Characterization of the Damping Behavior of Thin Films With Dynamic Mechanic Analysis in Bending Mode

Usually damped structures, consisting of a constrained layer damping (CLD) and free layer damping (FLD) design, are characterized via dynamic mechanic analysis (DMA) in bending mode. Since laminates with thicknesses from 10 to 100 μm exhibit a very low bending stiffness it isn’t possible to determine their damping properties in bending mode with standard DMA setups. Therefore in the present work the main objective was to introduce a new method to overcome this drawback. Two main geometries were used, such as a variation of the bending mode where the laminates were clamped at the outer supports and on the other hand a set-up where the geometry of a support of loudspeakers was replicated, which was called “speaker” mode. The damping behavior of the laminates then was characterized via the mechanical loss factor tan δ and subsequently compared to results in DMA shear mode. The second objective was to characterize the influence of the design, with a 2-layer laminate consisting of a free layer damping design and a 3-layer laminate with a constrained layer damping design. A method in DMA “speaker” mode was successfully set up. The test parameters were chosen in order to resemble the support of loudspeakers. Therefore with the laminates two beads with a height of approximately 1 mm were formed symmetrically in gaps of 3 mm between the outer fixtures and the drive shaft. Furthermore in the test the laminates were loaded with a dynamic displacement of 600 μm. Due to the low bending stiffness of the laminates the highest test frequency was limited to 10 Hz. In accordance with literature for the 2-layer laminates significant lower damping levels were found than for the 3-layer laminates. Whereas the constrained layer damping laminate (3-layer) showed a good correlation between measurements in “speaker” and in shear mode, the 2-layer laminate showed a significant loss factor increase at high temperatures in shear mode, which was related to entropy elastic effects.

Study on Failure Mechanism of PCT Reliability for BT Substrate Based CSP (Chip Scale Package)

In this paper, the study on failure mechanism of moisture sensitivity reliability is reported. It focuses on the PCT conditions which are 121°C, 2atm, 100RH%, and 168 hr. The general failure mode is delamination on the interface between die attach material and die backside. Interestingly, the delamination exists as a gap of 20∼40 μm. In addition, the paper discusses the relative materials influences — for example, the moisture uptake of mold compound systems and die backside surface property effects. The degradation of the die attach material was analyzed by Dynamic Mechanic Analysis (DMA). The delamination surfaces are analyzed by Scanning Electron Microscope (SEM), and Optical Microscope (OM). Furthermore, Scanning Acoustic Tomograph (SAT) through scanning results reveals that the mold compound formula affects the amount of moisture uptake, which obviously would affect the PCT reliability.