Package Etching
Destructive failure analysis procedures use concentrated acids to selectively dissolve polymer encapsulation material from microelectronic assemblies. Heated fuming nitric acid or sulfuric acid exposes the underlying silicon die, bond wires, and leadframe without damaging metallic interconnects. Performing chemical decapsulation exposes silicon dies to reveal microcracks and EOS damage during counterfeit verification.
The process requires precise temperature control and acid volume regulation to avoid etching aluminum bond pads or gold wires. Chemical removal applies to epoxy-encapsulated semiconductor packages and cannot be used on ceramic or hermetic metal cans.
Corrosion Mechanism
Acid blends target the resin binder while leaving inorganic fillers like silica suspended in liquid waste. Automated decapsulation equipment dispenses small acid doses directly onto the package surface while maintaining temperatures between sixty and one hundred degrees Celsius. Controlled exposure through chemical decapsulation preserves fragile internal structures for scanning electron microscopy and optical evaluation.
Over-exposure causes wire bond degradation and copper leadframe pitting, which invalidates subsequent physical analysis. Etch timing depends on epoxy cross-link density and mold compound thickness.
Failure Boundary
Physical grinding or laser ablation often precedes chemical exposure to reduce acid volume and exposure duration. Excess heat generated during chemical etching can alter latent electrical defects in silicon structures. Analysis results become inconclusive if the chemical reaction oxidizes silicon surface layers.
