JP2015185679A - Board for power module and board for power module with heat sink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a board for power module excellent in heat dissipation performance, and a board for power module with heat sink.SOLUTION: In a board 10 for power module where a circuit layer 12 is provided on one side of a ceramic substrate 11, and a metal layer 13 composed of aluminum is brazed to the other side, the metal layer 13 is formed of an aluminum alloy having a thickness of 0.1 mm or more and less than 0.4 mm, containing 97 mass% or more and 99.95 mass% or less of Al, 0.1 mass% or more and 1.0 mass% or less of Fe, and 2.0 mass% or less of Mn, where the ratio Mn/Fe of Mn to Fe is in a range of 0.5 or more and 20 or less.

Description

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

  As a conventional power module substrate, for example, as disclosed in Patent Document 1 and Patent Document 2, a circuit board (circuit layer) such as an aluminum plate is bonded to one surface of a ceramic substrate serving as an insulating layer. A structure in which a metal plate (metal layer) such as an aluminum plate is bonded to the other surface of the ceramic substrate is known. And the board | substrate for power modules with a heat sink by which the heat sink made from an aluminum alloy or a copper alloy was joined to this metal layer is manufactured.

  In the power module substrate with a heat sink configured as described above, the purity of the metal plate is formed to 98.00% or more and 99.90% or less as shown in Patent Document 1, or as shown in Patent Document 2. Thus, by making the Fe concentration on the surface side opposite to the brazing surface with the ceramic plate in the metal layer to be 0.1 wt% or more, it is possible to improve the bonding reliability between the metal layer of the power module substrate and the heat sink. .

JP 2007-81202 A JP 2008-109933 A

  However, as shown in Patent Document 1 and Patent Document 2, when a metal layer is formed by bonding relatively low-purity aluminum or aluminum containing Fe to a ceramic substrate, it is opposite to the surface bonded to the ceramic substrate. Deterioration (seepage) may occur on the surface of the metal layer. If such surface alteration (exudation) occurs, voids are generated at the bonding interface between the ceramic substrate and the metal layer, which may reduce the bonding reliability between the ceramic substrate and the metal layer.

  This invention is made | formed in view of such a situation, and it aims at providing the board | substrate for power modules and the board | substrate for power modules with a heat sink excellent in joining reliability.

As a result of intensive studies, the present inventor has confirmed the following. When Fe is contained in an Al base material in an amount of more than 0.1% by mass, aluminum in the brazing material diffuses into the metal layer by brazing the ceramic substrate and the metal layer, thereby forming the metal layer. The Al—Fe-based precipitates precipitated in the alloy react with Si to partially melt the metal layer. It was confirmed that when this partial melting reaches the surface of the metal layer (surface opposite to the ceramic substrate), the surface is altered (seepage). Then, it was confirmed that voids at the bonding interface between the ceramic substrate and the metal layer increased when such surface alteration (seepage) occurred. In addition, the increase in voids reduces the bonding reliability between the ceramic substrate and the metal layer. Such surface alteration (seepage) and voids are more prominent when the thickness of the metal layer is thin, particularly when the thickness is less than 0.4 mm.
Therefore, the power module substrate of the present invention solved the problem by the following configuration.

  The present invention is a power module substrate in which a circuit layer is provided on one surface of a ceramic substrate, and a metal layer made of aluminum is brazed and bonded to the other surface, and the metal layer has 97 mass% of Al. 99.95% by mass or less, Fe is 0.1% by mass to 1.0% by mass, Mn is 2.0% by mass or less, and the ratio of Mn to Fe is Mn / Fe of 0.5 to 20%. It is formed of an aluminum alloy having a thickness of 0.1 mm or more and less than 0.4 mm contained in the following range.

