US20080283408A1

US20080283408A1 - Aluminum Substrate for Printed Circuits, Manufacturing Method Thereof, Printed Circuit Board, and Manufacturing Method Thereof

Info

Publication number: US20080283408A1
Application number: US11/628,991
Authority: US
Inventors: Kazuyoshi Nishizawa
Original assignee: Showa Denko KK
Current assignee: Resonac Holdings Corp
Priority date: 2004-06-10
Filing date: 2005-06-10
Publication date: 2008-11-20
Also published as: WO2005122660A1

Abstract

A method of manufacturing an aluminum substrate for printed circuits, comprises an oxide layer forming step and a heat-drying step. At the oxide layer forming step, an anodic oxide layer is formed on at least one surface of an aluminum plate by anodizing the aluminum plate in an electrolytic solution of phosphoric acid concentration: 3 to 20 mass % and bath temperature: not less than 25° C. but less than 40° C. At the heat-drying step, the anodic oxide layer is dried by heating it at 150 to 300° C. for 0.5 hour or more. According to this method, a proper oxide layer can be formed, resulting in an aluminum substrate for printed circuits capable of enhancing adhesiveness to a resin plate.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a) claiming the benefit pursuant to 35 U.S.C. §119(e)(1) of the filing date of U.S. Provisional Application No. 60/580,372 filed on Jun. 18, 2004, pursuant to 35 U.S.C. §111(b).
This application claims priority to Japanese Patent Application No. 2004-172607 filed on Jun. 10, 2004 and U.S. Provisional Application No. 60/580,372 filed on Jun. 18, 2004, the entire disclosures of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

This invention relates to an aluminum substrate to be used as printed circuit boards, the manufacturing method thereof, printed circuit boards and the manufacturing method thereof. In this disclosure, the wording of “aluminum” denotes pure aluminum and its alloy.

BACKGROUND ART

The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
As a printed circuit board, a laminated board in which, for example, a copper base plate is laminated on an insulating layer of glass epoxy resin, is well known. In recent years, there is a tendency to preferably use aluminum alloy, which is light in weight and excellent in thermal conductivity, as a printed circuit board to meet strong demands for enhanced heat radiation and weight saving due to recent high integration of electronic components.
Conventionally, before making a resin plate as an insulation layer adhere to an aluminum substrate in a laminated manner, for the purpose of securing adhesiveness of the aluminum substrate to the resin plate, the aluminum substrate is subjected to sulfuric acid anodizing, oxalic acid anodizing, or sandblasting, to roughen the surface of the aluminum substrate to thereby improve the adhesiveness to the resin plate. However, it was difficult to secure sufficient adhesiveness.
Under the technical background mentioned above, as noticeable technique for making a resin plate adhere to an aluminum substrate, as disclosed by JP H10-135593, A (Patent document 1), JP S62-193296, A (Patent document 2), and JP H01-312894, A (Patent document 3), it is known to form a framework structured oxide layer on a surface of an aluminum substrate by anodizing the aluminum substrate using phosphoric acid.
However, in the oxide layer forming method as disclosed by the aforementioned patent document 1, it is difficult to control the growing of the oxide layer with a high degree of accuracy since the phosphoric acid concentration of the electrolytic bath is high. Therefore, appropriate framework structure cannot be secured, resulting in unstable adhesiveness. Moreover, the method could lead to contamination due to the adhering phosphoric acid on the oxide layer. Furthermore, since the aluminum substrate is immersed in a phosphate solution to form the oxide layer, water content remains in the oxide layer, resulting in deterioration of adhesiveness of the oxide layer to the resin plate (insulating layer).
In the oxide layer forming method as disclosed by the aforementioned patent document 2, it is difficult to control the growing of the oxide layer because of the high temperature electrolytic solution, resulting in unstable adhesiveness. Furthermore, in this oxide layer forming method too, in the same manner as the aforementioned patent document 1, since the aluminum substrate is immersed in a phosphate solution to form the oxide layer, water content remains in the oxide layer, resulting in deterioration of adhesiveness of the oxide layer to the resin plate (insulating layer).
On the other hand, according to the oxide layer forming method as disclosed by the aforementioned patent document 3, it is possible to control the growing of the oxide layer with a high degree of accuracy, causing appropriate framework structure, which in turn can secure sufficient adhesion stability. However, in this oxide layer forming method too, in the same manner as the aforementioned patent documents 1 and 2, since the aluminum substrate is immersed in a phosphate solution to form the oxide layer, water content remained in the oxide layer may cause deterioration of adhesiveness of the oxide layer to the resin plate (insulating layer).
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.
Other objects and advantages of the present invention will be apparent from the following preferred embodiments.

