JPH06101635B2 - EMI countermeasure circuit board - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an EMI countermeasure circuit board, and in particular, constitutes an electronic circuit connected to other equipment by a cable or the like, such as a home video game. EMI countermeasure circuit board.

(Prior Art) Recently, as in the FCC (Federal Communications Commission), regulations on electromagnetic interference (EMI) have become strict in Japan as well. The applicant of the present application was previously
We have proposed a device that can prevent such EMI, such as 58-72895.

(Problems to be Solved by the Invention) Since the above-described conventional technique uses the shield case, it is very effective for, for example, a personal computer and other independent devices.

However, it is not sufficient as an EMI countermeasure for electronic devices having an image processing function such as a home game machine such as a family computer (registered trademark) or a personal computer. The reason is that the main body of the game machine is connected to other devices such as a television receiver and a controller via a long cable, and the whole body cannot be covered with the shield case. That is, in the above-mentioned conventional technique, the electromagnetic wave energy is confined in the shield case to prevent unnecessary radiation, and it is not effective for the electromagnetic wave radiated through the cable extending from the game machine.

Therefore, the main purpose of the present invention is to provide a novel configuration of EM.
It is to provide a circuit board for countermeasures I.

Another object of the present invention is to effectively suppress unnecessary electromagnetic wave radiation from an electronic circuit formed on a circuit board.
It is to provide a circuit board for countermeasures I.

(Means for Solving the Problems) Briefly, the present invention provides a substrate, a conductive layer formed on at least one main surface of the substrate and having a circuit pattern including a ground pattern according to a desired circuit. Layer, an insulating layer formed to cover the conductive layer on the substrate except the ground pattern portion, and a shield electrode layer formed on the insulating layer and connected to the ground pattern. Resin mixture (20 to 60% by weight of melamine resin and 80 to 40% by weight of polyester polyol and at least one of polyester resin and alkyd resin) per 100 parts by weight of copper powder 15 to
An EMI countermeasure circuit board formed by a copper ink containing 50 parts by weight and 1 to 8 parts by weight of a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof. The copper ink is a copper paste composition.

(Function) In a conventional circuit board having no shield electrode layer on the conductive layer, stray capacitance or distributed capacitance is formed between adjacent patterns in the conductive layer. In the present invention, since the shield electrode layer is formed on and above the conductive layer, each pattern of the conductive layer is formed between the adjacent shield electrode layer rather than between the adjacent patterns. Form distributed capacitance. Since this shield electrode layer is connected to the ground pattern, it is grounded at a high frequency. Therefore, unnecessary electromagnetic waves generated in each pattern of the conductive layer by, for example, induction flow to the ground through the above-mentioned distributed capacitance. Therefore, unnecessary electromagnetic wave energy is removed from the circuit board itself.

(Effect of the Invention) According to the present invention, the energy of the unnecessary component in the circuit board itself constituting the electronic circuit is reduced, so that even if a cable or the like is connected to it, unnecessary radiation will not occur through the cable. Absent. Therefore, the present invention is very effective as an EMI countermeasure for electronic devices of all types. That is, unlike the conventional one, in the EMI countermeasure using the shield case, unnecessary electromagnetic waves were radiated through the cable extended from the electronic circuit board itself, but if the circuit board of the present invention is used, the circuit board itself will be radiated. Since unnecessary electromagnetic waves have already been removed in step 1, even if a cable or the like is connected thereto, it is possible to stably prevent unnecessary radiation regardless of them.

Moreover, since the copper ink may be applied, for example, only in order to form the shield electrode layer, there is no problem that the manufacturing process is complicated. Moreover, as the copper-based ink, a resin mixture (melamine resin 20 to 60% by weight, and polyester polyol and at least one of polyester resin and alkyd resin) from 80 to 40% by weight based on 100 parts by weight of metallic copper powder. 15 to 50 parts by weight of a resin mixture) and 1 to 8 parts by weight of a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof are used, so that the characteristic deterioration due to the oxidation does not occur and Stable characteristics are obtained.

