EIPC 2017 Winter Conference Review of Day 1

Estimated reading time: 19 minutes

Although Helmut Kroener from Isola in Germany apologised in advance that his presentation was very data-heavy, he in fact gave a very clear and thought-provoking explanation of the influences of laminate and PCB manufacturing tolerances on patch antenna and feed network characteristics for very high-frequency applications.

Taking as his example a 77GHz radar antenna, he demonstrated how the critical tolerances could be determined using a statistical technique known as Monte Carlo Simulation to study the impact of independent variables on desired performance characteristics. The procedure involved assigning a normal distribution for each independent variable, with user-defined mean and standard deviation, then randomly picking values for each independent variable, based on the probability for normal distribution, with each variable pick being independent of the other independent variables, then running many thousands of simulation runs with vectors of dielectric thickness, line width, copper thickness, bulk dielectric constant and pad size as independent variables.

The simulation study showed that changing the tolerance on dielectric constant from +0.05 to +0.02, which would be hugely expensive, had only minor effects on impedance and centre frequency, and that plated copper thickness had very minor influence overall. The largest influence came from etch tolerances, and the second largest was the dielectric thickness of the material. Kroener stressed the importance of laminate manufacturers having the right tools and capabilities to support the development of materials to fulfil customer requirements. He also proposed a performance-verification test that could be used by PCB suppliers for back-end-of-line testing, by incorporating an additional test coupon on the panel to enable measurement of resonance frequency with a vector network analyser.  

The current growth of the mobile data traffic of portable devices and machine-to-machine communications dramatically challenges the 4G cellular networks currently under deployment. To help satisfy mobile data demand, there was an expectation that millimetre-wave architecture would be used for 5G cellular phone. What technology would be needed to provide the necessary antenna characteristics? Jim Francey and Terry Bateman from Optiprint in Switzerland demonstrated that PCBs offered an attractive solution for millimetre-wave hardware and discussed technology requirements for interconnect and antennae, with reference to the work they had carried out as collaborators in the MiWaveS FP7 project.

Several substrates had been evaluated and liquid crystal polymer material was identified as a good candidate, having stable dielectric constant through the required frequency range, low moisture absorption and comparatively low loss. And it was available in non-woven-based copper-clad laminate and matching bond ply, simplifying the design process. The main manufacturing challenge was material movement, and careful precautions were needed to achieve precision in registration and feature positioning. 

In general, the PCB technology required thin-core processing competence, fine-line tight tolerance conductors and the capability to manage variable material movement. Essential facilities were off-contact metrology, liquid resist, laser direct imaging, laser machining, automatic alignment systems for drilling, milling and routing, plasma treatment, cleanroom conditions and the right systems for test and inspection, together with a culture of working with small-form high-precision components and a policy of continuous investment. 

Miniaturisation and increasing functionality in medical electronics, particularly in wearable and implantable devices continued to place increasing demands on substrate interconnection density. Karl-Heinz Fritz from Cicor, also in Switzerland, offered a practicable solution in his presentation on ultra-high-density-interconnection printed circuit boards.

Taking the simple example of a hearing aid, whose present function was simply to aid hearing, he predicted that “Hearing Aid 2.0” would incorporate a host of additional diagnostic and monitoring functions, but in the same size package. And with active components’ pitch sizes trending below 200 microns, and passives in 008004 format, established HDI technology could not offer sufficient routing density or component real-estate and was reaching its limit in terms of cost-effective high-yield production.

As well as their expertise in HDI PCB production, Cicor had long-term experience in thin film technology, which offered lines and spaces down to 10 microns but was expensive to manufacture and only available in small panels. They had now bridged the gap between the two technologies, and could offer an “ultra-HDI” solution with 25-micron lines and spaces, 90-micron capture pads and 35-micron holes, giving real estate savings of 37% on innerlayers and 30% on outer layers as compared with standard HDI. Their DenciTec product could be manufactured in 305 mm x 457 mm panels by all-PCB processes.

The final presentation in the morning session was given by Professor Rainer Thüringer, president of FED, the German-based professional association for design, printed circuit boards and electronic manufacturing.  His topic was EMC conformal board design, subtitled “It’s all about maximum inclusion of the operating RF energy,” which turned out to be an excellent basic tutorial on fundamental design principles.

He began by discussing how magnetic and electric RF-fields were created, the former by radiation by differential-mode currents generating RF-magnetic dipole fields, the latter by radiation by common-mode currents caused by inductive coupling generating an electric dipole field, then went on to describe how these effects could be mitigated by good design practice. He explained with clear illustrations how energy was distributed between paired traces on the same layer, paired traces on two layers, and single traces over a ground plane, and emphasised the significance of proximity effects in keeping the energy entrapped. Effectively the return current always took the path of lowest Add Imageimpedance, and for pulses with high frequency content the path of lowest inductance, which was underneath the trace. Discontinuities in the ground plane would cause the return signal to find another route, which would result in RF radiation and disturb the quality of the signal. He showed many examples of good practice in grounding and filtering, and minimising inductive loops on power connections, before focusing on PCB stackup for EMI control and signal integrity, with expert guidance on positioning of power supply and reference planes, controlled impedance, crosstalk reduction and screening, remarking that more than four layers were required if good signal integrity and EMC performance were required. 

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