Impact of the ROHS Directive on high-performance electronic systems

In this work, tensile creep tests for Sn-1.0Ag-0.5Cu-0.02Ni solder have been conducted at various temperatures and stress levels to determine its creep properties. The effects of stress level and temperature on creep strain rate were investigated. Creep constitutive models (such as the simple power-law model, hyperbolic sine model, double power-law model, and exponential model) have been reviewed, and the material constants of each model have been determined based on experimental results. The stress exponent and creep activation energy have been studied and compared with other researchers' results. These four creep constitutive models established in this paper were then implemented into a user-defined subroutine in the ANSYSä finite-element analysis software to investigate the creep behavior of Sn-1.0Ag-0.5Cu-0.02Ni solder joints of thin fine-pitch ball grid array (TFBGA) packages for the purpose of model comparison and application. Similar simulation results of creep strain and creep strain energy density were achieved when using the different creep constitutive models, indicating that the creep models are consistent and accurate.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Creep Properties of Sn-1.0Ag-0.5Cu Lead-Free Solder with Ni Addition

Zhu²,

Poh³

et al. 2011

“…11 Among all the leadfree solders, the eutectic Sn-Bi alloy is a promising candidate for low-temperature applications due to its low melting point (139°C). 12,13 However, only a few studies of EM have been reported concerning eutectic Sn-Bi solder.…”

Section: Introductionmentioning

confidence: 99%

Electromigration in Line-Type Cu/Sn-Bi/Cu Solder Joints

Chan

2008

In this study, the different electromigration (EM) behaviors of eutectic Sn-Bi solder in the solid and molten states were clarified using line-type Cu/Sn-Bi/Cu solder joints. When the eutectic Sn-Bi solder was in the solid state during the EM test, a Bi-rich layer formed at the anode side while a Sn-rich band formed at the cathode side, and the intermetallic compound (IMC) at the cathode side was thicker than that at the anode side. The growth of the Bi-rich layer exhibited a linear dependence on the time of stressing. While the actual temperature of the solder joint increased to 140°C and the solder was in a molten state or partially molten state, two separate Bi-rich layers formed at the anode side and a great many Cu 6 Sn 5 IMC precipitates formed between the two Bi-rich layers. Also, the IMC layer at the cathode side was thinner than that at the anode side. With a current-crowding-reduced structure, the products of diffusivity and effective charge number of Bi in the eutectic Cu/Sn-Bi/Cu solder joints stressed with current density of 5 9 10 3 A/cm 2 at 35°C, 55°C, and 75°C were calculated.

“…3 Lastly, increased levels of IMC formed through the EM process can lead to local embrittlement and premature mechanical failure. 4 The reduced current-carrying ability of the solder due to the formation of IMC and voids not only increases the current density but also introduces current stressing/crowding at the contact area between the solder and UBM. These factors further aggravate electromigration.…”

Section: Electromigrationmentioning

confidence: 99%

Effect of Grain Boundary Misorientation on Electromigration in Lead-Free Solder Joints

Tasooji

Lara

Lee

2014

Reduction in microelectronic interconnect size gives rise to solder bumps consisting of few grains, approaching a single-or bicrystal grain morphology in C4 bumps. Single grain anisotropy, individual grain orientation, presence of easy diffusion paths along grain boundaries, and the increased current density in these small solder bumps aggravate electromigration. This reduces the reliability of the entire microelectronic system. This paper focuses on electromigration behavior in Pb-free solder, specifically the Sn-0.7 wt.%Cu alloy. We discuss the effects of texture, grain orientation, and grain boundary misorientation angle on electromigration (EM) and intermetallic compound formation in EM-tested C4 bumps. The detailed electron backscatter diffraction (EBSD) analysis used in this study reveals the greater influence of grain boundary misorientation on solder bump electromigration compared with the effect associated with individual grain orientation.