It should be noted that it is conceivable to use a composition filled with powder of gold, silver nickel, carbon or the like instead of the copper powder of the copper ink, but the copper ink is the most practical in terms of cost.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

(Embodiment) FIG. 1 is a sectional view showing an embodiment of the present invention. The circuit board or printed board 10 includes a board 12 made of an insulating material such as synthetic resin or ceramics.
This substrate 12 is configured as a so-called double-sided substrate,
A conductive layer 14 such as a copper foil is formed on both main surfaces of the substrate 12, and a circuit pattern for a necessary circuit is formed on the conductive layer 14 by etching. In addition,
This circuit pattern usually includes a ground pattern.

A through hole 16 is formed in the substrate 12, and a plating layer 18 is formed on the inner wall of the through hole 16. The plating layer 18 is formed when it is necessary to connect the conductive layers 14 on both surfaces of the substrate 12 to each other, and both ends thereof are connected to the corresponding conductive layers 14. It should be noted that the plating layer 18 may be unnecessary when the through hole 16 is simply used as an insertion hole for a component (not shown).

A solder resist layer 20 is formed on both main surfaces of the substrate 12 so as to cover the conductive layer 14, but except for the ground pattern 14a. The solder resist layer 20 is to be formed in a region of the conductive layer 14 where solder should not be attached in a later step, and further includes a copper ink layer 22 and a conductive layer 14 described later. It can also be used to ensure insulation. Further, on the ground pattern 14a not covered with the solder resist layer 20, a copper-based ink
Are connected.

On both main surfaces of the board 12, on the solder resist layer 20, the board
A copper ink layer 22 is formed over substantially the entire surface of 12 so as to cover the conductive layer 14. As the copper-based ink for forming the copper-based ink layer 22, for example, copper-based ink manufactured by Tatsumi Electric Wire Co., Ltd. or the like can be used. By the way,
This copper ink, copper fine particles as a filler, and a binder for firmly adhering these fine particles,
It is made by mixing with various additives to keep the conductivity stable for a long time. The particle size of the copper fine particles is selected to be smaller than the mesh diameter of the silk screen when the copper ink layer 22 is formed by printing. Further, as the binder, for example, a thermosetting resin such as resol type phenol resin is used, and an appropriate solvent is used for adjusting the viscosity.

Specifically, in order to form the copper ink layer 22, 100 parts by weight of the metal copper powder is mixed with the resin mixture (melamine resin 2
0-60% by weight, and polyester polyol and at least one of polyester resin and alkyd resin
15 to 50 parts by weight of a resin mixture of 80 to 40% by weight, and 1 to 8 parts by weight of a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof are used. More preferably, at least one of polyester polyol and polyester resin and / or alkyd resin (hereinafter referred to as “polyester resin or / and alkyd resin”).
May be described as. ) With the following weight% ratio Is.

The metallic copper powder may have any shape such as flaky shape, dendritic shape, spherical shape, and indefinite shape, and its particle size is preferably 100 μm or less, particularly preferably 1 to 30 μm. Particles having a particle size of less than 1 μm are easily oxidized and the resulting coating film has a reduced conductivity, which is not preferable. And the compounding amount of the metal copper powder is
Always use 100 parts by weight.

The melamine resin in the resin mixture is an alkylated melamine resin, and at least one selected from methylated melamine or butylated melamine resin is used. Melamine resin is one that binds metallic copper powder and other components well.

The blending amount of the melamine resin in the resin mixture is determined by blending the polyester polyol used as another binder with the polyester resin or / and the alkyd resin,
It is used in the range of 20 to 60% by weight, preferably 30 to 50% by weight.

When the blending amount of the melamine resin is less than 20% by weight, the metal copper powder cannot be sufficiently bound, the three-dimensional network structure of the melamine resin becomes unstable, and the conductivity of the coating film is significantly reduced, which is preferable. Absent. On the other hand, when it exceeds 60% by weight, the conductivity of the coating film is significantly lowered, which is not preferable.

The polyol in the resin mixture is a polyester polyol represented by the following chemical structural formula and crosslinks with the melamine resin.

The polyester polyol used has a total of hydroxyl value and acid value of 100 mg / g or more, preferably 13 mg / g or more. If the total of the hydroxyl value and the acid value is less than 100 mg / g, the conductivity is lost, which is not preferable.

