JP2005216882A - Flexible printed circuit board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed circuit board in which an adhesion strength is firm without acting an adhesive and in which fine patterning is possible. <P>SOLUTION: In the flexible printed circuit having a metal conductor layer formed on a plastic film, fine irregularities which set an average spacing between convex parts or between recesses to 10 nm to 80 nm are formed by a nitrogen plasma treatment on the plastic film before the metal conductor layer is formed, and then a mixed layer of the metal and the plastic film material is formed in thickness of 0.01 μm or less on the plastic film. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a flexible printed circuit board in which a metal and a plastic film are laminated on a surface of an insulating plastic film and a manufacturing method thereof.

Many conventional flexible printed boards use copper for the metal conductor layer and polyimide as the plastic film. Since copper and polyimide have poor adhesion, many flexible printed boards that have increased adhesion using an adhesive between copper and polyimide are commercially available. As another flexible printed board, a flexible printed board in which a metal such as nickel or chromium having relatively good adhesion to polyimide is formed on polyimide and copper is formed on nickel and chromium is also commercially available. Furthermore, as a method for producing a flexible printed circuit board in which metal is directly formed on a plastic film, metal ions are implanted on polyimide to form a modified layer having a thickness of 0.1 μm or more on the polyimide surface, and a metal conductor layer is formed on the modified layer. The manufacturing method of the flexible printed circuit board which forms is disclosed. (For example, refer to Patent Document 1.)
In addition, there is a description of a flexible printed board in which plasma treatment is performed on one surface of a polyimide film with plasma containing oxygen, and the surface roughness of the polyimide film is 5 nm to 100 nm. (See Patent Document 2)
In recent years, low dielectric constant materials such as liquid crystal polymers and fluororesins have been used as flexible printed circuit board materials for high-frequency signal applications. However, as with polyimide, adhesion to metals such as copper is poor and high adhesion is obtained. There is a need for a method for forming a metal film on a substrate.

Further, a plastic film in which metal particles or a thin film is formed is required as a battery current collector material other than for flexible printed circuit boards, and it is desirable that the metal and the plastic film have high adhesion.
JP 2003-49013 A (Pages 24-30, FIGS. 1 and 2) JP-A-9-511163

  However, in the conventional configuration using an adhesive, when the metal conductor layer is processed into a necessary electric circuit pattern, the metal component constituting the metal conductor layer is likely to diffuse into the adhesive, so that the electric resistance at the adhesive portion. There is a problem in that insulation failure occurs at a portion of the electric circuit pattern that needs to be insulated. In the conventional configuration in which the metal conductor layer is formed on a metal having relatively good adhesion to polyimide such as nickel or chromium, nickel or chromium is not etched when the metal conductor layer is etched into a desired electric circuit pattern. It remains as a residue. Since nickel and chromium are electrically conductive, there is a problem that the insulation of the electric circuit pattern is caused by the residual nickel or chromium in the electric circuit pattern. The problem of residues can be solved by performing etching to remove nickel and chromium residues, but additional processing is required and extra processing costs are required, and the metal conductor layer is removed when removing nickel and chromium residues. There is a problem in that the electrical circuit pattern is excessively processed. If the electric circuit pattern of the metal conductor layer is processed excessively, there arises a problem that a necessary wiring dimension cannot be obtained.

  Further, in the manufacturing method of Patent Document 1, since a deep modified layer in which copper is implanted is formed on the polyimide surface, the electrical resistance on the polyimide surface is lowered by the implanted copper, which may cause an insulation failure of the electric circuit pattern. was there.

  Moreover, in the method described in Patent Document 2, a relatively high peel strength can be obtained. However, in the surface treatment using oxygen described as a desirable condition, a large amount of oxygen enters the polyimide surface and is formed on the polyimide surface. There was a possibility that the formed metal conductor layer was gradually oxidized with the lapse of time and the peel strength was lowered. In addition, in order to stably obtain a high peel strength required for a product by the method of Patent Document 2, it is necessary to roughen the surface to a surface roughness RMS value of 5 nm or more. When the surface roughness of the polyimide surface is rough and the metal conductor layer formed on the surface is formed in a shape along the uneven shape of the polyimide surface, the metal conductor layer is etched to create an electric circuit pattern The metal conductor layer constituting the electric circuit pattern has an uneven shape at the interface with the polyimide. In proportion to the increase in the frequency of the electric signal transmitted through the electric circuit pattern, the electric signal is transmitted only through the surface due to the skin effect, so if the metal conductor layer surface has an uneven shape, the electric signal is being transmitted. This will cause electrical noise. Since electrical noise increases in proportion to the size of the concavo-convex shape, the greater the roughness of the plastic film surface, the greater the noise. That is, when the polyimide surface is roughened as described in Patent Document 2, the adhesion between the polyimide and the metal conductor layer can be improved, but electrical noise is generated for high-frequency electrical signals, and the performance as an electric circuit board is improved. There was a problem that decreased. In order to flatten the surface of the metal conductor layer, the polyimide surface in contact with the metal conductor layer needs to be flattened, resulting in a decrease in adhesion between the metal conductor layer and the polyimide. That is, there are conflicting demands for reducing electrical noise by planarizing the polyimide surface and improving the adhesion between the metal conductor layer and the polyimide.

