Presentation slides for the ISTFA 2024 Tutorial session “Non-Destructive Defect Localization by Acoustic Microscopy.”

The Aerospace and Defense (A&D) markets are starting to use plastic packages more significantly for Space and Military ruggedized applications. But plastic packages are also inherently less reliable than ceramic devices for A&D applications. The key to the successful use of plastic devices in A&D application is to qualify the devices for the intended application using industry accepted plastic encapsulated microcircuit (PEM) qualification techniques. This paper briefly recaps the test techniques known to be effective in assessing plastic part reliability. But more importantly, it presents actual PEM qualification data gathered over the last 15 years involving over 400 individual PEM Qual lots. The paper also shows the failures modes associated with plastic packages and Cu bond wires. SEM, X-Ray, and Acoustic Microscope images were obtained for the failure modes associated with plastic packages and Cu bond wire.

Nondestructive observation of domain structure of ferroelectrics, dynamic behavior under external field and related phenomena is becoming significant. As a nondestructive and subsurface characterizing technique, the authors developed acoustic microscopy based on a commercial scanning probe microscope for direct observation of local ferroelectricity, elasticity and defects on several inorganic functional materials, transparent PLZT ceramics, relax-based PMN-PT crystal and lead-free bismuth titanate ceramics without any special processing (polishing or etching) to the sample. The direct observation is particularly useful and convenient for analyzing ferroelectrics/semiconductor integrated material and devices. The excitation frequency is in the range of several kHz to decades of kHz, which is much lower than that of the traditional acoustic imaging techniques. But several applications of scanning probe acoustic microscope (SPAM) involving ferroelectric samples with the resolution of 10nm were obtained. The expanding scope of application for SPAM shows exciting possibilities for non-destructive analyses in the microelectrics industry.

The acquisition of reliable Acoustic Micro Images (AMI) are an essential non-destructive step in the Failure Analysis (FA) of electronic packages. Advanced packaging and new IC materials present challenges to the collection of reliable AMI signals. The AMI is complicated due to new technologies that utilize an increasing number of interfaces in ICs and packages. We present two case studies in which it is necessary to decipher the acoustic echoes from the signals generated by the interface of interest in order to acquire trustworthy information about the IC package.

Die stacking package technology continues to become the trend of manufacturing integrated circuits (IC) today. This primary design offers smaller and thinner packages that would optimize board space and assembly cost. Consequently, this packaging technology has posed challenges in conducting failure analysis. Nondestructive techniques like acoustic microscopy are bound for advancement to make them feasible for use in this packaging technology. This paper will present frequency domain imaging in the field of acoustic microscopy as applied in the detection of delamination defect on a stacked die package. Fast Fourier Transform (FFT) was used as an algorithm to reconstruct and reveal the delamination defect which was not clearly detected in time domain imaging of the package. Frequency domain imaging was found to offer a better image contrast of delamination. This gives the failure analyst another approach to characterize the location and extent of delamination defect, a set of information that is substantial in the root cause analysis of adhesion related failures in stacked die packages.

Acoustic Micro Imaging (AMI) is an established nondestructive technique for evaluation of electronic packages. Non-destructive evaluation of electronic packages is often a critical first step in the Failure Analysis (FA) process of semiconductor devices [1]. The molding compound to die surface interface of the Plastic Ball Grid Array (PBGA) and Plastic Quad Flat Pack (PQFP) packages is an important interface to acquire for the FA process. Occasionally, with these packages, the standard acoustic microscopy technique fails to identify defects at the molding compound to die surface interface. The hard to identify defects are found at the edge of the die next to the bond pads or under the bonds wires. This paper will present a technique, Backside Acoustic Micro Imaging (BAMI) analysis, which can better resolve the molding compound to die surface interface at the die edge by sending the acoustic signal through the backside of the PBGA and PQFP packages.

Acoustic Micro Imaging (AMI) has been used for years to evaluate microelectronic packages for the presence of internal defects. The drive in micro electronic packaging is to reduce the size of the components as much as possible to keep pace with the shrinking size of the end products. This leads to smaller/thinner packages with internal features and possibly defects that are approaching the resolution limits for conventional AMI. Recently AMI has been combined with Fourier transforms of the acoustic signal to produce frequency domain images. Previously features that were at or below the accepted resolution limits for a given frequency were not detected in the time domain images, however these features are revealed in the frequency domain images.

A broadband model is proposed to describe the nature of ultrasonic pulses in multilayered systems with a sub-wavelength thickness layer. This model, which is targeted towards acoustic microscopy of microelectronic devices, can incorporate measured ultrasonic properties of electronic materials and predict the complete ultrasonic pulse-train for all the interfaces in an electronic device. The model is robust, and incorporates material and geometric variables commonly encountered in microelectronics applications. Results are presented to illustrate how delaminations and cracks with foreign material or moisture ingress can appear to be well-bonded and why acoustic images of interfaces with thin layers can sometimes give erroneous indications of the bond state.

Micro-Electrical Mechanical Systems (MEMS) is an emerging technology with demonstrated potential for a wide range of applications including sensors and actuators for medical, industrial, consumer, military, automotive and instrumentation products. Failure analysis (FA) of MEMS is critically needed for the successful design, fabrication, performance analysis and reliability assurance of this new technology. Many devices have been examined using techniques developed for integrated circuit analysis, including optical inspection, scanning laser microscopy (SLM), scanning electron microscopy (SEM), focused ion beam (FIB) techniques, atomic force microscopy (AFM), infrared (lR) microscopy, light emission (LE) microscopy, acoustic microscopy and acoustic emission analysis. For example, the FIB was used to microsection microengines that developed poor performance characteristics. Subsequent SEM analysis clearly demonstrated the absence of wear on gear, hub, and pin joint bearing surfaces, contrary to expectations. Another example involved the use of infrared microscopy for thermal analysis of operating microengines. Hot spots were located, which did not involve the gear or hub, but indicated contact between comb structures which drive microengines. Voltage contrast imaging proved useful on static and operating MEMS in both the SEM and the FIB and identified electrostatic clamping as a potentially significant contributor to failure mechanisms in microengines. This work describes MEMS devices, FA techniques, failure modes, and examples of FA of MEMS.