JPS6315497A - 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 EMI countermeasure circuit boards, particularly for configuring electronic circuits that are connected to other equipment via cables, such as home video games. This invention relates to a circuit board for EMI countermeasures.

(Prior Art) Recently, in Japan as well as the FCC (Federal Communications Commission), regulations regarding electromagnetic interference (EMI) have become stricter. 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 devices having image processing functions, such as home game machines such as Family Computer (registered trademark) and personal computers. 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) Briefly speaking, 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 to cover the conductive layer on the substrate except for the ground pattern part; a solderable copper-based ink layer comprising a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof, a metal chelate forming agent, and a soldering accelerator; This is an EMI countermeasure circuit board including a solder layer formed on an ink layer. Note that the copper-based 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 consisting of a solderable copper ink layer and a solder layer is formed on and close to the quadruple layer, so that each pattern of the conductive layer has a smaller distance between adjacent patterns. Rather, it forms a distributed capacitance with its close shield electrode. Since this shield electrode is connected to the ground pattern, it is grounded at high frequency.

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, it is sufficient to apply, for example, a solderable copper-based ink and form a solder layer thereon, so that the problem of complicating the manufacturing process does not occur. Moreover, the copper-based ink is a resin mixture consisting of 85 to 95% by weight of metallic copper powder and 15 to 5% by weight of a resin mixture (2 to 30% by weight of metal surface activated resin, and the remainder is a thermosetting resin). ) per 100 parts by weight of saturated fatty acids or unsaturated fatty acids or their metal salts.
Since a copper-based ink containing ~8 parts by weight, 1 to 50 parts by weight of a metal chelate forming agent, and 0.1 to 2.5 parts by weight of a soldering accelerator is used, conductivity is improved and the cured coating is Very good soldering can be performed on the entire surface of the film.

Note that instead of the copper powder in the copper-based ink, it is possible to use a composition filled with powders of gold, silver-nickel, carbon, etc., but the copper-based 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 t7i10 is a board 1 made of an insulating material such as synthetic resin or ceramic 7i.
Contains 2. 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.

The base plate 12 has a through hole, 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 in the plating layer 18, the through holes 16 are simply parts (
This may not be necessary if the hole is used as an insertion hole (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 between a copper ink layer 22 and a conductive layer 14, which will be described later. 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 copper 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 solderable copper ink layer (hereinafter simply referred to as "copper ink layer") 22 is formed over almost the entire surface of the substrate 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 Tac Electric Cable Co., Ltd., etc. can be used. By the way, this copper-based 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 the copper fine particles is selected to be smaller than the mesh size of the silk screen used to form the copper 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, 85-95% by weight of metallic copper powder and 15-5% by weight of resin mixture (2-30ffi of metal surface activated resin)
1 to 8 parts by weight of saturated fatty acids or unsaturated fatty acids or their metal salts and 1 to 50 parts by weight of a metal chelate forming agent, based on a total of 100 parts by weight of the resin mixture (resin mixture consisting of thermosetting resin and thermosetting resin) Part by weight and soldering accelerator 0.1-2
．． A copper-based ink containing 5 parts by weight is used.

Metallic copper powder is flaky. The particles may have any shape such as dendritic, spherical, or irregular shape, and the particle size is preferably 100 μm or less, particularly preferably 1 to 30 μm. Particles with a particle size of less than 1 μm are easily oxidized, resulting in decreased conductivity of the resulting coating film and poor semi-zero adhesion.

The amount of metallic copper powder mixed with the resin mixture is 85%.
It is used in the range of ~95% by weight, preferably 87~93% by weight.
It is a heavy percentage.

If the amount is less than 85% by weight, the conductivity will decrease and the solderability will deteriorate; if it exceeds 95% by weight, the metallic copper powder will not be sufficiently bound and the resulting coating will become brittle. As the conductivity decreases, screen printability also deteriorates.

The metal surface activated resin in the resin mixture includes activated rosin,
Alternatively, at least one modified rosin selected from partially hydrogenated rosin, fully hydrogenated rosin, esterified rosin, maleated rosin, disproportionated rosin, polymerized rosin, etc. is used. Preferred rosins are active or maleated rosins.

