JP2018029139A - Printed wiring board substrate and method for manufacturing printed wiring board substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate for a wiring board for a print circuit board which is relatively inexpensive and is excellent in sticking force between a base film and a metal layer.SOLUTION: A substrate for a print circuit board includes a base film including polyimide as a main component, a metal particle sintered body layer directly laminated on this base film, and an electric plating layer directly laminated on the metal particle sintered body layer. A ring opening rate of an imide ring of polyimide on a surface layer in a side in which the metal particle sintered body layer on the base film is laminated, is 5% or more and 30% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a printed wiring board substrate and a method for manufacturing a printed wiring board substrate.

  For example, a metal layer made of metal or the like is laminated on the surface of an insulating base film made of resin or the like, and a conductive pattern is formed by etching the metal layer to obtain a printed wiring board. Printed wiring board substrates are widely used.

  A printed wiring board having a high peel strength between the base film and the metal layer so that the metal layer does not peel from the base film when bending stress acts on the printed wiring board formed using such a printed wiring board substrate. Substrates are required.

  In recent years, with the miniaturization and high performance of electronic devices, it has been required to increase the density of printed wiring boards. In the printed wiring board having a high density, the conductive pattern easily peels off from the base film as the conductive pattern becomes finer. Therefore, there is a demand for a printed wiring board substrate that can form a fine conductive pattern and has excellent adhesion between a metal layer and a base film as a printed wiring board substrate that satisfies such a demand for higher density.

  In response to such a demand, a metal thin film layer and a base layer are formed by forming a copper thin film layer on the surface of the base film using, for example, a sputtering method, and forming a copper thick film layer thereon using an electroplating method. A technique for increasing the adhesion between the film and the film is known. However, it is known that when a metal layer is laminated directly on the base film, the main metal atoms of the metal layer diffuse into the base film with the passage of time, reducing the adhesion between the metal layer and the base film. Yes.

  Therefore, a technique has been proposed in which a thin film of chromium is deposited by sputtering on the joint surface of the copper foil to the base film and thermocompression bonded to the base film (see Japanese Patent Application Laid-Open No. 2000-340911). In this way, by interposing a thin film of a metal different from the main metal of the metal layer at the interface between the metal layer and the base film, the movement of the main metal to the base film is hindered. The effect which suppresses the fall of the adhesiveness between the metal layer and base film by the spreading | diffusion to the base film of a main metal atom is acquired.

JP 2000-340911 A

  In the configuration described in the above publication, a chromium thin film is formed on the surface of the copper foil using a sputtering method, so that a vacuum facility is required, and the costs for construction, maintenance, operation, etc. of the facility are high. Further, in terms of equipment, there is a limit to increasing the size of the substrate.

  The present invention has been made on the basis of the circumstances as described above, and is a printed wiring board substrate that is relatively inexpensive and excellent in adhesion between the base film and the metal layer, and a method for manufacturing the printed wiring board substrate. The issue is to provide.

  A printed wiring board substrate according to an aspect of the present invention made to solve the above problems includes a base film mainly composed of polyimide, a metal particle sintered body layer directly laminated on the base film, and An electroplating layer directly laminated on the metal particle sintered body layer, and the ring opening ratio of the polyimide imide ring on the surface layer on the side of the base film on which the metal particle sintered body layer is laminated is 5% or more and 30% It is as follows.

  Moreover, the manufacturing method of the board | substrate for printed wiring boards which concerns on 1 aspect of this invention made | formed in order to solve the said subject is an alkali treatment process which alkali-treats the surface of the base film which has a polyimide as a main component, and the said alkali treatment A metal particle sintered body layer forming step in which a metal particle dispersion is applied to the surface of the base film after the process and firing, and a metal particle sintered body layer formed in the metal particle sintered body layer forming step are covered. A printed wiring board substrate manufacturing method comprising an electroplating layer forming step of electroplating as an adherend, wherein the imide ring opening rate of the surface layer of the base film is 5% or more and 30% in the alkali treatment step. It adjusts below and performs metal plating directly to the said metal-particle sintered compact layer at the said electroplating layer formation process.

  The printed wiring board substrate according to one embodiment of the present invention is relatively inexpensive and has excellent adhesion between the base film and the metal layer. Moreover, the method for manufacturing a printed wiring board substrate according to one embodiment of the present invention can manufacture a printed wiring board substrate having excellent adhesion between the base film and the metal layer at a relatively low cost.

FIG. 1 is a schematic cross-sectional view showing a printed wiring board substrate according to an embodiment of the present invention. FIG. 2 is a flowchart showing the procedure of the method for manufacturing the printed wiring board substrate of FIG. FIG. 3 is a graph showing the relationship between the alkali treatment time of the base film and the ring opening rate of the imide ring of the polyimide. FIG. 4 is a graph showing the relationship between the ring opening ratio of the polyimide imide ring of the base film, the peel strength of the metal layer, and the pinhole ratio.

[Description of Embodiment of the Present Invention]
A printed wiring board substrate according to an aspect of the present invention includes a base film mainly composed of polyimide, a metal particle sintered body layer directly laminated on the base film, and a layer laminated directly on the metal particle sintered body layer. An opening ratio of the polyimide imide ring on the surface layer on the side where the metal particle sintered body layer of the base film is laminated is 5% or more and 30% or less.

