This is a good question. In the past, I have processed boards with both gold and tin-lead deposits on the same boards through an alkaline etchant and a hydrogen peroxide sulfuric acid based etch. We never detected any staining or darkening of the gold. However, the extent of undercut on the copper/nickel/gold plated traces was significantly greater than on the tin-lead/copper traces. We can attribute that to the galvanic reaction, but do not know if that is the reason for gold staining. Best regards, Mike Carano > -----Original Message----- > From: doug smith [SMTP:[log in to unmask]] > Sent: Thursday, February 18, 1999 11:49 AM > To: [log in to unmask] > Subject: [TN] Galvanic reactions > > In PCB fabrication process SnPb is used as an etch resist. On some boards > gold is selectively plated, for example on a BGA pattern. In this case > both the SnPb and the Au are being used as the etch resist. > > The etch process removes unwanted copper leaving the plated circuits and > component lands. > > Can copper staining on gold be the result of a galvanic cell that is > formed when the nickel/gold and tin/lead are used as an etch resist? > > Doug Smith > Technical Support Engineer > Yamamoto Mfg. (USA), Inc. > > (408)944-8308 > [log in to unmask] > > ################################################################ > TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c > ################################################################ > To subscribe/unsubscribe, send a message to [log in to unmask] with > following text in the body: > To subscribe: SUBSCRIBE TechNet <your full name> > To unsubscribe: SIGNOFF TechNet > ################################################################ > Please visit IPC's web site (http://www.ipc.org) "On-Line Services" > section for additional information. > For technical support contact Hugo Scaramuzza at [log in to unmask] or > 847-509-9700 ext.312 > ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################