DISCLOSURE OF INVENTION

The preferred embodiments of the present invention have been developed in view of the above-mentioned and/or other problems in the related art. The preferred embodiments of the present invention can significantly improve upon existing methods and/or apparatuses.
The present invention was made to solve the technical problems of the aforementioned prior arts, and aims to provide an aluminum substrate for printed circuits and the manufacturing method thereof capable of forming a preferable oxide layer with a high degree of accuracy, obtaining stable adhesiveness relative to a resin insulating material and improving adhesiveness to a resin insulating material. It also aims to provide a printed circuit substrate using the aforementioned aluminum substrate and the manufacturing method thereof.
To attain the aforementioned objects, the present invention provides the following means.
[1] A method of manufacturing an aluminum substrate for printed circuits, the method, comprising:
an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate in an electrolytic solution of phosphoric acid concentration: 3 to 20 mass % and bath temperature: not less than 25° C. but less than 40° C. (25° C.≦bath temperature<40° C.); and
a heat-drying step for drying the anodic oxide layer by heating it at 150 to 300° C. for 0.5 hour or more.
The aluminum substrate for printed circuits obtained by the manufacturing method of the present invention can secure sufficient adhesive strength to a resin insulating member when making the aluminum substrate adhere to the resin insulating member.
More specifically, in the present invention, phosphate anodizing is executed under the conditions specific to the present invention to form the oxide layer, which makes it possible to assuredly form an oxide layer of desired framework structure with larger pore diameters. Therefore, when a resin plate is thermally bonded on the oxide layer of the aluminum substrate, resin components of the resin plate can be deeply impregnated into pores of the oxide layer to be intricately-intertwined with cells of the oxide layer, resulting in stable and excellent adhesiveness.
Furthermore, in the present invention, since water content of the oxide layer is released by heating the oxide layer of the aluminum substrate, when making the aluminum substrate adhere to a resin plate, it is possible to prevent deterioration of adhesiveness to a resin plate due to adverse influences of the remained water content in the oxide layer, which in turn can further improve the adhesiveness.
[2] The method of manufacturing an aluminum substrate for printed circuits as recited in the aforementioned Item 1, wherein a thickness of the oxide layer is adjusted to 0.01 to 1 μm.
In this invention, adhesiveness of the aluminum substrate to a resin plate can be further stabilized.
[3] The method of manufacturing an aluminum substrate for printed circuits as recited in the aforementioned Item 1 or 2, wherein heating temperature at the heat-drying step is set to 200 to 250° C.
In this invention, adhesiveness of the aluminum substrate to a resin plate can be further improved.
[4] The method of manufacturing an aluminum substrate for printed circuits as recited in any one of the aforementioned Items 1 to 3, wherein heating time at the heat-drying step is set to 1 to 2 hours.
In this invention, adhesiveness of the aluminum substrate to a resin plate can be further improved.
[5] The method of manufacturing an aluminum substrate for printed circuits as recited in any one of the aforementioned Items 1 to 4, wherein an aluminum plate made of Al—Mg series alloy is used as the aluminum plate.
In this invention, the workability can be improved, which in turn can improve the product quality.
[6] The method of manufacturing an aluminum substrate for printed circuits as recited in the aforementioned Item 5, wherein an aluminum plate made of JIS (Japanese Industrial Standard) A5052 alloy is used as the aluminum plate.
In this invention, the workability can be further improved, which in turn can further improve the product quality.
[7] The method of manufacturing an aluminum substrate for printed circuits as recited in any one of the aforementioned Items 1 to 4, wherein an aluminum plate made of Al—Mg—Si series alloy is used as the aluminum plate.
In this invention, the workability can be further improved, which in turn can further improve the product quality.
[8] The method of manufacturing an aluminum substrate for printed circuits as recited in the aforementioned Item 7, wherein an aluminum plate made of aluminum alloy consisting essentially of Si: 0.2 to 0.8 mass %; Mg: 0.3 to 1 mass %; and the balance being Al and inevitable impurities is used as the aluminum plate.
In this invention, the workability can be further improved, which in turn can further improve the product quality.
[9] The method of manufacturing an aluminum substrate for printed circuits as recited in the aforementioned Item 7, wherein an aluminum plate made of aluminum alloy consisting essentially of Si: 0.2 to 0.8 mass %; Mg: 0.3 to 1 mass %; Fe: 0.5 mass or less; Cu: 0.5 mass % or less, at least one of Ti: 0.1 mass % or less and B: 0.1 mass % or less, and the balance being Al and inevitable impurities is used as the aluminum plate.
In this invention, the workability can be further improved, which in turn can further improve the product quality.
[10] A method of manufacturing an aluminum substrate for printed circuits, the method, comprising:
an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate in an electrolytic solution of phosphoric acid concentration: 3 to 20 mass % and bath temperature: not less than 25° C. but less than 40 (25° C.≦bath temperature<40° C.); and
a heat-drying step for releasing water content of the oxide layer by heating the aluminum plate with the anodic oxide layer.
In this invention, in the same manner as mentioned above, it is possible to manufacture an aluminum substrate having a preferable oxide layer and capable of securing stable adhesiveness to a resin insulating member and improving adhesiveness to the resin insulating member.
[11] An aluminum substrate for printed circuits manufactured by the manufacturing method as recited in any one of the aforementioned Items 1 to 10.
In the aluminum substrate for printed circuits according to this invention, in the same manner as mentioned above, it is possible to manufacture an aluminum substrate having a preferable oxide layer and capable of securing stable adhesiveness to a resin insulating member and improving adhesiveness to the resin insulating member.
[12] A method for releasing water content of an oxide layer of an aluminum substrate for printed circuits, wherein the oxide layer is heated at 150 to 300° C. for 0.5 hour or more.
In the aluminum substrate for printed circuits according to this invention, in the same manner as mentioned above, it is possible to manufacture an aluminum substrate having a preferable oxide layer and capable of securing stable adhesiveness to a resin insulating member and improving adhesiveness to the resin insulating member.
[13] A method of manufacturing a laminated plate for printed circuits, the method, comprising:
an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate at bath voltage of 10 V or above in an electrolytic solution of phosphoric acid concentration: 3 to 20 mass % and bath temperature: not less than 25° C. but less than 40° C. (25° C.≦bath temperature<40° C.); and
a laminating step for forming an insulating layer by laminating a resin insulating member on the oxide layer of the aluminum plate,
wherein water content of the oxide layer is released by pre-heating the oxide layer before executing the laminating step.
In this invention, in the same manner as mentioned above, it is possible to manufacture a laminated plate for printed circuits having a preferable oxide layer and capable of securing stable adhesiveness to a resin insulating member and improving adhesiveness to the resin insulating member.
[14] The method of manufacturing a laminated plate for printed circuits as recited in the aforementioned Item 13, wherein the pre-heating of the oxide layer is performed at 150 to 300° C. for 0.5 to 3 hours.
In this invention, the adhesiveness to a resin insulating member such as a resin plate as an insulting layer can be improved.
[15] A laminated plate for printed circuits manufactured by the method as recited in the aforementioned Item 13 or 14.
In the laminated plate for printed circuits according to this invention, in the same manner as mentioned above, the laminated plate can have a preferable oxide layer, and is capable of securing stable adhesiveness to a resin insulating member and improving adhesiveness to the resin insulating member.
[16] A method of forming an insulating layer of an aluminum substrate for printed circuits in which the insulating layer is formed by laminating a resin insulating member on an oxide layer of the aluminum substrate,
wherein water content of the oxide layer is released by pre-heating the oxide layer before laminating the resin insulating member on the aluminum substrate having the oxide layer.
According to this invention, in the same manner as mentioned above, it is possible to secure stable adhesiveness to a resin insulating member and improve adhesiveness to the resin insulating member.
[17] The method of forming an insulating layer of an aluminum substrate for printed circuits as recited in the aforementioned Item 16, wherein the pre-heating of the oxide layer is performed at 150 to 300° C. for 0.5 to 3 hours.
According to this invention, it is possible to further improve adhesiveness to a resin insulating member such as a resin plate.
[18] A method of manufacturing a printed circuit board, the method, comprising:
an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate in an electrolytic solution of phosphoric acid concentration: 3 to 20 mass % and bath temperature: not less than 25° C. but less than 40° C.; and
an adhering step for making a resin insulating layer and a metal circuit layer adhere to the oxide layer by disposing the resin insulating member and the metal circuit member on the oxide layer of the aluminum plate and then hot heating them,
wherein water content of the oxide layer is released by pre-heating the oxide layer before executing the adhering step.
In this invention, in the same manner as mentioned above, it is possible to manufacture a printed circuit board having a preferable oxide layer and capable of securing stable adhesiveness to a resin insulating member and improving adhesiveness to the resin insulating member.
[19] The method of manufacturing a printed circuit board as recited in the aforementioned Item 18, wherein the pre-heating of the oxide layer is performed at 150 to 300° C. for 0.5 to 3 hours.
In this invention, it is possible to further improve the adhesiveness to a resin insulating layer such as a resin plate.
[20] The method of manufacturing a printed circuit board as recited in the aforementioned Item 18, wherein the pre-heating of the oxide layer is performed at temperature higher than heating temperature at the adhering step.
In this invention, it is possible to further improve the adhesiveness to a resin plate.
[21] The method of manufacturing a printed circuit board as recited in the aforementioned Item 18, wherein insulating material containing any one of elements selected from the group consisting of phenol resin, epoxy resin, unsaturated polyester resin, polyimide resin, cross-linked polyolefin resin, high-melting point polyolefin resin, polyetherimide resin, polyethersulfone resin and fluorocarbon resin is used as the resin insulating material.
In this invention, it is possible to form a preferable insulating layer.
[22] The method of manufacturing a printed circuit board as recited in the aforementioned Item 18, wherein a metal foil containing any one of copper, aluminum and nickel is used as the metal circuit member.
In this invention, it is possible to secure a preferable circuit layer.
[23] A printed circuit board manufactured by the manufacturing method as recited in any one of the aforementioned Items 18 to 22.
In this printed circuit board according to this invention, in the same manner as mentioned above, the printed circuit board can have a preferable oxide layer, and is capable of securing stable adhesiveness to a resin insulating member and improving adhesiveness to the resin insulating member.

