Brussels, 14 Jul 2004
By combining pulse-plating and ultrasonic techniques, the ULTRAPLATE project has produced breakthrough improvements in the speed and precision of electrodeposition of metals and alloys for applications in electronics and micro-devices.
Pulse plating has been used by advanced end users for electrodeposition of metals and alloys in the electronics industry. It involves applying a pulsed current to the electrolytic bath to obtain a finer grained deposit with better characteristics than can be achieved using conventional techniques. And, until now, ultrasonic agitation, mainly at low frequencies, has been applied principally for pre-cleaning of substrates, although it had been found to improve the efficiency of the plating itself. Prior to ULTRAPLATE, little systematic effort had been devoted to studying the results of combining these individual process enhancements.
The three-year FP5 initiative, launched in February 2001 by the Institute for product development (IPU), based at the Technical University of Denmark (DTU), and ultrasound equipment manufacturer Reson, brought research experts in the two areas together with electronics and micro-device industrial end users. The objectives of the consortium, comprising eight participants from five countries, were to realise viable and environment-friendly combinations of the underlying technologies, and to demonstrate their relevance to key strategic industries.
Work began with basic research into ultrasonic phenomena and a feasibility study on the low- and high-frequency ultrasound in electrodeposition, coordinated by IPU. This led to the design of two laboratory-scale systems, combining computer-assisted pulse plating (CAPP) technology from DTU spin-off TCD Teknologi with low and high frequency ultrasound technology from RESON. Hardware was supplied to the partners for parameter optimisation and progressive development during the remainder of the project.
Evaluation of the relationships between process conditions, surface layer microstructures and the performance of user-selected alloys was greatly aided by electron microscopic studies and other analytical inputs provided by Linköping University, Sweden.
Several significant advances had been made by the end of the project in January 2004:
- Low-frequency (25 kHz) ultrasonic agitation proved to facilitate higher plating speeds as well as ensuring more dense and uniform coatings less prone to the formation of tin whiskers for high-speed deposition of lead-free solder contacts. This involved standard transducers built into a housing that fitted the plating tank. Reson – whose principal business is in marine sonar – also developed new types of air-cooled transducers operating at high frequencies (0.5 to 1 MHz) that would permit continuous system operation over longer periods;
- Contract plater PGE (NL) employed the low-frequency technique to demonstrate the processing of reel-to-reel stock for the stamping of electronic contacts. Achieving good solderability required very careful control, but satisfactory results were eventually obtained with pure tin, which turned out to be best choice for PGE. When scaled up to an industrial level, this will enable customers to meet the EU deadline for the elimination of lead in solder by July 2006;
- Electroplating of alloys such as nickel-iron (Ni-Fe) for soft magnetic layers was shown to be controllable using standing waves at around 500 kHz. The observation that wide-ranging variations in alloy composition could be obtained in this manner led to the registration of a patent on controlled alloy deposition;
- The Irish National Microelectronics Research Centre at University College Cork successfully established its applicability to the production of cores for planar on-chip microtransformers, as a replacement for bulky coil-wound components in appliances such as mobile telephones; and
- Siemens (DE) used the approach to modify electrolyte flow at the deposition surface, leading to improved coating uniformity on complex 3D structures, increasing process speed by several hundred percent – a second patent application is under preparation. The company had a particular interest in solving problems related to production of nickel micro-moulds for polymeric waveguides used to align optical fibres. Its existing process for electroforming of the metal onto etched silicon resulted in substrate deformation, making it impossible to meet the precise tolerance demands.
"Apart from commercial aspects, ULTRAPLATE brings significant environmental benefits," notes coordinator Dr Jens Dahl Jensen of the IPU. "Electrolytes in general use today contain a variety of organic additives that compromise longevity, create pollution risks and, in some cases, pose health hazards. We focused on aqueous solutions that extend bath lifetimes, simplify disposal and have the potential to improve workplace safety."
"This whole project has been distinguished by a remarkable spirit of openness and co-operation," says Jensen. "There were extensive exchanges of people, sharing of equipment and transfer of knowledge. Everyone seemed to enjoy working together, and the result has been a number of positive outcomes with early exploitation potential. We learned to trust and rely on one another. I am sure that collaboration between members of the network will continue, whether within or outside the context of EU-funded projects."
TCD and Reson have now entered discussions regarding the marketing of turnkey systems employing easy-to-use Windows-based software that will make the fruits of this research readily available to other European manufacturers within around three years.
A proposal for a follow-up initiative taking the technology forward into the nano-domain under FP6 has already been submitted.