JP2005005404A - Circuit substrate, heat dissipation module and semiconductor component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remarkably improve reliability of heat-proof cycle nature as compared with conventional arts, concerning a semiconductor component which is equipped with and constituted by a semiconductor element in the circuit substrate by joining a metal plate to a ceramics substrate and forming a circuit on the metal plate by etching and obtaining the circuit substrate. <P>SOLUTION: One surface of the ceramics substrate 2 is equipped with the metal plate 3, an insulation part 4 is formed in the metal plate 3 and a circuit is formed, thereby constituting the circuit substrate 5. A surface layer 3A specifies a thickness component in substantially constant region in hardness of the metal plate. The back layer 3B which has a higher hardness. Point A is a point of intersection of the boundary surface 3C of the surface layer 3A and the back layer 3B and an outer peripheral metal end surface of the metal plate 3. A metal end bottom of base end by the side of the ceramics substrate 2 of a metal end surface is made B. The interface of the ceramics substrate 2 and the metal plate 3 is made C. The circuit substrate 5 wherein ∠ABC=α is 30°≤α≤70° is offered. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a circuit board such as a power module including an IGBT used for inverter control of an electric vehicle, a hybrid vehicle, and a household device, a heat radiation module in which a heat radiation member is joined to the circuit board, and the circuit board or the heat radiation. The present invention relates to a semiconductor component formed by mounting a semiconductor element on a module.
[0002]
[Prior art]
As a semiconductor component such as a power module or a switching power supply module, a metal plate excellent in conductivity such as copper or aluminum is bonded to a ceramic substrate such as alumina (Al ₂ O ₃ ) or aluminum nitride (AlN), and the metal plate is bonded to the metal plate. There is a configuration in which a linear insulating portion constituting a circuit is formed by etching to form a circuit board, and a semiconductor element is mounted on the circuit board. The ceramic substrate and the metal plate of the circuit board are integrally bonded by a chemical bonding means such as a brazing method, a metallizing method, and a direct bond copper method.
[0003]
[Problems to be solved by the invention]
The semiconductor element generates heat when energized, and the heat is transmitted to the circuit board. In general, a ceramic substrate of a circuit board is bonded to a non-circuit side surface with a heat radiating member such as a metal plate or a heat sink, and heat of the semiconductor element is diffused from the heat radiating member to the outside. Of course, when the semiconductor element is de-energized, the heat generation stops and the temperature of the circuit board also decreases.
Since circuit boards are repeatedly subjected to such heat cycles, cracks may occur at the interface between the metal plate and the ceramic substrate that make up the circuit due to the effects of residual stress and thermal stress due to differences in the thermal expansion coefficient between ceramics and metals. There is a possibility that cracks may occur in the ceramic substrate itself. The occurrence of cracks at the interface between a metal plate and a ceramic substrate is a serious factor that directly affects the malfunction, life and reliability of semiconductor components, such as reduced heat dissipation performance and reduced withstand voltage. Cycle measures have been taken. In particular, in recent years, semiconductor devices have been highly integrated, and the amount of heat generated has increased rapidly in proportion thereto. Therefore, it is urgent to improve the heat cycle resistance of circuit boards.
[0004]
By the way, copper and aluminum with excellent electrical conductivity are used for the metal plates constituting the circuit, but these materials are relatively soft, so that they exert a buffering action against thermal stress and residual stress due to the heat cycle. It was thought that it would function effectively as a heat cycle countermeasure.
[0005]
However, when the ceramic substrate and the metal plate are joined by chemical joining means, for example, the components such as Ag, Sn, Ti, etc. contained in the brazing material diffuse and dissolve in the metal plate made of copper or aluminum to form an interface. Since the hardness is increased over a certain range, the buffering performance is reduced accordingly. Therefore, the conventional heat cycle countermeasures ignoring the hardening phenomenon resulting from the joining of the metal plates lack accuracy and reliability.
