JP5410175B2 - Membrane wiring board and manufacturing method thereof - Google Patents

Description

The present invention relates to a membrane wiring board and a manufacturing method thereof .

  Membrane wiring boards are used as connecting wiring materials for substrates of notebook computers and switch circuits for digital home appliances. The membrane wiring board is formed by printing a silver paste on a flexible film such as plastic to form a circuit layer (see Patent Document 1 below). Thus, the membrane wiring board can be easily manufactured at a lower cost than a flexible printed wiring board (FPC) in which a circuit layer is formed by etching or plating copper on a plastic film. It is becoming popular as a product.

JP 2006-261198 A

  By the way, in recent years, there has been a demand for further downsizing of the membrane wiring board, and accordingly, the circuit layer has been multilayered. In order to increase the number of circuit layers, it is necessary to coat each circuit layer with an insulating layer. As the conductive powder contained in the silver paste, flaky or spherical silver particles are used.

  However, if flaky silver particles are used as the conductive powder in the silver paste, the resistance of the circuit layer increases when the insulating coating layer is formed by applying the resin composition to the circuit layer and curing it. In some cases, the conductivity was lowered. This is an obstacle to manufacturing a membrane wiring board having multiple circuit layers.

  The membrane wiring board may be used in a bent state taking advantage of its flexibility. However, when the membrane wiring board is used in a bent state, the conductivity of the circuit layer may be lowered.

The present invention has been made in view of the above circumstances, and has a circuit layer that has excellent conductivity even when covered with an insulating coating layer and sufficiently suppresses the decrease in conductivity even in a bent state. It aims at providing the membrane wiring board manufactured using the electrically conductive paste which can be formed, and its manufacturing method .

  As a result of intensive research to solve the above-mentioned problems, the present inventors have found that when the resin composition is applied to the circuit layer and cured, the components in the resin composition enter the circuit layer and are contained in the circuit layer. It was thought that the conductive powder in contact with each other was separated by swelling or dissolving the binder resin to be separated, thereby reducing the conductivity. In addition, it was considered that the electrical conductivity of the circuit layer was lowered when the membrane wiring board was bent for the following reason. That is, when flaky silver particles are used as the conductive powder, the flaky silver particles have a large shape anisotropy. For this reason, when the membrane wiring board is bent and the circuit layer is bent accordingly, the flaky silver particles are easily separated from each other and the contact area is easily changed. For this reason, this inventor thought that the fall of electroconductivity would occur easily in a circuit layer. Therefore, as a result of further earnest research, the inventor mixed flaky particles having a large shape anisotropy and spherical particles having a smaller shape anisotropy as a conductive powder in the conductive paste, And it discovered that the said subject could be solved by making the ratio of the spherical particle in electroconductive powder into a predetermined ratio, and came to complete this invention.

That is, the present invention provides a first step of applying a conductive paste on a plastic substrate to form a first circuit layer, and coating the first circuit layer with a resin composition to form a first insulating coating layer. And a second step of forming a second circuit layer by applying a conductive paste, and coating the second circuit layer with a resin composition to form a second insulating coating layer. The conductive paste includes a binder resin and conductive powder, and the conductive powder is composed of flaky silver particles and spherical silver particles, and the conductive powder includes The proportion of the spherical silver particles is greater than 0% by mass and 15% by mass or less, the average particle size of the spherical silver particles is 0.1 to 20 μm, and the resin composition is an ultraviolet curable ink. It is a membrane wiring board . The present invention also provides a first step of forming a first circuit layer by applying a conductive paste on a plastic substrate, and forming a first insulating coating layer by applying a resin composition to the first circuit layer. And a second step of applying a conductive paste to form a second circuit layer, and applying a resin composition to the second circuit layer to form a second insulating coating layer, thereby producing a membrane wiring board A method for manufacturing a membrane wiring board, wherein the conductive paste includes a binder resin and conductive powder, and the conductive powder is composed of flaky silver particles and spherical silver particles, The ratio of the spherical silver particles in the powder is greater than 0% by mass and 15% by mass or less, the average particle size of the spherical silver particles is 0.1 to 20 μm, and the resin composition is an ultraviolet curable ink. This is a method for manufacturing a membrane wiring board.

