WO2010011701A2

WO2010011701A2 - Glass fiber composition and printed circuit board made from the glass fiber composition

Info

Publication number: WO2010011701A2
Application number: PCT/US2009/051329
Authority: WO
Inventors: John J. Kuhn; Kenneth D. Beer
Original assignee: Dielectric Solutions LLC
Current assignee: Dielectric Solutions LLC
Priority date: 2008-07-25
Filing date: 2009-07-22
Publication date: 2010-01-28
Anticipated expiration: 2011-01-25
Also published as: WO2010011701A3; TW201012771A

Abstract

Disclosed are glass fibers having a dielectric constant less than or equal to 6 and glass viscosity of 1000 poise at a temperature no greater than 2250 ° F (1232.2 °C). The glass fibers include between 45 Wt% and 65 Wt% of SiO2; between 15 Wt% and 25 Wt% of B₂O₃; between 8 Wt% and 16 Wt% of Al₂O₃; less than or equal to 10 Wt% of CaO; less than or equal to 10 Wt% of MgO; less than or equal to 3 Wt% of Na₂O; less than or equal to 2 Wt% of K₂O; less than or equal Io 2 Wt% of Li₂O; less than or equal to 5 Wt% of TiO₂; less than or equal to 2 Wt% of F₂; and less than or equal to 1 Wt% of Fe₂O₃. The glass fibers can have less than or equal to five hollow glass fibers per cubic centimeter of glass and are intended for use in a printed circuit board.

Description

GLASS FIBER COMPOSITION AND PRINTED CIRCUIT BOARD MADE FROM THE GLASS FIBER COMPOSITION

CROSS REFERENCE TO RELATED APPLICATION

[0001 J This application claims priority from U.S. Provisional Patent Application No. 61/083,706, filed My 25, 2008, entitled "Glass Fiber Composition", which is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

[0002] The present invention relates to glass fibers having a low dielectric constant, and particularly to glass fibers having a low dielectric constant for use in reinforcing printed circuit boards. Description of Related Art

[0003] Presently, so-called "E glass" is widely used in glass fiber form for reinforcing printed circuit boards. E glass is defined in specifications ASTM-D578 "Standard Specification for Glass Fiber Strands" and IPC-4412A "Specification for Finished Fabric Woven from 'E' Glass for Printed Boards" as comprising between 5 Wt% and 10 Wt% Of B₂O₃; between 16 Wt% and 25 Wt% of CaO; between 12 Wt% and 16 Wt% Of Al₂O₃; between 52 Wt% and 56 Wt% of SiO₂; between 0 Wt% and 5 Wt% of MgO; between 0 Wl% and 2 Wt% Of Na₂O; between 0 Wt% and 2 Wt% of K₂O; between 0 Wt% and 0.8 Wt% of TiO₂; between 0.05 Wt% and 0.4 Wt% of Fe₂O₃; and between 0 Wt% and 1 Wt% of F₂. Herein, all percentages of ingredients used to form a glass are expressed in terms of weight percentage, i.e., Wt%. [0004] As electronic circuitry is expected to operate at increasing clock speeds, printed circuit boards have become a limiting factor in equipment design. Signal propagation velocity is determined by a combination of circuit dimensions and laminate dielectric constant (Dk). Laminate Dk is determined by the respective Dk of the materials used to form the laminate, including resin and glass reinforcement. Typically, glass fibers are the dominant contributor to laminate Dk. There is a need for glass fibers with reduced Dk to meet the needs of high speed computing equipment.

[0005] A summary of the glass manufacturing process for use in printed circuit board (PCB) reinforcement is given by Eng (D. Eng, "Glass Fiber Glass Reinforcements Within Circuit Board Composites," The Board Authority, September 2001). The author describes glass melting, including the preprocessing step of making marbles or cullet, glass fiber forming, twisting, warping, slashing, weaving, heat cleaning and finishing processes. The author also identifies the need for glass with a low Dk and the limitations of current commercial offerings including higher glass melting temperature, higher energy cost and shorter glass melting and glass fiber forming equipment life.

[0006] The book by Lowenstein, K.L., "The Manufacturing Technology of Continuous Glass Fibres" 3^rd Revised Edition, Elsevier Publishing, 1993 (hereinafter "Lowenstein") describes the manufacture of glass yarns, including melting, glass fiber forming and twisting, in detail and is considered to be the standard work in the industry. Lowenstein includes critical details of equipment design and operation, glass fiber standards, and examples of low dielectric constant glass compositions and properties.

