JP5772088B2 - Power module substrate manufacturing method and power module substrate - 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, and a power module substrate.

Among semiconductor elements, a power element for supplying power has a relatively high calorific value, and as a substrate on which the power element is mounted, for example, as shown in Patent Document 1, a circuit is formed on a ceramic substrate made of AlN (aluminum nitride). 2. Description of the Related Art A power module substrate in which Al (aluminum) metal plates to be layers are joined through an Al—Si brazing material is widely used.
For example, as shown in Patent Documents 2 to 4, there has been proposed a power module substrate in which an aluminum alloy member is bonded onto a ceramic substrate by a molten metal bonding method to form a circuit layer.
In such a power module substrate, when subjected to a thermal cycle load during use, stress due to the difference in thermal expansion coefficient between the ceramic substrate and aluminum acts on the bonding interface between the ceramic substrate and the circuit layer, and bonding reliability May decrease. Therefore, conventionally, the circuit layer is made of aluminum having a relatively low deformation resistance, such as aluminum having a purity of 99.99% or more, and the thermal stress is absorbed by the deformation of the circuit layer, thereby improving the bonding reliability. ing.

JP 2005-328087 A JP 2002-329814 A JP 2005-252136 A JP 2007-092150 A

By the way, when the circuit layer is made of aluminum having a relatively low deformation resistance such as a purity of 99.99% or higher, the surface of the circuit layer may be swelled or wrinkled when subjected to a thermal cycle load. There was a problem. When waviness and wrinkles are generated on the surface of the circuit layer in this way, cracks are generated in the solder layer, which reduces the reliability of the power module.
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 such as semiconductor elements has increased. May cause waviness and wrinkles on the surface of the circuit layer.

  The present invention was made in view of such circumstances, and when subjected to a thermal cycle load, it can suppress the occurrence of plastic deformation such as swells and wrinkles on the surface of the circuit layer, and Provided are a method for manufacturing a power module substrate and a power module substrate, which can suppress thermal stress from acting on a bonding interface between a ceramic substrate and a circuit layer, and have improved bonding reliability.

In the method for manufacturing a power module substrate of the present invention, a circuit layer is bonded to the surface of the ceramic substrate, and a metal layer made of pure aluminum having a purity of 99.0% or more is bonded to the back surface of the ceramic substrate . A power module substrate manufacturing method in which a heat sink is bonded to the metal layer , wherein the circuit layer has an aluminum purity of 99.0% or more and 99.95% or less in terms of mass%. A clad material formed by laminating two or more layers including one layer and a second layer having an aluminum purity of 99.99% or more is used, and the second layer of the clad material is bonded to the ceramic substrate. And

  Since the brazing temperature in the power module substrate is as high as 640 to 650 ° C., for example, pure aluminum having a high melting point is used as aluminum for the circuit layer. Further, in this circuit layer, the second layer to be brazed to the ceramic substrate has a very high aluminum purity of 99.99% or higher, so that it has a good brazing property and is firmly bonded to the ceramic substrate. Moreover, since it consists of high purity aluminum, a deformation resistance is small and the thermal stress between ceramic substrates can be absorbed by a deformation | transformation. On the other hand, since the first layer constituting the electronic component mounting surface has a relatively low aluminum purity, the mechanical strength and hardness are high, and the plastic deformation of the electronic component mounting surface is suppressed, and the solder joint portion with the electronic component is formed. It can be kept healthy. If the aluminum purity of the first layer exceeds 99.95% by mass, there is no effect of suppressing plastic deformation. By forming the circuit layer with these at least two clad materials, it becomes possible to cope with the thickening of the circuit layer.

In the method for manufacturing a power module substrate of the present invention, the first layer may have a thickness of 100 μm or more and 400 μm or less.
Since the plastic deformation generated on the electronic component mounting surface of the first layer is accumulated in a range of a depth of 100 μm, the plastic deformation can be suppressed if the thickness of the first layer is 100 μm or more. If the thickness of the first layer exceeds 400 μm, it is useless for the effect of suppressing plastic deformation of the electronic component mounting surface, and it is not preferable because the entire circuit layer is increased in thickness.

