5G Communication Antenna Board

Project Overview

A telecommunications equipment manufacturer needed high-performance antenna boards for their 5G NR (New Radio) base station platform operating in both sub-6GHz and mmWave frequency bands. The boards required mixed-dielectric construction combining Rogers high-frequency materials with standard FR-4 for cost optimization.

Challenge

• mmWave performance: Antenna elements and feed networks operating at 24-28 GHz required extremely low insertion loss and precise impedance control that standard FR-4 cannot achieve.
• Mixed dielectric stackup: Combining Rogers RO4350B (for RF layers) with standard TU-872SLK (for digital/power layers) created manufacturing complexity in lamination and drill registration.
• Tight tolerances: Antenna element dimensions needed +/-0.5 mil accuracy to maintain radiation pattern specifications across the operating bandwidth.
• Step gold finger: The board-to-board interface required partial gold plating with step thickness (30u” contact area, 5u” transition), adding process complexity.

Solution

NimblePCB leveraged specialized high-frequency manufacturing capabilities for this demanding telecommunications application:

• Hybrid stackup design: 18-layer construction with Rogers RO4350B on the top 4 layers for antenna and RF feed network, transitioning to TU-872SLK for remaining layers. Sequential lamination process ensured layer-to-layer registration within +/-2 mil.
• RF precision: Achieved +/-3% impedance tolerance on 50-ohm microstrip lines at 28 GHz. Antenna element features fabricated with +/-0.3 mil dimensional accuracy using laser direct imaging (LDI).
• Step gold plating: Selective electroplating process with precision masking for dual-thickness gold fingers, verified by XRF measurement at multiple points per board.
• Controlled environment: All RF laminate handling and processing done in temperature/humidity controlled cleanroom environment to prevent material property variation.

PCB Specifications

Results

• Antenna radiation pattern matched simulation within 0.5 dB across full bandwidth
• Insertion loss 15% lower than customer’s previous supplier
• Step gold finger contact resistance met specification across 500+ mating cycles
• Qualified as primary supplier for the customer’s 5G base station program