[0007] Alternate glass fiber compositions are available including "D" and "S" glass which are mentioned by Eng and Lowenstein as having a low Dk. These glasses have very high melting temperature and high viscosity, making it difficult to eliminate bubbles in the glass melt as noted in U.S. Patent No. 4,824,806 to Yokoi et al. Also, as a result of the difficulty in processing, glass fibers produced with these glass compositions are not available with glass fiber diameters below 9 micrometers, which limits their use in high density printed circuit boards.

[0008] U.S. Patent No. 4,762,809 to Imai describes an improvement in water resistance and heat resistance compared to D glass while demonstrating a low Dk. The Imai patent discloses a glass composition similar to D glass but includes B₂O₃ up to 21.5% and alkali (R₂O = Na₂O + K₂O + Li₂O) up to 5% by weight. The high silica content, greater than 70%_s results in high melting temperature greater than 2800⁰F. Also, the high silica content makes a printed circuit board substrate which is reinforced with this glass difficult to drill.

[0009] The Yokoi et al. patent demonstrates low Dk and good water resistance compared to D glass by increasing earth alkali (CaO + MgO) and alumina levels, and sometimes introducing ZnO, while simultaneously reducing alkali level. This glass shows improved productivity compared to D glass but has a higher melting temperature than E glass.

[001 OJ The Yokoi et al. patent recognizes the consequences of high viscosity and high melting temperature as making it difficult to obtain homogeneous glass with no bubbles. Bubbles in the glass melt during glass fiber forming had previously been observed in E glass and was a concern to the inventor in U.S. Patent No. 4,542,106 to Sproull in the development of a Boron and Fluorine free variation of E glass which melted at higher temperature.

[0011] These bubbles, if small, pass through the glass fiber forming process and result in hollow glass fibers. If large, these bubbles cause an interruption in the process. In either case, bubbles and the resulting hollow glass fibers are to be avoided in glass fiber production, fabric woven from these glass fibers and laminate or composite including these glass fibers which is to be used for printed circuit board or electrical insulation.

[0012] Disadvantages of hollow glass fibers in printed circuit board laminate have been documented in numerous trade journals and professional publications such as: (1) K. Rogers, C. Hillman and M. Pecht, "Hollow Fibers Can Accelerate Conductive Filament Formation", ASM International Practical Failure Analysis, pp. 57-60, Volume 1, Issue A, August 2001; (2) K. Rogers, P. Driessche, C. Hillman and M. Pecht, "Do You Know That Your Laminates May Contain Hollow Fibers?", Printed Circuit Fabrication, Vol. 22, No. 4, pp. 34-38, April 1999; and (3) A. Shukla, T. Dishongh, M. Pecht and D. Jennings, "Hollow Fibers in Woven Laminates", Printed Circuit Fabrication, Vol. 20, No. 1, pp. 30-32, January 1997. A method for quantifying hollow glass fibers is given in the Sproull patent and an accepted upper limit of 5 hollow glass fibers per cubic centimeter of glass is established. This is in the range of hollow glass fiber limits established by various manufacturers of printed circuit board materials.

[0013] U.S. Patent No. 5,958,808 to Mori et al. discloses a glass with low dielectric constant which includes alkali content between 0 Wt% and 0.5 Wt%, B₂O₃ content between 20 Wt% and 30 Wt%, and TiO₂ content between 0.5 Wt% and 5 Wt%. U.S. Patent No. 6,309,990 to Tamura et al. discloses increasing the alkali content to between 0 Wt% and 1.0 Wl% and decreasing the amount of B₂O₃ to between 15 Wt% and 30 Wt% while still including TiO₂ between 0.5 Wt% and 5 Wt%.

[0014] The Mori et al. patent describes a lower limit of 20 Wt% Of B₂O₃ to avoid a high dielectric tangent, upper limits of 5 Wt% of CaO and 4 Wt% MgO to avoid a high dielectric constant and high dielectric tangent, and upper limit of 0.5 Wt% of R₂O to avoid high dielectric tangent and poor water resistance. The Tamura et al. patent describes a lower limit of 15 Wt% Of B₂O₃ to avoid a high dielectric constant and high dielectric tangent, an upper limit of 5 Wt% of MgO to avoid a high dielectric constant, high dielectric tangent and decreased water resistance, and upper limit of 12 Wt% of CaO to avoid high dielectric constant and high dielectric tangent, and an upper limit of 1.0 Wt% OfR₂O or the Dk will be too high and water resistance poor. [0015] The increased limits of earth alkali (CaO and MgO) and alkali (Na₂O, K₂O and Li₂O) would be expected to reduce melting temperature, reduce the incidence of hollow glass fibers and improve workability. A glass fiber glass made according to the teachings of the Mori et al. patent and the Tamura et al. patent is manufactured by Nitto Boseki and sold under the trade name of NE glass. NE glass exhibits low Dk, not as low as D glass, but lower than S glass. The glass fiber glass made according to the teachings of the Mori et al. patent and the Tamura et al. patent is still difficult to melt, which requires high temperature and leaves bubbles in the glass. NE glass is known in the electronics industry to exhibit hollow glass fibers which have been observed by the present inventors to far exceed the limits established by the Sproull patent. This is acknowledged in the Tamura et al. patent as "some slight difficulty in workability and productivity".