The first layer may be JIS standard product 1000 series aluminum .
After the electronic component is mounted by soldering, Al—Fe-based precipitates such as Al ₃ Fe and Al—Si—Fe-based precipitates are deposited on the solder joint surfaces, and these precipitates form the solder joint surfaces. It can be hardened to enhance its deformation suppressing effect .

  The power module substrate of the present invention is manufactured by the above manufacturing method, and the power module has an electronic circuit soldered to the circuit mounting surface of the first layer of the circuit layer of the power module substrate. It is characterized by being joined by.

According to the present invention, among the circuit layers made of the clad material, the second layer having an extremely high aluminum purity of 99.99% or higher improves the bondability by brazing to the ceramic substrate, and the aluminum purity is 99.0% or more. The first layer of 99.95% or less suppresses plastic deformation of the electronic circuit surface and increases the bonding reliability of the solder joint with the electronic component, and can cope with the thickening of the circuit layer. An output power module can be obtained.

It is a longitudinal cross-sectional view which shows the whole structure of the power module to which the manufacturing method of embodiment of this invention is applied.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a power module using a power module substrate according to the present invention. A power module 1 shown in FIG. 1 includes a power module substrate 3 having a ceramic substrate 2 made of ceramics, an electronic component 4 such as a semiconductor chip mounted on the surface of the power module substrate 3, and a power module. The heat sink 5 is bonded to the back surface of the substrate 3.

In the power module substrate 3, a circuit layer 7 is laminated by brazing on the front surface side of the ceramic substrate 2, and a metal layer 8 serving as a heat transfer layer for heat dissipation is laminated by brazing on the back surface side. The surface of the circuit layer 7 opposite to the ceramic substrate 2 is an electronic component mounting surface 7 a, and the heat sink 5 is attached to the metal layer 8.
The ceramic substrate 2 is formed of nitride ceramics such as AlN (aluminum nitride) and Si ₃ N ₄ (silicon nitride), or oxide ceramics such as Al ₂ O ₃ (alumina).

The circuit layer 7 is made of a clad material in which two layers of aluminum of a first layer 11 and a second layer 12 having different aluminum purities are clad in advance. The first layer 11 and the second layer 12 have a composition before brazing, the first layer 11 has an aluminum purity of 99.0% to 99.95% by mass, and the second layer 12 has an aluminum purity. 99.99% or more. In this case, the impurity component of the first layer 11 having relatively low aluminum purity is, by mass%, Si 0.01% to 1.0%, Fe 0.01% to 1.0%, and Cu 0%. 0.01% to 0.3%, Mn from 0 to 0.05%, Zn from 0 to 0.1%, and Ti from 0 to 0.05%. Among these impurity components, it is particularly preferable to contain Si, Fe and Cu.
In the JIS standard product, aluminum in the 1000s can be used as the first layer 11 and 1N99 can be used as the second layer 12.
The surface of the first layer 11 is the electronic component mounting surface 7a, and the surface of the second layer 12 (the lower surface in the figure) is the bonding surface to the ceramic substrate 3.

On the other hand, the metal layer 8 is made of pure aluminum having an aluminum purity of 99.0% or more with a composition before brazing.
In this case, the individual dimensions of the thickness of each layer are not limited, but the thickness of the ceramic substrate 2 is, for example, 635 μm, the thickness of the metal layer 8 is 400 μm, and the thickness of the circuit layer 7 is 600 μm. It is said. In the circuit layer 7, the first layer 11 has a thickness of 200 μm and the second layer 12 has a thickness of 400 μm.

  The ceramic substrate 2, the circuit layer 7, and the metal layer 8 are joined to each other by a brazing material such as Al—Si, Al—Ge, Al—Cu, Al—Mg, or Al—Mn. ing. The metal layer 8 and the heat sink 5 are joined by a solder material such as Sn—Ag—Cu, Zn—Al, or Pb—Sn, or a brazing material such as Al—Si—Mg, Al—Si, Alternatively, it is mechanically fixed with screws in a state of being in close contact with silicon grease. In the figure, an example of soldering is shown, and reference numeral 13 denotes a solder joint layer.

