Fluorocarbon prepreg and resin composition thereof

Abstract

A fluorocarbon resin composition is applicable to produce a prepreg for use in making a high-frequency circuit board, including a polytetrafluoroethylene resin; a fluorine-containing copolymer of poly fluoroalkoxy or fluorinated ethylene propylene; inorganic powders and an impregnation additive such as hydroxyethyl cellulose; resulted in that the prepreg is capable of increasing a plurality of times for proceeding impregnation-coating, the surface defects prone to occur on a fluorocarbon prepreg during drying, baking and sintering after impregnation are therefore improved at the same time.

Claims

1. A fluorocarbon resin composition, characterized in that the fluorocarbon resin composition comprises, on the basis of the total weight of the fluorocarbon resin composition being 100 wt %: (1) a polytetrafluoroethylene (PTFE) resin, in a range from 40 to below 60 wt % of the fluorocarbon resin composition; (2) a fluorine-containing copolymer, selected from a group consisting of at least one of poly fluoroalkoxy (PFA), fluorinated ethylene propylene (FEP) and combinations thereof in a range from 1 to 10 wt % of the solid content of the fluorocarbon resin composition; (3) inorganic powders in a range from 30-50 wt % of the solid content of the fluorocarbon resin composition; and (4) an impregnation additive uniformly mixed with said PTFE, fluorine-containing copolymer, and inorganic powders, said impregnation additive being selected from a group consisting of at least one of hydroxyethyl cellulose, nitrocellulose, polymethyl styrene, polymethyl methacrylate and polyethylene glycol, and accounting for 0.1 to 10 wt % of the solid content of the fluorocarbon resin composition.

2. The fluorocarbon resin composition according to claim 1, wherein the structure of the polytetrafiuoroethylene resin is as shown in Structural Formula (A): ##STR00009## where n is an integer and n≥1.

3. The fluorocarbon resin composition according to claim 1, wherein the structure of poly fluoroalkoxy (PFA) is as shown in Structural Formula (B): ##STR00010## where n and m are integers, and n≥1 and m≥1.

4. The fluorocarbon resin composition according to claim 1, wherein the structure of fluorinated ethylene propylene (FEP) is as shown in Structural Formula (C): ##STR00011## where n and m are integers, and n≥1 and m≥1.

5. The fluorocarbon resin composition according to claim 1, wherein the inorganic powders is one or more selected from the group consisting of silicon dioxide (SiO.sub.2), titanium dioxide (TiO.sub.2), aluminum hydroxide (Al(OH).sub.3), alumina (Al.sub.2O.sub.3), magnesium hydroxide (Mg(OH).sub.2), magnesium oxide (MgO), calcium carbonate (CaCO.sub.3), boron oxide (B.sub.2O.sub.3), calcium oxide (CaO), strontium titanate (SrTiO.sub.3), barium titanate (BaTiO.sub.3), calcium titanate (CaTiO.sub.3), magnesium titanate (2MgO.TiO.sub.2), boron nitride (BN), aluminum nitride (AlN), silicon carbide (SiC), cerium oxide (CeO.sub.2) and fume silica.

6. The fluorocarbon resin composition according to claim 1, wherein the structures of hydroxyethyl cellulose, nitrocellulose, polymethyl styrene, polymethyl methacrylate and polyethylene glycol are as shown in Structural Formulas (D) to (H): ##STR00012## where n=1 to 50, and R is H or CH.sub.2CH.sub.2O.sub.XH, X=1 to 10; ##STR00013## where n=1 to 50; ##STR00014## where n=1 to 50; ##STR00015## where n=1 to 50; and ##STR00016## wherein n=1 to 200.

7. A fluorocarbon resin prepreg manufactured by impregnation-coating the fluorocarbon resin composition of claim 1 onto a fiberglass cloth for a plurality of times.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a scanning electron microscope (SEM) image of a fluorocarbon prepreg according to one embodiment of the present invention;

(2) FIG. 2 shows a scanning electron microscope (SEM) image of a fluorocarbon prepreg of comparative example 1; and

(3) FIG. 3 shows a scanning electron microscope (SEM) image of a fluorocarbon prepreg of comparative example 2.

DETAILED DESCRIPTION OF THE INVENTION

(4) 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. The preferred embodiments of the present invention are described in detail below, but the scope of the present invention is not limited to the following embodiments. The present invention can be implemented with modifications within the scope of the claims.

