Ultrasonic Microscopy (SAM) is fundamentally critical in the semiconductor packaging and testing industry, with core applications spanning the following areas:

I. Non-Destructive Detection of Packaging Defects

A. Delamination Defect Recognition

• Principle: By analyzing the acoustic reflection signal differences at various material interfaces (e.g., chip-to-substrate, molding compound-to-metal lead), USM precisely detects delamination within packaging structures.
• Significance: This prevents reliability issues stemming from thermal stress or manufacturing defects.
• Typical Scenarios: Delamination at the molding compound-chip interface or adhesive failure in multi-layer stacked packages.

B. Bonding and Welding Quality Assessment

• Inspection Targets: Detecting voids, cold solder joints, and cracks in bonding layers (e.g., wire bonds/copper pillars) and solder joints (e.g., BGA solder balls).
• Goal: Ensuring the electrical connection integrity and stability of the assembly.
• Case Study: Batch NDT detection of electrical terminal welding defects (e.g., classifying non-conforming when void ratio exceeds 5%).

C. Internal Structure Integrity Analysis

• Method: Utilizing through-transmission C-Scan mode, USM performs layer-by-layer tomography on the 3D internal structure of the package (e.g., internal cracks within the die, air bubbles in the molding compound).
• Output: Quantification of defect area and distribution density.

II. Process Optimization and Quality Control (QC)

A. Packaging Material Characterization

• Parameter Evaluation: Assessing process parameters such as the curing uniformity of encapsulant materials or the thickness deviation of substrate copper foil.
• Guidance: Providing actionable feedback for improving overall packaging processes.
• Example: Quick screening for curing defects (bubbles, cracks) in epoxy resin-encapsulated chips.

B. Failure Analysis Support

• Process: Performing non-destructive internal imaging on failed devices.
• Goal: Locating the failure point (e.g., solder joint fracture, delamination extension) and significantly reducing the cycle time for root cause analysis.
• Typical Use: Analyzing the failure root cause of high-power IGBT modules.

C. Adaptation for Advanced Packaging Technologies

• Support Scope: Supporting the internal defect inspection for complex structures like 2.5D/3D integration and System-in-Package ($\text{SiP}$).
• Industry Trend: Keeping pace with the high-density integration demands of modern semiconductor packaging.

III. Technical Advantages and Industry Value

• Non-Destructive Testing (NDT): Eliminates the need for damaging destructive tests (such as tensile testing or cross-sectioning), making it suitable for mass production QC.
• High Resolution & Multi-Layer Scanning: The C-Scan mode can achieve micron-level resolution (e.g., using 500 MHz probes), enabling layer-by-layer imaging of multi-material stacks.
• Efficiency and Cost Optimization: Replaces manual visual inspection and parts of X-ray inspection, drastically increasing inspection speed and yield control capabilities.

IV. Key Application Case Studies

• Wafer-Level Packaging (WLP) Inspection: Verification of Through-Silicon Via (TSV) structural integrity.
• Power Device Inspection: Statistical analysis of void ratios and thermal performance evaluation in IGBT module bonding layers.
• Memory Chip Analysis: Screening for layer-to-layer defects in 3D NAND flash memory stacks.

Conclusion: Owing to its high sensitivity, non-destructive nature, and 3D imaging capabilities, USM has become a critical tool in the semiconductor packaging sector, playing a vital role in enhancing product reliability and elevating process control standards.