JPS58202590A - Method of producing substrate for printed circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing printed wiring boards, and in particular, the present invention relates to a method for manufacturing printed wiring boards with high heat resistance and withstand voltage through a series of continuous treatments. It is related to.

Conventionally, copper-clad laminates made of paper or glass fiber, thermosetting resin, and copper foil have been most widely used as cylinder wiring boards, which have poor heat dissipation effects and poor heat resistance. For this reason, as a substrate with a large heat dissipation effect, for example,
No. 13234 proposed an aluminum substrate on which an aluminum oxide film was applied by anodic oxidation. However, due to the cracking that occurs in the pulminilum oxide film at high temperatures due to the difference in thermal expansion coefficient between the aluminum oxide film and aluminum, and the micropores that exist in the aluminum oxide film, the aluminum oxide film alone cannot provide electrical insulation. Since they are imperfect in terms of their properties, various methods have been proposed to reduce them as much as possible or to seal them together.

For example, according to Japanese Patent Application Laid-Open No. 54-13967, when sealing micropores after forming an aluminum oxide film on the surface of an aluminum substrate by anodizing, a long period of □ sealing treatment is performed. Since cracks are generated during heating, a short-time sealing treatment is unavoidable, but it has been difficult to completely eliminate the occurrence of cracks using such methods. Furthermore, according to Japanese Patent Application Laid-open No. 54-66463, an aluminum oxide film is formed on the surface of an aluminum substrate by anodizing, and after sealing the fine pores formed in the oxide film, heating is performed to seal the oxide film. This method generates cracks and then performs anodic oxidation again, but with this method, cracks occur again in the anodized cracked portions, resulting in poor reliability in terms of electrical insulation. Furthermore, according to JP-A No. 54-66462, an aluminum substrate, an oxide film formed on the surface of the aluminum substrate by anodization, cracks generated in the oxide film, and a liquid insulator impregnated in the cracks are described. However, according to the manufacturing method of this substrate, it is difficult to completely fill the micropores with the liquid insulator because the micropores become dry due to the high-temperature treatment that causes the cracks.

An object of the present invention is to provide a manufacturing method that eliminates and improves the above-mentioned drawbacks of conventional printed wiring boards,
The above object can be achieved by providing a method for manufacturing a cylinder wiring board with high heat resistance and withstand voltage, which has a large heat dissipation effect through a series of continuous treatments. That is, the present invention completely eliminates cracks that occur at high temperatures in an aluminum oxide film formed by anodizing an aluminum substrate, and also completely seals micropores in the aluminum oxide film through a series of continuous treatments. It is characterized by the ability to form an electrically perfect insulating film extremely easily.

Next, the method for manufacturing a printed wiring board according to the present invention will be explained in detail based on the drawings.

FIG. 1 is a longitudinal cross-sectional view of an aluminum substrate and an aluminum oxide film after the first anodic oxidation is performed on the aluminum substrate in the manufacturing method of the present invention.
After degreasing and polishing at least one side of the base in a caustic powder solution or a phosphoric acid solution, washing with water, then pickling in a nitric acid solution, washing with water, and then applying a solution of at least one of phosphoric acid and chromic acid. An aluminum oxide film 2 is formed by anodic oxidation inside. Note that FIG. 2 is an enlarged longitudinal cross-sectional view and cross-sectional view of the aluminum substrate and the aluminum oxide film. In the aluminum oxide film 2, micropores 3 exist in a row, and the innermost ends of the micropores 3 are formed of aluminum. It reaches close to the surface of the substrate 1. As shown in FIG. 3, the aluminum oxide film 2 usually has open defect holes 4 in which aluminum oxide is missing. Also, defects such as non-open defect cavities 5 are scattered. According to the present invention, after performing the first anodic oxidation, it is washed with water, and then an aqueous solution of at least one of ammonium borate and ammonium tartrate, methanol, and ethanol.

Anodizing is performed again in a mixed solution with at least one selected from N-methylgyrolidone to form an aluminum oxide film. FIG. 4 is an enlarged vertical cross-sectional view of the aluminum substrate and the aluminum oxide film after the second anodic oxidation and further formation of the aluminum oxide film, and shows the micropores 3. The aluminum oxide film formed between the innermost end of the aluminum substrate 1 and the aluminum substrate l grows into the aluminum substrate below, and the aluminum oxide film becomes thicker at that portion. Reference numeral 6 in the figure indicates a portion where the aluminum oxide film described above has grown and its thickness has increased.