In this case, the rigidity can be increased by containing Fe. On the other hand, by containing Mn, partial melting of the metal layer due to the brazing material caused by containing Fe can be suppressed, and generation of voids can be prevented. In other words, by incorporating Si into the Al-Fe-Mn precipitates contained in the aluminum alloy that constitutes the metal layer, excessive diffusion of Si can be suppressed and partial melting of the metal layer can be prevented. . Therefore, even when the thickness of the metal layer is reduced to less than 0.4 mm, it is possible to prevent an increase in voids and form a power module substrate having excellent bonding reliability between the ceramic substrate and the metal layer.
Moreover, when Fe contains 1.0 mass% or Mn contains more than 2.0 mass%, the rigidity of a metal layer becomes high and there exists a possibility of producing the crack of a ceramic substrate at the time of a thermal cycle. Note that when the Fe content is less than 0.1% by mass, partial melting due to brazing does not occur, but the rigidity of the metal layer is lowered, so that the deformation resistance of the metal layer is lowered, and the heat sink is joined by soldering. In this case, cracks occur in the solder layer during the cooling and heating cycle. Moreover, when there is little content of Mn with respect to Fe, the spreading | diffusion of Si by brazing cannot be suppressed but there exists a possibility of generating a partial melting in a metal layer. For this reason, the ratio Fe / Mn of Mn to Fe is set to 0.5 or more and 20 or less.
Further, if the thickness of the metal layer is less than 0.1 mm, when the heat sink is soldered, if a thermal cycle is applied, the effect of buffering the thermal stress in the metal layer cannot be obtained, so that a crack occurs in the solder layer.

The present invention is a power module substrate with a heat sink in which a heat sink is soldered to the metal layer of the power module substrate.
Even when the metal layer is thinly provided with a thickness of 0.1 mm or more and less than 0.4 mm, good bonding reliability is maintained without impairing the bonding property when the power module substrate and the heat sink are soldered. A power module substrate with a heat sink can be formed.

  According to the present invention, even if the thickness of the metal layer is reduced, it is possible to form a power module substrate and a power module substrate with a heat sink having excellent bonding reliability between the ceramic substrate and the metal layer.

It is sectional drawing which shows the power module using the board | substrate for power modules with a heat sink of this invention. It is a figure explaining the manufacturing method of the board | substrate for power modules.

Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, a power module substrate 50 with a heat sink includes a power module substrate 10 and a heat sink 20, and an electronic component 30 such as a semiconductor chip is mounted on the surface of the power module substrate 50 with a heat sink. Thus, the power module 100 is manufactured.

  The power module substrate 10 includes a ceramic substrate 11, a circuit layer 12 laminated on one surface of the ceramic substrate 11, and a metal layer 13 laminated on the other surface of the ceramic substrate 11. The electronic component 30 is soldered to the surface of the circuit layer 12 of the power module substrate 10, and the heat sink 20 is soldered to the surface of the metal layer 13.

The ceramic substrate 11 is made of, for example, nitride ceramics such as AlN (aluminum nitride), Si ₃ N ₄ (silicon nitride), or oxide ceramics such as Al ₂ O ₃ (alumina). In this embodiment, AlN is used. Was used. Further, the thickness of the ceramic substrate 11 is set within a range of 0.2 to 1.5 mm, and in this embodiment is set to 0.635 mm.

  Aluminum having a purity of 99% by mass or more and a thickness of 0.2 mm or more and 3.0 mm or less is used for the circuit layer 12. 3N aluminum) or 1N99 (purity 99.99% by mass or more: so-called 4N aluminum) can be used. The circuit layer 12 may be made of aluminum alloy, copper, or copper alloy in addition to aluminum. In the present embodiment, the circuit layer 12 is an aluminum plate made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more, and the thickness thereof is 0.4 mm.

  The metal layer 13 has an Al content of 97% by mass to 99.95% by mass, an Fe content of 0.1% by mass to 1.0% by mass, an Mn content of 2.0% by mass or less, It is formed of an aluminum alloy having a thickness of 0.1 mm or more and less than 0.4 mm, which contains Mn in a range of Mn / Fe of 0.5 to 20 inclusive. In this embodiment, the metal layer 12 is a rolled 3003 aluminum alloy containing 0.25 mass% Fe, 0.21 mass% Si, 1.05 mass% Mn, and 0.15 mass% Cu. It is set as the aluminum plate which consists of a board, and the thickness is 0.2 mm.

  The circuit layer 12, the metal layer 13, and the ceramic substrate 11 are joined by brazing with a brazing material of an Al—Si alloy.

  The electronic component 30 constituting the power module 100 is formed on a Ni plating (not shown) formed on the surface of the circuit layer 12 with a 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 31 in FIG. 1 indicates the solder joint layer. The electronic component 30 and the terminal portion of the circuit layer 12 are connected by a bonding wire (not shown) made of aluminum.

