JP2009123980A - Aluminum-based heat dissipation substrate for electric circuit and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat dissipation substrate for an electric circuit, which has high heat dissipation characteristics and also has adhesive strength substantially the same as that of a conventional heat dissipation substrate having an adhesive resin layer between a metal layer for a metal circuit and an aluminum substrate. <P>SOLUTION: After an Al layer 3 and a metal seed layer 4 are formed, by a vapor deposition method, on a surface of an aluminum substrate 1 where an alumite coating 2 as an insulating film is formed using anodization, the Al layer 3 and alumite coating 2 are partially changed into a boehmite layer through hydration processing to form the boehmite layer 3a between the alumite coating 2 and metal seed layer 4. Then a conductive metal layer having a desired thickness is formed on the metal seed layer 4 by an electroplating method to obtain the heat dissipation substrate for the electric circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal base substrate used in a circuit that places importance on heat dissipation characteristics such as a high-power electronic circuit and a manufacturing method thereof, and more particularly to an aluminum-based heat dissipation substrate for an electric circuit and a manufacturing method thereof.

  Conventionally, for electronic circuit boards that require heat dissipation, a metal base substrate is used in which an insulating adhesive resin layer is formed on the surface of an aluminum plate or a copper plate, and a copper foil for circuit is further laminated thereon. Has been.

In these metal base substrates, it is possible to obtain a high adhesion strength of about 50 N / mm ² by a solder pull test method described later by appropriately selecting the material of the adhesive resin layer. However, the resin layer serves as a base. Since it is interposed between the metal and the circuit, the heat dissipation characteristics are only slightly improved as compared with a general printed circuit board. Therefore, it cannot be said that the metal base substrate is suitable as an electric circuit substrate for applications requiring high heat dissipation such as inverters, power supplies, and in-vehicle applications.

  In view of this, a method has been proposed in which an alumite treatment is performed on an aluminum substrate to form an insulating layer, and a metal layer is directly formed thereon, thereby improving the heat dissipation. For example, Japanese Patent Laid-Open No. 10-004260 (Patent Document 1) discloses a method of forming a metal layer on an alumite layer using an electroless plating method and an electrolytic plating method. When a heat dissipation board is manufactured using this method, a circuit board with superior heat dissipation characteristics can be obtained compared to a heat dissipation board using a conventional adhesive resin layer as an insulating layer, but the adhesion strength between the alumite layer and the metal layer In some cases, there may be a problem with the insulating properties between the aluminum base and the metal layer.

To solve these problems, a metal layer is formed on the alumite layer using a dry plating method (vapor phase growth method) such as vapor deposition or sputtering, or the surface is roughened. After forming an alumite layer on the surface of the finished aluminum substrate, a metal layer is formed on the surface using a dry plating method such as vapor deposition or sputtering, and the adhesion strength is improved by the anchor effect with the roughened surface Has been proposed.
JP-A-10-004260

  However, among these methods, for example, in the method of forming a metal layer on the alumite surface by vapor deposition or sputtering, the adhesion strength is significantly improved as compared with the method described in Patent Document 1, but the adhesive resin layer is used. Compared to the conventional heat dissipation substrate, there is a problem that the adhesion strength is low and the reliability is still poor. Moreover, about the method of roughening the surface of an aluminum base material, the adhesion strength obtained has a value equal to or higher than that of a conventional heat dissipation substrate using an adhesive resin layer, and the problems related to this have been solved.

  However, in this method, since the alumite surface used as the insulating layer is roughened, the surface of the metal layer formed thereon is uneven. As a result, when a circuit is formed on the metal layer by a photolithographic etching method, the focus for exposing the photoresist film is shifted, making it difficult to form a precise circuit pattern. In particular, this problem has become apparent when it is required to reduce the circuit pitch.

  The present invention overcomes such conventional problems, has high heat dissipation characteristics, and is comparable to a conventional heat dissipation board provided with an adhesive resin layer between a metal layer for an electric circuit and an aluminum substrate. An object of the present invention is to provide an electric circuit heat dissipation board having adhesion strength and a method for manufacturing the same.

  In order to achieve the above object, the present invention provides a method for manufacturing a heat dissipation substrate for an electric circuit, in which a metal seed is formed on a surface of an aluminum substrate on which an anodized film as an insulating film is formed by anodic oxidation by vapor deposition. In the method for manufacturing a heat dissipation substrate for an electric circuit, in which a metal film having a desired thickness is formed by electroplating after forming the layer, a boehmite layer is formed between the alumite film and the seed layer.

