JP2023101962A - Etching method of laminate - Google Patents

Abstract

To provide an etching method of a laminate having a thermoplastic polyimide resin layer on a base material, capable of forming an excellent opening shape even when a film thickness of the thermoplastic polyimide resin layer is thick.SOLUTION: An etching method of a laminate includes etching a laminate which has a thermoplastic polyimide resin layer on a base material, and in which the thermoplastic polyimide resin layer contains 3-21.5 mass% of a solvent based on a weight of the thermoplastic polyimide resin layer with an etching liquid which contains an alkali metal hydroxide and an ethanolamine compound.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a method for etching a laminate having a thermoplastic polyimide resin layer on a substrate.

2. Description of the Related Art In recent years, highly functional information electronic devices such as smart phones and tablet PCs, which require portability, have become widespread. These information electronic devices are required to be highly functional and to be light, thin, short and small. Electronic circuit boards mounted on these devices are required to mount highly integrated and miniaturized electronic devices at high density. In order to realize high-density mounting, it is necessary to increase the circuit pitch of the printed wiring board according to the device size.

Polyimide-based materials are attracting attention as organic materials that are excellent in adhesive strength, chemical resistance, mechanical strength, electrical properties, and are compatible with processes using lead-free solder, in addition to high definition. However, when a wet etching process (for example, Patent Document 1) is used for pattern formation such as drilling of the laminate, the etching rate of the thermoplastic polyimide resin is much slower than that of the thermosetting polyimide resin, and the etching process takes time. Therefore, there was a problem that the etching solution penetrated between the etching mask and the thermoplastic polyimide resin layer and the opening shape of the pattern collapsed.

Patent Document 2 discloses a method of adding an abrasive to an etchant as a method of efficiently etching a thermoplastic polyimide resin. However, in this method, the substrate may be scratched or the abrasive may remain on the substrate.

Patent Document 3 discloses an etchant containing an alkali metal hydroxide, water and ethanolamine as an etchant for thermoplastic polyimide resin, but the etching rate is not sufficient, and in particular when the thickness of the thermoplastic polyimide resin layer is thick, etching may be difficult.

JP-A-2007-8969 JP-A-2003-8171 WO 2007/060824 pamphlet

An object of the present invention is to provide an etching method for a laminate having a thermoplastic polyimide resin layer on a base material, which can form a pattern having a favorable opening shape even when the thickness of the thermoplastic polyimide resin layer is large.

The inventors have found that the above problems can be solved by the following means.

A laminate having a thermoplastic polyimide resin layer on a base material, and the thermoplastic polyimide resin layer containing 3 to 21.5% by mass of a solvent relative to the weight of the thermoplastic polyimide resin layer is etched with an etching solution containing an alkali metal hydroxide and an ethanolamine compound.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an etching method for a laminate having a thermoplastic polyimide resin layer on a substrate, which can form a pattern having a favorable opening shape even when the thickness of the thermoplastic polyimide resin layer is large.

Schematic process cross-sectional views showing one embodiment of the etching method of the present invention.

EMBODIMENT OF THE INVENTION Below, the form for implementing this invention is demonstrated.

<Thermoplastic polyimide resin>
The thermoplastic polyimide resin contained in the thermoplastic polyimide resin layer in the present invention is preferably a polyimide resin that softens by heating and exhibits adhesiveness, and particularly a solvent-soluble thermoplastic polyimide resin can be preferably used. Examples of commercially available products of the thermoplastic polyimide resin include Spixeria (registered trademark) AD manufactured by Somar Co., Ltd., PIAD (registered trademark) manufactured by Arakawa Chemical Industries, Ltd., and Q-AD-X0516 manufactured by P.I.

