JP4798171B2 - Power module substrate, power module, and method of manufacturing power module substrate - Google Patents

Description

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

Among semiconductor elements, a power module for supplying power has a relatively high calorific value. For example, an Al (aluminum) metal plate is mounted on a ceramic substrate made of Al ₂ O ₃ (alumina) as a substrate on which the power module is mounted. A power module substrate is used in which are bonded via an Al—Si brazing material.
The metal plate is formed as a circuit layer, and a power element semiconductor chip is mounted on the metal plate via a solder material.
In addition, a metal plate made of Al or the like is bonded to the lower surface of the ceramic substrate to form a metal layer for heat dissipation, and the entire power module substrate is bonded to the heat sink via this metal layer. Yes.

Conventionally, in order to obtain good bonding strength between the circuit layer and the metal plate as the metal layer and the ceramic substrate, for example, the following Patent Document 1 discloses a technique in which the surface roughness of the ceramic substrate is less than 0.5 μm. Has been.
Japanese Patent Laid-Open No. 3-234045

However, when the metal plate is bonded to the ceramic substrate, there is a disadvantage that a sufficiently high bonding strength cannot be obtained even if the surface roughness of the ceramic substrate is simply reduced, and the reliability cannot be improved. For example, even if the surface of the ceramic substrate is subjected to a honing process with Al ₂ O ₃ particles in a dry manner and the surface roughness is set to Ra = 0.2 μm, interface peeling may occur in the peeling test. I understood. Further, even when the surface roughness was set to Ra = 0.1 μm or less by the polishing method, there was a case where the interface peeling occurred in the same manner.

  In particular, recently, power modules have become smaller and thinner, and the usage environment has become harsh, and the amount of heat generated from electronic components tends to increase. It is necessary to dispose a module substrate. In this case, since the power module substrate is constrained by the heat radiating plate, a large shearing force acts on the bonding interface between the metal plate and the ceramic substrate at the time of thermal cycle load. There is a need for improvement in performance.

  The present invention has been made in view of the above-described circumstances, wherein a metal plate and a ceramic substrate are securely bonded to each other, and a power module substrate having high thermal cycle reliability, a power module including the power module substrate, and It aims at providing the manufacturing method of this board | substrate for power modules.

In order to solve such problems and achieve the above object, the power module substrate of the present invention is a brazing material in which a metal plate made of pure aluminum contains silicon on the surface of a ceramic substrate made of Al ₂ O _3. A power module substrate bonded by the step, wherein a high concentration portion having a silicon concentration of 5 times or more the silicon concentration in the metal plate is formed at the bonding interface between the metal plate and the ceramic substrate ; The thickness of the high-concentration part is 4 nm or less, and the mass ratio of Al, Si, and O obtained by analyzing the bonding interface including the high-concentration part by energy dispersive X-ray analysis is Al: Si: O. = 40 to 80 wt%: 2 to 10 wt%: 50 wt% or less .

In the power module substrate having this configuration, the ceramic substrate made of Al ₂ O ₃ and the metal plate made of pure aluminum are joined together by a brazing material containing silicon, and the silicon concentration is in the joining interface. Since the high concentration part which is 5 times or more the silicon concentration is formed, the bonding strength between the ceramic substrate made of Al ₂ O ₃ and the metal plate made of pure aluminum is improved by the silicon atoms present at the bonding interface. become. Here, the silicon concentration in the metal plate is a silicon concentration in a portion of the metal plate that is away from the bonding interface by a certain distance (for example, 50 nm or more).

  Silicon existing at a high concentration at the bonding interface is considered to be mainly silicon contained in the brazing material. During bonding, silicon diffuses into the aluminum (metal plate) and decreases from the bonding interface, but the interface between the ceramic and aluminum (metal plate) serves as a site for heterogeneous nucleation, and silicon atoms are interfaced. A high concentration portion that remains in the portion and has a silicon concentration of 5 times or more the silicon concentration in the metal plate is formed.

