Degradation of electroless Ni(P) under-bump metallization in Sn3.5Ag and Sn37Pb solders during high-temperature storage

The interfacial reaction between electroless Ni(P) under-bump metallization (UBM) and solders is studied. A P-rich layer forms in the UBM along the solder side after reflow and thermal aging. Crack formation inside the P-rich layer can sometimes penetrate throughout the entire UBM layer structure. The Ni(P) UBM degradation occurs earlier in the Sn3.5Ag solder than in Sn37Pb because of its higher reflow temperature. Despite the formation of a P-rich layer and cracks inside the UBM, it still keeps its original function within the high-temperature storage period in this study. Explanations for the formation of the P-rich layer and cracks in the UBM are outlined along with explanations for the Ni(P) UBM degradation process.

[1]  Fan Zhang,et al.  Failure mechanism of lead-free solder joints in flip chip packages , 2002 .

[2]  E. J. Rymaszewski,et al.  Microelectronics Packaging Handbook , 1988 .

[3]  Y. C. Chan,et al.  Reliability study of the electroless Ni-P layer against solder alloy , 2002, Microelectron. Reliab..

[4]  Solid state reactions , 1988 .

[5]  Y. C. Chan,et al.  Correlation between Ni_3Sn_4 intermetallics and Ni_3P due to solder reaction-assisted crystallization of electroless Ni–P metallization in advanced packages , 2000 .

[6]  Paul Conway,et al.  Electroless nickel bumping of aluminum bondpads. I. Surface pretreatment and activation , 2002 .

[7]  K. S. Kim,et al.  Isothermal aging characteristics of Sn-Pb micro solder bumps , 2003, Microelectron. Reliab..

[8]  Shu-Ming Chang,et al.  Investigation of electroplating Ni UBM for Pb-free solders , 2003, 53rd Electronic Components and Technology Conference, 2003. Proceedings..

[9]  Chwan-Ying Lee,et al.  The interaction kinetics and compound formation between electroless NiP and solder , 1994 .

[10]  Paul Conway,et al.  Electroless nickel bumping of aluminum bondpads. II. Electroless nickel plating , 2002 .

[11]  K. Paik,et al.  Pb-free bumping technology and UBM (under bump metallurgy) , 2001, Advances in Electronic Materials and Packaging 2001 (Cat. No.01EX506).

[12]  Andreas Ostmann,et al.  Electroless nickel/copper plating as a new bump metallization , 1995 .

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

[14]  Y. C. Chan,et al.  Interfacial reaction of Pb-Sn solder and Sn-Ag solder with electroless Ni deposit during reflow , 2002 .

[15]  D. R. Frear,et al.  Solder reaction-assisted crystallization of electroless Ni-P under bump metallization in low cost flip chip technology , 1999 .