Resin board to be subjected to ozone treatment, wiring board, and method of manufacturing the wiring board

Abstract

A resin board that consists of at least one of a mixture of a plurality of types of resins having different degrees of susceptibility to erosion by an ozone solution, and a resin having, in a molecule, a plurality of types of components having different degrees of susceptibility to erosion by the ozone solution is treated with ozone water to form a reformed layer, and a catalyst metal is adsorbed by the reformed layer so as to form a resin-metal composite layer, on which a plating process is performed. In the resin board, a component or components that is/are likely to be eroded on by the ozone solution dissolves into the ozone solution, and pores or clearances on the order of nanometers are formed between the component(s) and a component or components that is/are less likely to be eroded by the ozone solution. With the plating deposited in the pores or clearances, the adhesion strength is improved due to an anchoring effect. Thus, the adhesion strength of the plating film is improved even where the resin-metal composite layer has a thickness of 10 to 200 nm.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]This invention relates to resin boards for use in wiring boards, wiring boards formed from the resin boards, and a method of manufacturing the wiring boards.[0003]2. Description of the Related Art[0004]Resin is finding remarkably increased use in the fields where metal is conventionally used, owing to its features, such as the ease with which resin can be shaped, a high degree of flexibility in characteristic values, such as strength, and lightness in weight. However, resin also has drawbacks, such as the absence of electrical conductivity and low hardness, and therefore, it has been proposed to combine resin with metal, or the like, so as to eliminate these drawbacks.[0005]As an example of method for providing resin with electrical conductivity, powder of a conductive metal or carbon fibers, for example, is mixed into the resin. However, a large amount of conductive metal needs to be added to the resin so as to impart ...

AI Technical Summary

Benefits of technology

[0033]The resin board as described above may be used in a half-cured state in which the resin is not completely cured. To bring the resin board into the half-cured state, the above-described resin board is subjected to a half-curing heat treatment step in which the resin board is heated at 150° C. for 30 min. With the resin board heated in this manner, reactions between cyanato-groups and epoxy groups proceed to some extent, to thus form the oxazoline structure or triazine rings. By placing the resin board in the half-cured state, the degree of erosion by the ozone solution may be varied, and the relationship between the thickness and adhesiveness of the resin-metal composite layer may be changed to be within a more preferable range. Nonetheless, it is found that even where the resin board is in a fully cured state, a certain degree of adhesion strength can be ensured.

[0034]In an ozone treatment step, the resin board is treated with an ozone solution so that a reformed layer having polar groups on its surface is formed. The reformed layer has pores or clearances on the order of nanometers (nm) or smaller, which are formed on a surface of or within the resin board between a component(s) that is / are more likely to be eroded by the ozone solution and a component(s) that is / are less likely to be eroded by the ozone solution. To treat the resin board with the ozone solution, the resin board may be immersed in the ozone solution, or the ozone solution may be applied by spraying to the resin board. It is preferable to immerse the resin board in the ozone solution because ozone is less likely to be released from the ozone solution, as compared with the case where the resin board contacts with the ozone solution applied by spraying.

[0035]The ozone concentration in the ozone solution has a great influence on the activation of the resin board surface. While an effect of the activation is observed when the ozone solution is about 10 ppm or higher, the effect of the activation remarkably improves if the ozone solution is 20 ppm or higher, and the treatment can be accomplished in a more shortened time. Through oxidation by ozone contained in the ozone solution, polar groups, such as OH groups, CO═O groups, COOH groups, are produced in the reformed layer.

[0036]The ozone solution normally has water as a solvent, but preferably has an organic or inorganic polar solvent as a solvent. By using such a solvent, the treatment time can be further shortened. Examples of the organic polar solvent include alcohols, such as methanol, ethanol, and isopropyl alcohol, N, N-dimethyl formamide, N, N-dimethyl acetamide, dimethyl sulfoxide, N-methylpyrrolidone, hexamethylphosphoramide, organic acids, such as formic acid and acetic acid, and mixtures of these compounds with water or an alcohol base solvent. Examples of the inorganic solvent include inorganic acids, such as nitric acid, hydrochloric acid, and hydrofluoric acid.

[0037]While the reaction speed increases as the treatment temperature in the ozone treatment step increases in principle, the solubility of ozone in the ozone solution decreases as the temperature increases. To make the ozone concentration in the ozone solution equal to or hither than 40 ppm at a temperature that exceeds 40° C., a pressure equal to or higher than the atmospheric pressure needs to be applied to the treatment atmosphere, which requires large-sized equipment. The treatment temperature may be about the room temperature.

[0038]The duration of time that the ozone solution and the resin board are held in contact with each other in the ozone treatment step differs depending on the type of the resin, but is preferably 2 to 30 min. If the contact time is less than 2 minutes, the effect due to the ozone treatment is less likely or unlikely to appear even if the ozone concentration is 20 ppm or higher. If the contact time exceeds 30 minutes, the resin board may deteriorate.

Problems solved by technology

However, resin also has drawbacks, such as the absence of electrical conductivity and low hardness, and therefore, it has been proposed to combine resin with metal, or the like, so as to eliminate these drawbacks.

However, a large amount of conductive metal needs to be added to the resin so as to impart sufficiently high conductivity to the resin, which may cause adverse influences on the physical properties and increased cost.

The physical method generally requires large-sized equipment, such as a vacuum tank, and thus suffers from significant restrictions in terms of space or productivity, which undesirably results in increased cost.

In the case where a film of metal is formed on a resin surface by electroless plating, the strength of adhesion between the metal film and the resin is low, and the metal film is likely to peel off from the resin.

However, the method that makes the resin surface rough by etching causes a reduction of the surface smoothness, and requires the use of a poisonous or deleterious substance, such as chromic acid, permanganic acid, or sulfuric acid, giving rise to a problem concerned with treatment of waste liquid.

In the meantime, the technology disclosed in JP-A-2005-042029 has a problem that the adhesion strength of the plating film is low if the thickness of the resin-metal composite layer is small, more specifically, is about 20-200 nm.

Thus, if a resin-metal composite layer having a thickness greater than 200 nm is formed, it is difficult to completely remove the plating film and resin-metal composite layer between wires even with etching, causing a problem of insufficient or faulty insulation.

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