Environmentally sustainable manufacture of printed circuit boards
On 20 March 2007 in London, UK, the results of a project dedicated to making the Printed Circuit Board (PCB) manufacturing industry more environmentally sustainable will be revealed.
Professor Martin Goosey, who worked on the project while employed at Rohm & Haas Electronic Materials (now based at Loughborough University, UK), says, 'PCB manufacturing is a multi-stage process that can generate a lot of waste.
The etching and deposition of a number of different metals - such as copper for creating conductive traces and electroless nickel with immersion gold for soldering the exposed copper - consumes large quantities of water as well as organic chemicals in the form of formaldehyde and chelating agents. The resulting discharge of metal and chemical-bearing effluent solutions is potentially harmful to the environment and requires expensive and intensive treatment using materials such as activated carbon.
'The waste materials normally go into an effluent treatment process where they are precipitated out as solids, [which] are subsequently sent to landfill,' explains Goosey. 'So you end up throwing away raw materials and water that could be recycled.'
Supported by the DTI's Sustainable Technologies Initiative and led by Rohm & Haas, the 'Towards a Zero Discharge PCB Manufacturing Plant' (TAZDIS) initiative was therefore established in 2003, bringing together a consortium of organisations. Goosey says, '[Disposal of] waste costs money. It is about making the process more efficient and environmentally friendly, allowing UK manufacturers to compete more effectively.
The novel feature [of the new system] is the integration of separate technologies into a combination unit,' creating a closed loop process. The three main strands are: use of ion exchange and organic scavenger resins to capture metals and organic chemicals, respectively, from rinse waters, enabling the water to be purified and reused; electrochemical recovery of metals from the regenerant solution of the ion exchange process. The liquid can then be safely reused and the metals recycled; and advanced oxidation - developed by Rohm & Haas, this technique employs ozone and/or hydrogen peroxide alongside UV radiation to destroy harmful organic compounds concentrated by the capture resins. The contaminants are converted into carbon dioxide and water, and the resins are then acid regenerated and re-employed in the plant.
Commenting on the release of carbon dioxide, Goosey says, 'Nothing is truly 100% in the world of electronics manufacturing. The end result is a process that is much more sustainable than the standard route normally used.
A prototype unit was installed on the nickel-gold line at Printed Wiring Technologies' PCB plant. Based in Welwyn Garden City, UK, the company was one of the industrial partners on the project and experienced savings of 500,000 litres of water in just one month.
Moreover, the pilot scheme revealed that the technology could be applied without disrupting existing production lines.
Goosey adds, 'The conventional PCB process starts off with a substrate laminated with copper, but only a fraction of the surface ends up with copper [due to etching to create the conductive lines] in a subtractive process. The holy grail in the industry is the additive process, applying copper only where it is needed. There has been a lot of work on this [technique], but it has not taken off due to capability. It is a slow process and not very productive.' In the mean time, he argues, applying TAZDIS technology could be the way forward.
Louis Chan, email: email@example.com.