  The shape of the heat sink 6 is not particularly limited. The heat sink 6 is formed by extrusion molding of an aluminum alloy, and the cylinder 15 joined to the power module substrate 3 and the inside of the cylinder 15 are divided into a plurality of flow paths 16. The vertical wall 17 is integrally formed. The top plate portion 15 a of the cylinder 15 has a rectangular planar shape larger than the metal layer 8 of the power module substrate 3, and the vertical walls 17 are mutually spaced at equal intervals in the width direction of the cylinder 15. They are arranged in parallel and are provided along the length direction of the cylindrical body 15.

  Then, the electronic component 4 is bonded onto the electronic component mounting surface 7a of the first layer 11 of the circuit layer 7 by a solder material such as Sn—Ag—Cu, Zn—Al, or Pb—Sn. Reference numeral 18 in the drawing indicates the solder joint layer. The electronic component 4 and the terminal portion of the circuit layer 7 are connected by a bonding wire (not shown) made of aluminum.

And in order to manufacture the board | substrate 3 for power modules of such a structure, the circuit layer 7 and the metal layer 8 are laminated | stacked on each surface of the ceramic substrate 2 via the brazing material foil, and these laminated bodies are made into inert gas atmosphere The circuit layer 7 and the metal layer 8 are bonded to the ceramic substrate 2 by heating in a reducing gas atmosphere or a vacuum atmosphere in a state of being pressurized in the stacking direction and melting the brazing material foil. Among these, the circuit layer 7 is formed by previously forming the first layer 11 and the second layer 12 having different aluminum purity in a laminated state by clad rolling. The circuit layer 7 and the metal layer 8 are bonded to the ceramic substrate 2 by punching into a desired outer shape by pressing, or are bonded to the ceramic substrate 2 by a flat plate and then etched by etching. Either method can be adopted.
When the circuit layer 7 and the metal layer 8 and the ceramic substrate 2 are brazed, the temperature becomes 640 to 650 ° C. or higher, but both the circuit layer 7 and the metal layer 8 are pure aluminum having a high melting point or high purity. Since aluminum is used, a strong power module substrate 3 can be obtained by bonding at a high temperature.

A heat sink 5 is soldered to the metal layer 8 and the electronic component 4 is soldered on the circuit layer 7 to the power module substrate 3 thus manufactured. These soldering operations are performed in a reducing gas atmosphere in which nitrogen and hydrogen are mixed. Further, after cooling, wire bonding is performed between the electronic component 4 and the circuit layer 7 in the atmosphere.
The power module 1 is completed through this series of steps.

In the power module 1 configured as described above, since the circuit layer 7 is formed to be relatively thick, heat from the electronic component 4 can be quickly transferred to the circuit layer 7 and quickly dissipated. It is possible to cope with higher output of the electronic component 4. In that case, in the brazed joint between the circuit layer 7 and the ceramic substrate 2, the brazed joint surface of the circuit layer 7 is formed by the second layer 12 having an extremely high aluminum purity. And is firmly bonded to the ceramic substrate 2.
In this case, at the time of brazing, components such as Si contained in the brazing material diffuse into the second layer 12 of the circuit layer 7, but the diffusion layer is formed in a depth range of 200 μm. The thickness of 12 is preferably at least 200 μm. If it is thinner than 200 μm, the brazing material may ooze out to the side surface of the circuit layer 7.
Further, since the second layer 12 to be joined to the ceramic substrate 2 is made of high purity (99.99%) aluminum, the deformation resistance is small and the thermal stress between the ceramic substrate and the ceramic substrate can be absorbed by deformation.

