TW202134054A - Laminated body for flexible printed circuit board having low dielectric constant and low loss property - Google Patents

Abstract

The present disclosure relates to a laminated body for flexible printed circuit board. The laminated body for flexible printed circuit board includes: a dielectric having a dielectric constant (Dk) of 3.0 or less and a signal loss factor (Df) of 0.002 or less, which is obtained by mixing an inorganic filler having the dielectric constant of 15 or less in a fluorine resin composed of a tetrafluoroethylene (TFE) monomer in a range of 45 to 75 % of a total content of the dielectric by weight; and copper foils laminated on both surfaces of the dielectric.

Description

Laminated body for flexible printed circuit board with low dielectric constant and low loss characteristics

Field of invention

The present disclosure relates to a laminate for flexible printed circuit boards with low dielectric constant and low loss characteristics.

Background of the invention

With the opening of the 5G mobile communication era, it is necessary to provide a flexible printed circuit board with excellent bending flexibility, which has low dielectric constant and low loss characteristics in order to meet the increase in data volume and high-speed data transmission of mobile devices. Demand and can overcome the space constraints of mobile devices.

As a solution to the above requirements, various technological developments are being carried out to reduce the dielectric constant and signal loss factor of polyimide (PI) used in existing flexible printed circuit boards. However, this PI-based dielectric has the following limitations: it is difficult to achieve a dielectric constant of 3.0 or less and a signal loss factor of 0.005 or less at a frequency of 10 GHz. In addition, there is a problem that PI-based dielectrics have higher hygroscopicity than other materials.

As an alternative solution, a liquid crystal polymer (LCP) exhibiting a dielectric constant of 2.9 and a signal loss factor of 0.002 (which is lower than those of PI-based dielectrics) is used. However, in this type of LCP, in the case of a copper foil that has low surface roughness in the build-up layer and is particularly beneficial in reducing signal loss, the peel strength between the copper foil and the LCP can be reduced, which makes it difficult to handle the multilayer structure. A printed circuit board.

On the other hand, in the conventional fluorine-based laminate used as a board for wireless communication, a glass fiber fabric is used as a reinforcing member. In terms of the thermal expansion coefficient of the X-Y axis and its related dimensional stability, this configuration is advantageous, but it increases the thermal expansion coefficient and the flexural modulus in the Z axis. This makes it difficult to meet the bending flexibility required in flexible printed circuit boards.

Summary of the invention

The present disclosure provides a laminated body composed of a dielectric substance and a plurality of copper foils laminated on both surfaces of the dielectric substance, and the dielectric substance has a low dielectric constant and low signal loss at high frequencies Factor and can exhibit the bending flexibility required in flexible printed circuit boards.

According to the present disclosure, there is provided a laminate for a flexible printed circuit board, which includes: a dielectric having a dielectric constant (Dk) of 3.0 or less and a signal of 0.002 or less The loss factor (Df) is obtained by mixing an inorganic filler with a dielectric constant of 15 or less in a matrix of a fluororesin composed of tetrafluoroethylene monomer. Within the range of 45 to 75% of the total content of the dielectric substance; and a plurality of copper foils laminated on both surfaces of the dielectric substance.

Generally speaking, the fluororesin composed of tetrafluoroethylene monomer basically has a low dielectric constant (Dk) of 2.1 and a low signal loss factor (Df) of 0.0002. However, when used alone, the fluororesin may have a high coefficient of thermal expansion to reduce the dimensional stability required in processing printed circuit boards. As a solution to this problem, it is possible to realize a laminate that can be used to process flexible printed circuit boards while maintaining the low dielectric constant and low loss characteristics of the fluororesin at a specific level at high frequencies And by mixing inorganic fillers with a dielectric constant (DK) of 15 or less in the range of 45 to 75% by weight of the total dielectric content in the above fluororesin to ensure low thermal expansion coefficient and dimensional stability And the inorganic filler is evenly distributed in the dielectric.

When the content of the inorganic filler is less than 45% by weight, it may be difficult to ensure the low thermal expansion coefficient and dimensional stability necessary for processing the flexible printed circuit board. When the content of the inorganic filler exceeds 75% by weight, the output of the dielectric product can be reduced and the flexural modulus of the dielectric can be increased to reduce the bending flexibility of the flexible printed circuit board. Therefore, the reduction in the bending flexibility of the flexible printed circuit board will result in cracks in the dielectric, which leads to an increase in signal loss.

