:-)
As long as everyone knows I am pulling your leg - and getting back at
Mr. Hillman for telling I live in the 51st state!
Bev
________________________________
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Friday, January 18, 2008 10:07 AM
To: Bev Christian; TechNet E-Mail Forum
Subject: RE: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Bev,
In my case it's not "THERE YOU AMERICANS GO AGAIN" it's "THERE YOU OLD
GUYS GO AGAIN". After 65 years of using inches I'm having a difficult
time thinking in centimeters but I'm still can do conversions. My
apology, I should have said "10 to 13 mils (254 to 330 microns)"
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: Friday, January 18, 2008 8:37 AM
To: TechNet E-Mail Forum; Wenger, George M.
Subject: RE: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
Sigh. My replies below, again in BOLD.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: Friday, January 18, 2008 7:25 AM
To: [log in to unmask]
Subject: Re: [TN] SV: [TN] SV: [TN] Solderability of Tin-Gold
Intermetallic
I usually like to respond with answers not questions but un Bev,
I usually like to respond with answers not questions but until I
understand an issue it is hard to respond with answers. Your question
is still vague to me. Although you said that you are talking about
trying to make joints and not talking about joints already made, you
also said that what you are 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
intermetallics. I view Head-in-a-Pillow solder joints as joints that
have not wet for some reason.
WELL I GUESS THIS IS A CASE OF SEMANTICS. I DON'T CONSIDER THAT A JOINT
WAS EVER MADE. If I HAD BEEN TALKING ABOUT A FRACTURE BECAUSE OF HIGH
AMOUNTS OF GOLD in A SOLDER JOINT, ok, BUT THERE WAS NO METALLURIGICAL
BOND EVER MADE IN THE CASES I AM DISCUSSING.
If that is the case then I assume the
gold-tin intermetallics you are talking about are from the materials in
the BGA and not from the surface finish on your board. I'm having
difficulty believing that there is enough gold in under-bump
metallization to cause a gold-tin intermetallic issues.
TRUTHFULLY SO AM I, BUT WE ARE EXPLORING ALL AVENUES.
You indicated
that you used XRF to measure the gold concentration on samples that you
pried off. Ingemar anticipated that you meant the part of the ball that
was soldered to the board pads.
NO. I MEANT THE BALL OF THE PART.
However, from the way you worded your
inquiry I can't tell if you meant you looked at the board pad or the BGA
ball.
THE LATTER.
I assumed, maybe incorrectly, that you looked at the surface of the
ball after peeling the BGA off.
CORRECT, AFTER PEELING OFF THE BGA. WE MEASURED 1.28 +/- 0.15% [Au]
If that is the case then I would
assume that you should be able to take a non-soldered BGA and measure
the gold in a BGA ball CORRECT AND GOT 0.86 +/- 0.8% [Au]
and then put the BGA though a reflow process without any solder paste
and re-measure the ball after reflow to see if the gold concentration
changed.
ON THE LIST OF THINGS TO DO.
I'm assuming that you're talking about small size uBGA's with ball
diameters in the 10 to 13 mil range.
THERE YOU AMERICANS GO AGAIN. I KEEP TELLING YOU THE METRIC SYSTEM IS
NOT A COMMIE PLOT. :) THE BALL DIAMETERS ARE 300 MICRONS.
Since
the XRF penetration depth is typically between 1 and 2 mils you'll be
analyzing the gold in the top surface of the ball. I assume that if you
don't see a high gold concentration in the un-reflowed solder ball that
the gold-tin intermetallics you see after the reflow process migrated to
the surface of the ball during the cooling process. If that is the case
they probably aren't the reason for the Head-in-a-Pillow soldering
defects.
THAT'S WHAT ONE WOULD THINK. HOWEVER IF THE DIFFERENT BGA NEXT DOOR
SOLDERS PERFECTLY, YOU LOOK AT ALTERANTIVES.
MAN, THE E-MAILS ARE COMING FASTER THAN I CAN ANSWER... AND I DO HAVE A
JOB - OTHER THAN TECHNETTING. :)
Regards,
George
George M. Wenger
CommScope / Andrew Wireless Solutions
Senior Principal FMA / Reliability Engineer 40 Technology Drive, Warren,
NJ 07059
(908) 546-4531 [Office] (732) 309-8964 [Cell] -----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. 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. 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.
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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