JPH11233671A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the stress acting on ceramics and to prevent the deterioration of insulation owing to a crack by providing the junction part of an outer lead-through terminal and one copper plate by means of solder on a side further inside than the edge of the copper plate by a specified dimension. SOLUTION: Copper plates 2b and 2c are stuck on both faces of a ceramics substrates 2a (thickness of 0.635 mm). A semiconductor chip 3 is mounted on a copper plate 2c (thickness of 0.3 mm). The other copper plate 2b (thickness 0.2 mm) is fixed to the inner side of a heat discharge metal base 1. An outer lead-through terminal 4 is mounted on the copper plate 2c. The junction part of the outer lead-through terminal 4 and the copper plate 2c by solder is set to the side further inside than the edge of the copper plate 2c by at least 3 mm. Thus, maximum main stress deteriorates as the position of the solder connection part of the terminal becomes further than the edge part of the copper plate, and generated stress becomes 130 Mpa by setting it further into the inner side by 3 mm from the edge part. The stress generated is not more than the breaking stress of ceramics (aluminum nitride), and substrate damage can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device on a ceramic insulating substrate having a copper plate (copper foil) on its surface, such as a motor control, an inverter for an air conditioner or the like, or a power module used for NC control. The present invention relates to a semiconductor device on which elements are mounted.

[0002]

2. Description of the Related Art In recent years, there has been a remarkable development in power electronics mainly in power conversion and control technology, and applications thereof have been expanding in fields such as industry, transportation, information and consumer use. Power devices support the power electronics, and IGBTs, which are the main elements of today's power devices, have been increasing in capacity year by year. Particularly in the field of railway vehicles, which is one type of large-capacity power conversion, the use of IGBTs in power conversion devices has been remarkably progressing.

[0003] On the other hand, as global environmental problems become more severe,
The demand for clean electric energy is expected to increase further in the future, and practical use of new energy generation such as solar, wind, and fuel cells and the spread of electric vehicles will increase the capacity and decentralization of equipment. And the need for high-performance power converters will surely increase. Such a market environment also implies a need for higher performance, higher performance, and higher reliability of power modules. Particularly in high reliability, bad situations occur in the event of a trouble in the market. Therefore, it is important to design the reliability of the package in the power module.

FIG. 2 is a sectional view showing the configuration of a power transistor module on which an IGBT is mounted. In FIG. 2, an insulating substrate 2 fixed on a heat dissipating metal base 1 with solder or the like.
And a semiconductor chip 3 such as an IGBT mounted thereon, an external lead terminal 4 whose tip is soldered to a circuit pattern of a surface copper plate 2c of the insulating substrate 2, and a plurality of external lead terminals 4 mutually fixed. An aluminum wire 6 for bonding the lid 8, a semiconductor chip 3 and a circuit pattern to which the tip of the external lead-out terminal 4 is fixed, and a heat dissipating metal base 1;
And a resin case 5 fixed with an adhesive or the like, and a silicone gel resin 7 filled in the internal space. Then, if necessary, the top of the gel resin 7 is closed with an epoxy sealing resin. The external lead-out terminal 4 may be led out of the resin case 5 in addition to the lead-out terminal 4.

Here, the insulating substrate 2 is made of alumina (Al ₂
O ₃₎ or to the ceramic substrate 2a such as aluminum nitride (AlN), foil thin copper plates 2b on the front and back surfaces,
2c is produced, for example, by direct bond kappa method (Cu-forming by a reaction between copper and a small amount of oxygen without using a bonding material).
(A method of bonding by direct reaction using an O eutectic liquid phase as a bonding agent), and a circuit pattern (thick film circuit pattern) is formed on the copper plate 2c on the main surface side (front surface side). . The ceramic substrate 2a has excellent insulating properties (volume resistivity> 10 ¹⁴ Ω · cm ² ) and good heat dissipation among insulating materials (thermal conductivity: 20 to 200 W /
mK). The ceramic substrate for the power module has a thickness of 0.25 to
0.8mm thickness on the front and back of ceramic plate of about 0.8mm
A structure in which a copper plate of about 0.3 mm is bonded is general.
For joining the ceramic plate and the copper plate, an active metal joining method using a brazing material to which an active metal such as titanium or zirconium is added is applied in addition to the joining method described above. The direct bond copper method is mainly used for oxide ceramics such as alumina, and the active metal bonding method is used for nitride ceramics such as aluminum nitride. As the copper to be joined, oxygen-free copper or tough pitch copper is used for the direct bond copper method, and oxygen-free copper is used for the active metal joining method. In addition, there is one using aluminum in addition to copper.