Preferably, the inorganic filler may have a spherical shape instead of an angular shape, a plate shape or other irregular shapes. In addition to angular shapes, spherical shapes may refer to circular shapes. The term "spherical shape" described herein can be understood to include egg shape, elliptical shape and the like. In particular, when the particle size of the inorganic filler has a bimodal or trimodal particle size distribution, the filling rate of the inorganic filler in the fluororesin can be optimized. To perform this operation, one type of inorganic filler having a bimodal or trimodal particle size distribution may be used, or two or more types of inorganic fillers having different average particle diameters may be used in combination. When the particle size of the inorganic fillers is the same or the width of the distribution curve is narrow, it is difficult to improve the filling rate in the fluororesin, which makes it difficult to reduce the thermal expansion coefficient of the dielectric or to obtain dimensional stability in the flexible printed circuit board .

Preferably, the maximum particle size of the inorganic filler can be smaller than the thickness of the dielectric material to be realized. In particular, the maximum particle size of the inorganic filler can preferably be in the range of 30% to 90% of the thickness of the dielectric. When the maximum particle size of the inorganic filler is greater than the thickness of the dielectric or more than 90% of the thickness of the dielectric, fine protrusions can be formed on a surface of the laminated copper foil, which results in signal transmission delay and signal loss factor (Df) Increase.

In order to increase the peeling strength between the dielectric and the copper foils laminated on the two surfaces of the dielectric and in order to improve the flexural modulus of the dielectric, the dielectric can be measured by weight Add a fluoropolymer powder within the range of 2 to 20% of the total content. The fluoropolymer powder may be a copolymer compound composed of the following: tetrafluoroethylene (TFE) monomer and at least one monomer selected from the group consisting of hexafluoropropylene (HFP), perfluoroalkyl Vinyl ether (PPVE) and perfluoroalkyl vinyl ether (MVE) monomers, and can have an average particle size of 3 to 20 µm.

When the content of the fluoropolymer powder is less than 2%, the effect of improving the peeling strength between the dielectric material and the copper foils laminated on the two surfaces of the dielectric material is small, and the dielectric material is reduced. The effect of qualitative flexural modulus is not large. On the other hand, when the content of the fluoropolymer powder exceeds 20%, the peel strength between the dielectric and the copper foils laminated on the two surfaces of the dielectric tends to increase, and the The coefficient of thermal expansion of the dielectric material may become larger.

Preferably, the thickness of the dielectric substance can be in the range of 10 to 175 µm, so as to ensure the bending flexibility of the flexible printed circuit board. More preferably, the dielectric with a thickness of 25 to 150 µm can be suitable for antennas, FPC type coaxial cables or the like to be installed in the narrow internal space of mobile devices, such as in mobile device applications .

Preferably, the dielectric substance can be manufactured by a thin film casting process so as to uniformly distribute the inorganic filler and the fluoropolymer powder in the fluororesin composed of TFE monomer.

The laminated body provided by the present disclosure can also be implemented using a flexible printed circuit board having a multilayer structure, which is used together with a bonding layer, a cover layer, or the like.

According to the present disclosure, it is possible to provide a laminated body composed of a dielectric substance and a plurality of copper foils laminated on both surfaces of the dielectric substance, and the dielectric substance has a low dielectric constant and a low dielectric constant at a high frequency. Low signal loss factor and capable of exhibiting the bending flexibility required in flexible printed circuit boards.

Detailed description of the preferred embodiment

Hereinafter, the present disclosure will be described in detail with reference to the accompanying drawings having specific embodiments for realizing the present disclosure. The embodiments will be described in detail to the extent that the present disclosure can be easily practiced by a person skilled in the art. It should be understood that the various embodiments are different from each other but need not be exclusive. For example, without departing from the spirit and scope of the disclosure, the specific shapes, configurations, and features described in this specification can be modified in various embodiments. In addition, the position or arrangement of individual components in each embodiment can be modified without departing from the spirit and scope of the present disclosure. Therefore, the detailed description described below should be interpreted as a non-limiting meaning, and the scope of the disclosure should be understood to include the scope of the appended patent application and its equivalents.

