Study of Electromigration-Induced Stress of Solder

This study designed and produced a special microsolder specimen (Sn3.8Ag0.7Cu) to equalize current density under stressing. The specimen was generated to avoid temperature gradient and thermal migration. The inelastic deformation of the solder with electromigration (EM) alone was then measured with moiré interferometry. In addition, the EM-induced solder stress was evaluated using a finite element method (FEM). The precision of the FEM model was verified by comparing the simulated results with the experimental results with respect to EM-induced deformation. Findings indicated that the maximum spherical stress in the solder can reach 50 MPa. Moreover, the vacancy concentration is much higher on the cathode end than on the anode end. The simulation results can illustrate the failure mode of a solder and can therefore provide a basis for the comprehensive evaluation of solder reliability under EM.

Nanoparticle Enhanced Solders for Increased Solder Reliability

Due to environmental concerns traditional eutectic tin-lead solder is gradually being replaced in electronic assemblies by “lead-free” solders. During this transition, nanoparticle technology is also being investigated to see whether improvements in joint reliability for high temperature applications can be made. Nanoparticles can be used to harden the solder via Zener pinning of the grain boundaries and reduce fatigue failure. This paper explores the effects of adding Silica nanoparticles to SnAgCu solder, and how the mechanical properties induced in the solder vary with temperature. It is found that above 100 °C the mechanical response and microstructure of the normal and nanoparticle enhanced solders converge.

Solder Joints Reliability Assessment for Stacked CSP Module Based on Flexible Circuit Printed Board

Solder reliability assessments for stacked CSP module based on flexible printed circuit board (FPC) are performed in this research using a 3D global model with constraint equation and two levels submodeling technique. 3D global model with constraint equation(CE) was used to provide real boundary contiditons for 1st level submodeling,and quarter local model used as 2ndlevel submodeling was used to address cirtical solder joint failure locations ,to estimate solder reliability for the module and to provide reasonable boundary contiditons for 2ndlevel submodeling.slice model used as 2ndlevel submodeling was used to study that the effect on the cirtical solder damage parameter under various basefilm material of FPC and geometrical parameters. It is found that thinner CSP die thickness and thinner PCB ,thicker FPC basefilm and FPC adhesive thickness and CSP thickness,and higher solder standoff height, lead to smaller averaged accumulated viscoplastic strain energy density(ΔWavg) and higher fatigue life; It is also figures out,PI and PEN basefilm material lead to smaller ΔWavg and higher fatigue life for the most critical solder than LCP material.Weibull distributions and weibull probaility density function for the module under various FPC baseflim material were obtained,and 63.2% solder joints failure life was used as solder joints reliability assessment for stacked CSP module.

A study of high Cu behavior on electrolytic Ni and electroless Ni pad finish

It has been used various pad finish materials to enhance the reliability of solder joint and Electroless Ni Immersion Gold (the following : ENIG) pad has been used more than others. This study is about reliability according to being used in commercial Electrolytic Ni pad and ENIG pad, and was observed behavior of various Cu contents. After reflow, the inter-metallic compound (IMC) between solder and pad is composed of Cu6Sn5 (Ni substituted) by using EDS, and in case of ENIG, between IMC and Ni layer was observed the dark layer (Ni3P layer). Additional, it could be controlled the thickness of dark layer according to Cu contents. Investigated the different fracture mode between electrolytic Ni and ENIG pad after drop shock test, in case of soft Ni, accelerated stress propagated along the interface between 1st IMC and 2nd IMC, and in case of ENIG pad, accelerated stress propagated along the weaken surface such as dark layer. The unstable interface exists through IMC, pad material and solder bulk by the lattice mismatch, so that the thermal and physical stress due to the continuous exterior impact is transferred to the IMC interface. Therefore, it is strongly requested to control solder morphology, IMC shape and thickness to improve the solder reliability.