Victor 1) All plating systems have the aim of maintaining a surface with oxide layers that can be easily removed during the soldering operation. For that reason copper has to be kept protected from oxygen. One plating is nickel- gold. There are two problems associated with this system: - Nickel forms a very stable oxide layer - Gold reacts fast with copper even at room temperature and forms intermetallic layers that are not solderable. This means, you are protecting the copper with gold but you need a barrier layer of nickel between the gold and the copper. 2) There is no necessity to use gold when you plate copper with a tin- alloy. The flux of the solder materials is designed to break down the tin oxide. Besides, gold dissolver very fast in tin and a gold plating would be eaten away during the tin plating process 3) Actually I am not aware of a reason for that. One reason might be to prevent the formation of tin-copper intermetallics during the plating process. Another reason could be that the copper surface was originally nickel- gold plated and re-tinned later on. Best regards Guenter EMPA Swiss Federal Institute for Materials Testing and Research Centre for Reliability Guenter Grossmann, Senior Engineer 8600 Duebendorf Switzerland Phone: xx41 1 823 4279 Fax : xx41 1823 4054 mail: [log in to unmask] --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e 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 or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/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 ---------------------------------------------------------------------------------