[0006]
As a result of repeating the heat cycle test in consideration of the hardening of the metal plate by joining, the present inventor found out the correlation between the hardening of the metal plate and the shape of the outer peripheral metal end face of the metal plate. Has reached
[0007]
[Means for Solving the Problems]
A circuit board comprising a metal plate for circuit formation on one surface of a ceramic substrate, and an insulating portion provided on the metal plate to form a circuit, wherein the thickness of the metal plate has a substantially constant range. A is the intersection of the boundary surface between the surface layer and the back layer of higher hardness and the outer peripheral metal end surface of the metal plate, and B is the metal end bottom that is the base end of the metal end surface on the ceramic substrate side. Provided is a circuit board where ∠ABC = α is 30 degrees ≦ α ≦ 70 degrees, where C is the interface between the ceramic substrate and the metal plate. Here, the outer peripheral metal end surface of the metal plate includes all the metal end surfaces of the metal plate, such as the contour of the outer shape of the metal plate, the contour of the insulating portion, or the contour of a through hole for inserting a screw to be described later.
According to a second aspect of the present invention, there is provided a heat dissipating module in which a heat dissipating member is joined to the non-circuit side surface of the ceramic substrate.
According to a third aspect of the present invention, there is provided a heat dissipating module in which a heat dissipating plate as a heat dissipating member is bonded to the non-circuit side surface of the ceramic substrate, and a second ceramic substrate is bonded to the other surface of the heat dissipating plate. provide.
Furthermore, as described in claim 4, there is provided a semiconductor component comprising a semiconductor element mounted on the circuit board or a metal plate of the heat dissipation module.
The range of α was determined as follows.
[0008]
[Manufacture of semiconductor parts]
First, the semiconductor component 1 shown in FIGS. The semiconductor component 1 includes a circuit board 5 formed by bonding a metal plate 3 for circuit formation to an upper surface of a ceramic substrate 2 and forming an insulating portion 4 on the metal plate 3 by etching to form a circuit, and the circuit board 5. A semiconductor element 6 soldered on the circuit, a heat radiating plate 7 as a heat radiating member disposed on the lower surface side of the ceramic substrate 2, a second ceramic substrate 20 disposed on the lower surface of the heat radiating plate 7, Furthermore, it comprises a heat radiating plate 70 as a second heat radiating member disposed on the lower surface of the ceramic substrate 20. Each of the above members has the upper surface of the ceramic substrate 2 set on the lower surface side of the metal plate 3, the upper surface of the heat sink 7 is set on the lower surface side of the ceramic substrate 2, and the second ceramic is further formed on the lower surface of the heat sink 7. The upper surface of the substrate 20 is set, and the upper surface of the second heat dissipation plate 70 is set on the lower surface of the ceramic substrate 20, and all can be integrally bonded by brazing at 800 ° C. to 1000 ° C. for 30 to 60 minutes. .
[0009]
The ceramic substrate 2 and the second ceramic substrate 20 are made of silicon nitride and have a thickness of about 0.25 mm. The metal plate 3 is made of copper and has a thickness of about 0.4 mm. For bonding the ceramic substrate 2 and the metal plate 3, a paste brazing material containing Ti as an active metal was used on the bonding surface of the ceramic substrate 2.
The heat radiating plate 7 sandwiched between the two ceramic substrates 2 and 20 is made of copper and has a thickness of about 3 mm, and the ceramic substrate 2 and the heat radiating plate 7 or the heat radiating plate 7 and the second ceramic substrate 20 are joined. Is the same brazing material as the joining of the metal plate 3 and the ceramic substrate 2 described above. The second heat radiating plate 70 is made of copper and has a thickness of about 0.4 mm.
[0010]
Each thickness of the metal plate 3, the ceramic substrate 2 and the second ceramic substrate 20, the radiator plate 7 and the second radiator plate 70 may have a certain width, and the metal plate 3 is 0.25. -0.5 mm, the ceramic substrate 2 and the second ceramic substrate 20 are 0.25 mm to 0.4 mm, the heat sink 7 is 2 to 4 mm, and the second heat sink 70 is 0.2 to 0.5 mm. Is possible.
