Sustainable Technologies for the Regeneration of Acidic Tin Stripping Solutions used in PCB Fabrication

SUMMARYElectroplated tin deposits are used as etch resists during the processing of Printed Circuit Boards (PCB). The tin coating protects the copper tracks during etching but is subsequently removed (stripped), to expose the defined copper circuitry. The commonly used stripping solutions are based on nitric acid and after use they represent a very acidic waste product with a high metal content. The disposal of these spent strippers is typically via offsite neutralisation and precipitation followed by subsequent landfill. This is clearly a non-sustainable waste of valuable resources and a practice that is increasingly undesirable as environmental legislation becomes more stringent. This paper outlines the results of a scoping study carried out into current industry practices for tin- stripping and details components of a potential integrated treatment system for these stripping solutions. Individual technologies for such an integrated system incorporate the recovery of the tin oxide by filtration, the concentration and re-use of nitric acid solutions by diffusion dialysis and the reclamation of other metals, i.e., copper by electrowinning.