JP5455696B2 - Dry film resist thinning method - Google Patents

Description

The present invention provides a dry film resist thinning method capable of uniformly thinning a dry film resist.

  As a method for manufacturing a printed wiring board or a lead frame, there is a subtractive method in which an etching resist layer is formed on a substrate and a metal layer not covered with the etching resist layer is removed by etching. Compared to other methods, this method has advantages such as a shorter manufacturing process and lower cost, and stronger bonding strength between the metal pattern and the insulating plate. It has become. As a method of providing an etching resist layer by a subtractive method, a method using a sheet-like photosensitive material called a dry film resist and a liquid photoresist can be cited. A dry film resist is generally preferred because it can protect holes.

  Now, along with the recent downsizing and multi-functionalization of electronic equipment, printed wiring boards used inside the equipment are also being densified and miniaturized metal patterns, and the conductor width is now reduced by the subtractive method. A printed wiring board having a metal pattern of 50 to 80 μm and a conductor gap of 50 to 80 μm is manufactured. In addition, with higher density and finer wiring, ultrafine metal patterns of 50 μm or less are required. Along with this, the requirements for pattern accuracy and impedance are also increasing. In order to achieve such a fine metal pattern, a semi-additive method has been conventionally studied. However, there are problems such as a significant increase in the number of steps and poor adhesion of plated copper.

  When such a fine metal pattern is formed by the subtractive method, it is of course necessary to improve the technical level and the management level of all production lines, but etching is a major point among them. This is because side etching that proceeds from the side of the conductor, which is a feature of the subtractive method, becomes a problem. In order to suppress the amount of side etching, liquid composition management, the angle and strength of spraying the liquid onto the substrate, etc. It is necessary to adjust the optimum etching conditions. Further, side etching is influenced not only by adjusting the etching conditions but also by the film thickness of the etching resist layer. That is, the thicker the film, the more difficult the liquid circulates between the fine resist patterns, and as a result, the side etching increases. The thickness of the dry film resist which is currently mainstream is about 25 μm, while on the other hand, in order to form a fine metal pattern, it is necessary to make the resist film thickness as thin as possible. Dry film resists with the following thickness have been developed and commercialized. However, in such a thin dry film resist, there is a problem in that bubbles are not sufficiently mixed and irregularities followability with dust as a core, and the resist is peeled off or disconnected.

  In order to solve such a problem, in a method of producing a conductive pattern by a subtractive method, after pasting a dry film resist on a substrate, an alkaline aqueous solution having an inorganic alkaline compound content of 5 to 20% by mass, There has been proposed a metal pattern forming method characterized in that a dry film resist is thinned, and then a circuit pattern is exposed, developed, and etched. In this method, the thinning process was certainly possible, but due to the lack of uniformity of film thickness after thinning, foreign matter that seems to have adhered to the resist surface before the thinning process, In some cases, a defect portion in which thinning was inhibited was confirmed (for example, see Patent Document 1).

International Publication No. 2009/096438 Pamphlet

  The present invention provides a dry resist thinning method that can uniformly thin a dry film resist.

  As a result of the study, the above problem is obtained by pasting a dry film resist on the substrate, performing a water washing treatment, and then performing a thinning treatment with an alkaline aqueous solution having an inorganic alkaline compound content of 5 to 20% by mass. We were able to solve.

  In the present invention, a dry film resist on a substrate is uniformly thinned with a high-concentration alkaline aqueous solution. However, since the entire surface of the dry film resist does not exhibit the same hydrophilicity, a portion where the permeation rate of the alkaline aqueous solution is different occurs at the stage of thinning treatment, and this causes unevenness of thinning. It was a cause. Further, it was found that when contaminants or foreign substances exist on the surface of the dry film resist, the penetration of the alkaline aqueous solution is inhibited, so that the thinning of the portion is not promoted. In the case of forming a metal pattern by performing exposure, development and etching after performing the thinning treatment, when the thickness of the dry film resist is uneven or when a residual thickness occurs, in the subsequent exposure process, The exposure amount of the thick part is insufficient compared with other normal parts, resulting in insufficient curing. As a result, in the development process of the next process, the exposure amount becomes thinner than the normal part or completely. It will be dissolved. The part where the dry film resist originally exists and the part where the dry film resist is not present or the part which is thinner than the normal part is etched in the next etching process, and a metal pattern having no defect cannot be obtained. As a result of examining this problem, it has been found that it is effective to perform a water washing treatment as a pretreatment for performing a thinning treatment. By performing the water washing treatment, the hydrophilic group of the polymer present on the dry film resist surface is reoriented, the hydrophilicity is made uniform, and it becomes possible to remove contaminants and foreign substances adhering to the dry film resist surface, A uniform thinning process can be performed without remaining thick.

  The thinning process of the dry film resist of the present invention will be described in detail. First, a dry film resist is attached to at least one side of the substrate. For the pasting, for example, a laminator device that presses and presses a rubber roll heated to 100 ° C. is used. The substrate may be subjected to a pretreatment such as pickling. After pasting, the carrier film of the dry film resist is peeled off, and the thin film resist is subjected to a thin film treatment with an alkaline aqueous solution of 5 to 20% by mass.

