Low-temperature Soldering Of Aluminum Alloy/Stainless Steel Based On Copper Magnetron Sputtering

Cu films were deposited on different substrates by magnetron sputteringtechnique in this paper. Microstructure of copper films on Si wafer was researchedby orthogonal experiment in which sputtering current, working pressure andsubstrate bias voltage were the main factors. Sn-based solder was used to connectaluminum alloy, stainless steel and copper. Deposition parameters on the shearstrength of the joints were studied.Sputtering current had a significant impact on the copper film microstructureand morphology. Grain size, surface roughness and deposition rate of Cu filmsincreased as the sputtering current increased. Substrate bias voltage had a greatimpact on sectional morphologies of the films. When the bias voltage was50V, Cufilms showed a columnar grain growth mode. While the bias voltage increased to100V, columnar grain was inhibited. The working pressure had a little effect on themicrostructure of Cu films.The shear strength of the soldered joint was weak as Ar gas flow rate was lowduring the film deposition. Cu films were peeled off from the substrate directlyduring the tensile test. While Ar gas flow rate was high, the sputtering current wasthe most significant factor on shear strength of the joint. The joint strengthincreased with the current increased. The results showed that the increasing ofcopper films was the root cause of increasing of the joint strength.When the sputtering current reached1.1A, the shear strength of the jointreached the maximum value，then the joint of the shear strength depended on theproperties of the solder and soldering process.The maximum shear strength of aluminum/copper joints, stainless steel/copper joints and aluminum/stainless steel joints were up to41.47MPa，43.32MPa and38.74MPa. There were three kinds of joint fracture modes:completely broken at the solder layer, partly broken in the solder layer andcompletely broken in interface between film and substrate. The third fracture modeoccurred mainly because the film thickness was thin.When the sputtering current was1.3A, the metallurgical reaction occurred atthe interface of Cu film and the aluminum alloy, EDS and XRD analysis showed that CuAl2generated at the interface.With the increasing of holding time, thickness and shape of Cu6Sn5changed atthe interface of copper coated stainless steel/copper coated aluminum, which wascaused by the growth of the compound layer and grain coarsening caused by thediffusion.