JP2006245436A - Silicon nitride wiring board and semiconductor module using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon nitride wiring board which prevents cracks caused by thermal stress generated at a metallic circuit plate corner while keeping a satisfactory mounting area of a metallic circuit plate pattern, and a semiconductor module. <P>SOLUTION: The silicon nitride wiring board is composed of a silicon nitride substrate, a plurality of metallic circuit plates joined to one surface, and a metallic heat sink joined to the other surface. The thickness of the silicon nitride substrate is at least 0.2 mm, and the thickness of the metallic circuit plate and the metallic heat sink is at least 0.4 mm. In the silicon nitride wiring board, when the area of one surface of the silicon nitride substrate is S and the thickness is T, R of a curvature radius of 1.0 mm or more and 2.5 mm or less is formed at the corner of the metallic circuit plate pattern having an area of a value expressed by 10T<SP>2</SP>S<SP>1/2</SP>or more, and R is not formed at the corner of a metallic circuit plate pattern of an area of 13 mm<SP>2</SP>or less among metallic circuit plate patterns of an area of a value of 10T<SP>2</SP>S<SP>1/2</SP>or less (except R of a curvature radius of 0.5 mm or less applied inevitably), and the semiconductor module uses it. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is used in a silicon nitride wiring board, particularly a power semiconductor module, in which a metal circuit board serving as a conductive circuit board is joined to one surface of a silicon nitride substrate and a heat radiating metal plate is joined to the other surface. The present invention relates to a silicon wiring board and a semiconductor module using the same.

  In recent years, power semiconductor modules (IGBT, MOS FET, etc.) capable of high voltage and large current operation are used as inverters for electric vehicles. As a substrate used for a power semiconductor module, a conductive metal plate to be a circuit is bonded to one surface (upper surface) of an insulating ceramic substrate made of aluminum nitride or silicon nitride, and the other surface (lower surface) is used for heat dissipation. Ceramic wiring boards to which these metal plates are bonded are widely used. As this metal plate, a copper plate or an aluminum plate is used. And a semiconductor element etc. are mounted on the upper surface of the conductive metal plate used as a circuit. For joining the ceramic substrate and the metal plate, an active metal method using a brazing material or a so-called copper direct joining method in which a copper plate is directly joined is employed.

  However, in a power semiconductor module using a ceramic circuit board in which a metal circuit board and a metal heat sink are bonded to a ceramic board, the thickness of the metal circuit board and the metal heat sink is set to 0.3 to 0.00 mm so that a large current can flow. In many cases, it is relatively thick, 5 mm, especially when copper with high thermal conductivity is used for the metal circuit board and metal heat sink, if ceramics and metals with significantly different thermal expansion coefficients are joined, the cooling process after joining Thermal stress is generated. This stress is present as compressive and tensile residual stress in the vicinity of the joint portion of the ceramic substrate. This residual stress causes a crack in the ceramic substrate, causes a breakdown voltage failure, or causes the metal circuit board and the metal plate to peel off.

  In this respect, the aluminum nitride substrate has high thermal conductivity as a ceramic substrate, but its mechanical strength is low, and its reliability in terms of strength is low, making it difficult to apply. On the other hand, since the silicon nitride substrate has a relatively high thermal conductivity and high mechanical strength as a ceramic substrate, it is considered that a highly reliable ceramic wiring substrate can be realized.

However, even when a silicon nitride substrate having a high mechanical strength is used as a ceramic substrate, cracks may occur due to thermal stress caused by joining copper plates or thermal shock caused by heating / cooling cycles during semiconductor module operation. .
This crack often occurs at the outer periphery of the metal circuit board pattern, especially at the corners, which degrades the dielectric strength and strength of the ceramic wiring board, and when a voltage is applied to the mounted semiconductor element, the ceramic board is insulated. There was also destruction. Therefore, the reliability of the semiconductor module in which the semiconductor element is mounted on the ceramic wiring board is not sufficient.

  In order to prevent cracks in the ceramic substrate, in Patent Document 1, in the curve at the corner portion of the pattern of the metal circuit board, the curvature radius at the center portion of the curve and the curvature radius at the point entering the corner portion from the straight portion are changed. Technologies that satisfy this relationship have been proposed. By relaxing the stress near the corners of the metal circuit board, cracks in the ceramic substrate are suppressed.

Further, in Patent Document 2, the radius of curvature of the corner of the two adjacent corners of the metal circuit board pattern where stress is larger or concentrated, or the corner where the stress relaxation is higher is higher. By increasing the size, the stress applied near the corners of the metal circuit board is relaxed to prevent the occurrence of cracks.
As described above, as a method for preventing the occurrence of cracks in the ceramic substrate due to thermal stress, a structure in which R is provided at the corner of a metal plate has been proposed in the following documents.

