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January 2008

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From:
Joyce Koo <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Wed, 16 Jan 2008 13:56:47 -0500
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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
>
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