JP2002084046A - Ceramic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic circuit board having its modified solder flow properties. SOLUTION: A ceramic circuit board has a structure that a metallic circuit board is provided on a ceramic board and that a metal plate constituted of the same metal as that of the metallic circuit board or a metal different from that of the metallic circuit board is provided on the side of the surface opposite to the surface of this ceramic board and is characterized in that the ceramic circuit board is warped to the side of the circuit board into a projected form and in that the quantity of warpage of the circuit board is 0.15 to 0.30% of the length in the longitudinal direction of the ceramic circuit board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic circuit board. More specifically, the present invention provides
The present invention relates to a ceramic circuit board suitable for mounting high power transistors, power modules, and the like.

[0002]

2. Description of the Related Art In recent years, a ceramic circuit board has been used in which a metal circuit board made of a conductive material, for example, a copper plate, is provided on a ceramic substrate. Such a ceramic circuit board is particularly useful as a circuit board for a high-output transistor, a power module, or the like because it generally has high electrical insulation and good heat resistance.

[0003]

However, the ceramic substrate and the metal circuit board provided on the ceramic substrate usually have greatly different coefficients of thermal expansion, and the two are often joined under high temperature conditions. Therefore, when the ceramic circuit board is cooled after the joining, the ceramic circuit board may be concavely curved toward the metal circuit layer due to the residual stress between the two.

A ceramic circuit board which is concavely curved toward the metal circuit layer in this manner often has poor solder flow in a mounting process of an electronic element, for example, a high-output transistor or a power module, and causes a reduction in mounting reliability. Had become.

When a ceramic circuit board is mounted on, for example, an industrial machine or the like, particularly high mounting reliability is required. However, it is not easy to satisfy this requirement for the above-mentioned reason.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ceramic circuit board having improved solder flow in an electronic element mounting process.

Therefore, in the ceramic circuit board according to the present invention, a metal circuit board is provided on the ceramic substrate, and a metal plate made of the same or different metal as the metal circuit board is provided on the opposite side of the ceramic substrate. A ceramic circuit board, wherein the ceramic circuit board is warped in a concave shape on the metal plate side,
The amount of warpage is 0.15 to 0.30% of the length of the ceramic circuit board in the longitudinal direction.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ceramic circuit board according to the present invention will be described with reference to the drawings as necessary.

FIG. 1 shows a cross section of a preferred embodiment of a ceramic circuit board according to the present invention. The ceramic circuit board 1 is provided with a metal circuit board 3 provided on a ceramic board 2 and a metal board 4 provided on a surface of the ceramic board 1 opposite to the metal circuit board 3. The circuit board 1 is warped in a convex shape toward the metal circuit board 3 side, and the warp amount A is 0.15 to 0.15 of the longitudinal length B of the ceramic circuit board.
It is 0.30%. Thus, the amount of warpage A indicates the amount of warpage after joining the metal circuit boards. The term “longitudinal direction of the ceramic circuit board” indicates a direction which is longer than the length and width of the ceramic substrate. The length B in the longitudinal direction of the ceramic circuit board indicates the distance from the end to the end of the ceramic substrate after bonding. At this time, simply, the length in the longitudinal direction of the ceramic substrate having substantially no warp before joining the metal circuit boards may be applied as the length B. This is because the present invention is such that (the amount of warpage A / length B of the ceramic circuit board in the longitudinal direction) × 100 is 0.15 to 0.3.
This is because it is as small as 0% and the influence on the actual measurement is small.

The ceramic substrate used for such a ceramic circuit substrate according to the present invention is not particularly limited, and any suitable substrate can be used. For example, (a) nitride ceramics, for example, aluminum nitride, silicon nitride, titanium nitride, etc., (b) oxide ceramics, for example, aluminum oxide, a compound of aluminum oxide and zirconium oxide, (c) carbide ceramics, for example, Silicon carbide, titanium carbide, etc.
(D) boride-based ceramics such as lanthanum boride,
Can be used. Among these, aluminum nitride, silicon nitride, aluminum oxide, and a compound of aluminum oxide and zirconium oxide are preferable.

Each of these ceramics has a sintering aid,
For example, it may contain a rare earth oxide such as yttrium oxide or a metal oxide such as magnesium oxide. The content of the sintering aid is preferably in the range of 2 to 20% by weight.

