4-Layer Hybrid Custom 1.55mm PCB 10mil Rogers RO4350B and High Tg 170°C FR-4 ENIG

4-Layer Hybrid Custom 1.55mm PCB 10mil Rogers RO4350B and High Tg 170°C FR-4 ENIG

Product Description

This product is a 4-Layer Hybrid Rigid PCB designed to solve the engineering challenge of balancing RF performance with mechanical stability. By utilizing a "sandwich" construction of Rogers RO4350B for the outer layers and High Tg FR-4 for the core, this board offers a superior solution for mixed-signal applications. The primary advantage of this hybrid construction is the ability to place high-speed RF traces (requiring low loss and tight Dk stability) on the outer laminates, while utilizing the economical and mechanically robust FR-4 material for the inner layers and structural support.

The hybrid circuit board leverages the low-loss characteristics of Rogers 4350B—a hydrocarbon/ceramic laminate known for its PTFE-like electrical performance without the complex manufacturing requirements—combined with the thermal reliability of High Tg (170°C) FR-4. This specific 4-layerstackup hybrid PCB allows for a finished thickness of 1.55mm, providing a rigid substrate suitable for harsh environments. Advanced manufacturing processes are employed to achieve 4/4 mil trace/space resolution and 0.30mm mechanical drilling, alongside blind vias (L3-L4) to optimize routing density while maintaining signal integrity on the RF layers.

PCB Construction Details

The following table outlines the core physical and processing parameters that define the mixed material board's reliability and manufacturability.

PCB Stackup

The 4-layer stack up is meticulously designed to embed the RO4350B RF material on the outer layers while using a standard FR-4 core for mechanical support, ensuring impedance stability.

PCB Statistics

The statistical summary provides a quantitative overview of the assembly complexity and component density.

Technical Rationale & Performance Analysis

1). Hybrid Dielectric Strategy

The decision to utilize a 10mil RO4350B on the outer layers is driven by the requirement for precise 50Ωimpedance control. Rogers RO4350B offers a stable Dielectric Constant (Dk) of 3.48±0.05, which varies little with frequency. This stability is critical for maintaining consistent impedance across the 5/8mil differential pairs on the top side. Unlike standard FR-4, which can exhibit Dk drift at higher frequencies,RO4350Bsubstrate ensures minimal signal attenuation (Dissipation Factor 0.0037) and excellent phase stability.

By usingHigh Tg 170°C FR-4 for the inner layers (Layer 3 to 4), we significantly reduce material costs for the non-critical DC routing and power distribution sections. The FR-4 core provides excellent mechanical support and maintains a CTE (Coefficient of Thermal Expansion) compatible with standard assembly processes. The use of Blind Vias (L3-L4) allows us to route signals out of the bottom layer without drilling through the sensitive RF laminate, preserving the integrity of the top RF ground plane.

2). Thermal Management and Reliability

This design is built for thermal robustness. The RO4350B features a Z-axis CTE of only 32 ppm/°C and a Tg exceeding 280°C, which is crucial for maintaining plated through-hole (PTH) reliability during lead-free soldering reflow cycles. The 1.55mm total thickness, combined with the High Tg FR-4, ensures the board will not warp significantly under thermal stress. The 20 µm via plating thickness provides a safety margin against barrel cracks, surpassing the standard 15-18 µm typically required for Class 2 reliability.

3). Signal Integrity and Manufacturability

We have specified ENIG surface finish to support both fine-pitch SMT soldering (for the 16 top-side SMT pads) and to provide a durable, oxidation-free surface that maintains the low-loss characteristics of the RF traces. The artwork is supplied in Gerber RS-274-X format, ensuring compatibility with our direct imaging (DI) and automated optical inspection (AOI) systems. Adherence to the IPC-Class-2 standard ensures that while this is a high-performance hybrid board, it remains manufacturable at scale with a focus on long-term reliability in field conditions.

Typical Applications

The unique construction of this Hybrid PCB Board makes it an ideal candidate for applications requiring the convergence of high-speed digital logic and RF front-end circuitry. Typical use cases include:

• Microstrip and Stripline Circuits where precise impedance control is mandatory.
• Point-to-Point Digital Radio Antennas benefiting from the low-loss RO4350B.
• Radar and Guidance Systems requiring reliable operation under thermal stress.
• Millimeter Wave Applications leveraging the consistent Dk of the hybrid stackup.
• Commercial Airline Broadband Antennas needing a compact, high-reliability interconnect solution.

Conclusion & Availability

This 4 Layer Hybrid PCB represents a sophisticated solution for RF engineers needing the electrical performance of Rogers material combined with the mechanical properties of standard FR-4. It is ideally suited for applications such as point-to-point digital radio antennas, radar systems, and millimeter-wave circuits.

The product is designed for worldwide availability, utilizing globally sourced Rogers and FR-4 materials. We are currently qualified for high-volume production with lead times optimized for thishybrid stack-up configuration.