Circuit board and method for fabricating the same

Abstract

Embodiments of the present disclosure are directed to a circuit board. The circuit board comprises: an aluminum-based substrate; an alumina layer formed on at least one surface of the aluminum-based substrate; and a circuit layer formed on the alumina layer. The alumina layer comprises alumina and an element selected from a group consisting of chromium, nickel, a rare earth metal, and a combination thereof.

Claims

1. A circuit board, comprising: an aluminum-based substrate; an alumina layer formed on at least one surface of the aluminum-based substrate, wherein the alumina layer includes a circuit pattern formed by irradiation of an energy beam; and a circuit layer formed on the circuit pattern of the alumina, wherein the alumina layer comprises alumina and at least one element selected from chromium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, thulium, ytterbium, lutetium, scandium, or a combination thereof.

2. The circuit board according to claim 1, wherein a content of the element in the alumina layer ranges from 0.001 wt % to 20 wt %.

3. The circuit board according to claim 1, wherein the content of the element in the alumina layer ranges from 0.01 wt % to 1 wt %.

4. The circuit board according to claim 1, wherein a thickness of the alumina layer ranges from 10 m to 300 m.

5. The circuit board according to claim 1, wherein the thickness of the alumina layer ranges from 50 m to 100 m.

6. The circuit board according to claim 1, wherein the alumina layer is sealed with a sealing agent.

7. The circuit board according to claim 6, wherein the sealing agent is selected from one or more dichromate, one or more nickel salt, one or more rare earth metal salt, or a combination thereof.

8. The circuit board according to claim 6, wherein the sealing agent is selected from potassium dichromate, sodium dichromate, nickel fluoride, nickel acetate, nickel sulfate, or a combination thereof.

Description

DETAILED DESCRIPTION

(1) Reference will be made in detail to embodiments of the present disclosure. The embodiments described herein with reference to examples are explanatory, illustrative, and used to generally understand the present disclosure. The embodiments shall not be construed to limit the present disclosure.

(2) According to embodiments of the present disclosure, a circuit board is provided. The circuit board comprises: an aluminum-based substrate, an alumina layer, and a circuit layer. The alumina layer is formed on at least one surface of the aluminum-based substrate, and the circuit layer is formed on the alumina layer. The alumina layer comprises alumina and an element selected from a group consisting of chromium, nickel, a rare earth metal, and a combination thereof.

(3) In one embodiment, the rare earth metal may be selected from a group consisting of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, yttrium, and a combination thereof. In another embodiment, the rare earth metal may be selected from a group consisting of lanthanum, cerium, yttrium, and a combination thereof.

(4) An existing form of the element in the alumina layer is not limited herein. For example, the element(s) may exist in the alumina layer in a form of a compound, a simple substance, or a combination thereof.

(5) A content of the element(s) in the alumina layer is adjusted in such a way that the alumina layer may have a chemical plating activity by an irradiation with an energy beam. In some embodiments, the content of the element(s) in the alumina layer is 0.001 wt % or above, such that the alumina layer may have a chemical plating activity by the irradiation with the energy beam. In one embodiment, the content of the element(s) in the alumina layer is 0.005 wt % or above, or 0.01 wt % or above, for example, such that not only may the alumina layer have a chemical plating activity by the irradiation with the energy beam, but also a higher chemical plating rate may be achieved. In some embodiments, the content of the element(s) in the alumina layer ranges from 0.001 wt % to 20 wt %. In some embodiments, the content of the element(s) in the alumina layer ranges from 0.005 wt % to 10 wt %, more preferably from 0.01 wt % to 1 wt %, further preferably from 0.05 wt % to 0.5 wt %, most preferably from 0.08 wt % to 0.25 wt %. The content of the element(s) in the alumina layer may be measured by SEM-EDX (scanning electron microscope-energy dispersive X-ray detector), in which, for example, the content of the element(s) may be an average of 20 counting points.

