Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 135

An optimum combination of dielectric constant (D_k) and dissipation factor (D_f) 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 D_k and D_f relative to the original D‐glass composition. To achieve target product electrical properties, PWB laminators can use different resins with lower D_k and D_f. 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	1410	>1600
D (derivative I)	2.30	—	55–59	4.7–5.0	3.3–3.5	850	997–1270	1314–1382	>1550
D (derivative II)	2.30	2.5–3.1	57–64	5.4–5.8	4.0–4.9	830–875	1000–1054	1174–1298	1384–1502
D (derivative III)	2.34–2.42	3.3–4.1	73–82	4.8–5.6	4.1	944	1083–1287	1244–1388	1465–1641
R	2.55	4.1–4.5	85–87	6.4	3.3	952–975	1330	1410	—
R (derivative)	2.55–2.62	3.7–4.5	85–90	6.5	4.5–5.0	920–980	1170–1238	1265–1300	1468–1550
S	2.45–2.49	4.7–5.0	87–88	5.4	1.6–2.8	1030–1056	1439–1471	1424–1448	1620–1640
S (derivative)	2.53–2.56	4.2–4.8	86–95	—	2.8	920–968	1320–1450	1283–1450	—

Note: CTE values correspond to temperature range from room temperature to 300 ^oC; T_soft corresponds to glass viscosity of 10^7.6 Pa∙s as typically used in fiber glass production; T_F is defined by melt viscosity of 10² Pa∙s as a reference temperature for drawing fibers; T_M is defined by melt viscosity of 10 Pa∙s as a reference fining temperature to be reached in the industrial melting process.