Meaning
Non-destructive ultrasonic testing evaluates internal physical boundaries within encapsulated semiconductor assemblies without causing mechanical damage. A c sam inspection focuses high-frequency acoustic waves through a water medium onto microelectronic packages to capture reflections from internal material interfaces. Variations in acoustic impedance between mold compound and silicon dies reveal delamination or internal voiding.
The technique isolates specific depth planes through electronic time-gating, producing two-dimensional acoustic images of targeted internal layers.
Acoustic Reflection
Transducers emitting signals between ten megahertz and two hundred megahertz generate ultrasonic pulses that penetrate polymer and metallic media. In c sam inspection, interfaces containing air gaps reflect nearly one hundred percent of the acoustic energy back to the receiver due to severe impedance mismatches. Phase inversion in the returning waveform confirms the presence of sub-micron gaps between epoxy mold compounds and silicon dies.
Defect Resolution
Spatial resolution depends on acoustic frequency and lens focal length within the coupling fluid. Ultra-high frequency transducers resolve interfacial gaps down to several hundred nanometers across thin chip scale packages. High acoustic attenuation in thick encapsulants requires lower frequencies, trading spatial resolution for signal penetration depth.
Package Screening
Automated acoustic scanning detects post-reflow delamination during batch quality control in semiconductor assembly facilities. Standardized rejection criteria based on total delaminated area protect downstream manufacturing lines from latent thermal failure risks.