EFFECTS OF THE INVENTION

As mentioned above, according to the present invention, it is possible to form a preferable oxide film layer with a high degree of accuracy, secure stable adhesiveness to a resin insulating layer and improve adhesiveness to a resin insulating layer.
The above and/or other aspects, features and/or advantages of various embodiments will be further appreciated in view of the following description in conjunction with the accompanying figures. Various embodiments can include and/or exclude different aspects, features and/or advantages where applicable. In addition, various embodiments can combine one or more aspect or feature of other embodiments where applicable. The descriptions of aspects, features and/or advantages of particular embodiments should not be construed as limiting other embodiments or the claims.

BRIEF DESCRIPTION OF DRAWINGS

The preferred embodiments of the present invention are shown by way of example, and not limitation, in the accompanying figures, in which:

FIG. 1 is a scanning electron microscope (SEM) photograph showing a surface of an oxide layer formed on an aluminum plate by a manufacturing method according to this invention;

FIG. 2 is an enlarged photograph showing the surface of the oxide layer shown in FIG. 1;

FIG. 3 is a SEM photograph showing the cross-section of the oxide layer shown in FIG. 1;

FIG. 4 is a schematic view showing a part of the cross-section of the oxide layer shown in FIG. 1;

FIG. 5 is a SEM photograph showing a surface of an oxide layer formed on an aluminum plate by a conventional manufacturing method;

FIG. 6 is an enlarged photograph showing the SEM photograph shown in FIG. 5;

FIG. 7 is a SEM photograph showing the cross-section of the oxide layer shown in FIG. 5;

FIG. 8 is a schematic view showing a part of the cross-section of the oxide layer shown in FIG. 5;

FIG. 9 is a SEM photograph showing a surface of an oxide layer formed on an aluminum plate by another conventional manufacturing method;

FIG. 10 is an enlarged photograph showing the SEM photograph shown in FIG. 9; and