In the package structure shown in FIG. 2, the lower electrode (collector) of the semiconductor chip 3 and the heat dissipating metal base 1 are insulated by the insulating substrate 2, and a withstand voltage of 3000 to 6000 V is secured. Further, various physical properties such as metal, ceramics, and plastic are used for the package material. In particular, the package has a laminated structure in which the thermal expansion coefficient increases toward the lower layer from the semiconductor chip 3.

As described above, the package technology of the power module is summarized in such a form that it can respond to market demands by adding various performances including reliability while maximizing the performance of the semiconductor chip 3. . Regarding the reliability of the power module, the package needs various kinds of joint reliability and insulation reliability. At the solder joint, the solder is distorted by thermal stress generated due to the difference in thermal expansion coefficient between the structural component materials. If excessive strain is applied to the solder beyond the allowable value, cracks will occur in the solder,
The crack grows by repeated thermal stress. The propagation of the cracks causes an increase in thermal resistance and a decrease in the heat radiation effect in the solder under the semiconductor chip 3 and under the insulating substrate 2, resulting in destruction of the semiconductor chip 3. In addition, in the soldering of the terminal joining portion, the terminal is detached (terminal open).

On the other hand, the insulating substrate 2 is located immediately below the semiconductor chip 3. Therefore, the insulating substrate 2 is a base for mounting the semiconductor chip 3, dissipates heat when the semiconductor chip 3 generates heat, and ensures insulation between the semiconductor chip 3 and the ground. In addition, it is necessary to have a function as a relay for connection between the semiconductor chip electrode and the external electrode. Since the semiconductor chip 3 and the metal (copper) base having different coefficients of thermal expansion are joined to the insulating substrate 2, thermal stress is generated due to heat history in the assembly process, operation in actual operation, and temperature change in the use environment. I do. Therefore, the insulating substrate 2 is required to have mechanical properties that can withstand the generated stress. Most of the breakdown of ceramics is caused by the action of tensile stress, and this stress occurs not only at the time of cooling but also at the time of temperature rise. For this reason, it is important to evaluate the high-temperature tensile strength in addition to the commonly performed bending strength evaluation. In particular, in the stress analysis by simulation, the tensile strength value is a true strength, so that it is possible to perform a strength design with higher accuracy than in the case of using the bending strength value, which is an important characteristic.

FIG. 3 is a diagram showing the evaluation results of high-temperature tensile strength of various ceramics. From FIG. 3, it can be seen that the nitride ceramics such as aluminum nitride have less decrease in strength in a high temperature region than the oxide ceramics such as alumina. Also, it can be seen that among these, aluminum nitride has particularly low strength. The heat flux generated in the semiconductor chip 3 is transmitted to the radiating metal base 1 via the ceramic substrate 2a, and is released to the radiating fins. For this reason, it is necessary to transfer a large amount of heat flux to the heat-dissipating metal base 1 in order to reduce the thermal resistance of the module. Therefore, the ceramic substrate 2a is required to have high heat conduction and high heat dissipation. For this reason, to reduce the thermal resistance, ceramics having high thermal conductivity, such as aluminum nitride, have been applied, and ceramic plates have been made thinner.

