The rollout of 5G networks and the proliferation of millimetre-wave (mmWave) radar in automotive and industrial sensing applications have placed new demands on the dielectric materials used in PCB substrates, antenna housings, and radome structures. At frequencies of 28 GHz (sub-6GHz 5G), 39 GHz (mmWave 5G), and 77 GHz (automotive radar), the electrical performance of substrate materials degrades rapidly with increasing dielectric constant and loss tangent. The reinforcement fibers used in PCB laminates and composite radomes — materials often treated as inert structural filler — become a primary driver of system performance at these frequencies.
Standard E-glass, the dominant fiber reinforcement in PCB laminates (as woven fabric in FR4 and high-speed laminate grades), presents fundamental limitations at 5G and mmWave frequencies that cannot be overcome by resin system optimisation alone. Silica and quartz fibers offer a direct solution — lower Dk, lower loss tangent, higher temperature capability — at the cost of higher material price. For engineers designing to demanding RF specifications, understanding the precise trade-offs between fiber types is essential to making the right material selection.
The Dielectric Problem with E-Glass Above 700°C
E-glass — a calcium aluminoborosilicate glass formulated for electrical applications — has a dielectric constant (Dk) of approximately 6.0–7.0 at 1 MHz, rising somewhat at higher frequencies due to moisture absorption and compositional variability. More critically, its loss tangent (Df) is typically in the range of 0.001–0.003 at 10 GHz, which creates measurable insertion loss in signal traces at 5G frequencies and significant attenuation through composite radome panels.
At the structural level, E-glass softening begins at approximately 700–730°C. While this is not relevant for standard PCB applications (where the resin system fails first at 250–300°C), it becomes critical in high-temperature electronic enclosures, exhaust-side automotive sensors, satellite electronics operating through reentry thermal loads, or CMC surfacing applications where service temperatures exceed 500°C.
Both the dielectric and thermal limitations of E-glass are intrinsic to its composition. They cannot be addressed by fiber surface treatment, weave architecture, or coupling agent optimisation — the solution requires switching to a higher-purity silica or quartz fiber system.
Why Low Dielectric Constant Matters for 5G
The dielectric constant of a PCB substrate material determines the propagation velocity of electromagnetic signals through the medium. Signal propagation velocity is proportional to 1/√Dk — lower Dk means faster signal propagation, shorter effective electrical wavelength, and reduced phase delay through the substrate. For high-frequency PCB design at 28 GHz and above, this translates into:
- Reduced insertion loss per unit length: lower Dk and loss tangent directly reduce the attenuation of signal traces, enabling longer interconnects or lower transmit power for equivalent signal-to-noise ratios
- More accurate impedance control: controlled-impedance traces are dimensioned using Dk; lower and more uniform Dk enables finer trace width control and tighter impedance tolerance
- Reduced frequency-dependent behavior: E-glass Dk varies with moisture content and exhibits significant dispersion at mmWave frequencies; silica fiber Dk is stable across frequency and environmental conditions
- Lower dielectric heating: at high power densities (relevant for active antenna systems and phased arrays), lower loss tangent reduces dielectric heating within the substrate, improving thermal management
For radome applications — where the composite panel must transmit RF energy with minimum attenuation — the loss tangent of the fiber reinforcement is the most critical parameter. A silica or quartz fiber reinforced laminate achieves transmission efficiencies not achievable with E-glass at 28 GHz and above.
silica365 key parameters: Service temperature up to 1150°C · Very low dielectric constant · Non-combustible · Dimensionally stable · Fiber blend: quartz + silica gel fibers · Wet-laid nonwoven format
Silica Fiber vs. Quartz Fiber vs. E-Glass
| Property | silica365 (Quartz + Silica Gel) | Pure Quartz Fiber | E-Glass |
|---|---|---|---|
| Dielectric constant (Dk at 10 GHz) | ~3.5–3.8 | 3.4–3.5 | 6.0–7.0 |
| Loss tangent (Df at 10 GHz) | 0.0002–0.0005 | <0.0002 | 0.001–0.003 |
| Maximum service temperature | Up to 1150°C | Up to ~1250°C | ~700°C (softening) |
| SiO₂ content | 96–99% | >99.95% | 52–56% |
| Relative cost | Medium-high | Very high | Low |
| Nonwoven availability | Yes — silica365 (wet-laid) | Limited | Widely available (woven + nonwoven) |
silica365 achieves dielectric performance significantly closer to pure quartz fiber than to E-glass, at a cost premium over E-glass but below the price of pure quartz products. The wet-laid nonwoven format offers additional advantages over woven quartz fabric for many applications: the isotropic fiber distribution eliminates the directional Dk variation inherent in woven architectures, and the surfacing veil format enables integration into hybrid laminates where silica365 provides the outer surface while a lower-cost reinforcement forms the structural core.