JP-A-10-214915 JP 2002-198456 A

In addition to the metal circuit board pattern for mounting the semiconductor element, the circuit pattern of the ceramic wiring board used for the semiconductor module is provided with a metal circuit board pattern for extracting the terminal connected by wire bonding from the semiconductor element. In many cases, a plurality of types of metal circuit board patterns are arranged. Since the metal circuit board pattern for taking out the terminal does not have a semiconductor element, the metal circuit board pattern can have a comparatively small area. Can be aggregated. As a result, the structure of the apparatus incorporating the semiconductor module can be simplified.
Even when there is a large area metal circuit board pattern for mounting such semiconductor elements and other small area metal circuit board patterns, in order to prevent cracks in the ceramic substrate, The stress on the corners of the pattern must be relaxed. For example, it is necessary to provide a structure in which R is provided at the corners of the metal circuit board pattern as in the above-mentioned document.
However, in patent document 1, although the magnitude | size of a curvature radius is prescribed | regulated about the same corner | angular part of the same metal plate pattern of a metal circuit board pattern, the metal circuit of a comparatively small area is independent of the area of a metal circuit board pattern. R also has to be provided on the plate pattern, leading to a problem that the mounting area is reduced.
On the other hand, in Patent Document 2, the radius of curvature of R at the two adjacent corners of the metal circuit board pattern is changed. However, even in this case, at the portion where the two metal circuit board patterns having a relatively small area are adjacent to each other. , R having a large radius of curvature must be formed on one of the metal circuit board patterns, resulting in a problem that the mounting area is reduced. Therefore, in the metal circuit board pattern having a relatively small area, the area of the metal circuit board pattern has to be increased in order to provide R at the corner portion while securing the mounting area, which increases the size of the ceramic wiring board. Will lead to.
Thus, by joining a metal circuit board and a metal heat sink together with Patent Document 1 and Patent Document 2, it has a structure that relieves the generated thermal stress and prevents cracks in the ceramic substrate. There was a problem in securing the necessary mounting area.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a highly reliable silicon nitride having a structure capable of maintaining a sufficient mounting area of a metal circuit board pattern and preventing cracks due to thermal stress generated particularly at the corners of the metal circuit board. An object is to provide a wiring board and a semiconductor module.

The present invention relates to a silicon nitride substrate comprising a silicon nitride substrate, a plurality of metal circuit plates bonded to one surface of the silicon nitride substrate, and a metal heat dissipation plate bonded to the other surface of the silicon nitride substrate. In the wiring board, the thickness of the silicon nitride substrate is 0.2 mm or more, the thickness of the metal circuit board and the metal heat sink is 0.4 mm or more, and the area of one surface of the silicon nitride substrate is S, the thickness T If ^you, 10T in the corners of the metal circuit plate pattern having a value more than the area represented by the ^{2 S 1/2} will form the following R 2.5 mm or more radii of curvature 1.0mm, ^10T 2 ^{S 1 /} excluding further the area in the corners of the 13 mm ² or less of the metal circuit board pattern does not form R (provided that the radius of curvature 0.5mm following R which inevitably stick out of the metal circuit board pattern is the area of ² or less ) Silicon nitride wiring It is a substrate.
As described above, R is not formed at the corners of the metal circuit board pattern having a predetermined area or less, and R is provided at the corners of the metal circuit board pattern having a predetermined area or more. A sufficient mounting area can be secured, and stress around the corners of the metal circuit pattern that can cause cracks in the silicon nitride substrate can be relieved. The thickness of the silicon nitride substrate is effectively in the range of 0.2 mm or more and 1.0 mm or less, and preferably 0.3 to 0.6 mm. The thickness of the metal circuit board and the metal heat sink is also in the range of 0.3 mm or more and 2.0 mm or less, and is preferably 0.4 to 1.0 mm.

  In the silicon nitride wiring board of the present invention, the ratio between the creeping distance a from the outer edge of the silicon nitride substrate to the outer edge of the metal circuit board and the creeping distance b from the outer edge of the silicon nitride substrate to the outer edge of the metal heat sink. It is desirable that a / b is 0.5 or more and 2 or less, and the value of a−b is −0.5 mm or more and 0.5 mm or less. When the relationship between the creeping distance a from the metal circuit board and the creeping distance b of the metal heat sink is outside the above range, a large stress is generated near the outer periphery of the metal circuit board or the metal heat sink of the silicon nitride substrate, and a crack is generated. There is a possibility that it is not preferable.

The silicon nitride wiring board of the present invention has an area of 0.02 to 0.09 times the metal heat sink pattern area on the outer periphery of the metal heat sink pattern having an area of 70T ² S ^1/2 or more. In addition, it is desirable that a hole occupying a volume 0.01 to 0.09 times the volume of the metal heat sink pattern is formed. Further, it is desirable that the hole occupies an area 0.05 to 0.09 times the metal heat sink pattern area and a volume 0.05 to 0.09 times the metal heat sink pattern volume. By providing a hole in the metal heat sink, the stress generated in the silicon nitride substrate is dispersed, and the generation of cracks can be suppressed.

