The picture of bond 22 is the only picture where I see a loop. The lead-in angle for the loop looks pretty high. I suspect all of the failed bonds have similar angles.
Aluminum is great for ultrasonic welding but it is very brittle, so it is hard to get everything right. The brittleness manifests itself in heel cracks at the first bond, which is what you show here. The high lead-in indicates that the wire was likely worked pretty hard during loop formation. Furthermore, the intact bond looks like a crack has started.
The pictures show several other noteworthy items/contributors:
-The tails are all extremely even. This, and the lack of a visible back radius nick in the wire loop, suggests a "clamp tear" style bonder instead of "table tear" (used for deep access tools). These tails are even despite what looks like a lot of material deformation during the tail formation process. Also, the position of the wires on the pads are very precise. So I think the bonder itself and operator must be pretty high quality.
-The tails are way too short for my taste. I like to see at least 1 wire diameter of tail (you have about half that). All of the techs who develop programs can't resist cranking that tail down as low as it will go to show off what a great machine they have. But if you think about the danger in significant changes to the weld dynamics when the loop gets too short, you'll conclude a bit of tail is a very good thing.
-The wire deformation at the bond site is a bit on the high side. This is a big contributor to the heel cracks mentioned above.
To fix the problem, have your operator try to get a bit less first bond deformation and design a loop profile which doesn't stress the wire as much. If that doesn't get the job done, then you may have the wrong radii on your bonding tool, or you are trying to force the wrong loop into the aluminum. Also, as I indicated above, bring the tails out to 1 wire diameter so we're not trying to weld in the work hardened zone.
Wayne Thayer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mumtaz Bora
Sent: Friday, November 12, 2010 9:15 PM
To: [log in to unmask]
Subject: [TN] Wire Bond Pull failures
Hello TechNetters,
I have some wirebonds on a Hi -Rel package that pulled below 2.0 gm
minimum per Mil -Std -883. I have taken some SEM images of failed and
good bonds. Customer has a concern with plane of fracture of the failed
bonds even though it is break at "neck" . . It is Aluminum wire/to
Aluminum bond pad wedge bonded ultrasonically and aluminum wire to gold
plated post also bonded ultrasonic. Wire pull is post seal. I have
uploaded the file of images on the TechNet groupsite .I will appreciate
some feedback from wirebonding experts on the forum.
http://ipc-technet.groupsite.com/main/summary
<http://ipc-technet.groupsite.com/main/summary>
Thank-you, Mumtaz
Mumtaz Bora
Senior Packaging Engineer
Peregrine Semiconductor
9380 Carroll Park Drive
San Diego, CA 92121
858-795-0112-direct
858-731-9499 -fax
[log in to unmask]
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