JP2018080374A - Surface treatment method of plastic substrate, and production method of metal-clad laminated substrate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method of a plastic substrate capable of producing with high yield, a wiring circuit board hardly generating a trouble such as a poor appearance or a performance failure.SOLUTION: A plastic substrate such as a polyimide-based film having preferably an imide bond or a benzene ring in a molecule is brought into contact with process liquid preferably comprising water, containing micro-bubbles having preferably a diameter of 100 μm or less containing both ozone and oxygen.SELECTED DRAWING: None

Description

  The present invention provides a surface treatment method for treating the surface of a plastic substrate with a treatment liquid containing microbubbles, and a metal film formed on the plastic substrate surface-treated by the treatment method without using an adhesive. The present invention relates to a method for manufacturing a metal-clad laminated substrate, and a method for manufacturing a printed circuit board produced by patterning a metal-clad laminated substrate produced by the production method.

  Plastic substrates are widely used in various industrial fields because of their excellent electrical insulation. For example, a so-called metal-clad laminated substrate produced by forming a metal film on a plastic substrate is used as a base material for a printed circuit board. When a metal film is formed on a plastic substrate, a dry plating method such as sputtering, a wet plating method such as electroplating, or a film formation method using both of them is generally employed. A printed circuit board having a desired wiring circuit can be manufactured by patterning the formed metal film.

  As the metal film patterning method, a semi-additive method or a subtractive method is generally employed. In any of these patterning methods, a resist film having a predetermined pattern is formed by printing, exposing, and developing a photoresist on the surface of the metal film, or laminating, exposing, and developing a dry film resist. In the semi-additive method, an exposed portion that is not covered with the resist film becomes a wiring. Therefore, after a metal film is further formed on the surface of the metal film at the exposed portion to increase the film thickness, the exposed portion is covered with the resist film. Remove unnecessary metal film. On the other hand, in the subtractive method, since the portion covered with the resist film becomes the wiring, the exposed metal film not covered with the resist film is removed by etching.

  By the way, in the above-described method for manufacturing a printed circuit board, if foreign matter adheres to the surface of the starting plastic substrate, the foreign matter becomes an obstacle during film formation or wiring circuit formation, resulting in frequent pinholes and wiring leads. In some cases, defects such as chipping or disconnection occur, or because the etching is defective, the metal is not removed but remains so as to straddle between the wirings, resulting in frequent short circuits. In particular, in recent years, the wiring pitch tends to become increasingly finer, and even a minute foreign matter that has not been a problem in the past can cause the above-described defect, and therefore the importance of removing the foreign matter is increasing. Therefore, various techniques for removing these foreign substances have been proposed. For example, Patent Document 1 proposes a technique for removing foreign matter adhering to the surface of a long film substrate conveyed by roll-to-roll using an adhesive roller provided in the roll-to-roll conveyance path. Yes.

  In addition, a metal-clad laminated substrate may be required to have high peel strength, and the adhesion between the plastic substrate and the metal film is improved by modifying the surface of the plastic substrate. As a method for this surface modification, for example, in Patent Document 2, the surface of a plastic substrate is irradiated with an ultraviolet ray in the presence of an oxidizing agent, and then etched by a chemical reaction with an oxidizing agent such as permanganate. A surface treatment method has been disclosed in which the surface is roughened and the adhesion is improved by the anchor effect. As a simple modification method, Patent Document 3 discloses a technique for performing surface modification by irradiating the surface of a plastic substrate with ultraviolet light in an atmosphere of a gaseous oxidant such as ozone. In addition, a modification method has been proposed in which a plasma treatment is performed on the surface of a plastic substrate in a reduced-pressure atmosphere, thereby generating a reactive functional group capable of binding to a metal on the surface of the plastic substrate to exhibit adhesion. .