  In the method for manufacturing a heat dissipation substrate for an electric circuit of the present invention, an Al layer having a film thickness of 0.005 μm to 0.05 μm and a film thickness of 0.005 serving as the metal seed layer are formed on the surface of the alumite film. After forming a 0.03 μm Ni layer by vapor deposition, the surface layer of the Al layer and the alumite film can be changed to a boehmite layer by hydration in boiling water or pressurized steam atmosphere. preferable.

  Furthermore, the heat dissipation substrate for electric circuit provided by the present invention is for an electric circuit including an aluminum substrate having an alumite film as an insulating film formed by anodization, and a metal film formed on the surface of the aluminum substrate. A heat dissipation substrate, wherein the alumite film and the metal film are bonded via a boehmite layer.

  According to the present invention, there is no hindrance to the formation of a circuit pattern, high heat dissipation characteristics, and adhesion strength comparable to that of a conventional circuit board having an adhesive resin layer between a metal film and an aluminum substrate. It is possible to provide a heat dissipation board for an electric circuit.

  In the present invention, the aluminum material used as the base material of the heat dissipation substrate can be a general aluminum having a purity of 99% or more, or an aluminum alloy containing an additive of 10 parts by weight or less.

  First, normal processing is performed on the above aluminum base material to produce an aluminum substrate having a predetermined shape. The prepared aluminum substrate is subjected to a pretreatment such as an etching treatment, if necessary, and then an anodizing treatment. In the anodizing treatment, an aluminum substrate is immersed in an alumite treatment solution (electrolytic solution) made of an inorganic acid such as sulfuric acid or sulfamic acid, or an organic acid such as oxalic acid or citric acid, and electrolysis is performed under predetermined treatment conditions. As a result, an insulating aluminum oxide film (alumite film) having a predetermined thickness is formed on the surface of the aluminum substrate.

  The thickness of the alumite film is not particularly limited as long as it has desired properties such as insulation, thermal conductivity, and chemical resistance. An alumite treatment solution of phosphoric acid cannot be used in the present invention in which boehmite is formed by a hydration reaction because aluminum hydrate cannot be formed on the surface. The anodized aluminum substrate is washed with pure water or distilled water as necessary, and dried. The aluminum substrate on which the alumite film is formed may be sealed using an arbitrary hydration sealing method.

  Next, an Al layer is formed on the surface of the alumite film by vapor phase growth methods such as sputtering and vapor deposition. The thickness of the formed Al layer is preferably in the range of about 0.005 μm to 0.05 μm. If the thickness of the Al layer is less than about 0.005 μm, it will be alloyed with the Ni layer formed in the upper part in the next step over the entire thickness direction of the formed Al layer, and hydrated during the hydration reaction described later. This is because there is a shortage of Al to become a thing. On the other hand, if it is thicker than about 0.05 μm, the hydration reaction of the Al layer is not completely completed in the film thickness direction, and a part of Al remains.

  Next, for example, a Ni layer is formed as a metal seed layer on the surface of the Al layer by vapor phase growth methods such as sputtering and vapor deposition. The material used for the metal seed layer may be any material as long as a number of pinholes that serve as passages for boiling water or pressurized steam at the time of hydration treatment described later can be appropriately formed and can be combined with the boehmite layer. Examples thereof include Ni-based alloys such as Ni and Ni—Cr, Ti and Cr, and Ni is particularly preferable.

  The thickness of the metal seed layer typified by the Ni layer is desirably in the range of about 0.005 to 0.03 μm. The reason is that when the Ni layer is thinner than about 0.005 μm, sufficient adhesion strength cannot be obtained between the copper film formed on the Ni layer and the Ni layer. On the other hand, if it is thicker than about 0.03 μm, the number of pinholes existing in the Ni layer is reduced, and the hydration reaction does not proceed sufficiently in the underlying Al layer or alumite layer.

  Thereafter, the aluminum substrate on which the Al layer and the Ni layer are formed on the surface of the alumite film is exposed to boiling water or a pressurized steam atmosphere at a predetermined temperature to be hydrated. Thereby, the surface layer part of the Al layer and the alumite film is hydrated to form a boehmite layer.

