Scanning Acoustic Microscopy (SAM)
Scanning Acoustic Microscopy (SAM) is a technique used for the analysis of Flip-Chip Ball Grid Array (FCBGA) packages. It utilizes high-frequency sound waves to image and inspects the internal structure and integrity of the FCBGA. SAM can identify defects like voids, delamination, cracks, and solder joint quality, enabling thorough quality control and failure analysis in FCBGA packages.
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Scanning Acoustic Microscopy (SAM)
- Overview
- Scope, Applications, and Benefits
- Test Process
- Specifications
- Instrumentation
- Results and Deliverables
Scanning Acoustic Microscopy (SAM) Overview
Scanning acoustic microscopy (SAM) uses focused ultrasonic waves to image internal features of a material or component without sectioning or destroying it. A transducer generates pulses of ultrasound in the megahertz to gigahertz frequency range, which are focused into the material by a lens. At each interface where acoustic impedance changes – such as a delamination, void, crack, or disbond – a portion of the ultrasonic energy reflects back to the transducer. The timing and amplitude of those reflections are captured as the beam scans across the part, building a two-dimensional acoustic image of internal structure.
SAM operates in two principal modes. Pulse-echo mode captures reflections from within the material and is used to image subsurface features at specific depths. Through-transmission mode measures the attenuation of ultrasound passing through the full thickness and is used to assess overall bond integrity across large areas. The choice of operating frequency involves a trade-off between resolution and depth penetration – higher frequencies (above 100 MHz) resolve finer features but penetrate only shallow depths, while lower frequencies (5 to 50 MHz) image deeper features at lower spatial resolution.
SAM is extensively used in the electronics industry to inspect flip-chip packages, ball grid arrays, wire bond assemblies, and multi-layer ceramic capacitors for internal delaminations and voids that cannot be detected externally. It is also applied to bonded metal and composite structures, adhesive joints, and ceramic and polymer components where internal quality must be verified without destructive sectioning.
Scanning Acoustic Microscopy (SAM) Scope, Applications, and Benefits
Scope
SAM applies to any material or assembly where internal features – voids, delaminations, disbonds, cracks, or inclusions – must be detected without destructive preparation. The technique is particularly well-suited for materials that transmit ultrasound, including polymers, metals, ceramics, and composites, as well as multi-layer assemblies. Key evaluation areas include:
- Detection of internal delaminations, voids, and disbonds
- Assessment of die attach and underfill integrity in electronic packages
- Characterization of adhesive bond quality in structural assemblies
- Identification of internal cracks and inclusions in monolithic materials
- Measurement of layer thickness and coating uniformity in multi-layer structures
- Comparison of bond integrity before and after thermal or mechanical stress
Applications
- Electronic package inspection (flip-chip, BGA, QFN, CSP)
- Ceramic capacitor and electronic component quality verification
- Adhesive bond integrity assessment in aerospace and automotive structures
- Composite panel delamination detection
- Semiconductor wafer and die attach quality inspection
- Medical device and implant internal integrity evaluation
Benefits
- Non-destructive – full component integrity preserved after inspection
- Images internal features invisible to optical or X-ray examination
- Locates delaminations and voids with precise spatial coordinates
- Applicable to opaque materials where optical methods cannot penetrate
- Allows 100 percent inspection of production components without sampling
- Time-of-flight data enables depth profiling of internal features
Scanning Acoustic Microscopy (SAM) Process
Specimen Setup and Coupling
The component is immersed in deionized water or coupled to the transducer using a water jet.
1Scan Configuration
Scan area, step size, and gating parameters are configured. Gates define the depth range of interest for pulse-echo imaging.
2Acoustic Imaging
The transducer scans the component and C-scan images are generated showing the amplitude or time-of-flight of reflections
3Image Analysis and Reporting
Acoustic images are analyzed to identify and characterize internal anomalies.
4Scanning Acoustic Microscopy (SAM) Technical Specifications
| Parameter | Details |
|---|---|
| Technique | Scanning acoustic microscopy |
| Operating Modes | Pulse-echo (C-scan), through-transmission |
| Frequency Range | 5 MHz to 300 MHz (application dependent) |
| Coupling Medium | Deionized water (immersion or water jet) |
| Applicable Materials | Polymers, metals, ceramics, composites, electronic packages |
| Detectable Features | Voids, delaminations, disbonds, cracks, inclusions |
Instrumentation Used for Scanning Acoustic Microscopy (SAM)
- Scanning acoustic microscope with motorized X-Y stage
- Focused transducers in the required frequency range
- Pulser-receiver and time-of-flight measurement electronics
- Deionized water immersion tank or water jet coupling system
- C-scan imaging software with amplitude and time-of-flight display
- Reference standards with known internal features for calibration
Scanning Acoustic Microscopy (SAM) Results and Deliverables
- C-scan acoustic images of the inspected component
- Identification and dimensional characterization of internal anomalies
- Depth location of detected features from time-of-flight data
- Pass/fail assessment against defined acceptance criteria
- Overlay maps correlating acoustic features with component geometry
- Quality assurance documentation
Frequently Asked Questions
SAM is highly effective for detecting internal defects such as delamination, voids, cracks, non-bonds, and moisture-related damage within electronic packages and composite materials without damaging the sample.
Yes. SAM uses high-frequency ultrasonic waves to inspect internal structures, allowing defects to be identified while keeping the sample intact for further testing or analysis.
SAM is widely used for semiconductor packages, PCBs, ICs, MEMS devices, power electronics, and bonded assemblies where hidden internal defects may affect performance or reliability.
Yes. While X-ray is excellent for identifying density variations, SAM can reveal interface-related issues such as delamination and poor bonding that may not be apparent in radiographic images.
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