As 5G evolves toward 6G, communication frequencies are advancing from Sub-6GHz to millimeter wave (mmWave) and even terahertz (THz) ranges. This poses unprecedented challenges for PCB (Printed Circuit Board) design and manufacturing: signal loss, impedance control, thermal management, and manufacturing precision are all pushed to their limits. In such a demanding context, a structured and systematic New Product Introduction (NPI) process is crucial. This article delves into the NPI EVT/DVT/PVT framework, exploring how it helps engineers navigate every stage—from material selection and hybrid stack-up design to mass production testing—to ensure the ultimate success of 5G/6G communication PCBs.

At the outset of a project, a comprehensive and meticulous DFM/DFT/DFA review (Design for Manufacturability/Testability/Assembly) serves as the cornerstone of the entire NPI process. It identifies potential manufacturing bottlenecks early, optimizes designs to improve yield and reliability, and lays a solid foundation for subsequent EVT, DVT, and PVT phases.

The Core of NPI: The Role of EVT/DVT/PVT in 5G/6G PCB Development

The NPI EVT/DVT/PVT process breaks down complex product development into three manageable and verifiable key stages, each with clear objectives and deliverables, ensuring the optimal balance between performance, quality, and cost.

EVT (Engineering Validation Test): Engineering Validation Testing

The goal of this phase is to "prove the concept is feasible." In 5G/6G PCB development, EVT focuses on preliminary validation of core functionality and performance.

• Key Activities:
  • Material Selection and Evaluation: Choose suitable low-loss materials, such as Rogers or Teflon (PTFE), and conduct small-batch sample testing to verify their Dk/Df stability in the target frequency band.
  • Stack-Up Concept Validation: Design preliminary hybrid stack-up solutions, such as using Rogers PCB materials for RF layers and standard FR-4 for digital and power layers, to balance cost and performance.
  • Critical Signal Path Simulation and Measurement: Model key millimeter-wave transmission lines using simulation software (e.g., Ansys HFSS, Keysight ADS) and fabricate a small number of prototype boards for network analyzer (VNA) testing to validate insertion loss and return loss.
  • Preliminary First Article Inspection (FAI): Conduct detailed dimensional, stack-up, and critical process parameter checks on the first batch of prototype boards to ensure they align with design intent.

DVT (Design Validation Test): Design Validation Testing

The goal of this phase is to "prove the design meets all specifications." DVT is the most comprehensive testing phase in product development, ensuring the design operates stably and reliably under various working conditions.

• Key Activities:
  • Full Functional Testing: Test all PCB functions in a complete system environment, including signal integrity, power integrity (PDN), and electromagnetic compatibility (EMC).
  • Environmental and Reliability Testing: Perform thermal cycling, humidity testing, vibration, and shock tests to validate long-term reliability under extreme conditions. This is particularly important for assessing risks caused by CTE (Coefficient of Thermal Expansion) mismatches in hybrid stack-ups.
  • Impedance and Tolerance Verification: Use time-domain reflectometry (TDR) to test impedance across a large sample set, ensuring produced PCBs maintain impedance within specifications (typically ±5% or ±7%).
• Final Confirmation of DFM/DFT/DFA Review: During the DVT phase, all design details are frozen. The final DFM/DFT/DFA review conducted at this stage aims to ensure the design fully meets the requirements for mass production.

PVT (Production Validation Test): Production Validation Test

The goal of this phase is to "demonstrate a stable and reliable manufacturing process." PVT uses mass production equipment, tooling, and processes to produce a batch of products to validate the production line's capability and yield.