<Laminate>
The laminate used in the etching method of the present invention has a thermoplastic polyimide resin layer on a substrate, and the thermoplastic polyimide resin layer contains 3 to 21.5% by mass of a solvent based on the weight of the thermoplastic polyimide resin layer. The laminate can be obtained by preparing a coating liquid in which the thermoplastic polyimide resin as described above is adjusted to a viscosity suitable for the coating method described later with a solvent, coating the coating liquid on the substrate, and drying to form a thermoplastic polyimide resin layer. The thermoplastic polyimide resin layer contains 3 to 21.5% by weight of solvent, more preferably 7 to 16% by weight, based on the weight of the thermoplastic polyimide resin layer. If the content of the solvent is less than 3% by mass, the etching rate becomes slow, and the shape of the pattern collapses, making it impossible to obtain a good opening shape. Examples of the solvent include organic solvents such as N-methylpyrrolidone, N,N-dimethylacetamide, sulfolane, N,N-dimethylformamide, N,N-diacetylamide, gamma-butyrolactone, alkylene glycol monoalkyl ether, alkylene glycol dialkyl ether, alkyl carbitol acetate, and benzoic acid ester. These solvents may be used alone or in combination of two or more. As a result, even when the thickness of the thermoplastic polyimide resin layer is large, a pattern having a favorable opening shape can be formed.

In the present invention, the thermoplastic polyimide resin is adjusted to a viscosity suitable for the coating method with the solvent as described above, and can be applied onto the substrate by known methods such as dip coating, flow coating, roll coating, bar coating, screen printing, curtain coating, spin coating, casting, and spraying. A normal heat drying oven can be used for drying the applied thermoplastic polyimide resin. The atmosphere in the drying furnace includes air, inert gas (nitrogen, argon), and the like. The drying temperature can be appropriately selected depending on the boiling point of the solvent in which the polyimide copolymer of the present invention is dissolved and the amount of solvent to be left, but it is preferably 80 to 400°C, preferably 80 to 300°C. The drying time may be appropriately selected depending on the thickness, concentration, type of solvent, and amount of solvent to be left, and is preferably about 1 second to 360 minutes. Moreover, the drying process may be carried out in one step under the conditions as described above, or may be carried out in two or more steps under different conditions. The laminate etching method of the present invention can be preferably applied to a laminate having a thermoplastic polyimide resin layer with a thickness of 2 to 30 μm.

Any base material can be used depending on the application and manufacturing process of the final product. Examples include textiles such as cloth, glass, polyethylene terephthalate, polyethylene naphthalate, polyethylene, polycarbonate, triacetyl cellulose, cellophane, polyimide, polyamide, polyphenylene sulfide, polyetherimide, polyethersulfone, aromatic polyamide, or polysulfone, synthetic resins, metals such as copper and aluminum, ceramics, and paper. The substrate may be transparent, or may be colored by blending various pigments or dyes into the material constituting the substrate, and furthermore, the surface thereof may be processed into a matt state. The thickness of the substrate is also not particularly limited, but is preferably about 0.001 to 10 mm.

When a molded article of a thermoplastic polyimide resin is produced by the etching method of the present invention, fillers such as silica, alumina, mica, etc., carbon powder, pigments, dyes, polymerization inhibitors, thickeners, thixotropic agents, suspending agents, antioxidants, dispersants, pH adjusters, surfactants, various organic solvents, various resins, etc. can be added to the molded article according to various purposes.

<Etching solution>
The etchant according to the present invention is an etchant used for etching a thermoplastic polyimide resin.

The etching solution according to the present invention contains an alkali metal hydroxide and an ethanolamine compound. Thereby, the laminate in the present invention can be etched with a good opening shape.

The content of the alkali metal hydroxide contained in the etchant according to the present invention is preferably 15 to 45% by mass with respect to the total amount of the etchant. When the content of the alkali metal hydroxide is 15% by mass or more, the solubility of the thermoplastic polyimide resin is excellent, and when the content of the alkali metal hydroxide is 45% by mass or less, precipitation of the alkali metal hydroxide is difficult to occur. The content of alkali metal hydroxide is more preferably 30 to 45% by mass.

As the alkali metal hydroxide, at least one compound selected from the group consisting of potassium hydroxide, sodium hydroxide and lithium hydroxide is preferably used. As the alkali metal hydroxide, one of these may be used alone, or two or more thereof may be used in combination.

