Rework Method for Conformal Coating

Abstract

The research was implemented for the ABB Distribution Solutions -division. The protection relay production has received a module of cards with the addition of a varnish-like, protective conformal coating layer to prevent unwanted alarms and trips at substations. The thesis investigates the possibility of repairing and testing the conformal-coated cards. The aim is to find the best possible working method to remove the conformal coating from the card so that the cards can be retested. It will also be investigated whether broken cards can be repaired and how recoating is successful. The study was aided by a few different IPC standards for the conformal coating and circuit board repairs, as well as a manual based on them, including conformal coating suppliers' own articles on the use of conformal coating and their various properties. The methods proposed by the suppliers for removing the conformal coating were also carefully examined. The practical part of removing the conformal coating is largely focused on finding the necessary test points, as well as removing the conformal coating itself from the cards. The guidelines of the IPC standards were used to replace the components, as well as the experiences of the production quality team in replacing the components. The best possible conformal coating removal method among the conformal coating removal methods used was found in the research, as well as an estimate of the time taken to remove the conformal coating. Difficulties in removing the conformal coating and the importance of occupational safety were also observed during the work. The replacement of the components went better than expected and the conformal coating on the feet of the components came off more easily than on the card itself. Potential developments for conformal coating removal methods were found, as well. The study also identified opportunities to extend the varnished card repair method to other products in the Relion family.