  The present invention solves the above-mentioned conventional problems, and does not interpose an adhesive or a different kind of metal between the metal conductor layer and the plastic film, and without greatly roughening the surface of the plastic film, It aims at providing the manufacturing method of the flexible printed circuit board which can acquire high adhesiveness between plastic films. In current collector applications, fluororesin is used as a plastic film, and platinum is sometimes used as a metal. However, the performance of the current collector element deteriorates due to the peeling of platinum fixed on the fluororesin. However, it was necessary to firmly fix platinum on the fluororesin. However, since the fluororesin has poor adhesion to most metals, it was difficult to firmly fix platinum on the fluororesin.

In order to solve the above-mentioned conventional problems, the flexible printed board of the present invention is a flexible printed board in which a metal conductor layer is formed on a plastic film, and fine irregularities are formed on the plastic film surface before the metal conductor layer is formed. In addition, the average interval between the convex portions or the concave portions of the fine unevenness is 10 nm to 80 nm.

  The flexible printed board of the present invention is a flexible printed board in which a metal conductor layer is formed on a plastic film, and an average interval between convex portions or an interval between concave portions on the plastic film surface is 10 nm to 80 nm. After forming the fine irregularities, a mixed layer of metal and the plastic film material is formed on the plastic film surface to a thickness of 0.01 μm or less, and a metal conductor layer is subsequently formed on the mixed layer. It is characterized by doing.

  The flexible printed board of the present invention is a flexible printed board in which a metal conductor layer is formed on a plastic film, and an average interval between convex portions or an interval between concave portions on the plastic film surface is 10 nm to 80 nm. After forming the fine irregularities, a mixed layer of metal and the plastic film material is formed on the plastic film surface to a thickness of 0.01 μm or less, and the first metal conductor layer is continuously formed on the mixed layer. And a third metal conductor layer having a predetermined thickness is formed on the first metal conductor layer.

  Moreover, the manufacturing method of the flexible printed circuit board of this invention is a flexible printed circuit board manufacturing method which forms a metal conductor layer on a plastic film, The average space | interval between convex parts on the said plastic film surface is 10 nm to 80 nm. After forming fine irregularities, a mixed layer of metal and the plastic film material is formed on the plastic film surface to a thickness of 0.01 μm or less, and then a metal conductor layer is formed. is there.

  According to the flexible printed circuit board and the method of manufacturing the flexible printed circuit board of the present invention, high adhesion can be obtained between the metal conductor layer and the plastic film without using a metal such as nickel or chromium or an adhesive. In flexible printed circuit board applications, since there is no metal such as an adhesive, nickel, or chromium, it is possible to produce a product that is less prone to insulation failure of the electrical wiring pattern due to metal diffusion or etching failure. Furthermore, compared with the conventional flexible printed circuit board using nickel or chromium, additional etching processing for eliminating the insulation failure of the electric circuit pattern is not required, so that the processing cost of the electric circuit pattern can be reduced. Moreover, since the metal can be firmly fixed on the plastic film in the current collector application, the life of the current collector element due to the peeling of the metal from the plastic film can be improved.

  Below, the flexible printed circuit board which consists of a metal and a plastic film of this invention, and the manufacturing method of a flexible printed circuit board are demonstrated in detail with drawing. As the plastic film material of the flexible printed circuit board used in the present invention, polyimide, polyester, polycarbonate, polyamide, epoxy resin liquid crystal polymer, or the like can be used. Moreover, copper, gold | metal | money, silver, aluminum, nickel, chromium, titanium, zinc etc. can be used as a metal material for the metal conductor layer used by this invention. In an Example, the case where a polyimide film and copper metal are used is demonstrated.

  FIG. 1 shows a configuration diagram of a flexible printed circuit board in Embodiment 1 of the present invention.

  In FIG. 1, 1 is a plastic film, and a polyimide film was used in this embodiment. Specific examples of the polyimide film include Ube Industries' brand name Upilex, DuPont's brand name Kapton, Kaneka Chemical's brand name Apical, and the like. In this embodiment, Upilex made by Ube Industries is used. Reference numeral 2 denotes a metal conductor layer, and copper is used in this embodiment.

  FIG. 2 shows a manufacturing procedure of the flexible printed board shown in FIG. Moreover, the manufacturing apparatus of the flexible printed circuit board used in the manufacturing procedure shown in FIG. 2 is shown in FIG.

  In FIG. 3, 7 is a vacuum chamber, 8 is a substrate holder made of a conductor for fixing a polyimide film, and 9 is a high frequency power source for applying high frequency power to the substrate holder 8 made of a conductor. 10 is an exhaust device for exhausting the vacuum chamber 7 to a vacuum, 11 is a main valve connecting the vacuum chamber 7 and the exhaust device 10, 12 is a vapor deposition boat for heating and evaporating metal, and 13 is for vapor deposition. 14 is a gas introduction pipe for introducing a predetermined gas into the vacuum chamber, 15 is a polyimide film, and 16 is a heating mechanism for heating and dehydrating the polyimide film, specifically a tungsten boat. A resistance heating mechanism using infrared light or an infrared lamp can be used. Reference numeral 17 denotes an electrical grounding portion.

