JP7607616B2 - Printed Wiring Boards - Google Patents

Description

The present invention relates to a printed wiring board that supports high-frequency transmission.

In recent years, there has been a demand for communication devices such as smartphones and electronic devices such as next-generation televisions to transmit and receive large volumes of data at high speeds, and the frequency of electrical signals is becoming increasingly higher.

As the frequency of a signal increases, transmission loss increases, reducing the quality of the output signal, which can lead to misrecognition of information. This transmission loss is thought to consist of conductor loss caused by the conductor and dielectric loss caused by insulating resins that make up electrical and electronic components such as circuit boards in electronic and communication devices.

For this reason, in general, in order to reduce transmission loss, even in printed wiring boards, there is a demand for so-called low-dielectric resin materials with low relative dielectric constant and dielectric dissipation factor, which are factors related to dielectric loss. For this reason, development of low-dielectric resin materials with low relative dielectric constant and dielectric dissipation factor is underway, as shown in, for example, Patent Documents 1 to 3.

For example, Patent Document 1 discloses a liquid crystal polymer that is made low dielectric by incorporating a graft-modified polyolefin having a polar group. Patent Document 2 discloses a resin material formed into a porous film that is made low dielectric. Patent Document 3 discloses a low dielectric material that is made mainly of bismaleimide.

JP 2021-161286 A JP 2019-199616 A International Publication No. 2017/017923

In addition to Patent Documents 1 to 3, a wide variety of resin materials have been developed to achieve low dielectric constant. However, all of these have been developed with the idea of reducing transmission loss by using materials with low relative dielectric constants and dielectric tangents, and there are limitations to simply reducing loss due to the characteristics of the materials.

In this situation, the inventor of the present invention discovered that for high-frequency band signals, the combination of the conductive layer and resin layer of the printed wiring board causes the AC signal applied to the printed wiring board to resonate, and discovered that the transmission characteristics can be improved at that resonant frequency. Based on this discovery, it has become possible to design a printed wiring board that achieves high transmission characteristics even for high-frequency band signals.

(1) The printed wiring board according to the present invention comprises a conductive layer, a first resin layer in contact with one side of the conductive layer, and a second resin layer in contact with the other side of the conductive layer, and is characterized in that it resonates when a signal of 3 GHz to 5 GHz is applied to the conductive layer.

This printed wiring board can improve the gain in signal transmission by resonating with AC signals, significantly improving transmission characteristics.

(2) In the printed wiring board, at least one of the first resin layer and the second resin layer may be made of a low dielectric resin.

(3) In the printed wiring board, the first resin layer and the second resin layer may have a thickness of 4 μm to 12 μm, and the conductive layer may have a thickness of 12 μm to 16 μm.

(4) Either the first resin layer or the second resin layer may be formed by coating the conductive layer.

(5) Either the first resin layer or the second resin layer may have the conductive layer formed thereon after deposition.

(6) The first resin layer and the second resin layer may have a relative dielectric constant of 2.8 or less and a dielectric tangent of 0.0025 or less.

(7) At least one of the first resin layer and the second resin layer may have a porous structure.

(8) The conductive layer may have an average roughness of 1 μm or less on the one surface and the other surface.

(9) The conductive layer may include a copper plating layer.

(10) The conductive layer may comprise a directly written copper layer.

The present invention provides a printed wiring board that achieves high transmission characteristics even for high-frequency band signals.

1 is a cross-sectional view showing a layer structure of a printed wiring board according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a portion A shown in FIG. FIG. 1 is a conceptual diagram showing a measurement concept using a vector network analyzer for a TEG of a printed wiring board, which is an object to be measured. 1 is a graph showing transmission characteristics versus frequency measured by a vector network analyzer for a target sample of a printed wiring board according to an embodiment of the present invention, where (A) shows the transmission characteristics for forward transmission and (B) shows the transmission characteristics for reverse transmission. 1A is a graph showing transmission characteristics versus frequency measured by a vector network analyzer for a specification 1 sample in a first example of a printed wiring board according to an embodiment of the present invention, where (A) shows the transmission characteristics in forward transmission and (B) shows the transmission characteristics in reverse transmission. 11 is a graph showing transmission characteristics versus frequency measured by a vector network analyzer for two samples of specifications in a second example of a printed wiring board according to an embodiment of the present invention, where (A) shows the transmission characteristics in forward transmission and (B) shows the transmission characteristics in reverse transmission. 7 is a table showing magnifications (gains) of transmission characteristics at frequencies from 3 GHz to 5 GHz from the graphs shown in FIGS. 4 to 6.