The blending amount of the polyester polyol in the resin mixture is in the range of 50 to 95% by weight, preferably 60 to 90% by weight, in the blending of the polyester polyol and the polyester resin or / and the alkyd resin.

When the content of the polyester polyol is less than 50% by weight, the conductivity of the coating film is not good, and conversely, when it exceeds 95% by weight, good adhesion of the coating film cannot be obtained.

The polyester resin and / or the alkyd resin in the resin mixture have a relaxing or suppressing action in the condensation reaction between the melamine resin and the polyester polyol, and also improve the properties of the coating film as a vehicle.

The polyester resin and / or alkyd resin used has an average molecular weight of preferably 5,000 or more, preferably 8,000 or more. If the average molecular weight is less than 5,000, the adhesion of the coating film is significantly reduced, which is not preferable.

The blending amount of the polyester resin or / and the alkyd resin in the resin mixture is in the range of 5 to 50% by weight in the blending amount of the polyester polyol and the polyester resin or / and the alkyd resin, and preferably 10
~ 40% by weight. When the content of the polyester resin and / or the alkyd resin is less than 5% by weight, the adhesion of the coating film is not preferable, and when it exceeds 50% by weight, the conductivity of the coating film is remarkably lowered, which is not preferable. .

Here, the blending amount of the polyester polyol and the polyester resin or / and the alkyd resin in the resin mixture is 80 to 40% by weight in the blending with the melamine resin, and preferably 70 to 50% by weight. .

The amount of the resin mixture (melamine resin 20 to 60% by weight and resin mixture consisting of polyester polyol and polyester resin and / or alkyd resin 80 to 40% by weight) is 15 parts by weight based on 100 parts by weight of metallic copper powder. It is used in the range of 50 to 50 parts by weight, preferably 20 to 40 parts by weight.

Saturated fatty acid or unsaturated fatty acid or a metal salt thereof is a dispersant for dispersing metal copper powder in a resin mixture, and as saturated fatty acid, palmitic acid having 16 to 20 carbon atoms,
Stearic acid, arachidic acid, etc. are also used as the unsaturated fatty acids, such as zomarinic acid having 16 to 18 carbon atoms, oleic acid, and linolenic acid, and their metal salts are metals such as sodium, potassium, copper, zinc, and aluminum. Is the salt of.

The saturated fatty acid or unsaturated fatty acid or the metal salt thereof is used in the range of 1 to 8 parts by weight, preferably 2 to 6 parts by weight, based on 100 parts by weight of the metal copper powder.

When the content of the dispersant is less than 1 part by weight, it takes time for kneading to finely disperse the metal copper powder in the resin mixture, and when it exceeds 8 parts by weight, the conductivity of the coating film is lowered. It is not preferable because it causes.

Furthermore, in order to adjust the viscosity, a usual organic solvent can be appropriately used. For example, known solvents such as cellosolve acetate and butylcellosolve acetate.

Such a copper ink layer 22 has a specific resistance of, for example, 10 ⁻⁴ to 10 ⁻⁵ Ω · cm after it is hardened, and has long-term stability of its conductivity. Therefore, the copper ink layer 22 sufficiently functions as an electromagnetic wave shield.

On the upper surface of the substrate 12, further covering the copper ink layer 22,
A solder resist layer 24 as a second insulating layer is formed.

The above-mentioned copper ink layer 22 is effective as an EMI countermeasure. That is, the circuit pattern of the conductive layer 14 is a copper ink layer.
Being placed in close proximity to 22, a stray or distributed capacitance is formed in each circuit pattern of the conductive layer with the copper ink layer 22 rather than with an adjacent pattern.
Therefore, the energy of the unnecessary frequency component induced in the circuit pattern of the conductive layer 14 flows into the copper ink layer 22 via the formed distributed capacitance. Meanwhile, the copper ink layer 22
Is connected to the ground pattern 14a of the conductive layer 14 as described above and grounded in terms of high frequency. Therefore, the electromagnetic wave energy that has flowed into the copper ink layer 22 will eventually flow into the high frequency ground. Therefore, unnecessary electromagnetic wave energy is not accumulated in each circuit pattern of the conductive layer 14. Therefore, even if an electronic circuit is configured by the circuit board 10 and a cable or the like is connected to the electronic circuit, radiant energy does not ride on the cable.

