Mitigating tin whisker risks: theory and practice

This book covers key tin whisker topics, ranging from fundamental science to practical mitigation strategies. The text begins with a review of the characteristic properties of local microstructures around whisker and hillock grains to identify why these particular grains and locations become predisposed to forming whiskers and hillocks. The book discusses the basic properties of tin-based alloy finishes and the effects of various alloying elements on whisker formation, with a focus on potential mechanisms for whisker suppression or enhancement for each element. Tin whisker risk mitigation strategies for each tier of the supply chain for high reliability electronic systems are also described. Discusses whisker formation factors including surface grain geometry, crystallographic orientation-dependent surface grain boundary structure, and the localization of elastic strain/strain energy density distribution. Examines how whiskers and hillocks evolve in time through real-time studies of whisker growth with the scanning electron microscope/focused ion beaming milling (SEM/FIB). Covers characterization methods of tin and tin-based alloy finishes such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Reviews theories of mechanically-induced tin whiskers with case studies using pure tin and other lead-free finishes shown to evaluate the pressure-induced tin whiskers. Mitigating Tin Whisker Risks: Theory and Practice is intended for the broader electronic packaging and manufacturing community including: manufacturing engineers, packaging development engineers, as well as engineers and researchers in high reliability industries.

TITLE PAGE; COPYRIGHT; TABLE OF CONTENTS; LIST OF CONTRIBUTORS; INTRODUCTION; 1 A PREDICTIVE MODEL FOR WHISKER FORMATION BASED ON LOCAL MICROSTRUCTURE AND GRAIN BOUNDARY PROPERTIES; 1.1 INTRODUCTION; 1.2 CHARACTERISTICS OF WHISKER AND HILLOCK GROWTH FROM SURFACE GRAINS; 1.3 SUMMARY AND RECOMMENDATIONS; ACKNOWLEDGMENTS; REFERENCES; 2 MAJOR DRIVING FORCES AND GROWTH MECHANISMS FOR TIN WHISKERS; 2.1 INTRODUCTION; 2.2 UNDERSTANDING THE MECHANISMS BEHIND IMC-INDUCED STRESS EVOLUTION AND WHISKER GROWTH; 2.3 RELATION OF STRESS TO WHISKER GROWTH; 2.4 CONCLUSIONS; ACKNOWLEDGMENTS; REFERENCES.

3 APPROACHES OF MODELING AND SIMULATION OF STRESSES IN Sn FINISHES3.1 INTRODUCTION; 3.2 CONSTITUTIVE MODEL; 3.3 STRAIN ENERGY DENSITY; 3.4 GRAIN ORIENTATION; 3.5 FINITE ELEMENT MODELING OF TRIPLE-GRAIN JUNCTION; 3.6 FINITE ELEMENT MODELING OF S FINISH WITH MULTIPLE GRAINS; REFERENCES; 4 PROPERTIES AND WHISKER FORMATION BEHAVIOR OF TIN-BASED ALLOY FINISHES; 4.1 INTRODUCTION; 4.2 GENERAL PROPERTIES OF TIN-BASED ALLOY FINISHES (ASAO NISHIMURA); 4.3 EFFECT OF ALLOYING ELEMENTS ON WHISKER FORMATION AND MITIGATION (ASAO NISHIMURA).

4.4 DEPENDENCE OF WHISKER PROPENSITY OF MATTE TIN-COPPER FINISH ON COPPER …