SUMMARY OF THE INVENTION

[0016] Disclosed is a glass fiber that is desirably comprised of: between 45 Wt% and 65 Wt% of SiO₂; between 15 Wt% and 25 Wt% Of B₂O₃; between 8 Wt% and 16 Wt% Of Al₂O₃; less than or equal to 10 Wl% of CaO; less than or equal to 10 Wt% of MgO; less than or equal to 3 Wt% OfNa₂O; less than or equal to 2 Wt% Of K₂O; less than or equal to 2 Wt% of Li₂O; less than or equal to 5 Wt% of TiO₂; less than or equal to 2 Wt% of F₂; and less than or equal to 1 Wt% of Fe₂O₃, wherein said glass fiber has a dielectric constant less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

[0017] Also disclosed is a glass fiber that is more desirably comprised of: between 48 Wt% and 62 Wt% of SiO₂; between 17 Wt% and 23 Wt% of B₂O₃; between 9 Wt% and 15 Wt% Of Al₂O₃; between 2 Wt% and 10 Wl% of CaO; between 2 Wt% and 8 Wt% of MgO; less than or equal to 2 Wt% of Na₂O; less than or equal to 1 Wt% of K₂O; less than or equal to 1 Wt% of Li₂O; less than or equal to 2 Wt% of TiO₂; less than or equal to 1.5 Wt% of F₂; and less than or equal to 0.8 Wt% OfFe₂O₃, wherein said glass fiber has a dielectric constant less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

[0018] Also disclosed is a glass fiber that is most desirably comprised of: between

52 Wt% and 56 Wt% of SiO₂; between 18 Wt% and 22 Wt% Of B₂O₃; between 10

Wt% and 14 Wt% Of Al₂O₃; between 4 Wt% and 8 Wt% of CaO; between 2 Wl% and

6 Wt% of MgO; less than or equal to 2 Wt% OfNa₂O; less than or equal to 1 Wt% of

K₂O; less than or equal to 1 Wt% Of Li₂O; less than or equal to 0.5 Wt% of TiO₂; less than or equal to 1 Wt% of F₂; and less than or equal to 0.4 Wt% of Fe₂O₃, wherein said glass fiber has a dielectric constant (Dk) less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

[0019] Each of the foregoing glass fibers desirably includes no more than five hollow glass fibers per cubic centimeter of glass fiber.

[0020] Each of the foregoing glass fibers can further include one or more of the following in an amount totaling up to 5 Wt%: BaO; BeO; CaF₂; CdO; Mn₂O₃; P₂O₅;

PbO; SO₃; Sb₂O₃; SrO; ZnO; and ZrO₂.

[0021] Also disclosed is a printed circuit board comprising one or more laminates, wherein each laminate comprises glass fibers supported by a resin, said glass fibers having a dielectric constant (Dk) less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

[0022] The glass fiber comprising the printed circuit board is desirably comprised of: between 45 Wt% and 65 Wt% of SiO₂; between 15 Wt% and 25 Wt% Of B₂O₃; between 8 Wt% and 16 Wt% Of Al₂O₃; less than or equal to 10 Wt% of CaO; less than or equal to 10 Wt% of MgO; less than or equal to 3 Wt% Of Na₂O; less than or equal to 2 Wt% OfK₂O; less than or equal to 2 Wt% OfLi₂O; less than or equal to 5 Wt% of

TiO₂; less than or equal to 2 Wt% of F₂; and less than or equal to 1 Wt% OfFe₂O₃.

[0023] The glass fiber comprising the printed circuit board is more desirably comprised of: between 48 Wt% and 62 Wt% of SiO₂; between 17 Wt% and 23 Wt% of B₂O₃; between 9 Wt% and 15 Wt% of Al₂O₃; between 2 Wt% and 10 Wl% of

CaO; between 2 Wt% and 8 Wt% of MgO; less than or equal to 2 Wt% OfNa₂O; less than or equal to 1 Wt% of K₂O; less than or equal to 1 Wt% of Li₂O; less than or equal to 2 Wt% of TiO₂; less than or equal to 1.5 Wt% of F₂; and less than or equal to