The amount of metal surface activating resin in the resin mixture is 2 to 3.
Used in the range of 0% by weight, preferably 5-10% by weight
It is. Even if the amount of the metal surface activating resin is less than 2% by weight, it is possible to solder directly onto the coating film when appropriate amounts of the metal chelate forming agent and soldering accelerator described below are disposed. When the amount is added within such a preferable range, the soldering surface can be made smoother and have a metallic luster. On the other hand, when it exceeds 30% by weight, it is not preferable because it causes a decrease in conductivity and no effect of increasing the amount on solderability is observed.

The thermosetting resin in the resin mixture binds the metallic copper powder and other components, and may be any polymeric substance that is liquid at room temperature and becomes a polymeric substance by heating and curing, such as Phenol, acrylic, epoxy, polyester, or xylene-based resins can be used, but are not limited to these. Among them, resol type phenolic resins are preferably used. The blending amount of the thermosetting resin in the resin mixture is in the range of 98 to 70% by weight.

The amount of the resin mixture described above is used in the range of 15 to 5% by weight when mixed with the metal copper powder, and the content of the metal copper powder and the resin mixture is 100 parts by weight. In such a case, if the blending amount of the resin mixture is less than 5% by weight, the metallic copper powder will not be sufficiently bound, the resulting coating will become brittle, the conductivity will decrease, and the screen printability will deteriorate, which is undesirable. . On the other hand, if it exceeds 15% by weight, the solderability will not be favorable.

Saturated fatty acids, unsaturated fatty acids, or metal salts thereof include valmitic acid, stearic acid, aracic acid, etc. having 16 to 20 carbon atoms, and unsaturated fatty acids such as seamarin having 16 to 18 carbon atoms. acid,
These include oleic acid and linuric acid, and their metal salts include salts with metals such as potassium, copper, and aluminum.

The use of these dispersants is preferable in blending the metallic copper powder and the resin mixture because it promotes fine dispersion of the metallic copper powder into the resin mixture and forms a coating film with good conductivity.

The amount of the saturated fatty acid or unsaturated fatty acid or the metal salt thereof used 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 total amount of the metallic copper powder and the resin mixture. It is.

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 in the resin mixture, and if it exceeds 8 parts by weight, the tetraelectricity of the coating film will decrease. This is not preferable because it lowers the adhesion between the coating film and the substrate.

As the metal chelate forming agent, at least one selected from aliphatic amines such as monoethanolamine, jetanolamine, triethanolamine, ethylenediamine, triethylenediamine, and triethylenetetramine is used. The metal chelate forming agent added prevents oxidation of the metal copper powder and contributes to maintaining conductivity, and also exhibits a synergistic effect with the metal surface activating resin to further improve solderability. For example, a combination of metallic copper powder, thermosetting resin, and metal surface activation resin does not allow for good soldering on the paint film, but good soldering can be achieved by disposing a metal chelate forming agent. Therefore, their role as a synergistic effect is significant.

The metal chelate forming agent is used in an amount of 1 to 50 parts by weight, preferably 5 to 30 parts by weight, based on 100 parts by weight of the total amount of the metal copper powder and the resin mixture. If the amount of the metal chelate forming agent is less than 5 parts by weight, the conductivity will decrease and the semi-Ui adhesion will not be favorable.

On the other hand, when it exceeds 50 parts by weight, the viscosity of the paint itself decreases too much, which is undesirable, as it may cause problems in sealing.

The soldering accelerator is oxydicarboxylic acid, aminodicarboxylic acid, or a metal salt thereof, such as at least one selected from tartaric acid, malic acid, glutamic acid, aspartic acid, or a metal salt thereof.

The added soldering promoter exhibits a synergistic effect with the metal chelate forming agent to further improve solderability.

That is, a metal surface activated resin and a metal chelate forming agent,
By adding a soldering accelerator to the soldering promoter, a synergistic effect can be exhibited, and the soldering surface of the coating film can be made smoother and have a metallic luster.

