ECWC 2014: The Embedded Technology Session
The 13th Electronic Circuits World Convention in Nuremberg, Germany, provided an exceptional diversity of information and knowledge, through 123 presentations in 26 sessions.
The Embedded Technology session on the second day attracted an enthusiastic audience, keen to learn about PCBs with embedded RFID and embedded magnetic cores, interposers with embedded thin-film capacitors, and flexible microsystems with ultra-thin embedded silicon chips. The session was introduced and moderated by Dr. Eric Maiser of VDMA Productronic.
The first presentation was delivered by Martin Cotton, long-standing expert in embedded RFID, who demonstrated the scope offered by the technology beyond basic identification and product tracking. Reviewing the fundamental benefits of RFID, and its advantages over bar-code labeling, he stressed that he was describing a process for creating a wireless communication portal within the structure of, and if necessary electrically connected to, the PCB, which could achieve very much more in functionality than simply acting as a traceability device and could effectively become part of the “internet of things”. Read ranges of 9 to 10 metres were now attainable, at up to 200 devices per second, and line-of-sight was not a necessity. Bar codes, by comparison, could hold only limited data, could not be written-back to and could only provide a reference to be used with a database.
Embedded RFID devices could be could be connected to various sensors to enable additional functional features regarding safety, traceability, and working environment, and could be activated when a device was powered-up, for example, to lock the device against unauthorised use. Cotton listed and discussed many applications including reporting of performance data for maintenance planning and failure prediction, providing a complete cradle-to-grave information pipeline, and enabling the best security and anti-counterfeit strategies.
Next to speak was Chun Chen from Shenzen King Brother Electronics Technology, describing a method of manufacturing multilayer PCBs with embedded magnetic cores. He explained that embedded core technology was an effective route to achieving miniaturisation of power modules, but that certain fabrication difficulties had to be overcome.
For the core to function effectively, it was necessary to position it precisely within the multilayer construction, then to form insulated plated-via-hole conductors through the core by drilling clearance holes, vacuum plugging with resin, drilling concentric holes leaving insulating resin sleeves, then metallising these holes to become part of the windings of the inductor, with printed circuit features taking the place of wires. Chen explained the details of the lay-up and laminating technique and how the positional tolerances and bond strengths had been achieved. The magnetic cores were very fragile and the through-drilling of clearance holes was a critical operation for which drilling parameters had been optimised by serial DOE procedures. Problems of micro-cracking of the resin fill had been overcome by careful choice of materials and an enhanced vacuum lamination process. Other processing challenges which had been addresd included step-etching of asymmetric copper thicknesses.
The result was a process by which the customer’s design requirements for electrical insulation, inductor, and electromagnetic loss had been satisfied, and which demonstrated a practicable route for the manufacture of embedded magnetic products.
From embedded inductors to the effects of parasitic inductance in external decoupling capacitors on power supply quality. Masamitsu Yoshizawa from Noda Screen Company explained how thin-film decoupling capacitors embedded in organic interposers could achieve better noise reduction than PCB-mounted ceramic chip capacitors and effectively act as if they were on the chip itself, but without taking-up space on the silicon. He described a patented process for manufacturing stable thin-film strontium titanate capacitors by aerosol chemical vapour deposition at atmospheric pressure, with the advantages of flexibility in size, shape, and location.
Capacitors could be located very close to LSI pads, with optimised electrode positions. He reviewed the observed differences in characteristic performance between on-chip and on-PCB decoupling capacitors, believed to be related to the very low inductance between IC and embedded capacitor. Further studies to gain a more precise understanding of IC internal noise were being carried out in cooperation with the University of Tokyo.
The final paper of the session was presented by Jürgen Wolf form Wűrth Elektronik, reporting the outcome of a government-funded collaborative research project on ultra-thin silicon chips in flexible microsystems, which had many potential applications in medical electronics, wearable electronics, and automotive electronics. A growing demand for mechanically-flexible electronic systems and increasing levels of integration had led to the development of hybrid build-ups combining polymer substrates and ultra-thin silicon chips which could maintain their functionality under bent conditions.
Wolf described a proprietary process for wafer-scale fabrication and subsequent “pick, crack, and place” singularisation and handling of integrated circuits less than 20 microns in thickness, and explained their physical characteristics. He went on to detail methods of mechanically and electrically connecting them to flexible substrates, and discussed design issues such as the influence of piezoresistive effects and the layer- and structure-dependent management of mechanical stress. Several build-up techniques for embedding ultra-thin chips into flexible polymer substrates had been realised and characterised, and the technology represented another step in the evolution of flexible printed circuit assemblies.