Here, the mass ratio of Al, Si, and O obtained by analyzing the bonding interface by energy dispersive X-ray analysis is set to Al: Si: O = 40 to 80 wt%: 2 to 10 wt%: 50 wt% or less. Is preferred.
In this case, since the mass ratio of silicon present at the bonding interface including the high-concentration portion is 2 wt% or more, the bonding force between the ceramic substrate and aluminum (metal plate) can be reliably improved. Note that it is difficult for silicon to be present at the bonding interface so that the mass ratio exceeds 10 wt%.
Moreover, since the spot diameter at the time of performing the analysis by the energy dispersive X-ray analysis method is extremely small, measurement is performed at a plurality of points (for example, 10 to 100 points) on the bonding interface, and the average value is calculated. Further, when measuring, the bonding interface between the crystal grain boundary of the metal plate and the ceramic substrate is not measured, but only the bonding interface between the crystal grain and the ceramic substrate is measured.

A power module according to the present invention includes the power module substrate described above and an electronic component mounted on the power module substrate.
According to the power module having this configuration, the bonding strength between the ceramic substrate and the metal plate is high, and the reliability can be drastically improved even when the usage environment is severe.

In the method for manufacturing a power module substrate according to the present invention, a power module substrate is manufactured by bonding a metal plate made of pure aluminum to a surface of a ceramic substrate made of Al ₂ O ₃ with a brazing material containing silicon. A method in which a ceramic substrate and a metal plate are laminated through a brazing material and heated in a pressurized state to melt the brazing material to form a molten aluminum layer at the interface between the ceramic substrate and the metal plate. And a solidification step for solidifying the molten aluminum layer by cooling, and in the melting step and the solidification step, the silicon concentration at the bonding interface between the ceramic substrate and the metal plate is silicon in the metal plate. to produce a high-density portion which is a concentration five times or more, the thickness of the high density portion and 4nm or less, the junction field including the high concentration section Al which was analyzed by energy dispersive X-ray analysis, Si, the mass ratio of O, Al: Si: O = 40~80wt%: 2~10wt%: is characterized by the following 50 wt%.

According to the method for manufacturing a power module substrate of this configuration, in the melting step and the solidifying step, the silicon concentration at the bonding interface between the ceramic substrate and the metal plate is 5 times or more the silicon concentration in the metal plate. Therefore, the bonding strength between the ceramic substrate made of Al ₂ O ₃ and the metal plate made of pure aluminum can be improved by silicon atoms. In the melting step, the brazing material is sufficiently melted at the interface to form a molten aluminum layer, and then solidified by the solidification step, so that the ceramic substrate and the metal plate are firmly bonded. Can do.

Here, you may have the silicon adhesion process which adheres silicon previously to the joint surface of the said ceramic substrate before joining.
In this case, the silicon element can surely exist at the bonding interface between the ceramic substrate and the metal plate in the silicon adhesion step. As a result, it is possible to reliably generate a high concentration portion in which the silicon concentration is 5 times or more the silicon concentration in the metal at the bonding interface, and a ceramic substrate made of Al ₂ O ₃ and a metal plate made of pure aluminum. The joint strength can be improved. Silicon atoms can be attached to the bonding surface of the ceramic substrate by sputtering or vapor deposition.

  According to the present invention, there are provided a power module substrate having a high thermal cycle reliability in which a metal plate and a ceramic substrate are reliably bonded, a power module including the power module substrate, and a method for manufacturing the power module substrate. It becomes possible.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a power module substrate and a power module according to an embodiment of the present invention.
The power module 1 includes a power module substrate 10 on which a circuit layer 12 is disposed, a semiconductor chip 3 bonded to the surface of the circuit layer 12 via a solder layer 2, and a heat sink 4. Here, the solder layer 2 is made of, for example, a Sn—Ag, Sn—In, or Sn—Ag—Cu solder material. In the present embodiment, a Ni plating layer (not shown) is provided between the circuit layer 12 and the solder layer 2.

The power module substrate 10 has a ceramic substrate 11, a circuit layer 12 disposed on one surface (the upper surface in FIG. 1) of the ceramic substrate 11, and the other surface (lower surface in FIG. 1) of the ceramic substrate 11. And a disposed metal layer 13.
The ceramic substrate 11 prevents electrical connection between the circuit layer 12 and the metal layer 13, and is made of highly insulating Al ₂ O ₃ (alumina). In addition, 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.

