42 The PCB Magazine • April 2017
sults in a more uniform copper deposit thick-
ness in comparison to pattern-plating process.
The latter is sometimes regarded as semi-addi-
tive whereas the panel-plate process is subtrac-
tive in the formation of conductors. Uniformity
of copper thickness results in more consistent
electrical performance (e.g., line width varia-
tion). As mentioned earlier, copper etching is
an isotropic process and the industry practice of
etching-down copper was deployed in MiWaveS
to meet dimensional tolerance needs.
Much of the PCB work in MiWaveS required
both SMT and gold wire-bond. Autocatalytic sil-
ver/immersion gold (ASIG) and immersion sil-
ver/immersion gold (ISIG) are two silver-based
finishes that were used. Both finishes are univer-
sal (i.e., they support both SMT and gold wire
bond). Electroless nickel/electroless palladium/
immersion gold (ENEPIG) was a
universal fin-
ish
candidate but, being nickel-based, losses are
higher.
Conclusions
The work done by Optiprint AG in support
of MiWaveS substantiates that PCB technology
can satisfy the engineering requirements for
mmW circuitry providing the manufacturing
capabilities can match the positional accuracy,
feature tolerance and surface finish require-
ments.
Acknowledgment
The research leading to this paper has re-
ceived funding from the European Union Sev-
enth Framework Programme (FP7/2007-2013)
under grant agreement n°619563 (MiWaveS).
The authors would like to thank Professor
Ronan Sauleau, Université de Rennes 1 and Dr.
Jussi Säily, VTT Technical Research Centre of
Finland Ltd for their valuable inputs.
PCB
References
1. ETSI White Paper: E-Band and V-Band—
Survey on status of worldwide regulation.
2. MiWaveS.
3. Rogers Corporation LCP product page.
4. John Coonrod, Managing Circuit Materi-
als at mmWave Frequencies, published in Mi-
crowave Journal.
5. Wikipedia, Embedded Wafer Level Ball
Grid Array.
This paper was originally presented at the EIPC
Winter Conference in Salzburg, Austria, February
2−3, 2017, and published in the proceedings.
Jim Francey is sales manager
for Northern Europe with
Optiprint AG in Berneck,
Switzerland.
Terry Bateman is project
manager with Optiprint AG
in Berneck, Switzerland.
PCB TECHNOLOGY REQUIREMENTS FOR MILLIMETER-WAVE INTERCONNECT AND ANTENNA
Figure 4: Micrograph (a) shows etched resonator on side 1 and (b) shows depth-milled cavity on side
2, machined into dielectric and within ~50 µm of side 1 resonator.