0.8 Wt% OfFe₂O₃.

[0024] The glass fiber comprising the printed circuit board is most desirably comprised of: between 52 Wt% and 56 Wt% of SiO₂; between 18 Wt% and 22 Wt% of B₂O₃; between 10 Wt% and 14 Wt% of Al₂O₃; between 4 Wl% and 8 Wt% of

CaO; between 2 Wt% and 6 Wt% of MgO; less than or equal to 2 Wt% OfNa₂O; less than or equal to 1 Wt% of K₂O; less than or equal to 1 Wt% of Li₂O; less than or equal to 0.5 Wt% of TiO₂; less than or equal to 1 Wt% of F₂; and less than or equal to

[0025] The glass fiber comprising the printed circuit board can comprise one or more of the following in an amount totaling up to 5 Wt%: BaO; BeO; CaF₂; CdO;

Mn₂O₃; P₂O₅; PbO; SO₃; Sb₂O₃; SrO; ZnO; and ZrO₂.

[0026] The printed circuit board can further comprise no more than five hollow glass fibers per cubic centimeter of the glass fiber.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0027] The present invention is a glass fiber composition that can be used for reinforcing printed circuit boards. The glass fiber has low dielectric constant, low dielectric tangent, and low glass fiber forming temperature. The present inventors have observed that the glass fiber exhibits low melting temperature, low viscosity, and reduced bubbles in the melt with a corresponding reduction of hollow glass fibers, and excellent productivity.

[0028] The present inventors have observed that the amounts of the various glass ingredients must be carefully chosen to obtain the desired balance of electrical, chemical, mechanical and thermal properties. Heretofore, limits regarding acceptable properties of glass fiber and the contribution of various glass ingredients to these properties have not been well established.

[0029] Herein, four properties have been selected as performance metrics for a glass fiber composition in accordance with the present invention formed from the glass ingredients shown in the following Table I. These metrics include: dielectric constant (Dk); dissipation factor or dielectric tangent (Dl); high temperature viscosity (HTV) or the temperature (°F/°C) at which viscosity equals 1000 poise; and liquidus temperature (°F/°C). Liquidus temperature is a maximum temperature at which crystals can co-exist with the melt in thermodynamic equilibrium. [0030] hi view of the foregoing performance metrics, glass ingredients were assessed for acceptable levels of contribution to the four properties. To this end, the ingredients for the two commercial E glasses, the NE glass, and the Examples of experimental glasses shown in Table I were considered and the corresponding estimated values of Dk, Df, high temperature viscosity (HTV), and Liquidus temperature shown in Table II were determined for each glass of Table I. [0031] The estimated values of Dk and Df for each glass of Table 1 are reasonable compared to published data. Also, the actual glass fiber forming temperature is greater than the HTV which facilitates production of glass fibers at a diameter of 5 micrometers. This is also apparent in comparing the HTV and liquidus temperatures since glass fibers cannot be formed commercially below the liquidus temperature. [0032] Samples of the E glass and experimental glasses that were prepared with Dk and Df measured two different times at 10 GHz will now be described with reference to the following Table III and with continuing reference to Tables I and IL [0033] Examples

[0034] In glass fiber Example #1, relatively high weight percentages (Wt%) of silica (SiO₂), boron (B₂O₃), and titanium (TiO₂) were selected in combination with a relatively low Wt% of alumina (Al₂O₃) to reduce Dk. The glass fiber of Example #1 has excellent estimated electrical properties as shown in Table II and excellent measured electrical properties as shown in Table III. It is to be appreciated, that the order of magnitude difference in values of Df in Tables II and III for each glass fiber listed in both tables is due to the frequency used to measure Dk, namely, 1 MHz in Table II and 10 GHz in Table III. Historically, 1 MHz was utilized as the frequency for determining the value Dk for a glass fiber. However, printed circuit boards (PCB) today are increasingly being utilized with components that operate at GHz frequencies. Accordingly, for the purpose of determining an exemplary operational value for Dk, the measurements of Dk and Df in Table III were taken at 10 GHz. [0035] The calculated HTV for the glass fiber of Example #1 is considered relatively high and the glass fiber crystallized when being prepared. In the subsequent Examples described hereinafter, the Wt% of silica (SiO₂) was selected to be closer to the Wt% Of SiO₂ found in E Glasses #1 and #2 of Table I to avoid difficulty in drilling PCBs made with the glass fiber of each Example.

