TWI680871B - Fluorine resin composition, prepreg and copper foil substrate using the composition - Google Patents

Abstract

A fluororesin composition is composed of (1) polytetrafluoroethylene (PTFE) resin, (2) fluorine-containing copolymer, selected from tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoro One or more combinations of ethylene propylene copolymer (FEP), (3) low molecular weight polytetrafluoroethylene fine powder and (4) inorganic powder (filler), suitable for use in the production of high frequency circuit boards Prepregs and copper foil substrates, especially during the lamination process of making copper foil substrates, from 350℃ to 250℃, by controlling the appropriate lamination rate to reduce the temperature between 1~4℃/min, it can be improved The crystallinity of the fluororesin composition improves the copper foil substrate with a high thermal conductivity and a wide range of dielectric constant, and is suitable for use as a high-frequency circuit substrate.

Description

Fluorine resin composition, prepreg and copper foil substrate using the composition

The present invention relates to a fluororesin composition, especially a fluororesin composition containing inorganic powder and low molecular weight polytetrafluoroethylene micropowder in its components. It has excellent dielectric properties and thermal conductivity characteristics. Prepreg and copper foil substrate for high-frequency circuit boards.

With the rapid development of wireless networks, satellite radar and 5G communications, combined with the architecture of Intelligent Connectivity, Elastic RAN and Massive MIMO, 5G is opened for consumption The authors have brought a new type of electronic communication services and car smart driving services. However, the power output of 5G electronic products continues to increase, and the relevant application frequency has also been greatly increased to the millimeter wave band (30~300GHz). In contrast, the heat dissipation requirements for materials have also increased significantly. Under this condition, traditional FR4 substrates The dielectric properties, especially the signal attenuation characteristics at high frequencies, have been unable to meet the stringent high-frequency transmission requirements.

In order to improve the heat dissipation characteristics of electronic components, according to the teachings of the prior art, most of them improve the heat dissipation characteristics of electronic components in terms of materials, processes and processing. For example, U.S. Patent No. 9,508,648B2 teaches that a large amount of high thermal conductivity inorganic fillers occupying about 90% by weight of the resin are compounded, so that the resulting laminated semiconductor substrate has characteristics such as high heat dissipation and low thermal expansion. However, the consequence of adding a large amount of inorganic fillers to the stacked semiconductor substrates is likely to cause poor adhesion between the stacked layers. Holes are prone to copper shedding, and voids are prone to appear in the material, thereby causing problems with processing reliability.

For example, US Patent No. 5,975,201 teaches the use of both high thermal conductivity materials and low thermal conductivity materials in circuit boards, and the high thermal conductivity materials guide the heat flow to the heat sink for effective heat distribution to improve high-power electronic components at high The problem of heat accumulation under power operation.

In addition to improving thermal conductivity from the choice of materials, printed circuit boards can also improve heat dissipation characteristics through the structural design of printed circuit boards. For example, a copper block is embedded in a printed circuit board, and the high thermal conductivity of the copper block is used to improve the heat dissipation problem of high-power electronic components.

In addition, in the prior art high-frequency microwave substrates, the insulating resin materials of the substrates used are common insulating resin materials such as hydrocarbons, polyphenylene ether, cyanate esters and polytetrafluoroethylene. These insulating resins have a large number of symmetrical structures, so the dipole moment between the molecules is quite small, which greatly improves the insulating properties of high-frequency microwave substrates at high frequency bands.

Among them, most of the insulating resins such as hydrocarbons, polyphenylene ether, and cyanate esters are thermally hardened by modification of functional groups, so the type and number of functional groups significantly affect their dielectric properties. When multiple characteristics such as mechanical and chemical resistance need to be achieved at the same time, these resins must partially sacrifice their excellent dielectric properties.

