Electromigration behavior of Cu/Sn3.0Ag0.5Cu/Cu ball grid array solder joints

Abstract

Electromigration (EM) behavior induced by current crowding under the condition of multi-physical fields in Cu/Sn3.0Ag0.5Cu/Cu ball grid array (BGA) solder joints was investigated here. First, EM experiments using a specially designed BGA daisy-chain circuit were performed under a current density of 1.43 × 104 A/cm2 at 125 °C for up to 120 h. The experimental results indicated that the polarized growth of intermetallic compounds (IMCs) and void formation occurred in the solder joint. After the 120 h EM testing, the IMC thickness at the anode markedly increased from 5.24 to 32.21 µm, whereas at the cathode it gradually increased from 2.03 to 4.54 µm and subsequently decreased until it completely disappeared. Under the effect of the applied current, voids formed at the current crowding region of the cathode. Second, a finite element model was built to study the void formation considering four driving forces, i.e., the electron wind force, thermal gradient, stress gradient, and atomic concentration gradient. The simulation results showed that the electron wind force played a predominant role in void formation during the EM process, contributing to more than 90% of the total atomic flux. By comparing the experimental results with the simulation results, 0.91 mol/m3 was proposed as the critical atomic concentration of void formation for our specimens in this paper, and the void location was accurately predicted.