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January 2008

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Subject:
From:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Fri, 18 Jan 2008 10:16:30 -0500
Content-Type:
text/plain
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text/plain (341 lines)
Many many years ago when I first started working in the

Bev,



Many many years ago when I first started working in the

electronic/soldering area and attending conferences and listening to

papers being presented I realized that 1). either I was as smart as

those giving the presentations or 2). those giving the presentations

were as dumb as I was and it really didn't matter if 1). or 2). were

true.  



From our interactions on TN and IPC I can say with confidence that you

are as smart as or as dumb as the rest of us and it really doesn't

matter.





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: Friday, January 18, 2008 8:44 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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