(6) The alumina layer may be formed by various processes. In one embodiment, the alumina layer is formed by performing an anodic oxidation for the aluminum-based substrate. Then, the alumina layer may be filled with the element by various processes. In one embodiment, the alumina layer is immersed in a solution of a compound containing the element, and then is dried to form the alumina layer filled with the element. Alternatively or additionally, the alumina layer may be filled with the element by CVD (chemical vapor deposition). In another embodiment, the alumina layer may be formed by performing an anodic oxidation and a sealing for the aluminum-based substrate. In this way, not only may a corrosion resistance and/or a weather resistance of the alumina layer be improved, but also a hardness and/or an abrasion resistance of the alumina layer may be increased. Besides, the alumina layer may have a chemical plating activity by the irradiation with the energy beam.

(7) In one embodiment, a sealing agent used in the sealing may be a water soluble substance selected from a group consisting of a dichromate, a nickel salt, a rare earth metal salt, and a combination thereof. For example, the sealing agent may be selected from a group consisting of an alkali metal dichromate (such as sodium dichromate, potassium dichromate), nickel fluoride, nickel acetate, nickel sulfate, nickel chloride, nickel sulfamic acid, nickel bromide, nickel hydroxide (Ni(OH).sub.2), nickel carbonyl, a water soluble chloride of a rare earth metal, a water soluble sulfate of a rare earth metal, a fluoride of a rare earth metal, a bromide of a rare earth metal, and a combination thereof.

(8) In one embodiment, the sealing agent is selected from a group consisting of a dichromate, a nickel salt, and a combination thereof. In this case, the sealed alumina layer has a higher absorption for an energy beam, especially for an energy beam with a low energy. In another embodiment, the sealing agent is selected from a group consisting of potassium dichromate, sodium dichromate, nickel fluoride, nickel acetate, nickel sulfate, and a combination thereof.

(9) In some embodiments, a thickness of the alumina layer may range from 10 m to 300 m. In one embodiment, the thickness of the alumina layer ranges from 50 m to 100 m, such that not only does the circuit board have a high withstand voltage, but also the thickness of the circuit board is not too large.

(10) A thickness of the circuit layer is not limited herein, which may depend on the practical application, for example, the thickness of the circuit layer may range from 10 m to 100 m.

(11) With the circuit board according to embodiments of the present disclosure, the adhesive force between the circuit layer and the alumina layer is of levels 1-0, e.g., of level 0. The adhesive force may be measured using a BYK process disclosed in ISO 2409.

(12) According to embodiments of the present disclosure, a method for fabricating a circuit board is provided. The method comprises the following steps.

(13) At step S1, an aluminum-based substrate is provided. The aluminum-based substrate may be any type of substrate for a circuit board, such as an aluminum substrate or an aluminum alloy substrate. The aluminum-based substrate may be pretreated by rinsing or polishing to remove an oil stain and/or an oxide film on a surface of the aluminum-based substrate.

(14) At step S2, an anodic oxidation is performed for the aluminum-based substrate to form an alumina layer on at least one surface of the aluminum-based substrate.

(15) In one embodiment, the aluminum-based substrate is immersed into an electrolyte for the anodic oxidation. The electrolyte is not limited herein. For example, the electrolyte may be a solution containing any one of sulfuric acid, chromic acid, oxalic acid, and a combination thereof.

(16) In some embodiments, the anodic oxidation may be performed at a voltage ranging from 10 V to 30 V and at a temperature ranging from 20 C. to 70 C. for a duration of time ranging from 30 min to 120 min.

(17) At step S3, the aluminum-based substrate is contacted with a solution containing a sealing agent to perform a sealing for the alumina layer so as to fill an element in the alumina layer. The element is selected from a group consisting of chromium, nickel, a rare earth metal, and a combination thereof.

(18) In one embodiment, the sealing agent may be selected from a group consisting of a dichromate, a nickel salt, a rare earth metal salt, and a combination thereof. The rare earth metal may be selected from a group consisting of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutecium, scandium, yttrium, and a combination thereof. In one embodiment, the rare earth metal may be selected from a group consisting of lanthanum, cerium, yttrium, and a combination thereof. By using one or more of these sealing agents to seal the alumina layer, not only may micro pores in the alumina layer be closed so as to increase a corrosion resistance, a weather resistance, a hardness, and/or an abrasion resistance of the alumina layer, but also the sealed alumina layer may have a higher absorption for an energy beam, especially for an energy beam with a low energy so as to obtain a chemical plating activity by the irradiation with the energy beam, thus further forming a circuit on the alumina layer.

