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. 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