TWI646137B - Fluorine prepreg and resin composition thereof - Google Patents

Abstract

The present invention relates to a fluororesin composition for use in a prepreg for high frequency circuit boards The resin composition is: (1) a polytetrafluoroethylene (PTFE) resin; (2) a fluorine-containing copolymer selected from the group consisting of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA) or perfluorocarbon. a combination of one or more of ethylene propylene copolymer (FEP); (3) inorganic powder (filler); (4) impregnation aid, which may be hydroxyethyl cellulose, nitrocellulose, polymethyl styrene One or more combinations of polymethyl methacrylate or polyethylene glycol, the resin composition is characterized in that it can increase the amount of the prepreg during multiple impregnation coating and simultaneously improve the impregnation Surface defects that are prone to occur during drying, baking, and sintering.

Description

Fluorine prepreg and resin composition thereof

The invention relates to a prepreg for a high-frequency circuit board, wherein the resin used is a fluororesin composition and has excellent dielectric properties, and can be applied to high frequency such as microwave communication, satellite radar, automobile radar and wireless communication antenna. The circuit substrate, which contains an impregnation aid, is an organic polymer having high boiling point and high viscosity characteristics, and is characterized in that it can increase the amount of the above-mentioned material during impregnation and improve the surface defects of the prepreg, and at the same time retain fluorine. The superior dielectric properties of the polymer.

The high frequency of electronic equipment is the development trend of today's electronic products, especially in the wireless network, satellite radar communication and the current development of 5G communication, electronic communication products are bound to cooperate with the development of related technologies in the high frequency band (above 10GHz), making The popularity of fluorinated high-frequency substrates with better dielectric properties than those of the previous FR-4 or PPO high-frequency substrates has become increasingly prominent.

Due to the low surface energy characteristics of the fluorocarbon resin, it is not easy to feed the glass fiber cloth when the fluorocarbon resin is impregnated. Therefore, it is necessary to repeatedly impregnate the substrate to achieve the target content. In the case of multiple impregnation coatings, environmental control is not easy, and impurities are easily mixed into the impregnation process to reduce the quality of the finished product and affect the yield.

Many prior art techniques have been developed to increase the amount of feed on top of the impregnation coating to reduce the number of impregnation coatings. In the literature, a glass fiber cloth is impregnated with fluorocarbon resin, which is subjected to multiple impregnation to reach the target content, and the temperature of the furnace body is adjusted to be below the melting point of polytetrafluoroethylene by a process operation (about 250 ° C). Up to 320 ° C), so that PTFE is not sintered to form a film, which enhances the wetting effect of the surface of the substrate during subsequent impregnation coating to increase the amount of feeding. Although this method can reduce the number of times of impregnation, it is easy to make the high temperature calcination program Additives are not easily decomposed in the furnace zone, which in turn affects the subsequent substrate processing quality.

In the second document, a glass fiber cloth is impregnated with fluorocarbon resin, and the adhesion ability between the fluororesin and the decane-treated fiberglass cloth is improved by adding organic decane, but the impregnation property with the fiberglass cloth can be improved, for the subsequent The effect of multiple coatings to target levels is limited.

Although the above prior art can indeed increase the amount of impregnation, the amount of the material to be lifted is also easy to cause surface defects such as dents, blistering, cracking and crater phenomena on the surface of the substrate. Therefore, in order to avoid this phenomenon, many prior patents directly achieve the target content by means of interlayer filming between glass fiber cloth layers. As disclosed in Document 3, the copper foil substrate is directly formed by high-temperature vacuum bonding of a glass fiber cloth and a polytetrafluoroethylene film. This method can avoid the aforementioned process difficulties, and the non-melting property of the polytetrafluoroethylene itself is The fiberglass cloth is not easy to be completely adhered to the PTFE film, resulting in poor adhesion.

In the fourth part, the untreated pre-treated cloth is obtained by impregnating the fluororesin with a fiberglass cloth, and the pre-treated cloth is laminated with the fluororesin film to achieve the target content. This method can improve the fiberglass cloth and the method. The adhesion between the fluororesin films, however, the process of unsintering tends to cause processing defects to cause subsequent processing defects, and the use of a large amount of fluorocarbon resin film to increase the manufacturing cost is not satisfactory.