FIG. 11 is a SEM photograph showing the cross-section of the oxide layer shown in FIG. 9.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following paragraphs, some preferred embodiments of the invention will be described byway of example and not limitation. It should be understood based on this disclosure that various other modifications can be made by those in the art based on these illustrated embodiments.
A method of manufacturing an aluminum substrate for printed circuits according to the present invention includes an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate in an electrolytic solution of phosphoric acid concentration: 3 to 20 mass % and bath temperature: not less than 25° C. but less than 40° C. (25° C.≦bath temperature<40° C.), and a heat-drying step (pre-heating step) for drying the anodic oxide layer by heating it at 150 to 300° C. for 0.5 hour or more.
In the present invention, as the material of the aluminum plate, although pure aluminum and aluminum alloy can be used, it is preferable to use aluminum alloy. Among other things, Al—Mg series alloy such as JIS A5052 alloy and Al—Mg—Si series alloy can be preferably used.
As the Al—Mg—Si series alloy, concretely, it is preferable to use aluminum alloy consisting essentially of Si: 0.2 to 0.8 mass %; Mg: 0.3 to 1 mass %; Fe: 0.5 mass or less; Cu: 0.5 mass % or less, at least one of Ti: 0.1 mass % or less and B: 0.1 mass % or less, and the balance being Al and inevitable impurities. Among other things, it is especially preferable to use aluminum alloy whose electric conductivity is 55 to 60% (IACS).
In other words, Al—Mg series alloy and Al—Mg—Si series alloy is excellent in workability, and can be most suitably used as an aluminum substrate for printed circuits due to its excellent thermal conductivity and strength.
In this invention, an aluminum plate is anodized in a phosphate electrolytic solution to form an anodic oxide layer on the resin-adhering surface of the aluminum plate.
The phosphoric acid concentration of the electrolytic solution is preferably set to 3 to 20 mass %, more preferably 8 to 12 mass %. If the phosphoric acid concentration is excessively high, it is difficult to control the growing of the oxide layer with a high degree of accuracy, and therefore appropriate framework structure cannot be secured, resulting in unstable adhesiveness to a resin plate. Moreover, this could lead to contamination due to adhesion of phosphoric acid to the oxide layer. To the contrary, if the phosphoric acid concentration is too low, a sufficient oxide layer may not be formed, and therefore it is not preferable.
In this invention, the bath voltage for forming the oxide layer is set to 8 to 40 V, more preferably 10 to 15 V. If the bath temperature is less than 8 V, the oxide layer forming rate may deteriorate. To the contrary, if the bath voltage exceeds 40 V, the voltage control may become difficult. As the electrolytic current, DC (direct current), AC (alternative current), DC-AC superimposed current and square DC current can be preferably used.
In order to secure sufficient adhesiveness to a resin plate, it is preferable to adjust the thickness of the oxide layer to 0.01 to 1 μm.
In this invention, the bath temperature of the electrolytic solution is preferably set to not less than 25° C. but less than 40° C. (25° C.≦bath temperature<40° C.), more preferably set to 28 to 32° C. If the bath temperature is excessively high, it becomes difficult to control the growth rate of the oxide layer, which may cause unstable adhesiveness. To the contrary, if the bath temperature is too low, a prescribed oxide layer cannot be formed, and therefore it is not preferable.
Now, as will be explained later, the inventor analyzed in detail the relationship between the bath temperature of the electrolytic solution and the structure of the oxide layer by conducting experiments.
First, under the conditions of the aforementioned invention, i.e., using an electrolytic solution: phosphoric acid concentration: 15 mass %; and bath temperature: 30° C.; bath voltage: 12V (DC), an anodic oxide layer 0.5 μm thick was formed on a surface of an aluminum plate. FIG. 1 is a scanning electron microscope (SEM) photograph showing the surface of the oxide layer formed on the aluminum plate, FIG. 2 is an enlarged photograph showing the surface of the oxide layer shown in FIG. 1, and FIG. 3 is a SEM photograph showing the cross-section of the oxide layer shown in FIG. 1.
Another oxide layer was formed in the same manner as the oxide layer shown in FIG. 1 except that the bath temperature is set to 45° C. FIG. 5 is a SEM photograph showing the surface of the oxide layer, FIG. 6 is an enlarged photograph showing the SEM photograph shown in FIG. 5, FIG. 7 is a SEM photograph showing the cross-section of the oxide layer, and FIG. 8 is a schematic view showing a part of the cross-section of the oxide layer.
Still another oxide layer was formed in the same manner as mentioned above except that the bath temperature is set to 20° C. FIG. 9 is a SEM photograph showing the surface of the oxide layer formed on the aluminum plate, FIG. 10 is an enlarged photograph showing the SEM photograph, and FIG. 11 is a SEM photograph showing the cross-section of the oxide layer.
As shown in FIGS. 1 to 4, the oxide layer 1 formed at an appropriate bath temperature had porous or meshed structure with large and branched pores 2, and relatively stable surface configuration. Accordingly, it is believed that, when heat-joining a resin insulating material, which will be mentioned later, on the oxide layer 1, the resin components were impregnated deeply in the pores 2 to be intricately-intertwined with cells of the oxide layer 1, resulting in enhanced adhesive strength.
In the case of the oxide layer 1 formed at high bath temperature, as shown in FIGS. 5 to 8, the pore 2 was small in diameter, extended almost linearly without being branched. Furthermore, the oxide layer 1 had meshed structure with needle-like sharp pointed ends. Accordingly, it is believed that, when heat-joining a resin insulating material on the oxide layer 1, the resin components could not be impregnated sufficiently in the pores 2 not to be intertwined with cells of the oxide layer 1, resulting in deteriorated adhesive strength.
Furthermore, as shown in FIGS. 9 to 11, in the case of the oxide layer 1 formed at low bath temperature, the oxide layer 1 had meshed structure with varies pore diameter and unevenly distributed pores. Accordingly, it is believed that, when heat-joining a resin insulating material mentioned later on the oxide layer 1, the resin components could not be impregnated in the pores 2 over the entire layer surface in a balanced manner, resulting in unstable adhesive strength.