The content of the ethanolamine compound contained in the etching solution according to the present invention is preferably 5 to 40% by mass with respect to the total amount of the etching solution. When the content of the ethanolamine compound is 5% by mass or more, the solubility of the thermoplastic polyimide resin layer is excellent. The content of the ethanolamine compound is more preferably 15-35% by mass.

Any type of ethanolamine compound such as primary amine, secondary amine, and tertiary amine may be used, and one type may be used alone, or two or more types may be used in combination. Examples of typical ethanolamine compounds include 2-aminoethanol, which is a primary amine; 2-(2-aminoethylamino)ethanol, which is a mixture of a primary amine and a secondary amine (that is, a compound having a primary amino group and a secondary amino group in one molecule); 2-(methylamino)ethanol and 2-(ethylamino)ethanol, which are secondary amines; dimethylamino) ethanol and the like. Among them, 2-aminoethanol and 2-(2-aminoethylamino)ethanol are more preferable from the viewpoint of etching rate.

The etching solution according to the present invention can also contain a coupling agent, a leveling agent, a coloring agent, a surfactant, an antifoaming agent, an organic solvent, etc., as necessary. Examples of organic solvents include ketones such as acetone, methyl ethyl ketone and cyclohexanone; acetic acid esters such as ethyl acetate, butyl acetate, cellosolve acetate, propylene glycol monomethyl ether acetate and carbitol acetate; carbitols such as cellosolve and butyl carbitol; aromatic hydrocarbons such as toluene and xylene;

The etchant according to the present invention is preferably an alkaline aqueous solution. Tap water, industrial water, pure water, etc. can be used as the water used in the etching solution according to the present invention. Of these, it is preferable to use pure water. In the present invention, pure water that is generally used for industrial purposes can be used.

In the etching method of the present invention, the temperature of the etchant is preferably 60-95°C. Although the optimum temperature varies depending on the type of thermoplastic polyimide resin, the thickness of the layer, the shape of the etching pattern, etc., the temperature of the etchant is more preferably 70 to 90.degree.

<Etching method>
The etching method of the present invention will be described with reference to FIG.

First, a coating liquid containing a thermoplastic polyimide resin is prepared, applied onto the substrate 3, and dried to form the laminate 2 having the thermoplastic polyimide resin layer 1 (step (I)). At this time, the drying conditions are adjusted so that the content of the solvent contained in the thermoplastic polyimide resin layer 1 is 3 to 21.5% by mass. Next, a mask material 4 is formed on the thermoplastic polyimide resin layer 1 of the laminate 2 (step (II)). Next, the mask material 4 is patterned to form an etching mask 5 (step (III)). Next, the thermoplastic polyimide resin layer 1 is etched through the etching mask 5 using an etchant containing an alkali metal hydroxide and an ethanolamine compound, and washed with water (step (IV)). Next, the etching mask 5 is removed to obtain the laminate 2 having the thermoplastic polyimide resin layer 1 patterned on the substrate 3 (step (V)).

In the etching method of the present invention, methods such as immersion treatment, puddle treatment, spray treatment, brushing, and scraping can be used in the etching step. Among these, immersion treatment is preferable from the viewpoint of etching rate.

As the mask material 4, a resin mask such as a liquid resist or a dry film resist or a metal mask can be used. A resin mask is preferable because of the simplicity of the process.

In the etching method of the present invention, methods such as immersion treatment, puddle treatment, spray treatment, brushing, and scraping can be used in the water washing step. Among these, immersion treatment is preferable.

Tap water, industrial water, pure water, or the like can be used as washing water. Of these, it is preferable to use pure water. Pure water that is generally used for industrial purposes can be used.

EXAMPLES The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these Examples.