In view of the above, in order to solve the problem that the glass fiber cloth is impregnated with the fluorocarbon resin and the surface defects are not easy, the present invention provides a fluorine prepreg and a resin composition thereof to overcome the above problems.

[Document 1]: US Patent No. 5,979,719

[Document 2]: US Patent No. 0153610

[Document 3]: Chinese Patent No. CN101856900

[Document 4]: Chinese Patent No. CN102490413

The existing high-frequency substrates are mainly divided into FR-4 substrates, PPO ceramic substrates and fluorine substrates. For applications with higher frequency bands above 10 GHz, fluorinated substrates play the most high-frequency applications due to the need for more stringent dielectric performance requirements. Important role. In the prior art, the composition of the fluorine substrate is made of thermoplastic polytetrafluoroethylene as the main constituent resin, because the hydrogen atom around the main chain carbon atom is replaced by the fluorine atom having the highest electronegativity, and With extremely high crystallinity, polytetrafluoroethylene has quite a few unique properties as described below. (1) Excellent chemical inertness and good chemical resistance; (2) Excellent thermal stability, long-term use temperature from -50 ° C to 260 ° C; (3) symmetrical structure makes it an excellent medium Electrical properties (low dielectric constant, low dielectric loss) make it widely used in high-end electrical insulation materials; (4) has the lowest surface energy of all polymers, the surface of the product has lubricity and non-stick properties, and Not easy to wet.

However, PTFE also has many processing limitations, and there are still many obstacles to overcome in its application. Because PTFE maintains a very high viscosity at the melting point and does not have meltability, the molding process is not easily carried out by conventional thermoplastic plastic processing methods. Therefore, the conventionally introduced technology has a much lower crystallinity than that of polytetrafluoroethylene. Perfluoro or non-perfluoro-based meltable fluorine-based resins such as tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA), polyperfluoroethylene propylene (FEP), ethylene-tetrafluoroethylene copolymer ( ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) and polyvinylidene fluoride (PVDF) improve the processability. More perfluororesin (PFA, FEP) The excellent dielectric properties of the fluorine-based resin can be maintained, and the processing temperature is low, but the price is relatively expensive, which limits the popularity of the application. Non-perfluoro-based resins (ETFE, ECTFE, PVF, PVDF, etc.) have lower processing temperatures and superior mechanical properties, but they have a lower temperature for long-term use, and their thermal stability and resistance are resistant. The dielectric properties required for both high-performance and high-frequency circuit substrates are significantly worse.

When the printed circuit board is subjected to the through hole and the pad process, when the difference between the thermal expansion coefficient of the plate and the copper is too large, the hole of the through hole is easily broken, and even the delamination of the blast plate occurs. Polytetrafluoroethylene has a coefficient of thermal expansion (CTE) of about 220 ppm/°C at 25 ° C to 300 ° C. This property causes many processing problems of the back end printed circuit board when it is applied to the substrate material, so the conventional technology will be added. Organic or inorganic fillers (such as glass fibers, inorganic powders, hollow glass beads, and polymer powders) enhance the rigidity, dimensional stability, and thermal expansion coefficient of the overall substrate. In addition, the prior art techniques for high-frequency circuit substrate applications with high dielectric constant and low dielectric loss characteristics also adjust the dielectric properties of the overall plate by adding fillers having different dielectric properties to achieve high-frequency fluorination. The substrate is more oriented to the application.

PTFE is replaced by a fluorine atom whose carbon atoms around its main chain carbon atom are completely replaced by the highest electronegativity in the element, giving it the lowest surface energy of all polymers (surface tension of about 18.5 mN/m). Almost completely free of water, it is widely used in oil-free lubrication and friction-reduction applications. However, this property is a major disadvantage for multiple impregnation coatings. The poor feeding amount increases the number of impregnation coatings, and the poor wettability during impregnation coating tends to cause defects on the surface. The prior art mainly increases the wettability of the surface of the substrate by adding various organic decane compounds to carry out the reaction by using reactive groups to enhance the amount of the feed, and after high temperature drying, baking and sintering after impregnation coating or Surface defects caused by the sudden boiling phenomenon caused by high temperature are still a major problem.