  The manufacturing procedure of the flexible printed circuit board having the configuration of the present invention shown in FIG. 1 will be described in detail with reference to FIGS.

In FIG. 2, first, in step 3, the inside of the vacuum chamber 7 is evacuated. The pressure in the vacuum chamber 7 is set to 1.0 × 10 ⁻³ Pa or less. The polyimide film 15 is fixed in contact with the substrate holder 8 as shown in FIG.

Next, in step 4 of FIG. 2, the polyimide film 15 is dehydrated. For dehydration, the polyimide film 15 was heated at 140 ° C. for 3 hours using the heating mechanism 16. After the heating, cooling is performed until the temperature in the vacuum chamber 7 becomes 30 ° C. or lower, and vacuuming is performed until the pressure in the vacuum chamber 7 becomes 1.0 × 10 ⁻⁴ Pa or lower.

Next, as shown in step 5 of FIG. 2, the polyimide surface is plasma-treated. This plasma treatment roughens the polyimide surface. During the plasma treatment, nitrogen gas having a purity of 99.9% or more is introduced into the vacuum chamber 7, the pressure is set to 5.0 × 10 ⁻² Pa, and high-frequency power is applied to the substrate holder 8 that supports the polyimide film 15 by stable discharge means. Apply. By applying the high frequency power, glow discharge is generated in the vacuum chamber 7 and nitrogen plasma is generated. Along with the generation of nitrogen plasma, a first negative bias voltage is induced in the immediate vicinity of the polyimide film 15, and the polyimide film 15 is treated with nitrogen plasma. The polyimide surface is physically etched when nitrogen ions accelerated by a negative bias collide with the surface, and the polyimide surface is also chemically etched.

  The physical etching utilizes the effect of breaking molecular bonds on the polyimide surface when ions accelerated by a negative bias voltage generated in the vicinity of the polyimide film 15 collide with the polyimide surface. That is, the etching uses the kinetic energy of ions. If there is no variation in the amount of ions colliding on the polyimide surface, the polyimide surface is etched almost uniformly. In this embodiment, since the polyimide film is fixed within the uniform range of plasma, there is almost no physical etching variation. On the other hand, in chemical etching, ions that reach the polyimide surface break the molecular bond by drawing electrons from the polyimide surface, but electrons are drawn from the bond site with the weakest binding force near the ions. Therefore, the molecular bond is selectively broken. Further, when the polyimide surface is treated with nitrogen plasma, nitrogen ions may react with hydrogen atoms and oxygen atoms on the polyimide surface to form a compound, and the hydrogen atoms and oxygen atoms may be removed from the polyimide surface. Therefore, in the nitrogen plasma treatment, the removal effect of hydrogen atoms, oxygen atoms, and the like on the polyimide surface is also added, and the polyimide surface may be selectively etched to generate fine irregularities.

  In this embodiment, the plasma treatment is performed for 10 minutes with the first negative bias voltage set to 400V. However, the first negative bias voltage is adjusted to 200V to 1000V by adjusting the high frequency power applied to the substrate holder 8. It is possible to control to the value of the above, and an effect comparable to the effect of the present embodiment can be obtained.

Next, in Step 6 of FIG. 3, a copper film was formed. The procedure and conditions are as follows. First, the pressure in the vacuum chamber 7 is evacuated to 1.0 × 10 ⁻⁴ Pa or less. Next, copper was evaporated from the vapor deposition boat 8, and copper was vacuum-deposited on the polyimide film.

  In this example, the rate at which the copper thin film was formed was controlled between 0.1 nm / sec and 2.0 nm / sec. A film formation speed of 0.1 nm / sec or less is not practical because it takes too much time for production and increases costs. In addition, it seems that a flexible printed circuit board having a peel strength comparable to that in the case of film formation under conditions of 0.1 nm / sec to 2.0 nm / sec can be produced even at a film formation speed of 2.0 nm / sec or more. In the apparatus used in the example, when the film is formed at a speed of 2.0 nm / sec or more, the molten copper material overflows from the copper evaporation boat, so that the film formation speed is increased to 2.0 nm / sec or more. It was difficult. This can be improved by improving the copper evaporation mechanism.

  The flexible printed circuit board obtained by the production method of the present invention has a high plasma peel strength compared to the conventional method because the polyimide surface is subjected to nitrogen plasma treatment before forming a copper film and fine irregularities are formed on the polyimide surface. The inventors consider that the following is obtained.

  That is, it is considered that the peel strength is obtained by physical bonding. Physical bonding means 1) frictional resistance generated when copper thin film and polyimide are peeled off, and 2) resistance force generated by the action of micro unevenness on the surface of copper thin film digging up the polyimide surface when peeling copper thin film and polyimide. It is. The frictional resistance of 1) is considered to increase proportionally because the contact area increases due to the presence of fine irregularities. In addition, the digging effect of 2) is considered to be higher as there are many irregularities. For this verification, a sample in which the size of the fine irregularities on the polyimide film surface before the copper thin film was formed was prepared, and the peel strength was evaluated. In addition, it has been shown that the adhesion between metal and plastic film material is influenced not only by physical bonding factors but also by chemical bonding factors (that is, functional groups). The influence of nitrogen functional groups formed by plasma treatment on the adhesion was also investigated. Here, the chemical bond is a bonding force generated by bonding a cyano group formed by nitrogen plasma treatment and a copper atom. The inventors consider that the cyano group and the copper atom are coordinated via an unpaired electron pair of the cyano group.

