Solder Preforms Composed of High Cu-content Sn-xCu Alloys for Power Electronic Packaging and Characterization of the Processing Performance and Joint's Properties

With the rapid development of power electronics, how to make the power chips run stably at high temperature has become an important issue. This paper reports our latest work on development of Sn-xCu solder preforms with high Cu-contents (4 to 12 wt.%) for fabricating Cu/Sn-xCu-preform/Cu die-attachment joints whose interface and matrix are composed of Cu-Sn intermetallic compound (IMC) skeleton to ensure the joints capable of withstanding high temperature impact. Results show that the amount of Cu-Sn IMC skeleton in the Sn-Cu alloy can be changed by increasing Cu content. The fineness and uniformity of dispersion of the Cu-Sn IMC skeleton in Sn-xCu solder preforms with different Cu contents can be tailored by non-continuous rolling. Sandwich structure Cu/Sn-xCu-preform/Cu die-attachment joints are prepared by means of a conventional pressure reflowing process, and microstructures of solder preforms and die-attachment joints are characterized. The results show that the fraction of
${\beta}-\mathbf{Sn}$
decreases and the amount of
$\mathbf{Cu}_{6} \mathbf{S n}_{5}$
increases with increasing Cu content in Sn-xCu alloys. During subsequent non-continuous rolling process, the microstructure of Sn-xCu solder preforms becomes finer, meanwhile the dispersion of IMC is improved during the rolling process. Reflowed Cu/Sn-xCu-preform/Cu die-attachment joints consist of the Cu-Sn IMC skeleton filled with the
${\beta}-\mathbf{Sn}$
phase and exhibit high shear strength over 50 MPa.