In the present invention, after forming the oxide layer as mentioned above, by heat-drying (pre-heating) the oxide layer of the aluminum plate is heat-dried (pre-heated), the water content absorbed by the oxide layer, especially the water content absorbed at the time of anodizing treatment is released to thereby obtain an aluminum substrate.
In the present invention, by releasing water content of the oxide layer of the aluminum plate, adhesiveness to a resin insulating material to be joined at a later step is improved. In other words, if the insulating layer of the resin plate is heat-joined to the oxide layer, the adhesiveness to the resin plate deteriorates due to the adverse effects of the remaining water content.
In the present invention, since the water content in the oxide layer of the aluminum plate is reduced by releasing it, the adverse effects due to the remaining water content at the time of heat-joining of a resin plate can be eliminated, resulting in sufficient joining strength of the resin plate.
In the present invention, at the heat-drying step for releasing water content of the aluminum plate having an oxide layer, it is necessary to set the heating temperature to 150 to 300° C. The preferable heating temperature is 200 to 250° C. That is, if the heating temperature is excessively high, the oxide layer can be destroyed by the heat or the oxide layer can be cracked, which deteriorates the adhesiveness to a resin plate. To the contrary, if the heating temperature is too low, releasing of water content in the oxide layer cannot be sufficiently performed, causing deteriorated adhesiveness to a resin plate, and therefore it is not preferable.
At the heat-drying step, it is required to set the heating time to 0.5 hour (30 minutes) or more. The heating time is preferably set to 3 hours or less, more preferably 1 to 2 hours. That is, even if the heating time is set unnecessary long, corresponding effects cannot be expected. Rather, this may cause increased energy loss and deteriorated productivity. To the contrary, if the heating time is too short, sufficient releasing of water content in the oxide layer cannot be performed, which causes deteriorated adhesiveness to a resin plate due to the effects of the remaining water content, and therefore it is not preferable.
In the present invention, it is considered that when pre-heating the aluminum plate having an oxide layer (anodized substrate), releasing of water content initiates at around 150° C. and reaches a peak at around 200° C., during the period the water content in the surface (oxide layer) of the substrate is released.
Although the releasing of water content reaches a peak at around 400° C., it is considered that at this time water content contained in pores in the oxide layer is released.
On the other hand, in the present invention, at the time of pre-heating the aluminum plate having an oxide layer, the releasing of water content can also be effectively performed by setting the pre-heating temperature higher than the heating temperature at the time of joining (at the time of heat-forming) a resin insulating member and a metal circuit member, resulting in sufficient adhesiveness.
In detail, at the joining step, when a resin insulating member as an insulating layer and a metal circuit member as a circuit layer are joined to the aluminum plate each other, they are heated at about 200° C., particularly 150° C. to 230° C. to harden the resin content. By setting the heating temperature at the pre-heating (heat-drying) step higher than the heating temperature at the joining step, the water content can be effectively released, resulting in excellent adhesiveness.
In this invention, as already explained above, a resin insulating member and a metal circuit member made of, e.g., cupper are laminated on the pre-heat treated aluminum plate (aluminum substrate) to thereby form a printed circuit substrate.
As the material of the resin insulating material, thermosetting resin or thermoplastic resin can be used. As the thermosetting resin, phenol resin, epoxy resin, unsaturated polyester resin and polyimide resin can be exemplified. On the other hand, as the thermoplastic resin, cross-linked polyolefin resin, high-melting polyolefin resin, polyetherimide resin, polyethersulfone resin and fluorocarbon resin can be exemplified.
The resin insulating member is laminated on the aluminum substrate in the form of a thermoforming plate, a thermoforming sheet or film, a prepreg or a coating film.
As reinforcing material for the prepreg, paper, synthetic fiber fabric and glass fiber can be exemplified. Among other things, glass fiber woven fabric and glass fiber non-woven fabric can be exemplified.
As the metal circuit member, a metal foil made of copper, aluminum or nickel can be used. It is preferable to mechanically or chemically roughen the joining surface of the metal circuit member to be joined to the insulating layer to improve the adhesiveness.
As a method for joining the resin insulating member and the metal circuit member to the aluminum substrate, the following method can be exemplified. In this method, a resin plate or a prepreg as an insulating member is disposed on the oxide layer of the aluminum substrate in a laminated manner. Furthermore, a copper foil as a circuit member is superimposed on the insulating member. With this state, these members are heated under pressure to thereby join the insulating layer and the circuit member on the aluminum substrate.
At this joining step, as for the heating conditions, it is preferable that the heating temperature is set to 150 to 230° C., more preferably 170 to 180° C. and that the heating time is set to 30 minutes to 3 hours, more preferably 1 to 2 hours.
When the metal circuit layer is joined to the aluminum substrate via the resin insulating layer, the printed circuit board according to the present invention can be formed.
In this printed circuit board, the adhesive strength of the resin plate (insulating layer) to the aluminum substrate can be secured at sufficiently high level. More specifically, in the present invention, phosphate anodizing is executed under the conditions specific to the present invention to form the oxide layer on the aluminum substrate, which makes it possible to assuredly form an oxide layer of desired framework structure with larger pore diameters, as shown in FIGS. 1 to 4. Therefore, when the resin plate is thermally bonded on the oxide layer of the aluminum substrate, resin components of the resin plate can be deeply impregnated into pores of the oxide layer to be intricately-intertwined with cells of the oxide layer, resulting in stable and excellent adhesiveness.
Furthermore, in the present invention, since the water content of the oxide layer is released by heating the oxide layer of the aluminum substrate, when making the aluminum substrate adhere to the resin plate, it is possible to prevent deterioration of adhesiveness to the resin plate due to adverse influences of the remained water content in the oxide layer, which in turn can further improve the adhesiveness.