  FIG. 4 shows the evaluation results of the comparison results between the fine unevenness intervals and the peel strength. It was found that a peel strength of 0.7 N / mm or higher, which is the same as or higher than that of the conventional flexible printed circuit board, can be obtained when the interval between the fine irregularities on the polyimide surface is between 10 nm and 80 nm. That is, it was found that the fine irregularities on the polyimide surface greatly contributed to the peel strength. When the interval between the fine irregularities is about 30 nm, the highest peel strength tends to be obtained. As a result of observing the size of the crystal of the copper thin film of the flexible printed circuit board produced under the conditions of the present invention with an electron microscope, the size of the crystal was about 30 nm in the portion adjacent to the mixed layer on the polyimide surface. When the crystal size and the unevenness size are close, it is considered that the effect of improving the adhesion due to the biting of the copper crystal into the fine unevenness shape of the polyimide surface is increased.

  Specifically, the following is presumed. When the size of the copper crystal is sufficiently smaller than the uneven shape on the polyimide surface, a plurality of crystals are bonded to one concave portion on the polyimide surface. In this case, when force is applied to the copper thin film so as to peel it off from the polyimide, the convex portion of the copper thin film surface made of a plurality of copper crystals formed in the concave portion of the polyimide surface operates to dig up the polyimide. It shows resistance to peeling, but there is a part where the bond between the crystals is weak between the copper crystals on the convex part of the copper thin film surface. The bond between crystals is broken by a weak force. Therefore, only a weaker resistance than the expected resistance can be obtained. In addition, when the size of the copper crystal is sufficiently larger than the size of the concave portion on the polyimide surface, the copper crystal does not enter the concave portion on the polyimide surface, so that when the copper thin film is peeled off, the resistance due to the biting of the copper crystal is reduced. It does not occur and the peel strength may decrease.

  The fine unevenness described in the present example is the interval between the convex portions or the concave portions on the polyimide surface shown in FIG. In an actual film, a regular uneven shape as shown in FIG. 5 is not formed, but a cone is combined or overlapped. (The fine irregularities are basically conical.) The size of the cone is large and small, and the size and distribution of the cone are determined by the relationship between the distribution of polyimide molecules and the chemical etching effect of nitrogen plasma. . Therefore, since it is impossible to measure the interval between the fine irregularities quantitatively even if the shape is simply measured, in this embodiment, the fine irregularities are measured by an atomic force microscope (AFM) with a measurement range of about 1 μm square. Measure and digitize the shape of the fine irregularities as height and position data, and calculate the average repetition interval of the fine irregularities by Fourier transforming the measured data to determine the average interval between the convex or concave portions Asked. That is, the distribution of (average) fine unevenness intervals can be obtained by displaying the frequency of the amplitude (height). Specifically, an AFM manufactured by Digital instrument can be used, and a result as shown in FIG. 6 is obtained after Fourier transform. In the case of FIG. 6, the fine unevenness size is 30 nm.

  Moreover, when the surface of the polyimide film treated with nitrogen plasma under the conditions of this example was measured using AFM, the arithmetic average roughness was 2 nm to 4 nm in a measurement range of 1 μm square.

  That is, in the formation of the fine unevenness according to the present invention, the unevenness interval, that is, the interval between the concave portions or the convex portions is 30 nm, and roughening on a very shallow surface where the average depth of the unevenness is about 2 nm to 4 nm is strong. Excellent peel strength was obtained.

As described above, if the size of the unevenness on the surface is smaller than the size of the copper crystal, it is considered that the peeling strength decreases because the effect of the copper crystal biting into the polyimide is reduced. In addition, when the plasma treatment is performed for a long time or when a strong plasma treatment is performed to form large irregularities on the surface, the polyimide surface is damaged by the plasma treatment, so a force acts to peel the copper thin film from the polyimide. In some cases, the surface of the polyimide may be destroyed. If the size of each recess is larger than the size of the copper crystal, a plurality of copper crystals are bonded to one recess on the polyimide surface. In this case, when force is applied to the copper thin film so as to peel it off from the polyimide, the convex portion of the copper thin film surface made of a plurality of copper crystals formed in the concave portion of the polyimide surface operates to dig up the polyimide. It shows resistance to peeling, but there is a part where the bond between the crystals is weak between the copper crystals on the convex part of the copper thin film surface. There is a possibility that bonds between crystals may be broken by a weak force. For this reason, the inventors believe that there is an optimum range for the separation strength to keep the peel strength at a high value. In the present invention, a correlation between the peel strength and the size of the in-plane method of unevenness was found.

