JP5741913B2 - Manufacturing method of ceramic substrate for power module comprising blackened aluminum nitride substrate - Google Patents

Description

The present invention enables the brazing of the ceramic substrate in the power module substrate and the metal plate serving as the circuit layer in a short time and under a soaking condition, and prevents the occurrence of surplus brazing material from flowing out and climbing up. the method of manufacturing a ceramic board for a power module consisting of an aluminum nitride sintered body.

Conventionally, a power module for supplying power among semiconductor elements has a relatively high calorific value, and examples of substrates on which the module is mounted include aluminum nitride (AlN), aluminum oxide (Al ₂ O ₃ ), and silicon nitride (Si). ₃ N ₄ ), a power module substrate in which, for example, a metal plate such as Cu or Al is bonded to a ceramic substrate made of silicon carbide (SiC) via an Al—Si brazing material or the like. Yes. This metal plate forms a circuit layer by forming a circuit in a later etching process. After etching, a power module is configured by mounting a power element (electronic component) such as a semiconductor chip on the surface of the circuit layer via a solder material.

  Also known is that a metal plate such as Al is bonded to the lower surface of the ceramic substrate as a heat conducting layer for heat dissipation, and the entire power module substrate is mounted on a heat sink such as a heat sink via this metal plate. ing.

  However, in the conventional power module substrate described above, problems such as excess brazing material flowing out and climbing easily occur when the ceramic substrate and the metal plate are brazed, and various proposals have been made to solve this problem. ing.

  For example, in Patent Document 1, in a power module substrate in which a ceramic substrate made of aluminum nitride (AlN) and a metal plate made of aluminum are joined, the thickness of the metal plate made of aluminum in which a circuit is formed by etching is set as a semiconductor. It has been proposed that the mounting portion is made thin to prevent the brazing material from flowing out and the mounting chip from being displaced.

  Also, for example, in Patent Document 2, a conductor pattern made of pure Al or Al alloy is joined to the surface of a ceramic substrate made of aluminum nitride (AlN) or the like with an Al—Si brazing material, and the surface of this conductor pattern In the power module substrate provided with the semiconductor chip, the surface of the ceramic substrate is provided with a storage portion for storing a surplus of the molten brazing material, and at least on the surface of the conductor pattern on which the semiconductor chip is provided. It has been proposed to prevent the brazing material from climbing up at a portion 1 mm or more inward from the outer peripheral edge by setting the Si content of the brazing material to 3 wt% or less.

JP-A-10-242330 JP 2007-258416 A

  However, from the viewpoint of production efficiency and bonding reliability of the power module substrate, a metal plate that becomes a ceramic substrate and a circuit layer in a shorter time and in a homogeneous manner without causing problems such as excess brazing material flowing out and getting on. It is desirable to perform bonding with.

Accordingly, the present invention provides a soaking condition in a shorter time and with less variation in the joining temperature without causing problems such as brazing material flowing out and climbing when joining the ceramic substrate and the metal plate as the circuit layer. It may perform bonding under, and an object thereof is to provide a method of manufacturing a ceramic board for a power module.

  In order to achieve the above-mentioned problems, the present inventors have conducted intensive research and obtained the following knowledge.

That is, various ceramics conventionally used as a ceramic substrate for power module substrates (for example, aluminum nitride (hereinafter referred to as AlN), aluminum oxide (hereinafter referred to as Al ₂ O ₃ ), silicon nitride (hereinafter referred to as Si) ₃ N ₄ )))), and comparing characteristics from the viewpoints of thermal conductivity, bending strength, manufacturing cost, bondability, etc., each has advantages and disadvantages, but AlN is a ceramic substrate from the standpoint of outstanding thermal conductivity. Promising.

  By the way, AlN usually exhibits a brown or flesh tone, but when manufacturing an AlN sintered body constituting a ceramic substrate, when AlN is further blackened and the blackened AlN substrate is used as the ceramic substrate. In addition, the heat absorption efficiency due to radiation at the time of joining can be increased when soldering to a metal plate as a circuit layer, so that the joining time by brazing can be shortened, and there is little variation in joining temperature. Since joining can be performed under thermal conditions (for example, within the set temperature ± 1 ° C), no extra brazing material is required for joining, and problems such as excess brazing material flowing out and getting on are greatly generated. It has been found that it can be reduced.