According to this membrane wiring board and its manufacturing method , the conductive paste is applied to form the first circuit layer, and the resin composition is applied to the first circuit layer and cured to form the first insulating coating layer. Even so, an increase in the resistance of the first circuit layer is sufficiently suppressed. Similarly, the conductive paste is applied to the first insulating coating layer to form a second circuit layer, and the resin composition is applied to the second circuit layer and cured to form the second insulating coating layer. The increase in resistance of the first and second circuit layers is sufficiently suppressed. For this reason, the 1st and 2nd circuit layer which has the outstanding electroconductivity is implement | achieved. Further, even when the membrane wiring board is bent, the decrease in conductivity of the first and second circuit layers can be sufficiently suppressed. In the membrane wiring board, the resin composition is an ultraviolet curable ink, and the ultraviolet curable ink usually does not contain an organic solvent. For this reason, when apply | coating a resin composition to each of a 1st and 2nd circuit layer, the binder resin in a 1st and 2nd circuit layer is hard to swell or melt | dissolve, and flaky silver particles cannot separate easily. For this reason, the circuit layer which has the more excellent electroconductivity is implement | achieved.

In the membrane wiring board and the manufacturing method thereof , the ratio of the average particle diameter of the spherical silver particles to the average particle diameter of the flaky silver particles is preferably 0.1-1 .

  The ultraviolet curable ink contains, for example, polyurethane (meth) acrylate.

  In the present invention, the spherical silver particles are particles having a ratio of the maximum length to the minimum length of 0.9 to 1.1 when only the conductive powder is observed with an electron microscope with a magnification of 1000 to 3000 times. The flaky silver particles are particles whose ratio of the maximum length to the minimum length exceeds 1.1 when only the conductive powder is observed with an electron microscope having a magnification of 1000 to 3000 times.

According to the present invention, a conductive paste can be reduced also in conductivity in the state of and bent electrically conductive superior be coated with an insulating coating layer to form a circuit layer is sufficiently suppressed A membrane wiring board manufactured using the same and a manufacturing method thereof are provided.

It is a top view which shows one Embodiment of the membrane wiring board of this invention. It is sectional drawing along the II-II line of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2.

  FIG. 1 is a plan view showing an embodiment of a membrane wiring board according to the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG. As shown in FIGS. 1 and 2, the membrane wiring board 100 of the present embodiment includes a plastic substrate 1, a first circuit layer 2 a provided on the plastic substrate 1, and a first circuit on the plastic substrate 1. A first insulating covering layer 3 provided to cover the layer 2a, a second circuit layer 2b provided on the first insulating covering layer 3, and a second circuit layer 2b on the first insulating covering layer 3 And a second insulating coating layer 4 provided.

  Each of the first circuit layer 2a and the second circuit layer 2b includes conductive powder and a binder resin. The conductive powder is composed of flaky silver particles and spherical silver particles, and these flaky silver particles and spherical silver particles are held in contact with each other. And the ratio of the spherical silver particle in all the electroconductive powder is larger than 0 mass%, and is 15 mass% or less.

  The membrane wiring board 100 can be obtained as follows.

  First, a plastic substrate 1 is prepared. The plastic which comprises the plastic base material 1 will not be specifically limited if it is a plastic. Examples of such plastics include polyester resins such as polyethylene terephthalate resin (PET) and polyethylene naphthalate resin (PEN), polyimide, and polyetherimide.

  Next, a conductive paste is prepared. As the conductive paste, a paste containing conductive powder and a binder resin is used. The conductive powder is composed of flaky silver particles and spherical silver particles. And the ratio of the spherical silver particle which occupies in all the electroconductive powder shall be larger than 0 mass% and below 15 mass%. When the ratio of the spherical silver particles is 0% by mass, the conductivity of the first circuit layer 2a and the second circuit layer 2b is lowered when the resin composition is applied to the first circuit layer 2a and the second circuit layer 2b. At the same time, when the membrane wiring board 100 is bent, it is impossible to sufficiently suppress the decrease in the conductivity of the first circuit layer 2a and the second circuit layer 2b. When the ratio of the spherical silver particles exceeds 15% by mass, the resistance of the first circuit layer 2a and the second circuit layer 2b increases remarkably, and when the membrane wiring board 100 is bent, the resistance increases greatly. , The conductivity is significantly reduced.