  Further, as the heat sink 20 to be joined to the power module substrate 10, heat dissipation such as a plate-like heat sink, a cooler in which a refrigerant circulates inside, a cold liquid / air cooler with fins formed, a heat pipe, etc. Including metal parts intended to lower the temperature. The heat sink 20 is made of aluminum, an aluminum alloy, pure copper, a copper alloy, an AlSiC-based composite material formed by impregnating a porous body of silicon carbide (SiC) with aluminum or an aluminum alloy, and the like. In the present embodiment, the heat sink 20 is a plate-like heat sink made of oxygen-free copper, and the heat sink 20 and the metal layer 13 are lead-free such as Sn—Sb and Sn—Ag—Cu—Sb. The solder material is used for joining. A reference numeral 21 in FIG. 1 indicates a solder joint layer between the heat sink 20 and the metal layer 13.

Next, a method for manufacturing the power module substrate 1 with a heat sink will be described.
First, as shown in FIG. 2, an aluminum rolled plate made of 4N—Al is prepared as the circuit layer 12, and an aluminum rolled plate of 3003 series aluminum alloy is prepared as the metal layer 13. The aluminum rolled plate of 3003 series aluminum alloy has Al of 97 mass% or more and 99.95 mass% or less, Fe of 0.1 mass% or more and 1.0 mass% or less, and Mn of 2.0 mass% or less. In addition, the ratio of Mn to Fe is contained in the range of 0.5 to 20 in terms of Mn / Fe. These aluminum rolled sheets are laminated on one surface and the other surface of the ceramic substrate 11 with an Al—Si brazing filler metal foil 14 respectively, and are applied in the lamination direction at 0.2 MPa to 0.6 MPa. In a pressed state, heating is performed at a brazing temperature of 600 ° C. to 655 ° C., whereby the power module substrate 10 in which the aluminum rolled plate is bonded to one surface and the other surface of the ceramic substrate 11 is manufactured.

  Then, the power module substrate 10 thus configured is heat-treated at a heating temperature of 300 ° C. to 350 ° C. using a lead-free solder material such as Sn—Sb or Sn—Ag—Cu—Sb. By joining to, the power module substrate 50 with a heat sink can be manufactured.

  In the power module substrate 10 and the power module substrate 50 with a heat sink manufactured as described above, even if the metal layer 13 is thinly provided with a thickness of 0.1 mm or more and less than 0.4 mm, the power module substrate 10 is used. Good bonding reliability can be maintained without impairing the bonding property when soldering the substrate 10 and the heat sink 20.

Thus, by including Fe in the metal layer 13, the rigidity can be increased, while by including Mn, a partial portion of the metal layer 13 due to the brazing material caused by including Fe is included. Melting can be suppressed and generation of voids can be prevented. In other words, when the brazing material Si is taken into the Al—Fe—Mn precipitates contained in the aluminum alloy constituting the metal layer 13, partial melting of the metal layer 13 is suppressed while suppressing excessive diffusion of Si. Can be prevented.
Therefore, the thermal resistance between the power module substrate 10 and the heat sink 20 can be reduced, and the bonding reliability due to the thermal cycle load can be maintained well.

  In addition, when Fe contains 1.0 mass% or Mn exceeds 2.0 mass%, the rigidity of the metal layer 13 becomes high, and there is a possibility that the ceramic substrate 11 may be cracked during the cooling and heating cycle. In addition, when the Fe content is less than 0.1% by mass, partial melting due to brazing does not occur, but the rigidity of the metal layer 13 is reduced, so that the deformation resistance of the metal layer 13 is reduced, and the heat sink 20 is reduced. When joining by solder, a crack arises in a solder layer at the time of a thermal cycle. Moreover, when there is little content of Mn with respect to Fe, the spreading | diffusion of Si by brazing cannot be suppressed but there exists a possibility of generating partial melting in the metal layer 13. For this reason, the ratio Fe / Mn of Mn to Fe is set to 0.5 or more and 20 or less.