(19) In one embodiment, the sealing agent may be a water soluble substance selected from a group consisting of a dichromate, a nickel salt, a rare earth metal salt, and a combination thereof. For example, the sealing agent may be selected from a group consisting of an alkali metal dichromate (such as sodium dichromate, potassium dichromate), nickel fluoride, nickel acetate, nickel sulfate, nickel chloride, nickel sulfamic acid, nickel bromide, nickel hydroxide (Ni(OH).sub.2), nickel carbonyl, a water soluble chloride of a rare earth metal, a water soluble sulfate of a rare earth metal, a fluoride of a rare earth metal, a bromide of a rare earth metal, and a combination thereof.

(20) In one embodiment, the sealing agent is selected from a group consisting of a dichromate, a nickel salt, and a combination thereof. In this case, the sealed alumina layer has a higher absorption for an energy beam, especially for an energy beam with a low energy, so as to achieve a high chemical plating rate during the chemical plating. In another embodiment, the sealing agent is selected from a group consisting of potassium dichromate, sodium dichromate, nickel fluoride, nickel acetate, nickel sulfate, and a combination thereof.

(21) An amount of the sealing agent is adjusted in such a way that the alumina layer may have a chemical plating activity by an irradiation with an energy beam. In some embodiments, the amount of the sealing agent is adjusted so that a content of the element(s) in the alumina layer is 0.001 wt % or above, such that the alumina layer may have a chemical plating activity by the irradiation with the energy beam. In one embodiment, the amount of the sealing agent is adjusted so that the content of the element(s) in the alumina layer is 0.005 wt % or above, for example, 0.01 wt % or above, such that not only may the alumina layer have a chemical plating activity by the irradiation with the energy beam, but also a higher chemical plating rate may be achieved. In some embodiments, the amount of the sealing agent is adjusted so that the content of the element(s) in the alumina layer ranges from 0.001 wt % to 20 wt %. In one embodiment, the amount of the sealing agent is adjusted so that the content of the element(s) in the alumina layer ranges from 0.005 wt % to 10 wt %, e.g., from 0.01 wt % to 1 wt %, from 0.05 wt % to 0.5 wt %, or from 0.08 wt % to 0.25 wt %.

(22) In one embodiment, the sealing agent is a nickel salt solution with a concentration ranging from 0.8 g/L to 1.6 g/L and a pH ranging from 5.5 to 6.5. The sealing may be performed at a temperature ranging from 25 C. to 80 C. (such as from 25 C. to 45 C.) for a duration time ranging from 10 min to 20 min.

(23) In another embodiment, the sealing agent is a nickel salt and the solution of the sealing agent is a nickel salt solution with a concentration ranging from 1.4 g/L to 1.8 g/L. The nickel salt solution may also include an acetic acid solution with a concentration ranging from 0.1 wt % to 1 wt %, such that a pH of the nickel salt solution ranges from 5.5 to 6. The sealing may be performed at a temperature ranging from 85 C. to 95 C. for a duration of time ranging from 15 min to 20 min.

(24) In another embodiment, the sealing agent is a rare earth metal salt and the solution of the sealing agent is a rare earth metal salt solution with a concentration ranging from 0.01 mol/L to 0.1 mol /L and a pH ranging from 4.5 to 6. The sealing may be performed at a temperature ranging from 95 C. to 98 C. for a duration of time ranging from 15 min to 35 min.

(25) In another embodiment, the sealing agent is a dichromate and the solution of the sealing agent is a dichromate solution with a concentration ranging from 50 g/L to 70 g/L and a pH ranging from 6 to 7. The sealing may be performed at a temperature ranging from 90 C. to 95 C. for a duration of time ranging from 15 min to 35 min.

(26) By using the methods according to above embodiments to seal the alumina layer, the sealed alumina layer has a higher absorption for an energy beam, especially for an energy beam with a low energy.