In view of the above, the present invention provides a fluororesin composition for use in the production of a prepreg for a high-frequency circuit board, the resin composition characterized by: (1) polytetrafluoroethylene (PTFE) resin (2) a fluorine-containing copolymer selected from the group consisting of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP) or a combination thereof; (3) inorganic Powder (filler); (4) impregnation aid, which may be one or more combinations of hydroxyethyl cellulose, nitrocellulose, polymethyl styrene, polymethyl methacrylate or polyethylene glycol .

The present invention is a fluororesin composition characterized in that the resin composition contains the following components in an amount of 100% by weight based on the total weight of the resin composition: (1) a polytetrafluoroethylene (PTFE) resin, which accounts for 30% of the total resin composition. ~70wt%, (2) a fluorinated copolymer selected from the group consisting of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA) and perfluoroethylene propylene copolymer (FEP), one or more combinations, accounting for The solid resin composition has a solid content of 1 to 10% by weight, (3) the inorganic powder, which accounts for 5 to 60% by weight of the solid content of the whole resin composition, and (4) the impregnation aid, which may be hydroxyethyl cellulose or nitrocellulose. One or a combination of one or more of polymethylstyrene, polymethyl methacrylate or polyethylene glycol accounts for 0.1 to 10% by weight of the solid content of the entire resin composition.

The resin contained in the fluorine prepreg and the resin composition thereof is polytetrafluoroethylene (PTFE) and a fluorine-containing copolymer. The polytetrafluoroethylene accounts for 30 to 70% by weight, preferably 40 to 60% by weight, based on the solid content of the entire resin composition. The fluorine-containing copolymer is selected from one or a combination of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP), and the composition ratio of the whole resin composition is 1~10wt%. If the proportion of the fluorinated copolymer is more than 10% by weight, the flow of the glue is likely to occur after the press plate, which affects the processability and thickness uniformity of the sheet. Ratio of fluorocopolymer When it is less than 1%, it is easy to have voids.

The above polytetrafluoroethylene (PTFE) resin has a structure as shown in the structural formula (A):

a fluorine-containing copolymer, wherein the fluorine-containing copolymer is selected from one or a combination of tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP), and its structure is respectively As shown in Structural Formula (B) and Structural Formula (C):

The inorganic powder contained in the resin composition may be spherical or irregular cerium oxide (SiO ₂ ), titanium oxide (TiO ₂ ), aluminum hydroxide (Al(OH) ₃ ), or aluminum oxide (Al ₂ O ₃ ). , magnesium hydroxide (Mg(OH) ₂ ), magnesium oxide (MgO), calcium carbonate (CaCO ₃ ), boron oxide (B ₂ O ₃ ), calcium oxide (CaO), barium titanate (SrTiO ₃ ), titanic acid Barium (BaTiO ₃ ), calcium titanate (CaTiO ₃ ), magnesium titanate (2MgO.TiO ₂ ), boron nitride (BN), aluminum nitride (AlN), tantalum carbide (SiC), cerium oxide (CeO _{2 )} Or a combination of one or more of fume silica, wherein the inorganic powder preferably has an average particle diameter of 0.01 to 20 μm. Wherein, the smoked vermiculite is a porous nano-sized vermiculite particle having an average particle diameter of 1 to 100 nanometers (nm), wherein the cerium oxide is a molten type and a crystalline type, and the combination is considered. The dielectric property of the material is preferably a molten type of cerium oxide; wherein the inorganic powder accounts for 5 to 60% by weight, preferably 30 to 50% by weight, based on the solid content of the entire resin composition. Wherein, if the inorganic powder accounts for more than 60% by weight of the solid content of the resin composition, the suspension property of the resin composition is affected, precipitation is likely to occur during the impregnation process, and the uniformity of the prepreg is poor, and the processing is not easy.

The impregnation aid contained in the resin composition is used to adjust the overall viscosity, boiling point and wetting characteristics of the resin composition. In addition, another feature of the impregnation aid is that it can be cracked and eliminated at temperatures above 300 °C.

The impregnation aid may be one or a combination of one or more of hydroxyethyl cellulose, nitrocellulose, polymethyl styrene, polymethyl methacrylate or polyethylene glycol. If necessary, the impregnation aid is dissolved in a suitable solvent and added to the resin composition. The polyethylene glycol may have a molecular weight of 200 to 20,000, and may have different viscosity depending on its molecular weight, and is preferably PEG2000~PEG4,000 having an average molecular weight of 2,000 to 4,000. The impregnation aid accounts for 0.1~10wt%, preferably 3-5wt%, of the solid content of the whole resin composition. If the solid content is more than 10wt%, the viscosity of the whole resin composition is too high, which easily affects the prepreg film formation. Flatness, which in turn causes surface roughness. If the addition amount is <0.1%, the prepreg is liable to have surface void defects.

