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. 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