JP2006073668A - Wiring circuit and its forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method for more efficient formation by using a wiring circuit where circuit resistance is lowered rather than before by a plate shape metal filler, and without reduction in the accuracy of dimension and conductivity at the above wiring circuit. <P>SOLUTION: A wiring circuit is set in the section so that the average continuous length Y which follows the thickness direction of the wiring circuit of the metal phase originated from a plate shaped metal filler may be at the proportion 0.4 or more of Y/X to the average continuous length X which intersects the thickness direction of the wiring circuit of the above metal phase. As for the formation method, resin binder is stiffened by the heat at 100-250°C while pressurizing the thickness direction of a layer by 0.1-9 MPa after printing the electric conduction paste containing plate shaped metal filler and resin binder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wiring circuit having excellent conductivity and a method for forming the wiring circuit.

  A wiring circuit such as a printed wiring board is generally formed by applying a photosensitive resist on a copper foil laminated on the surface of a substrate and patterning it through the steps of exposure, development, and etching. However, since it can be patterned more easily, it is not necessary to go through a resist process or an etching process, and it does not require treatment of waste solvent after developing the resist, treatment of waste liquid after etching the copper foil, etc. In recent years, a wiring circuit in which a conductive paste containing a metal filler and a resin binder is printed on a substrate by a printing method such as a screen printing method has been widely used.

  In the above-described wiring circuit, a flat plate shape called flake shape or scale shape is generally used as the metal filler. When the conductive paste is printed by a printing method such as a screen printing method, the flat metal filler is oriented in the plane direction of the wiring circuit by the stress applied to the conductive paste by a squeegee, for example. And since electroconductivity is ensured by the contact of the metal fillers adjacent to a surface direction, predetermined | prescribed electroconductivity can be provided to a wiring circuit.

  However, at present, when the printed wiring board is becoming finer and the circuit width of the wiring circuit tends to be narrowed, the electrical conductivity of the wiring circuit is insufficient only by simply orienting the planar metal filler in the plane direction. Currently, there is a demand for further reduction in circuit resistance.

Therefore, in Patent Document 1, when forming wiring circuits or vias connecting the wiring circuits of a multilayer wiring board with a conductive paste, the conductive powder (metal filler) is replaced by a specific surface area instead of a flat one. In addition to using a fine noble metal powder having a thickness of ² to 5 m ² / g, the wiring circuit and vias after drying are heated while being pressurized at a pressure of 10 MPa or more to cure the resin binder, thereby increasing the noble metal powder. It has been proposed to lower the circuit resistance than the current state by filling.
JP 2002-245873 (Claims 1, 2, 0008, 0009 to 0010, 0013 to 0014, 0016 to 0020)

The fine noble metal powder having a specific surface area of ² to 5 m ² / g used in Patent Document 1 is expensive to manufacture and is not easy to mix and disperse uniformly with a resin binder. Since the manufacturing cost is high, there is a problem that the cost for forming the wiring circuit is high.

  In addition, as described in Patent Document 1, if the above-mentioned fine noble metal powder is heated at a pressure of 10 MPa or more and heated to harden the resin binder, it will surely be a circuit such as a wiring circuit. It is possible to reduce the resistance. However, although this configuration is very effective in a wiring circuit formed on a resin substrate reinforced with reinforcing fibers, such as a glass epoxy substrate, or a ceramic substrate, for example, it is frequently used for flexible wiring boards, There is also a problem that it is not suitable for forming a wiring circuit formed on a substrate made of a resin film or sheet that is not reinforced with a reinforcing fiber, such as a polyimide film.

  That is, the conductive paste is printed on a substrate made of a resin film or sheet not reinforced with reinforcing fibers, and then heated while being pressurized at a high pressure of 10 MPa or more in order to reduce the circuit resistance by high filling. When the resin binder is cured, the substrate is compressed in the thickness direction and greatly expanded in the surface direction, so that the dimensional accuracy of the wiring circuit formed on the substrate is remarkably lowered.

