JP2003168770A - Silicon nitride circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit board which hardly warps even when a metal circuit board is made 1 mm thick or more for raising the current capacity. <P>SOLUTION: A metal clad material which is at least 1 mm thick is jointed to at least one surface of a silicon nitride substrate. As the metal clad material, combination of a conductive material such as a Cu plate or an Al plate and a low thermal expansion metal such as a covar plate or a tungsten plate is preferable. The warp amount of a circuit board can be made at most 0.1 mm/ inch by using such a metal clad material. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride circuit board using a silicon nitride sintered body.

[0002]

2. Description of the Related Art In recent years, the amount of heat generated by a semiconductor element has become a problem as the capacity and speed of the semiconductor element increase. In order to solve these heat generation problems, a ceramic substrate has been used as a heat dissipation substrate. Among ceramic substrates, an aluminum nitride sintered body is drawing attention as a material having good thermal conductivity from the viewpoint of heat dissipation. However, the material strength of the aluminum nitride sintered body is lower than that of the silicon nitride sintered body, which has been a cause of problems such as breakage due to applications requiring high reliability and assembly stress. Further, as the heat generation amount of the semiconductor element increases and the heat generation amount increases due to high-density mounting of the semiconductor element, both heat dissipation and material strength are required for the circuit board. In particular, for high-density mounting of semiconductor elements, a plurality of semiconductor elements such as IGBTs are mounted on one ceramic substrate. In the case of such a form, even if the heat generation amount of each element is small, a considerable heat generation amount is reached as a whole.

As a ceramic substrate satisfying both heat dissipation and material strength, Japanese Patent Laid-Open Nos. 9-69672 and 2
000-34172 gazette, etc., has a thermal conductivity of 60 W / m.
A silicon nitride substrate using a high thermal conductivity silicon nitride sintered body having a K or higher and a three-point bending strength of 500 MPa or higher has been introduced. In addition, as an example of a circuit board, the above-mentioned JP-A-9-6
Japanese Patent No. 9672 discloses a silicon nitride circuit board in which a copper plate (copper circuit board) is bonded onto a silicon nitride substrate by an active metal bonding method using an active metal such as Ti, Hf, Zr, and Nb.

[0004]

However, in the conventional combination of the silicon nitride substrate and the copper circuit board, the thickness of the circuit is limited due to the difference in the coefficient of thermal expansion, and the copper plate of 0.5 mm or less is often used. It was As described above, in order to mount a plurality of semiconductor elements on one (one) silicon nitride substrate in a high-density mounting or a semiconductor element having a large capacity, the current carrying capacity of the metal circuit board must be obtained. Although it is necessary to increase the thickness of the metal circuit board in order to increase the current-carrying capacity, the thickness of the copper board is reduced to 1 in the conventional configuration with only the copper circuit board.
If the thickness is greater than or equal to mm, there is a problem that the amount of warp increases due to the difference in thermal expansion with the silicon nitride substrate. The present invention has been made to solve the above problems, and provides a circuit board using a metal clad material having a thickness of 1 mm or more and a silicon nitride substrate.

[0005]

SUMMARY OF THE INVENTION According to the present invention, the thickness of a metal circuit board is increased in order to increase the current-carrying capacity of the metal circuit board. In order to prevent the warp of the circuit board, the silicon nitride circuit board is characterized in that a metal clad material having a thickness of 1 mm or more is bonded to at least one surface of the silicon nitride board. Further, the thickness of the metal clad material is preferably 1 mm or more and 3 mm or less. Alternatively, a metal clad material having a thickness of 1 mm or more may be bonded to both surfaces of the silicon nitride substrate. The metal clad material is preferably made of a material in which a low thermal expansion metal and a conductive material are combined, and the plate thickness of the silicon nitride substrate is preferably in the range of 0.1 to 0.7 mm.

