Multilayer hybrid design refers to the practice of using multiple different materials in a single PCB stack-up, especially in high-frequency PCB designs. Since high-frequency and low-frequency circuits have different material requirements, hybrid stack-ups often involve mixing materials such as Rogers for high-frequency layers and FR4 for low-frequency or control layers. Outputting design files for multilayer hybrid structures is critical for production and must accurately reflect each layer’s material, routing, and process requirements. Below are the steps and considerations for outputting design files for high-frequency multilayer hybrid PCBs.

Main Steps for Design File Output
1. Determine the Stack-Up Order and Structure
Before outputting design files, it is essential to determine the materials and layer sequence based on the circuit requirements. Typically, hybrid structures involve:

High-frequency Layers: Using low dielectric constant (Dk) and low loss factor (Df) materials such as Rogers 4350, Rogers 5880, or PTFE.
Low-frequency or Control Layers: Using standard materials like FR4, which are cost-effective and suitable for handling lower frequency signals or power/control circuits.
Each layer’s material, thickness, and function must be clearly defined to meet signal transmission characteristics, mechanical performance, and thermal management needs.

2. Generate the Stack-Up Diagram
In hybrid designs, generating a clear stack-up diagram is crucial. The stack-up diagram must detail:

Material type for each layer (e.g., Rogers, FR4).
Thickness of each layer, including copper and dielectric thickness.
Bonding method between layers, such as prepreg usage.
Layout of ground, signal, and power layers to ensure impedance matching and signal integrity.
The stack-up diagram should be thoroughly communicated with the manufacturer to ensure that the chosen materials and thicknesses can be implemented during production.

3. Design Rule Check (DRC)
A comprehensive design rule check (DRC) must be performed before file output. Since hybrid structures involve different materials, each with unique processing requirements, DRC is particularly important. Key areas to check include:

Material Compatibility: Ensure that the thermal expansion coefficients (CTE) of different materials are compatible to prevent delamination or warping during production.
Trace and Spacing Requirements: Verify that the trace widths, spacing, and impedance control requirements for high-frequency signals meet the design guidelines without causing interference between layers.
Via Design: Ensure that the via design is optimized, especially when transferring signals between high-frequency and low-frequency layers. Pay special attention to the parasitic effects of vias.
4. Output Gerber Files
Gerber files are essential in PCB manufacturing, containing layer-by-layer information on the circuit patterns, drill holes, and solder mask. In multilayer hybrid designs, Gerber files should include:

Routing Patterns for Each Layer: Clearly define the routing for each layer, including high-frequency signal layers, low-frequency signal layers, ground layers, and power layers.
Drill and Via Locations: Minimize the number of vias in high-frequency signal paths and optimize via placement to reduce parasitic capacitance and inductance.
Solder Mask and Silkscreen Layers: Include information for solder mask and silkscreen layers to assist with manufacturing, soldering, and labeling during production.
When generating Gerber files, ensure that each file corresponds to the correct material and stack-up structure. Use design software to perform compliance checks on all files.

5. Generate Drill and Mechanical Files
Drill files (usually in Excellon format) define all the holes in the PCB, including through-holes, blind vias, and buried vias. In multilayer hybrid designs, pay attention to:

Vias in High-frequency Layers: Minimize vias in high-frequency layers to maintain signal integrity.
Buried and Blind Vias: For complex multilayer designs, buried and blind vias must be clearly defined between the relevant layers.
Mechanical Files: Include details for the board outline, mounting holes, and any special mechanical features.
6. Generate Assembly Files and Bill of Materials (BOM)
The assembly file in a hybrid design should include precise placement and mounting details for all components. The BOM should list all materials and components used, clearly distinguishing between materials needed for high-frequency and low-frequency layers. Each layer’s specific material type and thickness should be listed in the BOM.

7. Communicate with the Manufacturer for Verification
After generating all design files, communicate with the PCB manufacturer to verify that the stack-up structure, material choices, and manufacturing processes are feasible. Manufacturers may suggest modifications based on production capabilities to ensure the product’s manufacturability and reliability.

Key Considerations for Design File Output
1. Material Compatibility
Since hybrid stack-ups involve multiple materials, ensure compatibility in terms of CTE, mechanical strength, and processing characteristics. If the CTEs of different materials do not match, it may lead to delamination or deformation during production.

2. Impedance Control
Impedance control for high-frequency signal layers is critical in hybrid designs. Different materials have different dielectric constants, which can affect impedance control. Special attention must be paid to material selection to ensure consistent impedance during high-frequency signal transmission.

3. Via Design
Via design is crucial in multilayer hybrid designs, especially when high-frequency signals pass through multiple layers. Too many vias can introduce parasitic effects that degrade signal integrity. Therefore, minimize the number of vias in high-frequency signal layers and optimize their placement.

4. Thermal Management
Different materials in hybrid structures respond to heat differently, and high-frequency layers may generate more heat. The design files must address thermal management considerations, such as adding thermal layers or optimizing component placement to enhance overall heat dissipation.

5. Manufacturing Process Requirements
Since multilayer hybrid structures involve various materials, manufacturing complexity increases. When outputting design files, ensure that the design is aligned with the manufacturer’s capabilities, accounting for factors such as lamination temperatures and drilling processes.

By following these steps and considerations, engineers can ensure that the multilayer hybrid design files for high-frequency PCB production are accurate, manufacturable, and meet the performance requirements.