  The proportion of spherical silver particles in the conductive powder is preferably 5 to 10% by mass. If the proportion of spherical silver particles is less than 5% by mass, the bending characteristics tend to be worse than when the proportion is 5% by mass or more, and if the proportion of spherical silver particles exceeds 10% by mass, it is 10% by mass or less. As compared with the case, the resistance value tends to increase when the resists are stacked.

The average particle diameter of the flaky silver particles in the conductive powder is not particularly limited, but is usually 0.1 to 20 μm, preferably 0.5 to 10 μm. On the other hand, the average particle diameter of the spherical silver particles is not particularly limited, but is usually 0.1 to 20 μm, preferably 0.5 to 10 μm. The ratio of the average particle diameter of the spherical silver particles to the average particle diameter of the flaky silver particles is preferably 0.1-1. In this case, when the conductive paste is dried, the spherical silver particles easily enter the gaps between the flaky silver particles. As a result, even if the flaky silver particles are separated from each other, It is easy to secure a conductive path. The particle size of the flaky and spherical silver particles is the following formula when the silver particles are observed with an electron microscope:
Particle size = (minimum length + maximum length) / 2
The value calculated by.

  As the binder resin, a saturated polyester resin, an acrylic resin, an epoxy resin, or the like is used. Among these, a saturated polyester resin is preferable from the viewpoint of suppressing curing shrinkage of the conductive paste.

  The conductive paste usually contains a solvent in addition to the conductive powder and the binder resin. As the solvent, organic solvents such as ethanol, propanol, tetrahydrofuran, isophorone, terpineol, triethylene glycol monobutyl ether, butyl cellosolve acetate, and carbitol acetate can be used.

  In the conductive paste, the conductive powder is preferably added in an amount of 230 to 1900 parts by mass, more preferably 400 to 900 parts by mass, with respect to 100 parts by mass of the binder resin. When the addition amount of the conductive powder is within the above range, there is an advantage that the conductivity of the first circuit layer 2a and the second circuit layer 2b can be further improved, and the printability and coating film characteristics are also improved.

  Next, the conductive paste is applied onto the plastic substrate 1 by a printing method. As the printing method, for example, a screen printing method, a gravure printing method, a transfer printing method, a roll coating method, or the like can be employed.

  Next, the conductive paste is dried. The drying may be performed at a temperature of 120 ° C. to 180 ° C. for 30 to 120 minutes, for example. Thereby, the solvent in the conductive paste is removed, and the flaky silver particles and the spherical silver particles come into contact with each other. Thus, the first circuit layer 2 a is obtained on the plastic substrate 1.

  Next, the first insulating coating layer 3 is formed on the plastic substrate 1 so as to cover the first circuit layer 2a (first step). The first insulating coating layer 3 can be obtained, for example, by applying a resin composition to the first circuit layer 2a on the plastic substrate 1 and curing it. As the resin composition, solvent-based ink and ultraviolet curable ink can be used. The solvent type ink includes a thermoplastic resin and an organic solvent. Examples of the thermoplastic resin include a polyester resin and a urethane-modified polyester resin. On the other hand, the ultraviolet curable ink comprises an ultraviolet curable resin and a photopolymerization initiator.

  As the resin composition, an ultraviolet curable ink is preferable. Since the ultraviolet curable ink generally does not contain an organic solvent, it is difficult to swell or dissolve the binder resin in the first circuit layer 2a when the resin composition is applied to the first circuit layer 2a. For this reason, an increase in resistance of the first circuit layer 2a is suppressed, and the first circuit layer 2a having higher conductivity is realized.

  Examples of the ultraviolet curable resin include polyester (meth) acrylate, polyurethane (meth) acrylate, and polyether (meth) acrylate. When a polyester resin is used as the binder resin in the first circuit layer 2a, polyurethane (meth) acrylate is preferable because the binder resin in the conductive paste is less likely to swell.