This will be specifically described with reference to FIGS. 8 and 9. FIG. 8 is an equivalent circuit diagram of a conventional general circuit board. In this equivalent circuit, the signal lines 2 and 3 for connecting the elements 1a and 1b and the ground line 4 are respectively arranged according to their lengths. And a distributed capacitance corresponding to the distance between the lines is generated between the signal lines 2 and 3 and between the signal lines 2 and 3 and the ground line 4. However, if the ground line 4 has an inductance component, the ground line 4 does not act as a ground for the high frequency component in the signal, and a potential difference occurs at both ends of the ground line 4 due to the inductance, and energy due to this causes a difference in potential on the ground line 4. Remains in. When this energy becomes large, it becomes noise and leaks to the outside, causing electromagnetic interference to peripheral electronic component devices.

On the other hand, the circuit board of this embodiment has an equivalent circuit as shown in FIG. 9, and since the ground line 4'covers almost the entire pattern of the signal lines 2 and 3, the inductance component is included. Since no high frequency potential difference occurs, energy hardly stays in the earth line 4 '.

Further, in the conventional circuit board, the respective distributed capacitances differ depending on the distance between the signal lines 2 and 3 or the distance between the signal lines 2 and 3 and the ground line 4, and the distributed capacitance becomes non-uniform, so that the signal flow path The impedance changes on the way, causing a mismatch in high-frequency transmission. For this reason, unnecessary high frequency components in the signal stay on the signal lines 2 and 3, and this energy becomes noise and leaks or radiates to the external electrodes.

On the other hand, in the circuit board of this embodiment, each signal line 2
And 3 and the earth line 4'are almost uniform in distance, and accordingly, the distributed capacitance between them is made uniform,
In addition, the value is large enough to ignore the distributed capacitance between the signal lines 2 and 3. Therefore, in the conventional case, the energy of the high frequency component accumulated on each of the signal lines 2 and 3 flows to the earth line 4'through its distributed capacitance, so that unnecessary radiation does not occur.

In FIG. 10, line A shows the radiation level when the conventional substrate is used, and line B shows the case where the substrate of the embodiment of the present invention is used. As can be seen from FIG. 10, in the conventional case, there was a large amount of unwanted radiation of 50.60 dBμV at 67.03 MHz. On the other hand, if the circuit board of this embodiment is used, the radiation level is almost only the noise component, and the FCC and other regulations can be overcome without any problem.

Next, an example of a method for manufacturing the circuit board 10 of the embodiment shown in FIG. 1 will be described with reference to FIGS.

First, as shown in FIG. 2, the substrate 12 is prepared. The substrate 12 is made of, for example, a synthetic resin such as epoxy resin or paper phenol, or ceramics, and has a thickness of 1.2 to 1.6 mm, for example. Then, on both main surfaces of the substrate 12, a conductive layer 14 'on which a pattern corresponding to the first circuit is to be formed in a later step is formed by a copper foil having a thickness of about 30 to 70 .mu.m, for example.

Subsequently, as shown in FIG. 3, through holes 16 are formed in the substrate 12 so as to penetrate the conductive layer 14 ', for example, by using a multi-axis drilling machine. The through holes 16 are used to interconnect the conductive layers 14 'on both main surfaces and can also be used as mere lead wire insertion holes for electronic components. Then, after the perforated end face is polished, the process proceeds to the next step.

Next, as shown in FIG. 4, a plating layer 18 is formed on the inner wall of the through hole 16 by, for example, electrolytic plating or electroless plating. Therefore, the conductive layers 14 'on both surfaces of the substrate 12 are connected to each other.

Subsequently, the conductive layer 14 'is etched to form a circuit pattern corresponding to a necessary circuit including the ground pattern 14a, as shown in FIG. That is, first, an etching resist is printed according to a required circuit, "hole filling" of the through hole 16 is performed, and then wet etching or dry etching is performed to form a required circuit pattern.

After that, as shown in FIG. 6, a solder resist layer 20 which functions as a first insulating layer is printed. At this time, in order to prevent the conductive layer 14 from being oxidized or deteriorated, rust prevention treatment may be performed.

