JP5319463B2 - Silicon nitride substrate with improved positioning and semiconductor device using the same - Google Patents

Description

  The present invention relates to a silicon nitride substrate with improved positioning properties and a semiconductor device using the same.

For substrates on which semiconductor elements are mounted, alumina substrates and AlN substrates are mainly used. However, since the alumina substrate has a low thermal conductivity of about 20 W / m · K, the heat dissipation is poor. Since the AlN substrate has a heat conductivity as high as 170 W / m · K or higher, it has good heat dissipation, but its strength is as low as about 300 to 400 MPa, so it is not suitable for the field where stress such as screwing is applied.
Silicon nitride substrates are attracting attention as ceramic substrates that satisfy both thermal conductivity and strength. For example, Japanese Unexamined Patent Application Publication No. 2002-201075 (Patent Document 1) discloses a silicon nitride substrate having a thermal conductivity of 50 W / m · K or more and a three-point bending strength of 500 MPa or more. Since the silicon nitride substrate has high strength, the thickness of the substrate can be reduced. As a result, even when the thermal conductivity is about 50 to 100 W / m · K, the thermal resistance as the substrate can be lowered. The heat dissipation can be improved by reducing the thermal resistance of the substrate.
Such a silicon nitride substrate can be provided with a circuit portion and mounted with various semiconductor elements to form a semiconductor device.
Examples of the semiconductor element include various elements such as a power element, a light emitting diode (LED), and a solar cell element. For example, after a power element such as an IGBT is mounted on the power element, a heat radiating fin is mounted thereon. After mounting the light emitting diode, the light emitting diode is covered with a lens member. Also about a solar cell element, after mounting a solar cell element, a lens member is mounted.
As described above, many recent semiconductor devices have another member mounted after the semiconductor element is mounted.
In general, since a ceramic substrate is rectangular, when mounting a semiconductor element, or mounting a radiating fin or a lens member, the mounting process is performed with the four corners fixed.

JP 2002-201075 A

However, in the method of fixing the four corners, a lot of labor is required for fixing work, and a large amount of displacement occurs during fixing. When the position shift occurs, it is necessary to correct it. Further, when the semiconductor element is mounted with its position shifted, members (heat radiating fins, lens members, and the like) mounted thereafter are also displaced and the function of the semiconductor device is degraded.
An object of the present invention is to provide a silicon nitride substrate in which positioning of semiconductor elements is easy and the positioning performance is high and a semiconductor device using the silicon nitride substrate.

The silicon nitride substrate having improved positioning properties according to the present invention is characterized by having a through hole and a recess facing at least one side.
The thickness of the silicon nitride substrate is preferably 0.2 mm or more and 1 mm or less. The silicon nitride substrate preferably has a thermal conductivity of 60 W / m · K or more and a three-point bending strength at room temperature of 600 MPa or more.
Moreover, it is preferable that the diameter of the said through-hole is 1 mm or more and 5 mm or less. Moreover, it is preferable that the said recessed part is 1 mm or more and 5 mm or less in width, and 1 mm or more and 5 mm or less in depth. The shortest distance between the through hole and one side of the substrate is preferably 1 mm or more. The shortest distance between the recess and one side of the substrate is preferably 1 mm or more.
Such a silicon nitride substrate with improved positioning is suitable for a semiconductor device including a semiconductor element mounted on the silicon nitride substrate with improved positioning.

  According to the present invention, it is possible to provide a silicon nitride substrate in which positioning of semiconductor elements is easy and the positioning property with high strength is improved. Further, by using these silicon nitride substrates, a highly reliable semiconductor device can be provided. In particular, this is effective in a semiconductor device in which another member must be mounted after mounting a semiconductor element.

The top view of the silicon nitride board | substrate which improved the positioning property which concerns on embodiment of this invention. The top view of the silicon nitride board | substrate which improved the positioning property which concerns on other embodiment of this invention. 1 is a schematic diagram showing a semiconductor device according to an embodiment of the present invention. Schematic which shows the semiconductor device which concerns on other embodiment of this invention. The top view of the silicon nitride board | substrate of a comparative example.