  In addition, when the substrate extends greatly in the surface direction, the filling rate of the metal filler in the wiring circuit is lowered, and on the contrary, the effect of reducing the circuit resistance of the wiring circuit by filling the metal filler high may not be obtained. . In particular, in a wiring circuit using a flat filler that ensures conductivity by contact between adjacent metal fillers in the surface direction as described above, when the substrate extends in the surface direction, the contact between the metal fillers Are pulled apart, and the conductivity is significantly reduced. Further, for example, in a post-processing step such as attaching the insulating cover, there is a possibility that a defect such as a mismatch between the size of the insulating cover to be attached and the wiring circuit may occur.

  An object of the present invention is to provide a wiring circuit having a circuit resistance lower than before by using a normal flat metal filler. Another object of the present invention is to more efficiently form a low-resistance wiring circuit made of a flat metal filler as described above without reducing the dimensional accuracy and conductivity. It is in providing the formation method.

  In order to solve the above-mentioned problems, the inventor examined the distribution state of the metal filler in a wiring circuit formed by printing a conductive paste containing a flat metal filler and a resin binder. As a result, in the cross-section obtained by cutting in the thickness direction the wiring circuit in which the metal phase originating from the flat metal filler and the resin phase originating from the resin binder are mixed, the thickness direction of the wiring phase of the metal phase The ratio Y / X of the average value Y of the continuous lengths to the average value X of the lengths of the metal phases continuous in the direction perpendicular to the thickness direction of the wiring circuit is 0.4 or more, By making metal fillers not only those that are adjacent in the plane direction of the wiring circuit but also those that are adjacent to each other in the thickness direction orthogonal thereto, the conventional wiring circuit in which only a flat metal filler is used is used. In comparison, the inventors have found that the circuit resistance can be greatly reduced.

  Therefore, the invention described in claim 1 is formed by printing a conductive paste containing a flat metal filler and a resin binder, and a metal phase originating from the metal filler and a resin phase originating from the resin binder are mixed inside. In the cross section in the thickness direction, the average value Y of the length of the metal phase continuous in the thickness direction of the wiring circuit and the direction of the metal phase perpendicular to the thickness direction of the wiring circuit The ratio Y / X with respect to the average value X of continuous lengths is 0.4 or more.

  When the ratio Y / X exceeds 2.5, the connection between the metal fillers adjacent to each other in the plane direction of the wiring circuit is relatively reduced, so that the circuit resistance may not be lowered. The ratio Y / X is preferably 2.5 or less. Therefore, the invention according to claim 2 is the wiring circuit according to claim 1, wherein the ratio Y / X is 2.5 or less.

  In order to form a wiring circuit in which the ratio Y / X is adjusted within the above range, similarly to the invention described in Patent Document 1, after printing a conductive paste containing a flat metal filler and a resin binder A method is adopted in which the resin binder is cured by heating while pressing in the thickness direction. According to this method, the ratio Y / X can be arbitrarily and easily adjusted by changing the pressure and heating conditions.

  However, the layer formed by printing the conductive paste is compressed as efficiently as possible, and particularly when forming a wiring circuit on a substrate made of a resin film or sheet that does not contain reinforcing fibers, In order to prevent the conductivity from being greatly reduced and the conductivity from being lowered, the pressure of pressurization needs to be 0.1 to 9 MPa. Moreover, the heating temperature in that case needs to be 100-250 degreeC.

  Accordingly, the invention described in claim 3 is a method for forming the wiring circuit according to claim 1 or 2, wherein the conductive paste containing the flat metal filler and the resin binder is printed and then 0 in the thickness direction. A method of forming a wiring circuit, wherein the resin binder is cured by heating to 100 to 250 ° C. while pressurizing at 1 to 9 MPa.

The present invention is described below.
The wiring circuit of the present invention is formed by printing a conductive paste containing a flat metal filler and a resin binder as described above, and in the layer, a metal phase originating from the metal filler and a resin phase originating from the resin binder. In the cross section in the thickness direction, the average value Y of the length of the metal phase continuous in the thickness direction of the wiring circuit and the thickness direction of the wiring phase of the metal phase orthogonal to the thickness direction of the wiring circuit The ratio Y / X with respect to the average value X of the lengths continuous in the direction to be measured is 0.4 or more.

