Galvanic corrosion behaviors of Cu connected to Au on a printed circuit board in ammonia solution

Abstract

During etching treatments of printed circuit board (PCB) with ammnioa solution, galvanic corrosion occurs between electrically connected gold and copper, and resulting in unexpected over-etching problems. Herein, we determine corrosion of galvanic coupled Cu to Au quantitatively in ammonia solutions, and evaluate factors influencing corrosion of galvanic coupled Cu to Au (i.e., area ratio of anode to cathode and stirring speed). The difference of the corrosion rate (Delta i = i(couple, (Cu-Au))-i(corr, Cu)) of Cu connected to Au (117 mu A/cm(2)) and of single Cu (86 mu A/cm(2)) infers the amount of over-etching of Cu resulting from galvanic corrosion in ammonia solution (Delta i = 0.31 mu A/cm(2)). As the stirring speed increases from 0 to 400 rpm, the corrosion rate of galvanic coupled Cu to Au increases from 36 to 191 mu A/cm(2). Furthermore, we confirm that an increase in the area ratio (Au/Cu) from 0.5 to 25 results in a higher rate of corrosion of Cu connected to Au. The corrosion rate of galvanic coupled Cu to Au is approximately 20 times higher when the area ratio of Au to Cu is 25 (1360 mu A/cm(2)) than when the ratio is 0.5 (67 mu A/cm(2)).