[0011]
In the circuit, an insulating resist 4 was formed by forming an etching resist on the upper surface of the metal plate 3 and removing unnecessary copper outside the pattern with a ferric chloride solution. FIG. 1 is an enlarged view of the cross section of the insulating portion 4 formed by etching, and the metal end face shape (hereinafter also referred to as an etching end face shape) of the insulating portion 4 is rounded as shown. Since the etching end face shape can be appropriately controlled by adjusting the temperature, concentration, time, and jetting pressure of the ferric chloride solution, these are adjusted to finish various etching end face shapes.
Next, unnecessary brazing material remaining on the insulating portion 4 was removed with hydrofluoric acid, and then unnecessary registry remaining on the metal plate 3 was peeled off.
The etching process of the metal plate 3 was performed after the members were brazed together. However, after etching the metal plate 3 before brazing, the members were brazed together. May be.
[0012]
[Heat cycle test]
With respect to the semiconductor component 1 manufactured as described above, “−40 ° C. × 8 minutes → 25 ° C. × 5 minutes → 125 ° C. × 8 minutes → 25 ° C. × 5 minutes” is set as one cycle and 1,000 cycles are performed. A heat cycle test was conducted.
[0013]
[Measurement]
The circuit board 5 that has been subjected to the above heat cycle test is cut and mirror-polished, and first, the hardness (Vickers hardness) distribution from the interface of the metal plate 3 is measured, and the range in which the hardness is substantially constant is defined as the thickness component. The boundary surface 3 </ b> C between the surface layer 3 </ b> A and the back layer 3 </ b> B having higher hardness is specified, and the intersection A between the boundary surface 3 </ b> C and the metal end surface of the metal plate 3 is specified.
An example of the hardness distribution of the metal plate 3 is shown in the graph of FIG. The graph of FIG. 3 shows that the Vickers hardness of the metal plate 3 is constant by drawing a gentle curve with respect to the distance from the interface. Therefore, since the identification of the boundary surface 3C between the surface layer 3A and the back layer 3B includes some subjective factors, it must be described as “a range in which the hardness is substantially constant”. The error due to such subjective factors is negligible and acceptable.
Next, from the cut surface of the circuit board 5, the metal end bottom B which is the base end of the metal end face on the ceramic substrate 2 side and the interface C between the ceramic substrate 2 and the metal plate 3 are specified, and the value of ∠ABC = α is measured. did.
Further, the crack length generated at the interface C between the ceramic substrate 2 and the metal plate 3 from the metal end bottom B was measured, and the relationship between the crack length and the angle α was graphed. The result is shown in FIG.
[0014]
[Evaluation]
When the crack length exceeds 90 μm, the heat conduction characteristics deteriorate significantly, which is not preferable. Therefore, the upper limit of the crack length is set to 90 μm. Then, as apparent from the graph of FIG. 4, it was found that the crack length does not exceed the upper limit even after the heat cycle test of 1,000 cycles if the angle α ≦ 70 degrees.
On the other hand, if the angle α is less than 30 degrees, the distance between the metal end bottoms B, B facing each other may become too close when the insulating portion 4 is a thin line, and the insulating property may be impaired. did.
[0015]
【Example】
The specific conditions for manufacturing the semiconductor component 1 of FIGS. 1 and 2 with the above-described materials, dimensions, joining conditions, etc. are the temperature (about 40 ° C.) and concentration (2.7-3. 9 mol / L (specific gravity: 1.32 to 3.89)), time (30 minutes), and injection pressure (1.5 kg / cm ² ). Of course, this condition applies to the semiconductor component 1 such as the above-described material, dimensions, bonding conditions, and the like, and appropriate adjustment is required according to the configuration of the material, dimensions, bonding conditions, and the like.