The embodiment of the present invention will be described in detail with reference to the drawings.

First, the configuration of the printed wiring board P according to this embodiment will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view showing the layer configuration of the printed wiring board P according to this embodiment, and Figure 2 is an enlarged cross-sectional view of a portion of Figure 1, showing the interface between the conductive layer 30 and the first resin layer 10 of the printed wiring board P.

As shown in FIG. 1, the printed wiring board P according to the first embodiment includes a conductive layer 30, a first resin layer 10 in contact with one side of the conductive layer 30, and a second resin layer 20 in contact with the other side of the conductive layer 30.

In this embodiment, the conductive layer 30 is a single-layer copper plating layer formed by copper plating, and the first resin layer 10 and the second resin layer 20 are single-layer resin layers made of resin. The first resin layer 10 and the second resin layer 20 can be formed in layers by hardening a liquid resin material.

In the printed wiring board P of this embodiment, the conductive layer 30 forms an interface with the first resin layer 10 and the second resin layer 20. As a result, the printed wiring board P has a capacitance component when an AC signal is applied to it. In addition, the printed wiring board P generally has a resistance component of the conductive layer 30, and further has an inductance component when an AC signal is applied to it.

Therefore, when an AC signal is applied to the printed wiring board P, it has a resistance component (R), an inductance component (L), and a capacitance component (C), and can be replaced by an electrical equivalent circuit consisting of these components.

The printed wiring board P has a specific frequency, the so-called resonant frequency, at which it resonates with an AC signal applied to the printed wiring board P, depending on the values of the resistance component (R), the inductance component (L), and the capacitance component (C).

In this embodiment, the printed wiring board P has a resonant frequency at a predetermined frequency by modifying the first resin layer 10 as described below, and the transmission characteristics are improved by adjusting the applied AC signal to the resonant frequency.

Next, an experiment to measure the transmission characteristics of the printed wiring board P according to this embodiment will be described. In the examples described below, the first resin layer 10 is changed in each example. On the other hand, the conductive layer 30 and the second insulating layer are the same.

For the measurement of electrical signals, a Test Elementary Group (TEG) was fabricated as the printed wiring board P, which has the above-mentioned layer structure and is compatible with coplanar lines. In addition, a vector network analyzer (VNA) was used to measure AC signals (see Figure 3).

First, a target sample (Ref) was produced for comparison with the examples. The first resin layer 10 of the Ref has a single-layer structure of so-called glass epoxy, which has an epoxy resin base material and contains glass fiber. The conductive layer and the first resin layer of the Ref were produced using RF-4, which is well known in the art.

The Ref obtained the transmission characteristics shown in Figure 4. As shown in Figure 7, the Ref had an average voltage ratio of 3.99 x 10^(-4) in forward transmission S21 at 3 GHz to 5 GHz (both arrows h in Figure 4) and an average voltage ratio of 9.84 x 10^(-4) in reverse transmission S12. When these voltage ratios are converted to common logarithms, they become -6.80 x 10^(+1) [dB] in forward transmission S21 and -6.01 x 10^(+1) [dB] in reverse transmission S12.

The first embodiment is a first printed wiring board P1 (specification 1) having a resonant frequency. The first resin layer 10 of specification 1 is a resin layer made of a bismaleimide-based low-dielectric resin. Note that in specification 1, the first resin layer 10 does not contain a filler.

