I recently ran a few test assemblies (with immersion Ag finish, of course) through thermal cycling (for 2nd level reliability). At the end of the test, some of the non-soldered metal area (EMI contact) got the yellow tarnish. When probed with a multimeter I measured significant increase in contact resistance. I read a lot of comments on the presence of sulfur and chlorine (or their ionic counterparts) as being the possible root cause. My question is: what is the chemical reaction(s) here? Are those agents attacking the Ag or the organic co-deposited with the Ag? Does anybody know what the yellow stuff is? Mason Hu --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------