JP 2004-167688 A JP-A-9-157417 JP 2006-274176 A

  Foreign substances that cause defects in the above printed circuit boards include slit foreign objects (plastic waste) due to plastic substrate slits, organic substances such as monomers of plastic substrate raw materials, low molecular weight deposits such as catalysts, and uncured plastics. Examples include oligomer deposits such as products. Among these foreign substances, relatively large foreign substances adhering to the plastic substrate can be removed to some extent by the method of the above-mentioned Patent Document 1, but it is difficult to remove organic substances and fine foreign substances.

  If the organic substance remains attached to the plastic substrate, the organic substance volatilizes during vacuum film formation, and the film layer formed by the vacuum film formation is oxidized or carbonized, and the film layer cannot be etched well. There was a problem. In addition, when the organic substance adhering to the plastic substrate is an oligomer adhering substance, when electroplating is performed in the next process of vacuum film formation, the conductivity is lowered, and therefore the growth of the electroplated film is caused and the surface is abnormally formed. Concavities and convexities are generated, and short-circuiting or open defects may occur during subsequent wiring processing.

  In addition, in order to increase the peel strength of the metal-clad laminate substrate, the method of Patent Document 2 in which the surface of the plastic substrate is etched with an oxidizing agent can be cleaned while modifying the surface of the plastic substrate because the treatment is performed in a solution. However, the surface treatment of the plastic substrate with a liquid oxidant makes it difficult to control the chemical reaction, which may cause degradation such as breaking the molecules on the surface of the plastic substrate. In such a plastic substrate having a deteriorated surface, the adhesion to the metal film may be lowered. On the other hand, surface modification by ultraviolet irradiation or plasma treatment in an ozone gas atmosphere can secure a certain degree of adhesion between the plastic substrate and the metal film, but it is not a treatment in the liquid phase. Or cleaning foreign matter.

  The present invention has been made in view of the above problems, and removes foreign matters and organic substances adhering to the surface of a plastic substrate to cause defects such as pinholes during the production of a metal-clad laminated substrate. Accordingly, it is an object of the present invention to provide a surface treatment method for a plastic substrate that can produce a printed circuit board with high yield, which is difficult to cause, and thus has almost no defects such as poor appearance and poor performance.

  In order to achieve the above object, the plastic substrate surface treatment method of the present invention is characterized in that the plastic substrate is brought into contact with a treatment liquid containing microbubbles containing both ozone and oxygen.

  According to the present invention, foreign substances and organic substances adhering to the surface of the plastic substrate can be effectively removed, so that a metal-clad laminated substrate with almost no defects such as pinholes can be produced. It is possible to prevent defects such as defective appearance and poor performance from occurring in a printed circuit board manufactured by patterning a stretched laminated substrate.

  Hereinafter, a specific example of the surface treatment method for a plastic substrate according to the present invention will be described. The surface treatment method for a plastic substrate according to an embodiment of the present invention includes a microbubble containing both oxygen and ozone on a surface on which at least a metal film is laminated on a plastic substrate which is a base material of a metal-clad laminated substrate. Preferably, the treatment liquid containing water is brought into contact. In addition, since an active metal film is formed on the surface of the plastic substrate on the film formation side in vacuum film formation in a later step, it is preferable that the treatment liquid is also brought into contact with the surface on which the metal film is not laminated. The reason for this is that if there is a fine foreign material on the surface opposite to the surface on which the film is formed, the foreign material may contact and transfer to the active metal film during winding after film formation. This is because foreign matters can be removed by contact with the treatment liquid.

  The treatment liquid containing microbubbles containing ozone and oxygen used in this surface treatment method is preferably obtained by introducing a mixed gas of ozone and oxygen from water, for example, from an ozonizer into water consisting of pure water. Can be generated. Here, the microbubble is a bubble having a diameter of about 1 μm to several hundred μm. By bringing this treatment liquid (also referred to as ozone liquid) into contact with at least the surface of the plastic substrate on which the metal film is laminated, the organic matter adhering to the surface can be decomposed. In addition, by using microbubbles containing ozone, it is possible to modify the surface of the plastic substrate.