After performing the second anodic oxidation, if necessary, the polyimide resin is washed in an N-methylpyrrolidone solution, immediately immersed in an N-methylpyrrolidone solution, and then the polyimide resin is dried.

The fine pores 3 and open defect pores 4 existing in the aluminum oxide film 2 are cured. A defective portion such as a non-open defective cavity 5 is sealed with the above-mentioned plowed resin. Note that the polyimide resin permeates into the non-open defect cavity 5 through the fine pores 3 as well.

Next, the first anodic oxidation treatment in the manufacturing method of the present invention will be explained. Concentration in terms of orthophosphoric acid in a solution of at least one of phosphoric acid and chromic acid: 1 to 6-800 f/43, concentration in terms of chromic anhydride 1 to 400
7. clause.

Liquid temperature 0-70C, current density 0.1-10 k/dm2.
It is preferable to carry out anodic oxidation under conditions of a voltage of 10 to 200 V to form an oxide film with a thickness of 1 to 50 μm.

Next, the second anodic oxidation treatment will be explained.

An aqueous solution of at least one of ammonium borate and ammonium tartrate and at least one of methanol, ethanol, and N-methylgyrolidone.
Ammonium tetraborate concentration in mixed solution with seeds 0.1~
100i%/A, ammonium tartrate concentration 0.1-10
0? β, water 10~9oofPA+ liquid temperature 0~70t
:', current density 0.01 to I A/dm2. Voltage lO
Anodic oxidation is performed under the condition of ~1000 V, but since it is difficult to measure the oxide film thickness, the processing time is 10~120 V.
It is better to make it a fight.

Next, the immersion treatment of the Boliimi P resin in the N-methylpyrrolidone solution after the second anodic oxidation treatment will be described. Polyimide resin concentration in the solution 10-700□
, the liquid temperature was 100 C or less, and the immersion time was ITrIi
It is preferable to set it to R or more.

However, according to the present invention, the first anodizing treatment and the second anodizing treatment
It is necessary to perform the second anodizing treatment and the immersion treatment in the polyimide resin solution continuously. If the first anodizing treatment and the second anodizing treatment are not performed consecutively, air will be drawn into the micropores created by the first anodizing treatment, and the second anodizing treatment will be performed. The process will not be completed completely. Also, for the same reason, the second
If the aluminum oxide film dries between the second anodic oxidation treatment and the immersion treatment in the polyimide resin solution, parts of the micropores will not be completely filled with polyimide resin, reducing the electrical reliability of the aluminum oxide film. cannot be improved. That is, the present invention makes it possible to extremely easily form an electrically perfect insulating film by sequentially performing a process for forming an aluminum oxide film and a process for sealing micropores and defective areas, that is, open defective holes and non-open defective cavities. It is characterized by forming.

The aluminum oxide film formed by the first anodizing treatment does not generate cracks even at high temperatures of 3,000 or higher, but the anode in a solution other than the first anodizing solution 9, such as a sulfuric acid solution or an oxalic acid solution, The aluminum oxide film formed by oxidation treatment generates many cracks at temperatures below 200C. The reason for this is thought to be that the micropores in the aluminum oxide film formed by the first anodizing treatment are relatively large, which absorbs the difference in thermal expansion coefficient between the aluminum oxide film and aluminum. It will be done.

Furthermore, the second anodic oxidation treatment further forms an aluminum oxide film, thereby improving the withstand voltage.

The reason for this is that the increased aluminum oxide film thickness portion 6 is newly formed as described above, but it still lacks sufficient electrical reliability.

After the second anodizing treatment? The dipping treatment in the polyimide resin solution improves the withstand voltage by sealing the fine pores and defective portions, that is, open defective holes and non-open defective cavities, present in the aluminum oxide film with the polyimide resin. Note that polyimide resin has relatively high heat resistance and product resistance, so it is superior in heat resistance and chemical resistance to cases where other resins are used. Further, a thin film of the resin is automatically formed on the surface of the substrate sealed with the resin.

Next, the present invention will be explained with reference to Examples and Comparative Examples.

