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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