  In the printed wiring board substrate, the imide ring of the base film is opened when the ring opening ratio of the polyimide imide ring on the surface layer on the side where the metal particle sintered body layer of the base film is laminated is within the above range. Metal atoms are relatively easily bonded to the ring portion, and the strength reduction of the base film due to the opening of the imide ring is relatively small. Thereby, the adhesive force between the base film and the metal particle sintered body layer is relatively large, and the metal particle sintered body layer is hardly eroded by the plating solution. For this reason, the printed wiring board substrate can be manufactured at a relatively low cost by directly laminating the electroplating layer on the metal particle sintered body layer, but the laminate of the metal particle sintered body layer and the electroplating layer. The adhesion of the metal layer formed as a base film to the base film is relatively large.

  The porosity of the metal particle sintered body layer is preferably 0.001% or more and 2% or less. As described above, when the porosity of the metal particle sintered body layer is within the above range, the formation of the metal particle sintered body layer is relatively easy, and the erosion by the plating solution is more reliably suppressed. The adhesion between the base film and the metal layer can be further improved.

  The main component of the metal particle sintered body layer and the electroplating layer may be copper. Thus, when the main component of the metal particle sintered body layer and the electroplating layer is copper, a metal layer having relatively high conductivity can be formed at a relatively low cost.

  The average thickness of the metal particle sintered body layer is preferably 30 nm or more and 500 nm or less. As described above, when the average thickness of the metal particle sintered body layer is within the above range, the continuity of the metal particle sintered body layer can be secured and the metal particle layer can be reinforced by metal plating. it can.

  The peel strength between the base film and the metal particle layer is preferably 3 N / cm or more. Thus, when the peeling strength between the base film and the metal particle layer is equal to or higher than the lower limit, it is possible to effectively prevent disconnection of the conductive pattern of the printed wiring board formed using the printed wiring board substrate. .

  Moreover, the manufacturing method of the board | substrate for printed wiring boards which concerns on 1 aspect of this invention made | formed in order to solve the said subject is an alkali treatment process which alkali-treats the surface of the base film which has a polyimide as a main component, and the said alkali treatment A metal particle sintered body layer forming step in which a metal particle dispersion is applied to the surface of the base film after the process and firing, and a metal particle sintered body layer formed in the metal particle sintered body layer forming step are covered. A printed wiring board substrate manufacturing method comprising an electroplating layer forming step of electroplating as an adherend, wherein the imide ring opening rate of the surface layer of the base film is 5% or more and 30% in the alkali treatment step. It adjusts below and performs metal plating directly to the said metal-particle sintered compact layer at the said electroplating layer formation process.

  The printed wiring board substrate manufacturing method includes the step of adjusting the base film and metal particle sintering by adjusting the ring opening ratio of the polyimide imide ring on the surface layer of the base film to 5% or more and 30% or less in the alkali treatment step. The adhesion with the body layer can be made relatively large, and the metal particle sintered body layer is hardly eroded by the plating solution in the electroplating layer forming step. For this reason, the method for manufacturing a printed wiring board substrate, although the electroplating layer can be directly laminated on the metal particle sintered body layer and the printed wiring board substrate can be manufactured relatively inexpensively, The adhesion of the metal layer formed as a laminate of the body layer and the electroplating layer to the base film can be made relatively large.

  The dispersant for the metal particle dispersion used in the metal particle sintered body layer forming step may be a graft copolymer having a polyalkyleneimine as a main chain and a polyalkylene oxide compound as a side chain. Thus, the dispersant for the metal particle dispersion used in the metal particle sintered body layer forming step is a graft copolymer having a polyalkyleneimine as a main chain and a polyalkylene oxide compound as a side chain. The adhesion between the base film and the metal particle sintered body layer can be further improved.

Here, the “main component” means a component having the largest mass content, and is preferably a component contained in 90% by mass or more. Further, the “opening ratio of the imide ring of the polyimide on the surface layer” is the peak intensity around 1494 cm ⁻¹ in the absorption intensity spectrum at an incident angle of 45 ° by the infrared total reflection absorption measurement method on the surface of the base film, Pb, This is a value calculated as {1− (0.89 × Pc / Pb) × 100 [%]}, where Pc is the peak intensity in the vicinity of a wave number of 1705 cm ⁻¹ . The “void ratio” means the total area ratio of voids in an arbitrary cross section. “Peel strength” is a value measured based on JIS-K6854-2 (1999) “Adhesive-peeling adhesion strength test method-2 part: 180 degree peeling” as a flexible adherend. It is.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of a printed wiring board substrate and a printed wiring board manufacturing method according to the present invention will be described in detail with reference to the drawings.

[Substrates for printed wiring boards]
A printed wiring board substrate according to an embodiment of the present invention shown in FIG. 1 includes a base film 1 mainly composed of polyimide, a metal particle sintered body layer 2 directly laminated on the base film 1, and the metal particles. And an electroplating layer 3 directly laminated on the sintered body layer 2. Hereinafter, the laminate of the metal particle sintered body layer 2 and the electroplating layer 3 may be referred to as a metal layer.

<Base film>
In the base film 1, at least the surface on which the metal particle sintered body layer 2 is laminated is modified, and a part of the polyimide imide ring on the surface layer is opened. Such modification can be performed by a known treatment method such as alkali treatment or plasma treatment.

(Polyimide)
As the polyimide as the main component of the base film 1, thermosetting polyimide (also referred to as condensation type polyimide) or thermoplastic polyimide can be used. Among these, thermosetting polyimide is preferable from the viewpoint of heat resistance, tensile strength, tensile elastic modulus, and the like.

  The polyimide may be a homopolymer consisting of one type of structural unit or a copolymer consisting of two or more types of structural units, or a blend of two or more types of homopolymers. However, what has a structural unit represented by following formula (1) is preferable.

