Fatigue and Creep of Lead-Free Solder Alloys Fundamental Properties

Fatigue and Creep of Lead-Free Solder Alloys Fundamental Properties 

In order to predict the mechaiucal properties of the solder joint, it is necessary to understand the various structures and manner in which their properties effect those of the whole joint. The solder joint is comprised of the solder alloy, the substrate materials that are being joined together, and the interfaces between the substrate materials and the solder that is typically comprised of one or more intermetallic compound 

The mechanical performance of the solder joint is determined by the mechanical properties of the materials system—they are the solder, substrate materials, and the interface IMC layer(s)—combined with the joint geometry and the loading rate. Because of these many factors, it is often difficult to quantitatively predict the deformation response of a solder joint without the use of finite element analysis. However, it is possible to establish several generalized, qualitative trends. For example, factors that increase the apparent strength of the joint, which include 

On the other hand, relatively low stresses (e.g., below the yield stress) that are applied at reduced loading rates cause the deformation to shift into the solder material. These conditions characterize the service life environment of most solder interconnections as well as accelerated aging tests. As a consequence, the solder deformation will include time-dependent or creep deformation. In the case of cyclic loading environments, the solder deforms by a combination of creep and fatigue responses. Temperature vari- 

---

Chapter 3 Fatigue and Creep of Lead-Free Solder Alloys Fundamental Properties / 71... 

---