Editorial
Article Type: Editorial From: Circuit World, Volume 38, Issue 3
In recent conversations with circuit board makers and assemblers I have been reminded of the challenges that the electronics industry is still facing in respect of the conversion to lead-free solders and assembly. With Europe having taken a lead in environmental legislation that has a direct influence on the electronics industry, its PCB fabricators have long been used to meeting the requirements of the various directives introduced in recent years. One such piece of legislation that originated in the 1990 s, and which is still having a profound effect, is the RoHS directive. While not implemented until 2006, it was effectively responsible for converting electronics to lead-free assembly. That was over six years ago and yet, despite the huge amount of research and associated costs around the development of lead-free alloys and new assembly processes, it seems that there is still much more work to be done as the transition to lead-free continues to provide problems for both assemblers and circuit board makers.
For PCB fabricators, the move to lead-free assembly has meant that new, high Tg laminates with different properties to traditional materials are finding increasing use and, as the industry moves further away from the once standard“dicy” cured FR4, it is clear that there are often significant changes required in terms of board processing conditions. Where a fabricator might once have employed a single, fairly standard desmear process, the use of a range of high Tg materials, may mean that several desmear processes now have to be accommodated. Also, it is not just desmear that must be optimised, since these new materials have differing drilling characteristics and they may exhibit varying levels of moisture absorption; all of which needs to be taken into account if subsequent long term assembled device reliability is to be achieved. This is putting additional demands on PCB fabricators, but it does not end there, as the assemblers are also required to introduce new higher soldering temperatures that far exceed those used with conventional tin-lead solders. Every time a component is heated to a high temperature, its lifetime is reduced and, if a board and its components are exposed to multiple lead-free solder cycles, there may well be a significant negative impact on the overall service life functionality. The move to lead-free has certainly reduced the occurrence of lead in electronics, but at what cost? Simply by studying the published literature detailing current research activities, it is clear that there is still a long way to go before all electronic products will be able to offer the same type of performance that was standard with tin-lead solders.
In this issue of Circuit World there is the usual eclectic mix of papers covering a diverse range of subject matter from novel fabrication methods,through inspection, to the broader subject of counterfeit electronics. The issue opens with a paper on the development of electro-optical PCBs with polymer waveguides for high-speed intra-system interconnects. This is a subject that Circuit World has reported work on in previous issues and one that continues to generate much research activity around the world. There then follows a paper detailing a novel electroplating process for filling through holes and blind microvias with copper using reverse pulse plating and insoluble anodes. The process provides a viable alternative to the standard paste plugging route for core processing in substrate manufacturing, as well as offering a method for reducing the quantities of copper concurrently deposited on the outer surfaces of a substrate. As mentioned in the opening part of this editorial, the introduction of higher Tg materials for use with lead-free assembly has necessitated the use of new and often more aggressive desmear chemistries. In the third paper of this issue, the results of work to optimise the sonochemical surface modification of a high Tg laminates is reported. The research reported here shows that, by implementing ultrasound, it is possible to make significant reductions in both the temperature and use of aggressive chemicals for desmearing higher Tg substrates materials.
There then follows a trio of papers with each one detailing work on various aspects of inspection. The first of these covers the inspection of PCB line defects based on directionality measurements. The work reported provides a new way to detect PCB circuitry defects using texture directionality. The paper proposes evaluating the similarity between image texture directionalities using a Radon Transformation to search the areas being inspected. The authors report that the proposed method has been applied to an inspecting system used in practice and that it achieved a higher accuracy and efficiency in comparison with similar methods. The second of the three papers details the detection of flaws in solder deposits on flexible printed circuits and describes a new way to locate solder based on directionality. The method extracts contour features and defines directional parameters to help realize the accurate location of solder deposits, including those that that are deformed to some extent. The third paper reports details of the results of a study of a “Speed-Up Robust Feature”(SURF) – based image matching algorithm for PCB matching which does not require the use of special fiducial marks. The technique provides a new approach that can be the basis of a novel matching method for PCB AOI applications.
Finally, the seventh paper of the issue is on a subject that is a little different from the more usual PCB fabrication and testing papers normally included in this journal. The paper from CALCE covers the topical and extremely important problem of electronics counterfeiting. This is an increasingly serious global issue and one that has significant ramifications in a number of disparate ways. When one considers that counterfeiting and piracy have been estimated to cost over $125 billion per year and that there are 2.5 million jobs lost worldwide annually due to counterfeit products, the scale of the problem can truly be appreciated.
I hope that you enjoy reading the details of the work reported in this issue and that some of it is of direct relevance to your own activities. As always, I would welcome your comments and feedback, as well as submissions of papers detailing your own work. I can be contacted at: m.goosey@lboro.ac.uk.
Martin Goosey