  The structural unit represented by the above formula (1) synthesizes polyamic acid, which is a polyimide precursor, using, for example, pyromellitic dianhydride and 4,4′-diaminodiphenyl ether, and imidizes it by heating or the like. It is obtained by doing.

  As a minimum of content of the above-mentioned structural unit, 10 mass% is preferred, 15 mass% is more preferred, and 18 mass% is still more preferred. On the other hand, as an upper limit of content of the said structural unit, 50 mass% is preferable, 40 mass% is more preferable, and 35 mass% is further more preferable. When content of the said structural unit is less than the said minimum, there exists a possibility that the intensity | strength of the base film 1 may become inadequate. Conversely, if the content of the structural unit exceeds the upper limit, the flexibility of the base film 1 may be insufficient.

  The lower limit of the polyimide imide ring opening rate on the surface layer of the base film 1 on which the metal particle sintered body layer 2 is laminated is 5%, preferably 6%, more preferably 7%. On the other hand, the upper limit of the imide ring opening rate of the polyimide on the surface layer of the base film 1 on which the metal particle sintered body layer 2 is laminated is 30%, preferably 25%, more preferably 20%. When the ring-opening ratio of the polyimide imide ring on the surface layer of the base film 1 on which the metal particle sintered body layer 2 is laminated is less than the lower limit, the adhesion between the base film 1 and the metal particle sintered body layer 2 May not be improved sufficiently. Conversely, when the ring-opening rate of the polyimide imide ring on the surface layer on which the metal particle sintered body layer 2 of the base film 1 is laminated exceeds the above upper limit, the strength of the surface layer portion of the base film 1 decreases, There is a possibility that the metal layer is easily peeled off due to the base material destruction (the metal particle sintered body layer 2 and the electroplating layer 3 are peeled off from the portion other than the surface layer of the base film 1 together with the surface layer portion of the base film 1).

The ring-opening rate of the imide ring on the surface layer of the base film 1 can be measured by an infrared total reflection absorption measurement method. Specifically, the ring opening rate R [%] of the imide ring is a peak intensity in the vicinity of a wave number of 1494 cm ⁻¹ in an absorption intensity spectrum at an incident angle of 45 ° according to the infrared total reflection absorption measurement method on the surface of the base film 1. The peak intensity around Pb and the wave number of 1705 cm ⁻¹ can be calculated by the following equation (1) as Pc.

  R = 1− (0.89 × Pc / Pb) × 100 (1)

The above formula (1) will be described in detail. The peak intensity Pb near the wave number 1494 cm ⁻¹ in the absorption intensity spectrum is a peak intensity indicating the number of benzene rings, and does not change even when the imide ring of the polyimide is opened. Value. On the other hand, the peak intensity Pc near the wave number of 1705 cm ⁻¹ in the absorption intensity spectrum corresponds to the stretching vibration of the carbonyl group of the imide bond, and is the peak intensity indicating the number of carbonyl groups of the imide bond. This value decreases when the ring is opened. The ratio to the peak intensity Pb around wavenumber 1494cm ^-1 peak intensity Pc around wave number 1705 cm ^-1 in the ring opening of 0% of a polyimide which is not at all opened (Pc / Pb) is about 1.13. For this reason, by multiplying the peak ratio (Pc / Pb) in the absorption intensity spectrum of the base film 1 by 0.89 which is the reciprocal of 1.13, the ring is not opened in the polyimide of the surface layer of the base film 1. The ratio of benzene rings can be calculated.

  In addition, the ring-opening rate of the polyimide on the surface layer of the base film 1 in the printed wiring board substrate or the printed wiring board prepared using the printed wiring board substrate is determined by etching to be a metal layer (in the case of a printed wiring board, a metal By removing the conductive pattern formed using the layer, measurement by the infrared total reflection absorption measurement method can be performed.

  As an acidic solution used for etching for removing the metal layer, an acidic etching solution generally used for removing the metal layer can be used, and examples thereof include a copper chloride solution, hydrochloric acid, sulfuric acid, aqua regia and the like.

  As a minimum of the temperature of the above-mentioned etching solution at the time of etching, 10 ° C is preferred and 20 ° C is more preferred. On the other hand, the upper limit of the temperature of the etching solution is preferably 90 ° C, more preferably 70 ° C. When the temperature of the etching solution is less than the lower limit, the time required for etching becomes long and workability may be deteriorated. On the contrary, when the temperature of the etching solution exceeds the upper limit, the energy cost for temperature adjustment may increase unnecessarily.

  The lower limit of the etching time is preferably 1 minute, and more preferably 10 minutes. On the other hand, the upper limit of the etching time is preferably 60 minutes, and more preferably 30 minutes. When the said etching time is less than the said minimum, there exists a possibility that the density | concentration of etching liquid may become high and it may become difficult to handle. Conversely, if the etching time exceeds the upper limit, workability may be reduced.

<Sintered metal particle layer>
The metal particle sintered body layer 2 is compared with the surface of the base film 1 by applying and firing a metal particle dispersion (ink) containing metal particles on the surface of the base film 1 where the polyimide imide ring is opened. Can be formed easily and inexpensively.

  As the main metal of the metal particles of the metal particle sintered body layer 2, for example, copper (Cu), nickel (Ni), aluminum (Al), gold (Au), silver (Ag), or the like can be used. Among these, copper is preferably used as a relatively inexpensive metal that has good conductivity and excellent adhesion to the base film 1 and that can be easily patterned by etching. In addition, a main metal means the metal with the largest mass content rate, Preferably it is contained 90 mass% or more.