The thickness of the ceramic substrate is determined by taking into account the size and weight of the electronic elements to be mounted, the amount of heat generated, the size of the ceramic circuit substrate, the required strength, durability, etc. In view of the relationship between the thickness of the metal circuit board and the thickness of the metal plate provided on the opposite surface of the ceramic substrate (hereinafter, may be referred to as “back metal plate” in this specification) so as to be a quantity. Can be determined. The thickness of the ceramic substrate is not particularly limited, but is 0.3 to 1 mm, and more preferably 0.3 to 1 mm.
A range of 0.7 mm is preferred. If the thickness of the ceramic substrate is less than 0.3 mm, it is difficult to maintain the strength of the substrate, which is likely to cause cracking. On the other hand, if the substrate thickness exceeds 1 mm, it becomes difficult to reduce the thickness of the ceramic circuit board and it is difficult to maintain a predetermined amount of warpage.

The metal constituting the metal circuit board of the ceramic circuit board according to the present invention is a metal which forms a eutectic compound with the components of the ceramic substrate and which can be applied by a direct joining method or a joining method by an active metal method. It is not particularly limited. In the present invention, for example, a simple substance of copper, aluminum, iron, nickel, chromium, silver, molybdenum, cobalt, or an alloy thereof can be used. From the viewpoints of conductivity, cost, and the like, copper, aluminum, and alloys thereof are particularly preferable.

The thickness of the metal circuit board can be determined in consideration of the current carrying capacity and the amount of warpage of the ceramic circuit board. The thickness of the metal circuit board is preferably in the range of 0.25 to 1 mm, more preferably 0.25 to 0.6 mm. If the thickness of the metal circuit board is less than 0.25 mm, it is difficult to secure the current carrying capacity, and the effect as the circuit board is small. On the other hand, when the thickness of the metal circuit board exceeds 1 mm, the current carrying capacity can be secured, but it is difficult to secure a predetermined amount of warpage because the metal circuit board is too thick.

The joining of the ceramic substrate and the metal circuit board can be performed by a direct joining method or an active metal method. In particular, when a copper circuit board is used as a metal circuit board and bonded by a direct bonding method, oxygen is supplied in an amount of 100 to 100.
By using a copper circuit board made of tough pitch electrolytic copper containing 0 ppm, and further forming a copper oxide layer in a predetermined thickness on the surface of the copper circuit board in advance as described later, Cu-O eutectic generated at the time of direct bonding is formed. By increasing the amount, the bonding strength between the substrate and the copper circuit board can be further improved. The direct bonding method can be applied immediately when an oxide-based ceramic substrate such as aluminum oxide is used. However, the direct bonding method can be applied to a metal circuit such as a non-oxide-based ceramic (for example, aluminum nitride or silicon nitride). If the bonding strength with the plate is insufficient, it is preferable to form an oxide layer on the surface of the non-oxide ceramic substrate in advance. This oxide layer can be formed by subjecting the ceramic substrate to heat treatment in an oxidizing atmosphere at a temperature of 1000 to 1400 ° C. for 2 to 15 hours. In addition, it is also possible to use an Al-Si alloy plate as a metal circuit board and directly join them.

When the ceramic substrate and the metal circuit board are joined by the active metal method, a suitable brazing material, for example, Ag-containing at least one active metal selected from Ti, Zr, Hf and Nb is used. Bonding can be performed by using a Cu-based brazing material, preferably by heating at 700 to 950 ° C. in vacuum for 5 to 30 minutes.

The metal of the metal plate (back metal plate) provided on the ceramic circuit board on the side opposite to the metal circuit plate is not particularly limited. The back metal plate in the present invention can be made of the same or a different metal as the metal constituting the metal circuit board, but the preferred metal in the present invention is the metal constituting the metal circuit board. . By configuring the back metal plate with the same metal as the metal circuit board in this way, the bonding between the back metal plate and the ceramic substrate can be performed simultaneously with the bonding of the metal circuit board in the same manner as the metal circuit board. Become.

