Thursday, March 8, 2018 - 11:30 – 14:00
Hemisphere Ballroom C1 & C2, Poster Dialogue Sessions
Ly May Chew, Project Leader Paste Development at Heraeus Electronics
Die attachment on Cu surface by silver sintering has drawn rising attention in recent years due to its potential in reducing manufacturing cost since additional metallization layer is not needed.
In this study, we developed silver sinter paste for pressure sintering under air atmosphere not only on precious metal surfaces but also on copper surface. The faster self-diffusion of Ag than silver/copper interdiffusion explained the average initial die shear strength for Ag metallized substrate is higher than for bare Cu substrate.
It is believed that the sintering process is not yet completed under the mild sintering process conditions we used in this study and consequently Ag and Cu continued to diffuse during temperature cycling test and high temperature storage resulting in high bonding strength of sintered joint. This explained the interesting phenomenon we observed in the die shear strengths before and after temperature cycling test and high temperature storage in which die shear strength increased significantly after the tests.
Furthermore, we observed cohesive break in the Cu layer for the bare Cu substrate after 1000 h storage at 250°C. Our hypothesis is that during high temperature storage Cu in the substrate diffused into silver sintered layer and simultaneously Ag from the sintered layer diffused into the Cu substrate. The silver/copper interdiffusion generates strong interface joint between the sintered layer and the Cu substrate.
Authors: Ly May Chew, Wolfgang Schmitt