According to the silicon nitride substrate having a through hole and a recess facing at least one side, the silicon nitride substrate is displaced by inserting a fixing jig into the through hole and the recess when the semiconductor element is mounted. Therefore, the positional deviation of the semiconductor element can be prevented. In addition, even after mounting the semiconductor element, it is possible to prevent displacement of the substrate by inserting and fixing a fixing jig into the through hole and the concave portion, so that displacement of the member to be attached after mounting the semiconductor element such as a heat radiation fin or a lens member is prevented. be able to.
In addition, when fixing the semiconductor device to the mounting substrate (mounting member), positioning can be performed by fitting the through hole and the concave portion into a convex portion (for example, a screw portion) provided in the mounting substrate. Positioning becomes easy.

  In addition, since the silicon nitride substrate has high mechanical strength, for example, the substrate can be prevented from cracking when the semiconductor device is screwed to the mounting substrate or when vibration is applied to the semiconductor device.

Since the silicon nitride substrate has a high toughness of fracture toughness of 6 MPa · m ^1/2 or more, it is difficult to crack when screwing. In addition, there are fewer defects such as cracks due to vibration compared to other ceramic substrates (such as AlN substrates). Therefore, even if the thickness of the substrate is reduced, it is possible to avoid cracking of the substrate, so that the thermal resistance of the silicon nitride substrate can be lowered, so that heat dissipation can be improved.

Fracture toughness is obtained by the new original method using the new original equation shown in the following equation (1).
Niihara formula = 0.0114E ^0.4 P ^0.6 a ^-0.7 (C / a-1) ^-0.5 (1)
Where P is the load (Kgf), d is the diagonal length of the indentation (mm), E is the Young's modulus (Kgf / mm 2), C is the length of the crack from the center point of the indentation (mm), and a is the diagonal length of the indentation 1/2 (mm).

  The silicon nitride substrate desirably has a mechanical property of a three-point bending strength of 500 MPa or more at room temperature. Thereby, the crack at the time of screwing can be prevented. A more preferable range is 600 MPa or more.

  When a silicon nitride substrate is used as the ceramic substrate, the thickness of the silicon nitride substrate is preferably 0.2 mm or more and 1 mm or less. By making the plate thickness 0.2 mm or more, it is possible to prevent cracking when screwing. Moreover, high heat dissipation can be obtained by setting the plate thickness to 1 mm or less. Moreover, Preferably it is 0.2-0.5 mm.

  The silicon nitride substrate preferably has a thermal conductivity of 60 W / m · K or more and a three-point bending strength of 600 MPa or more at room temperature. Such a substrate is difficult to break when screwed and has excellent heat dissipation. As a silicon nitride substrate having excellent thermal conductivity, strength, and fracture toughness, there is a silicon nitride substrate disclosed in Japanese Patent Application Laid-Open No. 2002-201075 (Patent Document 1).

  A circuit portion can be provided on the silicon nitride substrate with improved positioning. A semiconductor element is mounted on the circuit portion. The circuit portion can be formed from, for example, a metal circuit board obtained by bonding a copper plate or an Al plate, or a thin film circuit layer provided with a metal thin film. The silicon nitride substrate to which the copper circuit board is bonded has excellent strength against vibration. The copper circuit board can be bonded by, for example, an active metal bonding method or a direct bonding method (DBC method). Further, the circuit portion can be provided by a metallization method using a high melting point metal paste such as tungsten or molybdenum.

Next, an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a plan view of a silicon nitride substrate with improved positioning according to an embodiment of the present invention. A silicon nitride substrate 1 with improved positioning (hereinafter referred to as substrate 1) has one recess 2 facing one long side and one through-hole 3 located near the other long side. .

  The size of the substrate 1 is not particularly limited, but the length of one side is preferably 10 mm or more and 300 mm or less. The length of each side may be 10 mm or more and 300 mm or less for each of the long side L1 and the short side L2 as illustrated in FIG. 1, but the range of all sides is 10 mm or more and 300 mm or less. The same length may be used.

  The diameter φ of the through hole 3 varies depending on the screw size used for screwing, but is desirably 1 mm or more and 5 mm or less in order to secure the installation area of the circuit portion.

