ICT Darlington Seminar 1st November 2011

The night was drawing in as I made the long drive to the north-east of England for the Institute of Circuit Technology 2011 Darlington Seminar on November 1st. British Summer Time had ended the previous weekend and at 5pm it was already too dark to see the autumn colours of the trees and hedgerows on the banks of the River Tees.

But on the bright side, ICT Technical Director Bill Wilkie had once again organised an excellent programme which attracted an attentive crowd of PCB fabricators and suppliers, and he introduced the seminar with the encouraging news that membership of the Institute continued to grow steadily and that events were increasingly well-supported.

First to present was Geoff Layhe, Technical Manager at Lamar Group, who explained how the technical demands of the rapidly growing market in LED lighting had driven the development of white solder mask inks specifically for high-luminance LED applications. The main challenge to be overcome was the discoloration of standard white solder mask by heat and UV exposure. Epoxy resins used for conventional high-performance solder masks had a natural tendency to discolour when subjected to sustained high temperatures. In cooperation with major LED OEMs, Taiyo Ink, who supplied over 45% of the world solder mask requirement, had carried out extensive studies of materials and formulations and introduced a new range of liquid photoimageable solder masks with high reflectance and resistance to UV and thermal discoloration. Their PSR-4000 LEW3 was the highest performing LED solder mask in terms of reflectance and discoloration, and Layhe showed test results that indicated its superior properties. He made some interesting practical observations on staining effects after gold plating. If pink or purple stains appeared on a white solder mask, this was an indication of inadequate rinsing, resulting in a subsequent chemical reaction between residues of gold salts with the titanium pigment in the mask.

As well as their range of white solder masks, Taiyo had introduced a white ink-jet marking ink which had become widely accepted and had been adopted as standard for Orbotech's Sprint printers.

ICT Chairman Professor Martin Goosey reported on two EU-funded projects: ASPIS and SUSONENCE. The ASPIS Project, aimed at enhancing the performance of nickel-gold solderable finishes, had been running for one year and had already produced some interesting data on the fundamental characteristics of the electroless nickel deposition process, particularly the effects of pH on deposition rate, phosphorus content, deposit morphology and grain-boundary characteristics. It had also been established that corrosion of the nickel surface was due to activity in the immersion gold process, and a high gold-bath pH together with a high citrate concentration was a combination of parameters which encouraged black-pad formation. Nickel deposition from ionic liquid chemistries offered a possible route to avoid the co-deposition of phosphorus, a by-product of the reducing agent in conventional chemistry and a known contributor to the black pad effect. ICT had the responsibility for training, exploitation and dissemination of the outcome of the programme. Papers had been published in industry journals and a website was operational at www.aspis-pcb.org.

SUSONENCE was a new FP7 eco-innovation project originating out of work supported by IeMRC and directed at the development of sustainable, ultrasonically enhanced surface modification processes to reduce chemical usage and decrease waste and environmental impact in the PCB and metal finishing industries, particularly in the areas of removing surface layers, etching and texturing of widely-used substrates.

Mike Partridge, MD of Lamar Group gave a very informative presentation on the mechanism and benefits of contact cleaning, with many hints and tips on how to maximise the effectiveness of the process, which had a wide variety of particle-removal applications in PCB manufacture. These typically included cleaning of laminates, prepregs, conformal films, press plates, artworks, exposure frames, boards prior to testing or assembly, and even clean-room walls and floors. Partridge discussed the critical attributes of elastomer rollers, which were available with different hardness values to suit particular applications, and adhesive transfer rolls. He described the principles of operation of panel-cleaning machines, which were often not fully appreciated, listed what types of contamination they would and would not remove, and advised how simple basic maintenance procedures could improve consistency of performance. There were many other industries where contact cleaning was employed to good effect and, as an illustration, Partridge explained how a dramatic yield improvement had been achieved in the manufacture of lorry windscreens by the introduction of contact cleaning, with the initial investment paid back after only 2½ days!

Deputy Chairman of the ICT and Head of Materials at Coventry University's Sonochemistry Centre, Dr Andy Cobley described the effects of ultrasound on the electroless copper plating process, being studied as part of the ULTElmet Project, funded by the Engineering and Physical Sciences Research Council via IeMRC. It had been observed that ultrasound had an apparently negative effect on plating rate at temperatures below 35ºC and a slightly positive effect above 35ºC. Very low or very high frequency tended to de-stabilise the electroless copper; and best results were obtained at frequencies near 40kHz. But the negative effect on plating rate had been found by x-ray photoelectron spectroscopy to correspond with the displacement of palladium catalyst from the activated surface, and the effect could be overcome by delaying the application of ultrasound to enable the electroless reaction to initiate without disturbance of the catalyst. Significant improvements in plating rate were then observed. An ecological objective of the project was to achieve acceptable plating rates with non-formaldehyde reducer chemistries. In addition to its effect on plating rate, ultrasound improved the morphology of the electroless copper deposit, with finer grain size and reduced porosity.

At the conclusion of the technical proceedings, delegates enjoyed a splendid buffet supper, courtesy of Lamar Group whose generous support of the event was gratefully acknowledged, and constructive conversation continued late into the evening.

Thanks to Bill Wilkie's unstinting endeavours, the regional evening seminar is now established as an essential meeting place for everyone interested both in keeping in touch with developments in printed circuit technology and in sharing experiences with their counterparts in the industry.

Pete Starkey

ICT Council

November 2011