(27) At step S4, a part of the alumina layer to be formed with a circuit is irradiated by an energy beam to activate the part of the alumina layer.

(28) In one embodiment, the energy beam may be a laser, an electronic beam, or an ion beam. In one embodiment, the energy beam is an laser with a wavelength ranging from 200 nm to 3000 nm, a power ranging from 5 W to 3000 W, and a frequency ranging from 0.1 KHz to 200 KHz. In another embodiment, the energy beam is an electronic beam with a power density ranging from 10 W/cm.sup.2 to 10.sup.11 W/cm.sup.2. In yet another embodiment, the energy beam is an ion beam with an energy ranging from 10 eV to 10.sup.6 eV. In one embodiment, the energy beam is a laser, such as a laser with a wavelength ranging from 532 nm to 1064 nm and a power ranging from 20 W to 100 W, or a laser with a wavelength of 1064 nm and a power ranging from 20 W to 30 W.

(29) If the laser is employed to irradiate the alumina layer, the laser may be generated by any type of laser devices, such as a YAG laser, a green light laser, and a fiber laser.

(30) According to embodiments of the present disclosure, the alumina layer formed by anodic oxidation is further sealed by the sealing agent selected from the group consisting of a dichromate, a nickel salt, a rare earth metal salt, and a combination thereof, such that the absorption of the sealed alumina layer for an energy beam is improved, and thus the sealed alumina layer can be activated to have the chemical plating activity by irradiating at least a part of the alumina layer using an energy beam with a low energy. By using the energy beam with a low energy to irradiate the alumina layer, in one aspect a fabrication cost can be reduced, and in another aspect a fine pattern may be formed in the alumina layer and thus a high precision circuit may be formed accordingly.

(31) At step S5, the chemical plating is performed for the aluminum-based substrate to form a circuit layer on the part of the alumina layer so as to form the circuit board.

(32) As the part of the alumina layer irradiated by the energy beam has the chemical plating capability, while a remaining part of the alumina layer not irradiated does not have the chemical plating capability, the circuit can be formed on the part of the alumina layer irradiated by the energy beam. For example, after the irradiation, the aluminum-based substrate is immersed into a copper plating solution containing a cupric salt and a reducing agent and with a pH ranging from 12 to 13. Copper ions in the cupric salt may be reduced to copper by the reducing agent. The reducing agent may be selected from the group consisting of glyoxylic acid, hydrazine, sodium hypophosphite, and a combination thereof.

(33) In one embodiment, after the chemical plating described above, an electroplating or one or more chemical plating steps may be additionally performed to increase a thickness of a plating layer or form another metal layer on a first chemical plating layer. For example, a nickel layer may be formed on a copper layer to reduce or prevent the copper layer from being oxidized.

(34) In order to make those skilled in the art better understand the present disclosure, examples and comparative examples are illustrated below, in which the adhesive force of the metal layer formed on the substrate is measured using the BYK process disclosed in ISO 2409. Firstly, a 1010 grid (including 1 mm1 mm test regions) was formed on a surface of a sample by using a BYK knife and the scraps were cleaned up, in which each cross-cut line reached a bottom of the metal layer. Secondly, an adhesive tape (such as adhesive paper 3M600) was attached to a region to be tested and then was torn off by holding one end of the adhesive tape and quickly moving in a direction perpendicular to the surface of the sample. Such a measurement was carried out twice at a same position, and a level of the adhesive force of the metal layer was thus determined according to following criterions.

(35) ISO level 0: an edge of a cross-cut line is smooth and there is no metal falling off at both edges and intersections of the cross-cut lines.

(36) ISO level 1: there is a small piece of metal falling off at the intersections of the cross-cut lines and an area of the small piece(s) is less than 5% of a total area of the metal layer.

(37) ISO level 2: there are small pieces of metal falling off at both the edges and intersections of the cross-cut lines and an area of the small pieces ranges from 5% to 15% of the total area of the metal layer.

(38) ISO level 3: there are pieces of metal falling off at both the edges and intersections of the cross-cut lines and an area of the pieces ranges from 15% to 35% of the total area of the metal layer.

