Big mistaken assumption: uncorrodable = no oxide formation Actually, the presence of a tough oxide film on the surface is what makes certain metals corrosion resistant. Virtually all metals form oxides in the presence of oxygen. It's the ability of that oxide film to "seal off the surface" from further corrosion that's key. Tim Reeves -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Sunday, May 25, 2003 9:15 PM Subject: Re: Sn-Ni PCB plating Happy, As I read your post, plating Gold, tin, tin-lead, silver, Pd, etc would be to provide a solderable surface, not to prevent oxides forming (since tin-nickel is uncorrodable, there should be no oxides, right?). Gold is not a finish that most people would want to solder to either as it causes solder embrittlement. The others are OK. Gold is normally only used to cover and protect another, solderable plated finish that DOES oxidise, but it's so thin that it doesn't impact on solder joint quality. I've not come across Gold as the material to actually solder to. Or have I missed a big something? Peter Happy Holden <[log in to unmask]> 23/05/2003 10:40 PM Sent by: TechNet <[log in to unmask]> Please respond to "TechNet E-Mail Forum."; Please respond to HTH To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: Re: [TN] Sn-Ni PCB plating Good question Jack, The property that makes it uncorrodable (a very thick-non porous oxide film) also makes it very difficult to solder. In the old days we could use an active acid flux but that is no longer true. The current non-clean type of flux would not even penetrate the oxide on a tin-nickel pad and it would end up non-wetted (not even de-wetted). Gold, tin, tin-lead, silver, Pd, etc all solder very nicely, so they need to be put over the tin-nickel to prevent the oxides from forming. The other factor is that the plating bath is difficult to control and you have to watch it to make sure it does not plate stressed. I once saw the traces 'jump' off the boards after etching, the tin-nickel was so stressed. But like I said, the sail boat metal parts are remarkable! Happy "Jack C. Olson" <[log in to unmask]> To: TechNet <[log in to unmask]> cc: [log in to unmask] 05/23/2003 09:32 AM Subject: Re: Sn-Ni PCB plating Ok, I'm probably showing my ignorance here, but with a stable non-corrodable finish like Sn-Ni, why do you need the gold? Jack (a PCB layout guy) --------------------------------------------------- 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 ----------------------------------------------------- [This e-mail is confidential and may also be privileged. If you are not the intended recipient, please delete it and notify us immediately; you should not copy or use it for any purpose, nor disclose its contents to any other person. Thank you.] --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------