EXAMPLES

Examples according to the present invention and Comparative Examples to evaluate the effects of the Examples will be explained.

	TABLE 1

	Anodizing

Phosphoric acid

Layer

Pre-heating

concentration	Bath temperature	thickness	Temperature	Heating
(mass %)	(° C.)	(μm)	(° C.)	time (hour)

Example 1	10	30	0.5	200	1
Example 2	10	30	0.5	200	2
Example 3	10	30	0.1	250	1
Example 4	5	38	0.9	220	2
Example 5	19	26	0.05	180	1.5
Example 6	10	30	0.5	160	2.9
Example 7	15	26	0.5	300	0.6
Comp. Ex. 1	10	30	0.5	—	—
Comp. Ex. 2	10	45	0.1	—	—
Comp. Ex. 3	10	20	0.1	—	—
Comp. Ex. 4	25	30	0.5	—	—
Comp. Ex. 5	10	42	0.1	200	2
Comp. Ex. 6	10	20	0.1	200	1
Comp. Ex. 7	25	30	0.5	200	1
Comp. Ex. 8	10	30	0.1	320	0.5

Example 1

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.5 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 200° C. for 1 hour to release the water content in the oxide layer.
Thereafter, on the surface (oxide layer surface) of the heat-dried aluminum plate, an epoxy resin plate was superimposed. Furthermore, on the resin plate, a copper foil 70 μm thick with a roughened lower surface was superimposed. With this state, these members were heated under pressure at 175° C. for 1 hour, to thereby manufacture a printed circuit board (Example 1) in which the insulating layer and the circuit layer were integrally laminated on the aluminum substrate.

Example 2

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.5 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 200° C. for 2 hours to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the heat-dried aluminum plate, to thereby obtain a printed circuit board (Example 2).

Example 3

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.1 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 250° C. for 1 hour to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the heat-dried aluminum plate, to thereby obtain a printed circuit board (Example 3).

Example 4

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 5 mass % and bath temperature: 38° C., to thereby form an anodic oxide layer 0.9 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 220° C. for 2 hours to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the heat-dried aluminum plate, to thereby obtain a printed circuit board (Example 4).

Example 5

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 19 mass % and bath temperature: 26° C., to thereby form an anodic oxide layer 0.05 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 180° C. for 1.5 hours (1 hour and 30 minutes) to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the heat-dried aluminum plate, to thereby obtain a printed circuit board (Example 5).

Example 6

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.5 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 160° C. for 2.9 hours (2 hours and 54 minutes) to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the heat-dried aluminum plate, to thereby obtain a printed circuit board (Example 6).

Example 7

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 15 mass % and bath temperature: 26° C., to thereby form an anodic oxide layer 0.5 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 300° C. for 0.6 hour (36 minutes) to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the heat-dried aluminum plate, to thereby obtain a printed circuit board (Example 7).