  When using an ultraviolet curable ink as the resin composition, after applying the resin composition to the first circuit layer 2a, the resin composition is cured by irradiating the resin composition with ultraviolet rays.

  Next, a conductive paste similar to the above is applied onto the first insulating coating layer 3 by a printing method and dried. Drying can be performed in the same manner as in the case of drying the conductive paste. Thus, the second circuit layer 2 b is obtained on the first insulating coating layer 3.

  Finally, the second insulating coating layer 4 is formed on the first insulating coating layer 3 so as to cover the second circuit layer 2b (second step). Similarly to the first insulating coating layer 3, the second insulating coating layer 4 can also be obtained, for example, by applying and curing a resin composition on the first insulating coating layer 3 so as to cover the second circuit layer 2b. Thus, the membrane circuit board 100 is obtained.

  According to the manufacturing method of the membrane circuit board 100, the conductive paste is applied on the plastic substrate 1 and dried to form the first circuit layer 2a, and the resin composition is applied to the first circuit layer 2a. Even when the first insulating coating layer 3 is formed by curing, an increase in resistance of the first circuit layer 2a can be suppressed, and the first circuit layer 2a having excellent conductivity can be realized. Similarly, a conductive paste is applied onto the first insulating coating layer 3 and dried to form the second circuit layer 2b, and a resin composition is applied to the second circuit layer 2b and cured to form a second insulating coating layer. Even when 4 is formed, an increase in the resistance of the second circuit layer 2b can be suppressed, and the second circuit layer 2b having excellent conductivity can be obtained. Therefore, the membrane wiring board 100 is extremely useful for multilayer circuit layers.

  Further, even when the membrane wiring board 100 is bent, the increase in resistance can be sufficiently suppressed in each of the first circuit layer 2a and the second circuit layer 2b. That is, the decrease in conductivity can be sufficiently suppressed.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, two circuit layers are formed, but three or more circuit layers may be formed. In this case, the step of forming a circuit layer using the conductive paste, applying the resin composition to the circuit layer, and curing it to form an insulating coating layer may be repeated.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and the content of this invention is demonstrated more concretely, this invention is not limited to a following example.

Example 1
First, a conductive paste was prepared as follows. That is, flaky silver particles, spherical silver particles, a binder resin, an organic solvent, and a curing agent were mixed and kneaded with three rolls to obtain a conductive paste. At this time, the flaky silver particles, the spherical silver particles, and the binder resin were mixed in the ratio shown in Table 1, and 20 parts by mass of the curing agent was added to 100 parts by mass of the binder resin. In addition, the ratio shown in Table 1 shows a ratio when the solid content base, that is, the total solid content is 100% by mass. As the flaky silver particles, spherical silver particles, binder resin, organic solvent, and curing agent, the following were specifically used.
Flaky silver particles: S-303 (average particle size 2.4 μm) manufactured by Daiken Chemical Industry Co., Ltd.
Spherical particles: S-602 manufactured by Daiken Chemical Industry Co., Ltd. (average particle size 1 μm)
Binder resin: Byron 300 manufactured by Toyobo Co., Ltd.
Organic solvent: Carbitol acetate curing agent: Dismodule TPLS2759 (Block HMDI)

  Next, the conductive paste was applied onto a plastic substrate made of polyethylene terephthalate having a thickness of 75 μm by a screen printing method so as to form a printing pattern of a predetermined shape, and dried at 150 ° C. for 30 minutes. The printed pattern is composed of a linear portion and a rectangular lead terminal portion provided at both ends of the linear portion, and the linear portion has a thickness after drying of 8 μm, a width of 0.4 mm, and a length of 5 cm. The extraction terminal portion was formed so that the thickness after drying was 8 μm, the width was 3 mm, and the length was 5 mm. A first circuit layer was thus obtained on the plastic substrate.