The steps up to this point are well known as general manufacturing steps for printed circuit boards as well as conventional multilayer boards.

Next, as shown in FIG. 7, a copper ink 22 'is formed on the first insulating layer, that is, the solder resist layer 20, so as to cover the conductive layer 14 over substantially the entire surface. That is, the substrate 12
A silk screen (not shown) having a printing pattern required as the copper ink layer 22 is arranged and positioned on the main surface of the, and printed with the predetermined copper ink as described above. The copper ink layer 22 'may be formed so as to cover the ground pattern 14a.

Then, the printed copper ink is heated and cured.
Phenolic resins are thermosetting, such as 14
It cures by condensation reaction at 5 ℃ for about 30 minutes. Upon curing, the copper ink shrinks not only in its surface direction but also in its thickness direction. According to an experiment conducted by the inventor, the adhesive strength of the cured copper ink layer 22 to the substrate 12 or the like can withstand a tensile load of 3 kg with a land of 3φ, for example. Almost equal to layer 14.

Finally, as shown in FIG. 1, a solder resist layer 24 as a second insulating layer is formed on the entire surfaces of both sides of the substrate 12 by, for example, coating or printing. In this way, the multilayer substrate 10 is manufactured.

In any of the above examples, the copper ink layer 22 as an electromagnetic wave shield was formed on both main surfaces of the substrate 12. However, according to the experiments by the inventor, these may be formed only on one main surface of the substrate 12.

Further, the copper ink layer 22 as an electromagnetic wave shield is provided on the substrate 12
When formed on both main surfaces, the ground pattern 14a is formed only on one main surface, several through holes are connected to the ground, and the copper ink layer 22 on the other main surface has the through holes. May be connected to.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of the present invention. 2 to 7 are cross-sectional views showing an example of a method of manufacturing the circuit board of FIG. 1 embodiment step by step. 8 and 9 are equivalent circuit diagrams for explaining the effects of this embodiment, respectively. FIG. 8 shows a conventional general circuit board, and FIG. 9 shows this embodiment. The circuit board is shown. FIG. 10 is a graph for explaining the effect of the present invention, in which the horizontal axis represents frequency and the vertical axis represents radiation electric field strength. In the figure, 10 is a circuit board, 12 is an insulating board, 14 is a conductive layer, 20 and 24 are solder resist layers, and 22 and 22 'are copper ink layers.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication location H05K 1/02 P 8824-4E (72) Inventor Shinichi Wakita 2-3 Iwata-cho, Higashiosaka-shi, Osaka No. 1 in Tatsuta Electric Wire Co., Ltd. (72) Inventor Hisatoshi Murakami 2-3-1, Iwata-cho, Higashi-Osaka City, Osaka Prefecture (3) In Tatsuta Electric Wire Co., Ltd. (72) Tsunehiko Terada 2 Iwata-cho, Higashi-Osaka City, Osaka 3-3-1 Tatsuta Electric Wire Co., Ltd. (72) Inventor Katsuya Nakagawa 115-19 Kamikasacho, Kusatsu City, Shiga Prefecture

Claims (3)

[Claims] 1. A substrate, a conductive layer formed on at least one main surface of the substrate, and having a circuit pattern including an earth pattern according to a desired circuit formed thereon, except for the earth pattern portion. An insulating layer formed to cover the conductive layer, and so as to cover the insulating layer, with respect to 100 parts by weight of the metal copper powder, a resin mixture (melamine resin 20 to 60% by weight, and a polyester polyol and 15 to 50 parts by weight of a resin mixture containing 80 to 40% by weight of at least one of a polyester resin and an alkyd resin, and 1 to 8 parts by weight of a saturated fatty acid or unsaturated fatty acid or a metal salt thereof. Also, an EMI countermeasure circuit board comprising a shield electrode layer connected to the earth pattern. 2. The circuit board for EMI countermeasure according to claim 1, further comprising a second insulating layer formed on the substrate so as to cover the shield electrode layer. 3. The blending ratio of the polyester polyol with at least one of a polyester resin and an alkyd resin is as follows. EMI according to claim 1 or 2
Countermeasure circuit board.