........................................................................................................................................................ ii Acknowledgments ........................................................................................................................................ iv List of Tables .............................................................................................................................................. viii List of Illustrations ......................................................................................................................................... x Chapter 1 ....................................................................................................................................................... 1 General Introduction................................................................................................................................. 1 1.1 Development in Packaging Technology .......................................................................................... 1 1.2 SMT components ............................................................................................................................. 1 1.2.1 QFP (Quad Flat Package) ............................................................................................................ 2 1.2.2 QFN (Quad Flat No-leads) .......................................................................................................... 4 1.2.3 PGA (Pin Grid Array) ................................................................................................................... 5 1.2.4 BGA (Ball Grid Array) .................................................................................................................. 6 1.2.5 LGA (Land Grid Array) ................................................................................................................. 8 1.3 PCB Substrate .................................................................................................................................. 9 1.4 Solder Mask ...................................................................................................................................... 9 1.5 Lead-free PCB Surface Finish ....................................................................................................... 10 1.5.1 HASL ......................................................................................................................................... 10 1.5.2 OSP ........................................................................................................................................... 11 1.5.3 ENIG .......................................................................................................................................... 12 1.5.4 ENEPIG ...................................................................................................................................... 13 1.5.5 ImAg ......................................................................................................................................... 14 1.5.6 ImSn .......................................................................................................................................... 15 1.6 Solder Paste ..................................................................................................................................... 15 1.7 Solder Alloys .................................................................................................................................. 16 vi 1.7.1 Sn-Ag-Cu Solder Alloy ............................................................................................................... 18 1.8 SMT Assembly ............................................................................................................................... 19 1.8.1 Assembly Process ..................................................................................................................... 21 1.9 Reflow-Soldering ............................................................................................................................ 23 1.10 Accelerated Life Testing ............................................................................................................... 24 1.11 Outline of the Dissertation ............................................................................................................ 25 Chapter 2 ..................................................................................................................................................... 27 Literature Review .................................................................................................................................... 27 2.
A mobile robot attempting to reach its goal using autonomous goal-directed navigation in an unknown environment may enter limit cycles while avoiding such concave obstacles as dead ends and U-shaped obstacles, thus lowering its efficiency. To cover a wider range of navigation tasks, this paper presents a novel memorization-based waypoint navigation method in polar coordinate that generates a set of feasible waypoints that avoids navigation limit cycle. Upon navigation limit cycles are detected, their avoidance is achieved by changing the orientation to follow from reactive goal-directed to opportunistic goal-repulsive behavior through creating and memorizing specific traversable, but less preferred areas (circular sectors) called repulsive area that may cause limit cycles in polar coordinate. This deadlock feedback scheme allows the robot to predict and avoid impending limit cycle situations more efficiently than wall-following based approaches. Simulations have verified the conservation of time and memory to compute paths using the new polar-coordinate based waypoint navigation, and an implementation of the navigation method on a real mobile robot using laser range finder works well in an indoor experiment with demonstrated real-time planning and route selection capabilities for waypoint navigation.
