JPH10178257A - Aluminum nitride circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable aluminum nitride circuit board which can suppress the occurrence of cracks caused by heat cycles. SOLUTION: In a circuit board, a metallic circuit 3 of copper, etc., is formed on an aluminum nitride substrate 1 in a state where the circuit 3 is joined to the substrate 1 and the surface of the circuit 3 is plated with nickel 4. The heat cycle resistance of the circuit board is improved by adjusting the maximum thickness 5 of the plated nickel 4 on the side face of the end section of the metallic circuit 3 to 1.5-5μm and, in addition, making the ratio of the maximum thickness to the minimum thickness of the plated nickel 4 on the same side face 1-3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum nitride circuit board having a metal circuit used for a power module of an electronic component requiring high reliability and heat radiation.

[0002]

2. Description of the Related Art Conventionally, alumina (Al2O3), aluminum nitride (Al
N), a circuit board in which a copper (Cu) circuit board or the like is integrally bonded as a conductive layer to the surface of a ceramic sintered body substrate such as beryllium oxide (BeO) is widely used.

[0003] Of these, the aluminum nitride circuit board forms a circuit with a metal such as Cu having excellent heat conductivity and electric conductivity, so that the delay of the circuit operation is reduced and the life of the circuit wiring is improved.

Several methods are known for manufacturing an aluminum nitride circuit board, but a full-etch method is often used to obtain good productivity. In the full-etch method, a brazing material paste is applied to the entire surface of an aluminum nitride plate, a metal plate is bonded to the entire surface so as to cover the paste, and a circuit pattern is formed on the metal plate serving as a circuit surface with an etching resist. Unnecessary portions are removed by etching. Further, the surface of the metal plate is generally coated with a plating layer of Ni or the like in order to prevent corrosion of the metal plate and improve solder jointability. Although the full-etch method has good productivity, it goes through an unnecessary circuit and brazing material removal process, so the aluminum nitride plate at the end of the circuit pattern after etching and the aluminum nitride plate between circuit patterns are compared with other methods. Large tensile stress remains.

In general, the surface of a metal circuit is provided with a Ni-based plating layer, so that the wettability to a bonding material such as solder is improved, and the metal circuit is provided with a semiconductor element (IC chip).
And the electrode plate can be joined with high joining strength, and as a result, there is an advantage that the heat dissipation from the semiconductor element and the operation reliability of the element can be kept good.

[0006]

Therefore, the aluminum nitride circuit board is made of an aluminum nitride plate between metal circuits or an aluminum nitride at an end of the metal circuit due to a thermal stress such as a mounting process to a power module or a heat cycle during use. There was a problem that cracks were generated in the plate and further cracks were propagated, leading to destruction and lowering of the withstand voltage, making it unusable. In particular, there is a problem that cracks are remarkably generated when a metal circuit is subjected to nickel plating or the like.

That is, when an aluminum nitride circuit board having a metal circuit plated is mounted on a power module, it is heat-treated and joined to a heat sink copper plate with solder. Further, the semiconductor chip and the electrode are joined to the metal circuit portion of the circuit board by soldering. These heat treatment steps further increase the large tensile stress remaining on the aluminum nitride plate between the metal circuits after etching and the aluminum nitride plate at the end of the metal circuit, and thus have the problem that cracks are likely to occur on the circuit board. there were.

[0008] In response to the above problems, Japanese Society of Electronic Materials Technology Autumn Conference, Vol. 29 (1992) pp. 1
03 “Ceramic-metal bonded substrate with excellent thermal shock resistance”, electroless N applied to a copper plate on an alumina substrate
It has been reported that when the thickness of the i-P plating exceeds 1 μm, the thermal shock resistance in a heating / cooling test decreases.

However, when the plating thickness is 1 μm or less, there is still a problem to be solved, such as the ability to protect against corrosion such as oxidation and the like, and the life of the circuit is shortened in power modules which are likely to be heated to a high temperature. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a circuit board for a power module that reduces the occurrence of cracks and does not impair the corrosion resistance and dielectric strength of the circuit board and that has high reliability. .

