Feng, Dan (M.S. Mechanical Engineering)

Optimizing Lifetime Buy Quantities To Minimize Lifecycle Costs

Mismatches between electronic part procurement lifecycles and the lifecycles of the products that they are used in cause products with long manufacturing and/or support lives to incur significant obsolescence management costs. Lifetime buy is one of the most prevalent mitigation approaches employed for electronic part obsolescence management. Making lifetime purchases of parts when they go obsolete involves managing many interacting influences and multiple concurrent buys for multiple parts. The focus of this paper is optimizing lifetime buy quantities by minimizing lifecycle cost. The factors that contribute to the lifecycle cost associated with a lifetime buy are: procurement cost, inventory cost, disposal cost, and penalty cost.

A methodology called Life of Type Evaluation (LOTE) is described; LOTE requires component and system data and uses stochastic analysis to determine the lifetime buy quantity per part that minimizes the lifecycle cost for the system. LOTE was used to determine the optimum lifetime buy quantities for a Motorola communications system with and without life extensions.

Myers, Jessica (M.S. Mechanical Engineering)

Integration of Technology Roadmapping Information into DMSMS-Driven Design Refresh Planning of the V-22 Advanced Mission Computer

Design refreshes and various reactive mitigation solutions are used to manage technology obsolescence (DMSMS) in systems. Design refreshing solely to manage obsolescence is, however, not practical for many systems, and therefore, obsolescence management refresh activities need to be coordinated with technology insertion roadmaps. This report describes the development of an information model that details technology roadmapping information for use within obsolescence-driven design refresh planning, and also describes a business case analysis for ascertaining the value of the resulting refresh plans. A case study on the V-22 Advanced Mission Computer using the MOCA (Mitigation of Obsolescence Cost Analysis) refresh planning tool is described in which optimum refresh plans (coupled with bridge and lifetime buys) with and without the inclusion of technology roadmapping constraints are determined.

Tuchband, Brian (M.S. Mechanical Engineering)

Implementation of Prognostics and Health Management for Electronic Systems

Prognostics and health management is the estimation of a product's remaining life based on current and historic conditions in terms that are useful to the maintenance decision-making process and the improvement of product design and reliability. An assessment has been undertaken to identify the state-of-practice for prognostics and health management of electronics in industry, government, and academia. Organizations involved in research, development and/or implementation of prognostics and health management have been categorized to ascertain which focus areas and applications of prognostics research are presently needed. Next, a methodology has been developed for enabling the implementation of prognostics and health management for electronic systems. This approach integrates virtual reliability assessment with a sensor selection process to identify the sensing parameters, measurement locations, and optimal sensor systems for in-situ health monitoring of electronics. The methodology has been applied to two circuit card assemblies located inside an avionics unit.

Varghese, Joseph (Ph.D. Mechanical Engineering)

Drop Testing of Portable Electronic Devices

This dissertation investigates the durability of solder interconnects of area array packages mounted on Printed Wiring Assemblies (PWAs) subjected to dynamic flexural loads. A test methodology is proposed to quantify the durability of the solder interconnect in terms of generic empirical metrics, PWA flexural strain and strain rate. It is shown that the proposed metrics (PWA strain and strain rate) can quantify the durability of the solder interconnect, irrespective of the loading orientation or the PWA boundary conditions.

An empirical rate-dependent durability model, based on mechanistic considerations, is developed to estimate the fatigue failure envelopes of the solder. 3D transient Finite Element Analysis (FEA) with rate-dependent solder material properties is used to develop transfer functions between PWA flexural strain and the solder plastic strain, for different values of PWA flexural strain rates. A strain-range fatigue damage model, based on strain-rate hardening and exhaustion of ductility principles, is used to quantify the durability and estimate the fatigue constants of the solder for high strain rates of loading. The test data also shows the existence of multiple competing failure sites (solder, copper trace, FR4, bulk intermetallic, interface between the intermetallics) and that the dominant failure site is strongly dependent on the loading conditions. Of these competing failure sites, this dissertation focuses on the solder and the interface between two intermetallic compound (IMC) layers. Interfacial fracture mechanics is used to provide a mechanistic perspective on the failure site transitions. Durability metrics, based on the mechanics of the problem is used to quantify the damage at the competing failure sites for a given loading condition and to estimate the durability of the solder interconnect. The test data shows good correlation with the model predictions.

This dissertation focuses on Sn37Pb eutectic solder interconnects. But the proposed test methodologies and mechanistic models are generic enough to be easily extended to other emerging lead free solder materials. Wherever possible, suggestions are provided for the development of test techniques or phenomenological models which can be used for engineering applications.