Embodiments 1 to 5, Comparative Examples 1 to 4

(5) Preparation of fluorocarbon resin composition prepreg: According to the formulations and ratios listed in Table 1, the preparation of the fluorocarbon resin composition prepreg is carried out, and the preparation steps are as follows. The PTFE resin emulsion and the fluorine-containing copolymer resin emulsion were uniformly stirred and mixed at a rotation speed of 100 rpm for 20 minutes. Then, inorganic powders were added to the above uniformly mixed emulsion, and stirred at a rotation speed of 500 rpm for 30 minutes until the inorganic powders were uniformly dispersed and suspended in the emulsion. Finally, an impregnation additive (for example, polyethylene glycol) was added to the above uniformly mixed emulsion and uniformly stirred and mixed at a rotation speed of 100 rpm for 20 minutes to obtain a fluorocarbon resin composition prepreg (this step is omitted if no impregnation additive is added). The viscosity of the final fluorocarbon resin composition was measured, and the measured viscosity values are listed in Table 1.

(6) Fiberglass cloth impregnated in fluorocarbon resin composition prepreg: A fiberglass cloth is impregnated in the fluorocarbon resin composition prepreg prepared above and it is fed into a furnace for drying (at 80 to 120° C.), baking (at 200 to 240° C.) and sintering (at 340 to 360° C.). All sections of the heating process are maintained for at least 20 minutes. The impregnation-coating and heating steps were repeated several times until the thickness of the fluorocarbon resin composition layer was about 55 μm. The actual impregnation times and thicknesses of the respective embodiments and comparative examples are listed in Table 1.

(7) 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.sup.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.

(8) In the embodiment, the viscosity is adjusted by adding impregnation additives with different viscosities in the fluorocarbon resin composition. The feeding amount during impregnation-coating is significantly improved compared with the comparative example 1 without the addition of immersion additives, resulting in enhanced viscosity and reduced number of times of impregnation-coating.

(9) In addition, the effect of adding impregnation additives on the appearance of the prepreg can be seen in the scanning electron microscope (SEM) image in FIG. 1 and FIG. 2. It can be seen from FIG. 1 that the appearance of the prepreg prepared in Embodiment 1 is evenly flat, and in FIG. 2, it is apparent that the prepreg of Comparative Example 1 has a significant surface coating defect.

(10) The viscosity of the fluorocarbon resin composition of the present invention is controlled to fall within an appropriate range by adjusting the content of the impregnation additive. From Comparative Example 2, it can be found that film formation of the prepreg is deteriorated such that the surface is rough and the resin is easy to fall off when the viscosity of the fluorocarbon resin composition is too high. The appearance is shown in the scanning electron microscope (SEM) image in FIG. 3.

(11) In Comparative Example 3, an excessive amount of poly fluoroalkoxy copolymer resin was added to cause severe glue overflow after pressing, which was disadvantageous for subsequent processing of the printed circuit board.

(12) In Comparative Example 4, an excessive amount of inorganic powders were added to cause poor suspension of the fluorocarbon resin composition and a large amount of powder precipitation at the bottom, which was disadvantageous for the impregnation process.

(13) The copper foil substrate prepared by high-temperature hot pressing of the prepreg according to the invention exhibits excellent dielectric properties, and the dielectric loss can be preferably as low as 0.0009, which meets the dielectric characteristics required for high frequency communication. The Dk and Df values of the embodiments and comparative examples at 10 GHz are listed in Table 1.

(14) Comparing the results of the embodiments and the comparative examples, the addition of the impregnation additive to the fluorocarbon resin composition can effectively increase the feeding amount during impregnation-coating and reduce the number of times of feeding. The number of times of feeding to the target thickness is related to the viscosity of the fluorocarbon resin composition. Furthermore, the high boiling point and wetting property of the impregnation additive overcome the problematic surface defects caused by high temperature heating after impregnation-coating so as to obtain a fluorocarbon resin composition prepreg with a uniformly smooth surface.

(15) TABLE-US-00001 TABLE 1 Composition of Prepreg Formulations of Embodiments and Comparative Examples and Their Implementation Results Enbodimnets Comparative Examples Composition (wt %) 1 2 3 4 5 1 2 3 4 polytetrafluoro-ethylene PTFE 40 40 60 60 60 42 35.8 30 25 resin fluorine-containing PFA 5 5 5 — 2.5 5.3 4.5 15 5 copolymer FEP — — — 5 2.5 — — — — inorganic powders SiO2 30 30 15 15 15 31.6 26.8 30 45 TiO2 20 20 15 15 15 21.1 17.9 20 20 impregnation PEG 5 — 5 5 5 — 15 5 5 additive 4000 PEG — 5 — — — — — — — 2000 Viscosity (cp) 120 50 100 105 100 30 300 110 100 Times of 5 7 6 6 6 8 4 5 — impregnation-coating Thickness (μm) 55 55 56 55 56 53 57 54 — Suspension of fluorocarbon good good good good good good good good poor resin composition Prepreg surface profile good good good good good poor poor good — Glue flow after pressing good good good good good poor poor poor — Dk (10 GHz) 3.42 3.40 2.81 2.90 2.852 3.35 3.54 3.23 — Df (10 GHz) 0.0018 0.0015 0.0009 0.0011 0.0012 0.0017 0.0039 0.0030 —