[0036] In glass fiber Examples #2 and #3, reducing the Wt% of sodium oxide (Na₂O), Lithium oxide (Li₂O), and fluorine (F₂) over the Wt% Of Na₂O, Li₂O and F₂ used to produce the glass fiber of Example #1 reduced the HTV of the glass fibers of Examples #2 and #3 versus the HTV of the glass fiber of Example #1. Moreover, increasing the Wt% of sodium oxide (Na₂O), and fluorine (F₂) over the Wt% OfNa₂O, and F₂ used to produce the NE glass of Tables I and II, reduced the HTV of the glass fibers of Examples #2 and #3 versus the HTV of the NE Glass. As show in Tables II and III, the glass fibers of Examples #2 and #3 have excellent estimated electrical properties and excellent measured electrical properties. However, the liquidus temperatures for the glass fibers of Examples #2 and #3 are higher than the liquidus temperature of the glass fibers of Example #1.

[0037] As shown for glass fiber Example #4, increasing the Wt% of calcium oxide (CaO) and Magnesium oxide (MgO) while simultaneously reducing the Wt% of titanium dioxide (TiO₂) over the Wt% of CaO, MgO, and TiO₂ in glass fiber Examples #1, #2 and #3 produced the glass fiber of Example #4 having a lower liquidus temperature than the glass fibers of Examples #1, #2 and #3. [0038] In each glass fiber Example, the Wt% of each ingredient is carefully selected to maintain an optimum balance of electrical properties (Dk and Df), HTV and liquidus temperature. In glass fiber Example #5, the Wt% of the various ingredients were adjusted, especially the Wt% of CaO and MgO, versus the Wt% of the ingredients used to form the glass fiber of Example #4 to further improve Dk, HTV and liquidus temperature. Lastly, in glass fiber Example #6, variations in the Wt% of CaO, MgO, Na₂O, K₂O, Li₂O, and F₂ versus the Wt% of these same ingredients in the glass fiber of Example #5 resulted in the changes to Dk, Df, HTV, and liquidus temperature shown in Tables II and III. The electrical properties of glass samples in Examples #1 through #5 were measured and reported twice in Table III to assess repeatability.

[0039] Based on the estimated properties in Table II and measured properties in Table III, the present inventors were surprised to learn that glass compositions (such as, without limitation, the glass compositions of Examples #1 through #6) are possible that exhibit melting and glass fiber forming properties very similar to E glass while simultaneously demonstrating excellent electrical properties. The present inventors believe that heretofore such combination of glass fiber forming properties and electrical properties were not known in the art. Table ] E

Glass Composition (Wt%)

E Glass E Glass NE Ex:

Ingredient Ex: #2 Ex: #3 Ex: #4 Ex: #5 Ex: #6 #1 #2 Glass #1

60.0

SiO₂ 55.07 53.20 55.27 52.80 52.85 52.69 54.99 55.58 0

20.0

B₂O₃ 5.53 8.38 18.45 18.80 18.97 20.49 19.93 19.69 0

Al₂O₃ 13.74 14.58 15.09 5.00 15.90 15.87 12.13 11.80 11.85

CaO 20.99 16.76 4.20 5.00 4.50 3.99 7.15 5.92 6.04

MgO 2.47 4.84 4.38 4.00 4.00 3.96 5.09 4.20 4.06

Na₂O 1.38 .33 .05 .75 .45 0.68 .60 1.60 1.80

K₂O .09 .23 .00 .00 .00 .61 .84 .16 .22

Li₂O .00 .00 .14 .75 .45 .10 .12 .19 .25

TiO₂ .50 .28 1.99 4.00 2.80 2.69 .37 .40 .41

F₂ .02 .62 .02 .50 .30 .29 .53 .79 .18

Fe₂O₃ .234 .335 .092 .015 .015 .017 .017 .017 .054

Table π

Estimated Properties at 1 MHz

E Glass E Glass NE

Property Ex: #1 Ex: #2 Ex: #3 Ex: #4 Ex: #5 Ex: #6

#1 #2 Glass

Dk 6.85 6.39 5.02 4.42 5.09 5.16 5.33 4.68 5.03

Dfx 10⁴ 8.35 12.12 10.57 14.69 6.17 5,74 7.29 5.10 4,65

HTV 1945/ 2122/ 2449/ 2395/ 2172/ 2088/ 2034/ 1966/ 1951/

(°F/°C) 1062.8 1161.1 1342.8 1312.8 1188.9 1142.2 1112.2 1074.4 1066.1

Liquidus 2074/ 2131/ 2251/ 2114/ 2248/ 2238/ 2110/ 2095/ 2090/

(°F/°C) 1134.4 1166.1 1232.8 1156.7 1231.1 1225.6 1154.4 1146.1 1143.3

Table πi

Measured Properties at 10 GHz (Measurement #1)

E Glass E Glass

Property Ex: #1 Ex: #2 Ex: #3 Ex: #4 Ex: #5 Ex: #6

#1 #2

Dk 6.85 6.29 5.07 5.04 5.08 5.12 5.08 5.17 Df .0094 .0059 .0047 .0052 .0053 .0053 .0074 .0064