The present invention is a semiconductor module in which a semiconductor element is mounted on any of the silicon nitride wiring substrates described above.
For example, a silicon nitride wiring board comprising a silicon nitride substrate, a plurality of metal circuit plates bonded to one surface of the silicon nitride substrate, and a metal heat dissipation plate bonded to the other surface of the silicon nitride substrate And a semiconductor element mounted on the metal circuit board pattern, wherein the silicon nitride substrate has a thickness of 0.2 mm or more, the metal circuit board and the metal heat sink have a thickness of 0.4 mm or more, and the silicon nitride When the area of one surface of the substrate is S and thickness T, R having a radius of curvature of 1.0 mm or more and 2.5 mm or less is formed at the corner of the metal circuit board pattern having an area of 10T ² S ^1/2 or more, In addition, among the metal circuit board patterns having an area of 10T ² S ^1/2 or less, a semiconductor module in which R is not formed at corners of the metal circuit board pattern having an area of 13 mm ² or less is used.

According to the silicon nitride wiring board of the present invention, when the area of one surface of the silicon nitride substrate is S and the thickness T, the metal circuit board pattern having an area equal to or greater than the value represented by 10T ² S ^1/2 R having a radius of curvature of 1.0 mm or more and 2.5 mm or less is formed in the corner portion, but among the metal circuit board patterns having an area of 10T ² S ^1/2 or less, the area is further 13 mm ² or less. R is not formed at the corners of the substrate, so that the mounting area of the metal circuit board pattern is secured, while nitriding is performed during cooling after joining the silicon nitride substrate, the metal circuit board, and the metal heat sink or during operation of the semiconductor module. Thermal stress generated in the silicon substrate can be relaxed. Therefore, it is possible to provide a silicon nitride wiring board and a semiconductor module that are resistant to thermal shock during operation of the semiconductor module and have high reliability while securing a mounting area.

Hereinafter, specific examples of the present invention will be described. However, the present invention is not limited to these examples.
[Example 1]
FIG. 1 shows a silicon nitride wiring board 1 according to an embodiment of the present invention. FIG. 1 (a) is a top view, FIG. 1 (b) is a bottom view, and FIG. 1 (c) is a side view.
A metal circuit board 12 made of a copper plate for mounting a semiconductor element is bonded to one surface (upper surface) of the silicon nitride substrate 11, and this metal circuit board 12 is predetermined as shown in FIG. The circuit pattern is formed of three types of circuit patterns, that is, a circuit pattern A (121), a circuit pattern B (122), and a circuit pattern C (123) having different areas. On the other hand, a metal heat radiating plate 13 made of a copper plate is bonded to the other surface (lower surface) of the silicon nitride substrate 11. The creepage distance a from the outer edge of the silicon nitride substrate 11 to the outer edge of the metal circuit board 12 and the creepage distance b from the outer edge of the silicon nitride substrate 11 to the outer edge of the metal heat sink 12 are both 1.5 mm. is there.

As a manufacturing method of the silicon nitride wiring substrate 1, first, an active metal brazing material is printed and formed on both surfaces of the silicon nitride substrate 11, and a copper plate having substantially the same rectangular shape as the silicon nitride substrate 11 is heated and bonded at 750 ° C. on both surfaces. To do. After cooling, the copper plate is etched so that the metal circuit board 12 and the metal heat sink 13 have a predetermined pattern. Further, as another manufacturing method, an integrated copper plate in which portions that become circuit patterns are connected by a part of connecting portions by press working is manufactured. This pattern forming plate is heat-bonded to the silicon nitride substrate 11 on which the active metal brazing material is printed in the same manner as described above, and finally the connecting portion connecting the circuit patterns is removed by cutting to form the silicon nitride wiring substrate 1. it can.
Here, the silicon nitride substrate 11 has a width of 24 mm, a length of 35.4 mm, an area of 849.6 mm ² and a thickness of 0.3 mm, and the area of the silicon nitride substrate 11 is S and thickness T. The value of 10T ² S ^1/2 was 26.2. Area of copper circuit board pattern 121 is 346.2Mm ² of the circuit pattern A, 122 of the circuit pattern B is 189.2mm ^2, 123 of the circuit pattern C are each 12.2 mm ^2. The corners of the circuit pattern A121, the circuit pattern B122, and the metal heat radiating plate 13 are provided with R having a curvature radius of 1.5 mm. On the other hand, no R is intentionally formed at the corners of the circuit pattern C123. However, a radius of curvature of about 0.2 mm is inevitably attached during etching.
Ten silicon nitride wiring substrates 1 were prepared and examined for the presence or absence of cracks, and then a heat cycle test at -40 ° C to 125 ° C was performed 1000 cycles. After the heat cycle test, the occurrence of cracks was examined again. Cracks were generated by a fluorescent flaw detection method.