Next, as a resist ink (resin composition), an ultraviolet curable ink (PTF-6D manufactured by Kyoyo Chemical Industry Co., Ltd.) is applied so as to cover the straight portion of the first circuit layer and expose the lead terminal portion. By using a metal halide lamp to output light having an intensity of 1000 mJ / cm ² , the ultraviolet curable ink was cured by irradiating the ultraviolet curable ink with ultraviolet rays. Subsequently, in the same manner as described above, the ultraviolet curable ink is applied on the ultraviolet curable ink cured by ultraviolet irradiation, and the ultraviolet curable ink is irradiated with ultraviolet rays in the same manner as described above. Then, the ultraviolet curable ink was cured. Thus, a first insulating coating layer having a thickness of 24 μm was obtained.

  Next, the conductive paste was applied onto the first insulating coating layer so as to form a pattern with a predetermined shape by screen printing, and dried at 150 ° C. for 30 minutes. This pattern is the same pattern as the first circuit layer, and the dimensions are the same as those of the first circuit layer. Thus, a second circuit layer was obtained on the first insulating coating layer.

  Finally, an ultraviolet curable ink, which is a resist ink used in the manufacture of the first circuit layer, is applied so as to cover the second circuit layer so as to cover the linear portion of the second circuit layer and expose the lead terminal portion. The ultraviolet curable ink was cured by irradiating the ultraviolet curable ink with ultraviolet rays in the same manner as described above. Subsequently, in the same manner as described above, the ultraviolet curable ink used for the production of the first circuit layer was applied over the ultraviolet curable ink cured by ultraviolet irradiation, and the ultraviolet curable ink was applied to the ultraviolet curable ink. The ultraviolet curable ink was cured by irradiating with ultraviolet rays in the same manner as described above. A second insulating coating layer having a thickness of 24 μm was thus obtained. A membrane wiring board was obtained as described above.

(Example 2)
As a resin composition for forming the first and second insulating coating layers, UV curable ink is used by using PTF-300G manufactured by Kyoyo Chemical Industry Co., Ltd. instead of PTF-6D manufactured by Kyoyo Chemical Industry Co., Ltd. A membrane wiring board was obtained in the same manner as in Example 1 except that the resin material was changed.

(Example 3)
A membrane wiring board was obtained in the same manner as in Example 1 except that the blending ratio of flaky silver particles and spherical silver particles in the conductive paste was changed as shown in Table 1.

Example 4
A membrane wiring board was obtained in the same manner as in Example 1 except that the blending ratio of flaky silver particles and spherical silver particles in the conductive paste was changed as shown in Table 1.

(Example 5)
As flaky silver particles in the conductive paste, S-302 (average particle size) manufactured by Daiken Chemical Industry Co., Ltd. was used instead of S-303 (average particle size 2.4 μm) manufactured by Daiken Chemical Industry Co., Ltd. A membrane wiring board was obtained in the same manner as in Example 2 except that the material of 6.2 μm) was used.

(Example 6)
As a spherical silver particle in the conductive paste, instead of S-602 (average particle size: 1 μm) manufactured by Daiken Chemical Industry Co., Ltd., S-410 (average particle size: 1.3 μm) manufactured by Daiken Chemical Industry Co., Ltd. The membrane wiring board was obtained in the same manner as in Example 2 except that the above was used.

(Comparative Example 1)
A membrane wiring board was obtained in the same manner as in Example 1 except that the blending ratio of flaky silver particles and spherical silver particles in the conductive paste was changed as shown in Table 1.

[Characteristic evaluation]
The following characteristics were evaluated for the membrane wiring boards obtained in Examples 1 to 6 and Comparative Example 1.

(1) Conductivity evaluation of the first circuit layer and the second circuit layer without bending the membrane wiring board During the production of the membrane wiring boards obtained in Examples 1 to 6 and Comparative Example 1, the first circuit layer The resistance (R1) immediately after printing / drying was measured, and the resistance (R1 ′) of the first circuit layer after completion of the membrane wiring board was measured. The results are shown in Table 1. At this time, the resistances R1 and R1 ′ were measured by a four-terminal method. And the resistance increase rate is given by the following formula:
Resistance increase rate = 100 × (R1′−R1) / R1
Calculated based on The results are shown in Table 1.