  That is, when the film thicknesses of the Al layer and the Ni layer are within the above ranges, a large number of pinholes exist in the Al layer and the Ni layer. Therefore, hot water or steam enters from the pinholes of the Ni layer and the Al layer during the hydration treatment. As a result, a hydration reaction as shown in the following chemical formulas 1 and 2 proceeds. Specifically, after Al in the Al layer or the alumite layer is ionized, it is reprecipitated as aluminum hydroxide oxide (boehmite). At this time, although the hydration reaction proceeds from the surface to the inside of the Al layer, the hydration reaction remains only in the surface layer portion of the alumite layer.

  A mode that a boehmite layer is formed by the said hydration reaction is typically shown in FIG. FIG. 1A is a cross-sectional view before hydration treatment, in which an Al layer 3 and a Ni layer 4 are laminated on an aluminum substrate 1 on which an alumite film 2 is formed. A large number of pinholes 5 exist in the Al layer 3 and the Ni layer 4. On the other hand, FIG. 1B is a cross-sectional view showing a state after the hydration treatment, and the surface layer portion of the Al layer 3 and the alumite film 2 shown in FIG. 1A is replaced with a boehmite layer 3a.

  The hydration treatment is preferably performed using an autoclave. The treatment time can be appropriately selected according to the thickness of the Al layer, but a treatment of about 15 minutes to 120 minutes is desirable. This is because if the treatment time is shorter than about 15 minutes, the hydration reaction does not proceed sufficiently and the adhesion strength may not be improved. On the other hand, even if it is longer than about 120 minutes, the treatment time is only increased, and further improvement in the adhesion strength cannot be expected. The treatment temperature may be a temperature at which boehmite is formed, that is, about 90 ° C. or higher. In general, the higher the treatment temperature, the more efficiently the boehmite formation.

  As described above, the boehmite layer is bonded to both the metal seed layer and the alumite film by dissolution of the surface layer portion of the Al layer and the alumite film and reprecipitation as the boehmite layer. As a result, the adhesion strength between the metal layer formed by electroplating and the aluminum substrate through the metal seed layer is improved.

  After the hydration treatment, a conductive metal layer such as Cu is laminated on the Ni layer as the metal seed layer to form a metal film. A metal circuit having a predetermined circuit pattern can be formed by using a normal patterning method such as a photolithography / etching method for a metal film having a desired thickness composed of the metal seed layer and the metal layer.

As described above, in the present invention, without roughening the surface of the alumite film,
After forming an Al layer and a seed layer made of a conductive metal such as Ni on the surface by vapor phase growth, the Al layer and the surface portion of the alumite film are changed to a boehmite layer by a hydration reaction, and this boehmite layer Thus, the alumite film and the metal seed layer can be firmly bonded to each other. In addition, since the surface of the metal layer formed by electroplating through the metal seed layer is flat without having irregularities, a precise circuit pattern can be formed.

  Next, the heat dissipating board for an electric circuit manufactured by the above method will be described with reference to FIG. The electric circuit heat dissipation substrate 10 has an alumite film 2 as an insulating film formed by anodizing treatment on the surface of the aluminum substrate 1. On the alumite film 2, a boehmite layer 3a is formed so as to cover the entire surface. Further, a metal film 7 composed of a metal seed layer 4 and a conductive metal layer 6 such as Cu is formed on the surface of the boehmite layer 3a.

  Thus, in the heat dissipation substrate for electric circuits according to the present invention, since the alumite film 2 and the metal film 7 are firmly bonded via the boehmite layer 3a, the metal film 7 and the metal film 7 have high heat dissipation characteristics. It becomes possible to have adhesion strength between the aluminum substrate 1 and the conventional heat dissipation substrate having an adhesive resin layer. The film thickness of the boehmite layer 3a is preferably in the range of 0.005 to 0.06 μm.

An aluminum plate (A1100) having a thickness of 1 mm and a length and width of 10 cm was used as the substrate. The surface of this substrate was etched with a 10 wt% NaOH aqueous solution at 40 ° C. for 1 minute, and then neutralized with a 50 wt% HNO ₃ aqueous solution at 25 ° C. for 30 seconds. Thereafter, an anodized aluminum solution having a thickness of 20 μm is formed on the surface of the aluminum substrate by using an alumite treatment solution comprising a 3 wt% oxalic acid aqueous solution under an anodizing treatment condition of a treatment temperature of 28 ° C., a current density of 3 A / dm ² , and a treatment time of 30 minutes. A film was formed.