(39) ISO level 4: there are pieces of metal falling off at both the edges and intersections of the cross-cut lines and an area of the pieces ranges from 35% to 65% of the total area of the metal layer.

(40) ISO level 5: there are pieces of metal falling off at both the edges and intersections of the cross-cut lines and an area of the pieces is greater than 65% of the total area of the metal layer.

(41) In the examples and comparative examples below, a method specified in GB/T 5598-85 was used to measure a thermal conductivity of the circuit board, a method specified in GB/T 5593-1996 was used to measure a withstand voltage of the circuit board, a method specified in GB/T 8014.1-2005 was used to measure the thickness of the alumina layer, and a method specified in GB/T 15717-1995 was used to measure the thickness of the circuit layer. The content of the element(s) in the alumina layer was measured by SEM-EDX, in which, the content of the element(s) was measured as an average of 20 counting points.

(42) In the examples and comparative examples below, unless specified otherwise, the aluminum-based substrate was an aluminum substrate.

EXAMPLE 1

(43) (1) Pretreatment

(44) An aluminum-based substrate was rinsed, then was immersed in a degreasing solution at a temperature ranging from 50 C. to 60 C. for about 10 min, and then was polished by a polishing solution for about 15 min. The degreasing solution comprised: NaOH (10 g/L), Na.sub.3PO.sub.4 (30 g/L), Na.sub.2CO.sub.3 (15 g/L), and sodium dodecylsulphonate (6 g/L), with water as a solvent. The polishing solution comprised: H.sub.2SO.sub.4 (20 wt %), HNO.sub.3 (10 wt %), and H.sub.3PO.sub.4 (70 wt %), with water as a solvent.

(45) (2) Anodic Oxidation

(46) The aluminum-based substrate was immersed in an electrolyte at 40 C. as an anode, and a stainless steel slice was used as a cathode. At a voltage of 18 V, electrolysis was performed to form an alumina layer with a thickness of 75 m on the aluminum-based substrate. The electrolyte comprised H.sub.2SO.sub.4 (20 wt %) and oxalic acid (2 wt %), with water as a solvent.

(47) (3) Sealing

(48) The aluminum-based substrate was immersed in a nickel fluoride solution at 25 C. for about 18 min, and then was dried. The nickel fluoride solution had a concentration of 1.6 g/L, and a pH ranging from 5.5 to 6, with water as a solvent.

(49) It was measured that a content of the element nickel in the alumina layer was 0.1 wt %.

(50) (4) Activation

(51) A part of the alumina layer was irradiated by a laser to form a circuit pattern. Irradiation was performed using a YAG laser with a wavelength of 1064 nm, a power of 25 W, a frequency of 50 kHz, a scanning speed of 100 mm/s, and a filling pitch of 0.05 mm.

(52) (5) Chemical Plating

(53) The aluminum-based substrate was immersed in a chemical plating solution for chemical plating to form a circuit layer with a thickness of 12 m on the alumina layer, so as to form a circuit board. The chemical plating solution comprised: CuSO.sub.4.5H.sub.2O (0.12 mol/L), Na.sub.2EDTA.2H.sub.2O (0.14 mol/L), potassium ferrocyanide (10 mg/L), 2,2-bipyridine (10 mg/L), and glyoxalic acid (HCOCOOH) (0.10 mol/L), with a pH of 12.5-13 adjusted by NaOH and H.sub.2SO.sub.4 solutions, and water as a solvent.

(54) It was calculated that a plating rate was about 2.5 m/h. It was measured that an adhesive force between the circuit layer (i.e., a plating layer) and the alumina layer was ISO level 0, and the circuit board had a thermal conductivity of about 16 W/(m.Math.K) and a breakdown voltage of about 2.2 kV.

COMPARATIVE EXAMPLE 1

(55) This example was performed by using substantially the same process as that described in Example 1 except that step (3) was omitted. As a result, the circuit layer was not formed.