Example 1 At least one surface of an aluminum substrate was coated with an orthophosphoric acid equivalent concentration of 55? in a phosphoric acid solution. liquid temperature 25C2 current density IA
/dm2. After anodizing at a voltage of 120 V to form an aluminum oxide film with a thickness of 20 μ-, the concentration of ammonium tetraborate in the mixed solution of ammonium borate aqueous solution and N-methylpyrrolidone was 11-/
A, water 1007/ffl, liquid temperature 20C2 current density 0°0
5 A/dm2. After anodizing again under the conditions of voltage 500V and treatment time 60 hours, and subsequent washing in N-methylpyrrolidone solution, the polyimide resin was immediately washed with poly10-imiP resin at a concentration of 200t/43 in N-methylpyrrolidone solution. The aluminum oxide film was immersed in a polyimide resin solution at a temperature of 25C and an immersion time of 60°C to seal the fine pores and defects present in the aluminum oxide film, that is, open defect pores and non-open defect cavities, with the polyimide resin. .

The insulating film formed by the series of continuous treatments was 30
No cracks occur even at 0C, and the withstand voltage after heat treatment at 300C is 2. OKV, thermal conductivity is 0.42 ml/'
It was R1-・Taku・C.

Example 2 At least one side of an aluminum wall plate was exposed to E in a phosphoric acid solution.
17 phosphoric acid equivalent concentration 5554/-6. After forming an anodic oxide film with a thickness of 20μ at a liquid temperature of 25C9 and a current density of 1A/dm” and a voltage of 120V, it was washed with water, and then diluted with tetraboron in a mixed solution of ammonium borate aqueous solution and ethanol. Ammonium acid concentration 7.5 t/
43, water 200t/I3. , liquid temperature 20C9 current density 0.05 A/dm2. Anodizing was performed again under the conditions of IK pressure of 500 V and treatment time of 60 min, followed by N
- After washing in the methylpyrrolidone solution, the polyimide resin is immediately immersed in the polyimide resin solution under the conditions of a polyimide resin concentration of 200P/A in the N-methylpyrrolidone solution, a solution temperature of 25C, and an immersion time of 60cm to form an aluminum oxide film. The micropores and defective areas, that is, open defective holes and non-open defective cavities, present in the IJ imide resin were sealed with /IJ imide resin. The insulating film formed by the above series of continuous treatments does not generate cracks even at 300C.
The withstand voltage after heat treatment is 2. OKV, thermal conductivity is Q,
42 ad/kl-t*-C.

Example 3 At least one surface of an aluminum substrate was coated in a chromic acid solution at a concentration of 30y-/A in terms of chromic acid anhydride. 40C
9. After forming an aluminum oxide film with a thickness of 20μ by anodizing under conditions of a current density of 0.5 A/dm2g and a voltage of 100 V, it was washed with water, and then the ammonium tartrate concentration in the mixed solution of ammonium tartrate aqueous solution and methanol was 7.
5b clause, water 200f/, e, liquid lagoon 20C9 current density 0
．． 05 A/dm*, voltage 400V, processing time 60-
The polyimide resin solution was anodized again under the following conditions, and then washed in an N-methylpyrrolidone solution, and immediately after the polyimide resin was washed with a polyimide resin solution under the following conditions: 4-limide resin concentration in the N-methylpyrrolidone solution was 200b, the liquid temperature was 25C, and the immersion time was 60m + 111cm. The polyimide resin was immersed in the polyimide resin to seal the fine pores and defects present in the aluminum oxide film, that is, open defect holes and non-open defect cavities. The edge membrane formed by the series of continuous treatments does not generate cracks even at 300C, has a withstand voltage of 1.8KV and a thermal conductivity of 0.42c after heat treatment at 300T:'.
al, AC-tyn, and C.

Comparative Example 1 At least one surface of an aluminum substrate was coated in a phosphoric acid solution with an equivalent concentration of orthophosphoric acid of 55b, a liquid temperature of 25C9, and a current density of IA.
/dtn'' + voltage 120μ to form an aluminum oxide film with a thickness of 20μ, followed by washing with water and drying. Ammonium borate concentration 10 t/13, water 100 PEA.

Liquid temperature 20C, current density 0.05 A/dm2. voltage 50
It was anodized again under the conditions of 0 V and treatment time of 60 wt, washed in N-methylpyrrolidone solution, and then dried. Next, polyimide resin concentration in N-methylpyrrolidone solution of polyimide resin is 200 f-/-8, liquid temperature is 25C, immersion time is 60
The aluminum oxide film was immersed in a polyimide resin solution under the conditions of No. 11111 to seal the micropores and defects present in the aluminum oxide film, that is, open defect holes and non-open defect cavities, with the polyimide resin.

The insulating film formed by the discontinuous treatment did not generate cracks even at 300C, and the withstand voltage after heat treatment at 300C was as low as 1.0 fv.

