Characterization of PCB Material & Manufacturing Technology for High-Frequency

Reading time ( words)

The cross sections for MS of both fabrication processes are depicted in Figure 6. The stated dimensions are the ones of the copper width only, which means that the whitish immersion nickel/gold surface finished is not taken into account. Closer investigation of the micro-sections of the evaluation boards showed that both samples had a slight penetration by immersion nickel/gold into the dielectric surface on the trace edges, which will also impact the occurring losses.


Figure 6: Trace cross-section.

The top surface of the traces is further evaluated by Scanning Electron Microscopy (SEM). It can be seen in Figures 6 and 7 that there is some overlap caused by the immersion of nickel/gold onto the dielectric surface on trace edges of the copper conductor. The panel plating evaluation board showed an overlap from the trace edge to dielectric surface of 9 µm ± 2µm while the measurement of the pattern plating test vehicle showed just 4 µm ± 2µm. The primary reason for this phenomenon can be found in the treatment process of the copper foil. Both structuring processes pictured in Figures 6 and 7 use the same base material and copper foil. Nevertheless, the slightly protruding copper residues are removed more thoroughly for the pattern plating process. Consequently, the end surface overlap into the dielectric material is reduced. A main result is the consequence that this observation has to be considered for the design preparation by the PCB manufacturer, to preserve the line characteristics as well as to ensure low losses for the higher frequency domains.


Figure 7: SEM analyses.

Analysis and Measurement Results: RF-Losses

Firstly, a process comparison is made for the MS line mode for three different line lengths L. As can be seen in Figure 8, for material type A for an MS line with L = 5 mm there is basically no measureable difference between the applied fabrication processes. However, for increasing line lengths there occur proportionally larger losses as shown for L = 10 mm and L = 25 mm. At the maximum measured frequency of 110 GHz, pattern plating shows about 0.65 dB more loss for L = 25 mm. For material type B (Figure 9) the same observations can be made for L = 5 mm where there is no difference at all for the two manufacturing processes, and for L = 10 mm and L = 25 mm losses increase with L. It is interesting to note that, at the maximum frequency, the longest line shows approximately the same difference between the losses of the compared processes as has been reported for material type A. The insertion loss can be appropriately fitted in a least-square manner with  with  and  being the factors to be determined over frequency f[2].  By fitting the insertion loss, measurement deviations are reduced and a smooth curve for the additional loss of panel plating over pattern plating can be obtained.


Figure 8: Material type A MS.


Figure 9: Material type B MS.



Suggested Items

Benchmarking Your Process Engineering

04/29/2021 | I-Connect007 Editorial Team
Mark Thompson has been in bare board fabrication for over 30 years. He is now laying out printed circuit boards at Monsoon Solutions, a high-tech design bureau near Seattle, Washington. With Mark’s extensive hands-on knowledge of PCB manufacturing, he brings a unique perspective to PCB design. In this discussion with the I-Connect007 editorial team, Mark shares what’s important from a process engineer’s point of view, and how to stay on top of evaluating and benchmarking your manufacturing process, along with insights from his new role as a designer.

Isola Releases IS550H Material

04/26/2021 | Nolan Johnson, I-Connect007
Nolan Johnson speaks with Michael Gay of Isola and Chris Hunrath of Insulectro about the release of their new halogen-free, high-thermal reliability material, which they hope fills the gap in the market between epoxies and polyimides.

EIPC Technical Snapshot: Supply Chain and Material Price Pressures

04/26/2021 | Pete Starkey, I-Connect007
EIPC’s seventh Technical Snapshot webinar on April 14 was timely and appropriate. In the context of current supply chain issues and material price pressures facing the PCB industry, particularly in Europe, the EIPC team brought together an outstanding group of experts—each a leading authority in his field—to analyse and comment upon the areas of concern and to respond to questions raised by a capacity audience. As Alun Morgan said, “If you don’t use the European supply chain, you won’t have it anymore!”

Copyright © 2021 I-Connect007. All rights reserved.