Bonding strength of multiple SiC die attachment prepared by sintering of Ag nanoparticles

Jianfeng Li,Christopher Mark Johnson,Cyril Buttay,Wissam Sabbah,Stéphane Azzopardi

doi:10.1016/j.jmatprotec.2014.08.002

Abstract

3mm×3mm dummy SiC dies with 100\\200\\200nm thick Ti\\W\\Au metallization have simultaneously been attached using sintering of Ag nanoparticle paste on AlN-based direct bonded copper substrates with 5\\0.1μm thick NiP\\Au finish. The effect of preparation and sintering parameters including time of drying the printed paste, sintering temperature and time, and pressure, on the average shear strength for multiple die attachments was investigated. The surfaces of the die attachments after the shear tests were observed and the individual shear strength values correlated with the “apparent” porosity and thicknesses of the corresponding die attachments (sintered layer). The results obtained are further discussed and compared with typical data reported in existing literature. Main conclusions include: (i) the present shear strength values and their variations are comparable with those reported for single die attachment samples, (ii) the effects of sintering parameters can be ascribed to the effectiveness of the organic content burnout and appropriate rate of growth and coalescence of the Ag nanoparticles during the sintering process, and (iii) thickness values of the sintered Ag die attachments may be taken as non-destructive measurements to monitor/evaluate the quality of die attachment during power electronic module manufacturing/assembly process.

Highlights

Wide band-gap semiconductor devices such as SiC power devices provide great opportunities to develop power electronic systems with increased power densities, high reliability in extreme environments and higher integration
10 direct bonded copper (DBC) substrates was measured, and surface flatness was found to be in the range of 6–15 ␮m
It is concluded that surface warpage has resulted in both a non-uniform thickness of the printed Ag paste, and non-uniform pressure being applied on the different dies during the sintering process; even though a 0.2 mm thick flexible silicone rubber was situated on the cold plate of the sintering press as shown in Fig. 2(a) for compliance

Summary

Introduction

Wide band-gap semiconductor devices such as SiC power devices provide great opportunities to develop power electronic systems with increased power densities, high reliability in extreme environments and higher integration. The eutectic or near eutectic Sn–Ag and Sn–Ag–Cu solders that are more commonly used for power die attachments are not reliable for high power density and high-temperature power electronic applications. Sn–Ag–Cu solder joints are not suitable for long-term usage at elevated temperature due to crack formation at the intermetallic (IMC)-solder interface. This is in agreement with the fact that the eutectic, or near eutectic, Sn–Ag and Sn–Ag–Cu solders are prone to creep at elevated temperatures and the accumulation of plastic strain leads to crack initiation and propagation. Rapid growth of IMCs between the solders and the metallization on both the devices and the substrates for high-temperature applications may result in brittle fracture of the joints

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