In addition, during the manufacture of the membrane wiring boards obtained in Examples 1 to 6 and Comparative Example 1, the resistance (R2) immediately after printing and drying of the second circuit layer was measured, and the second after the membrane wiring board was completed. The resistance (R2 ′) of the circuit layer was measured. The results are shown in Table 1. At this time, the resistances R2 and R2 ′ were also measured by the four-terminal method. And the resistance increase rate is given by the following formula:
Resistance increase rate = 100 × (R2′−R2) / R2
Calculated based on The results are shown in Table 1.

  In addition, the resistance value and resistance increase rate of each Example and comparative example in Table 1 show the average value of the resistance value and resistance increase rate measured about ten membrane wiring boards.

(2) Conductivity evaluation of the first circuit layer and the second circuit layer in a state in which the membrane wiring board is bent. The membrane wiring board obtained in Examples 1 to 6 and Comparative Example 1 is φ0 and the circuit forming surface is outside. The resistance value was measured for each of the first circuit layer and the second circuit layer in the state of being bent for the 10th time, and bent with respect to the resistance (Rb) before the bending. The resistance change rate of the resistance (Ra) in the later state is expressed by the following formula:
Resistance change rate = 100 × (Ra−Rb) / Rb
Calculated based on The results are shown in Table 2.

  From the results shown in Table 1, it can be seen that the membrane wiring boards of Examples 1 to 6 can realize a circuit layer having an excellent conductivity because the increase in resistance is remarkably suppressed as compared with the membrane wiring board of Comparative Example 1. It was. In addition, from the results shown in Table 2, the membrane wiring boards of Examples 1 to 6 have a smaller resistance change rate even in the bent state than the membrane wiring board of Comparative Example 1, and sufficiently reduce the conductivity of the circuit layer. It was found that it can be suppressed.

  Therefore, according to the conductive paste of the present invention, it is possible to form a circuit layer that has excellent conductivity even when covered with an insulating coating layer and sufficiently suppresses a decrease in conductivity even when bent. It was confirmed that

  DESCRIPTION OF SYMBOLS 1 ... Plastic base material, 2a ... 1st circuit layer, 2b ... 2nd circuit layer, 3 ... 1st insulating coating layer, 4 ... 2nd insulating coating layer, 100 ... Membrane wiring board.

Claims (5)

Applying a conductive paste on a plastic substrate to form a first circuit layer, and applying a resin composition to the first circuit layer to form a first insulating coating layer ;
A second step of applying a conductive paste to form a second circuit layer, and applying a resin composition to the second circuit layer to form a second insulating coating layer;
A membrane wiring board characterized by being obtained through,
The conductive paste is
A binder resin;
Containing conductive powder,
The conductive powder is composed of flaky silver particles and spherical silver particles,
The proportion of the spherical silver particles in the conductive powder is greater than 0% by mass and 15% by mass or less,
The spherical silver particles have an average particle size of 0.1 to 20 μm,
A membrane wiring board, wherein the resin composition is an ultraviolet curable ink . The membrane wiring board according to claim 1, wherein a ratio of an average particle diameter of the spherical silver particles to an average particle diameter of the flaky silver particles is 0.1-1. The membrane wiring board according to claim 1 or 2, wherein the ultraviolet curable ink contains polyurethane (meth) acrylate. Applying a conductive paste on a plastic substrate to form a first circuit layer, and applying a resin composition to the first circuit layer to form a first insulating coating layer;
  A second step of applying a conductive paste to form a second circuit layer, and applying a resin composition to the second circuit layer to form a second insulating coating layer;
A method for manufacturing a membrane wiring board through which a membrane wiring board is manufactured,
  The conductive paste is
  A binder resin;
  Containing conductive powder,
  The conductive powder is composed of flaky silver particles and spherical silver particles,
  The proportion of the spherical silver particles in the conductive powder is greater than 0% by mass and 15% by mass or less,
  The spherical silver particles have an average particle size of 0.1 to 20 μm,
  A method for producing a membrane wiring board, wherein the resin composition is an ultraviolet curable ink. The manufacturing method of the membrane wiring board of Claim 4 whose ratio of the average particle diameter of the said spherical silver particle with respect to the average particle diameter of the said flaky silver particle is 0.1-1.

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