Sustainable Technology for tin etch resist stripping solutions
Sustainable Technology for tin etch resist stripping solutions
Keywords: Technology, Sustainable development
In a collaborative project supported through the DTI's Sustainable Technology Initiative, ITRI is currently completing a Scoping Study to Assess Sustainable Technology for Tin Stripping. The project has investigated the recycling and reuse opportunities specifically relating to the end-of- life tin stripping solutions used by printed circuit board (PCB) manufacturers to remove tin-based etch resists. With inputs from Intellect and Shipley Europe Ltd, this 1 year project has sought to identify alternative possibilities for the treatment and recovery of the metal bearing, highly acid strippers currently used by the PCB industry. With sustainable development and sustainable technology becoming an increasingly important consideration in all activities, the current practice of disposing of spent strippers via external treatment to landfill represents a significant waste of valuable resources and a practice which is both costly for producers and increasingly environmentally unacceptable.
Although there are many types of tin etch resist strippers based on various chemistries, the two most popular choices are those utilising either nitric acid or methane sulphonic acid with nitric acid based chemistries being the preferred choice from an economic perspective. Typical ingredients of such strippers also include materials to enhance the dissolution of the tin-copper intermetallic formed between the copper and tin, as well as some kind of heterocyclic compound that reduces the rate of attack on the underlying copper. At the end of their useful lives the highly acidic waste stripper solutions contain all of the above ingredients plus some dissolved copper and a high level of tin, which exists as the oxide in a near colloidal form that is very difficult to remove and recover. Consequently, the current practice of disposing to landfill wastes not only the valuable tin oxide but also the copper, iron and nitric acid that could be recovered and recycled for further use.
During the project, a variety of approaches have been adopted in order to determine exactly what practices are currently being used to treat and dispose of spent stripping solutions and to identify established and possible new technologies that could be utilised in a more sustainable approach. Information on current practices has been obtained from a range of PCB manufacturers not only in the UK but also in North America and the rest of Europe. Potential recovery and recycling methodologies have been identified and the possibility of producing a fully recoverable/ recyclable process utilising a combination of new equipment and chemistry has been studied.
This project has been particularly pertinent because a related precursor project was undertaken several years back to address the similar problems experienced when the PCB industry used tin-lead based etch resists. In this case, a novel piece of equipment was developed that enabled the metals to be recovered from spent stripping solutions. However, with the arrival of the WEEE directive and with growing concerns over the use of lead in electronics generally, the PCB industry has largely switched to the use of pure tin as an etch resist. As the key novel technology of the earlier recovery equipment focussed on the recovery of lead and because no consideration was given to the possibility of recycling the acid from the spent strippers, the change-over to pure tin and the growing need to adopt a more sustainable approach has meant that there was a strong need to carry out the work undertaken in this study.
Led by Dr Charles Kerr of ITRI, the project has sought to identify sustainable technology approaches for end-of-life tin stripping solutions with particular emphasis being placed on the recovery and reuse of the materials that would normally be consigned to landfill. The publication date of this issue of Circuit World coincides with the completion of the project and a key part of the ongoing work is the dissemination of the findings. A detailed report is therefore being made freely available on request. It will also be posted on both the ITRI and Intellect Web sites. Finally, it is also anticipated that a technical paper covering the main activities of this project will be published in a forthcoming issue of Circuit World.
For further information or to request a copy of the report, please contact:Dr Charles Kerr at ITRI. E-mail: charles.kerr@tintechnology.comor visit the Tin Technology Web site: www.tintechnology.com
