Hi Jon,
Email your pictures to Steve Gregory at [log in to unmask] and
he will post them for you. If you ever meet Steve you owe him a beer.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon
Sent: Friday, November 07, 2008 10:06 AM
To: [log in to unmask]
Subject: Re: [TN] FW: [TN] AL CU DENDRTIES INSIDE PLASTIC IC
I appreciate all the responses and please continue. Anyone have the
knowledge where I can post the pictures for all of you to see?
I have enclosed an edited version to protect lab and component
manufacture. Let me know if you can read the document and see the
photos.
Thanks again for all the inputs, Jon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Woolley, Mark D.
(Mark)
Sent: Friday, November 07, 2008 9:39 AM
To: [log in to unmask]
Subject: Re: [TN] FW: [TN] AL CU DENDRTIES INSIDE PLASTIC IC
Corrosion of the aluminum conductors within the device which can lead to
dendrite formation as opposed to purple plague can be driven by moisture
that is captured within the device and phosphorous that is used in the
glass passivation over the IC to make it spread more easily. Together,
they form phosphoric acid which corrodes aluminum quite well. Other
contaminants need not be present, but will accelerate the corrosion
process if present. This was a big issue with "canned" devices because
all moisture had to be excluded from the can prior to hermetically
sealing it. The problem was reduced with the plastic encapsulation
because the plastic is molded around the IC and bondwires at
temperatures higher than the boiling point of water. So most vapor is
excluded during the molding process.
Historically, the amount of phosphorous in the glass has not been well
controlled and an excess amount in the glass will damage the component
within. Early ICs carried their own destruction mechanism! Perhaps
control has gotten better in recent years. I have been out of touch for
a while with this aspect of failures.
mark
Mark Woolley
PTRL Laboratory
Avaya, 1300 West 120th Ave, Area 33, Westminster, CO, 80234
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Syed Ahmad
Sent: Thursday, November 06, 2008 2:41 PM
To: [log in to unmask]
Subject: Re: [TN] FW: [TN] AL CU DENDRTIES INSIDE PLASTIC IC
Purple plague at the Au/Al interface would be aided by moisture and
contaminants like halides, Sb, etc., sometimes part of the molding
compound as flame retardants.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
(EHCOE)
Sent: Thursday, November 06, 2008 7:44 AM
To: [log in to unmask]
Subject: [TN] FW: [TN] AL CU DENDRTIES INSIDE PLASTIC IC
Subject: Re: [TN] AL CU DENDRTIES INSIDE PLASTIC IC
Purple plague is an intermetallic alloy that is formed at the junction
of the Aluminum pad where the Gold bondwire is bonded. But this is not
a dendrite, it is a "Barny"cle.
Dewey
It is a multi-crystalline growth that appears as a dark or
purple ring around the ball of the gold bondwire. Typically dendrites,
which will grow within a contaminated plastic IC, do not contain gold.
All it takes is the aluminum, moisture, and an electric field.
In the past purple plague has been generally caused by high temperature
whether or not the IC is powered. It usually causes an open circuit
(eventually) due to Kirkendahl voiding at the interface. With today's
very closely pitched bonding pads the purple plague growth may be able
to bridge between two adjacent bonding pads.
But again, this is not a dendrite. Dendrites need an electric field to
induce growth, purple plague occurs in the absence of an electric field.
It occurs at some rate continuously, but at normal operating
temperatures grows so slowly that it is not considered a primary factor
in calculating the lifetime of an IC.
mark
Mark Woolley
PTRL Laboratory
Avaya, 1300 West 120th Ave, Area 33, Westminster, CO, 8023
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