The present invention has been made based on the above findings,
“ (1) A blackened aluminum nitride sintered product characterized in that, by irradiating the aluminum nitride sintered body with high energy rays, the aluminum nitride is blackened so that the brightness specified in JIS Z 8721 is N4 or less. A method for producing a ceramic substrate for a power module comprising a bonded body. "
It is characterized by.

  The present invention will be described in detail below.

  FIG. 1 shows a schematic perspective view of a power module substrate using the ceramic substrate of the present invention.

  In FIG. 1, the power module substrate (1) has the ceramic substrate (2) of the present invention, and a metal plate serving as a circuit layer on the front side of the power module substrate of the ceramic substrate (2), that is, A circuit layer metal plate (3) is laminated, and a heat conductive layer metal plate (4) serving as a heat conductive layer for heat dissipation is laminated on the back side.

  These circuit layer metal plate (3) and heat conductive layer metal plate (4) are made of, for example, pure Al.

  The ceramic substrate (2) is composed of a blackened AlN sintered body to be described later. Here, the thickness of the ceramic substrate (2) is preferably, for example, 0.5 to 1.0 mm.

  On the lower surface of the ceramic substrate (2), for example, a metal plate (4) for a heat conductive layer formed of a metal having a high thermal conductivity such as Al is formed on the ceramic substrate by a brazing material layer (not shown). It is joined to (2). Here, the thickness of the heat conductive layer metal plate (4) is, for example, 0.1 to 5.0 mm. The brazing material layer is preferably formed of, for example, an Al—Si brazing material (for example, Al: 93 wt%, Si: 7 wt%, thickness of 10 μm or more and 15 μm) or an Al—Ge brazing material. .

  Further, on the upper surface of the ceramic substrate (2), similarly to the heat conductive layer metal plate (4), a circuit layer metal plate (3) formed of a metal having a high thermal conductivity such as Al, for example, A circuit is configured by arranging them at appropriate intervals. The circuit layer metal plate (3) is joined to the ceramic substrate (2) by a brazing material layer (not shown). Here, the thickness of the circuit layer metal plate (3) is, for example, 0.1 to 5.0 mm. The brazing material layer is preferably formed of, for example, an Al—Si based or Al—Ge based brazing material.

  An electronic component (not shown) is fixed to the upper surface of the circuit layer metal plate (3) by a solder layer. Here, for example, a semiconductor chip is applicable as the electronic component, and a power device such as an IGBT (Insulated Gate Bipolar Transistor) may be used as the semiconductor chip.

  As the ceramic substrate (2) of the present invention used for the power module substrate (1), for example, a blackened AlN sintered body having a brightness defined by JIS Z 8721 and having a brightness of N4 or less manufactured by the following method is used. Use.

  And in the ceramic substrate (2) for power modules of this invention, by using the ceramic substrate (2) which consists of the said blackening AlN sintered compact, a ceramic substrate (2) and the metal plate for circuit layers (3) When joining, heat absorption efficiency due to radiation at the time of joining can be increased, so that the joining time can be shortened and joining can be performed under soaking conditions with little variation in joining temperature. .

Further, as a result, no extra brazing material is required, and the occurrence of problems such as excess brazing material flowing out and getting on can be greatly reduced.
Blackened aluminum nitride (blackened AlN) sintered body:
Usually, an AlN sintered body has a brown or flesh tone, but as a means for blackening this, a sintering aid, an additive, etc. are added to the raw material powder made of AlN particles, and this is used. It is already known to obtain a blackened AlN sintered body by firing (see, for example, Japanese Patent Publication No. 5-64697).

  However, when a blackened AlN sintered body is obtained using a sintering aid, an additive, etc., although the radiation heat absorption efficiency is improved by blackening the AlN sintered body, on the other hand, the impurity component Since the thermal conductivity, strength, bondability and the like are reduced due to the increase in the thickness, it is not preferable as a ceramic substrate for a power module substrate.