Hereinafter, several preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, so that those skilled in the art can easily practice the present disclosure.

In the present disclosure, a fluororesin composed of tetrafluoroethylene monomer is used as the dielectric matrix. The fluororesin composed of tetrafluoroethylene monomer may include a dispersion in which a solid content of 40% to 70% by weight is dispersed in water or a solvent.

In order to reduce the dielectric constant and signal loss factor of the dielectric, one type of inorganic filler with a dielectric constant (Dk) of 15 or less can be used alone or as a mixture of two or more types of inorganic fillers. . Examples of the inorganic filler having a dielectric constant of 15 or less may include at least one selected from the group consisting of alumina (Al ₂ O ₃ ), aluminum nitride (AlN), silicon carbide (SiC) , Silicon oxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), zirconium dioxide (ZrO ₂ ), boron nitride (BN), beryllium oxide (BeO), zinc oxide (ZnO), magnesium oxide (MgO) And glass bubbles.

The inorganic filler can be mixed and used in an amount within the range of 45 to 75% of the total content of the dielectric substance by weight, thereby reducing the thermal expansion coefficient of the dielectric substance (including the fluororesin composed of tetrafluoroethylene monomer) ) And ensure the dimensional stability required in the manufacturing process of the flexible printed circuit board. In this case, in order to uniformly disperse the inorganic filler in the fluororesin and optimize the filling rate of the inorganic filler, the inorganic filler may preferably have the form of spherical particles rather than angular particles or plate-shaped particles. Or irregular particles. By allowing the inorganic filler to have the form of spherical particles, it is possible to exhibit the effect of reducing the generation of cracks in the dielectric when the flexible printed circuit board is flexed or bent, which is beneficial to ensure the flexible printed circuit board The bending flexibility.

Preferably, the inorganic filler can be used as a mixture of two or more types of inorganic fillers having different average particle diameters. By positioning the particles of the inorganic filler having a relatively small diameter in the space formed between the particles of the inorganic filler having a relatively large diameter, the inorganic filler having multiple diameters can be uniformly dispersed in the fluororesin at a high filling rate. The matrix.

Preferably, the maximum particle size of the inorganic filler may be smaller than the thickness of the dielectric material to be realized, and may be in the range of 30% to 90% in terms of the thickness of the dielectric material. For example, when the thickness of the dielectric is set to 50 µm, the maximum particle size of the inorganic filler can be in the range of 15 to 45 µm. In this case, a mixture of inorganic fillers having an average particle size of 0.5 to 5 µm, 10 to 20 µm, and 25 to 35 µm can be used as the inorganic filler. When the maximum particle size of the inorganic filler is greater than the thickness of the dielectric to be realized, the particles of the inorganic filler break through the surface of the dielectric, which causes unevenness on the surface of the dielectric. The unevenness on the surface of the dielectric is reduced to the adhesion of the copper foils and causes the signal loss of the copper foils to increase.

In order to increase the peeling strength between the dielectric and the copper foils laminated on the two surfaces of the dielectric and in order to reduce the flexural modulus of the dielectric, the dielectric can be Add a fluoropolymer powder within the range of 2 to 20% of the total content. The fluoropolymer powder may be a copolymer compound composed of a TFE monomer and at least one monomer selected from the group consisting of HFP, PPVE, and MVE monomers, and the average particle size may be 3 to 20 µm. The molar concentration (Mol%) of at least one monomer selected from the group consisting of HFP, PPVE and MVE monomers is not particularly limited. For example, it is preferable to use 1 to 5 mol% of the fluoropolymer powder in terms of heat resistance.

The fluoropolymer powder helps to achieve the effect of improving the peeling strength between the dielectric and the copper foils laminated on the two surfaces of the dielectric and reducing the flexural modulus of the dielectric The effect is that as the content of the fluoropolymer powder increases, the bending flexibility is improved. In order to achieve such effects, the fluoropolymer powder may be added in the range of 2% or more of the total content of the dielectric substance by weight. On the other hand, when the content of the fluoropolymer powder exceeds 20%, the coefficient of thermal expansion of the dielectric may tend to increase. It can be seen that as the content of the fluoropolymer powder increases, the content of the inorganic filler in the dielectric will relatively decrease, which causes the thermal expansion coefficient of the dielectric to increase.