  Examples of the method of bringing the treatment liquid into contact with the surface of the plastic substrate include a method of spraying the treatment liquid on the surface of the plastic substrate and a method of immersing the plastic substrate in the treatment liquid. At that time, the contact time between the treatment liquid and the plastic substrate is preferably 5 seconds or more and 60 seconds or less. If the contact time is less than 5 seconds, the effect of the surface treatment may not be obtained. Conversely, if the contact time exceeds 60 seconds, no further improvement in the effect can be expected. The temperature of the treatment liquid at the time of contact is not particularly limited, but is preferably 10 to 90 ° C and more preferably 20 to 60 ° C. If this temperature is less than 10 ° C., the efficiency of the decomposition reaction of the organic matter is remarkably reduced. Conversely, if it exceeds 90 ° C., the amount of microbubbles diffused from the liquid surface increases, making it difficult to obtain the effect.

  The ozone concentration in the mixed gas constituting the microbubbles is preferably 3% by volume or more and 20% by volume or less, depending on the performance of an ozonizer that generates ozone from oxygen gas. If the ozone concentration is less than 3% by volume, the adhesion of the plastic substrate described later may not be improved. Conversely, even if the ozone concentration exceeds 20% by volume, it is not economical because it cannot be expected that the effect is further improved. The oxygen supplied to the ozonizer may be pure oxygen supplied from an oxygen cylinder, or oxygen gas extracted from air in the atmosphere by a PSA (Pressure Swing Adsorption) type oxygen concentrator using an adsorbent. Good. The ozone generation method of the ozonizer is not particularly limited, and a known method such as ultraviolet ray irradiation or discharge with a mercury lamp or the like to oxygen gas can be used.

  It is preferable to use pure water as the water used for the treatment liquid, and it is more preferable to use pure water having a conductivity of 1 μS / cm or less. If this electrical conductivity exceeds 1 μS / cm, a large amount of impurities are contained, which may contaminate the plastic substrate. Such a method for producing pure water with few impurities is not particularly limited, and can be produced by, for example, a known pure water production apparatus using an ion exchange resin. The conductivity can be measured with a known conductivity meter.

  The upper limit of the diameter of the microbubbles contained in the treatment liquid is preferably 100 μm or less, and more preferably 50 μm or less. If the diameter of the microbubbles exceeds 100 μm, the contact area of the plastic substrate becomes narrow, which is not preferable. On the other hand, the lower limit of the diameter of the microbubbles is preferably as small as possible, and nano-sized ultrafine bubbles may be included, but the generation becomes difficult as the diameter of the bubbles becomes smaller, and the measurement of the diameter However, the lower limit is usually about several μm to several tens of μm. Here, the diameter of the microbubble is expressed by a median value of volume integration, and this can be instantaneously measured by a laser light scattering type particle size distribution measuring apparatus such as Microtrac (registered trademark). Note that the diameter of the microbubble is determined by the supply pressure of the mixed gas of ozone and oxygen when generating the microbubble and the shape of a nozzle described later used for blowing the mixed gas into the water.

  As a method of generating the microbubbles made of the mixed gas in water, the tip of the nozzle that discharges the mixed gas may be immersed in a liquid such as pure water, and the pressurized mixed gas may be introduced into the nozzle. A known nozzle can be used as the nozzle in this case. For example, a nozzle that generates a swirling flow of gas and liquid, a nozzle that includes a venturi-type generator, a cavitation type nozzle, and the like can be used.