[Comparative Example 1]
FIG. 2 shows a top view of a silicon nitride wiring substrate 2 that is Comparative Example 1. FIG. This example has the same structure as that of Example 1, and a metal circuit board 22 made of a copper plate for mounting a semiconductor element is joined to one surface (upper surface) of the silicon nitride substrate 21. 2 is processed into a predetermined circuit pattern shape as shown in FIG. 2, and is composed of three types of circuit patterns, a circuit pattern A221, a circuit pattern B222, and a circuit pattern C223, each having a different area. On the other hand, a metal heat radiating plate made of a copper plate is joined to the other surface (lower surface) of the silicon nitride substrate 21. The creepage distance a from the outer edge of the silicon nitride substrate 21 to the outer edge of the metal circuit board 22 and the creepage distance b from the outer edge of the silicon nitride substrate 21 to the outer edge of the metal heat sink are both 1.5 mm. .
Among the copper circuit board patterns, the area of the circuit pattern C223 is 15.1 mm ^2. However, since the corner portion is provided with an R having a curvature radius of 1.0 mm, the substantial area that can be used for mounting is as follows. The area is about 12 mm ² and is equivalent to the circuit pattern C123 of the first embodiment. Further, in order to arrange the circuit pattern C223, the areas of the circuit pattern A221 and the circuit pattern B222 are also larger than the circuit pattern A121 and the circuit pattern B122 of the first embodiment. Therefore, the area of the silicon nitride substrate is 926.7 mm ² , which is larger than that of Example 1.

[Comparative Example 2]
Although the structure is the same as that of the first embodiment, the circuit pattern A121, the circuit pattern B122, and the circuit pattern C123 are not formed with R at the corners, and have a curvature radius of about 0.2 mm that is inevitably attached during etching. A silicon nitride wiring substrate 1 with R was produced. In addition, the manufacturing method of the silicon nitride wiring board 1 was made the same as that of Example 1, and the presence or absence of the crack was similarly measured before and after the heat cycle test.

[Comparative Example 3]
Although the structure is the same as that of the first embodiment, R having a radius of curvature of 1.5 mm is provided only at the corner of the circuit pattern A121. A silicon nitride wiring board 1 having R with a radius of curvature of about 0.2 mm that is inevitably attached at the time of etching was prepared without forming R at the corners of the circuit pattern B122 and the circuit pattern C123. In addition, the manufacturing method of the silicon nitride wiring board 1 was made the same as that of Example 1, and the presence or absence of the crack was similarly measured before and after the heat cycle test.

[Comparative Example 4]
Although the structure is the same as that of the first embodiment, R having a radius of curvature of 1.5 mm is provided only at the corner of the circuit pattern B122. A silicon nitride wiring substrate 1 having no R formed at corners of the circuit pattern A121 and the circuit pattern C123 and having an R of a curvature radius of about 0.2 mm that is inevitably attached during etching was manufactured. In addition, the manufacturing method of the silicon nitride wiring board 1 was made the same as that of Example 1, and the presence or absence of the crack was similarly measured before and after the heat cycle test.

  Table 1 shows whether or not R is formed at the corners of each circuit pattern of the metal circuit board of the silicon nitride wiring board of Example 1 and Comparative Examples 1 to 4, the substrate area, and the ratio of the silicon nitride wiring board where cracks occurred. Show. The substrate area indicates the area of one surface of the silicon nitride substrate (the same applies hereinafter).

From Example 1 and Comparative Example 1, 10T ² S ¹ when the area of the silicon nitride substrate is S and the thickness T is the metal circuit board pattern in the silicon nitride wiring substrate configured as shown in FIGS. By forming R with a radius of curvature of 1.5 mm at the corners of the circuit patterns A and B having a larger area than the value of ^{/ 2} , the stress around the corners of the metal circuit board pattern can be relieved, and the silicon nitride substrate It has been found that the occurrence of cracks can be suppressed. In particular, in Example 1, R having a radius of curvature of 1.0 mm or more was not formed in the circuit pattern C, but no crack was generated before and after the heat cycle test. On the other hand, in Comparative Example 1, since R is also provided in the circuit pattern C having a small area, the substrate area is larger than that in Example 1. Further, in Comparative Example 1, since the distance between the metal circuit board patterns is increased due to the increase in the substrate area, it is necessary to lengthen the wire bonding when the semiconductor module is manufactured, and parasitic resistance, capacitance, and inductance are increased. There is also a problem that becomes larger.
Further, when R is not formed at the corners of the circuit patterns A, B and C as in Comparative Example 2, cracks are generated on the silicon nitride substrate around the corners of the circuit pattern A before and after the heat cycle test. there were. In Comparative Example 3, R having a radius of curvature of 1.5 mm is provided at the corner of the circuit pattern A, but R is not formed at the corner of the circuit pattern B. There was a silicon nitride wiring board in which cracks occurred on the silicon nitride substrate around the corner of the circuit pattern B before and after the test. Even in Comparative Example 4, R having a radius of curvature of 1.5 mm is provided at the corner of the circuit pattern B, but R is not formed at the corner of the circuit pattern A, so the periphery of the corner of the circuit pattern A before and after the heat cycle test. There was a silicon nitride wiring substrate in which cracks occurred on the silicon nitride substrate.