Further, the present invention can improve the above-mentioned problem of warpage, and is therefore effective even for a large substrate having a short side of the silicon nitride substrate of 50 mm or more. Furthermore, even if the substrate is a large one, the warpage amount of the silicon nitride circuit substrate can be reduced to 0.
It can be 1 mm / inch or less. Further, the metal clad material and the silicon nitride substrate may be bonded by an active metal bonding method, and the bonding strength of the metal clad material may be 5 kN / m or more in peel strength. By satisfying the above configuration, a plurality of semiconductor elements can be mounted on a silicon nitride circuit board, and a silicon nitride circuit board can be provided in which defects such as warpage are unlikely to occur even when a plurality of elements are mounted. Is.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the silicon nitride circuit board of the present invention will be described below. First, the present invention uses a silicon nitride substrate. The silicon nitride substrate is not particularly limited, and a known silicon nitride substrate can be used. However, the above-mentioned JP-A-9-69672 and JP-A-2-69672.
Thermal conductivity 6 as described in Japanese Patent Publication No. 000-34172.
It is preferably 0 W / m · K or more and three-point bending strength of 500 MPa or more.

The metal clad material (metal laminated plate) is not particularly limited as long as it is a composite metal plate formed by joining two or more kinds of metal plates and / or alloy plates, and the joining method is rolling, There is no particular limitation such as welding and explosive pressure bonding. However, in the present invention, a metal clad material does not include a material in which metal plates (or alloy plates) are multilayered with a resin adhesive layer interposed therebetween. In general, since the resin adhesive is insulative, it is difficult to make the entire metal clad material conductive with a metal clad material that is multilayered with an insulating layer, and it is difficult to obtain a current-carrying capacity.

In the present invention, the metal clad material has a thickness of 1
The thickness is 1 mm or more, preferably 1 mm or more and 3 mm or less. If the thickness of the metal clad material is less than 1 mm, it is not possible to say that it is necessary to use the metal clad material because the current carrying capacity cannot be sufficiently obtained. On the other hand, the thickness of the metal clad material is 3 mm
Although there is no problem even if it exceeds the above, it is rather thick from the viewpoint of current carrying capacity, but if it is too thick, the weight of the circuit board becomes heavy, so in the present invention, the preferred thickness of the metal clad material is 1 to 3 mm. did. In particular, since the metal clad material using a low thermal expansion metal plate described later tends to be heavy, the preferable plate thickness of the metal clad material is set as described above from the viewpoint of weight reduction.

The metal clad material may be provided on one surface of the silicon nitride substrate or may be provided on both surfaces. An example of the circuit board of the present invention is shown in FIGS. 1 shows a silicon nitride circuit board in which a metal clad material is bonded to only one surface (front surface), and FIG. 2 shows a silicon nitride circuit board in which a metal clad material is bonded to both surfaces.
In the figure, 1 is a silicon nitride substrate, 2 is a metal clad material, 3 is a low thermal expansion metal, 4 is a conductive material, and 5 is a back metal plate.
In the present invention, the metal clad material is bonded to the surface functioning as a circuit board, but it is preferable to provide the metal clad material on both surfaces in order to prevent the warpage of the silicon nitride substrate. In particular, the thickness of the silicon nitride substrate is 0.7 mm or less,
Furthermore, it is better to provide metal clad materials on both sides as the thickness becomes 0.4 mm or less. Further, in the silicon nitride circuit board of the type in which the metal clad material is bonded to only one surface, the back metal plate 5 is not always an essential component, and may be provided as needed.

Although a plurality of metal clad materials may be provided as shown in FIG. 3, the area ratio is 50 with respect to at least the total area of the metal circuit board existing on the same plane.
% Or more, it is desirable to use a metal clad material. Needless to say, the metal clad material can be used in various shapes according to the intended circuit shape. The metal clad material 2 is preferably made of a material in which the low thermal expansion metal 3 and the conductive material 4 are combined. As the low thermal expansion metal, a refractory metal such as tungsten or molybdenum, or an Fe-Ni alloy such as a Kovar alloy or an Invar alloy is desirable. In particular, the coefficient of linear expansion is 1 × 10 ⁻⁶ to 10
Within the range of × 10 ^-6 / ° C, the difference in thermal expansion from the silicon nitride sintered body becomes small, so that the warp of the circuit board can be made small. On the other hand, as the conductive material, a copper plate, a copper alloy plate, an aluminum plate, an aluminum alloy plate or the like having a low electric resistance value is suitable.

