SAT Ultrasonic Scanning Microscope
Scanning Acoustic Tomography (SAT)also known asSAM (Scanning Acoustic Microscope)It is a non-destructive imaging technology that uses high-frequency ultrasound to penetrate solid materials and reconstruct the internal structure of the sample based on acoustic reflection and scattering characteristics. In the fields of electronic packaging, semiconductors, thermal conductive materials, resin composites, and module reliability analysis, SAT is one of the most important interface inspection tools, particularly suitable for detecting "internal defects" that are difficult to identify with the naked eye and optical microscopes.
SAT uses ultrasonic frequencies above 20 kHz, while semiconductor-grade probes typically range from 15 to 230 MHz; the higher the frequency, the better the resolution, but the penetration depth decreases. Therefore, probes need to be selected professionally based on packaging thickness, resin type, and structural material. The medium for SAT is "pure water" as the acoustic wave transmission medium, which can effectively enhance acoustic coupling, allowing ultrasonic waves to enter the interior of resin, silicon, metal, or multilayer packaging with minimal loss, and reflect signals based on differences in acoustic impedance. Finally, the signals are reconstructed into A-scan, B-scan, C-scan, S-image, or 3D imaging through the machine software.
MA-tek has two advanced SAT devices, Hitachi FS300II and Sonoscan GEN6, which can meet the multi-layer interface analysis needs from general packaging, BGA, QFN to high-power modules, MEMS, and advanced materials.
- High frequency bandwidth probe (15–230 MHz):The probe frequency ranges from 15 to 230 MHz, allowing for the selection of different probes based on material characteristics, package thickness, and structural requirements, optimizing the choice between penetration and resolution. High-frequency probes can identify extremely fine interface defects, while low-frequency probes can detect products with thicker packages or more material layers, achieving the best balance between imaging penetration depth and resolution.
ultrasonic frequency Characteristics Scope of application 15–30 MHz strong penetration power Thick packaging, resin body, power module 30–100 MHz Balance between resolution and penetration power Most IC packages / PCBs 100–230 MHz High resolution, able to distinguish subtle defects WLP, MEMS, Microelectronics - High-speed scanning (up to 1000 mm/s):The high-speed scanning capability supports the inspection of a large number of samples, improving the efficiency of quality control for mass production. At the same time, it maintains positioning accuracy, making the interpretation of internal defects in packaging more reliable.
- High depth resolution (0.5 μm):MA-tek's SAT system has a high resolution of 0.5 μm, which can accurately distinguish the differences between adjacent layer interfaces, such as uneven adhesion of DAF (Die Attach Film), underfill cracks, and tiny voids within encapsulant resin.
- Multi-mode imaging capability:SAT has various scanning modes that allow the same sample to be fully analyzed from different angles. Through multi-mode integration, engineers can quickly interpret defect depth, interface anomaly locations, and subsequent quality conditions, significantly improving problem localization efficiency. At the same time, they can choose the most suitable measurement method based on material characteristics and defect types, ensuring that the analysis results are more accurate and reliable.
Scanning modes Features A-scan (single point waveform scan) Display the echo time and intensity at a single location, providing interface depth and reflection characteristic data. B-scan (Profile Scan) The side view section presented along the straight line direction clearly determines the depth of the defect location on the Z-axis. C-scan (planar scan) The 2D defect distribution at a specific depth is the most commonly used mode for packaging quality inspection. S-image (multi-layer image overlay) Integrate images of different depths for analyzing the differences in multi-layer interfaces of packaging structures. T-scan (transmission scan) Receiving sound waves from the other side is suitable for checking the overall material transmittance and large area defects. 3D Acoustic Imaging Integrate the multilayer scanning results into a three-dimensional structure for visualizing the crack trajectory, delamination range, and internal geometric characteristics of the material.
- Ultrasonic transmission and acoustic impedance differences:The core principle of SAT comes from the differences in "acoustic impedance". When ultrasonic waves pass from a water medium into different materials, such as silicon grains, metals, resins, air, adhesives, and ceramics, each material has a different acoustic impedance, resulting in varying reflection intensities. The greater the difference in acoustic impedance (for example: resin vs. air), the stronger the reflection. Therefore, SAT is particularly sensitive to "voids, delaminations, and cracks."
- Depth Profiling:After the ultrasonic emission, different echo signals will be generated according to the density and elasticity of the material interfaces. By calculating the time delay (Time of Flight), reflection intensity (Amplitude), and scattering pattern (Scattering Profile), the interfaces at different depths within the package can be reconstructed into a three-dimensional image. Through continuous depth scanning, the bonding status between the resin, grains, solder, and packaging structure can be checked layer by layer.
- High-frequency ultrasound and resolution:The frequency range of SAT probes generally covers 15–230 MHz, with low frequencies having stronger penetration, suitable for thick packaging; high frequencies provide higher resolution, capable of identifying small interface anomalies.SAT can detect encapsulated molded packages with a thickness greater than 4 mm.and can also identify subtle delamination structures in advanced packaging, suitable for large BGA, QFN, and Power modules.
SAT ultrasonic scanning microscope is commonly used to detect various hidden defects inside packages, such as delamination, voids, cracks, fractures, resin non-uniformity, and bonding anomalies, especially those interface issues that are difficult to capture with X-ray or optical methods. As IC packaging evolves towards thinner, larger, multi-layer stacking, and composite integration, SAT has become the standard analytical tool for verifying encapsulation quality, die attachment, interface integrity, and multi-layer structural reliability.
In package structure analysis, SAT can clearly identify issues such as package crack, delamination, die crack, void in resin, poor contact in fill holes, and uneven die attach with high-contrast imaging. Its high sensitivity is sufficient to reveal air gaps in extremely thin dielectric layers and tiny voids in metal fill holes, and it can assess the interface condition in resin packages after lead-free solder ball reflow.
In power modules, power components, and ceramic composite packaging, SAT is irreplaceable for the detection of metal/ceramic interfaces, heat dissipation material bonding layers, and silver paste connections. Ultrasound can penetrate resin, ceramics, and multilayer materials, presenting internal interface changes with high sensitivity, providing important evidence for process improvement, packaging optimization, and reliability analysis.
