Investigation of CaSO4-KPO3-Na2B4O7 System as a Basis for Synthesis of Low-Melting Glasses Used as a Glass-Solder Material

The possibility of using the compositions of CaSO4-KPO3-Na2B4O7 system as a glass-solder material is shown. A glass formation region has been established in ternary system. The concentration dependences of linear thermal expansion coefficient, the softening temperature and the glass transition temperature are determined and discussed.

Atomistic Investigation on Mechanical Properties of Sn-Ag-Cu Based Nanocrystalline Solder Material

In order to develop light weight electrical components, the nano-sized lead free solders have been identified as potential materials to provide better mechanical properties as compared to the conventional solders. Sn–Ag–Cu (SAC) solders have been widely acknowledged as one of the most promising replacements for Sn-Pb solders. In our previous work, mechanical properties of single crystal SAC solder material were investigated through atomistic simulation studies. In this work, the mechanical properties of nanocrystalline SAC305 (nc-SAC305) (96.5Sn-3.0Ag-0.5Cu) solder have been investigated through molecular dynamics (MD) simulations. A set of modified embedded atom method (MEAM) potential parameters have been proposed for nc-SAC solder. Impact of grain size, strain rate and temperature on the uniaxial tensile properties have been studied. The results have revealed an inverse Hall-Petch relationship in the nc-SAC305 material, and grain boundary decohesion is observed as the dominating failure mechanism. The results also suggest that the ultimate tensile strength of SAC305 significantly increases with increasing strain rate. Moreover, increased ductility and decreased ultimate tensile strength are observed at elevated temperatures.

Elevated Standoff Heights of Solder Joint Interconnections Can Result in Appreciable Stress and Warpage Relief

The “head-in-pillow” (HnP) defects in lead-free solder joint interconnections of Integrated Circuit (IC) packages with conventional (small) standoff heights of the solder joints, and particularly in packages with fine pitches, are attributed by many electronic material scientists to the three major causes: attributes of the manufacturing process, solder material properties, and design-related issues. The latter are thought to be caused primarily by elevated stresses in the solder material, as well as by the excessive warpage of the Printed Circuit Board (PCB)-package assembly and particularly by the differences in the thermally induced curvatures of the PCB and the package. In this analysis, the stress and warpage issue is addressed using an analytical predictive stress model. The model is a modification and an extension of the model developed back in 1980s by the first author. It is assumed that it is the difference in the postfabrication deflections of the PCB-package assembly that is the root cause of the solder material failures and particularly and perhaps the HnP defects. The calculated data based on the developed stress model suggest that the replacement of the conventional ball grid array (BGA) designs with designs with elevated standoff heights of the solder joints could result in significant stress and warpage relief and, hopefully, in a lower propensity of the IC package to HnP defects as well. The general concepts are illustrated by a numerical example, in which the responses to the change in temperature of a conventional design, referred to as BGA, and a design with solder joints with elevated standoff heights, referred to as column grid array (CGA), are compared. The computed data indicated that the effective stress in the solder material was relieved by about 40% and the difference between the maximum deflections of the PCB and the package was reduced by about 60%, when the BGA design was replaced by a CGA system. Although no definite proof that the use of solder joints with elevated standoff heights will lessen the package propensity to the HnP defects is provided, the authors nonetheless think that there is a reason to believe that the application of solder joints with elevated standoff heights could result in a substantial improvement in the general IC package performance, including, perhaps, its propensity to HnP defects.

Elevated Stand-Off Heights in Solder Joint Interconnections of Surface Mounted IC Packages Result in Appreciable Stress and Warpage Relief

The “head-in-pillow” (HnP) defects in lead-free solder joint interconnections of IC packages with conventional (small) stand-off heights of the solder joints, and particularly in packages with fine pitches, are attributed by many electronic material scientists to the three major causes: 1) attributes of the manufacturing process, 2) solder material properties and 3)design-related issues. The latter are thought to be caused primarily by elevated stresses in the solder material, as well as by the excessive warpage of the PCB-package assembly and particularly to the differences in the thermally induced curvatures of the PCB and the package. In this analysis the stress-and-warpage issue is addressed using an analytical predictive stress model. This model is a modification and an extension of the model developed back in 1980-s by the first author. It is assumed that it is the difference in the post-fabrication deflections of the PCB-package assembly that is the root cause of the solder materials failures and particularly and perhaps the HnP defects. The calculated data based on the developed analytical thermal stress model suggest that the replacement of the conventional ball-grid-array (BGA) designs with designs characterized by elevated stand-off heights of the solder joints could result in significant stress and warpage relief and, hopefully, in a lower propensity of the IC package to HnP defects as well. The general concepts are illustrated by a numerical example, in which the responses to the change in temperature of a conventional design referred to as ball-grid-array (BGA) and a design with solder joints with elevated stand-off heights referred to as column-grid-array (CGA) are compared. The computed data indicated that the effective stress in the solder material is relieved by about 40% and the difference between the maximum deflections of the PCB and the package is reduced by about 60%, when the BGA design is replaced by a CGA system. Although no proof that the use of solder joints with elevated stand-off heights will lessen the package propensity to the HnP defects is provided, the authors think that there is a reason to believe that the application of solder joints with elevated stand-off heights could result in a substantial improvement in the general IC package performance, including, perhaps, its propensity to HnP defects.