In contrast, the polytetrafluoroethylene resin is a thermoplastic resin. The hydrogen atoms around the main chain carbon atoms are replaced by the most electronegative fluorine atoms, and it has extremely high crystallinity and symmetry. The molecular weight is usually as high as 1,000,000~ 5,000,000, so PTFE has excellent chemical inertness, thermal stability (long-term use temperature can be from -50 ℃ to 260 ℃) and dielectric characteristics (ie, low dielectric constant and low dielectric loss). Therefore, PTFE materials have been widely used in micro Wave communication industry.

Although Teflon resin has excellent physical properties, but the characteristics of extremely large molecular weight, it has a very high viscosity at the melting point (about 10 ¹⁰ ~ 10 ¹² ), the flow is not easy, so it can not be molded by traditional thermoplastic processing methods . In addition, the melting point of polytetrafluoroethylene resin is as high as 327℃, which also makes the processing environment of PTFE more severe. It is not enough for processing machinery and electric equipment that is not traditional thermoplastic processing equipment.

In order to improve the difficult processing characteristics of polytetrafluoroethylene, the prior art introduced polytetrafluoroethylene perfluorinated or non-perfluorinated meltable fluorine resins, such as tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer ( PFA), polyperfluoroethylene propylene (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF), etc. .

Perfluorinated resins (PFA or FEP) can maintain the excellent dielectric properties of fluorinated resins, and have a lower processing temperature, but the price is more expensive, which limits their application. Although non-perfluorinated resins (ETFE, ECTFE, PVF, PVDF, etc.) also have lower processing temperatures and excellent mechanical properties, their long-term service temperature is lower, and their thermal stability and resistance Sexual and dielectric properties are significantly worse.

PTFE is a highly crystalline polymer with a raw material (without any thermal history processing after synthesis) crystallinity is as high as 92~98%, but after processing, sintering and cooling, the crystallinity will be greatly reduced to below 70% , The thermal conductivity coefficient is about 0.25W/mK, which can not be effectively used in high-power electronic component products. In order to solve this problem, the prior art teaches that by adding a large amount of high thermal conductivity inorganic ceramic powder, the thermal conductivity can be effectively increased to a level of about 1.5 W/m.K. However, the addition of a large amount of high thermal conductivity inorganic ceramic powder easily affects the workability and reliability of high-frequency substrates or plates, making The excellent physical and dielectric properties of the original polytetrafluoroethylene are weakened.

In view of the above, the present invention provides a fluororesin composition with excellent dielectric properties and thermal conductivity characteristics, suitable for use in the production of prepregs and copper foil substrates for high-frequency circuit boards; in particular, In the process of laminating copper foil substrates, when the temperature is reduced from 350℃ to 250℃, by controlling the proper lamination rate and lowering the temperature between 1 and 4℃/min, the crystallinity of the fluororesin composition can be improved, thereby improving The copper foil substrate has thermal conductivity, and has a high thermal conductivity coefficient and a wide range of dielectric constant, which is suitable for making a high-frequency circuit substrate.

The components of the fluororesin composition, based on the total weight of the resin composition, contain the following components and the sum of the components is 100 wt%: (1) polytetrafluoroethylene (PTFE) resin, accounting for 10 to 90 wt%; (2 ) Fluorine-containing copolymer, accounting for 1~10wt%, one or more than one selected from tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP); (3 ) Low molecular weight polytetrafluoroethylene fine powder, accounting for 5~50%, and the molecular weight of the polytetrafluoroethylene is 2,000~200,000, which can be prepared by thermal cracking degradation method or irradiation degradation method; and (4) inorganic powder, It accounts for 1~80wt%.

The beneficial effects of the fluororesin composition of the present invention include: 1. The fluororesin composition improves the thermal conductivity by introducing low molecular weight polytetrafluoroethylene fine powder, which can make the amount of each component in the resin composition more diverse and easier Control the dielectric properties of the fluororesin composition; 2. The copper foil substrate prepared using the fluororesin composition has a high thermal conductivity and a wide range of dielectric The electrical constant is suitable for making high-frequency circuit boards, which greatly improves the conventional problems of high thermal conductivity and high-frequency microwave substrates that cannot simultaneously take into account the thermal conductivity, dielectric characteristics and processing reliability.

