Influence of the chemicals used in Nickel and Copper plating solutions on the adhesion of screen-printed silver contacts
The present work deals with the attack of different chemicals used in nickel and copper plating electrolytes, on screen printed silver front side contacts, which lowers the adhesion and hinders industrial implementation. Dipping tests with four different self-made pastes in isolated electrolyte compounds show the dissolution of silver for pastes with glass content and acidic exposure conditions in chemical trace analysis (ICP-OES) of the dip solution. These results can be correlated to the macroscopic contact adhesion, measured with quantitative peel force tests. The results show that there is a link between the amount of silver that is found in the dipping solutions after the exposure of the contacts, the measured contact adhesion, and the presence of glass in the contact. The reaction between glass and silver during the firing process forms an oxidation layer between silver and glass which provides good adhesion. This interface seems to be dissolved by acidic plating chemicals. An additional SEM investigation shows the failure mechanism to take place exactly between the glass that covers the wafer after the firing process and the silver bulk, indicating a chemical attack at this interface.