What Can Acoustic Microscopy Do for You? Capabilities and Applications
What Is Acoustic Microscopy?
Acoustic microscopy — also called scanning acoustic microscopy (SAM) — uses focused ultrasonic waves at frequencies of 5 MHz to 2 GHz to image the internal structure of solid materials and components without physical sectioning or damage. At these high frequencies, the focused sound beam achieves imaging resolution approaching or exceeding optical microscopy — while providing the ability to detect subsurface features including cracks, delaminations, voids, and interface defects that are completely invisible to optical or X-ray methods.
SAM has become an indispensable tool in electronics failure analysis, materials characterisation, quality assurance of bonded assemblies, and medical device inspection.
How Acoustic Microscopy Works
A piezoelectric transducer generates a focused ultrasonic pulse that is directed through a coupling fluid (typically deionised water) into the specimen. The sound wave travels through the material and reflects from interfaces where acoustic impedance changes — including material surfaces, internal boundaries, cracks, voids, and delaminations. The reflected signals are recorded as a function of transducer position, generating a plan-view (C-scan) image of the internal structure at a defined depth.
The C-scan image displays signal amplitude or time-of-flight as a colour map — immediately revealing the location, shape, and extent of internal features without any physical preparation.
Key Capabilities of Acoustic Microscopy
Delamination Detection in IC Packages
SAM is the primary non-destructive method for detecting delaminations within integrated circuit plastic packages — separation at the die attach, mould compound-leadframe, and mould compound-die interfaces that cannot be detected by X-ray. Delaminations absorb acoustic energy (white/bright regions in amplitude images) or produce reflections at shifted time-of-flight — making them clearly visible in C-scan images.
JEDEC JESD22-A112 specifies SAM as the standard method for pre-conditioning moisture sensitivity level (MSL) inspection of IC packages — verifying absence of delamination before and after reflow simulation.
Void and Porosity Mapping in Solder and Die Attach
SAM quantitatively maps void content in solder joints, die attach adhesives, and sintered silver paste layers in power electronics packages. Void area fraction from SAM C-scan images directly correlates with thermal and electrical resistance of the attachment layer — a critical quality parameter for power device reliability.
IPC-7711 and IPC-A-610 specify maximum void percentages in solder joints; SAM provides the non-destructive measurement capability to verify compliance without cross-sectioning every joint.
Crack Detection in Ceramics and Advanced Materials
SAM detects internal cracks, pores, and microstructural anomalies in engineering ceramics, glass, composites, and bonded assemblies that are beyond the resolution or penetration depth of conventional UT methods.
Bond Line Integrity Inspection
Adhesively bonded assemblies — aerospace structural panels, laminated safety glass, medical device bonded housings — are inspected by SAM to verify bond line continuity, detect disbonds, and characterise adhesive void distribution.
Materials Characterisation
Beyond defect detection, high-frequency SAM measures local elastic properties — Young’s modulus, shear modulus — through analysis of acoustic wave velocity in the material. V(z) curve analysis extracts surface elastic parameters relevant to thin film and coating characterisation.
Frequency Selection for Acoustic Microscopy
The operating frequency determines the trade-off between depth penetration and spatial resolution:
- 5–50 MHz: Deeper penetration (5–50 mm), lower resolution — for thick components, PCBs, and composite panels
- 50–200 MHz: Intermediate — for IC package internal inspection, bonded assemblies, fine ceramics
- 200 MHz–2 GHz: Highest resolution (<10 µm), very shallow penetration (<0.5 mm) — for thin film characterisation, surface acoustic wave devices
Industrial Applications
In electronics manufacturing, SAM is used for 100% production screening of high-reliability IC packages (automotive, military, medical) for delamination and void defects. In aerospace, bonded honeycomb and composite panel SAM inspection verifies adhesive bond quality. In the medical device industry, SAM characterises implant surface condition and verifies bonded joint integrity.
Why Choose Infinita Lab for Acoustic Microscopy Services?
Infinita Lab provides scanning acoustic microscopy — C-scan, B-scan, and through-transmission imaging — for electronics, composites, ceramics, and bonded assemblies through our nationwide accredited materials characterisation laboratory network.
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 to learn more about our services and how we can support you.
Frequently Asked Questions (FAQs)
What is a C-scan image in acoustic microscopy and what information does it provide? A C-scan (plan view) image displays the reflected acoustic signal amplitude or time-of-flight as a colour map across the scanned area at a defined depth or gate. Areas with high reflection (delaminations, voids) appear as bright or distinctly coloured regions against the background. C-scan images immediately reveal the location, shape, and extent of internal features in the full plan view of the component.
What is the difference between acoustic microscopy and conventional ultrasonic testing? Conventional UT uses 0.5–25 MHz unfocused or lightly focused beams for large-area inspection of welds and thick sections. Acoustic microscopy uses tightly focused beams at 5 MHz–2 GHz with microscope-quality resolution for imaging fine internal features in small components, IC packages, and thin sections at sub-millimetre resolution.
How are void percentages quantified from SAM C-scan images? Image analysis software applies threshold intensity segmentation to the C-scan image — distinguishing void regions (high-amplitude reflection from air-solid interface) from bonded regions (lower-amplitude transmission signal). The void pixel area is divided by the total joint area and expressed as void percentage — compared against acceptance specifications (typically <25% for solder joints per IPC-A-610).
Can SAM inspect through the back side of an IC package (backside imaging)? Yes. Backside SAM (BSAM) images the package from the silicon die side rather than the moulding compound side — providing better image quality for die attach and bump inspection because the acoustic path through silicon has lower attenuation than through the moulding compound. BSAM requires package decapping or thinning in some configurations.
What specimen preparation is required for acoustic microscopy? Most acoustic microscopy is performed without any specimen preparation — the component is simply immersed in the water coupling bath or examined in a water jet system. For high-frequency (>500 MHz) characterisation requiring very smooth surfaces, light polishing may be needed to reduce surface scattering. No sectioning, coating, or chemical preparation is required for standard defect detection applications.
