Study On Interfacial Reaction And Mechanical Properties Of Ni-W-P/Cu Double-plated Solder Joints

In the field of electronic packaging,reliable lead-free tin-based solder joint was an important guarantee for the electronic components long-term service.On the one hand,the lead-free tin-based solder has a higher melting temperature and a higher Sn mass ratio than the conventional Sn-Pb solder,resulting in the soldering reaction rate between the lead solders and Cu substrate is faster,thus will affect the reliability of the package solder joints.On the other hand,the Cu₃Sn phase will formed at the interface between lead-free tin-based solder and Cu substrate,and the faster soldering reaction rate will promote the generation of Cu₃Sn.Since various defects will produce in the Cu₃Sn layer and affects the reliability of the packaged soldering joints.A new type of double-coated Cu/Ni-W-P structure can solve the above problems better.However,the research on the interfacial reaction and mechanical properties between the double-coated Cu substrate and lead-free solder was still unclear.The most widely used Sn-3.0Ag-0.5Cu?SAC305?solder alloys was used as the solder in this experiment,the interfacial reaction and mechanical properties of the double-plated solder joints were systematically studied.To study the effect of the surface roughness of Cu substrate on the characterization structure and performance of electronic packaged solder joints,the Cu substrate was polished by different kinds of sandpaper?800 mesh,1500 mesh,2000 mesh,3000mesh and polishing?,then Ni-W-P electroless plating was self-deposited on the rough Cu substrate surface.By observing the characteristic organization of Ni-W-P plating found that the Ni-W-P grains were surrounded by approximately full round granules on the Cu substrate surface during it has been deposited in water bath for 30 minutes.By observing the SAC305/Ni-W-P/Cu soldr joints which were soldered at 280 ? for 5min and then aged at 170 ? for various time.The results show that the?Cu,Ni?₆Sn₅ grain size decreased with the Cu substrate surface roughness decreasing and the?Cu,Ni?₆Sn₅ grain morphologies gradually changed from a coarse scallop-like to a smaller scallop and rod-like.In order to study the mechanical properties and failure modes of SAC305/Ni-W-P/Cu and SAC305/Cu/Ni-W-P/Cu solder joints,the aged lap joints interface between Ni-W-P/Cu,Cu/Ni-W-P/Cu substrate and SAC305 lead-free solder which were soldered at 280 ? for 5 mins and then aged at 170 ? for various time were observed.Shear rate was determined to be 1mm/min.The experimental results show that the double-plated solder joints interface were more stable.Under long-term solid-state aging,the shear strength maintains numerically stability.In order to study the SAC305/Ni-W-P/Cu and SAC305/Cu-?Ni-W-P?/Cu solder joints interface reaction and the Cu substrate consumpation.SAC305/Cu,SAC305/Ni-W-P/Cu and SAC305/Cu/Ni-W-P/Cu solder joints were prepared in this experiments.And initial Cu foil substrate was 35?m thickness.The results show that at the soldering reaction stage the consumption rate of uncoated Cu foil substrate was about 1.14×10^-8 m/s,the Cu/Ni-W-P foil substrate consumption rate of Cu was about1.06×10^-8 m/s.While for the double-coated Cu substrate,the rate of Cu consumption was approximately 2.0 x 10^-9 m/s.During the solid-state aging stage,the Cu substrate consumption rate of the uncoated structure was 2.89×10^-12 m/s,the Cu/Ni-W-P substrate consumption rate was 2.82×10^-12 m/s and the double-coated Cu/Ni-W-P/Cu substrate consumption rate was 1.81×10^-12 m/s.Due to the relatively low-temperature,the solder joints interfacial reaction was relatively moderate during the solid-state aging stage,resulting in a decrease of Cu atom consumption rate.