  When a copper thin film is formed on a polyimide surface with the same surface roughness and different irregularities, the surface roughness is the same, so it is estimated that the peel strength will be about the same from reports in the conventional literature. The sample produced in this embodiment had a difference in peel strength between samples having the same surface roughness. That is, the change in peel strength could not be explained by the surface roughness. For this reason, the present inventors have found that the surface irregularities have a greater influence on the peel strength than the surface roughness.

  Next, in order to investigate the influence of the nitrogen functional group, the change in peel strength was investigated when the size of the fine irregularities on the surface was the same and the amount of the nitrogen functional group was changed. Functional groups were measured by X-ray photoelectron spectroscopy (XPS). A sample having a nitrogen functional group halved as compared with the sample surface-treated under the nitrogen bombardment condition described in Embodiment 1 was prepared by measuring the peel strength by setting the interval between the convex portions of the fine concavo-convex shape to 30 nm. The peel strength was 0.88 N / mm. That is, even if there is a double difference in the amount of the nitrogen functional group, the peel strength is 0.9 N / mm and 0.88 N / mm in the sample where the interval between the convex portions of the fine irregularities is 30 nm, which is almost constant. there were. In other words, it can be said that the influence of the nitrogen functional group is small. Moreover, in order to see the effect of functional groups other than a nitrogen functional group, after the polyimide surface was argon bombarded, the copper thin film was formed and the peel strength was measured. The peel strength was 0.2 N / mm or less. As a result of measuring the surface after argon bombardment by XPS, functional groups such as oxygen and nitrogen were confirmed, but the peel strength was as low as 0.2 N / mm or less. That is, it is considered that the main factor affecting the adhesion in the flexible printed circuit board manufactured in this embodiment is a physical bonding force. That is, it can be said that the adhesion is improved by the metal biting into the fine irregularities. Because of the mechanism that copper bite into the fine unevenness greatly contributes to adhesion, even with materials other than the materials used in this embodiment, specifically, materials such as fluororesin and liquid crystal polymer, The same effect can be expected if fine irregularities can be formed on the metal thin film forming surface.

  The reason why nitrogen plasma is used for the plasma treatment of the polyimide surface in this example is that the nitrogen plasma treatment is effective for forming fine irregularities on the polyimide surface. Nitrogen gas is inert, but when it is turned into plasma, it shows chemical reactivity with polyimide and selectively etches the polyimide surface. Therefore, necessary fine irregularities can be formed on the polyimide surface in a short time. For comparison, the shapes of polyimide surfaces after surface treatment of argon plasma treatment and nitrogen plasma treatment, which are usually used for surface treatment, were compared. In the argon plasma treatment, fine irregularities are not formed on the polyimide surface unlike the nitrogen plasma treatment. Since argon plasma does not have a chemical etching effect on polyimide, it is considered that the polyimide surface exposed to argon plasma is evenly shaved in the depth direction and fine irregularities are not formed. If the plasma has a chemical etching effect on polyimide other than nitrogen plasma, it can be easily estimated that the same fine unevenness forming effect as that of nitrogen plasma can be expected.

  As a method for obtaining high peel strength by a conventional method, for example, there is a method of Patent Document 1, but since it is necessary to form a mixed layer of copper and polyimide from the polyimide surface to a depth of 0.1 μm or more, at the time of etching processing of a copper thin film Copper in the mixed layer tends to remain as an etching residue, which may cause insulation failure in the electric circuit pattern. However, since the copper thin film is formed by vacuum deposition in the present embodiment, the copper crystal is not formed by being implanted into the polyimide, and the mixed layer as in Patent Document 1 is not generated. For this reason, there is a feature that the insulation failure of the electric wiring does not occur after the copper thin film is etched.

  In the present invention, even if the depth of the fine unevenness is as very small as 0.1 micron or less, by setting the interval between the unevenness, that is, the interval between the recesses or the protrusions to 10 to 80 nm, Could get.

  As described in Example 1, it is possible to obtain sufficient peel strength by simply vacuum-depositing copper on a polyimide film having fine irregularities formed thereon, but copper is ionized at the time of forming a copper thin film, and negative on the substrate. A higher peel strength can be obtained by forming a copper thin film while applying a voltage to implant copper ions into the substrate. In this example, a method for further improving the method of Example 1 and obtaining higher peel strength will be described in detail.

  FIG. 7 shows a configuration diagram of the flexible printed circuit board in the second embodiment of the present invention.

  In FIG. 7, 19 is a plastic film, 18 is a metal conductor layer, and copper was used in this embodiment. Reference numeral 20 denotes a mixed layer formed by implanting copper formed on the polyimide film surface.

  FIG. 8 shows a manufacturing procedure of the flexible printed board shown in FIG. Moreover, the manufacturing apparatus of the flexible printed circuit board used in the manufacturing procedure shown in FIG. 8 is shown in FIG.

