I studied that report as well, naturally) and saw the problem as one of
there being too much solder.
The excess had to go somewhere, so it ran out and unfortunately by the
well known law touched some Au bonding wires. An immediate fault I would
have thought, and not dependant on the basis formulation of the solder.
The fact that the solder was indium wasn't really the problem. For
example had it been a tin based material in excess arguably the tin
would most probably have chewed its way through the gold bonding wires
around 10x faster than the indium giving a rather more immediate failure
than the 36 days they did in fact get. The failure mode then would most
likely have been an open circuit rather than a short, but the original
fault would have been the same.
Regards
Mike Fenner,
Apps Engineer
Indium Corporation
T: + 44 1908 580 400
M: + 44 7810 526 317
F: + 44 1908 580 411
E: [log in to unmask]
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Pb-free: www.Pb-Free.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Edwin Louis
Sent: Monday, October 13, 2003 2:31 PM
To: [log in to unmask]
Subject: Re: [TN] Flip Chip Diode 0205
NASA Goddard just came out with a warning about Indium and Gold. Some
Laser Diodes failed in space. Evidently in manufacturing some Indium had
melted and flowed around bonded Gold wires. The Indium reacted with the
Gold to form AuIn2 which has 4 times the volume of the starting
ingredients. The intermetallic has a popcorn type of texture anbd is
very brittle. This is, however, a situation where the Indium has
virtually an infinite supply of Gold and the Indium has a very fast rate
of diffusion into the Gold. They indicated that the same observations
were made with Lead/Indium solder.The conditions may be different with
Gold plating and Lead/Indium solder, where the Gold plating is not too
thick. In that case, the Indium is in excess over the Gold and the Lead
buffers the Indium/Gold areas.
-----Original Message-----
From: Dave Chapman [mailto:[log in to unmask]]
Sent: Thursday, October 09, 2003 11:47 AM
To: [log in to unmask]
Subject: Re: [TN] Flip Chip Diode 0205
Spec on component says use solder which does not scavenge gold such as
Indalloy #2, or conductive epoxy or low temp solder preform. Also says
cannot withstand 200 C for more than 10 seconds. Dave C.
-----Original Message-----
From: Werner Engelmaier [mailto:[log in to unmask]]
Sent: Thursday, October 09, 2003 10:27 AM
To: [log in to unmask]
Subject: Re: [TN] Flip Chip Diode 0205
Hi Dave,
You are not clear as to what "cannot go through Sn-Pb due to
embrittlement" means. Preforms, as well as Sipad are also Sn-Pb. I have
no experience with conductive epoxies, but know that they are not as
good as solder from a reliability perspective.
Werner Engelmaier
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