As the fluoropolymer powder, for example, the EA-2000 series commercially available from AGC can be used. The commercially available fluoropolymer powder has a dielectric constant (Dk) of 2.1 and a signal loss factor (Df) of 0.001, which can be preferably used as an additive to the dielectric substance of the present disclosure. The fluoropolymer powder exemplified herein can be used alone or mixed with other fluoropolymer powders. When the fluoropolymer powder is mixed with other fluoropolymer powders, the mixing ratio is not specifically limited.

The dielectric can be manufactured by a thin film casting process. From the viewpoint of ensuring the bending flexibility of the flexible printed circuit board, the thickness of the dielectric may be in the range of 10 to 175 µm, preferably 25 to 150 µm.

When the dielectric has a thickness of 50 µm, it can have a dielectric constant in the range of 2.5 to 2.8 and a low signal factor dielectric characteristic in the range of 0.001 to 0.002 at a frequency of 10 GHz. The method of measuring the dielectric characteristics of the dielectric is consistent with the IPC-TM 650 2.5.5.5.1 standard.

When the thickness of the dielectric substance is 50 µm, the thermal expansion coefficients on the X-Y axis and Z axis in the temperature range of 50°C to 150°C can be 10 to 20 ppm/°C and 20 to 40 ppm/°C, respectively. The method of measuring the coefficient of thermal expansion is consistent with the IPC-TM 650 2.4.41 standard.

It is obtained by laminating the copper foils of 1/2oz SVLP (Rz 1.2 µm) on the two surfaces of the dielectric with a thickness of 50 µm by hot pressing under the conditions of high temperature and high pressure In the laminate, the peel strength between the dielectric and the copper foils can be in the range of 4 to 7 lb/in (pounds per inch). A method for measuring the peel strength between the dielectric and the copper foils laminated on the two surfaces of the dielectric is consistent with the IPC-TM 650 2.4.8 standard.

The following examples and comparative examples are provided to describe the content of this disclosure.

In the Examples and Comparative Examples, the dielectrics were obtained in the same manufacturing sequence as follows.

Add additives (such as inorganic fillers, fluoropolymer powder, and surfactants) to the dispersion, in which the fluororesin composed of TFE monomer is dispersed in the aqueous solvent according to the composition described in Table 1, and It is then uniformly dispersed via a mixer.

In both Example 1 and Comparative Example 1, a _{mixture of three types of spherical SiO 2} having the following degree of distribution was used as the inorganic filler, in which the maximum particle size (Dmax) was 45 µm and the average particle size (D ₅₀ ) was respectively 3 µm, 15 µm and 25 µm, but the content of the inorganic filler is set at a different ratio to the total content of the dielectric.

_{In Comparative Example 2, spherical SiO 2} having an average particle size (D ₅₀ ) of 25 µm and a maximum particle size (Dmax) of 55 µm was used as the inorganic filler.

The steps of coating and firing the mixture uniformly dispersed on the polyimide (Pl) or metal coil support film by a mixer are performed one or more times to obtain a coating with a thickness of 50 µm.

Separate the coating from the thin film of the polyimide or metal coil support, and obtain a dielectric with a thickness of 50 µm.

Laminates are obtained by laminating these copper foils of 1/2 oz SVLP (Rz 1.2 µm) on both surfaces of the dielectric material obtained by the above-mentioned thin film casting process in a hot-compression bonding method under high temperature and high pressure conditions body.

The dielectric characteristics (Dk, Df at 10 GHz), thermal expansion coefficient, and peel strength were performed on each of the dielectrics obtained in the Examples and Comparative Examples and each of the laminates to which the dielectric was applied. The physical properties are evaluated, and the results of the evaluation are summarized in Table 2.