[Example 2]
A silicon nitride wiring board having a structure similar to that of Example 1 but having a larger area than that of Example 1 in which the area of the silicon nitride substrate is 1043 mm ² was produced. The thickness of the silicon nitride substrate was 0.3 mm, and the value of 10T ² S ^1/2 when the area of the silicon nitride substrate was S and the thickness T was 33.1.
The metal circuit board is composed of three types of circuit patterns, a circuit pattern A, a circuit pattern B, and a circuit pattern C, as in the first embodiment, and each area is 396 mm ² , 98 mm ^2, and 12.8 mm ² . The corners of the circuit pattern A, the circuit pattern B, and the metal heat radiating plate are provided with R having a curvature radius of 1.5 mm. On the other hand, no R is intentionally formed at the corners of the circuit pattern C. However, a radius of curvature of about 0.2 mm is inevitably attached during etching. The silicon nitride wiring substrate was manufactured in the same manner as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

[Comparative Example 5]
Although the structure is the same as that of the second embodiment, only a corner portion of the circuit pattern A is provided with R having a curvature radius of 1.5 mm. A silicon nitride wiring board with R having a radius of curvature of about 0.2 mm, which is inevitably attached during etching, was not formed at the corners of the circuit patterns B and C. The silicon nitride wiring substrate was manufactured in the same manner as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

[Comparative Example 6]
Although the structure is the same as that of the second embodiment, the circuit pattern A, the circuit pattern B, and the circuit pattern C do not have R at the corners and have a radius of curvature of about 0.2 mm that is inevitably attached during etching. A silicon nitride wiring board with R was produced. The silicon nitride wiring substrate was manufactured in the same manner as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

[Example 3]
A silicon nitride wiring board having a structure similar to that of Example 2 but having a silicon nitride substrate thickness of 0.6 mm was manufactured. The value of 10T ² S ^1/2 when the area of the silicon nitride substrate was S and the thickness T was 128.2. The corners of the circuit pattern A, the circuit pattern B, and the metal heat radiating plate are provided with R having a curvature radius of 1.5 mm. On the other hand, no R is intentionally formed at the corners of the circuit pattern C. However, a radius of curvature of about 0.2 mm is inevitably attached during etching. The silicon nitride wiring substrate was manufactured in the same manner as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

[Example 4]
Although the structure is the same as that of the third embodiment, only a corner portion of the circuit pattern A is provided with an R having a curvature radius of 1.5 mm. A silicon nitride wiring board with R having a radius of curvature of about 0.2 mm, which is inevitably attached during etching, was not formed at the corners of the circuit patterns B and C. The silicon nitride wiring substrate was manufactured in the same manner as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

[Comparative Example 7]
Although the structure is the same as that of the third embodiment, the circuit pattern A, the circuit pattern B, and the circuit pattern C do not have R at the corners, and have a radius of curvature of about 0.2 mm that is inevitably attached during etching. A silicon nitride wiring board with R was produced. The silicon nitride wiring substrate was manufactured in the same manner as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

  Table 2 shows whether or not R is formed at the corners of each circuit pattern of the metal circuit board of the silicon nitride wiring boards of Examples 2 to 4 and Comparative Examples 5 to 7, and the silicon nitride wiring board having cracks. Indicates the percentage. The substrate thickness indicates the thickness of the silicon nitride substrate (the same applies hereinafter).

As in Examples 2 to 4, the corners of the circuit patterns A and B having a larger area than the value of 10T ² S ^1/2 when the area of the silicon nitride substrate is S and the thickness T is the metal circuit board pattern. It was found that by forming R with a radius of curvature of 1.5 mm in the portion, the stress around the corner of the metal circuit board pattern can be relieved and the occurrence of cracks in the silicon nitride substrate can be suppressed.
In particular, when Example 4 and Comparative Example 5 are compared, in Comparative Example 5 in which the substrate thickness is 0.3 mm, the circuit pattern in which the value of 10T ² S ^1/2 is as small as 33.1 and R is not formed. There was a silicon nitride wiring board in which cracks occurred around the corners of B. On the other hand, in Example 4 where the substrate thickness is 0.6 mm, the value of 10T ² S ^1/2 is as large as 128.2, and R is not formed on the circuit pattern B, but cracks occurred before and after the heat cycle test. Was not seen.
Further, in Example 3, R having a curvature radius of 1.5 mm is formed in the circuit pattern B in Example 3, but the area of the circuit pattern B is sufficiently large. Sufficiently secured. Although the radius of curvature of R is 1.5 mm, it has been confirmed that the same effect can be obtained even at 1.0 mm. In addition, although it is considered that the same effect is obtained even with R having a curvature radius of 1.5 mm or more, in this case, not only the mounting area is reduced, but also the area of the portion where the metal circuit board on the silicon nitride substrate is not joined is increased. Since there is a possibility that the stress generated in the silicon nitride substrate is increased, it is necessary to prevent the problem from occurring. This is considered to be up to R2.5 mm.