Measured Properties at 10 GHz (Measurement #2)

E Glass E Glass

Property Ex; #1 Ex: #2 Ex: #3 Ex: #4 Ex: #5 Ex: #6 #1 #2

Dk 6.82 6.28 5.07 5.09 5.08 5.12 5.08 Df .0079 .0051 .0044 .0045 .0056 .0055 .0075

In Tables I, II and III "Ex:" = Example [0040] To determine glass melting conditions similar to E glass, consideration was given to the melt temperature of 2588⁰F (142O⁰C) disclosed in U.S. Patent No. 2,334,961 to Schoenlaub and the melt temperatures between 235O⁰F and 2450^DF (1288⁰C and 1343⁰C) disclosed in U.S. Patent No. 3,095,311 to von Wranau et al. For pot melting batches of borosilicate glass it is common practice to melt in two charges then hold the resulting melt at 247O⁰F (1354⁰C) for 14 hours. Subsequent to the laboratory melts for Examples #1 through #6 above, five different batches totaling over 6000 lbs. of the glass of Example #5 were prepared. In each case, the batch was melted in a clay crucible at 2500⁰F (1371⁰C) then held at 2500⁰F (1371⁰C) for 16 hours. The molten glass was then ladled from the crucible and quenched in water. The rapid cooling caused the glass to fracture into cullet pieces that could be remelted in a standard marble melt bushing.

[0041] The glass cullet pieces were subsequently remelted and formed into glass fibers in a standard marble melt bushing under process conditions similar to those utilized to melt and form E glass fibers as described on pages 115 - 121 of Lowenstein. Since processes of forming glass fibers are well-known in the art, such process will not be described herein for simplicity.

[0042] Although small reductions in glass flow and production efficiency were noted in the production of the glass fibers of Example #5 compared to the production of E glass, commercial viability of forming the glass fibers of Example #5 utilizing standard glass fiber forming processes was demonstrated. Glass samples were collected twenty times during the production of the glass fibers of of Example #5 and, to the surprise of the present inventors, no bubbles and no hollow glass fibers were observed for any sample.

[0043] Fabric was subsequently woven from these glass fibers, impregnated with a commercially available high performance resin, and pressed into a laminate of the type used for fabrication of PCBs. Laminates were made with the same resin at 68% resin content, by weight, with fabrics woven from E glass, NE glass, and the glass given in Example #5. Electrical properties measured at 10 GHz are shown in the following Table IV. Table IV

Electrical Properties of Laminate Measured at 10 GHz and 68% Resin Content

E Glass NE Glass Ex: #5

Dk 3.30 3.00 2.97 Df 0.0090 0.0080 0.0079

[0044] As shown in Table IV, PCB laminate manufactured utilizing the glass fibers of Example #5 demonstrated electrical properties equivalent to laminates manufactured utilizing existing high performance fiber glasses and resin. At the same time, the glass fibers of of Example #5 above demonstrated melting and glass fiber forming temperatures comparable to E glass with a corresponding improvement in productivity and the complete elimination of bubbles and hollow glass fibers. [0045] The range of each ingredient of each Example glass composition shown in Table I is not to be construed as limiting the invention. Rather, it is believed that a desirable range of each ingredient of Table I comprising a glass composition in accordance with the present invention can include: between 45 Wt% and 65 Wt% of SiO₂; between 15 Wt% and 25 Wt% OfB₂O₃; between 8 Wt% and 16 Wt% OfAl₂O₃; between 0 Wt% and 10 Wt% of CaO; between 0 Wt% and 10 Wt% of MgO; between 0 Wt% and 3 Wt% OfNa₂O; between 0 Wt% and 2 Wt% OfK₂O; between 0 Wt% and 2 Wt% Of Li₂O; between 0 Wt% and 5 Wt% of TiO₂; between 0 Wt% and 2 Wt% of F₂; and between 0 Wt% and 1 Wt% OfFe₂O₃.

[0046] It is believed that a more desirable range of each ingredient in Table I comprising a glass composition in accordance with the present invention can include: between 48 Wt% and 62 Wt% of SiO₂; between 17 Wt% and 23 Wt% of B₂O₃; between 9 Wt% and 15 Wt% OfAl₂O₃; between 2 Wt% and 10 Wt% of CaO; between 2 Wt% and 8 Wt% of MgO; between 0 Wt% and 2 Wt% Of Na₂O; between 0 Wt% and 1 Wt% of K₂O; between 0 Wt% and 1 Wt% Of Li₂O; between 0 Wt% and 2 Wt% Of TiO₂; between 0 Wl% and 1.5 Wt% of F₂; and between 0 Wt% and 0.8 Wt% of Fe₂O₃.

