High-Frequency Acoustic Imaging Using Adhesive-Free Polymer Transducer

The piezoelectric polymer PVDF and its copolymers have a long history as transducer materials for medical and biological applications. An efficient use of these polymers can potentially both lower the production cost and offer an environment-friendly alternative for medical transducers which today is dominated by piezoelectric ceramics containing lead. The main goal of the current work has been to compare the image quality of a low-cost in-house transducers made from the copolymer P(VDF-TrFE) to a commercial PVDF transducer. Several test objects were explored with the transducers used in a scanning acoustic microscope, including a human articular cartilage sample, a coin surface, and an etched metal film with fine line structures. To evaluate the image quality, C- and B-scan images were obtained from the recorded time series, and compared in terms of resolution, SNR, point-spread function, and depth imaging capability. The investigation is believed to provide useful information about both the strengths and limitations of low-cost polymer transducers.

Critical Insights in the Application of Convection and Pressure Curing in Eliminating DAF Voids

The absent of reliable production controls for Die Attach Film (DAF) voids detection allowed defect escapee for Ball Grid Array (BGA) devices using non-conductive film material leading to gross assembly rejection and customer complaints. This paper presents the evaluation of pressure curing as an alternative to the convection curing in die attach process with additional capability to eliminate the DAF voids on non-conductive films. Through Analysis of Variance (ANOVA) analysis, green peeling test, Scanning Acoustic Microscope (SAM), cross section analysis and reliability test performed between samples arrives to the conclusion that pressure oven has a significant impact in die shear strength improvement and DAF voids elimination with positive response in reliability requirement. The result of the study improves the assembly flow and production control of BGA devices through the transition of convection to pressure curing technology.

The Reference Phase Correction for the Fluctuated Scanning Lines and the Slope of the Stage in Tissue Characterization by Scanning Acoustic Microscope

In this study, a new approach was investigated to extract reference phases from the scanning acoustic microscope to calculate the speed of sound when dealing with the slope of the stage and fluctuation of the scanning lines. To capture the slope and the fluctuation pattern, data of the first lines along the horizontal and vertical axes on the stage were used. A corrective function was then utilized to improve the accuracy of reference phase extraction. The method was then corroborated by demonstrating tumor discrimination in mice skin by means of scanning acoustic microscopy (SAM). B16-F10 melanoma cells were used to grow the tumor. Hematoxylin and eosin (H&E) staining was applied for histology characterization of the sample. A comparison of both acoustics and histology was conducted. Phase analysis was performed to examine the effects of both slope and fluctuation. The results showed that our approach significantly improved the tumor detection and accuracy of scanning acoustic microscopy.