Comparative Example 2 At least one surface of an aluminum substrate was coated in a sulfuric acid solution with a sulfuric acid equivalent concentration of 183P/# and a liquid temperature of 25C9 and a current density of IA/d.
m2. After anodizing at a voltage of 10 V to form an aluminum oxide film with a thickness of 20 μm, it was washed with water and dried. Next, the ammonium tetraborate concentration in the ammonium borate aqueous solution was 31/A, the liquid temperature was 20C, and the current density was 0. IVd
It was anodized again under the following conditions: rn2+ voltage 350V, treatment time 60, washed with water, and then dried. Next, the polyimide resin was immersed in a polyimide resin solution under the conditions of a polyimide resin concentration of 200 f/43 in the N-methylpyrrolidone solution, a liquid temperature of 25 C, and an immersion time of 60 mm to remove the micropores present in the aluminum oxide film and The defective parts, that is, the open defect holes and the non-open defect cavities, were sealed with polyimide resin. The insulating film formed by the above-mentioned discontinuous treatment cracked at 200C, and the withstand voltage after heat treatment at 300t:' was 0.
It was as low as 5 KV. Furthermore, when an aluminum oxide film with a thickness of 5 μm is formed by the above method, the insulation film has a thickness of 30 μm.
Even with C, cracks may not occur in some cases, but the withstand voltage after heat treatment at 300 C was extremely low at 0.3'V.

By the way, according to JP-A No. 54-66463, in order to perform heat treatment between the first anodizing treatment and the second anodizing treatment, the fine pores generated by the first anodizing treatment are removed. In addition, it is difficult to perform the second anodic oxidation treatment completely at the innermost end of the micropores due to dryness inside the paper, and it is also difficult to avoid the disadvantage that paper cracks occur due to heat treatment. I can't. Furthermore, according to Japanese Patent Application Laid-Open No. 54-66462, since high temperature treatment is performed between the anodizing treatment and the immersion treatment in the liquid insulator, the inside of the micropores created by the anodizing treatment becomes dry, and the fine pores become dry. It is difficult to completely fill the holes with liquid insulator.

Therefore, the present invention is disclosed in Japanese Patent Application Laid-open No. 54-66463 and Japanese Patent Application Laid-open No. 54
It is clear that the present invention is not simply a combination of the inventions described in No. -66462, respectively. In other words, the present invention is based on the selection of the first anodizing solution.
The cracks that occur at high temperatures in the aluminum oxide film formed by the second anodizing treatment are completely eliminated, and the first
By successively performing the first anodizing treatment, the second anodizing treatment, and the immersion treatment in a polyimide resin solution, an electrically perfect insulating film can be formed extremely easily. Therefore, the cylindrical wiring board obtained by the manufacturing method of the present invention has a large heat dissipation effect, high heat resistance and withstand voltage, so that it is possible to increase the density of component mounting and improve the bridge axis. The benefits to the printed circuit board industry are huge.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of an aluminum substrate and an aluminum oxide film after the first anodic oxidation of the aluminum substrate, and FIGS. 2 and 3 are a longitudinal cross-sectional view of the aluminum substrate and an aluminum oxide film, respectively. FIG. 4 is an enlarged vertical cross-sectional view of an aluminum substrate and an aluminum oxide film after the second anodic oxidation is performed on the aluminum substrate. DESCRIPTION OF SYMBOLS 1... Aluminum substrate, 2... Aluminum oxide film, 3... Fine pore, 4... Open defect hole, 5...
Non-opening defect cavity, 6...portion with increased aluminum oxide film thickness. Patent applicant: Ibigawa Electric Industry Co., Ltd. Patent attorney Mura 1) Politics 17- Figure 4-432-

Claims (1)

[Claims] l. At least one surface of the aluminum substrate is coated with phosphoric acid. After anodizing in a solution of at least one of chromic acid to form an aluminum oxide film, it is washed with water, and then mixed with an aqueous solution of at least one of ammonium borate, ammonium tartrate, methanol, ethanol, N-
Anodic oxidation is performed again in a mixed solution with at least one selected from methylpyrrolidone to further form an aluminum oxide film, and if necessary, after washing in an N-methylpyrrolidone solution, polyimide is immediately removed. Heat resistance and withstand voltage achieved through a series of continuous treatments characterized by immersing the resin in an N-methylgyrolidone solution to seal the micropores and defective areas present in the aluminum oxide film with the polyimide resin. A method for manufacturing printed wiring boards with high performance.