Amaneh Tasooji

Design parameters influencing reliability of CCGA assembly: a sensitivity analysis

Area array microelectronic packages with small pitch and large I/O counts are now widely used in microelectronics packaging. The impact of various package design and materials/process parameters on reliability has been studied through extensive literature review. Reliability of ceramic column grid array (CCGA) package assemblies has been evaluated using JPL thermal cycle test results (-50deg/75 degC, -55deg/100degC, and -55deg/125degC), as well as those reported by other investigators. A sensitivity analysis has been performed using the literature data to study the impact of design parameters and global/local stress conditions on assembly reliability. The applicability of various life-prediction models for CCGA design has been investigated by comparing models predictions with the experimental thermal cycling data. Finite element method (FEM) analysis has been conducted to assess the state of the stress/strain in CCGA assembly under different thermal cycling, and to explain the different failure modes and locations observed in JPL test assemblies

Effect of Grain Boundary Misorientation on Electromigration in Lead-Free Solder Joints

Reduction in microelectronic interconnect size gives rise to solder bumps consisting of few grains, approaching a single- or bicrystal grain morphology in C4 bumps. Single grain anisotropy, individual grain orientation, presence of easy diffusion paths along grain boundaries, and the increased current density in these small solder bumps aggravate electromigration. This reduces the reliability of the entire microelectronic system. This paper focuses on electromigration behavior in Pb-free solder, specifically the Sn-0.7 wt.%Cu alloy. We discuss the effects of texture, grain orientation, and grain boundary misorientation angle on electromigration (EM) and intermetallic compound formation in EM-tested C4 bumps. The detailed electron backscatter diffraction (EBSD) analysis used in this study reveals the greater influence of grain boundary misorientation on solder bump electromigration compared with the effect associated with individual grain orientation.

Using students' previous experience and prior knowledge to facilitate conceptual change in an introductory materials course

One important finding that the book, How People Learn, highlights is that all learning involves transfer from prior knowledge and previous experiences which can facilitate or impede learning. Learning can be facilitated by activating prior knowledge from an earlier class and/or context can be created for new material from previous experiences. Conversely, learning can be impeded by misconceptions that originate from personal experience, prior knowledge from previous classes, or inappropriate application of prior knowledge. Misconceptions from prior knowledge and previous experience can be classified according to their origin as a type of “impediment” to learning for which there are two general types, each with subtypes. Null impediment refers to missing information (necessary for learning new material) due to students: 1) not having prior knowledge (deficiency) or; 2) not recognizing links between new material and their prior existing knowledge (transfer). Substantive impediment refers to faulty concept models students hold from: 1) personal experience or observations (experiential); 2) prior courses and teaching (pedagogic) and; 3) bending or misinterpreting of new concepts to fit prior knowledge (misinterpretive). In this paper on research-to-practice we address the question of what learning strategies are most effective in repairing misconceptions or “impediments” of different origin.