[0010]

Conventionally, Japanese Unexamined Patent Application Publication No.
As described in Japanese Patent No. 66969, a study has been made on the relationship between the end face of the ceramic substrate and the edge of the copper foil in order to prevent the insulating substrate from cracking due to the heat history of assembly. However, no consideration has been given to the relationship between the circuit pattern and an external lead-out terminal fixed on the circuit pattern by soldering. In addition, since the size of the insulating substrate has been reduced in order to reduce the size of the module, the circuit pattern of the solder bonding portion with the external lead-out terminal on the insulating substrate has only a solder bonding area.

FIG. 4 is a sectional view of a portion where the external lead-out terminal is fixed. When thermal stress analysis (two-dimensional elasticity analysis) was performed on the structure of FIG. 4, it was found that concentrated stress was generated at point A, which is a bonding interface between the end of the copper plate 2c and the ceramic substrate 2a. FIG. 5 shows this stress. FIGS. 5A and 5B are partially enlarged views of the joining portion of the external lead-out terminal. FIG. 5A is a state diagram at normal temperature, FIG. 5B is a state diagram at elevated temperature, and FIG. It is. On the circuit pattern side, the temperature rise process of the temperature cycle (233K
398K to 398K) during compression and cooling (398K to 298K).
In K), tensile stress is acting. Substrate damage due to temperature cycling is caused by the difference in thermal expansion coefficient during the cooling process, and the entire module is deformed, and a tensile stress is applied to the external lead terminals. In addition to high tensile stress,
A local tensile stress acts on the external lead terminal due to the tensile action. These stresses may reach the breaking strength and damage the substrate.

FIG. 6 is a cross-sectional view after a temperature cycle test in a state where an external lead terminal is mounted on an aluminum nitride insulating substrate. In FIG. 6, an aluminum nitride ceramic substrate 2a has a ceramic thickness of 0.635 m.
m, the copper plate 2 on one side on which the external lead-out terminal 4 is mounted
The thickness of C is 0.3 mm, and the thickness of the copper plate on the other side is 0.2 mm. The insulating substrate was heated at -40 ° C for 1 hour, at room temperature (23 to 25 ° C) for 30 minutes, and at 125 ° C for 1 hour.
When a temperature cycle test was performed for one cycle of 30 minutes at time and normal temperature, cracks B parallel to the surface direction were observed in the ceramic portion immediately below the solder joint of the external lead-out terminal 4 in 100 cycles. The crack extends from the edge of the copper plate at the joint interface between the copper plate 2c and the ceramic substrate 2a toward the center of the substrate.

Although this substrate damage does not cause a decrease in the dielectric strength, the CVC mounted on the railway vehicle
In a power module used for a converter / inverter such as F, VVVF, etc., it is necessary to consider the operating environment as performed in the above test. In order to further improve the insulation reliability of the high reliability power module, (1) use of a high-strength ceramic substrate, (2) low thermal expansion and high elastic modulus base material as a structure to prevent substrate damage , (3) abolition of the solder connection of the external lead-out terminal to the insulating substrate, (4) a shape of the external lead-out terminal having a stress relaxation / absorption effect. However, the above (1) and (2) require the use of an expensive material, which causes an increase in cost, and (3) and (4) complicate the routing of the internal wiring. There is a problem in that electrical characteristics such as switching speed due to the rise are affected.

An object of the present invention is to solve the above-mentioned problems and to prevent insulation deterioration in a structure having a solder connection of an external lead-out terminal to an insulating substrate and improve insulation reliability.

[0015]

In order to achieve the above object, a case frame made of an insulating resin, a metal heat dissipation base for closing one opening of the case frame, and a flat plate made of ceramic are provided on both surfaces. An insulating substrate on which a copper plate is stretched and a semiconductor element is mounted on one surface of the copper plate and the other surface of the copper plate is fixed to the inner surface of the heat dissipation base; and an external lead-out terminal mounted on the one surface of the copper plate and led out. In a semiconductor device having a resin sealing material for sealing the insulating substrate and a lid for closing the other opening of the case frame, a joint portion of the external lead-out terminal and the one-side copper plate by soldering is provided. It shall be at least 3 mm inside the edge of the copper plate.