  In FIG. 3, 7 is a vacuum chamber, 8 is a substrate holder made of a conductor for fixing a polyimide film, and 9 is a high frequency power source for applying high frequency power to the substrate holder 8 made of a conductor. 10 is an exhaust device for exhausting the vacuum chamber 7 to a vacuum, 11 is a main valve connecting the vacuum chamber 7 and the exhaust device 10, 12 is a vapor deposition boat for heating and evaporating metal, and 13 is for vapor deposition. 14 is a gas introduction pipe for introducing a predetermined gas into the vacuum chamber, 15 is a polyimide film, and 16 is a heating mechanism for heating and dehydrating the polyimide film, specifically a tungsten boat. A resistance heating mechanism using infrared light or an infrared lamp can be used. Reference numeral 17 denotes an electrical grounding portion.

  A manufacturing procedure of the flexible printed circuit board having the configuration of the present invention shown in FIG. 7 will be described in detail with reference to FIGS.

In FIG. 8, first, in step 21, the inside of the vacuum chamber 7 is evacuated. The pressure in the vacuum chamber 7 is set to 1.0 × 10 ⁻³ Pa or less. The polyimide film 15 is fixed in contact with the substrate holder 8 as shown in FIG.

Next, in step 22 of FIG. 8, the polyimide film 15 is dehydrated. For dehydration, the polyimide film 15 was heated at 140 ° C. for 3 hours using the heating mechanism 16. After the heating, cooling is performed until the temperature in the vacuum chamber 7 becomes 30 ° C. or lower, and vacuuming is performed until the pressure in the vacuum chamber 7 becomes 1.0 × 10 ⁻⁴ Pa or lower.

Next, as shown in step 23 of FIG. 8, the polyimide surface is plasma-treated. This plasma treatment roughens the polyimide surface. During the plasma treatment, nitrogen gas having a purity of 99.9% or more is introduced into the vacuum chamber 7, the pressure is set to 5.0 × 10 ⁻² Pa, and high-frequency power is applied to the substrate holder 8 that supports the polyimide film 15 by stable discharge means. Apply. By applying the high frequency power, glow discharge is generated in the vacuum chamber 7 and nitrogen plasma is generated.

  In the flexible printed board shown in FIG. 3, the first negative bias voltage is induced in the very vicinity of the polyimide film 15 together with the generation of nitrogen plasma, and the polyimide film 15 is subjected to nitrogen plasma treatment. The polyimide surface is physically etched by the impact of negative bias accelerated nitrogen ions on the surface, and because the nitrogen plasma is chemically reactive to the polyimide, the polyimide surface is also chemically etched. . Since a portion of the polyimide polymer is selectively etched by the chemical etching effect, fine irregularities are formed on the polyimide surface due to the difference between the portion that is easily etched by nitrogen plasma and the portion that is difficult to etch. In this embodiment, the plasma treatment was performed for 10 minutes with the first negative bias voltage set to 400V. However, the high frequency power applied to the substrate holder 8 as the first negative bias voltage was adjusted to 200V to 1000V. It is possible to control, and the same effect as that of the present embodiment can be obtained.

Next, in step 24 of FIG. 8, copper is implanted. In this example, the copper film formation in step 25 and the copper implantation in step 24 were continuously performed. The procedure and conditions are as follows. After the nitrogen plasma treatment described above, first, the pressure in the vacuum chamber 7 is evacuated to 1.0 × 10 ⁻⁴ Pa or less. Argon gas is introduced after evacuation, the pressure in the vacuum chamber 7 is set to 1.0 × 10 ⁻² Pa, copper is evaporated from the evaporation boat 12, and at the same time high frequency power is applied to the substrate holder 8 that supports the polyimide film 15. Apply. Application of the high frequency voltage causes glow discharge in the vacuum chamber 7, and argon and copper plasma is generated in the chamber. Along with the generation of argon and copper plasma, a second negative bias voltage is induced in the immediate vicinity of the polyimide film 15, so that argon ions and copper ions in the plasma are accelerated by the second negative bias voltage. Collides with the polyimide film surface. In this example, the second negative bias voltage was set to 400 V to form a copper film. A copper thin film is formed on the polyimide film surface by the effect that copper ions collide with the polyimide film surface to form a copper thin film and the effect that non-ionized copper is vacuum deposited.

  In this example, the rate at which the copper thin film was formed was controlled between 0.1 nm / sec and 1.0 nm / sec. Although a copper thin film is formed by the above operation, since a part of ionized copper is implanted into the polyimide surface at the initial stage of copper film formation, a mixed layer in which copper is implanted into the polyimide surface according to the above procedure and conditions. 20 is formed, and a copper thin film is formed on the mixed layer 20 by continuing the film formation.

  The inventor presumes that a high peel strength can be obtained in this embodiment because of the following copper thin film formation mechanism. In the initial stage of copper thin film formation, the copper ions accelerated by the second negative bias voltage collide with the polyimide surface, partly adhere to the surface as a copper thin film, part is implanted inside the polyimide, part is Reflected after collision with the surface. For copper ions implanted inside the polyimide, the depth at which the copper ions are implanted is proportional to the magnitude of the second negative bias voltage induced in the film. The greater the second negative bias voltage is, the deeper the copper ions are implanted. In the process of forming the copper thin film, as described above, a copper thin film is formed on the polyimide surface while copper ions are implanted into the polyimide. When the film formation is further continued, the total amount of copper ions implanted on the polyimide surface increases, and the implanted copper ions combine to grow crystals. The copper thin film on the polyimide surface becomes thicker. A part of the copper crystal grown inside the polyimide is bonded to the copper thin film on the polyimide surface. Bonding of the copper crystal grown inside the polyimide and the copper thin film on the polyimide surface results in a structure in which a portion of the copper thin film has digged into the polyimide, thereby improving the adhesion between the copper thin film and the polyimide due to the anchor effect. The closer the copper crystal is formed to the deeper part inside the polyimide, the better the adhesion. Therefore, in order to obtain high adhesion, the second negative bias voltage induced in the polyimide film 15 should be increased. It is effective.