The thickness of the back metal plate is usually larger than the thickness of the metal circuit board so that the ceramic circuit board is warped in a convex shape toward the metal circuit board and the amount of warp is a predetermined value. It is more effective to make it thinner. The specific thickness of the back metal plate varies according to the thickness of the metal circuit board, the thickness of the ceramic substrate, and the amount of warpage of the ceramic circuit board. A thickness of 5 times, preferably 0.5 to 0.8 times is suitable.

Further, in order to warp the ceramic circuit board to the metal circuit board side in a convex shape and to set the warpage thereof to a predetermined value, the area of the metal circuit board on the ceramic board and the area of the back metal plate must be equal. It is also effective to have a predetermined area ratio. That is, (area / area) × (area / area) × where the area of the joint area between the metal circuit board and the ceramic substrate is the area and the area of the joint area of the back metal plate to the ceramic substrate
Preferably, 100 is 40 to 95%, more preferably 50 to 90%. When the metal circuit board is composed of a plurality of metal circuit boards, a numerical value obtained by adding all areas of the metal circuit board is defined as an area. Similarly, when the back metal plate is composed of a plurality of metal plates, a numerical value obtained by adding the areas of all the back metal plates is defined as the area.

If the area of the metal circuit board exceeds 95% of the area of the back metal plate, the amount of warpage of the ceramic circuit board is insufficient, while the area of the metal circuit layer is less than 40% of the area of the back metal layer. In this case, the amount of warpage of the ceramic circuit board may be too large. As described above, there is the above-described method for providing a predetermined amount of warpage, and it is also possible to control the amount of warpage by combining these two methods. In addition, it goes without saying that the present invention is characterized in that the ceramic circuit board is provided with a predetermined amount of warpage, so the manufacturing method is not necessarily limited to the above method.

The warpage of the ceramic circuit board according to the present invention is 0.15 to 0.30%, preferably 0.15 to 0.2% of the longitudinal length of the ceramic circuit board.
0%. If the warpage is less than 0.15%, the effect of improving the solder flow property cannot be sufficiently obtained.
If it exceeds 0%, the amount of warpage of the ceramic circuit board may become too large, and problems in strength and mounting of electronic elements may occur.

[0022]

EXAMPLES (Examples 1 to 6, Comparative Examples 1 to 3) A ceramic substrate mainly composed of the materials shown in Table 1 having a length of 50 mm.
50mm wide x 0.635mm thick, metal circuit board length 30
2 × 10 mm × 0.25 mm thick copper plates (interval at joining is 1 mm), the back metal plate is 40 mm long × 40 mm wide
A ceramic circuit board having a predetermined warpage A was prepared by a direct bonding method or an active metal method using a copper plate having a size of mm × 0.20 mm in thickness.

The solder flow property when an electronic element was surface-mounted on the ceramic circuit board by the reflow method was examined. As for the measurement of the solder flow property, the presence or absence of a failure such as a short circuit of the metal circuit board due to the solder flow during the reflow process is measured for each 100 pieces, and the one having 0 to 1 failure occurrence is evaluated as having a good solder flow property. ", 2
４4 items are indicated as “slightly defective” and 5 or more items are indicated as “defective”. Table 1 shows the results.

For comparison, a ceramic circuit board having a warpage outside the range of the present invention was prepared, and the same measurement was performed. In the measurement of (amount of warpage / length in the longitudinal direction of the ceramic circuit board) × 100, 50 mm, which is the length in the longitudinal direction of the ceramic substrate before joining the metal circuit board, was used as the length B in the longitudinal direction of the ceramic substrate. Calculated using

[0025]

[Table 1] As can be seen from Table 1, the solder flow property of the ceramic circuit board according to the present example was good, and the occurrence of defects was suppressed to 0 to 1.

On the other hand, Comparative Example 2 having a large amount of warpage and Comparative Example 3 warping toward the back metal plate had many defects, and the solder flow property was poor or slightly poor. This is because the amount of warpage is insufficient and the distance between the two metal circuit boards is 1 mm.
This is because the solder flowed in between them and caused a short circuit. Further, it was found that Comparative Example 1 having a small amount of warpage was insufficient in the amount of warpage, so that the effect of warpage in the metal circuit board side was not sufficiently obtained.

(Examples 7 to 11, Comparative Example 4) Next, the relationship between the thickness and the area ratio of the metal circuit board and the back metal plate will be examined. An aluminum oxide substrate having a length of 60 mm, a width of 40 mm and a thickness of 0.8 mm was prepared. On the other hand, the warpage was measured when the plate thickness and the area ratio [(area / area) × 100 (%)] were changed as shown in Table 2.