  That is, as shown in FIG. 2, in the cross section of the formed wiring circuit cut in the thickness direction, the metal phase originating from the metal filler (in the plane direction and the thickness direction of the wiring circuit), which appears as a light-colored region in the figure. A plurality of adjacent metal fillers are formed integrally in the wiring circuit, and the length continuous in the thickness direction of the wiring circuit (the length indicated by a thick straight line) is measured, and the average value Y ( μm) and, as shown in FIG. 3, in the same cross section, measure the length of the metal phase continuous in the direction perpendicular to the thickness direction of the wiring circuit (the length indicated by the bold straight line). When the average value X (μm) is obtained and the ratio Y / X is obtained from the average values Y and X, the ratio Y / X is limited to 0.4.

  Thereby, as explained above, the flat metal filler is not only adjacent to the surface direction of the wiring circuit, but also adjacent to the thickness direction perpendicular to it, so that the circuit resistance of the wiring circuit Can be greatly reduced in resistance as compared with the conventional one using a flat metal filler.

  If the ratio Y / X exceeds 2.5, the circuit resistance may not be lowered. This is because there is relatively less connection between metal fillers adjacent to each other in the plane direction of the wiring circuit, and therefore the ratio Y / X is preferably 2.5 or less. In addition, considering the balance between the contact between the metal fillers adjacent to each other in the plane direction of the wiring circuit and the contact between the metal fillers adjacent in the thickness direction, the circuit resistance can be further reduced. Y / X is preferably 0.5 to 1.0 even in the above range.

  As the flat metal filler for forming the wiring circuit, the same conventional ones used for conductive pastes can be used, so that the very fine noble metal powder described in the cited reference 1 can be used. Compared to the case of using it, while reducing the manufacturing cost of itself, the flat metal filler is easy to mix and uniformly disperse with a resin binder, compared to a fine noble metal powder. The manufacturing cost of the conductive paste can be reduced, and as a result, the cost for forming the wiring circuit can be reduced.

  Examples of such flat metal fillers include simple metals such as silver, copper, nickel, aluminum, and zinc, or alloys of two or more metals containing these metals, or composite structures of two or more metals. Any metal filler having various flat plate shapes such as flakes and scales can be used. Of these, Ag filler and Cu filler coated with Ag on the surface are particularly suitable for use as metal fillers because they have little surface oxidation and hardly undergo oxidation due to heating. Although the magnitude | size of a metal filler is not specifically limited, In order to respond | correspond to refinement | miniaturization of a printed wiring board, it is preferable that the center particle size is 0.1-20 micrometers. In addition, suppose that flat form means that ratio L / D of the maximum length L and thickness D is 3 or more. Moreover, as a metal filler, in order to adjust the viscosity, printability, leveling property, etc. of an electrically conductive paste, you may use a spherical filler together with a flat thing.

  Moreover, as a resin binder which comprises an electrically conductive paste with the said metal filler, what is generally used for electrically conductive pastes similarly to the past can be used. That is, examples of the resin binder include thermosetting resins such as epoxy resins and phenol resins, and thermoplastic resins having high heat resistance such as polyester, polyamide imide, and polyimide. From the point of property and flexibility, it is suitably used as a resin binder. In addition, it is preferable from the viewpoint of flexibility that an epoxy resin having an uncured molecular weight of 10,000 or more is used.

  In addition to the above, for example, when the resin binder is a thermosetting resin, the conductive paste is blended with a curing agent or the like, and a solvent for adjusting the viscosity of the conductive paste. The blending ratio of each component is not particularly limited, but the metal filler is a total amount of solids, that is, in the total amount of the metal filler, the resin binder, and the curing agent when the resin binder is a thermosetting resin. It is preferable that the ratio to 40 to 75 volume% is more preferable, and it is more preferable that it is 50 to 70 volume%. If the ratio of the metal filler is less than this range, there is a possibility that a wiring circuit having sufficient conductivity may not be formed. If the ratio exceeds this range, the ratio of the resin binder is relatively reduced, so that the wiring circuit substrate can be reduced. There is a risk that the adhesion of the wiring and the strength of the wiring circuit itself will be insufficient.

