ESD - RF Cafe Forums
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Post subject: ESD Posted: Thu Aug 31, 2006 4:44 am
Joined: Tue Apr 25, 2006 2:01 am
An on-chip integrated TTL driver that we designed for a six bit phase
shifter appears prone to ESD issues. After on-wafer testing or after
assembly operations, certain bits in a previously working phase shifter
fail to turn on. Inspection under a microscope usually reveals a burnt
out device or fused transmission lines (at places where one metal layer
crosses over another, the separating dielectric is 0.15 microns thick
with a dielectric constant of 6.65) in the driver. As I stated earlier,
we suspect ESD; we have been careful to take the necessary precautions
such as wearing anti-static clothing and wrist straps when handling
the chips but the problems persist. I was wondering if there might be
other potential reliability issues that I was'nt aware off. I would
also like to hear from you on ESD protection circuitry that we could
ESDPosted: Thu Aug 31, 2006 7:14 am
Fri Feb 17, 2006 12:07 pm
Location: London UK
have read over the last year in the electronic press a lot of reports
of chip and circuit failures due to decreasing use of, or even elimination
of, lead for soldering, and an increased use of tin.
encounter solution of one metal into another that eventually "corrodes"
one track away.
Another problem is, with increasing presence
of tin, there is a crystalline growth in metallic tin that can track
across from one conductor to another. It is called "tin tree". Check
The intrinsic impedance of TTL is usually considered
so low that one can forget about ESD effects under normal lab or assembly
Post subject: Re:ESDPosted:
Thu Aug 31, 2006 7:57 am
Joined: Tue Apr 25,
2006 2:01 am
Thanks Nubbage for your reply. By 'TTL
driver' I actually meant to say that our on-chip driver accepts a TTL
input (0V/5V) and converts it to the voltage levels (-2.5V/+0.5V) needed
to switch the pHEMTs in the phase shifter. The driver was designed using
0.5 micron gate length pHEMTs and schottky diodes.
Post subject: ESDPosted: Thu Aug 31, 2006 9:31 am
Joined: Fri Feb 17, 2006 12:07 pm
Location: London UK
I had a lot of trouble with punch-through
failure of Schottky diodes in the presence of fast ie short rise-time
pulses in a radar system with PIN switches followed by Schottky diode
detectors (Agilent 2800 types). We ultimately traced the problem to
the presence of high current narrow pulse circulation on the ground-planes.
The diodes were lasting about 30 minutes to 2 hours, then failing due
The product never made it through the next phase
of re-design, as the division closed shortly afterwards.
only experience I can offer is that Schottky technology is not as robust
as the manufacturers would like us to believe, especially when diodes
are in the presence of transient pulses, or I guess static discharge,
which is a similar phenomenon.
subject: Posted: Sat Sep 02, 2006 12:41 am
Wed Jun 21, 2006 8:33 pm
Location: Queen Creek, Arizona
Your first question is correct, can you verify that
this is a true ESD issue.
My question for you is this:
you find the metal track fusing, do you also find a burned out device?
From your comments, it appears the metal track fusing is the more common
failure. But this is important as there are very few cases of ESD failure
due to metal only, metal failures as a result of ESD/EOS related issues
are almost always accompanied first by device burn-out/failures that
then conduct so much current at such high power densities that we see
Metal track and ILD breakdowns are almost always
the strongest link in the ESD currrent path, and the last parts to fail,
assuming proper diligence was designed into the ESD architecture (obviously
esd currents can not be expected to flow through a 1 um wide signal
Now, if you have device burnout, and it is located directly
under or near your melting metal tracks, or especially if it is part
of the ESD current paths, then this could likely be a result of ESD/EOS
events as the secondary effects of temperature and high currents passing
through or nearby your node could create this problem. But I again stress
that it is very unlikely that this track is your primary ESD failure.
If you are seeing only this track shorting, unaccompanied by failed
devices, the corrosion theory suggested by Nubbage would be a more likely
candidate, or maybe an electromigration issue. Another issue could be
antenna effects from processing and early testing, if the tracks failing
are high impedance nodes with no leakage paths. (essentially an EOS
I am going to end this, as further comments are even
more prone to speculation at this point, but to better answer your question
of wether it is ESD, more info must be shared regarding the types of
failure you are seeing, and what are the relationships of failing nodes
to bond pads and ESD current paths. (are the tracks part of the IO,
power busses, or internal signals with no direct relationship or connectivty
to bond pads, etc).
I hope this helps,
CMOS RF and Analog ESD Specialist!