The Influence Of Pulse Plating On The Packaging Interconnect Pure Sn Solder Sn Whisker Growth

With lead-free requirement and size miniature in electronic product field,Sn whisker growth becomes a more serious problem in electronic packaging interconnecting and affects electronic products' reliability and security.Recently,pulse plating becomes a main method in metallic deposition and has a breakthrough application in IC Cu interconnecting as well as in photolithography image.In this paper,pulse plating technique is applied in electronic packaging interconnecting,Ni barrier layer and Sn layer in Cu/Ni/Sn stacks are separately obtained by this technic,and effects of pulse plating and DC plating on Sn whisker growth are compared,further,the relative mechanism is discussed.First,the pulse plated Ni layer on the Cu substrate is studied through SEM(scanning electron microscopy) and XRD(X-ray diffraction),including on surface morphology and crystal structure.The results show that compared with DC plated Ni layer,pulse plated Ni layer is more even and arrays in a more order style,and the proper plating current density range is larger.What's more,Ni(200) has a larger orientation index in pulse plated Ni layer while Ni(200) has smaller crystal interspace,which is beneficial for inhibiting atomic grain boundary diffusion,thus improving Ni layer's barrier ability.Second,the effects of DC and PC plated Ni barrier on Sn whisker growth and Sn surface morphology are studied comparatively.The experiment results show that PC plated Ni barrier can effectively defer Sn whisker growth.This is ascribed to the following reasons:(1) Sn(321) has a larger orientation index in samples with pulse plated Ni barriers while Sn(321) has smaller crystal interspace and larger grain size compared with other Sn crystal planes.Therefore it's stronger for inhibiting Cu atom diffusion and the following Sn-Cu IMCs' formation,then preventing Sn whisker growth;also,Sn lateral diffusion is deferred which provides material for Sn whisker growth.(2) Pulse plated Ni barrier induces more Ni₄Sn₃ and less Sn-Cu IMCs formation,reducing the compressive stress in Sn layer,therefore greatly mitigating Sn whisker growth.(3) An alloy of Sn-0.7wt.%Cu is obtained in Cu/Ni/Sn with pulse plated Ni barrier during the reflow process,which is beneficial for mitigating Sn whisker growth.Third,the effects of DC and PC plated Sn layer on Sn whisker growth and Sn surface micromorphology are also studied comparatively.The study results show that PC plated Sn layer can effectively defer Sn whisker growth.This is because that pulse plating can greatly improve texture coeffecient of Sn(321)in Sn layer and reduce that of the unfavorable(220) plane.Furthermore,pulse plated Sn layer can induce more Ni₄Sn₃ and less Sn-Cu IMCs formation greatly reducing the compressive stress in Sn layer. Also,for Sn pulse plating,Sn structure's continuity is improved and Sn-0.7wt.%Cu alloy is formed during the reflow process,beneficial for deferring Sn whisker growth.