Interface Separation
Material failures occurring at the boundary between a semiconductor chip’s metallic mounting pad and the surrounding plastic molding compound compromise the mechanical and thermal integrity of the package. The occurrence of die paddle delamination represents a critical defect where the epoxy compound peels away from the metal lead frame. It creates micro-gaps that degrade thermal transfer and allow moisture to accumulate next to the silicon die.
This defect often originates from surface contamination or inadequate surface roughness on the metal frame before molding.
Moisture Release
Sudden expansion of trapped moisture within plastic electronic packages during high-temperature reflow soldering causes internal fracturing and blistering. This mechanism, closely related to die paddle delamination, leads to the popcorn effect as vapor pressure builds up and violently separates the plastic from the copper paddle. It results in sheared bond wires, cracked silicon, and complete component failure.
To prevent this occurrence, surface mount components are baked and stored in dry-pack bags with desiccant prior to assembly on the board.
Stress Concentration
Mechanical stress generated by mismatched thermal expansion coefficients between molding compounds and metal paddles causes interface cracks to propagate. The package is subjected to cycles of heating and cooling which slowly widen the detached zone. It terminates the operating life of the device by letting moisture reach the active circuitry.