• Key Activities:
  • Small-Batch Trial Production: Conduct trial production on the final production line to validate the effectiveness of all process parameters, standard operating procedures (SOPs), and quality control points.
  • Yield Statistics and Process Capability Analysis (Cpk): Collect production data, analyze yield bottlenecks, and perform Cpk analysis on critical processes (e.g., lamination, drilling, plating) to ensure stability and control.
  • Test Fixture and Process Validation: Finalize and validate equipment for in-circuit testing (ICT) and functional testing (FCT). An efficient Fixture design (ICT/FCT) is crucial for ensuring mass production testing efficiency and coverage.
  • Supply Chain Validation: Ensure stable supply and quality compliance for all components and raw materials.

Rogers/PTFE and FR-4 Hybrid Stack-up: Balancing Cost and Performance for 5G/6G PCBs

For millimeter-wave applications, using high-performance materials like Rogers or PTFE exclusively delivers optimal electrical performance but at an extremely high cost. Hybrid Stack-up technology addresses this by selectively combining different materials within the same PCB, achieving a delicate balance between cost and performance.

When Is Hybrid Stack-up Worth Adopting?

• RF and Digital Separation: When a PCB contains both high-speed digital circuits and millimeter-wave RF circuits, expensive low-loss materials (e.g., Rogers RO4350B) can be used for the surface or core layers carrying RF signals, while lower-cost FR-4 materials (e.g., High-Tg FR-4) can be employed for digital, control, and power layers.
• Antenna-in-Package (AiP) Design: In AiP or antenna array boards, only the antenna radiating elements and feed networks are highly sensitive to material Dk/Df, while other supporting and control circuits can use conventional materials.

How to Weigh the Pros and Cons?
The core challenge of hybrid stack-up design lies in the complexity of manufacturing processes. Differences in CTE, resin flow, press cycle, and drilling parameters between materials can lead to reliability issues like delamination, warping, and poor hole wall quality if not handled properly. This demands deep process expertise and advanced equipment from PCB manufacturers. Experienced manufacturers like HILPCB leverage advanced Traceability/MES (Manufacturing Execution Systems) to precisely track and control key parameters during production, ensuring consistent quality in the final product.

Copper Foil Roughness and Dielectric Loss: The Invisible Killers of Millimeter-Wave Signal Integrity

In the millimeter-wave frequency range, the success or failure of signal integrity (SI) often hinges on details that can be neglected at lower frequencies. Among these, dielectric loss (Df) and conductor loss are the two primary sources of signal attenuation.

• Dielectric Loss: Determined by the Dk/Df characteristics of the insulating material. The first step is selecting high-frequency PCB materials with extremely low Df values (e.g., <0.002) and stable Dk values.
• Conductor Loss: Primarily influenced by the skin effect and copper foil roughness. At millimeter-wave frequencies, current concentrates on the conductor's surface. If the copper foil surface is rough, the actual current path becomes longer, significantly increasing insertion loss. Therefore, using very low-profile (VLP) or hyper very low-profile (HVLP) copper foil is critical for minimizing losses.

Additionally, the glass weave effect is another factor that cannot be ignored. Traditional glass cloth weave structures can cause localized Dk value inconsistencies, affecting the signal skew and impedance uniformity of differential pairs. Employing spread glass or flat-type glass cloth can effectively mitigate this issue. The selection and validation of these materials must be thoroughly considered and tested during the NPI EVT/DVT/PVT process, particularly in the EVT phase.

Back Drilling and Via Optimization: Key Processes to Eliminate Reflections and Signal Attenuation

Vias serve as hubs for connecting signals across different layers in multilayer PCBs. However, in high-speed signal paths, they also represent major impedance discontinuities. The stub of a via—the unused portion of the via beyond the signal layer—can act like an antenna, causing resonance and severe signal reflections and attenuation at specific frequency points.

Backdrilling (controlled-depth drilling) is the most effective process to address this issue. It involves drilling away the excess portion of the via from the opposite side of the PCB, minimizing stub length and significantly improving signal integrity.

