Editorial

Citation

Goosey, M. (2012), "Editorial", Circuit World, Vol. 38 No. 4. https://doi.org/10.1108/cw.2012.21738daa.001

Editorial

Article Type: Editorial From: Circuit World, Volume 38, Issue 4

Printed circuit boards typically provide the well defined function of being a substrate on which components can be mounted and interconnected. Initially, PCBs were relatively simple structures, but as devices became more complex, the complexity of the boards also grew while line widths necessarily became finer and layer counts increased. More recently, the provision of interconnects using extensions of the basic printed circuit board approach has expanded to encompass many new types of devices and packaging approaches. The move from the use of through hole leaded components to surface mount devices was one major development that had to be accommodated, but this was nothing compared to the wide range of technology developments that have been witnessed in recent years. The list is large, but new approaches to interconnection and packaging have diversified in a number of radically different ways, be it system in package, the use of buried passives and actives within a board or any of the many other new techniques that are increasingly being reported. Coupled with this type of expansion and evolution, the PCB industry is also increasingly looking to do things that were not previously possible and within this activity comes the vast amount of work that has been undertaken to develop printed electronics technologies that cover both the additive deposition of interconnects and components using novel inks and printing processes. In this final issue of Vol. 38, there are five papers addressing novel aspects of both interconnection and componentry that contain or utilise circuitry in a form different to the more familiar and conventional mainstream applications.

In the paper by Bachman et al., details are given of how PCB fabrication processes can be extended for manufacturing micro electromechanical systems (MEMS) and their packages for use in sensing and actuation devices. MEMS represent a rapidly growing area of interest and the market for these devices reportedly tripled from 2009 to 2011. The market for MEMS in cell phones and tablets alone is predicted to be worth more than $5 billion by 2017. In this paper, the authors show that good quality MEMS devices can be manufactured using packaging style fabrication, particularly using stacks of laminates. Furthermore, these micro-devices can be built with a high degree of integration, pre-packaged and at low cost. The authors suggest that MEMS may offer a new opportunity for PCB fabricators, who could benefit greatly by expanding their offerings beyond serving the semiconductor industry and developing their own integrated MEMS products.

I am pleased to able to include in this issue a very substantial and highly detailed paper by Cummins et al. which gives an extensive review of the inkjet printing of conductive materials. Ink jet printing is a key enabling tool in the development of printed electronics and the paper explains the inkjet printing process and the various types of conductive inks that have been developed. It then examines the important factors that affect the quality of inkjet printed interconnects such as printing parameters, materials and substrate treatments. The authors also describe methods of characterising both the inkjet printing process and the electrical properties of printed conductive materials. Inkjet printing can be a low cost direct write technique and its use in electronic manufacturing, where interconnects and other conductive features are required, looks set grow significantly as it becomes a key enabling technology for many new types of products and applications.

In a paper entitled “A novel flip-chip interconnection process for integrated circuits”, Sugden et al. from Loughborough University give details of a their work to develop a new and interesting technology for providing the connections between a substrate and a flip chip device. In the approach reported metal coated polymer micro particles were selectively deposited onto the bond pads of integrated circuits using electrophoresis. Thermocompression bonding was then used to bond the devices to substrates. The use of an electrophoretic approach allowed the conductive particles to be deposited directly onto the bond pads of an integrated circuit without the need for conventional patterning. Thermocompression bonding of nickel/gold coated particles to gold coated substrates was then achievable at temperatures as low as 160°C.

One key challenge that has become increasingly important is the design and fabrication of circuitry that can operate at high frequencies. However, for many years, the design of high frequency electronic circuits was considered to be something of an art with numerous design iterations often being needed to achieve the required performance. Although the situation is now somewhat improved, various factors can still contribute to a less than expected agreement between modelled and measured electrical performance and the paper by Horne et al. covers this problem. One area highlighted is the need for accurate and appropriate determination of material permittivity and the authors highlight how the values obtained can vary significantly depending on the determination method. Ideally the measurement method should encompass a coupling configuration similar to that of the proposed final structure.

The possibility of integrating electronics into fabrics and clothing has been the subject of much research in recent years and one key challenge has been the provision of reliable interconnects. One approach to this problem is to provide stretchable circuitry and, in the paper by Vanfleteren et al., work undertaken on two such approaches is described which allow the use of standard printed circuit board patterning and assembly methods. Mechanical reliability was found to be strongly enhanced by introducing a flexible support material for the meandering conductors and by providing smooth transitions between the standard components and the soft and conformable stretchable interconnects.

The papers included in this final issue of Vol. 38 highlight novel aspects of circuitry that are at the forefront of interconnect technology development. Each one of them details a different direction in which circuitry and interconnections are evolving into new areas that provide new opportunities and which will enable new applications. I do hope that you find the selection of papers in this issue both interesting and stimulating. As always, I welcome your comments and feedback; I can be contacted at: m.goosey@lboro.ac.uk

Martin Goosey