[0010]

The present inventors have studied the plating layer applied to the surface of the metal circuit and found that the thickness of the plating layer on the side surface of the end of the metal circuit is not the average thickness of the plating layer. The inventors have found that the ratio between the maximum value of the thickness and the maximum value and the minimum value of the thickness is related to the occurrence of cracks in the circuit board, and completed the present invention. In particular, since the aluminum nitride plate has a smaller coefficient of thermal expansion than metal and tends to generate stress between the aluminum nitride plate and the metal circuit, the crack preventing effect according to the present invention is remarkable.

That is, the present invention relates to an aluminum nitride circuit board in which a metal circuit having a plating layer is provided on an aluminum nitride plate, wherein the maximum plating thickness on the side surface of the end of the metal circuit is 1.5 μm to 5 μm. An aluminum nitride circuit board, wherein the ratio between the maximum value and the minimum value of the plating thickness is 1 or more and 3 or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. Although there is no particular limitation on the aluminum nitride plate, in order to exhibit good heat dissipation, the thermal conductivity is 80 W /
Those having mK or more are suitable. Further, the bending strength affects the strength after the formation of the circuit board, so that the bending strength is 350M.
Those having Pa or more are suitable. The shape of the aluminum nitride plate is usually rectangular in many cases, but the shape is appropriately selected depending on the application, and the present invention is not limited at all by the shape of the circuit board.

The thickness of the aluminum nitride plate varies depending on the required strength of the circuit board, but is usually from 0.3 mm to 1.5 mm. As for the metal circuit and the metal radiator plate formed on the aluminum nitride plate, pure metal or alloy such as copper, nickel, aluminum, molybdenum, and tungsten is used. The thickness of the metal circuit or the metal radiator plate is usually 0.1 to 2.0 mm.

The thickness of the metal circuit to be joined is extremely important,
With a thickness of about 0.075 mm, in the case of the active metal method, a slight load is applied at the time of joining, so that the expansion of the metal plate is hindered, wrinkles may be generated on the metal plate, and there is a problem of lack of mass productivity. . Therefore, it is preferable to use one having a thickness of 0.1 mm or more. There is a need.

The joining process is performed in a vacuum of 10 ^-4 torr or less at a temperature equal to or higher than the melting point of the brazing material. However, it is preferable to select general conditions, that is, a temperature approximately 50 ° C. above the melting point of the brazing material. It is safe. Thereafter, in order to form the metal plate portion of the joined body into a target shape, unnecessary metal plates and brazing material are removed by a method such as chemical etching, and patterning, that is, a metal circuit is formed. Further, a circuit can be formed by a method such as the DBC method.

Further, after patterning and circuit formation, a metal portion is subjected to plating. The plating method is not particularly limited, such as an electrolytic plating method and an electroless plating method. However, the electroplating method is preferable because the pattern is complicated and it is difficult to set the electrode setting position. In the case of electroless plating, the conditions for controlling the plating thickness on the side surface of the metal circuit end and its uniformity include catalyst solution concentration and temperature,
The immersion time, plating solution concentration and temperature, immersion time, stirring conditions of the catalyst solution and the plating solution are important. If the catalyst concentration is too high and stirring is insufficient, the catalyst tends to adhere unevenly, making it difficult to obtain a uniform plating thickness. On the other hand, if the catalyst concentration is too low, a portion where the catalyst is not sufficiently adhered occurs, and in this case, the uniformity of the plating thickness is also reduced. Also, the higher the catalyst concentration, the faster the deposition of the plating, and the lower the catalyst concentration, the lower the deposition speed. Also, as the metal salt concentration of the plating solution is higher and the temperature is higher, the plating layer forming speed is higher and the plating tends to be non-uniform. The flow state of the plating solution such as stirring conditions particularly affects the uniformity of the plating thickness, and the more the stirring is sufficiently performed, the more the uniformity of the plating thickness tends to be improved.