The above impregnation aid is selected from one or more combinations of hydroxyethyl cellulose, nitrocellulose, polymethyl styrene, polymethyl methacrylate or polyethylene glycol, and the structures thereof are respectively as shown in structural formula (D). To the structural formula (H):

Where n=1~50, R can be H or , X=1~10;

Where n=1~50;

Where n=1~50;

Where n=1~50;

Where n=1~200.

The invention can utilize the high boiling point and the wetting property of the organic polymer by adding an impregnation aid to the fluorocarbon resin emulsion to dry, bake and sinter the glass fiber cloth after being subjected to impregnation coating to a high temperature furnace zone. The surface of the substrate is not easily affected by the lower surface energy of the fluororesin itself, which affects the leveling property during the impregnation coating, and the surface of the substrate is bumped to cause appearance defects. In addition, the addition of the impregnation aid can also increase the viscosity of the overall resin composition, increase the amount of loading during multiple impregnation coatings, and reduce the number of impregnation coatings. The impregnation aid is completely decomposed at about 300 ° C and does not leave ash, so it does not affect the processing characteristics of the subsequent copper foil substrate and maintains the excellent electrical properties of the fluorocarbon resin.

The copper foil substrate obtained by using the resin composition of the fluorine prepreg has excellent appearance, excellent electrical properties, low dielectric constant and low dielectric loss, and excellent dimensional stability and rigidity.

Figure 1 Example 1 Scanning electron microscope (SEM) image of the appearance of a fluorocarbon resin composition prepreg

Fig. 2 Comparative Example 1 fluorinated resin composition prepreg appearance Scanning electron microscope (SEM) image

Fig. 3 Comparative Example 2 fluorinated resin composition prepreg appearance Scanning electron microscope (SEM) image

The following examples are prepared by the inventors of the present invention, and the objects and advantages of the present invention will become more apparent from the comparative examples. BEST MODE FOR CARRYING OUT THE INVENTION The details are as follows, but are not limited to the following embodiments, and can be implemented within the scope of the claims.

[Examples 1 to 5, Comparative Examples 1 to 4]

Preparation of Fluorine Resin Composition Prepreg: According to the formulation and ratio of Table 1, the preparation of the fluororesin composition prepreg is carried out, and the preparation steps are as follows. The polytetrafluoroethylene resin emulsion and the fluorocopolymer resin emulsion were uniformly stirred and mixed at a number of revolutions of 100 rpm for 20 minutes. Next, the inorganic powder was added to the above uniformly mixed emulsion, and stirred at a number of revolutions of 500 rpm for 30 minutes until the inorganic powder was uniformly dispersed and suspended in the emulsion. Finally, the impregnation aid polyethylene glycol was added to the uniformly mixed emulsion and uniformly stirred and mixed at a rotation speed of 100 rpm for 20 minutes to obtain a fluororesin composition prepreg (this step is omitted if no impregnation aid is added). The viscosity of the final fluororesin composition was measured, and the measured viscosity values are listed in Table 1.

Glass fiber cloth impregnated fluororesin composition prepreg: impregnating the above-prepared fluorocarbon resin composition prepreg with glass fiber cloth, feeding it into a high temperature furnace for drying (80~120 ° C), baking (200 ~240 ° C) and sintering (340 ~ 360 ° C), each section of the heating process is maintained for at least 20 minutes of sufficient heating process. The above impregnation coating and heating steps were repeated several times until the resin composition layer thickness was about 55 μm, and the actual impregnation times and thicknesses of the respective examples and comparative examples are listed in Table 1.

The fluorocarbon resin composition impregnated body obtained above was pressed against a copper foil at a temperature of 350 ° C and a pressure of 50 kg/cm ² to obtain a copper foil substrate. The dielectric constant Dk and the dielectric loss Df at a frequency of 10 GHz were measured by a Dielectric Analyzer HP Agilent E4991A to evaluate the dielectric properties of the substrate.

