JP2022149296A - Print circuit board and manufacturing method thereof - Google Patents

Abstract

To provide a print circuit board manufactured using a substrate material in which a resin containing magnesium oxide is used as an insulating material, and from which magnesium oxide exposed on a resin surface is removed by processing so as not to affect product quality.SOLUTION: In a print circuit board using an insulating resin containing magnesium oxide as a substrate material, the side wall surface of a through hole of the print circuit board and the side wall surface and bottom surface of the bottomed hole are provided with an exposed surface of the insulating resin having a shape derived from the form of the magnesium oxide.SELECTED DRAWING: Figure 1

Description

The present invention relates to a printed wiring board and its manufacturing method.

In recent years, there is a demand for substrates with high heat dissipation and high reliability, and there are substrate materials in which a resin containing a filler such as magnesium oxide with high thermal conductivity is used as an insulating material. Such substrate materials have excellent heat dissipation properties and effective anti-tracking properties, and are beginning to be developed as substrate materials for printed wiring boards.

For example, Patent Document 1 discloses a substrate material containing an insulating resin containing alumina, aluminum nitride, boron nitride, silicon nitride, and magnesium oxide as thermally conductive fillers.
Patent document 2 discloses a substrate material in which the filling rate of magnesium oxide powder in the epoxy resin is 45-63% by volume.

Substrate materials using resins containing the above magnesium oxide are excellent in heat dissipation, but magnesium oxide alone has the property of being easily dissolved in acids and alkalis, and various chemical solutions in the manufacturing process of printed wiring boards. , there is concern about elution of magnesium into the treatment liquid.

For example, in the desmear treatment process for removing resin residue in the formed hole, magnesium oxide exposed on the side wall surface or the like due to hole processing is eluted into the desmear treatment liquid, and magnesium ions are mixed in the liquid. The desmear property is deteriorated, and there is a possibility of adversely affecting the subsequently formed plating.
In addition, the influence on the quality of the printed wiring board due to the normal substrate materials processed at the same time in the same manufacturing process is also taken into account.

JP 2012-211225 A JP 2015-232116 A

In view of such circumstances, the present invention provides a printed wiring board that is manufactured using a substrate material in which a resin containing magnesium oxide is used as an insulating material, by performing a treatment so as not to affect the product quality. An object of the present invention is to provide a printed wiring board from which magnesium oxide exposed on the resin surface is removed.

A first invention of the present invention is a printed wiring board using an insulating resin containing magnesium oxide as a substrate material, wherein the side wall surface of the through hole and the side wall surface and bottom surface of the bottomed hole of the printed wiring board have and a printed wiring board characterized by comprising an exposed surface of the insulating resin having a shape derived from the form of the magnesium oxide.

A second invention of the present invention is a printed wiring board characterized in that the form of magnesium oxide in the first invention is either filler or powder or both.

A third aspect of the present invention is a method for manufacturing a printed wiring board using an insulating resin containing magnesium oxide as a substrate material and including a desmear treatment step, wherein the desmear treatment step includes pretreatment with a sulfuric acid solution. It is a manufacturing method of the printed wiring board characterized by the above-mentioned.

A fourth aspect of the present invention is a printed wiring board characterized in that the desmear treatment step according to the third aspect comprises pretreatment with the sulfuric acid solution followed by swelling treatment, etching treatment, and neutralization treatment in that order. manufacturing method.

A fifth invention of the present invention is a printed wiring board characterized in that the pretreatment with a sulfuric acid solution in the third and fourth inventions is a sulfuric acid solution immersion treatment in which the printed wiring board is immersed in the sulfuric acid solution. manufacturing method.

According to the present invention, even in a printed wiring board manufactured using a substrate material in which a resin containing magnesium oxide is used as an insulating material, a printed wiring board having a surface from which magnesium oxide exposed on the resin surface has been removed can be obtained. It is possible to obtain easily, and it is possible to prevent contamination by magnesium in the manufacture of electronic/electrical elements and equipment using this printed wiring board, which has a remarkable industrial effect.

FIG. 1(A) shows the state of magnesium oxide exposed in the resin layer by drilling according to the present invention, and FIG. 1(B) is a schematic cross-sectional view showing the state after the exposed magnesium oxide is removed. FIG. 2 is a schematic flow diagram of a process for manufacturing a printed wiring board including a desmearing process to which pretreatment with a sulfuric acid solution is added according to the present invention; It is a schematic sectional drawing of the board|substrate material prepared for evaluation.