The amount of the soldering accelerator used is in the range of 0.1 to 2.5 parts by weight, preferably 0.5 to 2.5 parts by weight, based on 100 parts by weight of the total amount of the metal copper powder and the resin mixture. Parts by weight.

Even if the amount of the soldering accelerator is less than 0.11 parts by weight, soldering can be performed directly on the coating when the metal surface activating resin and metal chelate forming agent are disposed in appropriate amounts.
When the amount is added within such a preferable range, the soldering surface can be made smoother and more shiny than gold. On the other hand, when it exceeds 2.5 parts by weight, the conductivity decreases and the solderability becomes unfavorable.

Further, in order to adjust the viscosity, ordinary organic solvents can be used as appropriate. For example, butylcarpitol,
Butyl carpitol acetate.

These are known solvents such as butyl cellosolve, methyl isobutyl ketone, toluene, and xylene.

The copper ink layer 22 is formed using such a copper ink, and when the binder hardens, a solderable layer is formed near the surface of the copper ink layer 22. Then, this copper ink layer 22. A solder layer 26 is formed on the plating layer 18 and the conductive layer 14 on the inner wall of the through hole 16 by, for example, a solder dip. This solder layer 26, like the copper ink layer 22, is formed over almost the entire main surface of the substrate 12. At this time, since the solder resist layer 20 is removed from the ground pattern 14a, the solder layer 26 will eventually be connected to the ground pattern 14a.

Since the resistivity of solder is generally about 1 to 4×10 −′Ω・ω, the copper ink layer 22 to which the solder layer 26 is attached
is smaller than the resistivity of the copper-based ink layer 22 without the solder layer 26 (the conductivity is improved), and its mechanical strength is increased.

If the specific resistance of the copper ink layer 22 alone after hardening is, for example, on the order of 10-4 Ω·cm, then the solder layer 26
The equivalent resistivity of the copper-based ink layer 22 after forming is, for example, on the order of 10-'Ω·0.

Therefore, the copper-based ink layer 22 on which the solder layer 26 is formed in this manner exhibits a more excellent function as an electromagnetic shielding electrode.

At this time, the solder layer 26 may be formed to cover at least the copper-based ink layer 22 (but not necessarily the circuit pattern made of copper foil, that is, the conductive layer 14 or the plating layer 18).
It does not need to be formed on top.

A solder resist layer 24 serving as a second insulating layer is further formed on the upper surface of the substrate 12, covering the solder resist layer 20 and the solder layer 26.

As mentioned above, the circuit pattern of the conductive layer 14 is connected to the solder layer 26.
The solder layer 26 is placed in close proximity to the deposited copper-based ink layer 22 so that each circuit pattern in the conductive layer has a connection between the deposited copper-based ink layer 22 and the solder layer 26, rather than between adjacent patterns. A stray capacitance or distributed capacitance is formed between the two.

Therefore, the energy of unnecessary frequency components induced in the circuit pattern of the conductive layer 14 flows to the copper-based ink layer 22 to which the solder layer 26 is attached via the formed distributed capacitance. On the other hand, the copper ink layer 2 to which the solder layer 26 is attached
2 is the ground pattern 14a of the conductive layer 14 as described above.
and is grounded in terms of high frequencies. Therefore, the electromagnetic wave energy that has flowed into the copper ink layer 22 on which the solder layer 26 is formed 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, if
Even if an electronic circuit is configured using the circuit board Fi10 and a cable or the like is connected to it, radiant energy will not be transferred to this cable.