  By bringing the above-mentioned treatment liquid into contact with the surface of the plastic substrate, functional groups that contribute to the decomposition and removal of organic substances such as monomers and oligomers adhering to the surface of the plastic substrate and the adhesion to the metal film are improved. Surface modification such as introduction into the surface of the plastic substrate can be performed simultaneously. That is, foreign matters such as plastic scraps and organic substances adhering to the surface of the plastic substrate by contact with the treated water containing microbubbles are physically removed to clean the surface, and the microbubbles are configured. Functional groups that contribute to improving the adhesion to the metal film are introduced into the molecules constituting the plastic substrate by oxygen or ozone. As a result, a metal film having no defects can be formed on the surface of the plastic substrate in a later step, and thus a high-quality metal-clad laminated substrate free from defects such as pinholes can be manufactured. Such a high-quality metal-clad laminated substrate is less likely to cause poor appearance and poor performance even in a printed circuit board obtained by patterning it, so that a high-quality wired circuit board can be produced with a high yield. .

  Examples of the material of the plastic substrate that can be suitably treated by the surface treatment method of the above-described specific example of the present invention include a polyimide film, a polyamide film, a polyester film, a polytetrafluoroethylene film, a polyphenylene sulfide film, and a polyethylene film. Examples thereof include resin films such as phthalate film and liquid crystal polymer film. The surface treatment method can also be used for plastic substrates such as epoxy resins, glass epoxy substrates, and other resin boards. Among the above plastic substrates, those capable of introducing functional groups into the molecules of the plastic substrate are more preferable. Examples of such plastics include polyimide films, polyamide films, polyphenylene sulfide films, liquid crystal polymer films, and glass. An epoxy substrate can be mentioned. This is because these plastic substrates have an imide bond, a benzene ring, or the like in the molecule, so that functional groups can be easily introduced by ozone.

  For example, in an example in which a polyimide film is used for a plastic substrate, an uncured material with insufficient imidization remains on the surface of the polyimide film. The uncured material remaining on the surface of the polyimide film becomes a fragile layer of the polyimide film and reduces the adhesion between the metal film and the polyimide film. Therefore, this uncured product can be decomposed and removed by processing with a treatment liquid containing microbubbles containing ozone and oxygen, and oxygen atoms are introduced into the polyimide molecules on the surface from which the uncured product has been removed. be able to.

  Furthermore, the imide bond of the polyimide molecule reacts with ozone and oxygen in the microbubbles, thereby generating a functional group such as a carboxyl group that contributes to the bond with the metal film. In addition, a commercially available polyimide film contains about several hundred ppm of an organic solvent such as dimethylacetamide and a catalyst such as acetic acid. The impurities are decomposed and removed by the above treatment liquid. It becomes possible. Even when an uncured oligomer remains on the surface of the plastic substrate, it can be removed by the surface treatment with the treatment liquid, so that an improvement in adhesion to the metal film can be expected.

  After the surface treatment with the above treatment liquid, it is desirable to perform a treatment of exposing the plastic substrate to superheated steam. Thereby, washing | cleaning and drying of a plastic substrate can be performed simultaneously. That is, since the cleanliness of the plastic substrate can be further improved by using both the treatment with the treatment liquid containing the microbubbles and the treatment with superheated steam, the metal-clad laminate having a metal film with fewer defects Can be produced.

  The temperature of the superheated steam used for processing the plastic substrate is preferably 200 ° C. or higher and 500 ° C. or lower. If this temperature is less than 200 ° C., it cannot be expected that the plastic substrate will be washed well. Conversely, if it exceeds 500 ° C., the plastic substrate may be deformed, which is undesirable. Even when a polyimide film having a relatively high heat resistance temperature is used, the polyimide film may be deformed when exposed to superheated steam exceeding 500 ° C. The time for exposing the plastic substrate to the superheated steam is preferably 5 to 20 minutes. If this time is less than 5 minutes, the effect of cleaning with superheated steam may not be sufficiently obtained, and conversely, if it exceeds 20 minutes, it cannot be expected that the effect will be further improved, which is not economical. When the plastic substrate is exposed to the superheated steam, it is preferable to pay attention to the oxygen concentration of the atmospheric gas, and the oxygen concentration is preferably 0.3% by volume or less.