[0047] Lastly, it is believed that the most desirable range of each ingredient in Table I comprising a glass composition in accordance with the present invention can include: between 52 Wt% and 56 Wt% of SiO₂; between 18 Wt% and 22 Wt% of B₂O₃; between 10 Wt% and 14 Wt% Of Al₂O₃; between 4 Wt% and 8 Wt% of CaO; between 2 Wl% and 6 Wt% of MgO; between 0 Wl% and 2 Wt% OfNa₂O; between 0 Wt% and 1 Wt% of K₂O; between 0 Wt% and 1 Wt% Of Li₂O; between 0 Wt% and 0.5 Wt% of TiO₂; between 0 Wt% and 1 Wt% of F₂; and between 0 Wt% and 0.4 Wt% OfFe₂O₃.

[0048] While it is known in the art of glass fiber production to list ingredients in terms of oxides of the elements, ingredients may be added to the glass batch in several different forms. For example, without limitation, lithium may be added as carbonate, as can magnesium.

[0049] It is also known in the art of glass fiber production that one or more other compounds can be added to improve glass properties. For example, without limitation, U.S. Patent No. 2,335,463 to Steinbock discloses that the addition of BaO, SrO, Mn₂O₃, ZnO, and/or CdO to glass compositions of the type shown in Table I improved heat, moisture and chemical resistance. Moreover, the addition of BaO or SrO has also been observed to reduce the tendency of glass compositions of the type shown in Table I to devitrify. U.S. Patent No. 2,685,527 to Labino discloses that the addition of ZnO to glass compositions of the type shown in Table I improve the strength of the glass fibers. The von Wranau et al. patent (discussed above) discloses that glass compositions of the type shown in Table I, including the addition of BaO, CaF₂, PbO, ZnO and/or ZrO₂, exhibited low melting and fiber forming temperatures, corrosion resistance, chemical durability, electrical insulating properties and devitrification resistance. U.S. Patent Nos. 3,183,104 and 3,189,471 to Thomas disclose that the addition of BeO to glass compositions of the type shown in Table I improve tensile strength and modulus. U.S. Patent No. 4,582,748 to Bastes et al. discloses that the addition of ZnO reduces the thermal expansion and dielectric constant of glass compositions of the type shown in Table I. The Yokoi et al. patent (discussed above) discloses that the addition of ZnO also reduces the dielectric constant of glass compositions of the type shown in Table I. U.S. Patent No. 4,628,038 to Weirauch, Jr. discloses that the use of trace amounts of SO₃ in glass compositions of the type shown in Table I improves water and devitrification resistance. It is envisioned that one or a combination of the foregoing compounds can be added in an amount up to 5% by weight to improve glass properties. [0050] Lastly, International Application Publication No. WO/2002/094728 to Lecomte et al. discloses that substituting P₂O₅ for TiO₂ in glass compositions of the type shown in Table I reduces the dielectric constant of the glass. [0051] The invention has been described with reference to the preferred embodiments. Obvious modifications and alterations will occur to those of ordinary skill in the art upon reading and understanding the preceding detailed description. For example, all Wt%s between two Wt%s include said two Wt%s, e.g., between 17 Wt% and 23 Wt% are inclusive of 17 Wt% and 23 Wt%. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

The Invention Claimed Is:

1. A glass fiber comprised of: between 45 Wt% and 65 Wt% of SiO₂; between 15 Wt% and 25 Wt% OfB₂O₃; between 8 Wt% and 16 Wt% OfAl₂O₃; less than or equal to 10 Wt% of CaO; less than or equal to 10 Wt% of MgO; less than or equal to 3 Wt% OfNa₂O; less than or equal to 2 Wt% of K₂O; less than or equal to 2 Wt% OfLi₂O; less than or equal to 5 Wt% of TiO₂; less than or equal to 2 Wt% OfF₂; and less than or equal to 1 Wt% Of Fe₂O₃, wherein said glass fiber has a dielectric constant less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

2. The glass fiber of claim 1, further comprising no more than five hollow glass fibers per cubic centimeter of glass fiber.

3. The glass fiber of claim 1, further comprising at least one of the following in an amount of up to 5 Wt%: BaO; BeO; CaF₂; CdO; Mn₂O₃; P₂O₅; PbO; SO₃; Sb₂O₃; SrO; ZnO; and ZrO₂.