The length of the ceramic circuit board in the longitudinal direction when measuring the value of (the amount of warpage / the length of the ceramic circuit board in the longitudinal direction) × 100 (%) is the length B after joining the metal circuit board. Corresponded. In addition, three metal circuit boards having the same size were prepared, the area of all the metal boards was combined, and the area of the back metal plate was formed as one sheet.

As Comparative Example 4, a metal circuit board having a relationship between the thickness and the area ratio of the metal circuit board and the back metal plate outside the preferred range of the present invention was prepared. Each of the metal circuit board and the back metal plate was joined by a direct bonding method to produce a ceramic circuit board.

[0030]

[Table 2] As can be seen from Table 2, the thickness of the metal circuit board> the thickness of the back metal plate, (area of the metal circuit board / area of the back metal plate) × 10
In the case of 0 (%) = 50 to 95%, (warp amount A / length B of substrate in the longitudinal direction) × 100 (%) is 0.15 to 0.3%.
It turned out that it can be set to 0 (%).

In the eighth, tenth and eleventh embodiments, the ratio of the thickness of the back metal plate / the thickness of the metal circuit board is 0.5 to 0.8 (warpage A / substrate). Of the length in the longitudinal direction B) × 100 (%) was 0.15 to 0.20%, which was within the preferable range of the present invention.

Each of the ceramic circuit boards according to the present examples had good solder flow properties. On the other hand, in the case of Comparative Example 4, the direction in which the back metal plate was warped in a convex shape and the warping occurred was reversed.

(Examples 12 and 13) As a ceramic substrate, an aluminum nitride substrate (thickness 0.635 mm) and a silicon nitride substrate (thickness 0.35 mm) were prepared. Metal circuit board (thickness 0.35mm) and back metal plate (thickness 0.2
5 mm), an Al-6 wt% Si alloy plate was prepared.

The area ratio between the metal circuit board and the back metal plate [(area / area) × 100%] was adjusted to 80%, and directly bonded to the ceramic substrate. With respect to such a ceramic circuit board, (warp amount A / length in the longitudinal direction of the ceramic substrate) × 100 (%) was obtained, and solder reflow properties were measured under the same conditions as in Example 1. Table 3 shows the results.

[0035]

[Table 3] As can be seen from Table 3, even when the materials of the metal circuit board and the back metal plate were changed, the same effect was obtained.

[0036]

The ceramic circuit board according to the present invention comprises:
Since the warp is warped to the metal circuit board side on which the electronic element is mounted and the amount of warp is 0.15 to 0.30% of the longitudinal length of the ceramic circuit board, Solder flowability during mounting is improved, and localization of solder on the metal circuit board is suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a specific example of a ceramic circuit board according to the present invention.

FIG. 2 is a cross-sectional view schematically showing a conventional ceramic circuit board curved concavely toward the metal circuit board.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ceramic circuit board 2 ceramic board 3 metal circuit board 4 metal plate (back metal plate) A warpage B length of ceramic circuit board in longitudinal direction

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05K 1/03 610 H01L 23/14 C M 1/09 23/36 C

Claims (5)

[Claims] 1. A ceramic circuit board comprising: a metal circuit board provided on a ceramic substrate; and a metal plate made of the same or different metal as the metal circuit board is provided on the opposite side of the ceramic substrate. The ceramic circuit board is warped in a convex shape toward the metal circuit board, and the warpage is 0.15 to 0.30% of the longitudinal length of the ceramic circuit board. A ceramic circuit board. 2. The ceramic circuit board according to claim 1, wherein said metal plate is thicker than said metal circuit board. 3. The ceramic circuit board according to claim 1, wherein the area of the metal circuit board is 40 to 95% of the area of the metal plate. 4. The ceramic substrate according to claim 1, wherein said ceramic substrate is made of any one of aluminum nitride, silicon nitride, aluminum oxide, and a compound of aluminum oxide and zirconium oxide.
The ceramic circuit board according to any one of the above. 5. The ceramic circuit according to claim 1, wherein said metal circuit board is made of at least one of copper, copper alloy, aluminum, and aluminum alloy. substrate.