 |
|||||||
|
Corrosion in Die and Package (Page 2 of 2)
Lead
corrosion, as the name implies, refers to the corrosion of the lead
itself. Lead corrosion is often due to inadequate lead finish, the
presence of contaminants on the leads, and exposure of the leads to
excessive moisture. It can
be accelerated by higher temperatures and the presence of electrical
bias on the leads.
Leadframe corrosion refers to the corrosion of any part of the leadframe. Although this mechanism becomes more critical if it occurs on the silver-plated areas (die pad where the die is set and the bonding fingers) of the leadframe, corrosion on any part of the leadframe must be rejected because the contaminants in the corroded area can easily spread in the presence of moisture.
The most frequently encountered contaminants in fresh leadframes are chlorine, phosphorus, sulfur, and potassium. Newly-delivered leadframes from suppliers must undergo strict incoming quality screening for contaminants/foreign materials to minimize the risk of internal corrosion in semiconductor products.
Corrosion of the bond wires within a package can also occur, gross cases of which can lead to wire breaking or even total disintegration of the wire. This mechanism is more commonly encountered in aluminum wires that have been contaminated by chlorine, although rare cases involving gold wires have also be observed.
In the case of gold wires, delaminated areas around the wire can act as conduit of Cl-contaminated moisture that can expose the entire length of the wire to Cl and make it vulnerable to massive corrosion. Other contaminants that accelerate gold wire corrosion include bromide, iodide, and cyanide ions.
See Also:
Oxidation/Reduction Potential Values; Package
Failures; Die Failures;
Copyright © 2004-2005 www.SiliconFarEast.com. All Rights Reserved. |