The metal clad material has a two-layer structure consisting of the above-mentioned low thermal expansion metal and a conductive material, but it has a sufficient function, but preferably has a three-layer structure of "conductive material / low thermal expansion metal / conductive material". Is. Since the metal clad material provided on at least one surface functions as a circuit board,
It is better to have a material with a low electric resistance value (a material with high conductivity) in the table. Further, it is preferable that the conductive material is also present on the contact surface with the silicon nitride substrate because a bonding method using an active metal brazing material described later (active metal bonding method) can be easily applied.
From this point of view, the metal clad material has a five-layer structure of “conductive material / low thermal expansion metal / conductive material / low thermal expansion metal / conductive material” or a structure having five or more layers, which is sufficiently functional. However, it is not necessarily a preferable structure from the viewpoint of increasing the weight of the circuit board.

Therefore, as a preferable metal clad material, Cu / Invar alloy / Cu, Cu / Kovar alloy /
Cu, Cu / W / Cu, Cu / Mo / Cu, Al / Invar alloy / Al, Al / Kovar alloy / Al, Al / W
One having a three-layer structure of / Al and Al / Mo / Al can be mentioned.

The ratio of the thickness of the low thermal expansion metal to the thickness of the conductive material is not particularly limited, but the linear thermal expansion coefficient of the metal clad material is 4 when the thickness of the metal clad material is 1 mm or more. It is preferably in the range of × 10 ^-6 to 10 × 10 ^-6 / ° C. When the metal clad material as described above is used, even if a silicon nitride substrate having a thin plate thickness of 0.1 to 0.7 mm is used, the warpage amount of the circuit substrate is 0.1 m.
It can be less than m / inch (1 inch = 25.4 mm).
Furthermore, the short side length of the silicon nitride substrate is 50 mm.
Even in the above-described circuit board, the warp amount can be set to 0.1 mm / inch or less. In other words, by using the above-mentioned metal clad material, the warpage amount of the silicon nitride substrate is 0.7 mm or less and the short side length is 50 mm or more.
It can be set to m / inch or less. Moreover, since the length of the short side can be increased to 50 mm or more, a plurality of semiconductor elements can be mounted on one (one) silicon nitride substrate. If a plurality of semiconductor elements can be mounted on one silicon nitride circuit board, the length of wiring (including wire bonding) between the individual semiconductor elements can be shortened, resulting in space saving and module As a result, the weight reduction can be achieved.

Further, in the case where the metal clad material is provided on both surfaces as shown in FIG. 2, the metal clad material on the back surface side does not necessarily have to function as a circuit board, and is simply a back metal plate for preventing warpage. There is no problem even if there is. When the metal clad material is used as the back metal plate in this way, the metal clad material plays the role of a heat sink (radiation plate), so that it is not necessary to separately provide a heat sink, and the space can be saved from this point as well.

Next, the manufacturing method will be described. Although the manufacturing method is not particularly limited, for example, the following method is preferable.

A silicon nitride substrate made of a silicon nitride sintered body has a thermal conductivity of 60 W / m · K or more and a three-point bending strength of 5
A pressure of at least 00 MPa is preferable, and for example, JP-A-9-6
The silicon nitride sintered body (silicon nitride substrate) described in, for example, 9672 or JP 2000-34172 A is mentioned. In addition, a metal clad material which has been clad in advance is prepared. A brazing material containing an active metal (hereinafter referred to as "active metal brazing material") is used for joining the metal clad material and the silicon nitride substrate.
Is called). As an active metal,
Ti, Zr, Hf, Nb, and Si are mentioned. As an example of the active metal brazing material, when the conductive material of the metal clad material is a copper plate (or copper alloy plate), Ti, Zr, Hf, N
0.1-10 mass% of at least one active metal of b,
An Ag—Cu—active metal brazing material composed of 10 to 35% by mass of copper and the balance of silver is used. Further, 1 to 10% by mass of indium (In) or tin (Sn) may be added to the active metal brazing material. The junction temperature can be lowered by adding In or Sn. When an aluminum plate (aluminum alloy plate) is used as the conductive material,
As an active metal brazing material, 0.01 to 10 mass% of Si,
An Al-Si type brazing material composed of the balance Al can be used.