  As a method for exposing the plastic substrate to the superheated steam, for example, the plastic substrate may be inserted into the processing container and the superheated steam may be introduced into the processing container. The processing container in this case may be a sealed processing container that can batch-process single-wafer type plastic substrates, or a long plastic substrate (long plastic film) can be continuously processed by roll-to-roll. A processing container may be provided in the middle of the conveyance path. In the latter method, since the plastic substrate continuously passes through the processing container, slits are provided at the inlet and the outlet so that the superheated steam does not leak from the inlet and outlet of the plastic substrate provided in the processing container. It is preferable to provide a pair of rolls that sandwich the plastic substrate from both sides. Thereby, it is possible to avoid the superheated steam leaking from the processing container from condensing and adhering to the plastic substrate. The atmospheric pressure in the processing container when superheated steam is introduced is only required to be maintained at atmospheric pressure or higher, and the processing container needs to have a structure that can withstand such pressure and temperature. The superheated steam can be produced by a known means such as induction heating.

  After performing the treatment to dry the liquid adhering component in a dust-free environment as necessary on the plastic substrate surface-treated by the above method, without using an adhesive on one or both sides A metal film is formed by dry plating. Thereby, a metal-clad laminated substrate can be produced. A copper-clad laminate (plastic copper laminate), which is an example of this metal-clad laminate, is formed by first forming a base metal layer on the surface of the plastic substrate by a dry plating method, and then forming a copper coating layer on the base metal layer. It is produced by forming. In the dry plating method, since a metal film can be directly formed on the surface of the plastic substrate, it is not necessary to interpose an adhesive between the plastic substrate and the base metal layer.

  In particular, since the surface of the plastic substrate treated by the surface treatment method of one specific example of the present invention described above is cleaned, a functional group that contributes to improving the adhesion with the metal film is introduced. For example, when a dry film is formed by a sputtering method, atoms of sputtered particles deposited as a base metal layer on the surface of the plastic substrate and the plastic substrate are more firmly bonded, and as a result, the adhesion between the plastic substrate and the metal film is improved. improves. The base metal layer is made of, for example, a nickel-based alloy having a thickness of 3 to 40 nm and a nickel ratio of 50 to 95 mass%, and the copper coating layer is made of copper having a thickness of 10 nm to 35 μm, for example. By changing the composition and film thickness of the underlying metal layer and the coating layer thereon, a metal-clad laminate other than the plastic copper laminate can be produced. Since the base metal layer is generally formed by a dry plating method using a known vacuum film formation method such as a sputtering method or a vapor deposition method, for example, when forming a base metal layer having a predetermined alloy composition, the alloy Sputtering may be performed using an alloy target having a composition.

  The copper coating layer formed on the base metal layer can be formed by a wet plating method such as a dry plating method or an electroplating method, which is a known vacuum film formation method such as a sputtering method or a vapor deposition method. These dry plating methods and wet plating methods may be used in combination. For example, a copper thin film layer is formed on the surface of the underlying metal layer by a dry plating method, and a copper thick film layer is further formed on the copper thin film layer by an electroplating method. A film can be formed. Since the electroplating method has a higher film formation rate than the dry plating method, the entire film formation time can be shortened. A printed circuit board can be produced by patterning the metal-clad laminate produced in this way by the subtractive method or semi-additive method described above.

  9 pieces of 12 cm long x 12 cm wide film substrates are cut out from a 38 μm thick polyimide film (product name “Kapton 150EN” manufactured by Toray Deyupon Co., Ltd.) and immersed in a treatment liquid at 25 ° C. containing a microvalve for 60 seconds. In addition, each of the three sheets was treated by immersing in pure water at 25 ° C. subjected to ultrasonic vibration for 60 seconds, and the remaining three sheets were not subjected to these treatments. In addition, the treatment liquid including the above-described microvalve is a pure water having an electrical conductivity of 0.1 μS / cm and oxygen gas having an ozone concentration of 5% by volume using a swivel nozzle (manufactured by Nano Planet, model number M2-LM / SUS). Generated by using and blowing. The diameter of the microbubbles contained in the generated treatment liquid was measured using a laser light scattering particle size distribution measuring device (laser diffraction particle size distribution measuring device HELOS & RODOS manufactured by Sympatec), and the median value was 15 μm.

