Good description Mark
If I recall properly, having available excess of both metals on the two
sides is important as well for purple plague to occur. (e.g. Al wire on thick
gold pads or Au wire on thick Al pads) The problem was manifest in some early
Al wire bonding when relatively thick gold wire bond pads, common for gold
wire thermocompression and thermosonic bonding were used "as is" for Al wedge
bonding. Gold bonding on thin Al pads is very common these days.
Joe
In a message dated 11/5/2008 3:09:33 P.M. Pacific Standard Time,
[log in to unmask] writes:
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 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, 80234
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roberts, Jon
Sent: Tuesday, November 04, 2008 3:39 PM
To: [log in to unmask]
Subject: [TN] AL CU DENDRTIES INSIDE PLASTIC IC
Has anyone have knowledge or experience with AL Cu Dendrites growth in
plastic IC components? Reports or other information is appreciated,
Thanks, Jon
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