COMPARATIVE EXAMPLE 2

(56) This example was performed by using substantially the same process as that described in Example 1 except that step (3) was performed by immersing the aluminum-based substrate in a boiling water with a pH ranging from 5.5 to 6 for about 20 min. As a result, the circuit layer was not formed.

COMPARATIVE EXAMPLE 3

(57) A silicone layer with a thickness of 75 m was formed by hot pressing on a surface of an aluminum-based substrate treated as step (1) of Example 1, and then a copper foil (with a thickness of 100 m) was formed also by hot pressing on the silicone layer to form a laminated plate. Film-applying, developing, exposing, and etching were performed for the laminated plate to form a circuit layer in the laminated plate.

(58) It was measured that an adhesive force between the circuit layer and the aluminum-based substrate was ISO level 0, and the circuit board has a thermal conductivity of about 1.5 W/(m.Math.K) and a breakdown voltage of about 1.6 kV.

COMPARATIVE EXAMPLE 4

(59) An aluminum-based substrate with an alumina layer thereon was formed as steps (1)-(3) of Example 1.

(60) Then, a chemical activating was performed for the aluminum-based substrate, comprising steps of: immersing the aluminum-based substrate in a palladium solution for about 2 min, and then drying the aluminum-based substrate. The palladium solution comprised: PdCl.sub.2 (0.3 g/L) and HCl (2 mL/L), with water as a solvent.

(61) Then, a chemical plating was performed for the aluminum-based substrate as step (5) of Example 1, so as to form a plating layer with a thickness of 12 m.

(62) Then, the aluminum-based substrate was rinsed with deionized water, baked, applied with a film, left standing for 0.5 hour, exposed, developed with a developer (a Na.sub.2CO.sub.3 solution (1.0 wt %)), etched with an etchant (a CuCl.sub.2 solution), and stripped by a NaOH solution (2.0 wt %) to form a circuit layer, so as to form a circuit board.

(63) It was measured that an adhesive force of the circuit layer was ISO level 2, and the circuit board had a thermal conductivity of about 15 W/(m.Math.K) and a breakdown voltage of about 1.9 kV.

EXAMPLE 2

(64) This example was performed by using substantially the same process as that described in Example 1 except that step (3) was performed by immersing the aluminum-based substrate in a lanthanum chloride aqueous solution at 96 C. for about 30 min. The lanthanum chloride aqueous solution had a concentration of 0.05 mol/L, and a pH ranging from 5 to 5.5, with water as a solvent.

(65) It was measured that a content of the lanthanum element in the alumina layer was 0.11 wt %.

(66) It was calculated that a plating rate was about 2.0 m/h. It was measured that an adhesive force between the circuit layer (i.e., a plating layer) and the alumina layer was ISO level 0, and the circuit board had a thermal conductivity of about 17 W/(m.Math.K) and a breakdown voltage of about 2.3 kV.

EXAMPLE 3

(67) This example was performed by using substantially the same process as that described in Example 1 except that in step (4) the irradiation was performed using a fiber laser with a wavelength of 1064 nm, a power of 25 W, a frequency of 50 kHz, a scanning speed of 100 mm/s, and a filling pitch of 0.05 mm.

(68) It was calculated that a plating rate is about 2.5 m/h. It was measured that an adhesive force between the circuit layer (i.e., a plating layer) and the alumina layer was ISO level 0, and the circuit board had a thermal conductivity of about 16 W/(m.Math.K) and a breakdown voltage of about 2.3 kV.

EXAMPLE 4

(69) (1) Pretreatment

(70) An aluminum-based substrate was rinsed, then was immersed in a degreasing solution at a temperature ranging from 50 C. to 60 C. for about 10 min, and then was polished by a polishing solution for about 15 min. The degreasing solution comprised: NaOH (10 g/L), Na.sub.3PO.sub.4 (30 g/L), Na.sub.2CO.sub.3 (15 g/L), and sodium dodecylsulphonate (6 g/L), with water as a solvent. The polishing solution comprised: H.sub.2SO.sub.4 (20 wt %), HNO.sub.3 (10 wt %), and H.sub.3PO.sub.4 (70 wt %), with water as a solvent.