  Next, on one side of each of the above nine film substrates, a 7% by mass Cr— by a DC sputtering method using a 7% by mass Cr—Ni alloy target (manufactured by Sumitomo Metal Mining Co., Ltd.) as the first layer. A base metal layer made of a Ni alloy was formed. Of these nine films after film formation, three sheets with different surface treatments were extracted one by one and the thickness of the metal layer was measured using a transmission electron microscope (TEM: manufactured by Hitachi, Ltd.). there were. Next, a copper coating layer having a thickness of 8 μm was formed on each of the remaining six sheets by a direct current sputtering method using a Cu target (manufactured by Sumitomo Metal Mining Co., Ltd.) as a second layer. Thus, two samples of metal-clad laminates (copper-clad laminates) of Samples 1 to 3 having different surface treatments were produced.

  A circuit pattern having a pitch of 20 μm (line width: 10 μm, interval between adjacent lines: 10 μm) is formed on the copper coating layer with a photoresist on one of the obtained copper-clad laminates of each sample, Etching was carried out with an aqueous solution of ferric iron to produce three test pieces on which wirings made of copper having the circuit pattern were formed. Locations where the appearance of these three test specimens is broken, locations where the wiring is missing, locations where the copper layer protrudes from the line width of 10 μm, and the copper layer is not etched well. The number of short-circuited portions remaining across the wirings was counted. Further, the metal film is etched so that a line-shaped circuit pattern having a line width of 1 mm is formed on the other of the copper-clad laminated substrates of each sample, and the adhesion strength at room temperature is obtained. Was measured according to IPC-TM-650, Number: 2.4.9, Revision: E, Method: A. The measurement results are shown in Table 1 below together with the number of the above-mentioned defective portions.

As can be seen from Table 1 above, the copper-clad laminate produced using the film substrate treated with the treatment liquid containing microbubbles and the circuit board obtained by patterning the same were treated with ultrasonic cleaning or not. Compared to the case of processing, all inspection items were superior. The reason is that ultrasonic cleaning is less likely to remove foreign matter compared to the case of untreated, so it can be removed to some extent, but in the case of ultrasonic cleaning or untreated, The functional group that contributes to improving adhesion to the polyimide film molecules cannot be introduced and the fragile layer on the surface of the polyimide film is not sufficiently removed, so that the adhesion strength is particularly greater than when treated with a treatment liquid containing microbubbles. Is considered to have decreased significantly.

Claims (7)

  A plastic substrate surface treatment method comprising contacting a plastic substrate with a treatment liquid containing microbubbles containing both ozone and oxygen.   The surface treatment method for a plastic substrate according to claim 1, wherein the treatment liquid is water.   A method for producing a metal-clad laminate, comprising forming a metal film on the surface of a plastic substrate treated by the surface treatment method according to claim 1 without using an adhesive.   The metal film is formed by a step of forming a base metal layer on the surface of the plastic substrate by a dry plating method and a step of forming a metal film layer on the surface of the base metal layer. The manufacturing method of the metal-clad laminated substrate of Claim 3.   The step of forming the metal coating layer includes a step of forming a metal thin film layer by a dry plating method and a step of forming a metal thick film layer by a wet plating method on the surface of the metal thin film layer. The method for producing a metal-clad laminated substrate according to claim 4, wherein the method is characterized in that:   6. The method for producing a metal-clad laminate according to claim 4, wherein the metal coating layer is made of copper. A method for manufacturing a wired circuit board, wherein a wiring circuit is formed by patterning the metal film of a metal-clad laminated substrate produced by the manufacturing method according to claim 3.