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April 2005

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Subject:
From:
"Ingemar Hernefjord (KC/EMW)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ingemar Hernefjord (KC/EMW)
Date:
Mon, 11 Apr 2005 08:40:32 +0200
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Hi Ed,
does not look like electro migration. More like typical EOS damage. The spheres are typical for a short circuit with high temperature that melts both substrate and metallisation. Standing wave not likely, if you don't have a application in the 50-100 GHz region. To make a 'tele'diagnosis is impossible, I can just lean to associations with similar things I've seen. 

You need tell us more, if it's a FET or a bipolar, power range, metallisation system, applied biasing etc.

 Now, we saw something similar years ago with PA chips. 1st metal was ordinary Ti-system,followed by Cr and finally the normal TiAu/Au. The Cr oxidized, and caused damage to the fingers and, to make long story short, the FET channel changed from high to lower resistivity, the idle current increased, the temperature increased, more current, higher current caused gold migration and finally, the whole active area was blown. Remedy: the wafer manufacturer removed Cr, and since that we have had no problems. 

As analysis of damaged semiconductors is oftenly very complicated, I recommend you to cooperate with the semi maker. If it's a renowned and good company, you will get professional help and save time, at least if it is a US fab. If you have to deal with a far East supplier, you will also get assistance, but it will take a lot more time.

Ingemar Hernefjord
Ericsson Microwave Systems

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]
Sent: den 8 april 2005 23:47
To: [log in to unmask]
Subject: [TN] RF Power Transistor Failure


Hi all,

Please see the link below.  Any input as to what might cause
the periodic pattern of damage seen on the base contact fingers
would be sincerely appreciated.

http://www.semlab.com/RF-Power-Transistor.doc


Thanks,

Ed Hare
SEM Lab, Inc.

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