[0016]
In the semiconductor component 1 described above, the semiconductor element 6 is mounted on a heat dissipation module in which the heat dissipation plates 7 and 70 are integrally provided on the circuit board 5. For example, as shown in FIG. Alternatively, the semiconductor element 6 may be mounted on a simple circuit board 5 that does not have a single body. The heat countermeasure in this case can be dealt with by installing the circuit board 5 on an independent heat sink. Further, as shown in FIG. 6, the semiconductor element 6 may be mounted on a heat dissipation module that does not have the second heat dissipation plate 70 integrally.
[0017]
Moreover, as a material of the ceramic substrates 2 and 20, alumina, aluminum nitride, or the like may be used in addition to the above silicon nitride. However, silicon nitride is preferable because it is superior in mechanical properties such as fracture toughness and thermal shock resistance, and therefore excellent in heat cycle resistance, compared to alumina and aluminum nitride.
[0018]
Moreover, the heat sinks 7 and 70 are not limited to metals, and may be composite materials (for example, Cu ₂ O, SiC, Al ₂ O _3, etc.) containing an inorganic compound whose main component is a metal (for example, Cu, Al). Good.
[0019]
Moreover, although the description regarding said metal end surface was performed in the case of the thin linear insulating part 4 of the metal plate 3, the insulating part 4 is slightly wider as shown in FIG. 2 besides the linear one. The thing of the appropriate shape over the range is also included. The same applies to the outer periphery of the metal plate 3 and the metal end face when the through hole 40 for screw insertion is formed as shown in FIGS.
[0020]
【The invention's effect】
In the present invention, the metal end face shape is specified in consideration of the hardening phenomenon of the metal plate constituting the circuit, so that the reliability of the heat cycle resistance is greatly improved as compared with the conventional case.
[0021]
Further, if the heat sink as a heat radiating member is sandwiched between ceramic substrates as in claim 3, even if there is a large gap between the thermal expansion coefficient of the material constituting the heat sink and the ceramic substrate, Since the ceramic substrates cancel out the thermal stress caused by the thermal expansion difference on both sides of the heat sink, there is no problem of warping in either direction.
[Brief description of the drawings]
FIG. 1 is an enlarged cross-sectional view showing a main part.
FIG. 2 is a perspective view showing components separated.
FIG. 3 is a graph showing the hardness distribution of a metal plate.
FIG. 4 is a graph showing the relationship between crack length and angle α.
FIG. 5 is a perspective view showing components separated.
FIG. 6 is a perspective view showing components separated.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor component 2 ... Ceramic substrate 20 ... 2nd ceramic substrate 3 ... Metal plate 3A ... Surface layer 3B ... Back layer 3C ... Interface 4 ... Insulation part 5 ... Circuit board 6 ... Semiconductor element 7 ... Heat sink 70 ... Second Heat sink A ... intersection B of metal end face and boundary surface 3C ... metal end bottom C ... interface between ceramic substrate 2 and metal plate 3

Claims (4)

A circuit board comprising a metal plate for circuit formation on one surface of a ceramic substrate, and forming a circuit by providing an insulating portion on the metal plate,
The intersection between the boundary surface of the surface layer having a thickness component in the range in which the hardness of the metal plate is substantially constant and the back layer having a higher hardness, and the outer peripheral metal end surface of the metal plate is A,
B is a metal end bottom portion which is a base end of the metal end surface on the ceramic substrate side,
When the interface between the ceramic substrate and the metal plate is C,
A circuit board, wherein ABC = α is 30 degrees ≦ α ≦ 70 degrees. A heat dissipation module comprising a heat dissipation member joined to a surface of the ceramic substrate on the non-circuit side of the circuit board according to claim 1. A heat sink as a heat radiating member is bonded to the non-circuit side surface of the ceramic substrate of the circuit board according to claim 1, and a second ceramic substrate is bonded to the other surface of the heat sink. Heat dissipation module. A semiconductor component comprising a semiconductor element mounted on the circuit board according to claim 1 or the metal plate of the heat dissipation module according to claim 2 or 3.

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