Comparative Example 1

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.5 μm thick on the surface of the aluminum plate.
Subsequently, without pre-heating this aluminum plate, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 1).

Comparative Example 2

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 45° C., to thereby form an anodic oxide layer 0.1 μm thick on the surface of the aluminum plate.
Subsequently, without pre-heating this aluminum plate, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 2).

Comparative Example 3

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mas %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 20° C., to thereby form an anodic oxide layer 0.1 μm thick on the surface of the aluminum plate.
Subsequently, without pre-heating this aluminum plate, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 3).

Comparative Example 4

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized in high phosphoric acid concentration, i.e., the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 25 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.5 μm thick on the surface of the aluminum plate.
Subsequently, without pre-heating this aluminum plate, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 4).

Comparative Example 5

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 masse, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 42° C., to thereby form an anodic oxide layer 0.1 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 200° C. for 2 hours to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 5).

Comparative Example 6

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized at low bath temperature, i.e., the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 20° C., to thereby form an anodic oxide layer 0.1 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 200° C. for 1 hour to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 6).

Comparative Example 7

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was anodized in high phosphoric acid concentration, i.e., the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 25 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.5 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 200° C. for 1 hour to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 7).

Comparative Example 8

An aluminum plate (100 mm×100 mm×1 mm) made of Al—Mg—Si series alloy (Si: 0.5 mass %, Mg: 0.5 mass %, the balance being Al and inevitable impurities) was prepared. As shown in Table 1, the aluminum plate was pre-heated at high temperature, i.e., the aluminum plate was anodized at voltage of DC 12 V in an electrolytic solution of phosphoric acid concentration: 10 mass % and bath temperature: 30° C., to thereby form an anodic oxide layer 0.1 μm thick on the surface of the aluminum plate.
Subsequently, this aluminum plate with the oxide layer was pre-heated at 340° C. for 0.5 hour (30 minutes) to release the water content in the oxide layer. Thereafter, in the same manner as in Example 1, an epoxy resin plate and a copper foil were made to adhere on the surface of the aluminum plate, to thereby obtain a printed circuit board (Comparative Example 8).

As for each printed circuit board according to the aforementioned Examples and Comparative Examples, adhesiveness and heat resistance of the insulating layer were evaluated.
In the adhesiveness evaluation, peel strength (kN/m) of the resin insulating layer of each printed circuit board relative to the aluminum substrate was measured.
In the thermal resistance evaluation, in accordance with JIS C6481, the time (seconds) during which swelling of the resin insulating layer occurred when each printed circuit substrate was immersed in a soldering bath. The results are shown in Table 2.

	TABLE 2

	Peel strength	Soldering heat
	(kN/m)	resistance (sec.)

Example 1	2.1	450
Example 2	2.7	600
Example 3	2.8	620
Example 4	2.6	550
Example 5	2.5	650
Example 6	2.7	580
Example 7	2.9	700
Comp. Ex. 1	1.3	350
Comp. Ex. 2	1.0	200
Comp. Ex. 3	0.8	150
Comp. Ex. 4	1.5	370
Comp. Ex. 5	1.2	300
Comp. Ex. 6	1.1	290
Comp. Ex. 7	1.7	390
Comp. Ex. 8	1.8	395

As apparent from Table 2, in Examples 1 to 6 according to the present invention, the results revealed that the peel strength was high, the insulating layer adhered to the aluminum substrate with sufficient strength, and the heat resistance was excellent. Especially, in Examples 1 to 3 that anodizing and pre-heating were performed under the conditions falling within a preferred range of the present invention, the peel strength and the heat resistance were much more excellent.
To the contrary, in Comparative Examples 1 to 8 falling outside the gist of the present invention, in either the adhesiveness or the heat resistance, the results were unsatisfactory.

INDUSTRIAL APPLICABILITY

The method of manufacturing an aluminum substrate for printed circuit boards according to the present invention can be preferably utilized when manufacturing a printed circuit board to be used as an electric circuit board for various electronic products. Among other things, it can be utilized when manufacturing an aluminum substrate for such printed circuit boards.
While the present invention may be embodied in many different forms, a number of illustrative embodiments are described herein with the understanding that the present disclosure is to be considered as providing examples of the principles of the invention and such examples are not intended to limit the invention to preferred embodiments described herein and/or illustrated herein.
While illustrative embodiments of the invention have been described herein, the present invention is not limited to the various preferred embodiments described herein, but includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. For example, in the present disclosure, the term “preferably” is non-exclusive and means “preferably, but not limited to.” In this disclosure and during the prosecution of this application, means-plus-function or step-plus-function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) “means for” or “step for” is expressly recited; b) a corresponding function is expressly recited; and c) structure, material or acts that support that structure are not recited. In this disclosure and during the prosecution of this application, the terminology “present invention” or “invention” may be used as a reference to one or more aspect within the present disclosure. The language present invention or invention should not be improperly interpreted as an identification of criticality, should not be improperly interpreted as applying across all aspects or embodiments (i.e., it should be understood that the present invention has a number of aspects and embodiments), and should not be improperly interpreted as limiting the scope of the application or claims. In this disclosure and during the prosecution of this application, the terminology “embodiment” can be used to describe any aspect, feature, process or step, any combination thereof, and/or any portion thereof, etc. In some examples, various embodiments may include overlapping features. In this disclosure and during the prosecution of this case, the following abbreviated terminology may be employed: “e.g.” which means “for example;” and “NB” which means “note well.”