The fluororesin composition of the present invention contains an inorganic powder and a low molecular weight polytetrafluoroethylene micropowder as a component, has excellent dielectric properties and thermal conductivity characteristics, and is suitable for use in the production of high-frequency circuit boards Used prepreg and copper foil substrate.

The components of the fluororesin composition, based on the total weight of the resin composition, contain the following components and the sum of the components is 100 wt%: (1) polytetrafluoroethylene (PTFE) resin, accounting for 10 to 90 wt%; (2 ) Fluorine-containing copolymer, accounting for 1~10wt%; (3) Low molecular weight polytetrafluoroethylene fine powder, accounting for 5~50%; and (4) Inorganic powder, accounting for 1~80wt%.

The fluorine-containing copolymer is selected from one or more of tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP). When the use amount of the fluorinated copolymer of the fluororesin composition of the present invention is greater than 10 wt%, during the lamination process of manufacturing the copper foil substrate, flow glue easily occurs, which affects the processability and thickness uniformity of the copper foil substrate. If the proportion of the fluorinated copolymer is less than 1%, the copper foil substrate is likely to have voids.

其中，n為整數，且n

1。 The structure of the polytetrafluoroethylene (PTFE) resin is shown in structural formula (A):

Where n is an integer and n

1.

其中，n及m為整數，且n

1、m

1。 The structure of the tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer (PFA) is shown in structural formula (B):

Where n and m are integers, and n

1.m

1.

其中，n及m為整數，且n

1、m

1。 The structure of the perfluoroethylene propylene copolymer (FEP), as shown in structure (C):

Where n and m are integers, and n

1.m

1.

The low-molecular-weight polytetrafluoroethylene fine powder can be prepared by thermal cracking degradation method or irradiation degradation method, preferably by using irradiation degradation method with high energy application efficiency. The molecular weight of the low molecular weight polytetrafluoroethylene fine powder is 2,000-200,000, preferably 10,000-100,000, and the average particle size is 1-10 microns.

When the amount of the inorganic powder used in the fluororesin composition is greater than 80 wt%, it will affect the adhesion between the plates of the copper foil substrate and the adhesion between the plates and the copper foil, which may easily cause delamination of the copper foil substrate.

The average particle size of the inorganic powder ranges from 0.01 to 50 microns, which can be selected from spherical or irregular silica (SiO ₂ ), titanium dioxide (TiO ₂ ), aluminum hydroxide (Al(OH) ₃ ), Spherical or irregular 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), strontium titanate (SrTiO ₃ ), barium titanate (BaTiO ₃ ), calcium titanate (CaTiO ₃ ), magnesium titanate (2MgO.TiO ₂ ), spherical or agglomerated or flake boron nitride ( BN), aluminum nitride (AlN), silicon carbide (SiC), ceria (CeO ₂ ) or fumed silica (fume silica) one or more combinations. Wherein, the fumed silica can also be selected from porous nano-sized silica particles with an average particle size of 1 to 100 nanometers (nm). The silicon dioxide may be of a molten type and a crystalline type, and considering the dielectric properties of the composition, it is preferably a molten silicon dioxide. The titanium dioxide may be rutile, anatase or brookite, and considering the dielectric properties of the composition, it is preferably rutile.

The fluororesin composition of the present invention has the addition of low molecular weight polytetrafluoroethylene fine powder and inorganic powder, utilizes the excellent short molecular chain arrangement ability of low molecular weight polytetrafluoroethylene fine powder, and is matched with appropriate high temperature sintering and high temperature pressing. The process parameters can effectively increase the crystallinity of the prepreg and copper foil substrate. The purpose of increasing the crystallinity of the material is to increase the thermal conductivity of the material.

