. In addition, the thickness of the top plate portion of the cooler is set to 3 mm.

  The ceramic substrate 2 and the circuit layer 4, and the ceramic substrate 2 and the heat sink 3 are joined by brazing. As the brazing material, an alloy such as Al-Si, Al-Ge, Al-Cu, Al-Mg, or Al-Mn is used.

  The electronic component 5 constituting the power module 11 is formed on the surface of the circuit layer 4 with Ni plating (not shown), Sn—Ag—Cu, Zn—Al, Sn—Ag, Sn— Bonding is performed using a solder material such as Cu, Sn—Sb, or Pb—Sn. Reference numeral 51 in FIG. 1 indicates the solder joint layer. The electronic component 5 and the terminal portion of the circuit layer 4 are connected by a bonding wire (not shown) made of aluminum.

Next, the manufacturing method of the board | substrate for power modules with a heat sink of 1st Embodiment is demonstrated.
As shown in FIG. 2, a 4N aluminum plate serving as a circuit layer 4 is laminated on the other surface of the ceramic substrate 2 via a brazing material (not shown), and a heat sink 3 and By laminating the aluminum alloy (A1050) plate to be laminated via a brazing material (not shown), a plurality of laminated bodies 10 formed by laminating the circuit layer 4, the ceramic substrate 2 and the heat sink 3 are formed (in FIG. Two bodies 10 are formed).
Then, in a state where these plural sets of laminated bodies 10 are stacked, as shown by white arrows in FIG. 2, the ceramic substrate 2 and the 4N aluminum plate (circuit layer 4) are heated while being pressed in the laminating direction. And an aluminum alloy (A1050) board (heat sink 3) is joined (brazing process).

  In this brazing step, each laminate 10 is pressed in the stacking direction using, for example, a jig 112 constituted by two pressing plates 110 and columns 111 provided at the four corners thereof as shown in FIG. The pressure is applied by placing the stacked bodies 10 in a state of being stacked between the pressure plates 110. At this time, each laminated body 10 is laminated with the circuit layers 4 facing each other, and the back surface of each heat sink 3 is reinforced over the entire surface in a state where the reinforcing plate 6 is overlapped on the back surface of the heat sink 3 of each laminated body 10. In addition, a carbon graphite sheet 7 is disposed between the circuit layers 4 of the respective laminates 10 in order to avoid joining each other due to bleeding of the brazing material during brazing.

For the reinforcing plate 6, a material having heat resistance and a bending rigidity equal to or higher than the bending rigidity of the heat sink 3 can be suitably used. In this embodiment, the reinforcing plate 6 is formed of an isotropic graphite material (G347 manufactured by Tokai Carbon Co., Ltd.) having a thickness of 20 mm, and the characteristic value thereof is a coefficient of thermal expansion of 5.5 × 10 ⁻⁶ / K, thermal conductivity is 116 W / mK, Young's modulus is 10.8 GPa, Shore hardness is 58 HS, and Vickers hardness at a thickness of 20 mm is 424 HV.

  Then, the circuit layers 4 of the laminates 10 are laminated to face each other, and the reinforcing plate 6 is laminated on the back surface of the heat sink 3 of each laminate 10, and the stacking direction is increased to 0.1 MPa or more and 10 MPa or less. By heating at 580 ° C. or more and 660 ° C. or less while pressing, each member is brazed and the power module substrate 1 with a heat sink is manufactured.

  Note that the two pressure plates 110 of the jig 112 are made of a stainless steel material, and nuts 113 are fastened to columns 111 having screws cut at both ends so as to sandwich the pressure plate 110. Further, an urging means 115 such as a spring for urging the pressurizing plate 110 downward is provided between the top plate 114 supported by the column 111 and the pressurizing plate 110, and the stacking body 10 is applied in the stacking direction. The pressure is adjusted by tightening the biasing means 115 and the nut 113.

  Further, in the brazing process, the heat sink 3 is greatly thermally expanded and contracted with respect to the ceramic substrate 2 to be brazed, so that thermal stress is generated. As shown, there is a warp in which the circuit layer 4 side is convex. However, in this embodiment, since the back surface of the heat sink 3 of the laminate 10 is pressed through the reinforcing plate 6 over the entire surface, the load is made uniform over the entire back surface of the heat sink 3 and pressed. It is possible to reduce the warpage that occurs in the power module substrate 1 with a heat sink. Therefore, cracking of the ceramic substrate 2 due to warping can be reliably prevented.

  Although the carbon material (isotropic graphite material) is used as the reinforcing plate 6 in the first embodiment, the same aluminum alloy plate as the plate material constituting the heat sink 3 may be used for the reinforcing plate 6. it can. Even in this case, it is possible to make the load uniform and press the entire back surface of the heat sink 3 of each laminated body 10, and the warp generated in the power module substrate 1 with a heat sink can be sufficiently reduced.

