Morphological and structural characteristics presented by the Cu-Sn-Cu metallurgical system used in electronic joints

Results are presented concerning the morphological and structural characteristics exhibited by the Cu-Sn-Cu system to be used in electronic lead-free soldering processes, under different process temperatures and pressures. The results show that the Cu3Sn or Cu6Sn5 phases needed to supply the thermal, mechanical and electrical stability to the joints formed require Sn layers (either electrodeposited or by using preforms) whose thickness depends on the process temperature used. For process temperatures of 533 K the thickness of the Sn layer should be above 20 mu m, while for process temperatures of 573 K, the Sn thickness required is reduced to 10 mu m. The joints formed support shear stresses above 12 MPa, as required by electronic standards. Apart from that, microcracks start appearing if an excess of Sn is used during the soldering operation. The set of tests performed indicates that this new joint is quite promising to substitute the conventional solder process applied to power diodes.