The side wall surface of the through hole and the side wall surface and the bottom surface of the bottomed hole formed by the drilling process of the present invention are printed wiring boards having surfaces from which exposed magnesium oxide is removed and the resin is exposed. It is obtained by going through the steps shown in 2.

(1) First, a substrate material containing magnesium oxide in a resin is prepared.
Magnesium oxide contained in this resin is a solid, and is used in the form of powder, filler, or both.

(2) In the next drilling step, a through hole or bottomed hole of a required size is formed in a predetermined portion by means of drilling, laser, blasting, or the like. On the sidewall surface of the through hole formed here, the sidewall surface of the bottomed hole, and the bottom surface, the cross section of the magnesium oxide residue removed by the processing is exposed.

(3) A pretreatment (referred to as a sulfuric acid solution immersion treatment) is performed as a pretreatment for a so-called desmear treatment to dissolve and remove the magnesium oxide residue exposed on the surfaces of the through holes and bottomed holes with a sulfuric acid solution.
In this pretreatment, the remaining magnesium oxide exposed on the cross section or the like is dissolved and removed to form an exposed surface where the insulating resin is exposed in a shape derived from the shape of the removed magnesium oxide residue.
In this pretreatment, a "sulfuric acid solution" is used to dissolve and remove the residue of magnesium oxide, and immersion in the solution is preferred, but methods such as dissolving and removing by spraying a sulfuric acid solution using a spray gun. is also applicable.
The "range of concentration of sulfuric acid solution" in the immersion treatment is the range of concentration of dilute sulfuric acid, preferably about 1.0 to 25 [g/L].

(4) Smear remains in the through-holes and bottomed holes formed through the pretreatment, so they are put into the desmear treatment step. Normally, the smear swelling process, the swollen smear etching process, and the desmear process of neutralizing the residue with an etching treatment liquid are performed, and the side wall surface of the through hole and the side wall surface and bottom surface of the bottomed hole are smear-free. Apply surface treatment.

(5) After that, plating treatment or the like is performed in order to ensure conduction between the front and back copper foils in the same manner as in the normal process. Then, a circuit is formed on the plated substrate material, a solder resist or the like is formed, and a printed wiring board is obtained through post-processes such as surface treatment.

A substrate material having a four-layer structure shown in FIG. 3 was prepared, containing powdered magnesium oxide in a resin.
In this substrate material, the thickness of the resin layer containing magnesium oxide is 0.3 mm, the copper foil of the first layer is 100 μm, the copper foil of the second and third layers is 35 μm, and the copper foil of the fourth layer is 100 μm. is.

A drilling process was performed using this substrate material.
Specifically, through holes were formed at a pitch of 2.0 mm using a drill of φ1.0 mm.
The cross section of the resin layer of the substrate material exposes the remainder of the contained magnesium oxide, resulting in the state shown in FIG. 1(A).

A printed wiring board is usually manufactured through the steps shown in FIG.
First, a prepared substrate material is drilled, and a desmear process is performed to remove smear caused by the drilling. Thereafter, a desired printed wiring board is obtained through processes such as copper plating, etching for forming wiring, and surface treatment.
The desmearing process using a chemical solution is a process of swelling smears generated by drilling, removing the swollen smears by etching, and neutralizing residues with an etching solution.
In order to prevent quality problems due to magnesium eluted from the substrate material in the process of using the chemical solution after the drilling process, the following evaluations 1 and 2 were confirmed.

[Evaluation 1]
A sample for evaluation of 5 cm×5 cm was cut out from the substrate material subjected to the drilling process.
Two cut samples for evaluation are immersed in a sulfuric acid solution with a concentration of 0.1 N as a pretreatment, and a sulfuric acid immersion treatment is performed by stirring for about 10 minutes. After that, swelling of the smear with an alkaline aqueous solution, which is a normal desmear treatment process. Treatment, etching of swollen smears with an alkaline aqueous solution of permanganate, and neutralization of residues with an etching solution were carried out by immersion.
The concentration of sulfuric acid may be arbitrarily determined, but the elution rate tends to increase as the concentration or temperature increases, so it can be adjusted by adjusting the device configuration, processing time, and the like.