  Therefore, in the present invention, an AlN sintering process is performed by performing irradiation treatment of high energy rays (for example, ultraviolet rays and X-rays) in the manufacturing process of the AlN sintered body without adding a sintering aid, additives and the like. It was decided to blacken the knot.

  By appropriately selecting the irradiation conditions of the high energy rays, it is possible to adjust the brightness of the AlN sintered body and obtain a blackened AlN sintered body.

  Here, the brightness is a scale indicating a visual attribute for determining whether the reflectance of the object surface is large or small, and this display method is defined in “JIS Z 8721”.

When the brightness is higher than N4, the radiant heat absorption efficiency of the AlN sintered body does not increase, and as a result, the joining time cannot be shortened and the soaking condition (for example, the set temperature) is not achieved. In the present invention, it is necessary to set the degree of blackening of the AlN sintered body to N4 or less with the brightness specified in JIS Z8721. It is.
Method for producing blackened AlN sintered body:
First, a high-purity (purity 97% or more) AlN powder obtained by a reduction nitriding method is prepared as a raw material powder, and this high-purity AlN powder is prepared by, for example, a uniaxial pressure molding method or a cold isostatic press (CIP) method. After the molded body is molded by the hot pressing method or hot isostatic pressing (HIP) method, the molded body is reduced at a firing pressure of 300 kgf / cm ² or more and a firing temperature of 1750 to 1850 ° C. Bake in.

  Next, the brightness specified in JIS Z 8721 is N4 or less by irradiating the sintered AlN sintered body with high energy rays for a predetermined time (for example, ultraviolet light having a wavelength of 365 nm for 0.5 to 30 minutes). The blackened AlN sintered body can be obtained.

  By using the above blackened AlN sintered body as a ceramic substrate in a power module substrate, a soaking condition in which the maximum variation in the bonding temperature within the substrate is within 1.2 ° C. of the set temperature is short. Below, brazing can be performed.

  According to the ceramic substrate for a power module of the present invention, the ceramic substrate is composed of a blackened AlN substrate. Therefore, when brazing between the ceramic substrate and the metal plate serving as the circuit layer is performed, radiation due to bonding is performed. Since the heat absorption efficiency can be increased, brazing can be performed in a short time and under a soaking condition with little variation in the joining temperature, and not only does not need an extra brazing material, It is possible to provide an excellent power module substrate that is free from problems such as running out and getting on.

The schematic sectional drawing of one Embodiment of the board | substrate for power modules is shown. The apparatus schematic for a thermal uniformity test is shown, (a) is a perspective view, (b) shows a longitudinal cross-sectional view.

  Hereinafter, the present invention will be described by way of examples.

First, a ceramic substrate of the present invention made of a blackened AlN sintered body was produced by the following steps (a) to (d). That is,
(A) A high purity (purity 97 mass% or more) AlN powder obtained by the reductive nitriding method was prepared as a raw material powder.
(B) This high-purity AlN powder was molded by a cold isostatic press (CIP) method to obtain a molded body.
(C) The molded body was fired by a hot isostatic press (HIP) method in a reducing atmosphere at a firing pressure of 300 kgf / cm ² or more and a firing temperature of 1750 to 1850 ° C.
(D) The fired AlN sintered body is irradiated with ultraviolet light having a wavelength of 365 nm as a high energy ray under the conditions shown in Table 1, and is made of a blackened AlN sintered body having a thickness of about 0.65 mm. Invention ceramic substrates 1-10 were prepared.

For comparison,
(A) A high-purity (purity 97% by mass or more) AlN powder obtained by a reductive nitriding method is prepared as a raw material powder,
(B) The high purity AlN powder is molded by a cold isostatic press (CIP) method to obtain a molded body,
(C) The formed body is fired by a hot isostatic press (HIP) method in a reducing atmosphere having a firing pressure of 300 kgf / cm ² or more and a firing temperature of 1750 to 1850 ° C. (d) AlN firing after firing A thickness of about 0.65 mm can be obtained by irradiating a high energy beam without irradiating a high energy beam on the ligated body or by irradiating a high energy beam with a lightness outside the scope of the present invention (under the conditions shown in Table 1). Comparative ceramic substrates 11 and 12 made of an AlN sintered body were produced.