  As a minimum of the porosity of metal particle sintered compact layer 2, 0.001% is preferred and 0.01% is more preferred. On the other hand, the upper limit of the porosity of the metal particle sintered body layer 2 is preferably 2%, and more preferably 1%. When the porosity of the metal particle sintered body layer 2 is less than the above lower limit, the production cost may increase unnecessarily. Conversely, when the porosity of the metal particle sintered body layer 2 exceeds the above upper limit, the adhesion between the base film 1 and the metal particle sintered body layer 2 may be insufficient, or the metal particle sintered body layer 2 May be easily broken and the electroplating layer 3 may be peeled off.

  As a minimum of average thickness of metal particle sintered compact layer 2, 30 nm is preferred and 50 nm is more preferred. On the other hand, the upper limit of the average thickness of the metal particle sintered body layer 2 is preferably 500 nm, and more preferably 300 nm. When the average thickness of the metal particle sintered body layer 2 is less than the lower limit, there are many portions where the metal particles do not exist in a plan view, and the conductivity may be lowered. Conversely, if the average thickness of the metal particle sintered body layer 2 exceeds the above upper limit, it may be difficult to sufficiently reduce the porosity of the metal particle sintered body layer 2, or the metal layer is unnecessarily thick. There is a risk.

  The lower limit of the peel strength (adhesion force) between the base film 1 and the metal particle sintered body layer 2 is preferably 3 N / cm, and more preferably 5 N / cm. On the other hand, the upper limit of the peel strength between the base film 1 and the metal particle sintered body layer 2 is preferably 25 N / cm, and more preferably 20 N / cm. When the peeling strength between the base film 1 and the metal particle sintered body layer 2 is less than the lower limit, the conductive pattern of the printed wiring board manufactured using the printed wiring board substrate may be easily peeled off. On the contrary, when the peel strength between the base film 1 and the metal particle sintered body layer 2 exceeds the upper limit, a special treatment for improving the adhesion between the base film 1 and the metal particle sintered body layer 2 is necessary. Therefore, the manufacturing cost of the printed wiring board substrate may be unnecessarily increased.

(Electroplating layer)
The electroplating layer 3 is formed by further laminating a metal by electroplating on the surface of the metal particle sintered body layer 2 opposite to the base film 1. With the electroplating layer 3, the thickness of the metal layer can be adjusted easily and accurately. In addition, the thickness of the metal layer can be increased in a short time by using electroplating.

  As the main metal of the electroplating layer 3, for example, copper, nickel, aluminum, gold, silver, or the like can be used. Among them, copper that is relatively inexpensive and excellent in conductivity is preferably used. The main metal of the electroplating layer 3 is preferably the same metal as the main metal of the metal particle sintered body layer 2.

  The thickness of the electroplating layer 3 is set according to the type and thickness of the conductive pattern required for the printed wiring board formed using the printed wiring board substrate, and is not particularly limited. Generally, the lower limit of the average thickness of the electroplating layer 3 is preferably 1 μm and more preferably 2 μm. On the other hand, the upper limit of the average thickness of the electroplating layer 3 is preferably 200 μm, and more preferably 100 μm. If the average thickness of the electroplating layer 3 is less than the lower limit, the metal layer may be easily damaged. Conversely, when the average thickness of the electroplating layer 3 exceeds the above upper limit, the printed wiring board substrate may be unnecessarily thick, or the printed wiring board substrate may have insufficient flexibility. is there.

  In addition, when the metal particle sintered body layer 2 and the electroplating layer 3 are formed of the same metal, the metal particle sintered body layer 2 and the electroplating layer 3 have crystallite diameters when observed with an electron microscope. The difference can be determined relatively easily. Specifically, the metal particle sintered body layer 2 has an average crystallite size on the order of nm smaller than the particle size of the metal particles as a raw material, whereas the electroplating layer 3 has an average crystallite size on the order of μm or more. Have The “average crystallite diameter” is a value measured according to JIS-H7805 (2005).

<Advantages>
The substrate for the printed wiring board has a base film 1 and a metal that have a metal ring sintered body layer 2 of the base film 1 on the side where the imide ring of the polyimide on the surface layer is laminated within a certain range. The adhesive force with the particle sintered body layer 2 is relatively large, and the metal particle sintered body layer 2 is hardly eroded by the plating solution. For this reason, the printed wiring board substrate is relatively inexpensive by laminating the electroplated layer 3 directly on the metal particle sintered body layer 2 without reinforcing the metal particle sintered body layer 2 by electroless plating or the like. Despite being manufactured, the adhesion of the metal layer formed as a laminate of the metal particle sintered body layer 2 and the electroplating layer 3 to the base film 1 is relatively large.

[Method of manufacturing printed circuit board substrate]
The printed wiring board substrate can be manufactured by the method for manufacturing a printed wiring board substrate according to another embodiment of the present invention.

  As shown in FIG. 2, the printed wiring board substrate manufacturing method includes an alkali treatment step (step S1) in which the surface of the base film 1 mainly composed of polyimide is subjected to an alkali treatment, and the base film after the alkali treatment step. A metal particle sintered body layer forming step (step S2) in which a metal particle dispersion is applied to the surface of 1 and fired, and a metal particle sintered body layer 2 formed in this metal particle sintered body layer forming step An electroplating layer forming step (step S3) for electroplating as an adherend.

<Alkali treatment process>
In the alkali treatment process of step S1, a part of the polyimide imide ring, which is the main component of the base film 1, is opened by bringing the alkali solution into contact with the surface on which the metal layer of the base film 1 is to be laminated.

