Key Components of RO4350B
The three main constituents of RO4350B are:
- Ceramic filler
- PTFE (polytetrafluoroethylene)
- Woven glass reinforcement
Each of these materials contributes specific characteristics that together provide RO4350B’s outstanding performance. Let’s examine each component in more detail.
Ceramic Filler
Ceramic fillers are an essential part of RO4350B’s composition, typically making up 30-50% of the material by volume. The most commonly used ceramic is fused amorphous silica, which has a low dielectric constant and dissipation factor. This helps RO4350B achieve its excellent high-frequency electrical properties.
Other benefits of the ceramic filler include:
- Increased thermal conductivity for better heat dissipation
- Reduced coefficient of thermal expansion (CTE) for improved reliability
- Enhanced dimensional stability over a wide temperature range
The ceramic particles are carefully sized and dispersed throughout the PTFE matrix to ensure consistent properties. Typical ceramic loadings for RO4350B are on the higher end compared to other PTFE laminates to optimize performance.
PTFE Matrix
PTFE is a fluoropolymer well-known for its low dielectric constant, low dissipation factor, high temperature resistance, and chemical inertness. In RO4350B, PTFE serves as the matrix that binds the ceramic filler and glass reinforcement together.
Key characteristics of PTFE in RO4350B include:
- Dielectric constant of 2.1 at 10 GHz
- Dissipation factor of 0.0015 at 10 GHz
- Continuous operating temperature over 250°C
- Excellent chemical resistance and low moisture absorption
The PTFE matrix is modified with proprietary additives to optimize flow and adhesion during lamination. This ensures complete wetting of the glass reinforcement and strong bonding between layers.
Woven Glass Reinforcement
RO4350B incorporates woven fiberglass fabric to provide mechanical strength and dimensional stability. The glass fabric is typically a tight weave of E-glass or NE-glass yarns pre-impregnated with PTFE.
The woven glass offers several benefits:
- High tensile strength and stiffness
- Low z-axis CTE for plated through-hole reliability
- Controlled x-y dimensional stability
- Consistent thickness and good surface finish
Standard styles used in RO4350B include 1080, 1078, and 2113 glass fabrics at 5-10 plies thick depending on the desired laminate thickness. Glass content is approximately 40-55% by volume.
Interaction of Components
The ceramic, PTFE, and glass components of RO4350B don’t simply exist independently but interact synergistically to achieve a balanced set of properties.
The ceramic loading level and particle size distribution are optimized relative to the PTFE matrix for the best combination of electrical properties and rheology for lamination. Too little ceramic reduces the dielectric benefits, while too much can make lamination difficult.
Similarly, the glass fabric style and content are selected to provide sufficient mechanical reinforcement without excessively impacting electrical properties. The PTFE matrix must fully impregnate the glass weave to prevent voids.
During lamination, the PTFE softens and flows around the ceramic filler and glass fabric under heat and pressure. Precise control of lamination parameters is critical to achieve complete consolidation and strong interfacial bonding of the layers.
After lamination, RO4350B behaves as a composite material with properties derived from the combined contributions of its ceramic, PTFE, and glass constituents. The resulting properties are not simply a weighted average but reflect the complex interactions between the different phases.
Typical Composition of RO4350B
While the exact composition of RO4350B is proprietary, a typical formulation contains:
| Component | Content by Volume |
|---|---|
| Ceramic Filler | 30-50% |
| PTFE Matrix | 30-40% |
| Woven Glass Fabric | 40-55% |
Minor additives may include colorants, lubricants, or coupling agents at <1%. The specific ceramic type, particle size, and loading level are adjusted to optimize the dielectric constant and high-frequency loss properties for different applications.
Electrical Properties of RO4350B
The composition of RO4350B enables a desirable set of electrical properties for high-frequency circuit applications. Key properties include:
| Property | Value |
|---|---|
| Dielectric Constant (10 GHz) | 3.48 |
| Dissipation Factor (10 GHz) | 0.0037 |
| Dielectric Strength | >700 V/mil |
| Volume Resistivity | 10^7 Mohm-cm |
| Surface Resistivity | 10^7 Mohm |
These properties are stable over a wide frequency and temperature range. The low dielectric constant and dissipation factor enable high signal speed and low loss, while the high resistivity prevents leakage currents.
Mechanical Properties of RO4350B
In addition to its excellent electrical performance, RO4350B offers robust mechanical properties thanks to its woven glass reinforcement. Typical values include:
| Property | Value |
|---|---|
| Tensile Strength | 20 kpsi |
| Flexural Strength | 25 kpsi |
| Compressive Strength | 40 kpsi |
| Young’s Modulus | 2.7 Mpsi |
| Dimensional Stability (xy) | <0.05% |
| Coefficient of Thermal Expansion (z) | 30 ppm/°C |
| Peel Strength | 10 lb/in |
The high strength and modulus provide rigidity and prevent cracking, while the low CTE and high dimensional stability ensure layer-to-layer registration and reduced thermal stresses. Good peel strength is important for multi-layer board integrity.
FAQ
What is the dielectric constant of RO4350B?
RO4350B has a dielectric constant of 3.48 at 10 GHz. This low Dk value enables faster signal propagation and lower propagation delays compared to higher Dk materials like FR-4.
Is RO4350B suitable for multilayer PCBs?
Yes, RO4350B is an excellent material for multilayer PCB construction thanks to its combination of electrical and mechanical properties. The low loss and high dimensional stability enable reliable performance of buried and blind vias in complex designs.
How does the glass fabric affect RO4350B properties?
The woven glass fabric in RO4350B provides mechanical reinforcement, reduces the z-axis CTE, and controls the xy dimensional stability. However, the glass weave can also create anisotropic dielectric properties that may impact high-frequency performance for certain designs.
What is the maximum operating temperature of RO4350B?
RO4350B has a maximum continuous operating temperature of over 250°C thanks to its PTFE matrix and ceramic filler. This high temperature resistance enables use in demanding environments such as aerospace and military applications.
How does RO4350B compare to other high-frequency laminates?
RO4350B offers a balanced mix of properties that compares favorably to other PTFE-based laminates. Its Dk and Df values are similar to Rogers RO4000 series materials, but its higher ceramic loading and glass transition temperature provide enhanced thermal and mechanical performance. Compared to lower-cost materials like FR-4, RO4350B provides significantly better high-frequency electrical properties and temperature resistance, albeit at a higher raw material cost. Selection of RO4350B versus alternative materials depends on the specific application requirements and design constraints.
In conclusion, the composition of RO4350B is carefully engineered to provide an optimized blend of electrical, thermal, and mechanical properties for demanding high-frequency printed circuit board applications. Its unique combination of ceramic filler, PTFE matrix, and woven glass reinforcement enable high signal speed, low loss, temperature resistance, and mechanical robustness. By understanding the role and interaction of each component, designers can take full advantage of RO4350B’s capabilities and ensure reliable performance of their high-frequency circuits.
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