Degradation studies of epoxy-coatings on printed circuit boards after pressure-cooker test

The present work focusses on the investigation of the degradation of screen-printed epoxy coatings on printed circuit board under multiple corrosion load realized by the pressure cooker test. Since methods like the common mechanical shear strength tests are destructive and limited in information, the authors´ approach used the Electrochemical impedance spectroscopy (EIS) to study the change of their electrochemical behavior and the state of degradation. Complementarily, the Fourier Transformed Infrared Spectroscopy (FTIR) was used to investigate possible molecular change of the polymer due to the exposition. The experiments were carried out after different time of load. It could be shown that the complex conditions of the pressure cooker test initiate a controversial mechanism. The harsh corrosion load already results in a degradation of the polymer after 8 h but simultaneously the enhanced test temperature leads to ongoing curing processes consuming the remaining parts of resin and curing agents. As a result, the degradation kinetic seems to be delayed and after the recommended test time (96 h) the epoxy are less degraded than it was expected based on the results after a shorter time exposition.