The specific method for controlling the crystallinity of the low molecular weight polytetrafluoroethylene micropowder in the present invention is achieved by controlling and adjusting the cooling rate of the pressing process during the pressing process of making the copper foil substrate. The preferred cooling rate (or crystallization rate) is 1~4℃/min. When the cooling rate is too fast, the low molecular weight polytetrafluoroethylene powder can not be arranged and crystallized; but if the cooling rate is too slow, the process takes too long, affecting productivity, and is not practical.

The fluororesin prepreg of the present invention is obtained by using glass fiber cloth as a base material and performing the impregnation and coating of the fluororesin composition of the present invention multiple times.

The copper foil substrate of the present invention uses the fluororesin prepreg of the present invention as a substrate. After the copper foil is pasted on the upper surface and the lower surface, during the lamination process, when the temperature falls from 350°C to 250°C, Control the proper pressing rate and lower the temperature between 1~4℃/min, which can control and improve the fluororesin The crystallinity of the composition improves the thermal conductivity of the copper foil substrate, and a high-frequency circuit substrate having a high thermal conductivity and a wide range of dielectric constants is produced.

The following examples and comparative examples are cited to clarify the effect of the present invention, but the scope of rights of the present invention is not limited to the scope of the examples.

The copper foil substrates produced in the examples and comparative examples were evaluated for physical properties according to the following methods:

1. The cooling rate of copper foil substrate during the lamination process: It is controlled by the temperature control system of the hot press, and the controllable adjustment range is 1~20℃/min.

2. Differential scanning calorimetry (DSC) test: (TA Instruments' DSC Q20) differential scanning calorimeter was used to measure the primary melting enthalpy of the substrate.

3. Thermal conductivity analysis and testing: According to the ASTM-D5470 test method, thermal conductivity analysis and testing are performed using interface material thermal resistance and thermal conductivity coefficient measuring instruments (Taiwan Ruiling Technology Co., Ltd.; model LW-9389).

4. Dielectric constant Dk (10GHz): Use a dielectric analyzer (Dielectric Analyzer), model HP Agilent E4991A, to test the dielectric constant Dk at a frequency of 10G Hz.

5. Dielectric loss Df (10GHz): Use a dielectric analyzer (Dielectric Analyzer), model HP Agilent E4991A to test the dielectric loss Df at a frequency of 10G Hz.

[Examples 1 to 5, Comparative Examples 1 to 3]

Preparation of prepreg solution of fluorine resin composition :

According to the formulation and ratio of Table 1, the preparation of the fluororesin composition prepreg is performed. The preparation steps include: mixing Teflon resin emulsion and fluorocopolymer resin emulsion at 100 rpm for 20 minutes; then, adding low molecular weight polytetrafluoroethylene powder and inorganic The powder is mixed into the aforementioned homogeneously mixed emulsion, and stirred at 500 rpm for 30 minutes until the low molecular weight polytetrafluoroethylene fine powder and inorganic powder are uniformly dispersed and suspended in the emulsion; finally, it is stirred and mixed at 100 rpm for 20 minutes to prepare fluorine Prepreg of plain resin composition.

Production of fluorine resin prepreg :

The glass fiber cloth is impregnated with the prepreg solution of the fluorine resin composition prepared above, and then the glass fiber cloth impregnated with the prepreg liquid is sent into a high-temperature furnace body for drying at 80 to 120°C and baking at 200 to 240°C. , And sintering at 340~360℃, each section of the heating process maintains a sufficient heating process for at least 20 minutes. The above impregnation coating and heating steps are repeated until the thickness of the resin composition layer on the glass fiber cloth reaches about 100 μm, that is, a fluorine resin prepreg is prepared.

Making copper foil substrate :

Take the fluorinated resin impregnated body prepared above, after laminating the copper foil, press the copper foil under the conditions of temperature 350℃ and pressure 50kg/cm ² , keep the temperature and pressure for 2 hours, then lower the temperature to 250 After ℃, then lower the temperature to room temperature at a rate of 10 ℃/min to prepare a copper foil substrate; wherein, during the lamination process, the temperature is reduced from 350 ℃ to 250 ℃, the fluorine of Examples 1 to 5 and Comparative Examples 1 to 3 The crystallinity of the polytetrafluoroethylene fine powder in the plain resin composition will have different crystallinity due to the different cooling rate, which will affect the thermal conductivity.

