L-1520e
3rd Optical Inspection
Die Overcoat or Die Coating is the process of applying a pliant but moisture-resistive material over the surface of the die to minimize package stresses on the surface of the die and provide additional protection against corrosion.
Silicone materials are very effective for this purpose. Die coating may be selective or non-selective. Selective die coating, as the name implies, dispenses overcoat material on certain areas of the die only. Non-selective or full die coating covers the entire surface of the die with overcoat material.
The amount of overcoat material dispensed on the die surface must be precisely calculated, as excess overcoat material which rises above the ball bond may exert tremendous shearing stresses on the wire, resulting in neck breaks.