Tejas Shetty

Graduation Semester and Year

2014

Language

English

Document Type

Thesis

Degree Name

Master of Science in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Dereje Agonafer

Abstract

Quad Flat No-Lead (QFN) packages gained popularity in the industry during the last decade or so due to its superior thermal/electrical characteristics, low cost and compact size. QFN packages are widely used in handheld devices where space is a constraint; however, some customers require it for industry application demanding thicker printed circuit boards (PCB's). As the thickness of PCB increases, the fatigue life (MTTF) of the solder joints decreases. QFN being a leadless package, its board level thermo-mechanical reliability is a critical issue. This provides the motivation for this work. The QFN package on thick board was experimentally characterized under accelerated thermal cycling (ATC) loading. This test exhibited numerous insufficient joints and zero standoff height or a combination of both across the package edge. The primary objective of this work is to understand and mitigate the root cause of the solder joint failure and provide guidelines to improve the fatigue life of the package. Design for reliability method was used to approach this problem. Initially a parametric three-dimensional (3D) finite element (FE) model for the QFN package on thick PCBs was formulated in ANSYS. The fatigue correlation parameter was determined by simulation and various energy based and strain based models are examined to predict the characteristic life (cycles to 63.2% failure). A methodology to derive a new power equation to accurately predict the fatigue life has been proposed. Furthermore, design analysis of QFN was performed to study the effects of several key package parameters on the solder joint reliability. The results from FE modeling and reliability testing will be leveraged to propose "best practices" to have a robust design.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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