Bev,
We are all in this together. But I understand where you are coming from
(in being somewhat vague). I sure don't have a problem with it.
To quote Mr. Snoid:
Dem Commy spies are everywhere......
http://www.crumbproducts.com/comics.html
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: Friday, January 18, 2008 7:44 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
I am sorry I was confusing everyone, but I was being vague on purpose. I
started asking the questions on Technet without approval (and still
don't have it because I did not ask), but I get such good stuff out of
my participation, that I have thrown caution to the wind and have done
everything but name the company of the part, which I will NEVER do.
Dave and others,
There is little gold on the surface of the BGA balls before reflow.
More after. I have to go and ask my people HOW MUCH now that you and
Inge tell me that this AuSn IMC can indeed oxidize. This is what I did
not know. THANK YOU!
And that Thank you is for all Technetters - for either your answers or
for not telling me I am dumb for asking.
Bev
RIM
________________________________
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Friday, January 18, 2008 8:35 AM
To: TechNet E-Mail Forum; Bev Christian
Cc: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Hi Bev - I am just as confused on your exact conditions as everyone else
(at least I'm in good company) but I am starting to understand. If you
have AuSn IMC phase exposed on the surface of the solderball prior to
the soldering operation, then you will have little chance of achieving
wetting because the AuSn IMC will oxidize. It would take a really active
flux chemistry to make the AuSn IMC wettable again. As Inge described, a
fair amount of Au/Sn solder processes is conducted using a hydrogen
reducing reflow atmosphere instead of traditional fluxes because of this
issue. As George and other have mentioned, it would be really really
strange to have Au/Sn IMC platelets sticking out of an area array
solderball prior to soldering - are sure that the IMC platelets are
Au/Sn? Did you check to see if they are Ag/Sn? That would make more
sense.
Dave
Bev Christian <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
01/18/2008 07:24 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to Bev Christian
<[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold Intermetallic
Inge,
See my comments below in BOLD. I am not yelling at you. :) Bev RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Friday, January 18, 2008 4:45 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Finally, you disclosed what you really wanted to know. You pried off
BGAs and found unusual amount of AuSn platetlets on the surface of the
balls.
CORRECT - ON THE SURFACE OF THE BALLS.
This is my opinion: If the wetting on AuSn formations is good or not is
not the first thing you ought to think of. When you say the 'surface', I
anticipate that you mean the part of the ball THAT WAS SOLDERED TO THE
BOARD PADS.
NO! HOW CAN THAT BE THE SURFACE OF A BALL? I AM TALKING ABOUT THE
UNSOLDERED BALL "RESTING" AS A "HEAD" ON THE "PILLOW" OF THE REFLOWED
SOLDER PASTE.
If THAT surface has lots of AuSn formations, then I understand how the
BGAs could be pried off = probably too much gold from the ENIG pads =
something wrong in the soldering process. IF the solder joints were
normal, you would have a real problem to get the BGAs off the board,
because healthy solder joints are enormously strong.
As to your question, whether the solder wets to AuSn intermetallics, I
think all is depending on what atmosphere you had during the IMC
formation. AuSns are, as you know, not chemical bonds, but alloys with
its gold phases and its tin phases. Now, if the tin phases are not
oxidized, then you ought to get good wetting, and vice versa. In
practice, I think that there is a high risk of AuSn oxidation, that's
why you do AuSn soldering of RF details in vacuum or inert atmosphere.
THIS LAST SENTENCE IS VERY INTERESTING.
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bev Christian
Sent: den 17 januari 2008 16:42
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Bingo! There is the crux of it. I am not talking about joints already
made, I am talking about TRYING to MAKE joints.
I hope I don't get in trouble for this.
My original, vague question was because of - head in pillow. Inge
guessed correctly.
I don't mean to be rude, but we already have a very extensive fishbone
for this, so please don't come back with the usual reasons. They are
being addressed, trust me.
What I am exploring is whether unusual amounts of gold tin
intermetallics on the surface of the solder balls pried off of boards
that show head in pillow did not solder because of these materials.
Bev
RIM
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Thursday, January 17, 2008 10:36 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Hi All,
We know that Cu6Sn5 is non-solderable after oxidation. However, I do not
know whether we really KNOW that it is solderable prior to that, and we
know even less about the solderability of AuSn4, Ag3Sn, or for that
matter Sn3Ni4.
Werner
**************
Start the year off right. Easy ways to stay in shape.
http://body.aol.com/fitness/winter-exercise?NCID=aolcmp00300000002489
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