In the first embodiment, the heat sink 3 of each laminate 10 is reinforced by the reinforcing plate 6. However, like the manufacturing method of the second embodiment shown in FIG. By stacking the heat sinks 3 so as to face each other, the heat sinks 3 can also act as reinforcing plates that reinforce each other.
As shown in FIG. 3, when the laminated bodies 10 are laminated with the heat sinks 3 facing each other, the heat sinks 3 of the laminated bodies 10 are pressed against each other by the opposed heat sinks 3 having the same plane area. Therefore, the heat sinks 3 of the stacked bodies 10 reinforce each other, and the load can be made uniform and pressed against the entire back surface of each heat sink 3. For this reason, like the manufacturing method of 1st Embodiment, the board | substrate 1 for power modules with a heat sink which reduced curvature can be manufactured, without providing a separate reinforcement board.
Note that by applying boron nitride (BN) to the surface of the heat sink 3, brazing can be performed without bonding the heat sinks. Other configurations are the same as those of the first embodiment, and the same reference numerals are given and description thereof is omitted.

  In the first and second embodiments, the method of manufacturing the two power module substrates 1 with heat sinks by stacking the two stacked bodies 10 has been described. Brazing can also be performed in a stacked state. In this case, the circuit layers 4 or the heat sinks 3 of each laminate 10 are opposed to each other, and a plurality of laminates 10 are alternately laminated on the front and back, and the reinforcing plate 6 is attached to the portion where the heat sink 3 is exposed. Thus, warpage of each power module substrate 1 with a heat sink can be reduced, and cracking of the ceramic substrate 2 can be prevented. Furthermore, by stacking a plurality of laminated bodies and performing brazing, a plurality of power module substrates with heat sinks can be manufactured by a single bonding.

Next, examples and comparative examples performed for confirming the effects of the present invention will be described.
As an example, when the circuit layers 4 of the stacked bodies 10 are bonded to each other as shown in FIG. 2 (circuit layer matching), and the heat sinks 3 of the stacked bodies 10 are bonded together as shown in FIG. A sample of a power module substrate with a heat sink was manufactured when bonded in a state of facing each other (heat sink alignment). In addition, as a comparative example, a sample of a power module substrate with a heat sink was manufactured in the case where the laminated bodies 10 were joined in the order of stacked layers stacked in the same posture as illustrated in FIG. 4 (forward stacked).

Each sample is composed of a circuit layer made of 4N-Al having a thickness of 80 mm × 26 mm and a thickness of 0.9 mm, a ceramic substrate made of Al ₂ O _{3 having} a thickness of 84 mm × 30 mm and a thickness of 0.38 mm, and a thickness of 96 mm × 42 mm. A heat sink made of an A1050 aluminum alloy having a thickness of 2 to 4 mm was joined by an Al—Si brazing material. Further, the reinforcing plate used in “circuit layer matching” was formed of an isotropic graphite material (G347 manufactured by Tokai Carbon Co., Ltd.) having a thickness of 76.9 mm × 164 mm and a thickness of 20 mm. The bending rigidity of the reinforcing plate is sufficiently larger than the bending rigidity of the heat sink, and the bending rigidity of each member is as shown in Table 1 below. The bending rigidity is calculated by the product of the Young's modulus and the cross-sectional second moment of each material.

And the curvature amount Z which arose in the sample of the board | substrate for power modules with these heat sinks was evaluated, respectively. As shown in FIG. 5, the warpage amount Z is measured by setting the convex deformation on the circuit layer 4 side as a positive warpage amount, and measuring the change in flatness of the back surface of the heat sink 3 at a room temperature of 25 ° C. What was measured using the three-dimensional shape measuring machine was evaluated as a warpage amount Z. Moreover, the presence or absence of the crack of a ceramic substrate was evaluated by measuring the joining interface of a ceramic substrate and a heat sink with an ultrasonic flaw detector. The thing without a crack was evaluated as "(circle)", and the thing with a crack was evaluated as "*".
Table 2 shows the results.

  As can be seen from Table 2, in the samples of Example 1 and Example 2, the warpage amount Z could be significantly reduced as compared with the sample of Comparative Example 1 joined by forward lamination.

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, a method of joining using an active metal brazing material may be employed for brazing a copper circuit layer and a ceramic substrate. For example, an active metal brazing material (Ag-27.4 mass% Cu-2.0 mass% Ti) containing Ti, which is an active metal, is used, and a laminate of a copper circuit layer and a ceramic substrate is pressed. The circuit layer and the ceramic substrate can be joined by heating in a vacuum.

DESCRIPTION OF SYMBOLS 1 Power module board | substrate 2 with a heat sink Ceramic board | substrate 3 Heat sink 4 Circuit layer 5 Electronic component 6 Reinforcement board 7 Carbon graphite sheet 10 Laminate body 51 Solder joint layer 110 Pressure plate 111 Support | pillar 112 Jig 113 Nut 114 Top plate 115 Energizing means

Claims (1)

A method of manufacturing a power module substrate with a heat sink in which a heat sink having a larger plane area than the ceramic substrate is disposed on one surface of the ceramic substrate, and a circuit layer is disposed on the other surface,
Al—Si, Al—Ge, Al—Cu, Al—Mg, and Al—Mn brazing materials (excluding Al—Cu—Mg) are interposed on both sides of the ceramic substrate. Forming a laminate formed by laminating a circuit layer and a heat sink, and heating the ceramic substrate, the circuit layer, and the heat sink by applying pressure in the laminating direction in a state where a plurality of sets of the laminates are stacked. A brazing process for brazing,
In the brazing step, the laminated body is stacked such that the surfaces of the circuit layers face each other , and a pressure is applied in a state in which a reinforcing plate having higher bending rigidity than the heat sink is laminated on the back surface of the heat sink. A method for producing a power module substrate with a heat sink.

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