In the examples, the viscosity was adjusted in the fluororesin composition by adding the impregnation aids of different viscosities, and the loading of the immersion coating was significantly improved compared with the addition of the immersion aid in Comparative Example 1. The amount, so the viscosity is increased to reduce the number of times of impregnation coating.

In addition, the effect of adding an impregnation aid to the appearance of the prepreg can be seen in the scanning electron microscope (SEM) of Figures 1 and 2. It can be seen from Fig. 1 that the appearance of the prepreg prepared in Example 1 is even and flat, and Fig. 2 clearly shows that the appearance of the prepreg of Comparative Example 1 has obvious surface coating defects.

The resin composition of the present invention is controlled to have an appropriate viscosity by adjusting the content of the impregnation aid. From Comparative Example 2, it can be found that when the viscosity of the resin composition is too high, the film forming property of the prepreg is deteriorated. The surface is rough and the resin is easy to fall off. The appearance is shown in the scanning electron microscope (SEM) of Figure 3.

In Comparative Example 3, an excessive amount of the tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer resin was added, which was severely overflowed after the press plate, which was disadvantageous for subsequent processing of the printed circuit board.

In Comparative Example 4, an excessive amount of the inorganic powder was added, resulting in poor suspension property of the resin composition, and a large amount of powder precipitate appeared at the bottom, which was disadvantageous in the operation of the impregnation process.

The copper foil substrate prepared by the high temperature hot pressing of the prepreg of the invention has excellent dielectric properties, and the dielectric loss optimum embodiment can be as low as 0.0009, which can meet the dielectric characteristics required for high frequency communication. . The Dk and Df values of the examples and comparative examples at 10 GHz are detailed in Table 1.

Comparing the results of the examples and the comparative examples, the addition of the impregnation aid to the fluororesin composition can effectively increase the amount of the above-mentioned material during the impregnation coating, reduce the number of times of feeding, and the number of times of the material up to the target thickness and the resin composition Viscosity related. In addition, the high boiling point and wettability of the impregnation aid can improve surface defects caused by high temperature heating after impregnation coating, and a fluorocarbon resin composition prepreg having a smooth and uniform surface can be obtained.

Claims (4)

A fluororesin composition for impregnating a fiberglass cloth into a fluorocarbon substrate, characterized in that the resin composition comprises the following components, and based on the total weight of the resin composition, the sum of the following components is 100% by weight: (1) Polytetrafluoroethylene (PTFE) resin, 30 to 70% by weight; (2) fluorinated copolymer, 1 to 10% by weight, selected from tetrafluoroethylene-perfluoroalkoxy vinyl ether copolymer (PFA) or One or more of perfluoroethylene propylene copolymers (FEP); (3) inorganic powders, accounting for 5 to 60% by weight; (4) impregnation aids, accounting for 3 to 10% by weight, selected from high temperatures above 300 ° C One or more of hydroxyethyl cellulose, nitrocellulose, polymethyl styrene, polymethyl methacrylate or polyethylene glycol which are cleavage-removed, and the average molecular weight of the polyethylene glycol is 2,000 ~4,000. A fluorocarbon resin composition according to claim 1, wherein the inorganic powder is spherical or irregular cerium oxide (SiO ₂ ), titanium oxide (TiO ₂ ), aluminum hydroxide (Al(OH) ₃ ), Alumina (Al ₂ O ₃ ), magnesium hydroxide (Mg(OH) ₂ ), magnesium oxide (MgO), calcium carbonate (CaCO ₃ ), boron oxide (B ₂ O ₃ ), calcium oxide (CaO), titanic acid SrTiO ₃ , barium titanate (BaTiO ₃ ), calcium titanate (CaTiO ₃ ), magnesium titanate (2MgO.TiO ₂ ), boron nitride (BN), aluminum nitride (AlN), tantalum carbide (SiC) And one or a combination of one or more of cerium oxide (CeO ₂ ) or fume silica. A fluorocarbon resin composition according to claim 1, wherein the structures of hydroxyethyl cellulose, nitrocellulose, polymethyl styrene, polymethyl methacrylate or polyethylene glycol are respectively structural formulas ( D) to the structural formula (H): Where n=1~50, where R can be H or , X=1~10; Where n=1~50; Where n=1~50; Where n=1~50; Where n=1~200. A fluorocarbon resin prepreg obtained by using a glass fiber cloth as a substrate and impregnating a fluorocarbon resin composition of the first application of the patent application.