(71) (2) Anodic Oxidation

(72) The aluminum-based substrate was immersed in an electrolyte at 30 C. as an anode, and a stainless steel slice was used as a cathode. At a voltage of 18 V, electrolysis was performed to form an alumina layer with a thickness of 80 m on the aluminum-based substrate. The electrolyte comprised H.sub.2SO.sub.4 (25 wt %) and oxalic acid (2 wt %), with water as a solvent.

(73) (3) Sealing

(74) The aluminum-based substrate was immersed in a potassium dichromate solution at 90 C. for about 30 min, and then was dried. The potassium dichromate solution had a concentration of 60 g/L, and a pH ranging from 6 to 6.5, with water as a solvent.

(75) It was measured that a content of the element chromium in the alumina layer was 0.2 wt %.

(76) (4) Activation

(77) A part of the alumina layer was irradiated by a laser to form a circuit pattern. The irradiation was performed using a green laser with a wavelength of 532 nm, a power of 20 W, a frequency of 50 kHz, a scanning speed of 100 mm/s, and a filling pitch of 0.05 mm.

(78) (5) Chemical Plating

(79) The aluminum-based substrate was immersed in a chemical plating solution for chemical plating to form a circuit layer with a thickness of 85 m on the alumina layer, so as to form a circuit board. The chemical plating solution comprised: CuSO.sub.4.5H.sub.2O (0.12 mol/L), Na.sub.2EDTA.2H.sub.2O (0.14 mol/L), potassium ferrocyanide (10 mg/L), 2,2-bipyridine (10 mg/L), and glyoxalic acid (HCOCOOH) (0.10 mol/L) with a pH of 12.5-13 adjusted by NaOH and H.sub.2SO.sub.4 solutions, and water as a solvent.

(80) It was calculated that a plating rate was about 2.8 m/h. It was measured that an adhesive force between the circuit layer (i.e., a plating layer) and the alumina layer was ISO level 0, and the circuit board had a thermal conductivity of about 17 W/(m.Math.K) and a breakdown voltage of about 2.1 kV.

EXAMPLE 5

(81) (1) Pretreatment

(82) An aluminum-based substrate (i.e., an aluminum alloy substrate) was rinsed, then was immersed in a degreasing solution at a temperature ranging from 50 C. to 60 C. for about 10 min, and then was polished by a polishing solution for about 15 min. The degreasing solution comprised: NaOH (10 g/L), Na.sub.3PO.sub.4 (30 g/L), Na.sub.2CO.sub.3 (15 g/L), sodium dodecylsulphonate (6 g/L), with water as a solvent. The polishing solution comprised: H.sub.2SO.sub.4 (20 wt %), HNO.sub.3 (10 wt %), and H.sub.3PO.sub.4 (70 wt %), with water as a solvent.

(83) (2) Anodic Oxidation

(84) The aluminum-based substrate was immersed in an electrolyte at 60 C. as an anode, and a stainless steel slice was used as a cathode. At a voltage of 18 V, electrolysis was performed to form an alumina layer with a thickness of 90 m on the aluminum-based substrate. The electrolyte comprised H.sub.2SO.sub.4 (20 wt %) and oxalic acid (3 wt %), with water as a solvent.

(85) (3) Sealing

(86) The aluminum-based substrate was immersed in a nickel acetate solution at 85 C. for about 15 min, and then was dried. The nickel acetate solution had a concentration of 0.5 wt %, and a pH ranging from 5.5 to 6.0, with water as a solvent.

(87) It was measured that a content of the element nickel in the alumina layer was 0.15 wt %.

(88) (4) Activation

(89) A part of the alumina layer was irradiated by a laser to form a circuit pattern. The irradiation was performed using a green laser with a wavelength of 532 nm, a power of 20 W, a frequency of 50 kHz, a scanning speed of 100 mm/s, and a filling pitch of 0.05 mm.