  In this alkali treatment step, the ring opening rate of the polyimide imide ring on the surface layer of the base film 1 is adjusted within the range described for the printed wiring board substrate of FIG. Specifically, for example, by adjusting conditions such as pH, temperature, and contact time of the alkaline solution, the ring-opening rate of the polyimide imide ring on the surface layer of the base film 1 is set to a desired value.

  Examples of the alkali solution used in the alkali treatment step include aqueous solutions of sodium hydroxide, potassium hydroxide, ammonia, calcium hydroxide, tetramethylammonium hydroxide, lithium hydroxide, monoethanolamine, and the like and hydrogen peroxide. An aqueous solution etc. are mentioned, A sodium hydroxide aqueous solution is generally used.

  The pH of the alkali solution used in the alkali treatment step can be, for example, 12 or more and 15 or less. Moreover, as contact time with the alkaline liquid of the base film 1, it can be 15 seconds or more and 10 minutes or less, for example. The temperature of the alkaline liquid can be set at, for example, 10 ° C. or more and 70 ° C. or less.

  The alkali treatment step preferably includes a water washing step of washing the base film 1 with water. In this water washing step, the base film 1 is washed with water to remove the alkaline liquid adhering to the surface of the base film 1. Moreover, it is more preferable that the alkali treatment step has a drying step of drying the washing water in the water washing step. By evaporating the water in the base film 1, ions in the base film 1 are precipitated as metals and metal oxides, or combined with resin components of the base film 1 to stabilize the quality of the base film 1. can do.

<Metal particle sintered body layer forming step>
In the metal particle sintered body layer forming step of step S2, the metal particle sintered body layer 2 is formed by applying and heating a metal particle dispersion containing a plurality of metal particles.

  As the metal particle dispersion used in the sintered body layer forming step, a liquid containing a dispersion medium of metal particles and a dispersant for uniformly dispersing the metal particles in the dispersion medium is preferably used. By using the metal particle dispersion liquid in which the metal particles are uniformly dispersed in this manner, the metal particles can be uniformly attached to the surface of the base film 1, and the uniform metal particle sintered body layer can be applied to the surface of the base film 1. 2 can be formed.

(Metal particles)
The metal particles contained in the metal particle dispersion can be produced by, for example, a high temperature treatment method, a liquid phase reduction method, a gas phase method, etc., but the liquid phase reduction can produce particles having a uniform particle size at a relatively low cost. It is preferable to use what is manufactured by the method.

The lower limit of the average particle diameter D _LD of the metal particles is preferably 5 nm, and more preferably 10 nm. On the other hand, the upper limit of the average particle diameter D _LD is preferably 200 nm, and more preferably 100 nm. When the average particle diameter D _LD is less than the lower limit, the dispersibility and stability of the metal particles in the dispersion medium may be reduced. On the other hand, when the average particle diameter D _LD exceeds the upper limit, the density of the metal particles when the metal particle dispersion is applied tends to be non-uniform, and as a result, it is difficult to form a sufficiently dense metal layer. There is. The “average particle diameter D _LD ” means a particle diameter at which the volume integrated value is 50% in the particle diameter distribution measured by the laser diffraction method.

As a minimum of average particle diameter _DSEM computed based on the measurement by the scanning electron microscope (SEM) of the said metal particle, 1 nm is preferable, 5 nm is more preferable, and 10 nm is more preferable. On the other hand, the upper limit of the average particle diameter _{D SEM,} 250 nm is preferred, 150 nm is more preferable. When the average particle diameter _DSEM is less than the lower limit, the dispersibility and stability of the metal particles in the dispersion medium may be reduced. On the other hand, when the average particle diameter _DSEM exceeds the upper limit, the density of the metal particles when the metal particle dispersion is applied tends to be non-uniform, and as a result, it is difficult to form a sufficiently dense metal layer. There is. The “average particle diameter D _SEM ” means that the surface of the metal particles was observed with a scanning electron microscope (SEM), and 100 arbitrarily extracted metal particles were measured and the volumes were integrated in ascending order of the particle diameter. The particle diameter at which the cumulative volume is 50%.

The upper limit of the ratio of the average particle diameter D _SEM (D _SEM / D _LD ) calculated based on the measurement of the metal particles by the scanning electron microscope to the average particle diameter D _LD of the metal particles is preferably 2.0. 1.5 is more preferable, and 1.3 is more preferable. When the ratio (D _SEM / D _LD ) exceeds the upper limit, the shape of individual metal particles tends to be non-uniform. As a result, the smoothness of the surface of the metal layer formed by applying the metal particle dispersion may be insufficient. The lower limit of the ratio (D _SEM / D _LD ) is not particularly limited, and can be set to 1, for example.

  The lower limit of the content of the metal particles in the metal particle dispersion is preferably 20% by mass, and more preferably 25% by mass. On the other hand, the upper limit of the content of the metal particles is preferably 80% by mass, more preferably 50% by mass, and still more preferably 35% by mass. When content of the said metal particle is less than the said minimum, there exists a possibility that it may become difficult to form the metal layer which has sufficient thickness and density. Conversely, when the content of the metal particles exceeds the upper limit, it may be difficult to uniformly disperse the metal particles in the dispersion medium.

(Dispersant)
As the dispersant, a graft copolymer having a polyalkyleneimine as a main chain and a polyalkylene oxide compound as a side chain is preferable, and among them, a graft copolymer having a polyethyleneimine as a main chain and polyethylene oxide as a side chain. (Hereinafter sometimes referred to as PEI-PEO graft copolymer) is particularly preferred. Moreover, it is preferable that the PEI-PEO graft copolymer used as a dispersant has a dendrimer structure having a PEI portion as a core.

