Circuit World

ISSN: 0305-6120

Article publication date: 18 November 2013



Goosey, M. (2013), "Editorial", Circuit World, Vol. 39 No. 4. https://doi.org/10.1108/CW-08-2013-0028



Emerald Group Publishing Limited


Article Type: Editorial From: Circuit World, Volume 39, Issue 4

Light emitting diodes were first developed in the 1960s and have been commercially available for well over 40 years. However, it is only recently that they have begun to be used in mainstream lighting applications, where they are required to have much greater light outputs than their predecessors. These higher brightness devices also generate more heat and the evolution of LED lighting has posed new challenges for those fabricating printed circuit boards for use in such lighting assemblies. Indeed, the challenge of thermal management for LED lighting has encouraged the development of new circuit board materials and related fabrication technologies. PCBs based on metal in board (MiB) technology offer one new approach for meeting the thermal and power management demands of such applications. These boards can be required to accommodate very high power densities and currents, while in addition also needing to perform as conventional interconnect systems whose reliability is not compromised by the regular thermal excursions that can be experienced. The fact that the PCB industry has developed viable solutions for LED lighting is a good example of how the once humble PCB can be developed and adapted to provide new solutions for demanding applications.

The use of MiB substrates looks set to grow considerably in the next few years and will undoubtedly provide both challenges and opportunities for PCB fabricators and their material suppliers. I am pleased, therefore, that the first paper in this issue of Circuit World has been provided by William Burr and Nick Pearne of BPA Consulting, whose paper on “Learning curve theory and innovation” makes particular reference to novel interconnections solutions with potentially high levels of innovation such as MiBs. The authors discuss the inexorable downward price pressures on novel technologies and describe how a good understanding of these can give a competitive advantage to those bringing innovative technologies to the market.

The possibilities for embedding chips into substrates has also been the subject of much research over the last few years and, in the paper by Liang Wang, Maarten Cauwe, Steven Brebels, Walter De Raedt and Jan Vanfleteren, the authors discuss their work to develop a process for a self-aligned flat ultra-thin chip package that is specifically intended for use with flexible circuits. In the process described, a central photosensitive film is used, in which a cavity is made for the embedded chip. The cavity is defined by lithography using the chip as the photo-mask, which enables the cavity size and position to be determined by the chip itself. The packages could be produced in high yields and demonstrated good accelerated life test performance.

Carbon nanotubes are another relatively recent novel material development and, although there may have been some exaggerated claims about their likely potential applications, it does now seem that they have the potential to play an important role in the development of new materials for the electronics industry. In the paper by Andrew Wright, the “Multi-shot printing of conductive tracks using a dry carbon nanotube ink” is detailed. By employing a hard patterned stamp, it was possible to create prints on elastomeric substrates using direct compression transfer from their growth substrate to a receiving substrate with a unique multi-shot printing capability. A method for enhancing the electrical conductivity of these printed tracks is also described.

In a paper on the printing of silver circuits for fast moving consumer goods (FMCG) applications, David Tudor Gethin, Eifion Huw Jewell and Tim Charles Claypole detail the results of an investigation into the integration of silicon and printable circuits for the FMCG packaging industry to allow products with features such as brand protection, time-temperature indicators, customer feedback and visual product enhancement. Responding to interest from the FMCG packaging sector, work was carried out which investigated the printing of two conductive silver materials onto a number of different commonly used plastics and papers. The results highlighted the interactions between conductive materials and the substrates in flexible printed circuit applications and also demonstrated the implications of rheology, substrate absorbency and materials processing temperatures on circuit design.

A few years ago there were serious questions raised about the ability of conventional mechanical drilling approaches to meet the demands for ever reduced hole and via sizes. Laser drilling was increasingly promoted as the solution but, as is often the case when a mature technology is threatened with a new one, continual development of drilling machines and drill bits has enabled high speed drilling to progress to sizes that would once have been thought impossible. Much good work has been reported on developments in drilling technology from around the world and regular readers of this journal will be aware that there have been a number of papers published detailing the excellent work that is being carried out in China. In this issue, the theme is developed again, as the final three papers are all from authors based in China and they report on some very interesting work that will enable the capability of mechanical drilling to be pushed even further.

In the first of these three drilling related papers, Ming Chen, Xiaohu Zheng, Dapeng Dong, Lixin Huang and Xibin Wang describe an “Investigation of tool wear mechanisms and tool geometry optimization in drilling of PCB fixture hole”. In particular, the work had a focus on the relationship between the mechanisms of chip formation and drill geometry, the types of the chips formed, drill bit wear mechanisms and the influence of drill geometry on chip-removal. As a result of the study, it was possible to make specific recommendations about the drill geometries that would enable drilling performance to be optimized.

Although much of the effort to improve the quality and capability of PCB drilling has focussed on the materials and designs of drill bits, the paper by Lianyu Fu, Haitian Zou, Baolin Wang and Fumin Song reports on the use of novel materials in the construction of the actual drilling machines themselves. Their paper covers the application of mineral casting as a replacement for conventional materials such as cast iron and highlights the potential benefits this approach can offer. By using a mineral casting, it was possible to significantly reduce the overall weight and mechanical testing suggested that it could successfully meet the requirements for use in a high accuracy drilling machine. While perhaps being towards the periphery of the subject matter normally covered by this journal, the paper details yet another aspect of the important work that is being undertaken globally to further enhance the capabilities of mechanical drilling for advanced PCB fabrication.

Finally, for this issue, Lianyu Fu and Jian Wang and Qiang Guo from the Shenzhen Jinzhou Precision Technology Corporation discuss their work on the characterization of PCB routing processes and the optimization of tool design based on a study of routing temperatures. The authors detail how routing temperatures are sensitive to the properties of the PCB, the type of router and routing parameters. Very high temperatures were experienced if non-appropriate routers were used to process boards with aluminium substrates and this brings the issue neatly full circle and back to the subject of MiBs, which were also covered in the opening paper. This final paper gives a clear indication of how PCB manufacturing processes will also have to evolve to accommodate the newer designs of boards that are continuing to emerge.

This issue of Circuit World has focused on a number of diverse new approaches to the provision of future interconnects and illustrates how conventional printed circuit boards, their materials and manufacturing processes are continuing to evolve along an increasing number of diverging paths. I do hope that you find these papers interesting and, as always, I welcome your comments, suggestions and other feedback. I can be contacted at: mailto:m.goosey@lboro.ac.uk.

Martin Goosey
Loughborough University, Loughborough, UK

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