Radome and Defence Applications
Radomes — protective aerodynamic enclosures over radar and antenna systems — must simultaneously provide structural integrity, weatherproofing, and electromagnetic transparency. The transmission efficiency of a radome is governed by its wall thickness relative to the operating wavelength, and by the Dk and Df of the laminate at operating frequency. At 77 GHz automotive radar wavelengths (approximately 3.9 mm), even small increases in Dk or Df can cause insertion loss that compromises target detection range.
Silica fiber reinforced laminates are established in defence radar radomes for this reason. Aircraft nose radomes for airborne radar systems routinely use quartz or silica fiber as the primary reinforcement, often in woven form for structural laminates with a silica nonwoven surfacing veil for surface finish and smoothness. silica365 is suitable for this surfacing role, providing the EM-transparent surface layer that determines the electrical boundary condition of the composite panel.
For ground-based and shipborne radar systems, dimensional stability of the radome structure under thermal cycling is a critical qualification requirement. The low thermal expansion of silica fiber (coefficient of thermal expansion approximately 0.5 ppm/°C, versus 5 ppm/°C for E-glass) minimises thermally induced stress in the laminate and maintains panel geometry across operating temperature ranges from –55°C to +125°C.
Composite Surfacing Veils
Beyond standalone EM applications, silica fiber nonwoven finds application as a surfacing veil in ceramic matrix composites (CMCs) and carbon fiber reinforced polymer (CFRP) panels. In CMC manufacturing, a silica nonwoven veil applied to the tool-side surface of a preform improves surface finish by covering the coarse textile architecture of the structural reinforcement, reduces resin-rich surface layers that can microcrack under thermal cycling, and provides a protective barrier at the composite surface that maintains integrity through high-temperature service.
In CFRP panels destined for high-temperature applications — exhaust panels, fire walls, heat shields adjacent to hot structures — a silica fiber surfacing veil provides thermal protection that carbon fiber reinforced polymer alone cannot offer, since the polymer matrix begins to degrade above 200–300°C. silica365 veils in these locations extend the effective service temperature of CFRP structures while adding minimal mass.
For high-temperature sealing applications — gaskets, burner tiles, turbine entry seals — silica365 in heavier basis weights provides a conformable, high-temperature-resistant sealing material that complements metallic and ceramic sealing systems.
Explore silica365 for Your RF or High-Temperature Application
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Explore silica365 →Frequently Asked Questions
Silica and quartz fibers exhibit a very low dielectric constant (Dk) in the range of 3.4–3.8 at frequencies up to 10 GHz, compared to 6.0–7.0 for standard E-glass. When used as a reinforcement in a PCB or radome laminate, the composite Dk is a weighted combination of fiber and resin Dk values. Silica fiber nonwoven reinforcement enables finished laminate Dk values of 3.5–4.5 depending on resin system and fiber volume fraction, with significantly lower loss tangent than equivalent E-glass laminates.
E-glass fiber starts to soften at approximately 700–730°C (its softening point), and loses dimensional stability under mechanical load well before this temperature. For PCB substrates processed through high-temperature lead-free soldering (peak temperature ~260°C), E-glass itself is not the limiting factor — the resin system typically fails first. However, for high-temperature electronic enclosures, exhaust-side automotive electronics, or CMC surfacing applications where service temperatures exceed 400–500°C, E-glass is unsuitable. Silica fiber maintains structural integrity and dimensional stability up to 1150°C, making it the appropriate choice for these applications.
The terms 'silica fiber' and 'quartz fiber' are sometimes used interchangeably but refer to materials with different purity levels. Pure quartz fiber (fused silica, >99.95% SiO2) has the lowest dielectric constant and loss tangent, the highest temperature capability (up to ~1250°C), and the highest cost. Standard silica fiber (typically 96–99% SiO2) offers slightly lower performance but at significantly reduced cost. silica365 uses a combination of quartz and silica gel fibers, optimising the balance of dielectric performance, temperature capability, and cost for demanding electronics and composite applications.
Yes. Silica fiber nonwovens are an established reinforcement material for radome structures. Their very low dielectric constant and loss tangent minimise signal attenuation through the radome wall, while their dimensional stability and non-combustible character meet the structural and safety requirements of defence and aerospace radome specifications. silica365 can be used as a surfacing veil in glass-silica hybrid laminates or as the primary reinforcement in thin, EM-transparent panels. Custom thickness and areal weight specifications are available for defence and aerospace qualification programs.
silica365 is dimensionally stable up to 1150°C, making it suitable as a surfacing veil or interlayer in ceramic matrix composites (CMCs) used for gas turbine hot section components, burner tiles, and high-temperature sealing applications. In CMC manufacturing, a silica nonwoven surfacing veil improves surface finish, reduces microcracking at ply boundaries, and protects against fiber-matrix debonding at elevated temperatures. The non-combustible, dimensionally stable character of silica fiber is maintained through the CMC consolidation and high-temperature processing steps.