SMTA International Conference Proceedings

A Study of the ENEPIG IMC for Eutectic and LF Solders

Authors: G. Milad, D. Gudeczauskas, G. O'Brien, and A. Gruenwald
Company: Uyemura International Corporation
Date Published: 10/24/2010   Conference: SMTA International

Abstract: The solder joint formed on an ENEPIG surface with 4 different pastes namely eutectic Sn/Pb solder, copper doped Sn/Pb solder, SAC 305 and Sn/Ag were analyzed after thermal stress ageing. The nature of the IMC and its propagation were examined by SEM in cross section as well as top down view. The top down view was obtained by stripping the reflowed paste, so that the examination of variability in the IMC surface can be conducted.

The study shows that the SAC 305 and copper doped (1%) Sn/Pb make a very robust solder joint on the ENEPIG surface, when compared with eutectic Sn/Pb or Sn/Ag solder. The IMC is limited in thickness and more important limited in its propagation under extended thermal stress conditioning (500 hours at 150C).

EPMA analysis show that the copper is an integral part of the IMC and its presence allows for the Pd to be evenly distributed in the IMC. In contrast, in the absence of copper, there are distinct clusters of Pd,Ni/Sn segregated from the Ni/Sn forming the IMC.

The effect of palladium thickness on the integrity of the solder joint, when using SAC 305 solder, was also evaluated using a similar protocol. The data shows that increasing the palladium thickness will adversely impact the solder joint reliability.

Key Words: 

ENEPIG, IMC, Eutectic, LF solder

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