  An Al layer having a thickness of 0.01 μm was formed on the surface of the obtained alumite film by vapor deposition, and a Ni layer having a thickness of 0.01 μm was formed as a metal seed layer on the surface. Then, the autoclave process for 60 minutes was performed at 130 degreeC, and the surface layer part of the Al layer and the alumite film | membrane was hydrated.

  Thereafter, a copper layer of 0.3 μm was formed on the surface of the Ni layer using a vapor deposition method, and a copper plating layer having a thickness of 10 μm was further formed using an electrolytic copper plating method. Next, 5 × 5 circular patterns having a diameter of 1 mm were formed on the prepared copper plating surface by screen printing, and then etching was performed to form a copper layer having 25 circular patterns.

  The obtained heat radiating board was used as sample 1, and after soldering a tin-plated copper wire having a diameter of 0.6 mm to each copper layer having a circular pattern so as to be perpendicular to the pattern surface, the tin-plated copper wire was A solder pull test was carried out to pull up vertically, and the adhesion strength between the base and the metal film (copper layer) was measured.

  Although it produced similarly to the said sample 1, the film thickness of the Al layer was 0.05 micrometer, the film thickness of Ni layer was 0.03 micrometer, and the autoclave process was performed for 120 minutes at 130 degreeC, and the heat dissipation board of the sample 2 was produced. About this sample 2, the solder pull test was implemented on the conditions similar to the sample 1, and the adhesive strength was measured.

  A heat radiating substrate of Sample 3 was prepared in the same manner as Sample 1 except that the Al layer thickness was 0.003 μm and the Ni layer thickness was 0.01 μm. And the adhesion strength was measured.

  A heat-dissipating substrate of Sample 4 was prepared in the same manner as Sample 1 except that the Al layer thickness was 0.07 μm and the Ni layer thickness was 0.01 μm, and a solder pull test was performed under the same conditions as Sample 1. And the adhesion strength was measured.

  A heat-dissipating substrate of Sample 5 was prepared in the same manner as Sample 1 except that the Al layer thickness was 0.01 μm and the Ni layer thickness was 0.003 μm. The solder pull test was performed under the same conditions as Sample 1. And the adhesion strength was measured.

  A heat-dissipating substrate of Sample 6 was prepared in the same manner as Sample 1 except that the Al layer thickness was 0.01 μm and the Ni layer thickness was 0.05 μm, and a solder pull test was performed under the same conditions as Sample 1. And the adhesion strength was measured.

  A sample 7 was prepared by directly forming a Ni layer having a thickness of 0.01 μm. Thereafter, the hydration treatment was not performed, and a solder pull test was performed under the same conditions as Sample 1 to measure the adhesion strength.

  The results of measuring the adhesion strength of Samples 1 to 7 are shown in Table 1 below.

From these results, the adhesion strength of Samples 1 and 2 is higher than that of Samples 3 to 7, and is equal to or higher than the adhesion strength (about 50 N / mm ² ) of the conventional heat dissipation substrate provided with the adhesive resin layer. I understand that.

It is sectional drawing which shows typically the manufacturing method of the heat sink for electric circuits which concerns on this invention. It is sectional drawing which shows typically the heat sink for electric circuits which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aluminum substrate 2 Anodized film 3 Al layer 3a Boehmite layer 4 Metal seed layer 5 Pinhole 6 Conductive metal layer 7 Metal film 10 Electric circuit heat dissipation board

Claims (3)

  An electrical circuit in which a metal seed layer is formed by vapor deposition on the surface of an aluminum substrate on which an anodized aluminum film is formed using anodization, and then a metal film having a desired thickness is formed by electroplating. A method for manufacturing a heat dissipation board for an electric circuit, comprising: forming a boehmite layer between an alumite film and a metal seed layer.   After forming an Al layer having a film thickness of 0.005 μm to 0.05 μm and a Ni layer having a film thickness of 0.005 to 0.03 μm to be the metal seed layer on the surface of the alumite film, 2. The heat dissipation substrate for an electric circuit according to claim 1, wherein a surface layer portion of the Al layer and the alumite film is changed to a boehmite layer by hydrating in a boiling water or pressurized steam atmosphere. Method.   An electric circuit heat dissipation board comprising an aluminum substrate having an alumite film as an insulating film formed by anodization, and a metal film formed on the surface of the aluminum substrate, wherein the anodized film and the metal film are A heat dissipation board for an electric circuit, which is bonded through a boehmite layer.

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