Next, examples of the present invention and comparative examples performed for confirming the effects of the present invention will be described.
As an example of the present invention and a comparative example, a circuit layer 12 made of 4N-Al having a thickness of 0.4 mm and an aluminum or aluminum alloy containing elements (Al, Fe, Mn, Si, Cu) having the composition shown in Table 1 A sample of the power module substrate 10 in which the metal layer 13 formed to a thickness t in Table 1 is bonded to a ceramic substrate made of AlN having a thickness of 0.635 mm with an Al—Si brazing material foil 14 having a thickness of 25 μm. Produced. The planar size of the circuit layer 12 and the metal layer 13 was 37 mm × 37 mm, and the planar size of the ceramic substrate 11 was 40 mm × 40 mm.
In addition, a heat sink made of oxygen-free copper having a thickness of 3 mm is soldered to the metal layer 13 of each power module substrate 10 with a 400 μm-thick Sn—Ag—Cu—Sb solder material as a heat sink. A sample of the module substrate 50 was produced. The planar size of the heat sink was 70 mm × 70 mm.

  For these samples of the power module substrate 50 with heat sink, after the solder bonding of the “ceramic substrate-metal layer interface” generated during brazing during manufacture of the power module substrate and the power module substrate and the heat sink "Ceramics substrate cracking" and "solder cracking" generated during the cooling and heating cycle were evaluated.

Evaluation of “void at the interface between the ceramic substrate and the metal layer” was performed by first measuring the bonding interface between the metal layer 13 and the ceramic substrate 11 using an ultrasonic flaw detector and calculating the void ratio from the following equation.
Here, since the void is indicated by a white portion in the ultrasonic flaw detection image, the area of the white portion is defined as the void area.
Void ratio (%) = {(Void area) / (Metal layer area)} × 100 And “Good” indicates that the void ratio is less than 3%, and the void ratio is 3% or more. Were evaluated as “×”.

For the evaluation of “ceramic substrate crack”, the ceramic substrate 11 was checked for cracks and cracks after the thermal cycle test.
In the thermal cycle test, a thermal shock tester TSPE-51 manufactured by Espec was used, and 1000 cycles of -40 ° C. × 5 minutes ← → 125 ° C. × 5 minutes were performed in the liquid phase (Fluorinert). The presence or absence of cracks or cracks in the ceramic substrate 11 was evaluated by measuring the bonding interface between the circuit layer 12 and the ceramic substrate 11 using an ultrasonic flaw detector. When the ceramic substrate 11 was confirmed to have good results without being cracked or cracked, it was evaluated as “◯”, and when it was confirmed that cracking or the like was confirmed, it was evaluated as “x”.

The evaluation of “solder crack” was performed by measuring the solder interface between the metal layer 13 and the heat sink 20 with an ultrasonic flaw detector and calculating the crack progress rate from the following equation.
Here, since the solder crack is shown by the white part in the ultrasonic flaw detection image, the area of this white part was made into the crack area.
Crack growth rate (%) = {(crack area) / (metal layer area)} × 100
And the thing with which the favorable result which makes a crack progress rate less than 10% was obtained was evaluated as "(circle)", and the thing with a crack progress rate of 10% or more was evaluated as "x".
Table 1 shows the evaluation results of each sample.

  As can be seen from Table 1, Al is 97 mass% or more and 99.95 mass% or less, Fe is 1.0 mass% or less, Mn is 2.0 mass% or less, and the ratio of Mn to Fe is Mn / Fe. In the samples of Examples 1 to 9 of the present invention produced using a metal layer contained in a range of 0.5 or more and 20 or less, “a void at the ceramic substrate-metal layer interface”, “ceramic substrate crack” and “ In the evaluation of “solder crack”, good results were obtained.

  In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.

DESCRIPTION OF SYMBOLS 10 Power module substrate 11 Ceramic substrate 12 Circuit layer 13 Metal layer 14 Brazing material foil 20 Heat sink 21 Solder joint layer 30 Electronic component 31 Solder joint layer 50 Power module substrate with heat sink 100 Power module

Claims (2)

  A power module substrate in which a circuit layer is provided on one surface of a ceramic substrate and a metal layer made of aluminum is brazed and bonded to the other surface, wherein the metal layer has an Al content of 97% by mass or more and 99.95. Mass% or less, Fe is 0.1 mass% or more and 1.0 mass% or less, Mn is 2.0 mass% or less, and the ratio of Mn to Fe Mn / Fe is in the range of 0.5 or more and 20 or less. A power module substrate comprising an aluminum alloy having a thickness of 0.1 mm or more and less than 0.4 mm.   2. A power module substrate with a heat sink, wherein a heat sink is soldered to the metal layer of the power module substrate according to claim 1.

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