4. A glass fiber comprised of: between 48 Wt% and 62 Wt% of SiO₂; between 17 Wt% and 23 Wt% OfB₂O₃; between 9 Wt% and 15 Wt% OfAl₂O₃; between 2 Wt% and 10 Wt% of CaO; between 2 Wt% and 8 Wt% of MgO; less than or equal to 2 Wt% OfNa₂O; less than or equal to 1 Wt% of K₂O; less than or equal to 1 Wt% OfLi₂O; less than or equal to 2 Wt% of TiO₂; less than or equal to 1.5 Wt% of F₂; and less than or equal to 0.8 Wt% of Fe₂O₃, wherein said glass fiber has a dielectric constant less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

5. The glass fiber of claim 4, further comprising no more than five hollow glass fibers per cubic centimeter of glass fiber.

6. The glass fiber of claim 4, further comprising at least one of the following in an amount of up to 5 Wt%: BaO; BeO; CaF₂; CdO; Mn₂O₃; P₂O₅; PbO; SO₃; Sb₂O₃; SrO; ZnO; and ZrO₂.

7. A glass fiber comprised of: between 52 Wt% and 56 Wt% of SiO₂; between 18 Wt% and 22 Wt% OfB₂O₃; between 10 Wt% and 14 Wt% OfAl₂O₃; between 4 Wt% and 8 Wt% of CaO; between 2 Wt% and 6 Wl% of MgO; less than or equal to 2 Wt% OfNa₂O; less than or equal to 1 Wt% of K₂O; less than or equal to 1 Wt% Of Li₂O; less than or equal to 0.5 Wt% of TiO₂; less than or equal to 1 Wt% OfF₂; and less than or equal to 0.4 Wt% of Fe₂O₃, wherein said glass fiber has a dielectric constant (Dk) less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

8. The glass fiber of claim 7, further comprising no more than five hollow glass fibers per cubic centimeter of glass fiber.

9. The glass fiber of claim 7, further comprising at least one of the following in an amount totaling up to 5 Wt%: BaO; BeO; CaF₂; CdO; Mn₂O₃; P₂O₅; PbO; SO₃; Sb₂O₃; SrO; ZnO; and ZrO₂.

10. A printed circuit board comprising one or more laminates, wherein each laminate comprises glass fibers supported by a resin, said glass fibers having a dielectric constant (Dk) less than or equal to 6 and a glass viscosity of 1000 poise at a temperature no greater than 225O⁰F (1232.2⁰C).

11. The printed circuit board of claim 10, wherein the glass fibers are comprised of: between 45 Wt% and 65 Wt% of SiO₂; between 15 Wt% and 25 Wt% OfB₂O₃; between 8 Wt% and 16 Wt% OfAl₂O₃; less than or equal to 10 Wt% of CaO; less than or equal to 10 Wt% of MgO; less than or equal to 3 Wt% OfNa₂O; less than or equal to 2 Wt% of K₂O; less than or equal to 2 Wt% of Li₂O; less than or equal to 5 Wt% OfTiO₂; less than or equal to 2 Wt% of F₂; and less than or equal to 1 Wt% OfFe₂O₃.

12. The printed circuit board of claim 10, wherein the glass fibers are comprised of: between 48 Wt% and 62 Wt% of SiO₂; between 17 Wt% and 23 Wl% OfB₂O₃; between 9 Wt% and 15 Wt% OfAl₂O₃; between 2 Wt% and 10 Wt% of CaO; between 2 Wt% and 8 Wt% of MgO; less than or equal to 2 Wt% OfNa₂O; less than or equal to 1 Wt% of K₂O; less than or equal to 1 Wt% OfLi₂O; less than or equal to 2 Wt% of TiO₂; less than or equal to 1.5 Wt% of F₂; and less than or equal to 0.8 Wt% OfFe₂O₃.

13. The printed circuit board of claim 10, wherein the glass fibers are comprised of: between 52 Wl% and 56 Wt% OfSiO₂; between 18 Wt% and 22 Wt% OfB₂O₃; between 10 Wt% and 14 Wt% OfAl₂O₃; between 4 Wt% and 8 Wt% of CaO; between 2 Wt% and 6 Wt% of MgO; less than or equal to 2 Wt% OfNa₂O; less than or equal to 1 Wt% of K₂O; less than or equal to 1 Wt% OfLi₂O; less than or equal to 0.5 Wl% OfTiO₂; less than or equal to 1 Wt% of F₂; and less than or equal to 0.4 Wt% OfFe₂O₃.

14. The printed circuit board of claim 10, wherein the glass fibers comprise one or more of the following in an amount totaling up to 5 Wt%: BaO; BeO; CaF₂; CdO; Mn₂O₃; P₂O₅; PbO; SO₃; Sb₂O₃; SrO; ZnO; and ZrO₂.

15. The printed circuit board of claim 10, further comprising no more than five hollow glass fibers per cubic centimeter of the glass fiber.