  Next, the degree of blackening of the ceramic substrates 1 to 10 of the present invention and the comparative ceramic substrates 11 and 12 was measured to determine the brightness.

  First, the degree of blackening is described in “Journal of the Ceramic Society of Japan” 101 [10] p. As described in 1189 to 1191 (Discoration of Allumina Ceramics with Ultraviole Radiation and Elucidation of It's Machinery), 500 W of xenon arc lamp (wavelength range: 230 to 1000 nm) is used as the light source for 1 to 3 minutes. Each ceramic substrate was irradiated and a 300-700 nm DRS (diffuse reflection spectrum) was measured with a “Hitachi U-3200” recorder.

  Then, the measured value was quantified according to JIS Z 8721.

  That is, in JIS Z 8721, the ideal black brightness is 0, the ideal white brightness is 10, and the brightness of the color is perceived between the ideal black and the ideal white. Since each color is divided into 10 so as to have a rate and displayed with symbols N0 to N10, the lightness of the AlN sintered body constituting the ceramic substrates 1 to 10 of the present invention and the comparative ceramic substrates 11 and 12 is determined. The standard color charts corresponding to N0 to N10 were compared with the surface color of the AlN sintered body to determine the brightness of the AlN sintered body. At this time, in principle, the brightness was determined to the first decimal place, and the value of the first decimal place was set to 0 or 5.

  Table 1 shows the measured brightness.

次いで、図１、図２に示すように、回路層用金属板（３）および熱伝導層用金属板（４）を純度９９．９８％の純Ａｌで構成し、Ａｌ−Ｓｉ系（Ａｌが９３ｗｔ％、Ｓｉが７ｗｔ％）のろう材を用いて、上記本発明セラミックス基板（２）１〜１０、あるいは、比較例セラミックス基板（２）１１、１２と、回路層用金属板（３）、熱伝導層用金属板（４）とをろう材層を介して仮固定した。

Next, as shown in FIGS. 1 and 2, the circuit layer metal plate (3) and the heat conductive layer metal plate (4) are made of pure Al having a purity of 99.98%, and an Al—Si system (Al is used). 93 wt%, Si is 7 wt%) using the brazing material of the present invention ceramic substrates (2) 1-10, or comparative ceramic substrates (2) 11, 12, and circuit layer metal plate (3), The metal plate (4) for heat conductive layers was temporarily fixed through the brazing material layer.

  Here, the thickness of the metal plate for heat conduction layer (4) and the metal plate for circuit layer (3) is about 0.4 mm, and the thickness of the brazing filler metal layer is about 13 μm.

  Temporary fixation was performed using a volatile organic medium (octanediol).

  Next, the metal plate for the heat conductive layer (4) / the brazing material layer / the ceramic substrate (2) of the present invention (1) -10 / the brazing material layer / the metal plate for the circuit layer (3) or the metal plate for the heat conducting layer (4 ) / Brazing material layer / comparative example ceramic substrate (2) 11 to 13 / brazing material layer / circuit layer metal plate (3). It inserted in the thermal test apparatus (11).

  The soaking test apparatus (11) in FIG. 2 is composed of a graphite support (12), a graphite base (14) on which a test piece (13) is placed, and a graphite top covering the upper surface of the test piece (13). It is comprised with the frame provided with the board (15).

  Next, as shown in FIG. 2, through holes (16-1) to (16-4) are formed at four locations on the graphite upper plate (15), and the through holes (16-1) to (16-4) are formed. ), The thermocouples (17-1) to (17-4) are inserted in contact with the position corresponding to the temperature measurement point of the test piece (13). In the present invention, the temperature measurement for thermal uniformity evaluation is performed at four locations on the circuit layer metal plate (3), that is, the short side center, the long side center, the center, and the corners of the circuit layer metal plate (3). The four through holes (16-1) to (16-4) into which the thermocouples (17-1) to (17-4) are inserted were formed at positions corresponding to the holes.

