Since the first volume of The Printed Circuit Assembler’s Guide to: Low-temperature Soldering was published over five years ago, considerable changes have occurred in the low-temperature soldering landscape. In this book, the authors review the evolution of solder alloys from traditional eutectic SnBi solder to the fourth-generation HRL3 low-temperature solders, including key properties and solder joint formation, focusing mainly on the thermomechanical performance of third- and fourth-generation low-temperature solders for various package types and sizes. Readers will find a discussion of innovations and challenges for achieving optimal processing and electrical reliability properties in low-temperature solder pastes, as well as what’s next in LTS and related research topics.