  After the thin film treatment of the dry film resist of the present invention, the circuit pattern is exposed, further developed to form an etching resist layer, and then a metal pattern other than the etching resist layer is etched to form a metal pattern .

  The substrate according to the present invention includes a printed wiring board or a lead frame substrate. Examples of the printed wiring board include a flexible substrate and a rigid substrate. As the flexible substrate, polyester, polyimide, aramid, or polyester-epoxy base is usually used as a material for the insulating layer. The thickness of the insulating layer of the flexible substrate is 5 to 125 μm, and a metal layer of 1 to 35 μm is provided on both sides or one side thereof, which is very flexible. The thickness of the insulating layer or metal layer may be outside this range. The flexible substrate may be in a sheet form or a roll form. If it is a roll form, processes such as thinning, exposure, development, and etching can be processed by a roll-to-roll system. As a rigid substrate, a necessary number of insulating substrates in which epoxy resin or phenol resin is dipped in a paper base material or glass base material are stacked to form an insulating layer, and a metal foil is placed on one or both sides, and heated and pressed. A laminated layer provided with a metal layer can be used. In addition, a multilayer shield plate produced by laminating prepreg, metal foil, etc. after processing the inner layer wiring pattern, and a multilayer plate having through holes and non-through holes are also included. The thickness is 60 μm to 3.2 mm, and the material and thickness thereof are selected according to the final use form as a printed circuit board. Examples of the material for the metal layer include copper, gold, silver, and aluminum, with copper being the most common. These printed circuit boards include, for example, “Printed Circuit Technology Handbook-Second Edition” (edited by the Printed Circuit Society of Japan, published by Nikkan Kogyo Shimbun) and “Multilayer Printed Circuit Handbook” (JA Scarlet, edited by Co., Ltd.). What is described in Modern Chemical Co., Ltd.) can be used. Examples of the lead frame substrate include iron nickel alloy and copper alloy substrates.

  The dry film resist according to the present invention is a commonly used photosensitive material for circuit formation, and examples thereof include a negative resist in which a light irradiation part is cured and insolubilized in a developer. The dry film resist is composed of at least a photosensitive resin layer. The photosensitive resin layer is provided on a carrier film (transparent support) such as polyester, and in some cases, the photosensitive resin layer is covered with a protective film such as polyethylene. It has a configuration. The negative photosensitive resin layer includes, for example, a binder polymer containing a carboxyl group, a photopolymerizable unsaturated compound, a photopolymerization initiator, a solvent, and other additives. Their blending ratio is determined by a balance of required properties such as sensitivity, resolution, hardness and tenting property. Examples of photosensitive resin compositions are “Photopolymer Handbook” (edited by Photopolymer Social Society, published in 1989, published by Kogyo Kenkyukai Co., Ltd.) and “Photopolymer Technology” (edited by Atsuo Yamamoto and Mototaro Nagamatsu, published in 1988). , Published by Nikkan Kogyo Shimbun), etc., and a desired photosensitive resin composition can be used. The thickness of the photosensitive resin layer is preferably 15 to 100 μm, and more preferably 20 to 50 μm. If the thickness is less than 15 μm, resist peeling or disconnection may occur due to mixing of bubbles with dust as a nucleus or uneven followability, and if it exceeds 100 μm, the amount dissolved and removed by thinning increases. The thinning time may be long.

  The water washing treatment according to the present invention is a step of making the hydrophilicity of the dry film resist surface uniform and removing contaminants and foreign substances present on the dry film as a pretreatment for thinning treatment. Examples of water used for the water washing treatment include tap water, industrial water, and pure water. Among these, pure water is preferably used. Pure water that is generally used for industrial purposes can be used. For example, it can be obtained by treating tap water with a filter treatment, activated carbon treatment, or an ion exchange resin. Although there is no restriction | limiting in particular as the amount of organic substances in pure water, 1000 ppb or less is preferable. The specific resistance value indicating the amount of ions is not particularly limited, but is preferably in the range of 0.1 to 15 MΩ · cm. The washing method includes a dipping method, a battle method, a spray method, brushing, scraping and the like, and the spray method is most suitable for removing contaminants and foreign matters on the dry film resist. Although the conditions (temperature, spray pressure, time) of the spray treatment can be adjusted as appropriate, specifically, the treatment temperature is preferably 10 to 30 ° C, more preferably 20 to 25 ° C. The spray pressure is preferably 0.01 to 0.5 MPa, more preferably 0.05 to 0.3 MPa.

  Examples of the inorganic alkaline compound according to the present invention include alkali metal carbonates such as lithium or sodium or potassium carbonate or bicarbonate, alkali metal phosphates such as potassium or sodium phosphate, lithium, sodium or potassium. Mention may be made of inorganic alkaline compounds selected from alkali metal hydroxides such as hydroxides and alkali metal silicates such as potassium and sodium silicates. Among these, particularly preferable compounds include alkali metal carbonates.