  Thus, by using a polyalkyleneimine as a main chain and a polyalkylene oxide compound as a side chain as a dispersant, and using a polar graft copolymer, the metal particles can be dispersed well in the dispersion medium. Can be made. Thereby, the film quality of the obtained metal particle sintered body layer 2 is made dense and defect-free, and the adhesion between the base film 1 and the metal particle sintered body layer 2 can be improved more reliably.

  In particular, the PEI-PEO graft copolymer exists in a state where the nitrogen atom of the polyethyleneimine moiety is coordinated to the metal particle side in the dispersion medium. For this reason, the PEI-PEO graft copolymer suppresses the aggregation of the metal particles more effectively, and uniformly disperses the metal particles in the dispersion medium. The metal particle dispersion may contain other dispersant as the above-mentioned dispersant together with the PEI-PEO graft copolymer. However, in order to effectively improve the uniform dispersibility of the metal particles, other dispersions may be used. It is preferable not to contain an agent.

  The lower limit of the mass average molecular weight of the polyethyleneimine moiety of the PEI-PEO graft copolymer is preferably 300, and more preferably 400. On the other hand, the upper limit of the mass average molecular weight is preferably 1,000, and more preferably 850. If the mass molecular weight is less than the lower limit, the effect of preventing the aggregation of the metal particles and maintaining the dispersion of the metal particles may not be sufficiently obtained, and as a result, a sufficiently dense metal layer is formed. May be difficult. Conversely, when the mass average molecular weight exceeds the upper limit, the bulk of the dispersant becomes too large, and in the firing process performed after the application of the metal particle dispersion, voids are generated by inhibiting the sintering of the metal particles. As a result, it may be difficult to form a dense and low-resistance metal layer. Moreover, when the bulk of a dispersing agent is too large, there exists a possibility that the electroconductivity of a metal layer may fall resulting from the decomposition | disassembly residue of a dispersing agent. The “mass average molecular weight” is a value measured using a gel permeation chromatography (GPC) apparatus, using N-methyl-2-pyrrolidone as a developing solvent, and using monodisperse polystyrene as a standard.

  The lower limit of the molar ratio of the polyethylene oxide chain to the nitrogen atom of the polyethyleneimine moiety of the PEI-PEO graft copolymer is preferably 10, more preferably 15, and even more preferably 20. On the other hand, the upper limit of the molar ratio is preferably 50, more preferably 40, and even more preferably 35. When the said molar ratio is less than the said minimum, there exists a possibility that the dispersibility in the dispersion medium of the said PEI-PEO graft copolymer may fall. Conversely, when the molar ratio exceeds the upper limit, it may be difficult to produce the PEI-PEO graft copolymer.

  The lower limit of the mass average molecular weight of the PEI-PEO graft copolymer is preferably 3,000, more preferably 4,000, and still more preferably 6,000. On the other hand, the upper limit of the mass average molecular weight of the above PEI-PEO graft copolymer is preferably 54,000, more preferably 45,000, and even more preferably 35,000. When the mass average molecular weight of the PEI-PEO graft copolymer is less than the lower limit, the effect of preventing the aggregation of the metal particles and maintaining the dispersion of the metal particles may not be sufficiently obtained. There is a possibility that it becomes difficult to form a sufficiently dense metal layer. On the contrary, when the mass average molecular weight of the PEI-PEO graft copolymer exceeds the upper limit, the bulk of the dispersant becomes too large, and in the heat treatment performed after the application of the metal particle dispersion, There is a possibility that voids are generated by inhibiting the binding, and as a result, it becomes difficult to form a dense and low resistance metal layer. Moreover, when the bulk of a dispersing agent is too large, there exists a possibility that the electroconductivity of a metal layer may fall resulting from the decomposition | disassembly residue of a dispersing agent.

  As a minimum of the content rate of the nitrogen atom derived from the dispersing agent (PEI-PEO graft copolymer) with respect to the above-mentioned metal particles, 0.01 mass% is preferred and 0.05 mass% is more preferred. On the other hand, as an upper limit of the said content rate, 10 mass% is preferable, 1 mass% is more preferable, and 0.5 mass% is further more preferable. When the said content rate is less than the said minimum, the said metal particle cannot fully be surrounded by a dispersing agent, and there exists a possibility that aggregation of the metal particle in a dispersion medium cannot fully be prevented. On the other hand, when the content ratio exceeds the upper limit, in the heat treatment performed after the application of the metal particle dispersion, the metal particles are inhibited from sintering to generate voids, resulting in a dense and low resistance metal layer. It may be difficult to form.

  Moreover, as a content rate with respect to the metal particle of a dispersing agent, 1 to 60 mass% is preferable. The dispersing agent surrounds the metal particles to prevent aggregation and disperse the metal particles satisfactorily. However, when the content of the dispersing agent is less than the lower limit, the aggregation preventing effect may be insufficient. On the contrary, when the content ratio of the dispersant exceeds the above upper limit, in the firing step after the application of the metal particle dispersion, the dispersant may inhibit the sintering of the metal particles, and voids may be generated. The decomposition residue may remain as impurities in the metal particle sintered body layer 2 to reduce the conductivity.

(Dispersion medium)
The dispersion medium contained in the metal particle dispersion is not particularly limited, but water is typically used.