  However, when an electric circuit pattern is formed by etching a flexible printed circuit board having a structure in which copper crystals are formed in a deep portion inside the polyimide, the copper crystals in the deep portion inside the polyimide are difficult to be etched and are likely to remain as a residue. The copper crystal remaining in the polyimide without being etched reduces the insulation of the polyimide and causes an insulation failure of the electric circuit pattern. Therefore, in order to maintain the insulation as an electric circuit board while improving the peel strength, the depth of penetration of the copper crystal into the polyimide can be removed by etching without leaving a residue in the etching process when producing the electric circuit pattern. It is necessary to control the depth range.

  It is better to be shallow in order to leave no residue in the etching process when creating the electric circuit pattern, and deeper to improve the adhesion between the copper thin film and the polyimide due to the anchor effect. Control to a certain depth range.

  In the flexible printed circuit board produced by the method of this example, the cross section was observed at a magnification of 100,000 times with an electron microscope. As a result, the desired performance was obtained by forming the copper crystal near the surface having a depth of 0.01 μm or less. Turned out to be.

  In the substrate manufactured by the method of this example, the copper crystal was formed near the surface having a depth of 0.01 μm or less. As a result of evaluating the peel strength of the flexible printed circuit board produced by the method of the present embodiment by the peel strength test method shown in JIS C6471, it is 1.2 N / mm. When the peel strength of a conventional flexible printed circuit board using nickel or chromium as an intermediate layer is evaluated by the same method, the peel strength is 0.7 N / mm. It was found that peel strength can be obtained. Moreover, even if compared with the flexible printed circuit board produced by the method of Embodiment 1, high peel strength is obtained. Since the mixed layer was formed between the copper thin film and the polyimide film, it is considered that the peel strength was improved by the anchor effect.

  In order to obtain sufficient peel strength in the conventional method described in Patent Document 1, a mixed layer in which the surface of a polyimide film into which 0.1 μm or more of copper is implanted is modified is required. The flexible printed circuit board can obtain a peel strength of 1.2 N / mm with a thin mixed layer of 0.01 μm.

  Since the flexible printed circuit board obtained by the manufacturing method of the present invention has a polyimide surface subjected to nitrogen plasma treatment before forming a copper film, a large number of fine irregularities having an interval of 10 nm to 80 nm are formed on the polyimide surface. Even with a modified mixed layer thinner than the above condition, high peel strength is obtained. Furthermore, since a mixed layer region in which both materials are mixed is formed between the polyimide film and the copper thin film by implanting copper ions on the surface having fine irregularities, a high peel strength is obtained by the anchor effect. It is thought that there is.

  The same electrical circuit pattern was applied to the flexible printed circuit board produced by the method of this embodiment and the same flexible printed circuit board in which copper ions were implanted to a depth of 0.05 μm at a deposition voltage of 1000 V after the same nitrogen plasma treatment as in this embodiment. As a result of observing the mixed layer of the etched part, the copper in the mixed layer was removed by etching in 5 minutes in the flexible printed circuit board produced by the method of this example. The sample implanted with copper ions to the depth required an etching time of 10 minutes. A ferric chloride solution having a solution temperature of 40 ° C. was used for the etching.

  That is, the flexible printed circuit board produced in this example can etch the electric circuit pattern in a shorter time than the flexible printed circuit board produced by the manufacturing method described in Patent Document 1 in which a mixed layer is formed to have a thickness of 0.1 μm or more. It can be said. Therefore, the processing cost is reduced. Furthermore, since the etching time is short, the dimensional change due to excessive etching of the electric circuit pattern portion where the etching process is completed can be suppressed to a small level while etching the copper in the mixed layer. Also, copper in the mixed layer can be easily removed by etching, and copper hardly remains in the mixed layer, so that defects due to a decrease in insulation are less likely to occur.

  In order to use a substrate having a copper thin film formed on the polyimide produced as described above by processing an electric circuit pattern, the thickness of the copper thin film needs to be about 10 μm. In this example, a 5000-thick copper thin film was formed by the apparatus shown in FIG. 3, and then the copper thin film was formed thick by electroplating. Since the electroplating copper thin film formation speed is about 10 times faster than the vacuum film forming apparatus as shown in FIG. 3, a product can be manufactured in a short time. Therefore, the product can be manufactured at a low cost.