(Examples 1-5, Comparative Examples 1-2)
A thermoplastic polyimide resin solution (Spixeria AD001 manufactured by Somar Co., Ltd.) was dissolved in N-methylpyrrolidone to prepare a coating liquid having a polyimide resin concentration of 25% by mass. The coating liquid was applied onto a 18 μm-thick copper foil (substrate 3) by a spin coating method so that the film thickness after primary drying was 15 μm, and primary drying was performed at 80° C. for 5 minutes. Subsequently, secondary drying was performed under the conditions shown in Table 1 in a nitrogen atmosphere to obtain laminates 2 of Examples 1 to 5 and Comparative Examples 1 and 2 having a thermoplastic polyimide resin layer 1 on a copper foil (base material 3). A part of each laminated body 2 thus obtained was cut into a 3 cm square, and the weight thereof was measured. Next, the weight-measured laminated body 2 was placed in a dryer, and the temperature was raised from 150° C. to 300° C. over 30 minutes to dry it completely. The weight of the laminate 2 after being completely dried was measured, and the amount of solvent contained in the thermoplastic polyimide resin layer 1 after secondary drying was calculated from the weight change before and after being completely dried. Table 1 shows the solvent content of each laminate 2 and the film thickness after secondary drying.

On the thermoplastic polyimide resin layer 1 of the laminates 2 of Examples 1 to 5 and Comparative Examples 1 and 2 after the secondary drying, a negative dry film resist (DFR) (manufactured by AGC Co., Ltd. ASG302) was laminated as a mask material 4 using a roll laminator under the conditions of a temperature of 100 ° C., a speed of 0.5 m / min, and a pressure of 0.5 MPa. After that, a circular image with a diameter of 50 μm was exposed to the mask material 4 with an ultra-high pressure mercury lamp (12 W) (exposure amount 30 mJ), and the thermoplastic polyimide resin layer 1 was developed with a 1% by mass sodium carbonate aqueous solution to form an etching mask 5 patterned on the thermoplastic polyimide resin layer 1.

Laminate 2 in which etching mask 5 was formed on thermoplastic polyimide resin layer 1 was etched by immersion method using etching liquid through etching mask 5 . The etching temperature was 80° C., and the etching mask 5 was peeled off using a 40° C. aqueous solution of 3 mass % sodium hydroxide after etching and washing with water. For Examples 1, 3 to 5 and Comparative Examples 1 and 2, an etching solution (pH>13.7) containing 35% by mass of an alkali metal hydroxide (potassium hydroxide), 30% by mass of an ethanolamine compound (2-aminoethanol), and 35% by mass of water was used. >13.7) was used.

"Evaluation of opening shape"
Using the difference in opening diameter between the upper and lower openings of the pattern openings formed in the thermoplastic polyimide resin layer 1, the following criteria were used. Table 1 shows the results.
(Evaluation Criteria for Opening Shape)
◯: The difference in opening diameter between the upper portion and the lower portion of the opening is 2.8 times or less of the opening depth.
Δ: The difference in opening diameter between the upper portion and the lower portion of the opening exceeds 2.8 times the opening depth and is 3.4 times or less.
x: The difference in opening diameter between the upper portion and the lower portion of the opening exceeds 3.4 times the opening depth.

"Evaluation of DFR peelability"
After the thermoplastic polyimide layer 2 was etched and washed with water, the laminate 2 was immersed in a 3% by mass sodium hydroxide aqueous solution at 40° C., and the time required for peeling off the etching mask 5 (DFR) was evaluated according to the following criteria. Table 1 shows the results.

(Evaluation Criteria for DFR Peelability)
◯: It can be peeled off within 5 minutes with a 3% by mass sodium hydroxide aqueous solution at 40°C.
Δ: More than 5 minutes with a 3% by mass sodium hydroxide aqueous solution at 40° C., can be peeled off within 10 minutes.
x: Cannot be peeled off within 10 minutes with a 3% sodium hydroxide aqueous solution at 40°C.

The results in Table 1 show the effects of the present invention.

The method for etching a thermoplastic polyimide resin layer of the present invention can be applied to fine processing of resins in, for example, multilayer build-up wiring boards, component-embedded module boards, flip-chip package boards, motherboards for mounting package boards, and the like.

1 thermoplastic polyimide resin layer 2 laminate 3 base material 4 mask material 5 etching mask

Claims (1)

A laminate having a thermoplastic polyimide resin layer on a base material, and the thermoplastic polyimide resin layer containing 3 to 21.5% by mass of a solvent relative to the weight of the thermoplastic polyimide resin layer is etched with an etching solution containing an alkali metal hydroxide and an ethanolamine compound.