From the above, by not providing R at the corners of the circuit pattern having an area of 13 mm ² or less, the silicon nitride wiring board can be reduced in size while ensuring a sufficient mounting area. By providing R only at the corners of the circuit pattern having a larger area than the value of 10T ² S ^1/2 when S is the thickness T, the stress generated in the silicon nitride substrate can be reduced. Thus, it was found that a small and highly reliable silicon nitride substrate having a sufficient mounting area can be produced. This is because the stress generated near the corners of the metal circuit board of the silicon nitride substrate is due to the deformation of the silicon nitride substrate due to the difference in thermal expansion between the metal circuit board and the silicon nitride substrate, and the area of the metal circuit board pattern is sufficiently large. This is because, if it is small, the difference in thermal expansion between the metal circuit board and the silicon nitride substrate is also small, so that the stress generated near the corner of the metal circuit board of the silicon nitride substrate is also small.

[Example 4]
The creeping distance from the outer edge portion of the silicon nitride substrate 11 to the outer edge portion of the metal circuit board 12 and the creeping distance from the outer edge portion of the silicon nitride substrate 11 to the outer edge portion of the metal heat radiating plate 13 are the same as in the first embodiment. A silicon nitride wiring board 1 having a thickness of 1.0 mm was produced. The area and shape of the metal circuit board 12 and the metal heat sink 13 were the same as in Example 1, and the width and length of the silicon nitride substrate 11 were made 1.0 mm smaller than in Example 1. In addition, the manufacturing method of the silicon nitride wiring board 1 was made the same as that of Example 1, and the presence or absence of the crack was similarly measured before and after the heat cycle test.

[Example 5]
The creeping distance from the outer edge of the silicon nitride substrate 11 to the outer edge of the metal circuit board 12 is 1.0 mm with the same structure as in the first embodiment, and from the outer edge of the silicon nitride substrate 11 to the outer edge of the metal heat sink 13. A silicon nitride wiring board 1 having a creepage distance of 0.5 mm was produced. The area and shape of the metal circuit board 12 are the same as those of the first embodiment, the width and length of the metal heat sink 13 are 1.0 mm larger than those of the first embodiment, and the width and length of the silicon nitride substrate 11 are implemented. It was 1.0 mm smaller than Example 1. In addition, the manufacturing method of the silicon nitride wiring board 1 was made the same as that of Example 1, and the presence or absence of the crack was similarly measured before and after the heat cycle test.

[Comparative Examples 8 to 10]
The creeping distance a from the outer edge of the silicon nitride substrate 11 to the outer edge of the metal circuit board 12 and the creeping distance from the outer edge of the silicon nitride substrate 11 to the outer edge of the metal heat sink 13 with the same structure as in the comparative example 3. Silicon nitride wiring boards 1 having different b were produced. The creepage distance of each comparative example is shown in Table 2.
In Comparative Example 8, the area and shape of the metal circuit board 12 are the same as in Comparative Example 3, the width and length of the metal heat dissipation plate 13 are made 2.0 mm smaller than those in Comparative Example 3, and the width of the silicon nitride substrate 11 and The length was made 1.0 mm smaller than Comparative Example 3.
Further, in Comparative Example 9, the area and shape of the metal circuit board 12 are the same as in Comparative Example 3, and the width and length of the metal heat radiating plate 13 are made 2.0 mm smaller than those in Comparative Example 3, so that the silicon nitride substrate 11 The width and length were 2.0 mm smaller than Comparative Example 3.
In Comparative Example 10, the area and shape of the silicon nitride substrate 11 and the metal circuit board 12 were the same as in Comparative Example 3, and the width and length of the metal heat radiating plate 13 were made 2.0 mm larger than in Comparative Example 3. In addition, the manufacturing method of the silicon nitride wiring board 1 was made the same as that of Example 1, and the presence or absence of the crack was similarly measured before and after the heat cycle test.

  Table 3 shows the creepage distance from the outer edge of the silicon nitride substrate to the outer edge of the metal circuit board of Examples 1, 4 and 5 and Comparative Examples 3, 8 to 10, and the outer edge of the silicon nitride substrate. The creepage distance to the outer edge part of a metal heat sink, and the ratio of the silicon nitride wiring board in which the crack occurred in the outer peripheral part of the metal circuit board before and after the heat cycle test are shown.