With specification 1, the transmission characteristics shown in Figure 5 were obtained. When compared to the Ref, a waveform peak was observed between 3 GHz and 5 GHz (both arrows h in Figure 5). This confirmed that with specification 1, AC signals between 3 GHz and 5 GHz resonate, improving the transmission characteristics.

In Specification 1, as shown in Figure 7, the average voltage ratio in forward transmission S21 at 3 GHz to 5 GHz was 8.41 x 10^(-2), and the average voltage ratio in reverse transmission S12 was 9.98 x 10^(-2). When these voltage ratios are converted to common logarithms, they become -2.15 x 10^(+1) [dB] in forward transmission S21 and -2.00 x 10^(+1) [dB] in reverse transmission S12.

The second example is a second printed wiring board P2 (specification 2) having a resonant frequency. The first resin layer 10 of specification 2 is a resin layer made of a maleimide-based low-dielectric resin. In specification 2, the first resin layer 10 contains hollow silica as a filler and has a porous structure.

With specification 2, the transmission characteristics shown in Figure 6 were obtained. When compared to the Ref, a waveform peak was observed between 3 GHz and 5 GHz (both arrows h in Figure 6). This confirmed that with specification 2, AC signals between 3 GHz and 5 GHz resonate, improving the transmission characteristics.

As shown in Figure 7, in Specification 2, the average voltage ratio in forward transmission S21 at 3 GHz to 5 GHz was 2.14 x 10^(-2), and the average voltage ratio in reverse transmission S12 was 1.75 x 10^(-2). When these voltage ratios are converted to common logarithms, they become -3.34 x 10^(+1) [dB] in forward transmission S21 and -3.51 x 10^(+1) [dB] in reverse transmission S12.

Summarizing the above results, in Specification 1, the transmission characteristics are 210.71 times higher for forward transmission S21 and 101.43 times higher for reverse transmission S12 in AC signals of 3 GHz to 5 GHz compared to Ref. In addition, in Specification 2, the forward transmission S21 is 53.67 times higher and reverse transmission S12 is 17.81 times higher in AC signals of 3 GHz to 5 GHz compared to Ref.

It was therefore confirmed that in a printed wiring board P including a resin layer made of low dielectric resin and a conductive layer 30, as in specification 1 or specification 2, resonance occurs when an AC signal of 3 GHz to 5 GHz is applied, improving the transmission characteristics. Therefore, by selecting a resin layer in contact with the conductive layer 30 so that the AC signal resonates, it is possible to design a printed wiring board P with high transmission characteristics in the transmission of AC signals by resonance.

In addition, when comparing specifications 1 and 2, it was confirmed that the printed wiring board of specification 1 has transmission characteristics that are 3.93 times higher in forward transmission S21 and 5.70 times higher in reverse transmission S12 than the printed wiring board of specification 2. This shows that by changing the resin layer in contact with the conductive layer 30, it is possible to change the transmission characteristics at the frequency at which the AC signal resonates. In other words, by appropriately selecting the resin layer in contact with the conductive layer 30, it is possible to design a printed wiring board P with high transmission characteristics in the transmission of AC signals by resonance.

In the present embodiment shown in specifications 1 and 2, the conductive layer 30 is formed as a copper plating layer by copper plating. In addition, in specifications 1 and 2, the resin layer in contact with the conductive layer 30 is formed from a low dielectric resin.

In the present embodiment shown in specifications 1 and 2, the first resin layer 10 is formed as a resin film made of a low-dielectric resin, and then a copper plating layer is formed as a conductive layer 30 on the resin film by electroless plating. In specification 2, the film is formed by including hollow silica as a filler, so that the first resin layer 10 of specification 2 has a porous structure.

In the first printed wiring board P and the second printed wiring board P of this embodiment, the first resin layer 10 is formed as a film, and then the conductive layer 30 is laminated by plating. However, the first resin layer 10 may be laminated by applying a resin material to the conductive layer 30 and then curing it.

The conductive layer 30 of the printed wiring board P in this embodiment preferably has a thickness of 12 μm to 36 μm. In addition, the conductive layer 30 preferably has a surface roughness of 1 μm or less.

