High-Frequency 5G Small Cell PCBA for Dutch Telecommunications Equipment Manufacturer
Achieving <0.5dB insertion loss on Rogers 4350B substrate, managing 0.3mm pitch QFN assembly, and delivering 200-unit NPI in 3 weeks
Project Overview
An Eindhoven-based telecommunications equipment company was developing a 5G small cell radio unit for indoor enterprise deployment. The RF front-end board used Rogers 4350B high-frequency laminate for the antenna array section and standard FR4 for the digital baseband section — a hybrid stackup that required careful material management and specialized assembly processes. The customer had a 3-week NPI timeline for 200 units to support a field trial with a major European mobile operator.
The Challenge: Rogers 4350B Hybrid Stackup and Sub-mm Pitch RF Components
The hybrid Rogers 4350B/FR4 stackup required a specialized PCB fabrication process: the Rogers material has a different coefficient of thermal expansion (CTE) than FR4, and improper lamination bonding can cause delamination at the Rogers/FR4 interface during reflow. Most PCB fabricators do not stock Rogers 4350B and have to special-order it, adding 2-3 weeks to the standard lead time.
The RF front-end included a 5G PA module (Qorvo QPF4519) in a 5×5mm QFN package with 0.3mm pitch exposed pad. The exposed pad required precise solder paste volume control to prevent bridging — a common failure mode on QFN packages with fine pitch.
The antenna array section had 50Ω microstrip transmission lines with a target insertion loss of <0.5 dB at 3.5 GHz. Achieving this required a controlled-impedance PCB with a measured impedance accuracy of ±5% — tighter than the standard ±10% tolerance.
The 3-week NPI timeline left no room for PCB fabrication delays or assembly rework. The customer needed a partner with in-house Rogers material stock and a proven high-frequency assembly process.
Our Engineering Approach
Our PCB fabrication partner maintains a standing stock of Rogers 4350B in standard thicknesses (0.508mm, 0.762mm, 1.524mm), eliminating the 2-3 week material procurement delay. We worked with our fabrication partner to develop a hybrid lamination process for the Rogers/FR4 stackup, using a low-flow prepreg at the Rogers/FR4 interface to minimize CTE mismatch stress during reflow. The first production panel was cross-sectioned and inspected for delamination — none was found.
For the QFN solder paste application, we used a 0.1mm-thick laser-cut stainless steel stencil with a 1:1 aperture ratio for the QFN pads and a 70% aperture reduction for the exposed pad — a standard technique for preventing QFN bridging that requires precise stencil design. Our SPI system verified paste volume on every board before placement.
We worked with our PCB fabrication partner to design the microstrip stackup for 50Ω impedance on Rogers 4350B (trace width: 1.08mm, dielectric thickness: 0.508mm, εr: 3.66). TDR measurements on the first production panel confirmed an impedance of 50.3Ω ±2.1% — within the ±5% specification. Insertion loss measurements at 3.5 GHz: 0.38 dB — below the 0.5 dB target.
We ran a dedicated production line for this project with 24-hour shifts for the first week, delivering the first 50 units for customer validation within 8 days of order placement. The remaining 150 units were delivered in week 3, meeting the field trial timeline.
Measurable Results
""The RF performance of Kingdta's boards exceeded our simulation predictions. The 0.38 dB insertion loss on Rogers 4350B is better than what we achieved with our previous supplier using the same design. Their understanding of high-frequency materials is exceptional."
— RF Systems Engineer, Telecom Equipment Company (Eindhoven)
Start a Similar Project
Send us your Gerber files and BOM. Our engineering team will review your design within 24 hours — free DFM analysis included.
WhatsApp: +86 134 2427 5990