(90) (5) Chemical Plating

(91) The aluminum-based substrate was immersed in a chemical plating solution for chemical plating to form a circuit layer with a thickness of 88 m on the alumina layer, so as to form a circuit board. The chemical plating solution comprised: CuSO.sub.4.5H.sub.2O (0.12 mol/L), Na.sub.2EDTA.2H.sub.2O (0.14 mol/L), potassium ferrocyanide (10 mg/L), 2,2-bipyridine (10 mg/L), and glyoxalic acid (HCOCOOH) (0.10 mol/L) with a pH of 12.5-13 adjusted by NaOH and H.sub.2SO.sub.4 solutions, and water as a solvent.

(92) It was calculated that a plating rate was about 2.6 pm/h. It was measured that an adhesive force between the circuit layer (i.e., a plating layer) and the alumina layer was ISO level 0, and the circuit board had a thermal conductivity of about 16 W/(m.Math.K) and a breakdown voltage of about 2.2 kV.

EXAMPLE 6

(93) (1) Pretreatment

(94) An aluminum-based substrate was rinsed, then was immersed in a degreasing solution at a temperature ranging from 50 C. to 60 C. for about 10 min, and then was polished by a polishing solution for about 15 min. The degreasing solution comprised: NaOH (10 g/L), Na.sub.3PO.sub.4 (30 g/L), Na.sub.2CO.sub.3 (15 g/L), and sodium dodecylsulphonate (6 g/L), with water as a solvent. The polishing solution comprised: H.sub.2SO.sub.4 (20 wt %), HNO.sub.3 (10 wt %), and H.sub.3PO.sub.4 (70 wt %), with water as a solvent.

(95) (2) Anodic Oxidation

(96) The aluminum-based substrate was immersed in an electrolyte at 30 C. as an anode, and a stainless steel slice was used as a cathode. At a voltage of 30 V, electrolysis was performed to form an alumina layer with a thickness of 82 m on the aluminum-based substrate. The electrolyte comprised H.sub.2SO.sub.4 (25 wt %) and oxalic acid (2 wt %), with water as a solvent.

(97) (3) Sealing

(98) The aluminum-based substrate was immersed in a nickel sulfate solution at 25 C. for about 15 min, and then was dried. The nickel sulfate solution has a concentration of 1.1 g/L, and a pH ranging from 5.5 to 6.0, with water as a solvent.

(99) It was measured that a content of the element nickel in the alumina layer was 0.1 wt %.

(100) (4) Activation

(101) A part of the alumina layer was irradiated by a laser to form a circuit pattern. The irradiation was performed using a fiber laser with a wavelength of 1064 nm, a power of 25 W, a frequency of 50 kHz, a scanning speed of 100 mm/s, and a filling pitch of 0.05 mm.

(102) (5) Chemical Plating

(103) The aluminum-based substrate was immersed in a chemical plating solution for chemical plating to form a circuit layer with a thickness of 78 m on the alumina layer, so as to form a circuit board. The chemical plating solution comprised: CuSO.sub.4.5H.sub.2O (0.12 mol/L), Na.sub.2EDTA.2H.sub.2O (0.14 mol/L), potassium ferrocyanide (10 mg/L), 2,2-bipyridine (10 mg/L), and glyoxalic acid (HCOCOOH) (0.10 mol/L) with a pH of 12.5-13 adjusted by NaOH and H.sub.2SO.sub.4 solutions, with water as a solvent.

(104) It was calculated that a plating rate was about 2.4 m/h. It was measured that an adhesive force between the circuit layer (i.e., a plating layer) and the alumina layer was ISO level 0, and the circuit board had a thermal conductivity of about 16 W/(m.Math.K) and a breakdown voltage of about 2.3 kV.

(105) Reference throughout this specification to an embodiment, some embodiments, one embodiment, another example, an example, a specific example, or some examples, means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present disclosure. Thus, the appearances of the phrases such as in some embodiments, in one embodiment, in an embodiment, in another example, in an example, in a specific example, or in some examples, in various places throughout this specification are not necessarily referring to the same embodiment or example of the present disclosure. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

(106) Although explanatory embodiments have been shown and described, it would be appreciated by those skilled in the art that the above embodiments cannot be construed to limit the present disclosure, and changes, alternatives, and modifications can be made in the embodiments without departing from spirit, principles, and scope of the present disclosure.