Issue link: https://iconnect007.uberflip.com/i/1500943
56 DESIGN007 MAGAZINE I JUNE 2023 OSP and immersion silver are proven to be the best surface finish options for optimal per- formance with high-frequency operation. Category 2 ENIG and ENEPIG with typical (4 µm EN) thickness show significant signal losses over the construction compared to all other test candidate finishes. As previously stated, the magnetic and low conductivity of the thick EN deposit place limits on suitability for high-fre- quency operation. Category 3 Silver-gold, EPIG, and reduced nickel thick- ness ENEPIG options all showed a similar insertion loss response with increasing fre- quency. It is therefore difficult to say if any of these three finishes are significantly different in performance. It was surprising to find that the total elimi- nation of the EN layer with the EPIG and sil- ver-gold options did not outperform finishes with a very thin EN layer. Despite not show ing the per fect high- frequency performance of OSP and immer- sion silver, the Category 3 finishes were able to demonstrate significant improvements in insertion loss over ENEPIG and ENIG and may well bring other performance advant- ages not realized with OSP and immersion silver. Conclusion ENIG and ENEPIG are challenged by sig- nal losses at higher frequency, with OSP and immersion silver demonstrating no losses over the construction. e new generation surface finishes (Ag- Au, thin EN-ENEPIG, and EPIG) continue to outperform traditional ENIG and ENEPIG. Other selection criteria, such as environmen- tal resistance, soldering performance, solder joint reliability, and wire bonding, make these newer finishes attractive for certain applica- tions where OSP and silver cannot meet per- formance needs. Our next article will be a data-driven review, examination, and comparison on high-speed ball shear, drop shock, wirebonding, and sol- der joint reliability performance of the newer generation and traditional surface finishes. A decision matrix will be included to assist designers in aligning performance needs with surface finishes capabilities. DESIGN007 References 1. "The study of nano anchoring copper foil for PWB," by M. Sato, N. Obata, Y. Kokaji, K. Okubo, and O. Suzuki, 2017 International Conference on Elec- tronics Packaging (ICEP), IEEE, 2017. 2. "Insertion Loss Performance Differences Due to Plated Finish and Circuit Structure," by John Coon- rod, Design007 Magazine, September 2019. 3. "The Effects of PCB Fabrication on High Fre- quency Electrical Performance," by John Coonrod, IPC APEX EXPO, 2015. 4. Conductor Bulk Resistivity and Skin Depths, rfcafe.com. Frank Xu, Ph.D, is surface finish technology manager at MacDermid Alpha Electronics Solutions. Martin Bunce is product director for MacDermid Alpha Electronics Solutions. John Coonrod is technical marketing manager for Rogers Corporation.