JPH045892A - Machining method for through-hole in multilayer circuit board - Google Patents

Abstract

PURPOSE:To reduce the extraction of an organic section, and to prevent environmental pollution by treating a resin on the inner surface of a through-hole by using a heated alkaline aqueous solution when smear in the through-hole formed in a multilayer circuit board is removed. CONSTITUTION:The aqueous solution of sodium hydroxide, potassium hydroxide or lithium hydroxide is heated and used as a liquid employed in a swelling process. A trace quantity of a surface active agent are added to the liquid, and the wettability of the liquid to the inwall of a through-hole 3 can also be improved. A multilayer board dipped in the liquid is washed by water or dipped in a de-smear treatment. Accordingly, the discharge of an organic section is reduced, thus preventing environmental pollution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a processing method for removing smear generated in through holes of a multilayer circuit board.

[Prior Art] Conventionally, a multilayer circuit board, as shown in FIG. As shown in FIG. 2, a through hole 3 is bored, and through hole plating 4 is applied as shown in FIG. 3 in order to provide continuity between the inner and outer layers and the intermediate circuit 2.2. When forming the through hole 3 in this series of steps, as is clear from the enlarged view of part A in FIG. 2 shown in FIG. A so-called smear 5 occurs in which the epoxy resin or the like melts and covers the end face of the circuit 2.

If through-hole plating 4 is applied in this state, smear 5 of insulating layer 1 will be formed between circuit 2 and through-hole plating 4.
remains, resulting in poor continuity. Therefore, it is necessary to perform through-hole plating after removing smear 5.

Conventional smear removal methods include concentrated sulfuric acid immersion, chromic acid immersion, and plasma methods, but recently it has become common to use an alkaline permanganate solution. This method usually consists of three steps: (1) swelling, (2) desmearing, and (2) reduction. Among these, the swelling step (2) swells the resin by immersing the resin in a solution with a high organic content and promotes oxidative dissolution of the resin by the action of alkaline permanganate in the desmear step (2). In the reduction (2), manganese attached to the resin is reduced and removed.

[Problems to be Solved by the Invention] In the swelling step (1) in the prior art described above, organic components in the swelling liquid enter between the network structures of the resin, increasing the amount of organic components discharged to the next step. However, from the perspective of environmental protection these days, it is important to reduce the amount of organic matter discharged from factories.

Therefore, in the present invention, the organic component is completely or hardly contained.
The purpose is to provide a method for removing smear using a liquid that does not contain liquid, and to prevent pollution.

[Means for Solving the Problems] The present invention has been made to solve the above problems, and
When removing smear from through holes in a multilayer circuit board,
This is a method for processing through-holes in a multilayer circuit board in which the resin on the inner surface of the through-hole is treated using a heated alkaline aqueous solution.

That is, in the present invention, an aqueous solution of sodium hydroxide, potassium hydroxide, or lithium hydroxide is heated and used as the liquid used in the swelling step (1) in the prior art. The concentration of this solution is 1, considering the amount of solution pumped and the amount of evaporation.
A suitable temperature is 0 to 500 g/l, preferably 50 to 800 g/l, and the temperature is 60 to 100'C, preferably 75 to 90'C. A very small amount of surfactant can be added to this liquid to improve the wettability of the liquid to the inner wall of the through hole.

The concentration of this surfactant is preferably as low as 101/I or 10 g/l or less. The multilayer substrate immersed in this liquid is then washed with water or subsequently immersed in a desmear treatment liquid.

Examples of the desmear treatment liquid include the trade name CP 922 (manufactured by Nippon Mining Co., Ltd.). This liquid is KMn O440-9
The treated substrate is immersed in a solution containing 0 g/l, 30 to 60 g/l of NaOH, and less than 1/1 surfactant at 60 to 90° C. for about 10 minutes. Thereafter, the material is washed with water and further subjected to a reduction treatment to dissolve and remove manganese dioxide formed on the wall surfaces of the through holes. As the liquid, a weakly acidic solution containing a reducing agent, trade name CP933 (manufactured by Nippon Mining Co., Ltd.), can be used. The substrate is immersed in this for about 2 to 5 minutes at room temperature. After that, wash the board again with water.

Following the above smear removal process, electroless copper plating and electrolytic copper plating are performed to form through holes.

[Example] A multilayer epoxy resin board (P
R-4 grade) was formed with through holes of 0.3 and 0.8 mm in diameter, treated with a solution containing Na0HSKOH or LiOH, and then treated with a desmear treatment solution (trade name: CP
922) and a reduction treatment solution (trade name CP H3). Desmear treatment at 85℃ for 10 minutes, reduction treatment at 25℃
I went for 3 minutes.

Electroless copper plating (0.5 μm) and electroplating (35 μm) were applied to the through holes of the circuit board whose through holes were thus cleaned. The through holes of this test board are embedded in hardening resin,
The cross section of the through hole was observed under a microscope to check for the presence or absence of smear residue.

The results are shown in Table 1.

Table 1 Note 1) COD (chemical oxygen demand ff1) is monthly S K
-0102,17.

Note 2) Commercially available organic swelling liquid: Solution containing a polyether compound and sodium hydroxide As is clear from Table 1, the COD of the desmear pretreatment liquids of Examples 1 to 5 were all less than 5 ppm. This value of less than 5 ppm is not a problem at all in terms of wastewater treatment, and when discharging this treated liquid, HCI and H
This can be easily carried out only by neutralization with 2SO4.

On the other hand, the COD of the commercially available organic swelling liquid shown as a comparative example is
110,000 pp, and before discharging this solution, it is necessary to perform oxidation treatment in addition to neutralization treatment.

[Effects of the Invention] In the present invention, the pretreatment in the desmear treatment is performed using an alkaline hydroxide solution, so that when using a conventional swelling agent containing an organic component, there is no problem in the discharge treatment caused by lifting out and discharging the liquid. Problems can be resolved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the structure of a multilayer circuit board, which is the object to be processed by the present invention, Fig. 2 is an explanatory diagram of the state in which through holes are bored in the substrate of Fig. FIG. 4 is an enlarged explanatory view of section A in FIG. 2. ■...Insulating layer, 2...Circuit, 3...Through hole, 4...
...Through hole plating, 5...Smear.

Claims (2)

[Claims] (1) A method for processing a through hole in a multilayer circuit board, which comprises treating the resin on the inner surface of the through hole using a heated alkaline aqueous solution when removing smear from the through hole provided in the multilayer circuit board. (2) Heated alkaline aqueous solution at 60-100℃
The method for processing through holes in a multilayer circuit board according to claim 1, wherein the solution is a sodium hydroxide, potassium hydroxide or lithium hydroxide solution having a concentration of 00 g/l.