Next, the amounts of magnesium eluted from the sulfuric acid solution, the swelling treatment solution, and the neutralization treatment solution were measured by atomic absorption spectrometry. The etching solution contains manganese, which has a similar wavelength, and magnesium is not measured because it cannot be accurately analyzed. Incidentally, the measurement result of the magnesium concentration in the unused swelling treatment liquid was 66.7 mg/l.

Table 1 shows the magnesium concentration measurement results of the sulfuric acid solution, the swelling treatment liquid, and the neutralization treatment liquid of Evaluation 1.

In evaluation 1, the magnesium concentration in the sulfuric acid solution was 154.8 mg/l. The magnesium concentration in the swelling treatment liquid was 66.1 mg/l, which was equivalent to the magnesium concentration in the unused swelling treatment liquid (66.7 mg/l).

From this result, the magnesium oxide exposed on the cross section of the resin layer shown in FIG. 1(A) was eluted into the sulfuric acid solution due to the pretreatment with the sulfuric acid solution, and as shown in FIG. 1(B), the magnesium oxide was removed from the cross section of the resin layer. determined to have been removed.
From this, it was determined that magnesium originating from the substrate material was eluted into the sulfuric acid solution and was not eluted into the chemical solution after the swelling treatment.

[Evaluation 2]
As in Evaluation 1, a 5 cm × 5 cm evaluation sample is cut out from the substrate material that has been perforated, and the two cut out evaluation samples are subjected to a normal desmear treatment process, smear swelling treatment, swollen smear. Etching treatment and neutralization treatment were performed by immersion.

Next, the concentrations of magnesium eluted into the swelling treatment liquid and the neutralization treatment liquid were measured by an atomic absorption method. As in Evaluation 1, the etching solution contains manganese with a similar wavelength, and magnesium was not measured because it could not be accurately analyzed.

Table 2 shows the magnesium concentration measurement results of the swelling treatment liquid and the neutralization treatment liquid in Evaluation 2.

In evaluation 2, the magnesium concentration in the swelling treatment liquid was 107.8 mg/l, and the magnesium concentration in the unused swelling liquid was 66.7 mg/l, so about 40 mg/l was removed from the substrate material. Elution of magnesium was confirmed.
It was 0 mg/l in the neutralized solution.

In Evaluation 2, since there was no elution of magnesium into the neutralization treatment liquid, it is considered that magnesium oxide was dissolved by the etching treatment and magnesium was eluted into the etching treatment liquid.
The magnesium concentration in the sulfuric acid solution of evaluation 1 is 154.8 mg/l, and the magnesium concentration in the swelling treatment liquid of evaluation 2 is 107.8 mg/l. ) is not incorporated, it is considered that 40 mg/l or more of magnesium is eluted into the etching solution.

In the process of evaluation 2, which is a conventional process, magnesium is eluted into the swelling treatment liquid and the etching treatment liquid, so the magnesium in the treatment liquid increases due to continuous production.
On the other hand, in the step of evaluation 1 according to the present invention, by performing pretreatment (sulfuric acid immersion treatment) with a sulfuric acid solution, it is possible to prevent magnesium from eluting into each chemical solution for swelling treatment and etching treatment. And it can be judged that the same quality as the conventional product can be maintained even with the substrate material containing magnesium oxide in the resin.

10 Magnesium oxide-containing resin 11 Magnesium oxide 12 Side wall surface from which magnesium oxide is exposed by drilling 13 Side wall surface from which exposed magnesium oxide is removed 20 Copper foil

Claims (5)

A printed wiring board using an insulating resin containing magnesium oxide as a substrate material,
A printed wiring board characterized in that the side wall surface of the through hole and the side wall surface and bottom surface of the bottomed hole of the printed wiring board are provided with an exposed surface of the insulating resin having a shape derived from the form of the magnesium oxide. . 2. The printed wiring board according to claim 1, wherein the magnesium oxide is in the form of filler, powder, or both. In a method for manufacturing a printed wiring board using an insulating resin containing magnesium oxide as a substrate material and including a desmear treatment step,
A method for producing a printed wiring board, wherein the desmear treatment step includes pretreatment with a sulfuric acid solution. 4. The method of manufacturing a printed wiring board according to claim 3, wherein said desmear treatment step comprises pretreatment with said sulfuric acid solution followed by swelling treatment, etching treatment and neutralization treatment in that order. 5. The method for producing a printed wiring board according to claim 3, wherein the pretreatment with the sulfuric acid solution is a sulfuric acid solution immersion treatment in which the printed wiring board is immersed in the sulfuric acid solution.

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