The size of the recess 2 varies depending on the screw size used for screwing, but the width W1 is 1 mm or more and 5 mm or less and the depth W2 is 1 mm or more and 5 mm or less in order to secure the circuit area. It is desirable that Here, the width W1 is the maximum length among the lengths of the recesses 2 parallel to one side of the substrate, and the depth W2 is the maximum distance among the distances from one side of the substrate to the inner wall of the recesses 2.
It is desirable that the shortest distance L3 between the through hole 3 and one side of the substrate and the shortest distance L4 between the concave portion 2 and one side of the substrate are 1 mm or more. Thereby, it is possible to avoid breakage such as cracking of the substrate at the time of screwing.

  The number of the recesses 2 and the through holes 3 provided in the substrate 1 can be one or more. In the case of providing a plurality, one may be provided on one side of the substrate 1 or one on each side. For example, as illustrated in FIG. 2, a plurality of recesses 2 may be provided on one long side of the substrate 1.

FIG. 3 shows an embodiment of a semiconductor device in which a semiconductor element is mounted on a silicon nitride substrate with improved positioning performance according to this embodiment. In addition, about the member similar to having demonstrated in FIG. 1, the same code | symbol is attached | subjected and description is abbreviate | omitted.
As shown in FIG. 3, the semiconductor device includes a silicon nitride substrate 1 with improved positioning properties, a circuit portion 5 provided on the silicon nitride substrate, and a semiconductor element 4 provided on the circuit portion 5.

This semiconductor device is fixed to a mounting member (housing, pedestal, etc.) with screws 6 to form a semiconductor module. Further, when screwing, a washer may be bitten as necessary. 3 and 4, the screwing structure is shown, but the present invention is not limited to the screwing, and a fixing member can be inserted into the recess and the through hole for mounting.
3 shows a structure in which one solar cell element is mounted, but a structure in which two or more semiconductor elements are mounted on a silicon nitride substrate as shown in FIG. 4 may be adopted.

  Further, when a power element is used as the semiconductor element, a heat dissipating fin, a light emitting diode, or a solar cell element can be used, and a lens member or the like can be further mounted.

  Such a silicon nitride substrate with improved positioning can fix the substrate with through holes and recesses, so when mounting a semiconductor element, mounting a radiating fin or lens member, mounting a semiconductor device, etc. In either case, misalignment can be prevented. For this reason, the positioning can be improved in a plurality of steps from mounting of the semiconductor element to mounting of the semiconductor device.

  Further, since the silicon nitride substrate has high strength, the screwing torque can be increased to 10 N · m or more, and further to 20 N · m or more. For this reason, it is suitable for a headlight substrate that needs to be firmly fixed. In particular, a silicon nitride substrate is preferable because it can maintain a strength of 600 MPa or more even if it has through holes and recesses. The upper limit of the screwing torque is affected by the strength of the mounting member, but is preferably 40 N · m or less.

(Examples 1-5)
The recess 2 and the through hole 3 shown in FIG. 1 were formed on the silicon nitride substrate 1 by punching. The diameter (φ) of the through hole, the shortest distance L3 (mm) between the through hole 3 and one side of the substrate, the width W1 and depth (depth) W2 (mm) of the concave portion 2, and the shortest distance L4 between the concave portion 2 and one side of the substrate ( mm) is shown in Table 1 below.
(Comparative Examples 1-2)
A ceramic substrate in which neither a recess nor a through hole was formed was prepared.

Materials of ceramic substrates used in the above examples and comparative examples, three-point bending strength (MPa) at room temperature, thermal conductivity (W / m · K), fracture toughness (MPa · m ^1/2 ), size (longitudinal ( L2) × width (L1) × thickness (mm)) is shown in Table 1 below. The three-point bending strength was measured according to JIS-R-1601. In addition, the laser conductivity was used for the thermal conductivity. Fracture toughness was determined by the Niihara equation according to the microindication method of JIS-R-1607.

The copper circuit board shown in Table 2 was joined to the ceramic substrate which concerns on Examples 1-5 and Comparative Examples 1-2 using the Ag-Cu-Ti active metal brazing material. A back copper plate for warpage prevention was joined.
Using each circuit board, a semiconductor circuit was mounted at a predetermined position on the copper circuit board to obtain a semiconductor device. In the mounting process, the semiconductor element was joined on the copper plate with solder.

