The primary objective of this paper is to investigate the accuracy of the finite element (FE) smeared properties approach for the determination of the mode shapes and frequencies of a printed wiring board (PWB) populated with electronic modules. Smearing of the material and/or structural properties is a recognized means of reducing a complicated structure to a less complicated approximation. Comparisons of both the natural frequencies and mode shapes are made between the smeared FE model and those obtained from vibration testing. The extent of correlation between the mode shapes is characterized by the modal assurance criterion (MAC). Since the intent of this study is to examine the effectiveness of the smearing technique, free boundary conditions are assumed. It is shown that the smearing technique can produce good correlation of both natural frequencies and mode shapes of PWBs populated with modules. A case study of a PWB with both surface mount technology (SMT) and pin-in-hole (PIH) components is presented.
Verified/predictive modeling has become an integral part of electronic packaging product development in order to reduce costs and cycle time. In this paper, interferometric displacement measurement methods are utilized to verify the validity of numerical models for microelectronics packaging design. Three optical methods with submicron sensitivities are employed: moire´ interferometry, microscopic moire´ interferometry and Twyman/Green interferometry. The first two provide contour maps of in-plane displacement fields, and the third maps out-of-plane displacement fields. Their high sensitivity and high spatial resolution make them ideally suited for verification of numerical models. By combining numerical modeling and experimental verification until the results merge, numerical models become more accurate and dependable. Then, the models can be applied extensively to optimize the package designs with confidence that the models provide effective information on material and geometry sensitivity.
As the mechanical, thermal, and electrical demands on 2nd and 3rd level electronic packages increase, so does the need for early dynamic analysis of the proposed design. Estimating effect of dynamic transients (shock inputs) is of primary concern and the current topic of discussion. The computational determination of a damage boundary curve/s (DBC) for a proposed 2nd/3rd level package may seem a formidable task. With the experienced use of the finite element method (FEM), engineering insight, and some relatively simple mechanical testing, the task can be reasonably accomplished. This is not to say that every failure mechanism can be foreseen, predicted or modeled, but some failures can be avoided during qualification testing. The proposed method of DBC determination requires some initial ideas related to where failures may occur due to transient inputs. Failures may include a given maximum stress level, strain, deflection of a particular point or the force at a riveted connection. These suspect areas of failure will tend to guide the modeling technique. Models must be constructed not only to address the specific areas of concern but also to reasonably represent the overall dynamics of the package. Examples of this technique will be presented, each with varying degrees of verification.
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