From the results of Examples 1, 4 and 5, the circuit pattern A121 and the circuit pattern having a larger area than the value of 10T ² S ^1/2 when the area of the silicon nitride substrate 11 is S and the thickness T as shown in FIG. The silicon nitride wiring substrate 1 is composed of the metal circuit board 12 formed of the metal circuit board 12 in which R is formed at the corner of B122 and R is not formed at the corner of the circuit pattern C123 having an area smaller than 13 mm ^2. When the creepage distance a from the outer edge portion of the metal circuit board 12 to the outer edge portion of the metal circuit board 12 and the creepage distance b from the outer edge portion of the silicon nitride substrate 11 to the outer edge portion of the metal heat radiating plate 13 are 0.5 or more, It is possible to obtain a structure in which the stress generated in the silicon nitride substrate 11 is relaxed by setting the value of ab to be -0.5 mm or more and 0.5 mm or less, both before and after the heat cycle test. Crap It was found that a silicon nitride wiring board free from generation of defects can be obtained.
On the other hand, as in Comparative Examples 8 to 10, the relationship between the creepage distance a and the creepage distance b is such that a / b is 0.5 or more and 2 or less, or the value of ab is −0.5 mm or more and 0.5 mm or less. In the case where the metal circuit board and the heat radiating plate are separated from each other, a larger stress is applied to the outer peripheral portion of the metal circuit board and the metal heat radiation plate, particularly around the corner portion, and both the cracks before and after the heat cycle test than Comparative Example 3 where the area and shape of the metal circuit board are the same. There were many silicon nitride wiring boards on which this occurred.

[Examples 6 and 7]
FIG. 3 shows a bottom view of the silicon nitride wiring board 3 according to the sixth embodiment. On the outer peripheral portion of the metal heat dissipating plate 33 joined to the bottom surface of the silicon nitride substrate 31, holes of φ1.0 mm are formed at intervals of 2.0 mm. The hole 34 passes through the metal heat radiating plate 33 and reaches the surface of the silicon nitride substrate 31. In the seventh embodiment, as in the sixth embodiment, φ34 mm holes 34 are formed in the outer peripheral portion of the metal heat radiating plate 33 at intervals of 2.0 mm. However, the holes 34 penetrate the metal heat radiating plate 33. However, it is formed to a depth of 2/3 of the thickness of the metal heat radiating plate 33. Both Examples 6 and 7 have the same structure as that of Example 1 except for the metal heat radiating plate 33. The method for producing the silicon nitride wiring board 3 was the same as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

[Comparative Examples 11 and 12]
Comparative Example 11 has the same structure as Comparative Example 3, but holes of φ1.0 mm are formed at intervals of 20 mm on the outer periphery of the metal heat sink. The hole penetrates the metal heat radiating plate and reaches the surface of the silicon nitride substrate. Further, in Comparative Example 12, as in Comparative Example 11, holes of φ1.0 mm are formed at intervals of 20 mm in the outer peripheral portion of the metal heat sink, but the metal heat sink is not penetrated, It is formed to a depth of 2/3 of the thickness. Both Comparative Examples 11 and 12 have the same structure as Comparative Example 3 except for the metal heat sink. The silicon nitride wiring substrate was manufactured in the same manner as in Example 1, and the presence or absence of cracks was measured before and after the heat cycle test.

  Table 4 shows the area of the holes and the ratio of the volume and the volume of the metal heat sink formed in the outer peripheral portion of the metal heat sinks of Examples 1, 6 and 7 and Comparative Examples 3, 11 and 12 to before and after the heat cycle test. Shows the ratio of the silicon nitride wiring board in which cracks occurred.

From the results of Examples 6 and 7, the circuit pattern A121 and the circuit pattern B122 having a larger area than the value of 10T ² S ^1/2 when the area of the silicon nitride substrate 11 is S and the thickness T as shown in FIG. The silicon nitride wiring board 1 is composed of the metal circuit board 12 formed with the corners of the circuit pattern C123 having an R smaller than 13 mm ^{2 and} not formed with the corners of the circuit pattern C123. A hole 34 occupying an area 0.02 to 0.09 times the metal heat sink pattern area and 0.01 to 0.09 times the metal heat sink pattern volume is formed in the outer periphery of the heat sink 34. Thus, it was found that a structure in which the stress generated in the silicon nitride substrate 31 was relaxed could be obtained, and that a silicon nitride wiring substrate free from cracks could be obtained before and after the heat cycle test.
Further, in order to verify the effect of the hole formed in the outer peripheral portion of the metal heat sink, the silicon nitride wiring board of Example 1 in which no hole is formed and the silicon nitride wiring of Example 6 and Example 7 in which the hole is formed The heat cycle test of the substrate was performed under more severe conditions of −60 ° C. to 180 ° C. and 1000 cycles. As a result, generation of cracks was observed only in the silicon nitride wiring substrate of Example 1. It was found that by forming a hole in the outer peripheral portion of the metal heat radiating plate, the stress on the silicon nitride substrate can be further relaxed, and a more reliable silicon nitride wiring substrate can be obtained.
On the other hand, as in Comparative Examples 11 and 12, the area of the formed hole is outside the range of 0.02 to 0.09 times the metal heat sink pattern area, or the volume of the formed hole is a metal heat sink pattern. When the volume is outside the range of 0.01 times to 0.09 times, even if a hole is formed in the outer periphery of the metal heat sink, the effect of relieving the stress generated in the silicon nitride substrate is small. The ratio of the substrate where cracks occurred before and after was the same as that of the silicon nitride wiring substrate of Comparative Example 3 in which holes were not formed with the same structure of the silicon nitride substrate.