  In the wiring circuit of the present invention, the conductive paste containing each of the above components is patterned on the surface of the substrate by an arbitrary printing method such as a screen printing method. It is preferable to form by the forming method of the present invention, which is heated while pressing in the thickness direction using a press machine or the like. At this time, when the resin binder is a thermosetting resin, the resin binder is cured by heating.

  In the method for forming a wiring circuit of the present invention, the pressure of the pressurization is limited to 0.1 to 9 MPa, and the heating temperature is limited to 100 to 250 ° C. When the pressure is less than 0.1 MPa, depending on the heating temperature, even if a sufficient heating temperature is applied and the resin binder is softened, the layer has a ratio Y / X of 0.4 or more. It cannot be fully compressed until Also, when the heating temperature is less than 100 ° C., although depending on the pressure of the pressurization, the resin binder is not sufficiently softened even if a sufficient pressure is applied. Cannot be sufficiently compressed until the value becomes 0.4 or more. Further, when the resin binder is a thermosetting resin, the resin binder cannot be sufficiently cured. Therefore, in any of these cases, it is impossible to efficiently compress the layer and form the wiring circuit of the present invention in which the ratio Y / X is 0.4 or more.

  When the pressure exceeds 9 MPa, a substrate made of a resin film or sheet not reinforced with reinforcing fibers, such as a polyimide film frequently used for flexible wiring boards, is compressed in the thickness direction. Since it extends greatly in the surface direction, the dimensional accuracy of the wiring circuit formed on the substrate significantly decreases. Further, the ratio of Y / X in combination with the fact that the contact between the metal fillers adjacent to each other in the plane direction is separated from the increase in the contact between the metal fillers overlapping in the thickness direction by greatly extending the substrate in the plane direction. May exceed 2.5.

  In addition, even when the heating temperature exceeds 250 ° C., the substrate made of a resin film or sheet not reinforced with reinforcing fibers is expanded in the surface direction by being compressed in the thickness direction. The dimensional accuracy of the wiring circuit formed on the substrate is significantly reduced. Further, the resin binder may be thermally deteriorated, and the adhesion of the wiring circuit to the substrate and the strength of the wiring circuit itself may be insufficient.

  Note that the pressure of the pressurization is 0.1 to 2 MPa, particularly within the above range, in consideration of forming the wiring circuit more efficiently without reducing the dimensional accuracy and conductivity. Is preferred. Moreover, although the temperature of a heating is based also on the kind of resin binder, in the case of an epoxy resin, it is preferable that it is 180-220 degreeC.

  Furthermore, it is preferable that the time required for the heating step while applying pressure is 1 hour or less in consideration of improving the productivity of the wiring circuit and preventing thermal deterioration of the resin binder or the like. Further, in order to sufficiently pressurize and heat the layer formed by printing the conductive paste so that the ratio Y / X is 0.4 or more, it is preferably 15 minutes or more.

  The wiring circuit mentioned here includes not only a two-dimensional wiring circuit on a substrate but also a three-dimensional wiring circuit connecting different layers. For example, via holes such as blind via holes, buried via holes, and interstitial via holes, and through-holes such as through holes, The entire three-dimensional wiring circuit including the interlayer connection portion and two or more layers of two-dimensional wiring circuits connected by the interlayer connection portion can be configured as the configuration of the present invention.

  Hereinafter, the present invention will be described based on examples and comparative examples.

Example 1:
60 parts by weight of a tabular silver filler (center particle size 2.6 μm) as a metal filler and a butyl carbitol acetate solution of a bisphenol A type epoxy resin (molecular weight 50,000) as a resin binder (solid content concentration 40 weight) %) 11 parts by weight and mixed with three rolls, an imidazole-based latent curing agent was added and mixed again to prepare a conductive paste. The total amount of the solid content of the silver filler, that is, the ratio of the silver filler to the total amount of the epoxy resin and the curing agent was 60% by volume.