  As described above, the flexible printed circuit board of the present invention is formed of a plastic film and a metal conductor layer, and is not provided with an adhesive layer or an intermediate layer for enhancing adhesion between the plastic film and the metal conductor layer, and nitrogen plasma. A metal conductor layer having desired adhesion to the plastic film can be formed by providing fine irregularities on the surface of the plastic film at intervals of 10 to 80 nm by the treatment. Further, it is possible to obtain higher adhesion by forming a shallow mixed layer with a modified mixed layer thickness of 0.01 μm or less on the plastic film surface, and poor insulation in the mixed layer after etching processing A flexible printed circuit board that can eliminate the above can be realized.

  That is, since the mixed layer is thin while having a predetermined peel strength, it is possible to realize a flexible printed board that can eliminate insulation failure in the mixed layer after etching.

  The flexible printed circuit board and the method for producing a flexible circuit board according to the present invention can provide a flexible printed circuit board that has excellent insulation and sufficient peel strength, and is useful as a material for electrical wiring inside electronic equipment. It is useful as a material for electric wiring inside an electronic device having a simple electric circuit pattern.

Sectional drawing of the flexible printed circuit board in Example 1 of this invention The flowchart which shows the manufacturing method of the flexible printed circuit board in Example 1 of this invention. The figure which shows typically the manufacturing apparatus of the flexible printed circuit board in Example 1 and Example 2 of this invention. The figure which shows the relationship between the surface roughness of the polyimide film surface in Example 1 of this invention, and peeling strength The figure which shows typically the surface roughness of the polyimide film surface in Example 1 of this invention The figure for showing distribution of the surface roughness of the polyimide film surface in Example 1 of the present invention Sectional drawing of the flexible printed circuit board in Example 2 of this invention The flowchart which shows the manufacturing method of the flexible printed circuit board in Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plastic film 2 Metal conductor layer 7 Vacuum chamber 8 Substrate holder 9 High frequency power supply 10 Exhaust device 11 Main valve 12 Deposition boat 13 Deposition metal 14 Gas introduction pipe 15 Polyimide film 16 Heating mechanism 17 Electrical grounding part

Claims (14)

In a flexible printed circuit board in which a metal conductor layer is formed on a plastic film,
The flexible film is characterized in that fine irregularities are formed on the plastic film surface before forming the metal conductor layer, and an average interval between the convex portions of the fine concave and convex portions or an interval between the concave portions is 10 nm to 80 nm. Printed board. The flexible printed circuit board according to claim 1, wherein the fine unevenness is formed by roughening the plastic film surface by plasma treatment. The flexible printed circuit board according to claim 2, wherein the plasma treatment is a nitrogen plasma treatment. The flexible printed circuit board according to claim 3, wherein the plastic film is heated and dehydrated in a vacuum container before the plasma treatment. The flexible printed circuit board according to claim 1, wherein the metal conductor layer is formed at a rate of 0.1 nm to 2.0 nm / sec. In a flexible printed circuit board in which a metal conductor layer is formed on a plastic film,
After forming fine irregularities having an average interval between protrusions or recesses of 10 nm to 80 nm on the plastic film surface, a mixed layer of metal and the plastic film material on the plastic film surface Is formed to a thickness of 0.01 μm or less, and a metal conductor layer is subsequently formed on the mixed layer. The flexible printed circuit board according to claim 6, wherein the mixed layer is formed by depositing metal by plasma treatment using an inert gas gas. In the inert gas plasma treatment, a mixed gas containing an inert gas as a main component is used to apply a high frequency power to a substrate holder that supports the plastic film to cause glow discharge. 8. The flexible print according to claim 7, wherein a metal comprising an alloy as a main component is melted, the metal is ionized by ionized plasma existing in the glow discharge, and a metal thin film is deposited on the plastic film. substrate The flexible printed circuit board according to claim 8, wherein the thickness of the mixed layer is adjusted by controlling the high-frequency power. In a flexible printed circuit board in which a metal conductor layer is formed on a plastic film,
After forming fine irregularities having an average interval between protrusions or recesses of 10 nm to 80 nm on the plastic film surface, a mixed layer of metal and the plastic film material on the plastic film surface Is formed to a thickness of 0.01 μm or less, a first metal conductor layer is subsequently formed on the mixed layer, and a third metal conductor layer having a predetermined thickness is formed on the first metal conductor layer. Forming a flexible printed circuit board. In the flexible printed circuit board manufacturing method of forming a metal conductor layer on a plastic film, fine irregularities having an average interval between convex portions of 10 nm to 80 nm are formed on the plastic film surface, and then on the plastic film surface. A method for producing a flexible printed circuit board, comprising forming a mixed layer of a metal and the plastic film material to a thickness of 0.01 μm or less, and subsequently forming a metal conductor layer. The method for manufacturing a flexible printed circuit board according to claim 11, wherein the fine irregularities are formed by roughening the plastic film surface by plasma treatment. The method for manufacturing a flexible printed circuit board according to claim 12, wherein the plasma treatment is a nitrogen plasma treatment. The mixed layer uses a mixed gas containing an inert gas as a main component, applies high frequency power to the plastic film to cause glow discharge, and under the glow discharge, a metal made of copper or an alloy containing copper as a main component. The method for producing a flexible printed circuit board according to claim 11, wherein the metal is ionized by ionized plasma existing in the glow discharge and a metal thin film is deposited on the plastic film.

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