The resin layer of the printed wiring board P according to this embodiment may have a thickness of 4 μm to 12 μm, and preferably has a thickness of 8 μm to 10 μm. However, the resin layer may have a thickness of more than 12 μm. Furthermore, the resin layer may have a relative dielectric constant of 3.00 or less and a dielectric loss tangent of 0.006 or less at a frequency of 10 GHz, and preferably has a relative dielectric constant of 2.80 or less and a dielectric loss tangent of 0.0025 or less.

In this embodiment, the printed wiring board P is described as resonating with an AC signal of 3 GHz to 5 GHz. However, the printed wiring board P may also resonate with an AC signal of a higher frequency.

In this embodiment, the conductive layer 30 has been described as having a single-layer structure composed of a copper plating layer. However, the conductive layer 30 may have a multi-layer structure in which a gold plating layer is provided on at least one of the two surfaces of the copper plating layer. Furthermore, the conductive layer may include other metal plating layers in addition to the gold plating in the layer structure. Furthermore, the conductive layer 30 is not limited to a copper plating layer, and may include a rolled copper layer in the structure. Furthermore, the conductive layer 30 may include a conductive layer that is directly drawn from a conductive material in the layer structure.

By changing the conductive layer 30, the resistance component and inductance component of the printed wiring board P change. In addition, if the material constituting the outermost surface of the conductive layer 30 changes, the interface with the first resin layer 10 changes, and the capacitance component of the printed wiring board P changes.

In this embodiment, a so-called single-layer printed wiring board P has been described, which is composed of a conductive layer 30 and a first resin layer 10 and a second resin layer 20 in contact with both sides of the conductive layer 30. However, the printed wiring board P may be a so-called multilayer board that includes two or more conductive layers 30, as long as an interface is formed between the conductive layer 30 and a resin layer made of a low-dielectric resin on at least one side.

In this embodiment, the first resin layer 10 is described as being made of a single layer of low-dielectric resin. However, as long as the first resin layer 10 has a layer of low-dielectric resin in the portion in contact with the conductive layer 30, it may be a multilayer structure in which layers made of the same resin are stacked on top of each other, or a multilayer structure in which layers made of different resins are stacked on top of each other.

In this embodiment, the first resin layer 10 and the second resin layer may form an insulating layer of the printed wiring board, or may form an adhesive layer for another insulating layer.

Although the embodiments of the present invention have been described above, the present invention is not limited to these descriptions. Any design modifications made by a person skilled in the art to the above-mentioned embodiments are also included within the scope of the present invention as long as they have the characteristics of the present invention.

The present invention can be used for printed wiring boards P.

P: printed wiring board 10; first resin layer 20; second resin layer 30; conductive layer S21: forward transmission; S12: reverse transmission

Claims (4)

A conductive layer;
a first resin layer in contact with one surface of the conductive layer;
a second resin layer in contact with the other surface of the conductive layer,
By changing at least the first resin layer, the piezoelectric element has a resonant frequency in the range of 3 GHz to 5 GHz;
A signal of 3 GHz to 5 GHz is applied to the conductive layer to cause resonance,
At least one of the first resin layer and the second resin layer is made of a low dielectric maleimide resin or a low dielectric bismaleimide resin ,
the first resin layer and the second resin layer have a thickness of 4 μm to 12 μm, and the conductive layer has a thickness of 12 μm to 36 μm;
the first resin layer and the second resin layer have a relative dielectric constant of 3 or less and a dielectric loss tangent of 0.0025 or less;
the conductive layer includes a copper plating layer, and the average roughness of the one surface and the other surface is 1 μm or less;
A printed wiring board in an electronic device or a communication device. The printed wiring board according to claim 1, wherein either the first resin layer or the second resin layer is formed by coating on the conductive layer. The printed wiring board according to claim 1, wherein the conductive layer is formed on either the first resin layer or the second resin layer after film formation. The printed wiring board according to claim 1 , wherein at least one of the first resin layer and the second resin layer has a porous structure.

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