Meaning
Acoustic impedance differences allow for the non destructive detection of internal air gaps and cracks in semiconductor packages. Technicians utilize scanning acoustic microscopy inspection to find delamination or voids that are invisible to X-ray or visual checks. Differences in the acoustic impedance of materials allow the software to create a detailed map of the internal structure.
Acoustic Physics
Transducers emitting frequencies between 5 and 400 megahertz provide the resolution needed to see tiny gaps inside a semiconductor package. During scanning acoustic microscopy inspection, the sound wave travels through the material until it hits an air gap or a change in density. Air is an excellent reflector of ultrasound, which causes a high amplitude signal whenever a void or delamination is encountered.
The time it takes for the echo to return determines the depth of the feature within the sample. Water serves as the necessary coupling medium to transmit the high frequency waves from the probe to the component surface.
Defect Discovery
Separations between the mold compound and the silicon die or the lead frame are the most common issues found by this method. If scanning acoustic microscopy inspection reveals marked delamination, the component is likely to fail during the high temperatures of the solder reflow process. Internal cracks in ceramic capacitors or voids in the die attach material also appear clearly in the acoustic images.
Operational Integration
Routine use of this technology in Chinese high tech manufacturing zones supports the production of automotive and aerospace electronics. While it takes longer than X-ray inspection, the ability to see interface gaps makes scanning acoustic microscopy inspection indispensable for high reliability builds. Test reports generated by the system are often required as part of the production part approval process.
Historical data from acoustic scans provide proof of internal integrity during regulatory inspections.
