a C‐Glass (China) is specified by Chinese Standard JC583‐1995.
b A‐glass fiber (close to window glass composition) has low hydrolytic resistance, sensitive to moisture attack at room temperature, and, hence, is inappropriate for GRP composite applications.
c ZrO2 in AR‐glass is specified by ASTM C1666/C1666M‐08.
2.1.4 AR‐Glass
As named for its alkali‐resistant properties, AR‐glass fiber was invented in the mid‐1960s and first commercialized by Pilkington Brothers in the United Kingdom in the early 1970s under the trade name Cem‐Fil®. It was presented as a glass fiber option for reinforcing concrete structures. The glass chemistry was actually developed by a chemist at the Building Research Establishment and licensed to Pilkington by the National Research and Development Corporation, leading to its initial commercial application. The glass chemistry is primarily comprised of Na2O, CaO, ZrO2, and SiO2 with a small amount of Al2O3. The higher Al2O3 found in most commercial glass fibers results in lower ZrO2 solubility. Unlike E‐CR fibers, AR‐glass fiber offers high resistance to alkaline corrosion as well as to acid corrosion. This resistance is attributed to the formation of a protective layer rich in ZrO2 on the fiber surface in corrosive media. Because of the relatively high Na2O and low Al2O3 levels, the fiber modulus and tensile strength are lower than for E‐glass fibers despite the high concentration of ZrO2. The overall higher production and material cost of AR‐glass limits its utility to challenging fiber applications in cement reinforcement. Current developments are focused on increasing ZrO2 solubility to improve further corrosion resistance and to improve melting and fiber‐forming costs.
2.1.5 D‐Glass
An optimum combination of dielectric constant (Dk) and dissipation factor (Df) over a frequency range of 1 MHz to 40 GHz is provided by pure SiO2 glass. This property set is of particular utility in the field of PWB and electronic chips and circuitry, driven by the dramatic growth of computers and consumer electronics. It is to allow production of glass fibers approaching the performance of SiO2 glass in a reasonable commercial process that D‐glass has been designed. The earliest D‐glass fiber composition was essentially a binary mixture of SiO2 and B2O3. Although D‐glass fiber has significantly lower processing temperatures than pure SiO2, these temperatures are still substantially higher those of E‐glass fibers for PWB yarns. Melting temperatures are greater than 1600 oC and fiber drawing temperatures greater than 1400 oC. Recent developments have widened the D‐glass fiber composition space by introducing Al2O3, alkaline earth oxides (MgO, CaO, BaO, and SrO), and/or small amounts of Li2O (Table 1) [5]. These composition modifications significantly lowered glass melting and fiber drawing temperatures, providing more favorable production costs and improved commercial viability. The drawback is a modest increase in Dk and Df relative to the original D‐glass composition. To achieve target product electrical properties, PWB laminators can use different resins with lower Dk and Df. It is also possible to change the PWB layer stack and layout to meet target electrical performance for high‐end PWB substrates. Another development is to lower the coefficient of thermal expansion of the glass fiber to improve PWB substrate thermal stability. This reduces thermal fatigue susceptibility and leads to a reduction in thermally induced cracking on chips. Continuing improvements in D‐glass compositions keeps glass fiber at the forefront as a key element of choice in smaller, faster, lighter, and more electrically dense electronic components.
Table 2 Typical properties of fiberglass found in literature and/or commercial market [3, 4, 6, 7].
| Fiberglass | Fiber density ρ (g/cm3) | Pristine strength σf (GPa) | Sonic modulus E (GPa) | Dielectric constant Dk (1 GHz) | Coefficient thermal expansion CTE (10−6/oC) | Softening temperature Tsoft (oC) | Liquidus temperature Tliq (oC) | Forming temperature TF (oC) | Melting temperature TM (oC) |
|---|---|---|---|---|---|---|---|---|---|
| E (including E‐CR) | 2.60–2.65 | 2.8–3.5 | 70–85 | 6.6–7.1 | 5.4–5.9 | 846–920 | 1080–1220 | 1180–1282 | 1345–1460 |
| C (China) C (Europe) | 2.53 2.52 | 2.6 3.3 | 65 69 | 7.5 — | 8.4 — | — 750 | 1095 1127 | 1217 1157 | 1469 1400 |
| A | 2.46 | 3.0 | 62 | 10.6 | 9.0 | 704 | 996 | 1185 | 1443 |
| AR | 2.68–2.78 | 3.2–3.7 | 73–77 | — | — | 820–847 | 1049–1192 | 1237–1247 | 1430–1467 |
| D | 2.11–2.14 | 2.4‐2.5 | 52–55 | 3.8–4.0 | 3.1 | 771 | 953 |