Inhibiting the growth of Cu3Sn and Kirkendall voids in the Cu/Sn-Ag-Cu system by minor Pd alloying

In this study, the metallurgical reaction between Cu substrates (electrolytic type) and a Sn3Ag0.5Cu-xPd alloy at 180°C was examined using a scanning electron microscope (SEM), electron probe microanalyzer (EPMA), focused ion beam (FIB) microscope, and transmission electron microscope (TEM). The results showed that the growth of Cu3Sn in the Cu/Sn-Ag-Cu solder joints was substantially suppressed by doping with a minor quantity of Pd (0.1–0.7 wt. %) in the solder alloy. The sluggish growth of Cu3Sn reduced the formation of Kirkendall voids at the Cu/Cu3Sn interface and significantly improved the mechanical reliability of the joint interface. It was argued that a minor addition of Pd into the solder stabilized the Cu6Sn5 phase and enlarged the interdiffusion coefficient of Cu6Sn5 but diminished that of the neighboring phase (Cu3Sn), thereby decreasing the Kirkendall effect in the Cu/Sn-Ag-Cu reactive system.

[1]  C. Kao,et al.  Minimum effective Ni addition to SnAgCu solders for retarding Cu3Sn growth , 2009 .

[2]  C. Kao,et al.  Inhibiting the formation of microvoids in Cu3Sn by additions of Cu to solders , 2010 .

[3]  Jin Yu,et al.  Effect of Zn on the intermetallics formation and reliability of Sn-3.5Ag solder on a Cu pad , 2007 .

[4]  W. Wu,et al.  Comparative study between Sn37Pb and Sn3Ag0.5Cu soldering with Au/Pd/Ni(P) tri-layer structure , 2010 .

[5]  Feng Gao,et al.  Depressing effect of 0.2wt.%Zn addition into Sn-3.0Ag-0.5Cu solder alloy on the intermetallic growth with Cu substrate during isothermal aging , 2006 .

[6]  William J. Boettinger,et al.  Diffusion Parameters and Growth Mechanism of Phases in the Cu-Sn System , 2011 .

[7]  C. Kao,et al.  Strong Zn concentration effect on the soldering reactions between Sn-based solders and Cu , 2006 .

[8]  G. Ghosh.  Kinetics of interfacial reaction between eutectic Sn-Pb solder and Cu/Ni/Pd metallizations , 1999 .

[9]  Yiyu Qian,et al.  Improvement of microstructure and interface structure of eutectic Sn–0.7Cu solder with small amount of Zn addition , 2005 .

[10]  L. H. Hsu,et al.  Influence of Pd Concentration on the Interfacial Reaction and Mechanical Reliability of the Ni/Sn-Ag-Cu-xPd System , 2011, Journal of Electronic Materials.

[11]  Iver E. Anderson,et al.  Suppression of void coalescence in thermal aging of tin-silver-copper-X solder joints , 2006 .

[12]  Chang-Da Tsai,et al.  A study on the reaction between Cu and Sn3.5Ag solder doped with small amounts of Ni , 2003 .

[13]  Tomi Laurila,et al.  Effect of Ag, Fe, Au and Ni on the growth kinetics of Sn-Cu intermetallic compound layers , 2009, Microelectron. Reliab..

[14]  Jin Yu,et al.  Effects of residual S on Kirkendall void formation at Cu/Sn–3.5Ag solder joints , 2008 .

[15]  Feng Gao,et al.  Effects of Co and Ni addition on reactive diffusion between Sn–3.5Ag solder and Cu during soldering and annealing , 2006 .

[16]  I. Anderson,et al.  Elevated temperature aging of solder joints based on Sn-Ag-Cu: Effects on joint microstructure and shear strength , 2004 .

[17]  Jin Yu,et al.  Interfacial reactions of Sn-Ag-Cu solders modified by minor Zn alloying addition , 2006 .

[18]  K. Tu,et al.  Time- and temperature-dependent wetting behavior of eutectic SnPb on Cu leadframes plated with Pd/Ni and Au/Pd/Ni thin films , 1998 .

[19]  Tomi Laurila,et al.  Impurity and alloying effects on interfacial reaction layers in Pb-free soldering , 2010 .

[20]  Young-Ho Kim,et al.  Mechanism of the Delayed Growth of Intermetallic Compound at the Interface between Sn−4.0Ag−0.5Cu and Cu−Zn Substrate , 2010 .

[21]  W. Gierlotka,et al.  Strong effect of Pd concentration on the soldering reaction between Ni and Sn-Pd alloys , 2010 .

[22]  Jin Yu,et al.  Effects of sulfide-forming element additions on the Kirkendall void formation and drop impact reliability of Cu/Sn-3.5Ag solder joints , 2009 .

[23]  C. Kao,et al.  Effects of minor Fe, Co, and Ni additions on the reaction between SnAgCu solder and Cu , 2009 .

[24]  K. Tu,et al.  Six cases of reliability study of Pb-free solder joints in electronic packaging technology , 2002 .

[25]  Jin Yu,et al.  Effects of Ag on the Kirkendall void formation of Sn–xAg/Cu solder joints , 2010 .

[26]  Tomi Laurila,et al.  Interfacial reactions between lead-free solders and common base materials , 2005 .

[27]  R. Kubiak,et al.  Refinement of the crystal structures of AuSn4 and PdSn4 , 1984 .

[28]  Peter Borgesen,et al.  On the root cause of Kirkendall voiding in Cu^3Sn , 2011 .

[29]  C.E. Ho,et al.  Effects of Pd concentration on the interfacial reaction and mechanical reliability of the Sn–Pd/Ni system , 2011 .