Other Key Points for Via Optimization:

• Transition Zone Design: Optimizing the dimensions of pads and anti-pads to match the impedance of the transmission line.
• Ground Vias: Strategically placing ground vias around signal vias to provide clear return paths for signals and suppress crosstalk.
• Microvias: In HDI PCB designs, laser-drilled microvias offer smaller sizes and lower parasitic capacitance, making them ideal for high-density, high-speed applications. The design and back-drilling requirements of vias must be thoroughly communicated with the PCB manufacturer during the DFM/DFT/DFA review phase to ensure their process capabilities meet the design requirements.

Hybrid Manufacturing Yield: Precision Control of Alignment, Plating, and Lamination

The yield of hybrid PCBs directly depends on the control accuracy of several key processes.

1. Interlayer Alignment: PTFE materials exhibit significant dimensional expansion/contraction during high-temperature lamination, differing greatly from FR-4's coefficient. Manufacturers must ensure alignment accuracy through precise expansion/contraction compensation calculations, high-precision CCD alignment systems, and step-by-step lamination techniques.
2. Drilling & Plating: PTFE material has a soft texture and is prone to producing smear during drilling, which affects the plating quality of hole walls. Specialized drill bits, optimized drilling parameters, and the Plasma De-smear process must be employed to ensure reliable metallized through-holes.
3. Lamination: The lamination of hybrid boards requires precise control of heating rates, pressure, and dwell time to accommodate the characteristics of different materials, preventing uneven resin flow or material delamination.

In these complex processes, reliability requirements extend to the assembly stage. For example, CTE mismatch may cause THT/through-hole soldering joints to endure greater stress during long-term thermal cycling, thereby imposing higher demands on soldering processes and quality control.

From Prototype to Mass Production: Testing, Traceability, and Reliability Validation

Successful mass production relies not only on excellent design and manufacturing but also on a closed-loop quality validation system.

• First Article Inspection (FAI): During the PVT phase, the First Article Inspection (FAI) process becomes more stringent. In addition to dimensional and visual inspections, it must include cross-section analysis (to verify layer stacking and hole wall quality), TDR impedance testing, and validation of key performance indicators to ensure the first batch of mass-produced items is fully consistent with DVT-phase samples.
• Testing Strategy and Tooling: As PCB integration increases, traditional testing methods may no longer suffice. A well-planned Fixture design (ICT/FCT) solution, combined with Boundary Scan and System-Level Testing (SLT), is key to ensuring test coverage and efficiency.
• End-to-End Traceability: A robust Traceability/MES system is a standard requirement for modern high-end PCB manufacturing. It records complete information—from raw material intake and key production parameters (e.g., lamination temperature, plating current) to final test data. In the event of quality issues, the root cause can be quickly traced, enabling rapid response and continuous improvement. This is also critical for ensuring long-term reliability in key assembly steps such as THT/through-hole soldering.

HILPCB offers comprehensive services from PCB manufacturing to one-stop PCBA assembly, ensuring seamless integration of design, manufacturing, and assembly to provide reliable support for customers' high-performance products.

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Conclusion

Mastering the millimeter-wave challenges of 5G/6G communication PCBs is a comprehensive engineering endeavor involving materials science, electromagnetic field theory, precision manufacturing, and systematic quality management. A rigorous NPI EVT/DVT/PVT process serves as the guiding framework throughout, ensuring every step—from concept to mass production—is thoroughly validated. From material selection and stack-up exploration in the EVT phase, to comprehensive performance and reliability validation in the DVT phase, and finally to manufacturing process stabilization in the PVT phase, each step is intricately interconnected. By deeply understanding core technologies such as hybrid lamination techniques, copper foil roughness, and back-drilling processes, and leveraging rigorous First Article Inspection (FAI) and full-process Traceability/MES systems, enterprises can stand out in the fiercely competitive market. Choosing a partner like HILPCB, with its profound expertise in RF PCB manufacturing and strong engineering support capabilities, will be key to your success on the path to the 6G era.

Related links

• Rogers PCB materials
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