SMT007 Magazine


Issue link:

Contents of this Issue


Page 59 of 145

60 SMT007 MAGAZINE I JULY 2019 Feature by Howard "Rusty" Osgood, David Geiger, Robert Pennings, Christian Biederman, Jie Jiang, and Jon Bernal FLEX INC. Abstract The electronics industry could benefit greatly from using a reliable, manufacturable, reduced- temperature, SMT solder material (alloy com- position), which is cost competitive with tradi- tional Sn3Ag0.5Cu (SAC305) solder. The many possible advantages and some disadvantages or challenges are discussed. Until recently, the use of Sn/Bi-based mate- rials has been investigated with negative con- sequences for high strain rate (drop-shock) applications; thus, these alloys have been avoided. Recent advances in alloy "doping" have opened the door to revisit Sn/Bi alloys as a possible alternative to SAC-305 for many applications. We tested the manufacturability and reliabil- ity of three low-temperature and one SAC-305 (used as a control) solder paste materials. Two of these materials are doped Sn/Bi/Ag, and one is just Sn/Bi/Ag1%. We will discuss the tests and related results. Lastly, we will discuss the prospects, applica- tions, and possible implications (based on this evaluation) of these materials together with future actions. Introduction A typical SAC305 reflow profile will have peak temperatures in the range of 235–245°C. Tin/bismuth or tin/bismuth/silver solder alloys may use a peak temperature in the range of 165–195°C. This represents a peak temper- ature delta of more than 50°C. Aside from the obvious energy cost savings, there are many other benefits to using a low-temperature sol- der (LTS) material, and they will be discussed later in this article. We also discuss some of the known and unknown risks as well. Tin/bismuth and tin/bismuth/silver alloys are well-known to the industry and have been used routinely in consumer products that are not likely to be subjected to shock, drop, vibra-

Articles in this issue

Archives of this issue

view archives of SMT007 Magazine - SMT007-July2019