  The dispersion medium may contain an organic solvent as necessary. As the organic solvent, various water-soluble organic solvents can be used. For example, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert- Examples thereof include alcohols such as butyl alcohol, ketones such as acetone and methyl ethyl ketone, polyhydric alcohols such as ethylene glycol and glycerin and other esters, glycol ethers such as ethylene glycol monoethyl ether and diethylene glycol monobutyl ether, and the like.

  When the said dispersion medium contains an organic solvent, as a minimum of content of the said organic solvent in a metal particle dispersion liquid, 25 mass% is preferable and 30 mass% is more preferable. On the other hand, the upper limit of the content of the organic solvent is preferably 75% by mass, and more preferably 70% by mass. When content of the said organic solvent is less than the said minimum, there exists a possibility that effects, such as viscosity adjustment and vapor pressure adjustment by the said organic solvent, may not fully be acquired. On the contrary, when the content of the organic solvent exceeds the upper limit, the swelling effect of the dispersant by water becomes insufficient, and the metal particles may be aggregated in the metal particle dispersion.

  As a method for applying the metal particle dispersion liquid to the base film 1, conventionally known application methods such as a spin coating method, a spray coating method, a bar coating method, a die coating method, a slit coating method, a roll coating method, and a dip coating method are used. Can be used. Further, for example, the metal particle dispersion may be applied to only a part of the surface of the base film 1 by screen printing, a dispenser, or the like.

  By baking to heat the coating film of the metal particle dispersion obtained by applying the metal particle dispersion to the base film 1, the solvent dispersant of the metal particle dispersion evaporates or pyrolyzes, and the remaining metal particles are sintered to form the base film 1. Thus, the metal particle sintered body layer 2 fixed on one surface is obtained. In addition, it is preferable to dry the coating film of a metal particle dispersion before the said heating.

  The firing is preferably performed in an atmosphere containing a certain amount of oxygen. As a minimum of the oxygen concentration of the atmosphere at the time of baking, 1 volume ppm is preferable and 10 volume ppm is more preferable. On the other hand, the upper limit of the oxygen concentration is preferably 10,000 volume ppm, more preferably 1,000 volume ppm. When the oxygen concentration is less than the lower limit, the amount of metal oxide generated in the vicinity of the interface of the metal particle sintered body layer 2 is reduced, and the adhesion between the base film 1 and the metal particle sintered body layer 2 is sufficiently increased. May not be improved. On the contrary, when the oxygen concentration exceeds the upper limit, the metal particles are excessively oxidized, and the conductivity of the metal particle sintered body layer 2 may be lowered.

  As a minimum of the said calcination temperature, 150 degreeC is preferable and 200 degreeC is more preferable. On the other hand, the upper limit of the firing temperature is preferably 500 ° C, and more preferably 400 ° C. When the said calcination temperature is less than the said minimum, between metal particles cannot be connected and there exists a possibility that the metal particle sintered compact layer 2 may collapse | disintegrate in the next electroplating layer formation process. On the contrary, when the baking temperature exceeds the upper limit, the base film 1 may be deformed.

  As a lower limit of the dissolution rate of the metal particle sintered body layer 2 in the copper sulfate plating solution containing 200 g / L of copper sulfate pentahydrate, 70 g / L of sulfuric acid, and 40 mg / L of chloride ions, 0.01 nm / min is used. Preferably, 0.1 nm / min is more preferable. On the other hand, the upper limit of the dissolution rate of the metal particle sintered body layer 2 in the copper sulfate plating solution is preferably 3 nm / min, and more preferably 1 nm / min. If the dissolution rate of the metal particle sintered body layer 2 in the copper sulfate plating solution is less than the lower limit, the metal particle sintered body layer 2 may not be easily formed. Conversely, when the dissolution rate of the metal particle sintered body layer 2 in the copper sulfate plating solution exceeds the upper limit, the metal particle sintered body layer 2 may be eroded in the next electroplating layer forming step.

(Electroplating layer forming process)
In the electroplating layer forming step, the electroplating layer 3 is laminated by performing metal plating directly on the metal particle sintered body layer 2. In the electroplating layer forming step, the thickness of the entire metal layer is increased to a desired thickness.

  In this electroplating, a metal layer having a desired thickness is rapidly formed without defects using a conventionally known plating solution corresponding to the metal to be plated, such as copper, nickel, silver, and the like. Can be done.

<Advantages>
By adjusting the ring-opening rate of the polyimide imide ring on the surface layer on the side where the metal particle sintered body layer 2 of the base film 1 is laminated in the alkali treatment step, the printed wiring board substrate is within a certain range. Since the adhesive force between the base film 1 and the metal particle sintered body layer 2 is improved, the metal particle sintered body layer 2 is hardly eroded by the plating solution used in the electroplating layer forming step. For this reason, in the manufacturing method of the said printed wiring board board | substrate, since it is not necessary to reinforce the metal particle sintered body layer 2 by electroless plating etc. before an electroplating layer formation process, a printed wiring board original board is compared. The metal layer formed from the metal particle sintered body layer 2 and the electroplating layer 3 has a relatively high adhesion to the base film 1.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  The printed wiring board substrate may be manufactured by a method different from the manufacturing method of FIG. Specifically, the printed wiring board substrate may be one in which the surface of the base film is modified by, for example, plasma treatment or the like without being subjected to alkali treatment.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

  In the following manner, a prototype No. of a printed wiring board substrate in which a metal layer is laminated on a base film obtained by subjecting the surface of a commercially available polyimide film to an alkali treatment (some prototypes are not treated). 1-No. 9 was created.