[Table 1] (Content unit: wt%) Example 1 Comparative example 1 Comparative example 2 PTFE 30 53 30 Inorganic filler Mixture of three types of SiO ₂ 62 40 (D ₅₀ : 3, 15, 25 µm: Dmax: 45 µm) A type of SiO ₂ (D50: 25 µm, 62 Dmax: 55 µm) Fluoropolymer powder 5 5 5 Additives 3 2 3

Table 2 (Unit: ppm/℃, lb/in) Example 1 Comparative example 1 Comparative example 2 Dielectric constant (Dk) 2.6 2.5 2.6 Signal loss factor (Df) 0.0012 0.0011 0.003 Thermal expansion coefficient xy axis 14 35 17 Thermal expansion coefficient Z axis 26 66 31 Peel strength 5.4 5.9 4.5

The test results show that the low dielectric constant and low loss characteristics are exhibited at a frequency of 10 GHz, and the low thermal expansion coefficient is exhibited in Example 1 at a temperature range of 50 to 150°C. In addition, the peel strength between the 1/2 oz SVLP dielectric with relatively low surface roughness and the copper foils showed excellent values. On the other hand, in Comparative Example 1 in which the content of the inorganic filler was decreased compared with Example 1, there were problems that the dielectric characteristics such as Dk and Df were low and the peeling strength was good, and the thermal expansion coefficient tended to increase, which caused Decrease in dimensional stability. In Comparative Example 2 in which a corner inorganic filler with a maximum particle size exceeding the thickness of the dielectric is applied, Dk is at a level of 2.6, but it is observed that the particles that exceed the thickness of the dielectric are attributable to the thickness of the laminated copper foil Fine protrusions are formed on the surface. Therefore, there is a problem that Df rises sharply. Compared with the example using spherical inorganic fillers, the peel strength also tends to decrease.

Although the present disclosure has been described above with the aid of specific features such as specific components and the like, and exemplary embodiments, these embodiments are provided to further promote the overall understanding of the present disclosure, and the present disclosure does not Limited to this. Those who are familiar with this technology can make various modifications and changes to the above description.

Therefore, the spirit of the disclosure should not be limited to the above-mentioned embodiments, and not only the scope of the attached patent application, but also all of them that are equivalently or equivalently modified to the scope of the patent application are intended to fall within the scope of the spirit of the disclosure.

(without)

FIG. 1 is a diagram showing the structure of a laminate for a flexible printed circuit board according to an embodiment of the present disclosure.

Claims (7)

A laminate for flexible printed circuit boards, which comprises: A dielectric substance having a dielectric constant (Dk) of 3.0 or less and a signal loss factor (Df) of 0.002 or less, which is composed of a tetrafluoroethylene (TFE) monomer It is obtained by mixing an inorganic filler with a dielectric constant of 15 or less in a matrix of a fluororesin, and the inorganic filler is within a range of 45 to 75% of the total content of the dielectric by weight ;and A plurality of copper foils laminated on both surfaces of the dielectric substance, Wherein the copper foils are laminated on the dielectric by a hot-press bonding method, The dielectric has a uniform surface to prevent the signal loss of the copper foils from increasing, and a maximum particle size of the inorganic filler is limited to make the surface of the dielectric uniform, and In addition to the inorganic filler, the matrix of the fluororesin composed of the tetrafluoroethylene monomer further includes a fluoropolymer powder. The laminate for flexible printed circuit boards of claim 1, wherein the inorganic filler has a spherical shape to enhance the bending flexibility of one of the dielectrics, and has two or more types with different average particle diameters A mixture of the inorganic filler is used as the inorganic filler to increase a filling rate and enhance the dimensional stability of the dielectric. The laminate for flexible printed circuit boards of claim 2, wherein the maximum particle size of the inorganic filler is within a range of 30% to 90% of a thickness of the dielectric substance. The laminate for flexible printed circuit boards of claim 3, wherein the fluoropolymer powder is included in the fluororesin in a range of 2 to 20% of the total content of the dielectric substance by weight In the matrix, a peeling strength between the dielectric substance and the copper foils laminated on the two surfaces of the dielectric substance is increased and the bending flexibility of the dielectric substance is improved. The laminate for flexible printed circuit boards of claim 4, wherein the fluoropolymer powder is a copolymer compound composed of: the tetrafluoroethylene monomer and at least one selected from one of the following groups Monomers: Hexafluoropropylene (HFP), perfluoroalkyl vinyl ether (PPVE) and perfluoroalkyl vinyl ether (MVE) monomers, and have an average particle size (D ₅₀ ) from 3 to 20 µm . The laminate for flexible printed circuit boards according to claim 5, wherein the thickness of the dielectric substance is in a range of 10 to 175 µm. A flexible printed circuit board comprising the laminated body as claimed in any one of claims 1 to 6 as an electric signal transmission circuit.

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