Claims

1-23. (canceled)

24. A method of manufacturing an aluminum substrate for printed circuits, said method comprising:

an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate in an electrolytic solution of phosphoric acid at a concentration of 3 to 20 mass % and a bath temperature of not less than 25° C. but less than 40° C. (25° C.=bath temperature<40° C.); and

a heat-drying step for drying the anodic oxide layer by heating it at 150 to 300° C. for 0.5 hour or more.

25. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 24, wherein the thickness of the oxide layer is from 0.01 to 1 μm.

26. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 24, wherein the heating temperature of the heat-drying step is from 200 to 250° C.

27. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 24, wherein the heating time of the heat-drying step is from 1 to 2 hours.

28. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 24, wherein an aluminum plate made of an Al—Mg series alloy is used as the aluminum plate.

29. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 28, wherein an aluminum plate made of JIS A5052 alloy is used as the aluminum plate.

30. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 24, wherein an aluminum plate made of an Al—Mg—Si series alloy is used as the aluminum plate.

31. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 30, wherein an aluminum plate made of an aluminum alloy consisting essentially of 0.2 to 0.8 mass % Si; 0.3 to 1 mass % Mg; and the balance being Al and inevitable impurities is used as the aluminum plate.

32. The method of manufacturing an aluminum substrate for printed circuits as recited in claim 30, wherein an aluminum plate made of an aluminum alloy consisting essentially of 0.2 to 0.8 mass % Si; 0.3 to 1 mass % Mg; 0.5 mass or less Fe; 0.5 mass % or less Cu; at least one of 0.1 mass % or less Ti and 0.1 mass % or less B; and the balance being Al and inevitable impurities is used as the aluminum plate.

33. A method of manufacturing an aluminum substrate for printed circuits, said method comprising:

an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate in an electrolytic solution of phosphoric acid at a concentration of 3 to 20 mass % and a bath temperature of not less than 25° C. but less than 40° C. (25° C.≦bath temperature<40° C.); and

a heat-drying step for releasing the water content of the oxide layer by heating the aluminum plate having the anodic oxide layer.

34. An aluminum substrate for printed circuits manufactured by the manufacturing method as recited in claim 24.

35. A method for releasing the water content of an oxide layer of an aluminum substrate for printed circuits, wherein the oxide layer is heated at 150 to 300° C. for 0.5 hour or more.

36. A method of manufacturing a laminated plate for printed circuits, said method comprising:

an oxide layer forming step for forming an anodic oxide layer on at least one surface of an aluminum plate by anodizing the aluminum plate at a bath voltage of 10 V or above in an electrolytic solution of phosphoric acid at a concentration of 3 to 20 mass % and a bath temperature of not less than 25° C. but less than 40° C. (25° C.≦bath temperature<40° C.); and

a laminating step for forming an insulating layer by laminating a resin insulating member on the oxide layer of the aluminum plate,

wherein the water content of the oxide layer is released by pre-heating the oxide layer before executing the laminating step.

37. The method of manufacturing a laminated plate for printed circuits as recited in claim 36, wherein the pre-heating of the oxide layer is performed at 150 to 300° C. for 0.5 to 3 hours.

38. A laminated plate for printed circuits manufactured by the method as recited in claim 36.

39. A method of forming an insulating layer on an aluminum substrate for printed circuits in which the insulating layer is formed by laminating a resin insulating member on an oxide layer of the aluminum substrate,

wherein the water content of the oxide layer is released by pre-heating the oxide layer before laminating the resin insulating member on the aluminum substrate having the oxide layer.

40. The method of forming an insulating layer of an aluminum substrate for printed circuits as recited in claim 39, wherein the pre-heating of the oxide layer is performed at 150 to 300° C. for 0.5 to 3 hours.

41. A method of manufacturing a printed circuit board, said method comprising:

an adhering step for making a resin insulating layer and a metal circuit layer adhere to the oxide layer by disposing the resin insulating member and the metal circuit member on the oxide layer of the aluminum plate and then heating them under pressure,

wherein the water content of the oxide layer is released by pre-heating the oxide layer before executing the adhering step.

42. The method of manufacturing a printed circuit board as recited in claim 41, wherein the pre-heating of the oxide layer is performed at 150 to 300° C. for 0.5 to 3 hours.

43. The method of manufacturing a printed circuit board as recited in claim 41, wherein the pre-heating of the oxide layer is performed at a temperature higher than the heating temperature at the adhering step.

44. The method of manufacturing a printed circuit board as recited in claim 41, wherein an insulating material selected from the group consisting of phenol resin, epoxy resin, unsaturated polyester resin, polyimide resin, cross-linked polyolefin resin, high-melting point polyolefin resin, polyetherimide resin, polyethersulfone resin and fluorocarbon resin is used as the resin insulating material.

45. The method of manufacturing a printed circuit board as recited in claim 41, wherein a foil containing a metal selected from the group consisting of copper, aluminum and nickel is used as the metal circuit member.

46. A printed circuit board manufactured by the manufacturing method as recited in claim 41.