MIL-STD-883 Method 2030 C-SAM
Scanning acoustic microscopy is particularly useful for locating gaps and separations inside a package. As an ultrasonic pulse passes through the device, part of the signal is reflected whenever it encounters a change in acoustic impedance. The contrast becomes especially strong at a solid-to-air interface, which is why even a very thin delamination, potentially only a fraction of a micrometer thick, can produce a strong acoustic response. A void that may not appear in an X-ray image can therefore show clearly on the acoustic scan.
MatX Lab uses acoustic microscopy to examine packaged electronic devices, evaluate die-attach interfaces, and inspect assemblies used in commercial electronics and commercial space applications.
What C-Mode Acoustic Imaging Detects
Within Method 2030, the target is die attach. The method detects unbonded regions and voids in the die-attach material without destroying the device, making it usable as a screen rather than a sample-only test.
The technique responds to material and density changes, including voids, porosity, cracks, and delamination, at any interface the sound can reach.
Air gaps are the extreme case. Because the acoustic impedance mismatch between a solid and air is so large, the technique is sensitive to air features well below a micrometer in thickness, which puts it ahead of every other non-destructive option for finding ultrathin separations in multilayer packages.
Scan Modes
Three modes come out of the same data acquisition, and knowing which one produced an image matters when reading it.
A-scan is the raw waveform at a single point: an amplitude-versus-time trace showing every echo the pulse returned as it passed through the layers. It underpins depth gating and helps verify what a feature actually is.
B-scan assembles A-scans along a line into a vertical slice, giving a non-destructive cross-section through the package.
C-scan: This is the standard image in plan view. The system gates at the selected depth level, ignores the remaining sections of the scan lines, and displays either peak amplitude and polarity information or time-of-flight values. Polarity is important: a phase inversion indicates an interface between air and solid, as opposed to solid/solid.
Method 2030 Acceptance Criteria
The test places reject conditions on the die attach coverage as follows:
- a void of more than 15% of the contact area
- a void of more than 10% at the corners
- more than 70% of a quadrant detached
These three conditions represent different ways a bond can fail. A large void in the middle, a void at a corner that can create a high-stress region, and widespread disbonding over one quadrant may look very different, yet each can represent a serious failure. A percentage-of-area measurement alone may not capture the significance of the defect’s location.
No standard applies specifically to acoustic microscopy. For die-attach inspection, Method 2030 is the relevant document. For plastic-encapsulated components, the appropriate standard is the one that covers moisture sensitivity classification.
Frequency Selection Sets What You Can See
Transducer frequency trades resolution against penetration, and choosing it is the main setup decision.
| Transducer frequency | Feature resolution | Penetration |
| Lower frequency | Coarser | Reaches deep interfaces and thick substrates |
| Mid frequency | Moderate | General package and die attach work |
| Above 200 MHz | Features around 5 µm | Roughly 500 µm depth in silicon |
The choice of frequency depends upon both resolution and penetration. Higher frequencies make it easier to distinguish small objects, but signal intensity drops faster as it enters the material, reducing penetration. At low frequencies, signals penetrate deeper into the sample but offer less resolution. A 200 MHz frequency can resolve defects about 5 µm in size at depths of about 500 µm in silicon.
The appropriate transducer depends on the interface being examined. A die attach layer located beneath a relatively thick substrate may require a different transducer than delamination at the interface between the mould compound and the die surface.
Depth gating is what isolates the interface of interest. The system selects the portion of the returning waveform corresponding to a chosen depth, so a package with four interfaces produces four separate C-scans rather than one composite image.
Coupling, Preparation, and Where the Technique Fails
Air prevents the ultrasonic signal from reaching the package effectively, so the transducer needs a continuous coupling medium to carry the sound into the device. Most inspections use water for this purpose, either by immersing the package or by maintaining a water column between the transducer and the package surface. That makes water compatibility an important consideration when selecting samples for inspection. Devices that cannot tolerate water exposure must be adequately sealed, or the inspection has to be performed using an alternative dry-coupling arrangement.
There are also conditions that can limit what the acoustic scan can reveal. A delamination close to the package surface may reflect most of the incoming pulse at the air gap, preventing enough energy from reaching interfaces underneath it. A rough or uneven surface can scatter the signal before it enters the package and reduce the quality of the resulting image. Small packages and thin dies can present another problem when several interfaces are located very close together, since their echoes may overlap in time and become difficult to separate. Materials that strongly attenuate ultrasound can further reduce the inspection depth, and simply changing the operating frequency may not overcome that limitation.
The technique also shows where something is without saying what it is. A bright feature at the die attach interface can be a disbond, a void, or a crack, and separating those often requires cross-sectioning on a sacrificial device.
MIL-STD-883 Method 2030: Output and Reporting
For each device, the report includes C-scan images from the individual interfaces examined. The scans are separated by depth using the appropriate gates, and the transducer frequency used for each inspection is recorded.
Void content is stated as a percentage of the total available contact area and is also provided with the respective acceptance criteria for Method 2030. This is done separately for corner areas and quadrants, since different acceptance criteria may apply to these areas. The polarity of the acoustic signal is used sufficiently to indicate an air interface from the material interface, in which case it is clearly specified in the report.
Scan parameters accompany the images: transducer frequency, focal arrangement, gate settings, scan resolution, and coupling arrangement. Where a device was scanned before and after an environmental stress such as temperature cycling or reflow, the image pairs appear together, since the change between them is usually the finding.
MIL-STD-883 Method 2030 FAQs
Is the inspection non-destructive?
Absolutely. In fact, the machine remains intact during the scan, so all units can be examined instead of taking samples. Since the package will be placed in water or scanned using water coupling, the machine should endure this process.
Should I scan before and after reflow or cycling?
Yes, comparing the two conditions provides much more useful information than looking at the post-stress scan alone. The initial scan establishes what was already present so that you can identify any change after reflow or cycling directly. Without that baseline, a small void that existed before stressing may look identical to a void that developed during the test.