EIPC 2025 Winter Conference, Day 2: A Roadmap to Material Selection

Estimated reading time: 8 minutes

The EIPC 2025 Winter Conference, Feb. 4-5, in Luxembourg City, featured keynotes and two days of conference proceedings. The keynote session and first-day conference proceedings are reported separately. Here is my review of the second day’s conference proceedings.

Delegates dutifully assembled bright and early, well-rested and eager to participate in the second day’s proceedings of the EIPC Winter Conference in Luxembourg.

The opening session was themed, “Key factors influencing PCB material selection: Requirements and solutions,” and was introduced and moderated by Martyn Gaudion, sales and marketing director of Polar Instruments.

The first presenter, Dr. Anna Graf, marketing manager of PWB materials at Resonac Europe in Germany, discussed materials for radar applications, and asked “What influences the radar application performance, and is it only the electrical performance which matters?” To explain, she chose 77 GHz automotive radar technology as her basis.

She showed an infographic with an outline of a car with colour-coded zones indicating the directions, ranges, and functions of its multiple on-board radar systems: short- and medium-range radar for parking assistance, cross-traffic alert, junction assistance, medium-range radar for blind side detection support, long-range radar for adaptive cruise control, automatic emergency braking, frontal collision warning, and driver monitor radar for 3D positioning, driver alertness, and driver awareness.

So, which material properties are required to enable the performance of next-level 4D chip technology?

Graf systematically examined base-material factors influencing signal propagation: glass, resin, and copper, and then considered the effects of mechanical properties such as dimensional stability and coefficient of thermal expansion on reliability. The preferred material was based on low-Dk glass, modified thermoset resin and very-low-profile copper foil.

Similarly, looking at electrical requirements, the preferred material had Dk value between 3.0 and 3.4 and a Df of 0.0017 at 77GHz, with Dk stability over the frequency range 10 GHz to 77 GHz and the temperature range -40°C to +120°C. At every stage, she showed comprehensive physical data and test results.

Her overall conclusion was that, to support high advanced 4D imaging radar chip technology, the material should have these electrical characteristics combined with low thermal expansion and low modulus material properties in order to enable RF board production, board level reliability, and RF antenna electrical performance.

Looking a bit further into the car of the future, Andreas Folge, Nan Ya consultant for 5G OEM marketing in Europe, discussed opportunities enabled by high-speed digital (HSD) materials.

He began by defining the four macrotrends of the automotive industry—MADE—to deliver Mobility as a service, to drive Autonomously, to operate in a fully connected and Digitalised environment, and to be powered by an Electric drivetrain.

Folge declared that the automotive industry is facing one of the greatest transformations in its history and added another acronym to the collection: the car of the future will be a software defined vehicle (SDV), with its attributes characterised by how it operates, communicates, and integrates with the broader digital ecosystem. Server on wheels (SOW) is yet another acronym to describe the enormous quantity of data emanating from the vehicle. In fact, cars will be built around software platforms rather than around engines.

It seemed only logical to label high-speed digital materials (HSDM), as Folge explored their role and explained their indispensability in the transformation of the automotive industry, facilitating the integration and functioning of advanced electronic systems in vehicles by handling high-speed data transmission, ensuring signal integrity, providing robustness and ensuring reliability.

He gave examples of new functional requirements for advanced, highly integrated logic PCBs and power PCBs and new assembly concepts. New external and internal loads resulted in requirements for material adoptions and special concepts for automotive electronics. These in turn demanded very good technical skills and understanding.

Nan Ya has developed product solutions for the different automotive application segments. Folge listed their HSDM products and classifications from mid-loss to extreme-low-loss with examples of typical applications, and he predicted a steeply increasing automotive PCB demand, with a forecast market value of $11.4 billion by 2028. He commented that Nan Ya had a strong product line-up and the R&D capability to address these new needs.

Rogers Corporation has long been identified as specialists in low-loss laminates for RF applications. Rogers application development manager Stefano Dada gave an update on advancing safety and reliability in automotive radar with specialised PCB materials.

He listed key RF material properties for 77 GHz radar sensor PCBs, in terms of dielectric constant, insertion loss, reliability and stability, fabrication and total cost, remarking that Rogers materials were available in a wide range of performance/cost options, including ceramic-filled PTFE, ceramic-filled PTFE/woven glass and hydrocarbon thermoset, together with prepregs and bondplies.

A significant property of Rogers ceramic-filled PTFE material is its resistance to the effects of temperature and humidity on radar antenna gain at 77-81 GHz.  At 85°C, 85% humidity, it changed by less than 0.1 dB whereas a competitive polyphenyl ether material showed a degradation of more than 2 dB.

