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The effects of cyclic loading conditions (either thermal or mechanical) on the reliability of electronic assemblies are strongly dependent on the performance of solder joints. Most solder joint fatigue models, and the supporting experimental data, do not treat the crack propagation processes that lead to failure. The benefits from a physically based description of crack propagation in solder joints include an accurate representation of the damage produced by cyclic loading and, therefore, a superior basis to evaluate attachment designs and materials. The development of crack growth rate models has been hampered by the lack of experimental capabilities to observe and characterize crack propagation in solder joints and a computational capability to describe the propagation of cracks in solder joints. This paper describes several approaches that have been used to measure crack propagation rates in solders and a new approach to quantify the crack growth rate and its driving force in solder joints by a quantitative analysis of the fracture surface topography.

The low-cycle fatigue behavior of surface-mount solder joints is influenced by the constitutive behavior and the structural response of all the elements that make up the attachment system including the solder joint, the board, and the package. Modifications to the Coffin-Manson low-cycle fatigue model that describe the constitutive behavior and structural response of a surface-mount solder joint on a leadless ceramic chip carrier have been developed that lead to a closed-form relationship between the cycles to failure and the displacement range. The model is shown to describe accurately the fatigue life of mechanically cycled surface-mount solder joints.

12-mil pitch processing is achievable with solder paste. It may however be the limit of solder paste printing technology, mainly due to the scooping problem associated with thin stencils. With decreasing pitch size, both smear and insufficiency rates increase. Tapering of the stencil aperture helps thick stencil prints, but harms thin stencil printing. Apertures with orientation parallel to squeegee movement results in a higher print defect rate. Overall, the use of fine powders is the most effective means to meet most challenges. It helps in achieving high performance in printability, tack, and non-slump, with acceptable trade-off in rheology and tack time. Solder balling may be the primary hurdle. The problem may be resolved by using an inert reflow atmosphere or through flux chemistry improvements. A metal load of 90.5–91% seems to be the optimum for most properties. Besides paste technology, the chemistry of solder alloys is also a focus for future electronics manufacturing technology. Environmental and toxicity concerns related to the use of lead have initiated the search for acceptable, alternative joining materials for electronics assembly. This paper describes a novel lead-free solder designed as a ‘drop in’ replacement for common tin-lead eutectic solder. The physical and mechanical properties are discussed in detail with comparison to tin-lead eutectic solder. The performance of this solder when used for electronics assembly is discussed and compared to other common solders. Fatigue testing results are reported for thermal cycling electronics assemblies soldered with this lead-free composition.