JPS6315498A - Circuit board for countermeasure against emi - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a circuit board for EMI countermeasures, and particularly to a circuit board for configuring an electronic circuit connected to other equipment via a cable or the like, such as in a home video game. EMI
Regarding countermeasure circuit boards.

(Prior Art) Recently, regulations regarding electromagnetic interference (EMI) have become stricter in Japan as well as the FCC (Federal Communications Commission). The applicant has previously proposed such EM
proposed a device that can prevent I.

(Problems to be Solved by the Invention) The above-mentioned conventional technology uses a shield case and is therefore very effective for, for example, personal computers and other independent devices.

However, it has not been sufficient as an EMI countermeasure for electronic equipment having an image processing function, such as a home game machine such as Family Computer (registered trademark) or a personal computer. The reason for this is that the main body of the game machine is connected to other devices such as a television receiver or controller via a long cable, and the entire game machine cannot be covered with a shield case. That is, the above-mentioned conventional technology prevents unnecessary radiation by confining electromagnetic wave energy within a shield case, and is not effective against electromagnetic waves radiated through a cable extending from a game machine.

Therefore, the main object of this invention is to
An object of the present invention is to provide a circuit board for MI countermeasures.

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

(Means for Solving the Problems) Simply put, the present invention provides a conductive conductor which is formed on at least one main surface of a substrate and a circuit pattern including a ground pattern according to a desired circuit. layer, an insulating layer formed on the substrate to cover the conductive layer except for the ground pattern part, and a shield electrode layer formed on the insulating layer and connected to the ground pattern, and the shield electrode layer is made of metal. For 100 parts by weight of copper powder, resin mixture (20 to 60% by weight of melamine resin, and 80 to 60% by weight of polyol and polyester resin or/and alkyd resin)
This is a circuit board for EMI countermeasures formed with a sinus ink containing 15 to 50 parts by weight of a resin mixture (40% by weight) and 1 to 8 parts by weight of saturated fatty acids or unsaturated fatty acids or metal salts thereof. . Note that the sinus ink refers to a copper paste composition.

(Function) In a conventional circuit board without a shield electrode layer on the conductive layer, stray capacitance or distributed capacitance is formed between adjacent patterns in the conductive layer. In this invention, a shield electrode layer is formed on and in close proximity to the conductive layer, so that each pattern of the conductive layer is connected to its adjacent shield electrode layer rather than to an adjacent pattern. Forming distributed capacitance.

Since this shield electrode layer is connected to the ground pattern, it is grounded at high frequencies. Therefore, unnecessary electromagnetic waves generated in each pattern of the conductive layer by induction or the like flow to the ground through the above-mentioned distributed capacitance. Therefore, unnecessary electromagnetic energy is removed from the circuit board itself.

(Effects of the Invention) According to this invention, the energy of unnecessary components in the circuit board itself constituting an electronic circuit is reduced, so even if a cable is connected to it, unnecessary radiation will not occur through the cable. do not have. Therefore, the present invention is very effective as an EMI countermeasure for all types of electronic equipment.

In other words, with conventional EMI countermeasures that use a shield case, unnecessary electromagnetic waves are radiated through cables extended from the electronic circuit board itself.
By using the circuit board of this invention, unnecessary electromagnetic waves are already removed from the circuit board itself, so even if cables are connected to it, unnecessary radiation can be stably prevented. .

Further, in order to form the shield electrode layer, it is sufficient to simply apply the sinus ink, so that the problem of complicating the manufacturing process does not occur. Moreover, the sinusoidal ink is made of a resin mixture (20 to 60% by weight of melamine resin, and 80 to 40% by weight of polyol and polyester resin or/and alkyd resin) based on 100 parts by weight of metallic copper powder. ) 15 to 50 parts by weight and 1 to 1 of saturated fatty acids or unsaturated fatty acids or metal salts thereof
Since a tonal ink containing 8 parts by weight is used, properties do not deteriorate due to oxidation, and stable properties can be obtained over time.

Although it is possible to use a composition filled with powders of gold, silver nickel, carbon, etc. instead of the copper powder in the tonal ink, the tonal ink is the most practical in terms of price.