Evaluate the crystallinity, thermal conductivity and dielectric properties of the substrate. The results of each physical property measurement are shown in Table 1.

The result :

For the fluororesin compositions of Examples 1 to 3, the crystallinity is adjusted by adding different proportions of low molecular weight polytetrafluoroethylene fine powder. When the amount of low molecular weight polytetrafluoroethylene added increases, the crystallinity of the fluororesin composition is significantly improved To further increase the thermal conductivity of the substrate to the highest 1.33W/m.K, and still maintain excellent dielectric properties and heat resistance. Compared with the fluororesin composition of Comparative Example 1, without adding any low molecular weight polytetrafluoroethylene fine powder, after pressing the plate, although the substrate has excellent heat resistance and electrical properties, but the thermal conductivity coefficient is only 0.61W/mK, showing fluorine The addition of low molecular weight polytetrafluoroethylene to the plain resin composition has the effect of significantly improving the thermal conductivity.

The fluororesin compositions of Examples 4 and 5 are adjusted by adjusting the type of inorganic powder and the ratio of polytetrafluoroethylene resin, the cooling rate is increased to 4.0m/min and the excellent crystallinity and thermal conductivity are maintained, and the dielectric constant of the substrate Dk can be adjusted from 2.5 to 12.5. The wider dielectric constant range is beneficial to the circuit design of different printed circuit boards. The low dielectric constant can be used for product applications with high-speed transmission characteristics. The high dielectric constant can make the circuit miniaturized. , Reduce the size of the overall electronic components.

Compared with Example 2, Comparative Example 2 increases the substrate cooling rate of Example 2 from 1.0°C/min to 5.0°C/min, and the thermal conductivity of the substrate is reduced from 1.15W/mK to 0.79W/mK. The effect of molecular arrangement of low molecular weight polytetrafluoroethylene powder on crystallinity and thermal conductivity. In Comparative Example 3, the temperature drop rate of pressing is reduced to 0.5°C/min, which has no significant effect on improving the crystallinity and thermal conductivity, and consumes time and energy, and the processing cost is greatly increased.

Comparative Example 4 A large amount of inorganic powder is added, and low molecular weight polytetrafluoroethylene fine powder is not added. Although the thermal conductivity can be effectively improved to 1.83W/mK after pressing, the large amount of inorganic powder causes the inorganic powder of the substrate not to be dispersed Good, uneven interface leads to high dielectric loss, and poor heat resistance, which is easy to cause reliability problems in printed circuit board processing.

The copper foil substrates of Examples 1 to 5 are made by pressing the produced fluororesin prepreg, which has excellent thermal conductivity, dielectric properties and stable processing reliability, and can simultaneously achieve a wide range of dielectrics The constant interval meets the requirements for heat dissipation and dielectric characteristics of high-frequency high-power electronic products.

Claims (7)

A fluororesin composition used for making a high-frequency circuit board, characterized in that, based on the total weight of the resin composition, it contains the following components and the sum of the components is 100 wt%: (1) Polytetrafluoroethylene (PTFE) Resin, accounting for 10~90wt%; (2) Fluorine-containing copolymer, accounting for 1~10wt%, selected from tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP ); (3) low molecular weight polytetrafluoroethylene fine powder, accounting for 5~50%, and the molecular weight of the low molecular weight polytetrafluoroethylene fine powder is 2,000~200,000, and the low molecular weight polytetrafluoroethylene The average particle size of the fine ethylene powder is 1-10 microns; (4) inorganic powder, accounting for 15wt%~80wt%; wherein, the inorganic powder is silicon dioxide, titanium dioxide, aluminum hydroxide, aluminum oxide, magnesium hydroxide , Magnesium oxide, calcium carbonate, boron oxide, calcium oxide, strontium titanate, barium titanate, calcium titanate, magnesium titanate, boron nitride, aluminum nitride, silicon carbide, ceria, and fumed silica One or more than one combination. The fluorine resin composition as described in item 1 of the patent application scope, wherein the polytetrafluoroethylene resin has the structure of structural formula (A):