  The circuit layer 12 is formed by brazing a conductive metal plate 22 to one surface of the ceramic substrate 11. In the present embodiment, the circuit layer 12 is formed by brazing a metal plate 22 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more to the ceramic substrate 11. Here, in this embodiment, an Al—Si based brazing material containing Si as a melting point lowering element is used.

  The metal layer 13 is formed by brazing a metal plate 23 to the other surface of the ceramic substrate 11. In the present embodiment, like the circuit layer 12, the metal layer 13 is brazed to the ceramic substrate 11 with a metal plate 23 made of a rolled plate of aluminum (so-called 4N aluminum) having a purity of 99.99% or more. It is formed with. In this embodiment, an Al—Si based brazing material is used.

The heat sink 4 is for cooling the power module substrate 10 described above, and includes a top plate portion 5 joined to the power module substrate 10 and a flow path 6 for circulating a cooling medium (for example, cooling water). It has. The heat sink 4 (top plate portion 5) is preferably made of a material having good thermal conductivity, and in this embodiment, is made of A6063 (aluminum alloy).
In the present embodiment, a buffer layer 15 made of aluminum, an aluminum alloy, or a composite material containing aluminum (for example, AlSiC) is provided between the top plate portion 5 of the heat sink 4 and the metal layer 13. .

When the bonding interface 30 between the ceramic substrate 11 and the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) is observed with a transmission electron microscope, as shown in FIG. A high concentration portion 32 in which silicon is concentrated is formed. In the high concentration portion 32, the silicon concentration is 5 times or more higher than the silicon concentration in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23). The thickness H of the high concentration portion 32 is 4 nm or less.
Note that, as shown in FIG. 2, the bonding interface 30 observed here is a lattice image of the interface layer side edge of the lattice image of the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23) and the ceramic substrate 11. The center between the interface side end of the reference surface S is defined as a reference plane S.

  The mass ratio of Al, Si, and O when the bonding interface 30 is analyzed by energy dispersive X-ray analysis (EDS) is Al: Si: O = 40-80 wt%: 2-10 wt%: 50 wt%. It is set within the following range. In addition, the spot diameter at the time of performing the analysis by EDS is 1 to 4 nm, the joint interface 30 is measured at a plurality of points (for example, 20 points in the present embodiment), and the average value is calculated. Further, the bonding interface 30 between the crystal grain boundaries of the metal plates 22 and 23 constituting the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 is not measured, and the metal plate 22 constituting the circuit layer 12 and the metal layer 13 Only the bonding interface 30 between the crystal grains 23 and the ceramic substrate 11 is a measurement target.

Such a power module substrate 10 is manufactured as follows. As shown in FIG. 3, a metal plate 22 (4N aluminum rolled plate) serving as a circuit layer 12 is formed on one surface of a ceramic substrate 11 made of Al ₂ O ₃ with a thickness of 15 to 30 μm, and in this embodiment, 20 μm. A metal plate 23 (4N aluminum rolled plate) that is laminated through the brazing material foil 24 and becomes the metal layer 13 on the other surface of the ceramic substrate 11 has a thickness of 15 to 30 μm, and in this embodiment, a brazing material foil 25 of 20 μm. It is laminated through.

The laminated body 20 thus formed is charged in the lamination direction (pressure 1 to 3 kg / cm ² ) in a vacuum furnace and heated to melt the brazing material foils 24 and 25 ( Melting process). Here, the degree of vacuum in the vacuum furnace is set to 10 ⁻³ Pa to 10 ⁻⁵ Pa. As shown in FIG. 4, a part of the metal plates 22 and 23 that become the circuit layer 12 and the metal layer 13 and the brazing material foils 24 and 25 are melted by this melting step, and a molten aluminum layer is formed on the surface of the ceramic substrate 11. 26 and 27 are formed.

Next, the laminated body 20 is cooled to solidify the molten aluminum layers 26 and 27 (solidification step). By the melting step and the solidifying step, a high concentration portion 32 in which silicon is concentrated is formed at the bonding interface 30 between the ceramic substrate 11 and the metal plates 22 and 23 that become the circuit layer 12 and the metal layer 13.
In this way, the power module substrate 10 according to the present embodiment is manufactured.