  Next, a semiconductor module was manufactured using the silicon nitride wiring substrates of Examples 1 to 7 and Comparative Examples 1 to 12 described above as the silicon nitride wiring substrate. The semiconductor element was soldered on a metal circuit board and wire-bonded to obtain a semiconductor module. In addition, only the silicon nitride wiring board which confirmed that there was no crack generation after production was used. Ten semiconductor modules were produced for each silicon nitride wiring board, and a heat cycle test was performed 1000 cycles at -40 ° C to 125 ° C.

Table 5 shows the ratio of the semiconductor modules in which cracks occurred in the silicon nitride substrate before and after the heat cycle test among the semiconductor modules manufactured using the silicon nitride wiring substrates of Examples 1 to 7 and Comparative Examples 1 to 12.

As in Examples 1 to 7, in the semiconductor module manufactured using the silicon nitride wiring board in which no crack was generated even after 1000 cycles of the heat cycle test, no crack was observed before and after the heat cycle test. . On the other hand, the generation of cracks was not observed in the semiconductor module manufactured using the silicon nitride wiring board of Comparative Example 1, but the size of the silicon nitride wiring board was larger than those of Examples 1 to 7, and The size has also increased.
Moreover, although the semiconductor module produced using the silicon nitride wiring board of Comparative Examples 1-12 was produced using the silicon nitride wiring board which did not generate | occur | produce a crack, after producing a semiconductor module or heat Many cracks occurred after the cycle test.
As described above, according to the present invention, for example, by using a silicon nitride wiring board having a structure in which stress is relieved as in Examples 1 to 7, a small semiconductor module that is resistant to thermal shock, has high reliability, and is provided. We were able to.

It is a figure which shows the form of the silicon nitride wiring board of Example 1 of this invention, (a) is a top view, (b) is a bottom view, (c) is a side view. It is a top view which shows the form of the silicon nitride wiring board of the conventional comparative example 1. FIG. It is a bottom view which shows the form of the silicon nitride wiring board of Example 6 of this invention.

Explanation of symbols

1, 2, 3: Silicon nitride wiring substrate 11, 21, 31: Silicon nitride substrate 12, 22: Metal circuit board 121, 122, 123, 221, 222, 223: Circuit pattern 13, 33: Metal heat sink 34: Hole

Claims (4)

In a silicon nitride wiring board comprising a silicon nitride substrate, a plurality of metal circuit boards bonded to one surface of the silicon nitride substrate, and a metal heat sink bonded to the other surface of the silicon nitride substrate, When the thickness of the silicon nitride substrate is 0.2 mm or more, the thickness of the metal circuit board and the metal heat sink is 0.4 mm or more, and the area of one surface of the silicon nitride substrate is S and thickness T, 10T R having a radius of curvature of 1.0 mm to 2.5 mm is formed at the corner of the metal circuit board pattern having an area greater than or equal to the value represented by ² S ^1/2 , but an area of 10T ² S ^1/2 or less. R is not formed at the corners of the metal circuit board pattern of which the area is 13 mm ² or less (except for the inevitable R having a radius of curvature of 0.5 mm or less). Silicon nitride wiring board . The ratio a / b between the creeping distance a from the outer edge of the silicon nitride substrate to the outer edge of the metal circuit board and the creeping distance b from the outer edge of the silicon nitride substrate to the outer edge of the metal heat sink is 0.5 or more 2 2. The silicon nitride wiring board according to claim 1, wherein a value of ab is −0.5 mm or more and 0.5 mm or less. In the metal heat radiating plate, an area of 0.02 to 0.09 times the metal heat radiating plate pattern area and a metal heat radiating plate pattern volume on the outer periphery of the metal heat radiating plate pattern having an area of 70T ² S ^1/2 or more. 3. A silicon nitride wiring board according to claim 1, wherein a hole occupying a volume of 0.01 times to 0.09 times is formed. A semiconductor module comprising the silicon nitride wiring board according to claim 1 and a semiconductor element mounted on the silicon nitride wiring board.

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