(Polyimide film)
Prototype No. 1-No. 6 used Kaneka's polyimide sheet “Apical NPI” (average thickness 25 μm) as a base film. On the other hand, prototype No. 7-No. For No. 9, a polyimide sheet “Kapton ENS” (average thickness 25 μm) manufactured by Toray DuPont was used as a base film.

(Alkali treatment process)
As an alkaline solution, it was immersed in an aqueous solution of sodium hydroxide having a temperature of 40 ° C. and a concentration of 10% by mass for each time shown in Table 1, and was washed with water for 10 seconds three times.

(Imide ring opening rate)
About the base film after an alkali treatment, the ring-opening rate of the imide ring of the surface polyimide was measured. The ring-opening rate of the imide ring is determined by using a thermoreflector infrared total reflection absorption measurement (FT-IR) apparatus “Nicolet 8700” and a single reflection ATR accessory “Dura Scope” (diamond prism) manufactured by SensIR. The absorption intensity spectrum in the range of the measurement wave number around 4000 to 650 cm ⁻¹ at an incident angle of 45 ° was set to 16 cm and the resolution was set to 4 cm ⁻¹ , respectively. In the obtained absorption intensity spectrum, the peak intensity in the vicinity of wave number 1494 cm ⁻¹ is Pb, the peak intensity in the vicinity of wave number 1705 cm ⁻¹ is Pc, and calculated as {1− (0.89 × Pc / Pb) × 100 [%]}. did. Table 1 also shows the ring opening rate of the polyimide imide ring.

  FIG. 3 is a graph of Table 1. As this graph shows, it was confirmed that the ring-opening rate of the polyimide imide ring on the surface layer of the base film was substantially proportional to the alkali treatment time.

(Metal particle sintered body layer forming step)
Is the surface on the metal particle dispersion (solvent pure water of the base film, 30 mass% average particle diameter _{D SEM} is copper particles 30nm as metal particles, BASF Corp. PEI-PEO graft copolymer as a dispersant (Sokalan HP20) (including 1.5% by mass) was applied and dried at room temperature, and fired in a nitrogen atmosphere at 350 ° C. (oxygen concentration 150 ppm) for 2 hours to form a sintered metal particle layer having an average thickness of 150 nm.

(Electroplating layer forming process)
Copper was directly laminated on the metal particle sintered body layer by electroplating (copper sulfate plating) to form an electroplated layer having an average thickness of 20 μm.

  Prototype No. obtained above. 1-No. For No. 9, the peel strength of the metal layer (laminated body of metal particle sintered body layer and electroplating layer) and the pinhole ratio on the surface of the electroplating layer were measured.

(Peel strength)
The peel strength of the metal layer was measured according to JIS-K6854-2 (1999) “Adhesive—Peeling peel strength test method—2 parts: 180 degree peeling” with the base film as a flexible adherend.

(Pinhole rate)
The pinhole ratio on the surface of the electroplating layer was obtained by photographing the surface of the electroplating layer with a scanning electron microscope (SEM) and calculating the ratio of the total area of pinholes in the image.

  Table 2 below shows the prototype No. 1-No. 9 shows the measurement results of peel strength and pinhole ratio for No. 9;

  FIG. 4 is a graph showing the peel strength and pinhole ratio in Table 2 with respect to the imide ring opening ratio in Table 1. As shown in the figure, by making the imide ring opening ratio of the polyimide on the surface of the base film 5% or more and 30% or less, the peel strength between the base film and the metal layer is relatively large, and the pinhole ratio is relatively It was confirmed that a small printed wiring board substrate was obtained.

  The printed wiring board substrate and the printed wiring board manufacturing method according to the embodiment of the present invention can be widely used for manufacturing a printed wiring board.

DESCRIPTION OF SYMBOLS 1 Base film 2 Metal particle sintered body layer 3 Electroplating layer S1 Alkali processing process S2 Metal particle sintered body layer formation process S3 Electroplating layer formation process

Claims (7)

A base film based on polyimide;
A metal particle sintered body layer directly laminated on the base film;
An electroplating layer directly laminated on the metal particle sintered body layer,
The printed wiring board board | substrate whose ring-opening rate of the polyimide imide ring of the surface layer by which the metal particle sintered compact layer of the said base film is laminated | stacked is 5-30%.   The printed wiring board substrate according to claim 1, wherein a porosity of the metal particle sintered body layer is 0.001% or more and 2% or less.   The printed wiring board substrate according to claim 1 or 2, wherein a main component of the metal particle sintered body layer and the electroplating layer is copper.   4. The printed wiring board substrate according to claim 1, wherein the metal particle sintered body layer has an average thickness of 30 nm to 500 nm.   The printed wiring board substrate according to any one of claims 1 to 4, wherein a peel strength between the base film and the metal particle layer is 3 N / cm or more. An alkali treatment step of alkali-treating the surface of the base film mainly composed of polyimide;
A metal particle sintered body layer forming step in which a metal particle dispersion is applied to the surface of the base film after the alkali treatment step and fired,
An electroplating layer forming step of electroplating the metal particle sintered body layer formed in the metal particle sintered body layer forming step as an adherend, and a method for producing a printed wiring board substrate,
In the alkali treatment step, the ring opening rate of the polyimide imide ring on the surface layer of the base film is adjusted to 5% or more and 30% or less,
A method for producing a printed wiring board substrate, wherein the metal particle sintered body layer is directly subjected to metal plating in the electroplating layer forming step.   The print according to claim 6, wherein the dispersant for the metal particle dispersion used in the metal particle sintered body layer forming step is a graft copolymer having a polyalkyleneimine as a main chain and a polyalkylene oxide compound as a side chain. A method for manufacturing a substrate for a wiring board.

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