On the other hand, in the solder joint between the circuit layer 7 and the electronic component 4, the electronic component mounting surface 7a of the circuit layer 7 is formed by the first layer 11 having a relatively low aluminum purity, and its mechanical strength and hardness are low. Since it is high, plastic deformation such as waviness and wrinkles is less likely to occur when a thermal cycle load is applied, and the flatness of the electronic component mounting surface 7a can be stably maintained over a long period of time, greatly improving the bonding reliability. be able to. In order to effectively exhibit the effect of suppressing plastic deformation, the aluminum purity of the first layer 11 is preferably 99.90 to 99.95% by mass, and if it exceeds 99.95% by mass, there is no effect of suppressing plastic deformation. If it is less than 0.0% by mass, it becomes hard and it becomes difficult to clad.
In particular, when Si or Fe is contained as an impurity component of aluminum constituting the first layer 11, Al-Fe-based or Al-Si-Fe-based precipitates are deposited on the electronic component mounting surface 7a. The electronic component mounting surface 7a is hardened by these precipitates (precipitation hardening), and the deformation suppressing effect can be further enhanced. When the content of Si and Fe is less than 0.01% by mass, there is no deformation suppressing effect, and when it exceeds 1.0% by mass, it becomes hard and it becomes difficult to clad.
The thickness of the first layer 11 is preferably 100 μm or more in order to exert the effect of suppressing deformation of the electronic component mounting surface 7a.

As described above, regarding the circuit layer 7, the first layer 11 may be 100 μm or more and the second layer 12 may be 200 μm or more. However, the circuit layer 7 as a whole has a heat from the electronic component 4 mounted thereon. It is intended to quickly absorb and dissipate heat, and for that purpose, aluminum should be as high purity as possible. Therefore, when the circuit layer 7 is thickened, it is preferable to secure at least 100 μm as the first layer 11 and to use the remaining thickness as the second layer 12 with high aluminum purity. When the thickness of the circuit layer 7 is set to 600 μm, the thickness ratio between the first layer 11 and the second layer 12 may be set to the first layer: second layer = 1: 5 to 1: 2.
The first layer 11 has an aluminum purity of 99.0% or more and 99.95% or less, and the conductive layer preferably has a high aluminum purity (for example, 99.90% or more).

In order to confirm the effect by the manufacturing method of the present invention, a circuit layer using a clad material of a first layer having an aluminum purity of 99.0% and a second layer having an aluminum purity of 99.99%, aluminum The power module substrate of the example and the power module substrate of the comparative example were manufactured by joining the single layer having a purity of 99.99% to the ceramic substrate by brazing. As the circuit layer, the first layer was 100 μm, the second layer was 500 μm, and the comparative example was 600 μm. After bonding a semiconductor chip as an electronic component to the electronic component mounting surface in the circuit layer of the power module substrate by soldering, a thermal cycle test was performed. As the thermal cycle test, the temperature increase and cooling were repeated 3000 cycles in the temperature range of −40 ° C. to 125 ° C.
After the test, as a result of cross-sectional observation of the joint with the electronic component, no abnormality was particularly observed in the example, and the solder joint was uniformly formed by the flat circuit layer (first layer). In the comparative example, wrinkles were found on a part of the electronic component mounting surface of the circuit layer.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the concrete structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

DESCRIPTION OF SYMBOLS 1 Power module 2 Ceramic substrate 3 Power module substrate 4 Electronic component 5 Heat sink 7 Circuit layer 7a Electronic component mounting surface 8 Heat radiation layer 11 First layer 12 Second layer 13 Solder joint layer 15 Cylindrical body 16 Channel 17 Vertical wall 18 Solder Bonding layer

Claims (5)

A circuit layer is bonded to the surface of the ceramic substrate, and a metal layer made of pure aluminum having a purity of 99.0% or more is bonded to the back surface of the ceramic substrate, and a heat sink is bonded to the metal layer . A method for manufacturing a substrate, wherein the circuit layer includes a first layer having an aluminum purity of 99.0% or more and 99.95% or less by mass%, and an aluminum purity of 99.99% or more as the circuit layer. A method for manufacturing a power module substrate, comprising: using a clad material formed by laminating two or more layers including a second layer, and bonding the second layer of the clad material to the ceramic substrate.   The method for manufacturing a power module substrate according to claim 1, wherein the first layer has a thickness of 100 μm to 400 μm.   3. The method for manufacturing a power module substrate according to claim 1, wherein the first layer is JIS standard product 1000 series aluminum. 4.   The power module substrate manufactured by the manufacturing method of the power module substrate as described in any one of Claims 1-3.   5. The power module according to claim 4, wherein an electronic component is joined to the electronic component mounting surface of the first layer of the circuit layer of the power module substrate according to claim 4 by soldering.

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