  Next, the semiconductor devices of Examples 1 to 5 were fixed to the mounting member by screwing. In the screwing step, screwing was performed at two locations of the through hole and the recess through a screw having a diameter of 1.9 mm and a washer having an outer diameter of 3 mm. The torque for screwing was 25 to 30 N · m.

On the other hand, as shown in FIG. 6, the semiconductor devices of Comparative Examples 1 and 2 were fixed using screws 22 via jigs 21 while suppressing the four corners of the substrate 20. The torque at the time of screwing was set to the same value as in the example.
The ratio of the substrate that was broken when each substrate was screwed was measured. In addition, the occurrence rate of misalignment was measured when the position of the semiconductor element was not mounted at the target location. The results are shown in Table 2.

As is apparent from Table 2, the substrates according to Examples 1 to 5 were not cracked. This is because the silicon nitride substrate having a strength of 600 MPa or more is used. Also, there was little occurrence of misalignment. This is because the substrate is fixed by the recess and the through-hole, so that it is difficult for deviation to occur.
On the other hand, since Comparative Examples 1 and 2 are of the type in which the four corners are fixed, the occurrence of positional deviation was large. Also, the probability of cracking increased when torque was applied to four locations.

(Examples 6 to 10)
The same substrate as Example 2 or Example 4 was prepared except that L3 and L4 were changed as shown in Table 3, and the results of the same measurement are shown below.

In the case of a silicon nitride substrate having high strength and toughness such as a silicon nitride substrate, it can be seen that cracks can be prevented if the through holes and the recesses are 1 mm or more from the edge (L3 and L4 are 1 mm or more). Therefore, the silicon nitride substrate can be provided with through holes and recesses at the ends, so that the area for joining the copper plates can be increased or the degree of freedom can be increased. It is possible to mount a plurality of semiconductor elements on a silicon nitride substrate if the copper plate is enlarged or if the degree of freedom increases in the bonding position of the copper plate.
In addition, regarding the establishment of misalignment, only the misalignment at the time of mounting the semiconductor element was measured this time. However, the same misalignment is also observed when mounting the heat dissipating fin or lens member and screwing to the mounting member. Occur. For this reason, it is desirable that no positional deviation occurs as in this embodiment. In other words, it is effective to be able to fix with fixing portions having different shapes such as through holes and concave portions.

DESCRIPTION OF SYMBOLS 1 ... Silicon nitride board | substrate 2 which improved positioning property ... Recess 3 ... Through-hole 4 ... Semiconductor element 5 ... Circuit part 6 ... Screw

Claims (8)

A silicon nitride substrate having a thermal conductivity of 60 W / m · K or more, a three-point bending strength at room temperature of 600 MPa or more, a plate thickness of 0.2 mm or more and 1 mm or less, a through hole, and a recess facing at least one side; The shortest distance between the through hole and one side of the substrate is 1 mm or more, the shortest distance between the recess and one side of the substrate is 1 mm or more, and the screwing torque can be 10 N · m or more . Improved silicon nitride substrate. The silicon nitride substrate for improving positioning according to claim 1, wherein the diameter of the through hole is 1 mm or more and 5 mm or less. 3. The silicon nitride with improved positioning properties according to claim 1 , wherein the recess has a width of 1 mm or more and 5 mm or less and a depth of 1 mm or more and 5 mm or less. substrate. The fracture toughness value of the silicon nitride substrate is 6 MPa · m ^1/2 The silicon nitride substrate with improved positioning properties according to any one of claims 1 to 3, wherein the silicon nitride substrate is improved. The silicon nitride substrate with improved positioning properties according to any one of claims 1 to 4, wherein the screwing torque can be 20 N · m or more. A silicon nitride substrate with improved positioning according to any one of claims 1 to 5 , and a semiconductor element mounted on the circuit part, the circuit part being provided on the silicon nitride substrate. A featured semiconductor device. 7. The semiconductor device according to claim 6 , wherein a plurality of semiconductor elements are mounted. The semiconductor device according to claim 6 , wherein the semiconductor element is any one of a power element, a light emitting diode, and a solar cell element.

Images