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Surface Finishes
Dr. Kunal Shah, president and chief scientist at LiloTree, discussed selection criteria of surface finishes for better reliability of next-generation electronic assemblies
He commented that high frequency PCBs is one of the fasted growing areas in the electronics industry and that a novel approach to surface finish is essential to obtain optimum performance and better reliability of electronic assemblies. Insertion loss is a particular consideration. With reference to the skin effect, he indicated that finishes based on electroless nickel contribute significantly to signal loss at high frequencies.
Shah believes that a low insertion-loss surface finish should be cost-effective and avoid nickel whilst offering robust solder joints for high reliability and having a gold-based final finish for long shelf-life.
He noted that the predominant surface finish—electroless nickel immersion gold— besides its effect on signal loss, can suffer from hyper-corrosion and brittle solder joints. Immersion silver, although exhibiting lower loss, has limited shelf life and is prone to corrosion. Current gold-based alternatives, direct immersion gold, electroless palladium immersion gold, and electroless palladium autocatalytic gold resort to higher thickness of precious metals and show concerns in terms of higher insertion loss and brittle solder joints as well as not being cost-effective or eco-friendly.
Shah offered a novel nickel-free surface finish, with 50 nanometres of cyanide-free gold on copper treated with a nano-engineered barrier layer. This finish gives robust solder joints with thin and distinct intermetallics, and is cost effective with its significantly lower gold thickness than the alternative precious metal finishes.
Independent testing has indicated the insertion loss of the finish to be almost exactly identical to that of bare copper over the 0–100 GHz frequency range. Solder joints require a higher force to failure than equivalent joints on electroless nickel immersion gold, with no brittle intermetallic failure. A cost comparison shows savings better than 40% in gold usage compared with conventional electroless nickel immersion gold and electroless nickel electroless palladium immersion gold. The process is cyanide-free as well as being RoHS and REACH compliant.
iNEMI Roadmap
The final session of the conference was an interactive discussion on the subject of PCB technology in the iNEMI Roadmap, with an introduction and overview of the iNEMI Roadmap from Dr. Frank Mullany, iNEMI director of roadmapping.
He introduced iNEMI as the International Electronics Manufacturing Initiative, a global, industry-led consortium which enables its members to anticipate and shape industry needs, ensure supply chain readiness and accelerate innovation.
He outlined the technical scope of the roadmap and iNEMI’s vision to influence technology investment decisions by moving to shorter, online documentation, updated in real time by a diverse community of experts.
Mullany’s current focus is an online roadmap of future technology needs. Together with Tarja Rapala-Virtanen, he invited delegates to submit post-it notes on their top three subjects which were then collected and will be used as input to the roadmap.
Alun Morgan wrapped-up the conference, noting that Stig Kallman is retiring at the end of the month after 43 years with Ericsson. Morgan thanked him for his considerable and lasting input to our industry over those years and especially for his valuable contribution as an EIPC board member. He commented that Kallman’s retirement was bittersweet in that EIPC wishes him a long and happy retirement but on the other hand will miss his technical competence and good humoured presence. He will always be welcome at the EIPC.
Morgan’s closing comments were to thank the sponsors, the delegates, the speakers, the moderators, Tarja Rapala-Virtanen for putting the programme together, and Kirsten Smit-Westenberg and Carol Pelzers for their flawless organisation of another splendid event. He announced that the 2024 summer conference will be at ESA/ESTEC, kindly arranged by Stan Heltzel, and that the 2024 winter conference will likely be at a large German PCB producer, yet to be confirmed.
My personal thanks to EIPC for making me feel so welcome and to Alun Morgan for providing first-class photographs as ever.
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