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

(Embodiment) FIG. 1 is a sectional view showing an embodiment of the present invention. This circuit board or printed board 10 includes a substrate 12 made of an insulating material such as synthetic resin or ceramics. This board 12 is constructed as a so-called double-sided board, and a conductive layer 14 such as copper foil is formed on both main surfaces of the board 12, and a necessary circuit is formed on this conductive layer 14 by etching. A circuit pattern is formed. Note that 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. This plating layer 18 is formed when it is necessary to interconnect the conductive layers 14 on both sides of the substrate 12, and both ends thereof are connected to the corresponding conductive layers 14. Note that the plating layer 18 may be unnecessary if the through hole 16 is simply used as an insertion hole for a component (not shown).

Solder resist layers 20 are formed on both main surfaces of the substrate 12 so as to cover the conductive layer 14, but excluding the ground pattern 14a. This solder resist layer 20 is formed in a region of the conductive layer 14 to which solder is not to be attached in a later process, but it is also formed in a region where solder is not to be attached in a later step. It can also be used to ensure insulation. In addition, the ground pattern 14a that is not covered by the solder resist layer 20 has
A sinus ink layer 22, which will be described later, is connected.

On the ambidextrous surface of the substrate 12, on the solder resist layer 20,
A sinusoidal ink layer 22 is formed over substantially the entire surface of the substrate 12 so as to cover the conductive layer 14 . Examples of the tonal ink for forming the sinus ink layer 22 include:
Tonal ink manufactured by Tac Electric Cable Co., Ltd., etc. can be used. By the way, this tonal ink is made by mixing fine copper particles as a filler, a binder to firmly adhere these fine particles to each other, and various additives to maintain stable conductivity over a long period of time. There is. The particle size of copper fine particles is
The mesh diameter is selected to be smaller than the mesh diameter of the silk screen used to form the sinus ink layer 22 by printing. Furthermore, as the binder, a thermosetting resin such as a resol type phenol resin is used, and an appropriate solvent is used to adjust the viscosity.

Specifically, in order to form the sinus ink layer 22,
Resin mixture (20-60% by weight of melamine resin, and 80-40% by weight of polyol and polyester resin or/and alkyd resin) per 100 parts by weight of metallic copper powder.
A tonal ink containing 15 to 50 parts by weight of a resin mixture consisting of 1 to 8 parts by weight of a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof is used. More preferably, the polyol and the polyester resin or/and alkyd resin are blended in the following weight percent ratio of polyester resin or/and alkyd resin.

The metallic copper powder may have any shape such as a flaky shape, a dendritic nine-spherical shape, or an irregular shape, and its particle size is preferably 100 μm or less, particularly preferably 1 to 30 μm. Particle size is 1μm
If it is less than that, it is not preferable because it is easily oxidized and the conductivity of the resulting coating film decreases. The amount of metallic copper powder used is always 100 parts by weight.

The melamine resin in the resin mixture is an alkylated melamine resin, and at least one selected from methylated melamine, butylated melamine resin, etc. is used. Melamine resin binds metal copper powder and other ingredients well.

The amount of melamine resin in the resin mixture depends on the amount of polyol used as other binder and polyester resin or/and
and alkyd resin, it is used in a range of 20 to 60% by weight, preferably 30 to 50% by weight.

If the blending amount of the melamine resin is less than 20% by weight, the metallic copper powder cannot be sufficiently bound, and the three-dimensional mesh structure of the melamine resin becomes unstable, which significantly reduces the conductivity of the coating film, so it is preferable. do not have. On the other hand, when it exceeds 60% by weight, it is also not preferable because it significantly reduces the conductivity of the coating film.

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

The polyol used has a total hydroxyl value and acid value of 10.
It is 0 mg/g or more, preferably 130 mg/g or more. If the total of the hydroxyl value and acid value is less than 100 mg/g, the conductivity will be lost, which is not preferable.

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

If the amount of polyol is less than 50% by weight, the conductivity of the coating film will not be good, and if it exceeds 95% by weight, good adhesion of the coating film will not be obtained.

The polyester resin and/or alkyd resin in the resin mixture has a moderating or suppressing effect on the condensation reaction between the melamine resin and the polyol, and serves as a vehicle to improve the properties of the coating film.

The average molecular weight of the polyester resin and/or alkyd resin used is preferably 500 or more, preferably 80
00 or more are used. It is not preferable to use a polymer having an average molecular weight of less than 5,000 because it significantly reduces the adhesion of the coating film.

