Principles of Soldering
Since the first edition of Principles of Soldering and Brazing, published in 1993, the authors have received valuable feedback from readers representing a wide range of technical interests. This has prompted the decision to expand the text and organize it into two companion books, one covering soldering and the other brazing. This first book primarily aims at providing information about soldering in a form that is hopefully readily accessible and as easy to assimilate as possible. Priority is given to the fundamental principles that underlie this field of technology rather than recipes for making joints. The largely artificial distinctions between soldering and brazing are preserved because, despite their many commonalities, it has been found that practicing engineers are either concerned with soldering or brazing and seldom are involved with both simultaneously. The planned companion book, Principles of Brazing, addresses this complementary need. A large proportion of the literature on soldering and brazing may be charged with being heavy on description and light on critical analysis. We have endeavored to redress the balance, while striving to avoid being unduly simplistic or overly mathematical in our approach. Admittedly we may not always have succeeded in this aim.
As in Principles of Soldering and Brazing, we have striven to maintain the focus on the fundamental aspects of soldering and have deliberately avoided entering into specific joining technologies in detail. At the same time, we recognize that the range and extent of the knowledge base of metal joining is not immediately obvious, and it requires a fairly deep understanding of materials. To cite a single example, nichrome (an alloy of nickel and chromium), which is a perfectly satisfactory and widely used metallization for soldering, is rendered useless if the solder contains bismuth. If there is an evident bias towards electronic and photonics applications, this reflects the recent professional orientation of the authors. Some topics are inevitably not accorded due consideration, although it is hoped that sufficient references are provided to enable the reader to pursue these further.
No attempt has been made to gather a comprehensive list of published papers. Those that are included have been selected because they are useful basic texts, cover important subject matter, or relate to exemplary pieces of work, whether in respect of methodology, technique, or other noteworthy features. It was felt that if the value of the book depended on its bibliography, it would rapidly become dated. The advent of computer search facilities and databases of scientific journal and conference abstracts should enable the reader who wishes to find references on a specific topic to obtain further information without too much difficulty. The search term “lead-free solder” will yield an astounding 25,000+ publications in the public domain, virtually none of which are more than 10 years old.
The reader should note that all compositions given in this book are expressed in weight percentage in accordance with the standard industrial practice. These have, for the most part, been rounded to the nearest integer. The ratio of elements in intermetallic compounds, again by convention, refers to the atomic weight of the respective constituents. The general convention used for specifying alloy compositions is that adopted by the alloy phase diagram community, namely in the alphabetical order of the elements, by chemical symbol. We have not been entirely rigorous in this regard as it is sometimes helpful to group alloys by the dominant constituents. Minor additions to bulk compositions are given in order of concentration; for example, Pb-62Sn-0.5Lu-0.02Ce.
Specific references are given with each chapter. For those wishing to read more generally on particular topics, the authors would recommend the texts listed as Selected References in Appendix 2.
Many phase diagrams are subject to ongoing research, resulting in continued improvement in the accuracy and detail of the information. The most recent version of a diagram may be identified by consulting the latest cumulative index of phase diagrams, published in the Cumulative Index of the periodical Journal of Phase Equilibria (ASM International). This will refer to the source of the thermodynamically assessed diagram of interest. The reader is advised that the four compendia of binary phase diagrams published in the 1960s, ’70s and ’80s (colloquially referred to as Hansen, Elliott, and Shunk) are now known to contain many errors and omissions.
Information on new developments in soldering and brazing is scattered throughout a wide range of periodicals, as reflected in the sources cited in the references appended to the individual chapters. To keep abreast of the literature, the authors have found especially useful the following abstract publications: Metals Abstracts and Science Abstracts. Technical libraries can provide automated searches against specified key words as a monthly service.
We wish to thank our many colleagues and ex-colleagues for their helpful advice and encouragement, particularly James Vincent, for insights into lead free soldering.
David M. Jacobson