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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