The blending amount of polyester resin or/and alkyd resin in the resin mixture is 5 to 5 in the blending amount of polyol and polyester resin or/and alkyd resin.
It is used in a range of 50% by weight, preferably 10 to 40% by weight. When the amount of polyester resin and/or alkyd resin is less than 5% by weight, the adhesion of the coating film is unfavorable, while when it exceeds 50% by weight,
This is not preferable because the conductivity of the coating film decreases significantly.

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

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

Saturated fatty acids, unsaturated fatty acids, or their metal salts are dispersing agents for dispersing metallic copper powder in a resin mixture, and examples of saturated fatty acids include palmitic acid, stearic acid, and arachidic acid having 16 to 20 carbon atoms. As unsaturated fatty acids, seamarinic acid, oleic acid, lylunic acid, etc. having 16 to 18 carbon atoms are used, and their metal salts are sodium.

It is a salt with metals such as potassium, copper, zinc, and aluminum.

The amount of the saturated fatty acid, unsaturated fatty acid, or metal salt thereof is 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.

If the amount of the dispersant is less than 1 part by weight, it will take time to knead to finely disperse the metallic copper powder into the resin mixture, and if it exceeds 8 parts by weight, the conductivity of the coating will decrease. This is not desirable because it causes

Furthermore, ordinary organic solvents can be used as appropriate to adjust the viscosity. For example, it is a known solvent such as cellusolve acetate butyl cellosolve acetate.

After such an antral ink layer 22 is cured,
Its specific resistance is, for example, 10-4 to 10-5 Ω·cm, and its conductivity is stable over a long period of time. Therefore, this sinus ink J1g22 sufficiently functions as an electromagnetic wave shield.

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

The above-described sinus ink layer 22 is effective as a countermeasure against EMI. That is, because the circuit patterns of the conductive layer 14 are placed in close proximity to the antral ink layer 22, each circuit pattern of the conductive layer has an antral ink layer 22, rather than an adjacent pattern. Stray capacitance or distributed capacitance is formed. Therefore, the energy of unnecessary frequency components induced in the circuit pattern of the conductive layer 14 flows to the sinus ink layer 22 via the formed distributed capacitance. On the other hand, the sinus ink layer 22 is connected to the ground pattern 14a of the conductive layer 14 and grounded in terms of high frequencies, as described above. Therefore, the electromagnetic wave energy that has flowed into the sinus ink layer 22 will eventually flow to 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 using the circuit board 10 and a cable or the like is connected to it, radiant energy will not be transferred to the cable.

This will be specifically explained 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 connecting elements la and 1b and the ground line 4 are
Each has an inductance according to its length, and distributed capacitance is generated between each signal line 2 and 3 and between each signal line 2 and 3 and earth line 4 according to the distance between the lines. However, if there is an inductance component in the ground line 4, the ground line 4 will not function as a ground for high frequency components in the signal, and a potential difference will occur between both ends of the ground line 4 due to the inductance, and the resulting energy will be transferred onto the ground line 4. remain in the When this energy becomes large, it leaks outside as noise and causes electromagnetic interference to surrounding electronic components and equipment.

On the other hand, in the circuit board of this embodiment, the equivalent circuit is as shown in FIG. 9, and since the ground line 4' covers almost the entire surface of the pattern of each signal line 2 and 3, the inductance component is not included. Since no high-frequency potential difference is generated, almost no energy remains in the ground line 4'.

Furthermore, in conventional circuit boards, each distributed capacitance varies depending on the distance between the signal lines 2 and 3 or between each signal line 2 and 3 and the ground line 4, making the distributed capacitance non-uniform and the path of the signal flowing. Impedance changes along the way, causing mismatching in high frequency transmission. Therefore, 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 electrode.

On the other hand, in the circuit board of this embodiment, each signal line 2
and the distance between 3 and the ground line 4' is almost uniform, and accordingly, the distributed capacitance between the two is uniform,
Moreover, the value is so large that the distributed capacitance between the signal lines 2 and 3 can be ignored. Therefore, since the energy of high frequency components conventionally accumulated on each signal line 2 and 3 flows to the ground line 4' via its distributed capacitance, no unnecessary radiation occurs.