  In the power module substrate 10 and the attached power module 1 according to the present embodiment configured as described above, the metal plates 22 and 23 to be the circuit layer 12 and the metal layer 13 and the ceramic substrate 11 are joined by brazing. The silicon concentration at the bonding interface 30 between the metal plates 22 and 23 and the ceramic substrate 11 is at least five times the silicon concentration in the circuit layer 12 (metal plate 22) and the metal layer 13 (metal plate 23). Since the high concentration portion 32 is formed, the bonding strength between the ceramic substrate 11 and the metal plates 22 and 23 can be improved by silicon present at the bonding interface 30.

  Further, since Al: Si: O = 40-80 wt%: 2-10 wt%: 50 wt% or less analyzed by energy dispersive X-ray analysis of the bonding interface 30, silicon atoms 31 present at the bonding interface 30 are used. Since the mass ratio of silicon is 10 wt% or less and the mass ratio of silicon existing at the bonding interface 30 including the high concentration portion 32 is 2 wt% or more, the bonding force between the ceramic substrate and aluminum (metal plate) is ensured. Can be improved. Note that it is difficult for silicon to be present in the bonding interface 30 so that the mass ratio exceeds 10 wt%.

  In addition, since the Al—Si brazing material is used for joining the metal plates 22 and 23 and the ceramic substrate 11, the brazing material foils 24 and 25 can be reliably secured even if the joining temperature is set relatively low. The molten aluminum layers 26 and 27 can be formed by melting.

As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
For example, the metal plate constituting the circuit layer and the metal layer has been described as a rolled plate of pure aluminum having a purity of 99.99%, but is not limited to this, and aluminum having a purity of 99% (2N aluminum) It may be.
Moreover, although demonstrated as what provided the buffer layer which consists of aluminum, the aluminum alloy, or the composite material containing aluminum (for example, AlSiC etc.) between the top-plate part of a heat sink and a metal layer, even if this buffer layer is not provided Good.

Moreover, in order to make a silicon atom interspersed reliably in a joining interface, you may have the silicon adhesion process which adheres a silicon atom to the joining surface of the ceramic substrate before joining.
Furthermore, although the heat sink has been described as being made of aluminum, it may be made of aluminum alloy, copper or copper alloy. Further, although the description has been given of the heat sink having a cooling medium flow path, the structure of the heat sink is not particularly limited.

A comparative experiment conducted to confirm the effectiveness of the present invention will be described.
As shown in FIG. 5 , in Comparative Example 1-3 and Example 1-3, a ceramic substrate 11 made of Al 2 O 3 with a thickness of 0.635 mm, and a circuit layer 12 made of 4N aluminum with a thickness of 0.6 mm, A metal layer 13 made of 4N aluminum having a thickness of 0.6 mm, a top plate part 5 made of an aluminum alloy (A6063) having a thickness of 5 mm, and a buffer layer 15 made of 4N aluminum having a thickness of 1.0 mm are commonly used. is doing.
Using this test piece, the bonding interface was observed and the bonding strength was evaluated.

The observation of the bonding interface was performed at an acceleration voltage of 200 kV using a JEM-2010F manufactured by JEOL Ltd. as a field emission transmission electron microscope (FE-TEM).
The observation sample was produced as follows. First, a sample is sliced from a sample obtained by bonding a metal plate and a ceramic substrate with a diamond cutter, and mechanically polished with a diamond grindstone to a thickness of about 30 μm. Thereafter, ion milling was performed with argon ions (5 kV, 30 μA), and an observation sample having a portion of 0.1 μm or less, which is a thickness through which an electron beam can be transmitted, was produced.
In the observation of the bonding interface, the thickness of the high concentration portion formed at the bonding interface was measured at 20 points, and the average value was calculated. Table 1 shows the result of measuring the average thickness of the high concentration part.