  Next, the whole temperature uniformity test apparatus (11) is charged into a heating furnace (not shown), heated in a vacuum atmosphere from room temperature to a brazing setting temperature, and held at the brazing setting temperature for a predetermined time. Thus, a power module substrate (2) of the present invention (hereinafter referred to as the present invention 1 to 10) and a comparative power module substrate (2) (hereinafter referred to as comparative examples 11 and 12) were produced.

  Tables 2 and 3 show the brazing welding set temperature of the present inventions 1 to 10 and Comparative Examples 11 and 12 prepared above, and the heating time required for heating up to the set temperature. Maximum temperature of the test piece (13) measured after holding at the contact set temperature for 57 minutes (namely, the temperature at the center of the short side, the center of the long side, the center and the corner of the circuit layer (3)). The variation temperature was shown.

  Further, Tables 2 and 3 show the observation results of observing the brazing material flowing out in the vicinity of the brazed portion after joining and the riding state of the brazing material.

  In addition, regarding the evaluation of the presence or absence of the flow of the brazing material, whether or not the necessary brazing material remains at the bonding interface is measured by ultrasonic inspection, and the bonding rate of the bonding interface is 97.0% or more by ultrasonic inspection. In some cases, “no flow out” was determined, and when the joining rate was less than 97.0%, “flow out” was determined.

  In addition, regarding the evaluation of the presence or absence of the brazing material, the case where there is a brazing material on 10% by area or more of the surface of the metal plate for circuit layer (3) is “riding”, and the riding area is The case of less than 10 area% was determined as “no ride”.

表１〜３に示す結果から、本発明１〜１０においては、そのセラミックス基板１〜１０がいずれもＪＩＳ Ｚ ８７２１に規定する明度がＮ４以下の黒色化ＡｌＮ焼結体で構成されており、このため、パワーモジュール用基板を作製する際の回路層用金属板、熱伝導層用金属板とのろう接を、短時間で、しかも、接合温度のバラツキの少ない均熱条件下で行う事ができ、さらにその結果として、ろう材の流れ出し、乗り上げ等の問題を生じることはない。

From the results shown in Tables 1 to 3, in the present inventions 1 to 10, the ceramic substrates 1 to 10 are each composed of a blackened AlN sintered body having a brightness specified in JIS Z 8721 of N4 or less. Therefore, brazing with the metal plate for the circuit layer and the metal plate for the heat conduction layer when producing the power module substrate can be performed in a short time and under a soaking condition with little variation in bonding temperature. Further, as a result, there is no problem of the brazing material flowing out and getting on.

  However, the ceramic substrates 11 and 12 of Comparative Examples 11 and 12 both have a long time for bonding because the brightness specified in JIS Z 8721 exceeds N4, and the variation in bonding temperature is also observed. In addition, problems such as flowing out of the brazing material and getting on the board occurred.

  In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention. For example, although the power module substrate 1 has been described in the present embodiment, the present invention is not limited thereto, and an electronic component (not shown) such as a semiconductor chip is mounted on the surface of the power module substrate 1, and the power module substrate 1 is mounted. A power module may be formed by bonding a heat sink (not shown), which is a heat exchanger, to the back surface of the heat exchanger.

1... Power module substrate 2... Ceramic substrate 3... Metal plate 4 for circuit layer... Metal plate 11 for heat conduction layer・ ・ ・ ・ ・ ・ ・ Soaking test device 12 ・ ・ ・ ・ ・ ・ Graphite support 13 ・ ・ ・ ・ ・ ・ Test piece 14 ・ ・ ・ ・ ・ ・ Graphite base 15 .. Graphite upper plate 16-1 to 16-4 Through hole 17-1 to 17-4 Thermocouple

Claims (1)

It consists of a blackened aluminum nitride sintered body characterized in that the aluminum nitride sintered body is blackened so that the lightness specified in JIS Z 8721 is N4 or less by irradiating high energy rays. Manufacturing method of ceramic substrate for power module.

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