The above-mentioned active metal brazing material paste is applied on a silicon nitride substrate, a metal clad material is placed thereon, and then heat treatment is performed for bonding. The application amount of the active metal brazing material paste is preferably about 10 to 50 μm. The shape of the metal clad material to be arranged may be one that has been processed into a circuit shape in advance, or may be a flat plate shape. When a flat plate is used, a method of processing into a circuit by etching or the like after joining is preferable. Heat treatment temperature (bonding temperature)
Is preferably 800 to 930 ° C. when using the above Ag—Cu—active metal brazing material, and 700 to 820 ° C. when further adding In or Sn. In addition, Al-Si
When using a brazing filler metal, it is possible to join at about 500 to 650 ° C. When a metal plate or a metal clad material is bonded to the back surface of the silicon nitride substrate, it is preferable to bond the metal plate or the metal clad material using an active metal brazing material like the metal clad material bonded to the front surface.

[0019]

[Examples] (Examples 1 to 13, Comparative Examples 1 to 3) Thermal conductivity of 60 W / mK or more, three-point bending strength of 500 MPa or more, substrate thickness of 0.635 mm, vertical x horizontal 2 inch square (one side) A silicon nitride substrate having a length of 50.8 mm) and various metal clad materials were joined by an active metal brazing material, and Example 1 shown in Table 1 was performed.
13 silicon nitride circuit boards were produced. The metal clad material was unified into a length of 30 mm × width of 30 mm, and the metal clad material was bonded to only one surface (front surface) of the silicon nitride substrate. The warpage amount was measured for such a silicon nitride circuit substrate. The bonding strength (peel strength) of the metal clad material was also measured.

For comparison, Comparative Examples 1 to 3 are those using only the copper plate or the Al plate as the circuit board. The warp amount is obtained by calculating the warp amount (mm / inch) of the circuit board after joining, and as shown in FIG. 4, the silicon nitride circuit board (the metal circuit board is not shown) is moved from the opposite end to the end. When a straight line is drawn, the distance farthest from the straight line is the warp width S
(Mm) and calculated by converting it to the ratio with the substrate width W (inch). The substrate width W is based on the short side of the silicon nitride substrate. In addition, when the circuit board warps during the bonding of the circuit boards, the board width W value slightly changes before and after the bonding (the W value decreases as much as the curve), but the silicon nitride circuit board of the present invention warps. Since the amount is small, it is not necessary to consider a slight variation. When a copper plate is used as the conductive material as the metal clad material, 70Ag-27Cu-
3 Ti (mass%) active metal brazing material is used, and when an Al plate is used as the conductive material, 99Al-1Si (mass%) active metal brazing material is used for joining. In the table, “K” in the “material of metal clad material” column represents Kovar alloy, and “I” represents Invar alloy.

[0021]

[Table 1]

As can be seen from Table 1, the silicon nitride circuit boards according to the examples of the present invention had a small amount of warpage. Also,
The joint strength was higher in the case of using the Ag-Cu-active metal-based brazing material than in the case of using the Al-Si-based brazing material. On the other hand, in Comparative Examples 1 to 3, the warpage amount was large.

(Examples 14 to 19 and Comparative Examples 4 to 5) Examples 1 and 7 except that the thickness of the silicon nitride substrate was changed.
A circuit board similar to the silicon nitride circuit board of Comparative Example 1 was prepared. The amount of warpage was measured for each silicon nitride circuit board using the same method.

[0024]

[Table 2]

As can be seen from Table 2, the circuit board according to the present embodiment has a small amount of warp even if the silicon nitride board is thin.

(Examples 20 to 25, Comparative Examples 6 to 8) Example 1, Example 15, Comparative Example 1, Comparative Example 1 except that the sizes of the silicon nitride substrate and the metal clad material were changed as shown in the table. The same silicon nitride circuit substrate as in Example 5 was prepared and the amount of warpage was measured. In addition, all the back metal plates have a creepage distance of 1
It was set to 0 mm. Further, when a plurality of metal clad materials to be joined to the front surface side are joined, the creepage distance is set to 10 mm or more and they are arranged symmetrically on the same plane.

[0027]

[Table 3]

As can be seen from the table, the silicon nitride circuit board according to this example had a small amount of warp even if the board was enlarged. Further, the warp amount was small even in the form in which a plurality of circuit boards were provided.

(Examples 1B to 13B, Comparative Examples 1B to 3)
B) A heat cycle test was performed on each of the circuit boards of Examples 1 to 13 and Comparative Examples 1 to 3. Regarding the heat resistance cycle test (TCT characteristics), -40 ° C x 30 minutes → RT (2
5 ℃) × 10 minutes → 125 ℃ × 30 minutes → RT × 10 minutes 1
When the cycle was set to 1000 cycles, the metal plate of the circuit board was dissolved and removed, and the amount of cracks on the silicon nitride substrate was measured and evaluated by η. (Η = 100% → no crack, η = 0% → cracking on the entire surface) The results are shown in Table 4.

