Clean contact surfaces on the lead frame are essential to ensure reliable contacting of the die with the lead frame. Even the slightest organic contamination reduces the quality of the aluminum-to-copper bonds. It will not be possible to generate enough heat to melt the wire, so the resulting bond will be a cold one.
Cleaning of the lead frames before wire-bonding, either by low-pressure plasma or by Openair-Plasma®, removes organic contaminants effectively and reliably.
The quality of ultrasonic friction welding is particularly improved by this cleaning process.