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 --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------