What is important in the present invention is that the maximum value of the plating thickness on the side surface of the metal circuit end is 1.5 μm or more and 5 μm or less, and the ratio of the maximum value to the minimum value of the plating thickness is 1 or more and 3 or more. It is as follows. If the maximum value exceeds 5 μm, the stress generated due to the difference in thermal expansion when mounting a heat sink or receiving a heat cycle due to heat generation of the element, etc., increases, and cracks occur between the metal circuits or on the ceramic substrate around the convex portion. The rate increases, which is not preferable. On the other hand, if the thickness is less than 1.5 μm, it is difficult to form a uniform plating thickness, and a portion with insufficient coating is likely to be formed. Therefore, it is difficult to achieve the prevention of corrosion of the metal circuit and the improvement of the solder bondability, which are the objects of the plating layer, which is not preferable. Therefore, the maximum value of the plating thickness on the side surface of the metal circuit end is 1.5 μm or more and 5 μm or less, and more preferably 2.0 μm or more and 4 μm or less.

It is important that the maximum value is 1.5 μm or more and 5 μm or less, and that the ratio of the maximum value to the minimum value is 1 or more and 3 or less. When the ratio of the maximum value to the minimum value exceeds 3, the uniformity of the thickness of the plating layer becomes low, the generated stress due to the difference in thermal expansion becomes non-uniform, the stress of the portion where the plating thickness is large is amplified, and the ceramic substrate is amplified. Cracks easily occur, which is not preferable.

The plating thickness on the side surface of the metal circuit end as referred to in the present invention refers to the plating thickness attached to the surface forming the periphery in the thickness direction of the metal circuit as shown by the arrow in FIG. Hereinafter, the present invention will be described in more detail with reference to Examples.

[0020]

EXAMPLE A 2 to 4% by weight of yttrium oxide powder was mixed with aluminum nitride powder and molded by a doctor blade method at 1850 ° C. to 1900 ° C. in a nitrogen atmosphere to obtain an aluminum nitride plate. The physical properties of the obtained aluminum nitride plate were a thermal conductivity of 150 W / (m · K) and a relative density of 99.9%. The shape was 50 × 60 × 0.635 mm in thickness. Next, 75 parts by weight of silver powder and copper powder 2 were added to each metal powder of silver, copper and zirconium.
To 5 parts by weight, 15 parts by weight of zirconium powder and 15 parts by weight of terpineol, and 1.5 parts by weight of a solid solution of a toluene solution of polyisobutyl methacrylate as an organic binder were added, and the mixture was kneaded well. The strike was adjusted. This brazing paste was applied to both sides of the aluminum nitride sintered substrate by screen printing. The coating amount at that time was (after drying) 6 to 8 mg / cm ² .

Next, a copper plate (thickness: copper plate for metal circuit 0.1 mm) is formed on both sides of the aluminum nitride substrate coated with the brazing material paste.
3 mm, a copper plate for heat radiation of metal 0.15 mm) was placed in contact with the furnace and charged into a furnace. The temperature was 900 ° C. under a vacuum of 1 × 10 ⁻⁴ torr.
At 30 ° C. for 30 minutes. The mixture was cooled at a temperature lowering rate to produce a joined body.

Then, an ultraviolet-curing type etching resist is pattern-printed on the copper plate of the joined body by a screen printing method, unnecessary copper portions are dissolved and removed using a cupric chloride solution, and the remaining copper is left outside the pattern. The unnecessary brazing filler metal and reaction products were dissolved and removed with a 10% ammonium fluoride solution at 60 ° C. Thereafter, the etching resist was stripped with a 5% caustic soda solution to obtain a circuit board having a desired shape. This was subjected to electroless Ni-P plating to selectively form a plating film on the copper circuit portion. First, it was immersed in a 10% nitric acid aqueous solution for 1 minute to perform pretreatment, and was sufficiently washed with distilled water.
Next, an aqueous solution of 2-fold dilution of a commercially available H2O2-H2SO4-based chemical solution (CPB manufactured by Okuno Pharmaceutical Co., Ltd.) was kept at 50 ° C., immersed for 2 minutes, and then sufficiently washed with distilled water. Then, it was immersed in a 10% aqueous sulfuric acid solution for 5 seconds, and washed sufficiently with distilled water.

