Team

The increasing demand for power electronics packaging with higher power densities requires the use of new semiconductor materials, which consequently requires the development of alternative connection technologies between semiconductor components and carrier substrates. In addition, since 2006 the use of lead-containing materials in electronic products has been banned by the environmental protection authorities in directives and laws (RoHS and WEEE) due to their toxic properties. This is why the replacement of high-lead soldering materials in the widespread and well-established soft soldering technology is required. In view of the promising properties of silver, the low-temperature joining technology of silver sintering has drawn considerable attention over the past years. Silver sinter materials are very suitable as an alternative connection material due to their excellent properties such as a high melting temperature at relatively moderate process tem-peratures as well as high thermal and electrical conductivity [1][2].

The diffusion-based silver sinter technology works very well on noble surfaces such as silver or gold. However, the use of bare copper surfaces is widespread due to the potential in reducing manufacturing costs since no additional surface metallization layer is needed. The copper surface of the metal-ceramic substrate has a wide range of surface roughness and grain structures due to the different processing methods for bonding copper sheets on ceramic insulation layer during sub-strate manufacturing. Observations show that the surface properties of the substrate influence the bonding strength of the sintered layer.

The aim of the project is to identify the key factors for forming a strong bond between silver sinter paste and copper surface and to understand their influence on the sintering process. In addition to the potential influencing factors of surface roughness and grain structure, impurities on the sub-strate surface also play a significant role. These surface contaminations can inhibit the diffusion of silver particles into the substrate material. Another influencing factor is the copper oxide layer that is formed in air atmosphere. Thus, the effect of copper oxide on the diffusion mechanism is also of interest.

Furthermore, the aim of the project is to develop a silver sinter paste that is able to overcome the above-mentioned factors and to create superior and reliable bonding on copper-ceramic sub-strates.

[1] W. R. Osório, D. R. Leiva, L. C. Peixoto, L. R. Garcia und A. Garcia, „Mechanical properties of Sn–Ag lead-free solder alloys based on the dendritic array and Ag3Sn morphology“, Journal of Alloys and Compounds, Jg. 562, S. 194–204, 2013, doi: 10.1016/j.jall-com.2013.02.050.

[2] A. Masson et al., „Die attach using silver sintering. Practical implementation and analysis“, E.J.E.E, Jg. 16, 3-4, S. 293–305, 2013, doi: 10.3166/ejee.16.293-305