Corrosion in Semiconductor Die and Package

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Corrosion in Die and Package (Page 2 of 2)

Lead/Leadframe Corrosion

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.

Fig 3. SEM photos of corroded areas on contaminated die pads of various leadframes

Wire Corrosion

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.

Fig 4. SEM photo of a corroded aluminum wire and wedge bond

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Failure Analysis; Basic FA Flows; Reliability Models

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