Where n is an integer and n

1. The fluorine resin composition as described in item 1 of the patent application scope, wherein the tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer has the structure of structural formula (B):

Where n and m are integers, and n

1.m

1. The fluorine resin composition as described in item 1 of the patent application scope, wherein the perfluoroethylene propylene copolymer (FEP) has the structure of structural formula (C):

Where n and m are integers, and n

1.m

1. The fluororesin composition as described in item 1 of the patent application range, wherein the low molecular weight polytetrafluoroethylene fine powder is prepared using a thermal cracking degradation method or a radiation degradation method. A fluororesin prepreg for making high-frequency circuit boards, comprising: a substrate made of glass fiber cloth; and a fluororesin composition impregnated and coated on the substrate; wherein, Based on the total weight of the fluororesin composition, the fluororesin composition contains the following components and the sum of the components is 100 wt%: (1) Polytetrafluoroethylene (PTFE) resin, which accounts for 10 to 90 wt%; ( 2) Fluorine-containing copolymer, accounting for 1 to 10% by weight, one or more than one selected from tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP); (3) Low molecular weight polytetrafluoroethylene fine powder, accounting for 5~50%, and the molecular weight of the low molecular weight polytetrafluoroethylene fine powder is 2,000~200,000, and the average particle size of the low molecular weight polytetrafluoroethylene fine powder is 1 ~10 microns; (4) inorganic powder, accounting for 15wt%~80wt%; wherein, the inorganic powder is silicon dioxide, titanium dioxide, aluminum hydroxide, aluminum oxide, magnesium hydroxide, magnesium oxide, calcium carbonate, oxidation One or a combination of boron, calcium oxide, strontium titanate, barium titanate, calcium titanate, magnesium titanate, boron nitride, aluminum nitride, silicon carbide, ceria, and fumed silica. A copper foil substrate for manufacturing a high-frequency circuit board, comprising: a substrate, which is a fluororesin prepreg; wherein, the fluororesin prepreg includes: a substrate, which is made of glass fiber Cloth; and a fluororesin composition impregnated and coated on the substrate; wherein, based on the total weight of the fluororesin composition, the fluororesin composition contains the following components and the sum of the components is 100wt%: (1) Polytetrafluoroethylene (PTFE) resin, accounting for 10~90wt%; (2) Fluorine-containing copolymer, accounting for 1~10wt%, selected from tetrafluoroethylene/perfluoroalkoxy vinyl ether copolymer (PFA) or perfluoroethylene propylene copolymer (FEP); (3) low molecular weight polytetrafluoroethylene fine powder, accounting for 5~50%, and the molecular weight of the low molecular weight polytetrafluoroethylene fine powder 2,000~200,000, and the average particle size of the low molecular weight polytetrafluoroethylene fine powder is 1~10 microns; (4) inorganic powder, accounting for 15wt%~80wt%; wherein, the inorganic powder is silica , Titanium dioxide, aluminum hydroxide, aluminum oxide, magnesium hydroxide, magnesium oxide, calcium carbonate, boron oxide, calcium oxide, strontium titanate, barium titanate, calcium titanate, magnesium titanate, boron nitride, aluminum nitride, One or more combinations of silicon carbide, cerium oxide, and fumed silica; wherein, a copper foil is attached to the upper and lower surfaces of the substrate, respectively, and the substrate and the two copper foils The copper foil substrate is prepared by pressing against each other under a pressing temperature of 350° C. and a pressing pressure of 50 kg/cm ² , and then cooling to normal temperature; wherein, the copper foil substrate is in the process of manufacturing The pressing temperature is reduced from 350℃ to 250℃, and the temperature is lowered at a cooling rate between 1~4℃/min.