In FIG. 10, line A shows the radiation level when the conventional substrate is used, and line B shows the radiation level when the substrate according to the embodiment of the invention is used. As can be seen from FIG. 10, in the conventional case, for example, at 67.03MHz, the frequency is 50.60MHz.
There was a large amount of unnecessary radiation of dBμ■. On the contrary,
If the circuit board of this embodiment is used, the radiation level will be reduced to almost only noise components, and all FCC and other regulations can be overcome without any problems.

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. 2 to 7.

First, as shown in FIG. 2, a substrate 12 is prepared. The substrate 12 is made of, for example, a synthetic resin such as epoxy resin or phenol, or ceramics, and has a thickness of, for example, 1.2-1.6 Im. Then, on both main surfaces of the substrate 12, for example, 3O-To
A conductive layer 14' on which a pattern corresponding to the first circuit is to be formed in a later step is formed using a copper foil having a thickness of approximately μm.

Subsequently, as shown in FIG. 3, a conductive layer 14 is formed on the substrate 12.
For example, using a multi-spindle drilling machine,
A through hole 16 is formed. This through hole 16 is used to interconnect the conductive layers 14' on both main surfaces, and can also be used simply as a lead wire insertion hole for an electronic component. Then, after polishing the end face of the perforation, the process moves to the next step.

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

The conductive layer 14' is then etched to form a circuit pattern corresponding to the required circuitry, including a ground pattern 14a, as shown in FIG. That is, first, an etching resist is printed according to the required circuit, and the through holes 16 are filled in. Thereafter, the necessary circuit pattern is formed by wet etching or dry etching.

Thereafter, 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 oxidation and deterioration of the conductive layer 14,
Rust prevention treatment may be applied.

The steps up to this point are well known as general manufacturing steps not only for conventional multilayer boards but also for printed circuit boards.

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

The printed sinus ink is then heated and cured.

Phenol resin is thermosetting, for example 1
It is cured by condensation reaction at 45°C for about 30 minutes. During curing, the sinus ink shrinks not only in its surface direction but also in its thickness direction. According to the inventor's experiments, the adhesion strength between the sinus ink layer 22 and the substrate 12 after curing is such that a land of 3φ can withstand a tensile load of 3 kg, and a land of 3 φ can withstand a tensile load of 3 kg. Almost equal to conductivity N14.

Finally, as shown in FIG.
For example, it is formed by coating or printing. In this way, the multilayer substrate 10 is manufactured.

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

Furthermore, when forming the sinusoidal ink layer 22 as an electromagnetic wave shield on both main surfaces of the substrate 12, the ground pattern 1
4a may be formed only on one main surface, several through holes may be connected to the ground, and the sinus ink layer 22 on the other main surface may be connected to the through holes.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention. FIGS. 2 to 7 are cross-sectional views sequentially showing an example of a method for manufacturing the circuit board of the embodiment shown in FIG. 1. 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. This shows the circuit board. FIG. 10 is a graph for explaining the present invention in detail, with the horizontal axis representing frequency and the vertical axis representing radiated electric field strength. In the figure, 10 is a circuit board, 12 is an insulating substrate, 14 is a thin electrical layer, 20 and 24 are solder resist layers, 22.22
' indicates the sinus ink layer. Patent applicant Nintendo Co., Ltd. agent Patent attorney Yama 1) Yoshito (and 1 other person) No. 11 No. 2'c'i zu4゛ No. 5 Fig. 8 Fig. 9

Claims (1)

[Scope of Claims] 1. A substrate, a conductive layer formed on at least one main surface of the substrate, and on which a circuit pattern including a ground pattern is formed according to a desired circuit; An insulating layer is formed on the substrate to cover the conductive layer, and a resin mixture (melamine resin 20 to 60% by weight, and polyol) is added to 100 parts by weight of metallic copper powder to cover the insulating layer. and polyester resin or/and alkyd resin (resin mixture consisting of 80 to 40% by weight) 15 to
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, and a shield electrode layer connected to the ground pattern. 2. The EMI countermeasure circuit board according to claim 1, comprising a second insulating layer formed on the substrate so as to cover the shield electrode layer. 3. The blending of the polyol and the polyester resin or/and the alkyd resin is as follows: polyol/(polyester resin or/and alkyd resin)=95 to 5/5 to 50, claim 1 or EM described in Section 2.
I countermeasure circuit board.