  Next, using a screen printing machine, the conductive paste was applied to one side of a 25 μm-thick polyimide film [Kapton (registered trademark) EN manufactured by Toray DuPont Co., Ltd.] as a substrate. After printing in the shape of a wiring circuit including a circuit part of 80 mm, preheating at 100 ° C. for 10 minutes and drying, the printed layer was pressed in the thickness direction with a pressure of 3.9 MPa using a press machine. Then, heating was carried out for 30 minutes at a temperature of 200 ° C. to form a wiring circuit.

  The formed wiring circuit was cut in the thickness direction to expose the cross section, and the cross section was photographed using a scanning electron microscope. As shown in FIG. 1, the metal phase originated from the metal filler and the resin binder originated. It was confirmed that the resin phase was mixed. In addition, from this image, as shown in FIG. 2, the length of the metal phase that is continuous in the thickness direction of the wiring circuit (the length indicated by a bold straight line) was measured. The measurement was performed on images of arbitrary three cross sections on the wiring circuit including the cross section of the figure, and the average value Y (μm) was obtained from all the measured values, and was 1.22 μm.

  Further, from the same image, as shown in FIG. 3, the length (length indicated by a thick straight line) of the metal phase that is continuous in the direction orthogonal to the thickness direction of the wiring circuit was measured. In the same manner as described above, the measurement was performed on images of arbitrary three cross sections on the wiring circuit including the cross section of the figure, and the average value X (μm) was obtained from all the measured values. The ratio Y / X was 0.88.

Example 2:
A wiring circuit was formed in the same manner as in Example 1 except that the heating temperature was 150 ° C. The formed wiring circuit was cut in the thickness direction to expose the cross section, and the cross section was photographed using a scanning electron microscope. As shown in FIG. 4, the metal phase originated from the metal filler and the resin binder originated. It was confirmed that the resin phase was mixed. Further, for the images of the cross-sections at arbitrary three points on the wiring circuit including the image of FIG. 4, the length of the metal phase continuous in the thickness direction of the wiring circuit (thick straight line) in the same manner as in Example 1. The average value Y (μm) was determined from all the measured values, and was 0.77 μm.

  In addition, regarding the image of the cross section at any three points on the wiring circuit including the image of FIG. 4, the length of the metal phase that is continuous in the direction orthogonal to the thickness direction of the wiring circuit (the length indicated by the bold line) ) And the average value X (μm) was determined from all the measured values, and was 1.60 μm, and the ratio Y / X was 0.48.

Example 3:
A wiring circuit was formed in the same manner as in Example 1 except that the pressure applied was 1.5 MPa. The formed wiring circuit was cut in the thickness direction to expose the cross section, and the cross section was photographed using a scanning electron microscope. As shown in FIG. 5, the metal phase originating from the metal filler and the resin binder originating It was confirmed that the resin phase was mixed. Further, for the images of the cross-sections at arbitrary three points on the wiring circuit including the image of FIG. 5, the length of the metal phase continuous in the thickness direction of the wiring circuit (thick straight line) in the same manner as in Example 1. The average value Y (μm) was determined from all the measured values, and was 1.52 μm.

  In addition, regarding the image of the cross section at any three points on the wiring circuit including the image of FIG. 5, the length of the metal phase continuous in the direction orthogonal to the thickness direction of the wiring circuit (the length indicated by the bold line) ), And an average value X (μm) was determined from all the measured values. As a result, it was 2.67 μm and the ratio Y / X was 0.57.

Example 4:
A wiring circuit was formed in the same manner as in Example 1 except that the pressure of the pressurization was 0.5 MPa. The formed wiring circuit was cut in the thickness direction to expose the cross section, and the cross section was photographed using a scanning electron microscope. As shown in FIG. 6, the metal phase originated from the metal filler and the resin binder originated. It was confirmed that the resin phase was mixed. Further, for the image of the cross section at any three points on the wiring circuit including the image of FIG. 6, the length of the metal phase continuous in the thickness direction of the wiring circuit (thick straight line) in the same manner as in Example 1. The average value Y (μm) was determined from all the measured values and found to be 1.50 μm.