This will be specifically explained with reference to FIGS. 9 and 10. FIG. 9 is an equivalent circuit diagram of a conventional general circuit board. In this equivalent circuit, signal lines 2 and 3 connecting elements 1a and 1b and ground line 4 are arranged according to their lengths. has an inductance of
Distributed capacitance is generated between each signal line 2 and 3 and between each signal line 2 and 3 and earth line 4 depending on 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, the circuit board of this embodiment has an equivalent circuit as shown in FIG.
Since no inductance component is included and no high-frequency potential difference occurs, 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 distribution between the signal lines 2 and 3 has such a large value that the capacitance 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. 11, line A shows the radiation level when the conventional substrate is used, and &iB shows the radiation level when the substrate according to the embodiment of the present invention is used. As can be seen from FIG. 11, in the conventional case, for example, at 67.03MHz, the frequency is 50.6MHz.
There was a large amount of unnecessary radiation of 0 dB/jV. On the other hand, if the circuit board of this embodiment is used, the radiation level will be almost only noise components, and the FCC and other regulations can be completely overcome.

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 8.

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 am. Then, on both main surfaces of the substrate 12, for example, 30-70
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.

Subsequently, the conductive layer 14' is etched to form a circuit pattern corresponding to a necessary circuit, 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 with holes, followed by wet etching or dry etching to form the necessary circuit pattern.

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 copper ink layer 22' is formed over almost the entire surface of the first insulating layer, that is, the solder resist layer 20 and/or the conductive layer 14. Specifically, on the main surface of the substrate 12, a silk screen (
(not shown), and printed with a predetermined copper-based ink as described above. .

Thereafter, the printed copper-based ink is heated and cured.

The phenol resin is, for example, thermosetting, and is cured by a condensation reaction at, for example, 145° C. for about 30 minutes. During this curing, the copper ink shrinks not only in its surface direction but also in its thickness direction. According to the inventor's experiments, the adhesive strength of the copper ink layer 22' with the substrate 12 etc. after curing can withstand a tensile load of 3k+r with a land of 3φ, for example, and that of copper foil. conductive layer 14 such as
almost equal to

Further, when the copper-based ink is cured, a solderable layer is formed near the surface thereof. That is, the copper ink layer 22'
The surface can be soldered.

Thereafter, as shown in FIG.
A solder layer 26 is formed thereon. To be more specific, the process shown in Figure 14 involves soldering.

Solder is applied to the main surface of the substrate 12 by reflow soldering or solder dipping.

As described above, this solder layer 26 mechanically reinforces the copper ink layer 22 and improves its conductivity as an electromagnetic shield.

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

In each of the above embodiments, the copper ink layer 22 and the solder layer 26 as electromagnetic shielding electrodes were formed on both sides 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 copper ink layer 22 and the solder layer 26 as electromagnetic shielding electrodes on both surfaces of the substrate 12, the ground pattern 14a is formed only on one main surface, and several through holes are formed. It may be connected to ground, and the copper ink layer 22 on the other main surface may be connected to the through hole.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention. FIGS. 2 to 8 are cross-sectional views showing one example of a method for manufacturing the circuit board of the embodiment shown in FIG. 1 in the order of steps. 9 and 10 are equivalent circuit diagrams for explaining the effects of this embodiment, respectively. FIG. 9 shows a conventional general circuit board, and FIG. 10 shows this embodiment. This shows the circuit board. FIG. 11 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 conductive layer, 20 and 24 are solder resist layers, 22.22
' indicates a copper-based ink layer, and 26 indicates a solder layer. Patent applicant Nintendo Co., Ltd. agent Patent attorney Yama 1) Yoshito (and 1 other person) Figure 1 Figure 5C (+ Figure 8 Figure 9 Figure 10 P-Mae #1)

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 formed on the substrate to cover the conductive layer; a solderable copper ink layer comprising a saturated fatty acid or an unsaturated fatty acid or a metal salt thereof, a metal chelate forming agent and a soldering accelerator; and a solderable copper ink layer formed on the solderable copper ink layer. EMI countermeasure circuit board equipped with a solder layer. 2. The EMI according to claim 1, including a second insulating layer formed on the substrate so as to cover the solder layer.
Countermeasure circuit board. 3. The solderable copper ink layer is made of metallic copper powder 85~
Saturated fatty acid or unsaturated fatty acids or their metal salts 1-8
The EMI countermeasure circuit board according to claim 1 or 2, comprising 1 to 50 parts by weight of a metal chelate forming agent and 0.1 to 2.5 parts by weight of a soldering accelerator.