Darlington in the north-east of England has become an established venue for the Institute of Circuit Technology’s annual Northern Seminar, a not-to-be-missed opportunity for the UK’s PCB technologists to keep abreast with current developments and to network and exchange ideas and experiences with their peers. Coordinated by ICT technical director Bill Wilkie, and generously supported by Merlin PCB Group, the programme consisted of papers on funded projects and project funding, and updates on chemical process technology.
With a presentation entitled Advanced PCB Manufacturing, Anjali Krishnanunni, project officer from Coventry University working with Stevenage Circuits, explained how Knowledge Transfer Partnerships (KTPs) supported by Innovate UK, the UK's innovation agency, assisted businesses to gain a competitive edge through better use of knowledge and technology, by promoting collaboration between academia and manufacturing industry
With reference to her “Pitch Perfect” project, she considered current and future issues in the PCB industry from the viewpoints of the designer, the fabricator and the assembler. Fine pitch component packaging demanded improved routability and higher interconnection density, using finer conductor geometries whilst keeping layer count to a minimum by cost-effective any-layer via-in-pad design rules. For maximising assembly yield, a critical factor was precision of solder paste application, and this was heavily influenced by the effect of PCB and solder mask topography on the consistency of contact between PCB feature and stencil. Established PCB fabrication techniques were approaching their capability limits and new methodologies were required.
Although at this stage of the project she was not at liberty to disclose practical details of process procedures, she explained that the objective of this KTP was to develop an ultra-high-density-interconnection fabrication technology compatible with a broad range of substrate materials, with low-cost interstitial vias and the potential for 25-micron lines and spaces, using low-impact surface modification techniques to minimise surface morphology. The technology would integrate straightforwardly with current process infrastructure, incurring minimal additional capital expenditure, and would be compliant with appropriate IPC standards.
From future developments concerning the minimisation of surface morphology to the current state-of-the-art in surface preparation chemistries: Nigel White, European product marketing manager at Atotech, declared tongue-in-cheek “You’ve just heard about using technology for making the surface smooth - now I’ll discuss how to make it rough!” - although in his context the reference was to the chemical micro-roughening of copper to promote photoresist and solder mask adhesion. He described two proprietary chemistries, one based on sulphuric-peroxide and the other on cupric chloride.
Generic peroxide-sulphuric systems were well-established as adhesion-promoting micro-etches for dry film photoresist, and modern formulations offered improved stability and copper-carrying capacity whilst providing controlled etching and uniform structures. However, they were highly sensitive to chloride contamination at levels as low as 3 ppm and there was an industry demand for chemistry with high chloride tolerance together with low process cost. Atotech’s new product contained organic modifiers which gave optimised surface topography through preferential grain-boundary attack, with consistent results at chloride levels up to 40 ppm and copper loadings up to 40 g/l for an etch depth of 0.7 micron in a simple three-step process. Customers had observed yield improvements of 7%-10%.
Although mechanical cleaning had been the traditional pre-treatment technique for solder mask, chemical methods were now preferred and it was essential the pre-treatment was compatible with final finishing processes such as ENIG and immersion tin as well as maximising solder mask adhesion. Atotech had developed a formulation based on cupric chloride, which gave an optimum surface condition as measured by relative surface area increase at an etch depth of only 0.3 micron, with minimal copper removal although performance remained stable at copper loadings up to 40 g/l. The simple three-step process was compatible with horizontal equipment with titanium components and operated at low process temperatures, with cost savings over competitive products
In a second presentation, Nigel White turned his attention to direct metallisation technology.
Atotech’s original direct plating system, based on tin-free colloidal palladium, had been launched 21 years ago and still fulfilled all specification requirements as a highly versatile and reliable process for all base materials including PTFE, with excellent acid-copper adhesion on surfaces with low roughness or low surface energy. But there was a market demand for an environmentally friendly and cost-effective direct metallisation process for MLB, HDI and flex/flex-rigid production, independent of the precious-metal price issues associated with palladium. He described Atotech’s most recent generation of thiophene-based conductive polymer chemistry, which exhibited outstanding environmental benefits in addition to its technical attributes and low operating costs. The process was short and simple, with very low chemical and water consumption, and no hazardous materials such as formaldehyde or cyanide. It represented a mature technology, compatible with a wide range of base materials and delivering consistent high reliability, proven world-wide in mass production.
Returning to the subject of the funding of research by government agencies, consultant Dr. Dominique Morrison clarified many of the perceived mysteries and obscurities surrounding the rules for qualification of projects for support and the procedures for preparing project proposals and gaining access to funding. Based on her many years of experience in senior research positions, and more recently as a project monitor, she gave an enlightening presentation entitled Research Funding for UK Small to Medium Enterprises. She explained the definition of an SME, basically a company with no more than 250 employees, turning over no more than 50 million euros, and the meaning of a Technology Readiness Level as a measure of the maturity of evolving research. Innovate UK, earlier referred to by Anjali Krishnanunni in connection with her KTP project, provided support for collaborative projects in the TRL range 3-6. The objective of the funding bodies was to help businesses to bring innovative products or services to market that would benefit the UK or Europe economically, socially or environmentally. Numerous types of funding were available for individual or collaborative projects: she gave examples including Smart, Horizon 2020 and SME Instrument, and gave a step-by-step guide to the application procedure. A well organised plan was essential for success; the process was very competitive and the drafting of good proposal was not an easy task. Key elements of her advice were to consider initially whether the project offered a real solution to a business problem, was there a significant market opportunity and was it innovative? Then to prepare methodically before starting to write a realistic project plan, building a consortium and identifying a route to market, making sure the idea was innovative by conducting an IP search, and allowing plenty of time before the deadline. Expert help was available, and was to be recommended.
ICT technical director Bill Wilkie never fails to put together an outstanding programme, and the 2015 Darlington Seminar will go on record as yet another extremely successful, informative and enjoyable event.
Pete Starkey
I-Connect007
November 2015