Intermetallic Compound Growth Induced by Electromigration in Sn-2.5Ag Solder Joints with ENEPIG Surface Finish

Abstract

The equation for predicting the growth behavior of intermetallic compounds (IMC) by electromigration (EM) of the Cu/ENEPIG/Sn-2.5Ag/Cu solder joint was modeled, and the actual behavior observed through experiments and the predicted behavior were compared. After reflow, (Cu, Ni)<sub>6</sub>Sn<sub>5</sub> was formed near the ENEPIG/solder interface, and Cu<sub>6</sub>Sn<sub>5</sub> was produced near the solder/Cu interface. Furthermore, Cu<sub>6</sub>Sn<sub>5</sub> islands and Ag<sub>3</sub>Sn were formed with the β-Sn matrix in the solder. The mobility of Cu, Ni, and Sn atoms at the ENEPIG/IMC/solder interface was calculated to derive a thickness variation equation of the IMC with respect to the current application time. The modeling predicted that if the current density was maintained for 250 h at 10 kA/cm<sup>2</sup>, the IMC thickness increased by 4.2 ㎛. As a result of the EM experiment, the IMC at the ENEPIG/solder interface grew by 4.2 ㎛; this exactly matched the prediction. A comparison of the thickness of the IMC layer indicated that the OSP/solder interface produced approximately 9 ㎛, and the ENEPIG/solder interface grew by approximately 4.2 ㎛. Therefore, the Ni plating layer of the ENEPIG surface treatment prevented the diffusion of Cu and suppressed the growth of IMC by approximately 50 %.

Bonding Property of Middle Temperature Sn-Ag-Cu Solder Ball Joint of Ball Grid Array Package

“…12 by the width at Fig. 13 Total IMC thickness before and after thermal cycling test which IMC was formed 12) . For Cu 6 Sn 5 IMC formed on the PCB-side joints with SACNB, the thickness was the lowest at 5.2 ㎛, while those with SAC1205N and SAC305 had thicker layers at 5.4 ㎛ and 6.7 ㎛, respectively.…”