Acoustic Micro Imaging (SAM/SAT) — Principles, Applications & Benefits
What Is Acoustic Micro Imaging?
Acoustic Micro Imaging (AMI) — also referred to as Scanning Acoustic Microscopy (SAM) or Scanning Acoustic Tomography (SAT) — is a high-resolution non-destructive technique that uses focused ultrasonic waves to image internal structures and detect defects within electronic packages, semiconductor assemblies, and materials without causing any damage. It is uniquely capable of detecting delaminations, voids, cracks, and disbonds at internal interfaces that are completely invisible to optical, X-ray, or surface inspection methods.
AMI is indispensable in the semiconductor, electronics, aerospace, and medical device industries for package qualification, failure analysis, and incoming inspection of assembled electronic components.
Principles of Acoustic Micro Imaging
Pulse-Echo Mode (C-SAM)
In C-mode SAM (C-SAM), a focused transducer emits short ultrasonic pulses (5–300 MHz) into the sample immersed in deionized water (acoustic coupling medium). The pulse reflects from internal interfaces — boundaries between materials with different acoustic impedances. A delamination or void reflects nearly all incident acoustic energy (bright white or black indication depending on polarity convention), while well-bonded interfaces transmit energy with minimal reflection.
The transducer rasters across the sample in an XY grid, building a two-dimensional amplitude map (C-scan) at a selected depth by time-gating the return signal. Multiple gates produce images at different depths, enabling layer-by-layer examination of complex multilayer packages.
Transmission Mode (THRU-SAM)
In transmission mode, the transducer and receiver are on opposite sides of the sample. Defects attenuate transmission; through-holes and complete delaminations show as complete signal loss. Used for rapid screening of large-format samples including PCBs and ceramic substrates.
Time-of-Flight (TOF) Imaging
TOF mapping measures the arrival time of reflections from a selected interface rather than amplitude, producing a depth map that reveals warpage, tilt, and thickness variations with sub-micron depth resolution. Critical for solder ball coplanarity and package warpage characterization in surface-mount technology.
Defects Detected by AMI
- Delaminations at die-attach, molding compound-leadframe, and substrate-molding compound interfaces
- Voids in solder joints, underfill, die-attach adhesive, and encapsulant
- Cracks in silicon die, ceramic substrates, and solder interconnects
- Disbonds in adhesive layers and laminated substrates
- Moisture-induced damage (popcorning) in moisture-sensitive packages after reflow simulation
Industry Applications
Semiconductor manufacturers use C-SAM for 100% lot screening of flip-chip BGA packages, power modules, and MEMS devices before shipment. Automotive electronics suppliers perform AMI qualification of ECUs and power converters per AEC-Q100 requirements. Aerospace avionics manufacturers use SAT for inspection of multi-chip modules and RF assemblies. Medical device companies inspect implantable electronics and sensor assemblies for void-free encapsulation.
Conclusion
Acoustic Micro Imaging (SAM/SAT) is a highly effective non-destructive evaluation technique used to detect internal defects such as voids, cracks, and delamination within materials and electronic components. By utilizing high-frequency ultrasonic waves, it provides detailed internal images without damaging the sample. This method is essential for quality assurance, failure analysis, and reliability testing, ensuring the integrity and performance of critical components across industries.
Why Choose Infinita Lab for Acoustic Micro Imaging?
With Infinita Lab, you are guaranteed a Nationwide Network of Accredited Laboratories, the best consultants from around the world, convenient sample pick-up and delivery, and fast turnaround time. Our team understands the stakes of every AMI inspection — from failure analysis to qualification testing.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090. [Request a Quote]
Frequently Asked Questions
What frequency range is used in acoustic micro imaging? Frequencies from 5 MHz (deep penetration, lower resolution) to 300 MHz (shallow penetration, sub-micron resolution) are used depending on sample thickness and required defect resolution. Most semiconductor package inspection uses 15–75 MHz transducers.
What is the difference between SAM and SAT? SAM (Scanning Acoustic Microscopy) typically refers to laboratory-grade instruments used for high-resolution failure analysis. SAT (Scanning Acoustic Tomography) often implies production-oriented systems with automated part handling optimized for throughput. Both use the same physical principles.
Why is deionized water used as the coupling medium in AMI? Water provides acoustic impedance coupling between the transducer and sample without introducing contaminants. Deionized water is specified to prevent ionic contamination of electronic components. Isopropanol or specialized coupling fluids are used for moisture-sensitive devices.
Can AMI detect defects inside silicon die? Yes. High-frequency transducers (100–300 MHz) can image defects within silicon including subsurface cracks, voids in through-silicon vias (TSVs), and delaminations at metal-dielectric interfaces, though depth penetration is limited to a few hundred microns.
What JEDEC standards reference acoustic micro imaging? JEDEC JESD22-B111 (board-level drop test), JESD22-A113 (preconditioning for moisture/reflow sensitivity), and JESD47 (stress-test-driven qualification) all reference acoustic micro imaging as the verification method for detecting delamination and cracking after stress tests.