  In addition, regarding the image of the cross section at any three points on the wiring circuit including the image of FIG. 6, the length of the metal phase that is continuous in the direction orthogonal to the thickness direction of the wiring circuit (the length indicated by the bold line) ) And the average value X (μm) was determined from all the measured values, and was 2.28 μm, and the ratio Y / X was 0.66.

Example 5:
A wiring circuit was formed in the same manner as in Example 1 except that the pressure applied was 0.2 MPa. The formed wiring circuit was cut in the thickness direction to expose the cross section, and the cross section was photographed using a scanning electron microscope. As shown in FIG. 7, the metal phase originated from the metal filler and the resin binder originated. It was confirmed that the resin phase was mixed. In addition, with respect to the image of the cross section at any three points on the wiring circuit including the image of FIG. 7, the length of the metal phase continuous in the thickness direction of the wiring circuit (thick straight line) in the same manner as in Example 1. The average value Y (μm) was determined from all the measured values, and was 1.10 μm.

  In addition, regarding the image of the cross section at any three points on the wiring circuit including the image of FIG. 7, the length of the metal phase that is continuous in the direction orthogonal to the thickness direction of the wiring circuit (the length indicated by the bold line) ), And an average value X (μm) was determined from all the measured values. As a result, it was 2.00 μm, and the ratio Y / X was 0.55.

Comparative Example 1:
A wiring circuit was formed in the same manner as in Example 1 except that the patterned layer was not pressurized and heated in an oven set at 200 ° C. for 30 minutes at normal pressure. The formed wiring circuit was cut in the thickness direction to expose the cross section, and the cross section was photographed using a scanning electron microscope. As shown in FIG. 8, the metal phase originated from the metal filler and the resin binder originated. It was confirmed that the resin phase was mixed. Further, as shown in FIG. 9, images of arbitrary three cross sections on the wiring circuit including the image of FIG. 8 are continuous in the thickness direction of the wiring circuit in the same manner as in Example 1. The measured length (length indicated by a thick straight line) was measured, and the average value Y (μm) was determined from all the measured values, which was 0.47 μm.

  Further, as shown in FIG. 10, for the images of the cross sections at arbitrary three points on the wiring circuit including the image of FIG. 8, the length of the metal phase that is continuous in the direction orthogonal to the thickness direction of the wiring circuit ( The length (indicated by a bold straight line) was measured, and the average value X (μm) was determined from all the measured values. As a result, it was 1.60 μm, and the ratio Y / X was 0.29.

Comparative Example 2:
A wiring circuit was formed in the same manner as in Example 1 except that the temperature of pressurization was 30 ° C. The formed wiring circuit was cut in the thickness direction to expose the cross section, and the cross section was photographed using a scanning electron microscope. As shown in FIG. 11, the metal phase originated from the metal filler and the resin binder originated. It was confirmed that the resin phase was mixed. Further, for the image of the cross section at any three points on the wiring circuit including the image of FIG. 11, the length of the metal phase continuous in the thickness direction of the wiring circuit (thick straight line) in the same manner as in Example 1. The average value Y (μm) was determined from all the measured values, and was 0.74 μm.

  In addition, for images of cross sections at arbitrary three points on the wiring circuit including the image of FIG. 11, the length of the metal phase that is continuous in the direction orthogonal to the thickness direction of the wiring circuit (the length indicated by the bold line) ) And the average value X (μm) was determined from all the measured values, and found to be 2.24 μm and the ratio Y / X was 0.33.

Comparative Example 3:
A conductive paste was prepared in the same manner as in Example 1 except that the same amount of spherical silver filler (average particle size: 0.3 μm) was used as the metal filler. Then, a wiring circuit was formed in the same manner as in Example 1 except that this conductive paste was used and the pressure applied was 14.7 MPa.

Comparative Example 4:
A wiring circuit was formed in the same manner as in Example 1 except that the pressure applied was 10 MPa.

  About the wiring circuit formed in each said Example and comparative example, the following each test was done and the characteristic was evaluated.