Moreover, the joint interface between a metal plate and a ceramic substrate was analyzed using a Voyager manufactured by Nolan as an energy dispersive X-ray analyzer (EDS). The analysis results are shown in Table 1. Here, as a result of analyzing similarly the position away from the joining interface by 50 nm in the metal plate, the silicon concentration (silicon concentration in the metal plate) was 0.2 to 0.3 wt%.
In addition, the holder for biaxial inclination analysis was used for the above-mentioned TEM observation and EDS analysis.

  As evaluation of joining strength, the joining rate after repeating 3000 times a thermal cycle (-45 degreeC-125 degreeC) was compared. The evaluation results are shown in Table 1.

In Comparative Example 1-3 in which silicon is not present at a high concentration at the bonding interface, it was confirmed that the bonding rate after the thermal cycle test was low and the thermal cycle reliability was poor.
On the other hand, in Example 1-3 in which silicon is present at the bonding interface at a concentration of 5 times or more that in the metal plate, the bonding rate is 90% or more even after 3000 cycles, and the thermal cycle reliability is improved. It was confirmed.
In Example 3, the thickness of the high-concentration portion was 0.0 nm, but all the measured values at 20 points in the transmission electron microscope observation were 0.0 nm. Even if the high concentration portion was not clearly observed in this way, as a result of EDS analysis of the bonding interface, the silicon concentration was 5.5 wt% and the silicon concentration in the metal plate (0.2 to 0.3 wt%). It is clear that there is a high concentration part.

It is a schematic explanatory drawing of the power module using the board | substrate for power modules which is embodiment of this invention. It is a schematic diagram of the junction interface of the circuit layer of the board | substrate for power modules which is embodiment of this invention, a metal layer (metal plate), and a ceramic substrate. It is explanatory drawing which shows the manufacturing method of the board | substrate for power modules which is embodiment of this invention. It is explanatory drawing which shows the joining interface vicinity of the metal plate in FIG. 3, and a ceramic substrate. It is explanatory drawing which shows the board | substrate for power modules used for the comparative experiment.

Explanation of symbols

1 Power module 2 Semiconductor chip (electronic component)
DESCRIPTION OF SYMBOLS 10 Power module substrate 11 Ceramic substrate 12 Circuit layer 13 Metal layer 22, 23 Metal plate 24, 25 Brazing material foil (brazing material)
26, 27 Molten aluminum layer 30 Bonding interface 32 High concentration part

Claims (4)

A power module substrate in which a metal plate made of pure aluminum is joined to a surface of a ceramic substrate made of Al ₂ O ₃ by a brazing material containing silicon,
At the bonding interface between the metal plate and the ceramic substrate, a high concentration portion is formed in which the silicon concentration is 5 times or more of the silicon concentration in the metal plate, and the thickness of the high concentration portion is 4 nm or less. And
The mass ratio of Al, Si, and O analyzed by energy dispersive X-ray analysis of the bonding interface including the high concentration portion is Al: Si: O = 40 to 80 wt%: 2 to 10 wt%: 50 wt% or less. power module substrate characterized in that it is. A power module comprising: the power module substrate according to claim 1 ; and an electronic component mounted on the power module substrate. A method of manufacturing a power module substrate by bonding a metal plate made of pure aluminum to a surface of a ceramic substrate made of Al ₂ O ₃ with a brazing material containing silicon,
A ceramic substrate and a metal plate are laminated through a brazing material and heated in a pressurized state to melt the brazing material to form a molten aluminum layer at the interface between the ceramic substrate and the metal plate, and by cooling A solidifying step for solidifying the molten aluminum layer,
In the melting step and the solidifying step, a high concentration portion in which a silicon concentration is 5 times or more of a silicon concentration in the metal plate is generated at a bonding interface between the ceramic substrate and the metal plate ,
The mass ratio of Al, Si, and O when the thickness of the high-concentration part was 4 nm or less and the bonding interface including the high-concentration part was analyzed by energy dispersive X-ray analysis was expressed as Al: Si: O = 40- 80 wt%: 2 to 10 wt%: 50 wt% or less, A method for producing a power module substrate. 4. The method for manufacturing a power module substrate according to claim 3, further comprising a silicon adhesion step in which silicon is adhered in advance to a bonding surface of the ceramic substrate before bonding.

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