Also, the insulating substrate is made of aluminum nitride,
The thickness of the ceramic substrate is 0.25 to 0.8 mm, and the thickness of the copper plate is 0.2 to 0.3 mm. According to the configuration of the present invention, the stress acting on the ceramic can be suppressed to be equal to or less than the fracture stress of the ceramic, and the deterioration of insulation can be prevented.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a ceramic structure of a package structure according to an embodiment of the present invention, in which a solder joint between an external lead-out terminal and a copper plate and a distance (X) from an end of the copper plate (circuit pattern) are variously changed. FIG. 3 is a diagram illustrating a maximum principal stress of a substrate. The ceramic substrate used was aluminum nitride, the thickness of the ceramic substrate was 0.635 mm, the thickness of the copper plate on one surface on which the external lead-out terminals were mounted was 0.3 mm, and the thickness of the copper plate on the other surface was The thickness is 0.2 mm.

In FIG. 1, the maximum principal stress decreases as the position of the solder connection part of the terminal is located inside the edge of the copper plate, and the generated stress becomes 130 MPa when it is located 3 mm inside the edge. This generated stress was equal to or less than the breaking stress of ceramics (aluminum nitride), thereby preventing damage to the substrate.

[0019]

According to the present invention, the stress acting on the ceramics can be suppressed to below the breaking stress of the ceramics by setting the joint of the external lead-out terminal and the copper plate by solder to be 3 mm inside the edge of the copper plate. In addition, insulation deterioration due to cracks could be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing the maximum principal stress of a ceramic substrate when the distance (X) from a solder joint between an external lead terminal and a copper plate and an end of the copper plate in the package structure of the embodiment of the present invention is variously changed.

FIG. 2 is a sectional view of the configuration of a power transistor module.

FIG. 3 is a diagram showing evaluation results of high-temperature tensile strength of various ceramics.

FIG. 4 is a sectional view of a fixing portion of an external lead-out terminal.

FIG. 5 is a partially enlarged view of a joint portion of an external lead-out terminal, and (a).
Is a phase diagram at a normal temperature, (b) is a phase diagram at an elevated temperature, and (c) is a phase diagram at a decreased temperature.

FIG. 6 is a cross-sectional view after a temperature cycle test in a state where an external lead terminal is mounted on an aluminum nitride insulating substrate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 heat radiation metal base 2 insulating substrate 2 a ceramic substrate 2 b copper plate 2 c copper plate 3 semiconductor chip 4 external lead-out terminal 5 resin case 6 aluminum wire 7 gel-like resin 8 lid

Claims (4)

[Claims] 1. A case frame made of an insulating resin, a metal heat dissipation base for closing one opening of the case frame, and a copper plate stretched on both sides of a flat plate made of ceramics, and a semiconductor element is mounted on one surface of the copper plate. An insulating substrate having a copper plate on the other surface fixed to the inner surface of the heat dissipation base, an external lead-out terminal mounted on the copper plate on the one surface and led out, and a resin sealing material for sealing the insulating substrate. A semiconductor device having a lid for closing the other opening of the case frame, wherein a solder joint between the external lead-out terminal and the one surface copper plate is at least 3 mm inside the edge of the copper plate. Semiconductor device. 2. The semiconductor device according to claim 1, wherein the ceramic substrate of the insulating substrate is aluminum nitride. 3. The method according to claim 1, wherein the thickness of the ceramic substrate of the insulating substrate is 0.
2. The semiconductor device according to claim 1, wherein the thickness is 25 to 0.8 mm. 4. The thickness of a copper plate of an insulating substrate is 0.2 to 0.3 m.
2. The semiconductor device according to claim 1, wherein m is m.