Next, the catalyst was immersed in a catalyst treatment solution at room temperature for 1 minute to perform the catalyst treatment. As the catalyst treatment liquid, a commercially available Pd-based catalyst stock solution (manufactured by Okuno Pharmaceutical Co., Ltd., trade name: Activator) was prepared at the concentration shown in Table 1 and used. After the catalyst treatment, the substrate was ultrasonically washed with distilled water for 2 minutes. Next, Ni kept at the temperature shown in Table 1
It was immersed in a P-based electroless plating solution for the time shown in Table 1. As the plating solution, a commercially available Ni-P-based plating solution (manufactured by Okuno Pharmaceutical Co., Ltd., trade name: Nimden SX) was prepared at the concentration shown in Table 1 and used.
While immersed in the plating solution, stirring by the rotating blade and stirring by ultrasonic waves were performed. Thus, a circuit board having a plating thickness on the side surface of the end of the metal circuit under various conditions shown in Table 1 was produced. Note that the concentration mL / L in Table 1 is a concentration when the amount ml of the stock solution was diluted to 1 L with distilled water.

The heat cycle test of these circuit boards was performed at -40 ° C. for 30 minutes, and the heating and cooling operation at 125 ° C. for 30 minutes was defined as one cycle.
The test was carried out for 200 cycles according to the 025 temperature change test method. After the test, the test was carried out by observing the presence or absence of cracks generated in the aluminum nitride sintered substrate between circuits by a fluorescent flaw detection test. The percentage of circuit boards where cracks were confirmed was shown as crack occurrence rate. In addition, the measurement of the plating thickness on the side surface of the end of the copper circuit board was performed by measuring the sample after each test by 0.3.
0.15mm depth from the surface of a copper circuit board
The copper circuit board was removed by grinding and polishing until the plating thickness on the side surface of the end was observed by SEM. The plating maximum film thickness and the minimum film thickness were measured, and the ratio of the maximum film thickness to the minimum film thickness was calculated. Table 1 collectively shows the relationship between the maximum value of the plating thickness on the side surface of the end portion of the copper circuit board, the ratio of the maximum value to the minimum value, and the crack occurrence rate.

[0025]

[Table 1]

As is evident from Table 1, when the maximum plating thickness on the side surface of the end of the metal circuit board exceeds 5 μm, the crack generation rate sharply increases. Also, it can be seen that the smaller the ratio between the maximum value and the minimum value of the plating thickness, the lower the crack occurrence rate. Therefore, from the results of these examples and comparative examples, it has been found that a highly reliable circuit board can be manufactured by controlling the plating thickness on the side surface of the end portion of the metal circuit board within the scope of the present invention.

[0027]

According to the present invention, it is possible to provide a highly reliable aluminum nitride circuit board in which the rate of occurrence of cracks due to a heat cycle is suppressed.

[Brief description of the drawings]

FIG. 1 is a conceptual cross-sectional view of the vicinity of an edge of a plated metal circuit board.

[Explanation of symbols]

1: Aluminum nitride plate 2: Brazing material layer 3: Metal circuit board 4: Plating layer (actually several μm, the size of the metal circuit board is different from the actual) 5: Plating thickness on the side surface of the end of the metal circuit board

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Ryuichi Terasaki Inventor 3-5-1 Asahicho, Machida-shi, Tokyo Denki Kagaku Kogyo Co., Ltd.

Claims (1)

[Claims] 1. An aluminum nitride circuit board comprising a metal circuit having a plating layer on an aluminum nitride plate, wherein the maximum plating thickness on the side surface of the metal circuit end is 1.
An aluminum nitride circuit board having a thickness of 5 μm or more and 5 μm or less, and a ratio between a maximum value and a minimum value of a plating thickness on a side surface of an end portion of the metal circuit is 1 or more and 3 or less.