the Au-Sn phase diagram got two eutectic point, 10% Au and 80% Au. The 4% normally do not cause that much of problem if the Au is in the metallic format. jk > It's a misunderstanding, that intermetallics like AuSn or its sisters have > bad wetting. In fact, the surface energy of such intermetallics is > perfectly > matching Tin or Tin/Lead solder and the wetting is good. It's the > crystallographic structure, that decides whether there will be a > sufficiently strong joint or not. If large crystals or needles or disks > are > formed, mechanical forces have a tendency to concentrate along these > features, thus resulting in a weak and brittle joint. One of my friends, > dr > Becker, made a pioneer job in the 60s, calculating the famous 4% Au level, > which one has caused little of gold content paranoia. In his paper, he > points out, that it's not the 4%Au in itself, that is dangerous, but the > said macro crystal forming. I have presented such macro crystals, Werner > have the photos. > > Inge > > -----Ursprungligt meddelande----- > Från: TechNet [mailto:[log in to unmask]] För Bev Christian > Skickat: den 16 januari 2008 15:39 > Till: [log in to unmask] > Ämne: Re: [TN] Solderability of Tin-Gold Intermetallic > > Bingo! This is the type of answer I was looking for. Thx. > Bev > RIM > > ----- Original Message ----- > From: Wenger, George M. <[log in to unmask]> > To: Bev Christian; TechNet E-Mail Forum <[log in to unmask]> > Sent: Wed Jan 16 09:20:00 2008 > Subject: RE: [TN] Solderability of Tin-Gold Intermetallic > > Bev, > > I'm not sure I can give you a direct answer for tin but I can give you > an answer for SnPb solder. In the RF world there are lots of gold > plated components that can have very thick gold (>2.5um). Because of > solder joint reliability reliability concerns it has been standard > practice to pre-tin (expose to SnPb wave or use a double dip in to > solder pots) to dissolve most of the gold) and the resulting pre-tinned > surface does contain some gold. The amount of gold remaining in the > solder on the surface of the components is dependent on the quality of > the pr-tinning process. However, we've seen many surfaces of pre-tinned > components with up to at least 4% gold and have not seen any > solderability issues. > > > Regards, > George > George M. Wenger > Senior Principle FMA / Reliability Engineer > CommScope / Andrew Wireless Solutions > 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 > [log in to unmask] > > > -----Original Message----- > From: Bev Christian [mailto:[log in to unmask]] > Sent: Wednesday, January 16, 2008 9:04 AM > To: Wenger, George M.; TechNet E-Mail Forum > Subject: RE: [TN] Solderability of Tin-Gold Intermetallic > > George, > Correct of course. That is what I meant. How about my question? > Bev > RIM > > -----Original Message----- > From: Wenger, George M. [mailto:[log in to unmask]] > Sent: Wednesday, January 16, 2008 9:03 AM > To: TechNet E-Mail Forum; Bev Christian > Subject: RE: [TN] Solderability of Tin-Gold Intermetallic > > Bev, > I think I would re-state your first sentence. "We all know that > tin-copper intermetallic that has come to the surface and been exposed > to the environment has terrible solderability." I view tin-copper as > the glue layer between solder and copper when solder touches copper and > forms an intermetallic the solder above the intermetallic must wet it > otherwise it would fall off. > > > Regards, > George > George M. Wenger > Senior Principle FMA / Reliability Engineer CommScope / Andrew Wireless > Solutions 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 > [log in to unmask] > > > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian > Sent: Wednesday, January 16, 2008 8:52 AM > To: [log in to unmask] > Subject: [TN] Solderability of Tin-Gold Intermetallic > > Technetters, > We all know that the tin-copper intermetallic has terrible > solderability. I also know there are high melting tin-gold solders. My > question is: what is the solderability of surfaces of tin with small > amounts of gold (<4%) in it? As good as 100% tin, better, worse? If > worse, how much so? > Bev > RIM > > --------------------------------------------------------------------- > This transmission (including any attachments) may contain confidential > information, privileged material (including material protected by the > solicitor-client or other applicable privileges), or constitute > non-public information. Any use of this information by anyone other than > the intended recipient is prohibited. If you have received this > transmission in error, please immediately reply to the sender and delete > this information from your system. 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