  The treatment liquid used for the thinning treatment according to the present invention contains 5 to 20% by mass of the inorganic alkaline compound with respect to the treatment liquid. If it is less than 5% by mass, the micelles in the middle of dissolution and removal tend to dissolve and diffuse, and the thinning process becomes non-uniform due to the flow of the treatment liquid. Moreover, when it exceeds 20 mass%, precipitation will occur easily and it will be inferior to the temporal stability of a liquid, and workability | operativity. The pH of the solution is preferably in the range of 9-12. In addition, a small amount of a surfactant, an antifoaming agent, a solvent and the like can be added as appropriate.

  The thinning treatment according to the present invention is a treatment for reducing the thickness of the dry film resist substantially uniformly, and is 0.05 to 0.9 times the thickness before the thinning treatment. Thinning methods include a dip method, a battle method, a spray method, brushing, scraping, and the like, and the spray method is most suitable for the removal rate of the dry film resist. The conditions (temperature, spray pressure, time) of the spray treatment are appropriately adjusted according to the dissolution / removability of the dry film resist to be used. Specifically, the treatment temperature is preferably 10 to 50 ° C, more preferably 15 to 40 ° C, and further preferably 15 to 35 ° C. The spray pressure is preferably 0.01 to 0.5 MPa, and more preferably 0.02 to 0.3 MPa.

  The thinning treatment according to the present invention needs to be sufficiently washed with water after being treated with 5 to 20% by mass of an inorganic alkaline compound aqueous solution. The washing method includes a dip method, a battle method, a spray method, and the like, and since the processing speed is fast, the spray method is most suitable.

  In the present invention, a fine circuit pattern can be formed by performing exposure, development, and etching after thinning treatment. Circuit pattern exposure methods include xenon lamps, high-pressure mercury lamps, low-pressure mercury lamps, ultra-high-pressure mercury lamps, reflection image exposure using UV fluorescent lamps as light sources, single-sided, double-sided contact exposure using photo tools, proximity method, projection method And laser scanning exposure. When performing scanning exposure, a laser light source such as a He—Ne laser, He—Cd laser, argon laser, krypton ion laser, ruby laser, YAG laser, nitrogen laser, dye laser, or excimer laser is used according to the emission wavelength. The exposure can be performed by wavelength conversion and scanning exposure, or by scanning exposure using a liquid crystal shutter and a micromirror array shutter.

  As a development method according to the present invention, a developer corresponding to the dry film resist to be used is used and sprayed from the vertical direction of the substrate toward the substrate surface to remove unnecessary portions as a resist pattern, thereby forming a circuit pattern. A corresponding etching resist layer is formed. In general, a 1 to 3% by mass aqueous sodium carbonate solution is used.

  The etching according to the present invention is a method for removing an exposed metal layer other than an etching resist layer formed by development. In the etching process, a method described in “Handbook of Printed Circuit Technology” (edited by Japan Printed Circuit Industry Association, published in 1987, published by Nikkan Kogyo Shimbun) can be used. The etching solution may be one that can dissolve and remove the metal layer, and at least the etching resist layer has resistance. In general, when copper is used for the metal layer, a ferric chloride aqueous solution, a cupric chloride aqueous solution, or the like can be used.

  Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to these examples.

Examples 1-6, Comparative Examples 1-3
Double film copper-clad laminate (area 510 mm x 340 mm, copper foil thickness 12 μm, substrate thickness 0.2 mm, manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name: CCL-E170) and dry film resist (Asahi Kasei E-Materials Co., Ltd.) Manufactured, trade name: Sunfort AQ-4038, thickness 40 μm). Next, after peeling the carrier film, as shown in Table 1, with respect to what was washed with tap water and pure water, what was not performed, using the alkaline aqueous solution shown in Table 1, Dry film resist thinning treatment was performed. The pure water used what was processed to the specific resistance value 10Mohm * cm using the organo Co., Ltd. make, cartridge pure water device G-10C type. In addition, the water washing treatment was performed at a spray pressure of 0.1 MPa and the treatment temperature was 20 ° C., and the thinning treatment was conducted at a spray pressure of 0.05 MPa, a treatment temperature of 25 ° C., and the treatment time as shown in Table 1. The dry film resist thickness was 10 μm on average. After the thinning treatment, the film thickness of the dry film resist was measured at 40 points, and the variation in film thickness was evaluated by the value of standard deviation σ. The film thickness was measured by non-contact and non-destructive using a small high-resolution spectroscopic device SolidLambdaUV-NIR manufactured by Spectra Corp. and calculated from reflectance spectroscopy.

  As is apparent from Table 1, it can be seen that the dry film resist can be thinned more uniformly by performing the pretreatment by washing with water. It can also be seen that the use of pure water is more uniform than tap water. This is considered to depend on the amount of impurities contained in the water used for the pretreatment.

  The present invention is widely used for forming a metal pattern in a subtractive method, and can be used, for example, for producing a printed wiring board, a lead frame and the like.

Claims (1)

  A method of thinning a dry film resist, comprising: pasting a dry film resist on a substrate, performing a water washing treatment, and then performing a thinning treatment with an alkaline aqueous solution having an inorganic alkaline compound content of 5 to 20% by mass. .