The company’s new version features very-low-profile copper and smaller, rounded filler particles, resulting in reduced insertion loss and enabling designs with smaller-diameter micro vias, while maintaining the same thermal stability and peel strength as the legacy product. Data reviewed PCB design trends for patch antennas, substrate integrated waveguides and higher-angular-resolution radar, and nominated appropriate materials and builds.

Rogers’ roadmap for automotive radar includes new next-generation thermoset RF laminates and new antenna technology for Level 2+ autonomy. New antenna technology for imaging radar and new feed board thermoset RF laminates will support Level 3 autonomy and the Levels 4 and 5 anticipated for 2028-2030. New materials are in development to further improve the performance of corner radar with wide field-of-view, front-looking radar with narrow and wide field-of-view, and highest resolution imaging radar. 

The final technical session, “PCB processes: Historical insights and innovations in copper and surface finishes,” was introduced and moderated by Oldrich Simek, owner of PragoBoard in the Czech Republic.

The evolution of electrodeposited copper through technological advancements and innovations in modern electronics manufacturing was related in a fascinating presentation by Antoine Marot, Europe and North America sales team manager at Circuit Foil in Luxembourg.

Although copper foil has been used by makers of stained glass since the 1880s, the story effectively began in 1937, when Anaconda produced the first electrodeposited copper foil in the U.S. Paul Eisler invented the printed circuit in 1936 and electrodeposited copper foil grew from being a minor curiosity to the first-choice material for the electronics industry. Mass production began in the U.S. in 1955.

Marot explained that the foil is produced in a continuous process, basically by immersing a rotating drum cathode in copper sulphate solution and applying a DC current, causing highly pure copper to deposit on the drum. He showed a diagrammatic cross-section indicating that the base foil has a rough crystalline structure on its matt side and is given nodular treatment to improve bonding.

Foils are undergoing continuous improvement. Every aspect is being carefully studied: copper microstructure, thickness, roughness on both sides, size and shape of nodular treatment, type and content of passivation, and type and content of silane treatment.

He discussed details of work on grain structure, grain size optimisation, thickness control, base foil roughness, treated side roughness, and chemical adhesion promoters, concluding that the extensive expertise within the industry, combined with growing research and development efforts, has significantly enhanced various characteristics of electrodeposited copper foil. Further innovations are anticipated in the near future.

The final technical presentation of the morning session came from Erik Pedersen, FAE and quality director at ICAPE Group in France, who promoted the use of autocatalytic silver immersion gold (ASIG) as an alternative surface finish with improved properties over electroless nickel immersion gold (ENIG) for RF designs and wire bonding.

He reported the results of an ICAPE study of insertion loss, comparing ASIG with ENIG as surface treatments. Surface finish has played an important role in RF PCB applications, and although ENIG had been a dominant finish for many years, nickel has been a ferromagnetic material with a negative influence on high-frequency performance because of increased insertion loss due to the “skin effect.”

ASIG was developed for high-frequency PCBs as a replacement for nickel-based surface finishes. It exhibits excellent RF performance due to the pure, dense deposit of silver, which has the lowest loss of all metals. Additionally, silver has a higher thermal conductance than copper and promoted heat transfer, which enables faster wetting than any other surface finish.

It provides surface protection equal to ENIG, with a flat surface and very long shelf life. It is solderable through multiple soldering processes with very good joint strength because the intermetallic is a tin-copper interface. It has good ductility and does not crack under mechanical stress.

ASIG also provided a cost-effective surface for aluminium and gold wire-bonding. It met the requirements for millimetre-wave and did not suffer from “skin-effect” insertion loss. ASIG has been tested by the European Space Agency to demonstrate its feasibility, manufacturability, reliability, and performance, and has been approved for further use in space activities.

Pedersen gave details of the experimental conditions used in the ICAPE study and discussed the measurement results. It was concluded that ASIG has significant lower insertion loss than ENIG for transmission lines on FR-4 and proprietary woven-glass reinforced hydrocarbon/ceramic substrates, even better than copper without any surface finish. Similarly, ASIG has significant lower insertion loss for filters on both substrates and almost identical to values on copper without any surface finish. The bandwidth of ASIG was closer to simulated values than that of ENIG on FR-4 and almost identical to values on copper without any surface finish.

The conference finished with the “quick-fire walk-in” panel session that has become a popular innovation. Moderated by Alun Morgan, the panel comprised Otto Pukk of InCap Corporation, Michael Matthes of Würth Elektronik, Marcus von Euler of PaperShell Electronics, and Daniel Hamandouche of ForSURE Technology, who responded spontaneously to a range of questions from the audience.

Finally, Morgan formally brought proceedings to a close, remarking upon the outstanding success of yet another splendid EIPC conference and thanked everyone who had participated, with special credit to Tarja Rapala-Virtanen for coordinating the program and to Kirsten Smit-Westenberg and Carol Pelzers for their professional organisation and management of the event.

Again, I offer my personal thanks to Alun Morgan for generously sharing his photographs.