Volume resistivity measurement:
In Examples and Comparative Examples, among the wiring circuits formed through the above-described steps, the resistance value was measured by a four-terminal method for a circuit portion having a width of 3 mm and a length of 80 mm to obtain a volume resistivity.

Measurement of substrate dimensional change rate:
In the polyimide film used in the examples and comparative examples, markings on the surface forming the wiring circuit were made at two locations with a separation of 80 mm along the width direction. Two markings were made along the length direction with an interval of 80 mm. Then, before and after forming the wiring circuit through the above-described steps, the intervals between the markings arranged in the width direction of the polyimide film and the intervals between the markings arranged in the length direction are measured. Then, after obtaining the average value, from these two average values, the dimensional change rate is expressed by the formula:
Sought by.

Observation of cracks:
In the examples and comparative examples, it was observed whether or not the wiring circuit formed through the above steps had cracks. The results are shown in Table 1.

  From the table, it was found that the wiring circuit of Comparative Example 1 that did not pressurize the printed layer had a ratio Y / X of less than 0.4 and a high volume resistivity, so that the conductivity was low. Further, the wiring circuit of Comparative Example 2 in which the heating temperature at the time of pressing is less than 100 ° C. is low in conductivity because the ratio Y / X is also less than 0.4 and the volume resistivity is high. all right. Moreover, while using a spherical thing as a metal filler and using the wiring circuit of the comparative example 3 which made the pressure of pressurization the range exceeding 9 MPa, and the flat metal filler, pressurization at the time of press It was found that the wiring circuit of Comparative Example 4 having a pressure exceeding 9 MPa was not suitable for practical use because cracks occurred.

  On the other hand, it was confirmed that the wiring circuits of Examples 1 to 5 all had a ratio Y / X in the range of 0.4 or more, a low volume resistivity, and excellent conductivity. Moreover, since the dimensional change rate was small, it was also confirmed that all the wiring circuits of the respective examples were excellent in dimensional accuracy.

It is a scanning electron micrograph which shows the cross section of the wiring circuit formed in Example 1 of this invention. FIG. 2 is a diagram for explaining a method for measuring a length of a metal phase continuous in a thickness direction of a wiring circuit in the cross section of FIG. 1. It is a figure explaining the measuring method of the length which continues in the direction orthogonal to the thickness direction of a wiring circuit of a metal phase in the cross section of FIG. It is a scanning electron micrograph which shows the cross section of the wiring circuit formed in Example 2 of this invention. It is a scanning electron micrograph which shows the cross section of the wiring circuit formed in Example 3 of this invention. It is a scanning electron micrograph which shows the cross section of the wiring circuit formed in Example 4 of this invention. It is a scanning electron micrograph which shows the cross section of the wiring circuit formed in Example 5 of this invention. It is a scanning electron micrograph which shows the cross section of the wiring circuit formed in the comparative example 1 of this invention. FIG. 9 is a diagram for explaining a method for measuring the length of the metal phase continuous in the thickness direction of the wiring circuit in the cross section of FIG. 8. FIG. 9 is a diagram illustrating a method for measuring a length of a metal phase that is continuous in a direction orthogonal to a thickness direction of a wiring circuit in the cross section of FIG. 8. It is a scanning electron micrograph which shows the cross section of the wiring circuit formed in the comparative example 2 of this invention.

Claims (3)

  A wiring circuit formed by printing a conductive paste containing a flat metal filler and a resin binder, and in which a metal phase originating from the metal filler and a resin phase originating from the resin binder are mixed, In the cross section in the thickness direction, the average value Y of the length of the metal phase continuous in the thickness direction of the wiring circuit, and the average value X of the length of the metal phase continuous in the direction perpendicular to the thickness direction of the wiring circuit, A wiring circuit, wherein the ratio Y / X is 0.4 or more.   The wiring circuit according to claim 1, wherein the ratio Y / X is 2.5 or less. A method of forming a wiring circuit according to claim 1 or 2, wherein after printing a conductive paste containing a flat metal filler and a resin binder, pressurizing at 0.1 to 9 MPa in the thickness direction, 100 A method of forming a wiring circuit, wherein the resin binder is cured by heating to ˜250 ° C.