[0030]

[Table 4]

As can be seen from the table, the silicon nitride circuit board according to this example has excellent TCT characteristics. In addition, as in Examples 11B to 13B and Comparative Example 3B, those using the Al plate had relatively good TCT characteristics because the Al plate was softer than the Cu plate.

(Examples 1C to 13C) In the silicon nitride circuit boards of Examples 1 to 13, the same metal clad material was bonded to the back surface side to bond the metal clad material to both surfaces. Further, the surface side metal clad material was subjected to etching treatment to form two circuit shapes. A 1000 TCT test was performed on the silicon nitride circuit board thus manufactured.
The amount of warpage of the substrate after the cycle was measured. In the comparative example, the same copper plate or Al plate as the front surface was joined to the back surface,
The surface side was etched to form two circuit shapes and the amount of warpage was measured. The results are shown in Table 5.

[0033]

[Table 5]

As can be seen from the table, the silicon nitride circuit board having the metal clad material bonded to both sides according to the embodiment is TCT.
It can be seen that there is almost no warpage even after 1000 cycles of the test.

As described above, when the silicon nitride circuit board of the present invention is used, even if the thickness of the circuit board is increased in order to secure the current capacity, there is little warpage and a circuit board having excellent heat cycle resistance is obtained. Can be provided. It is possible to mount a plurality of semiconductor elements on one substrate as long as the circuit substrate has such excellent TCT characteristics. Further, the metal clad material can be used as a heat sink, and since warpage can be suppressed, it is possible to adopt a structure in which a heat sink is omitted by directly joining a thick clad material.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a silicon nitride circuit board of the present invention.

FIG. 2 is a diagram showing an example of a silicon nitride circuit board of the present invention.

FIG. 3 is a diagram showing an example of a silicon nitride circuit board of the present invention.

FIG. 4 is a diagram showing an example of a method for measuring the amount of warpage of a substrate of the present invention.

[Explanation of symbols]

1 ... Silicon nitride substrate 2 ... Metal clad material 3 ... Low thermal expansion metal 4 ... Conductive material 5 ... Back metal plate S ... Warp width W ... Board width

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) // H05K 3/20 H01L 23/36 C B23K 103: 18 23/14 C F term (reference) 4E351 AA08 BB01 BB30 BB38 CC18 DD04 DD10 DD54 GG03 GG04 4G026 BA17 BB22 BF16 BF20 BH07 5E343 AA02 AA24 BB14 BB17 BB24 BB28 BB67 DD52 GG02 GG20 5F036 AA01 BA23 BB08 BD14

Claims (10)

[Claims] 1. A silicon nitride circuit board, characterized in that a metal clad material having a thickness of 1 mm or more is bonded to at least one surface of the silicon nitride board. 2. The metal clad material has a thickness of 1 mm or more and 3
The silicon nitride circuit board according to claim 1, wherein the silicon nitride circuit board has a thickness of not more than mm. 3. The silicon nitride circuit board according to claim 1, wherein a metal clad material having a thickness of 1 mm or more is bonded to both surfaces of the silicon nitride substrate. 4. The silicon nitride circuit board according to claim 1, wherein the metal clad material is made of a material in which a low thermal expansion metal and a conductive material are combined. 5. The plate thickness of the silicon nitride substrate is 0.1 to 0.
It is within the range of 7 mm. 5.
The silicon nitride circuit board according to any one of 1. 6. The short side length of the silicon nitride substrate is 50 m.
6. The silicon nitride circuit board according to claim 1, wherein the silicon nitride circuit board has a length of m or more. 7. The warpage amount of the silicon nitride circuit board is 0.1 m.
7. The width is less than m / inch.
The silicon nitride circuit board according to any one of 1. 8. The silicon nitride circuit board according to claim 1, wherein the metal clad material and the silicon nitride substrate are bonded by an active metal bonding method. 9. The silicon nitride circuit board according to claim 1, wherein the peel strength of the metal clad material is 5 kN / m or more. 10. The silicon nitride circuit board according to claim 1, wherein a plurality of semiconductor elements are mounted on the silicon nitride circuit board.