The Effect of Bismuth on Intermetallics Growth between Lead-Free Solders and Electroless Nickel Immersion Silver (ENIMAG) Surface Finish

Abstract:

Surface finish is coating layer plated on a bare copper board of printed circuit board (PCB). Among PCB surface finishes, Electroless Nickel/Immersion Gold (ENIG) finish is a top choice among electronic packaging manufacturer due to its excellent properties for PCB. However, the use of gold element in ENIG is very high cost and the black pad issue have not been resolved. Thus, by introducing an Electroless Nickel/Immersion Silver (ENImAg) as alternative surface finish hopefully can reduce the cost and offer better properties. The aim of this study is to investigate the effect of bismuth on interfacial reaction during reflow soldering between Sn-2.5Ag (SA25), Sn-3.4Ag-4.8Bi (SAB3448) and ENIMAG surface finish. Solder balls with sizes of 500μm diameters were used. The characteristics of intermetallic compound (IMC) were analyzed by using scanning electron microscopy (SEM), optical microscope and energy dispersive x-ray (EDX). After reflow soldering, the result revealed that only the irregular circle-shape of (Cu,Ni)₆Sn₅ IMC layer was formed at the interface and change to an irregular rod-like shape meanwhile the irregular needle-shape (Ni,Cu)₃Sn₄ was appeared after aging treatment. The result also indicated that, the grain size and thickness of IMC for SAB3448 is smaller and thinner compared to the SA25. The IMC thickness is proportional to the aging duration and IMC morphology for both solder are became thicker, larger and coarser after isothermal aging. No bismuth particle has been detected on SAB3448 solder during top surface examination. In addition, the Bi has been observed can reduce the grain size and the growth rate of IMC. Keywords: ENIMAG, reflow soldering, lead-free solder, intermetallic compound, bismuth

• Periodical: Key Engineering Materials (Volume 796)
• Pages: 183-188
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.796.183
• Online since: March 2019
• Authors: Jaidi Zolhafizi, Saliza Azlina*
• Keywords: Bismuth, ENIMAG, Intermetallic Compound, Lead-Free Solder, Reflow Soldering

References

[1] WOOD E P, NIMMO K L. In search of new lead-free electronic solders [J]. Journal of Electronic Materials, 1994, 23(8): 709-713.

DOI: 10.1007/bf02651363

[2] HARRISON M R, VINCENT J H, STEEN H AH. Lead-free reflow soldering for electronics assembly [J]. Soldering & Surface Mount Technology, 2001, 13(3): 21-38.

DOI: 10.1108/09540910110407388

[3] GADAG S, PATRA S. Numerical prediction of mechanical properties of Pb-Sn solder alloys containing antimony, bismuth and or silver ternary trace elements [J]. Journal of Electronic Materials, 2000, 29(12): 1392-1397.

DOI: 10.1007/s11664-000-0124-2

[4] LEE T Y, CHOI W J, TU K N, JANG J W, KUO S M, LIN J K. Morphology, kinetics, and thermodynamics of solid-state aging of eutectic SnPb and Pb-fiee solders (Sn-3.5Ag, Sn-3.8Ag- 0.7Cu and Sn-0.7Cu) on Cu [J]. Journal of Materials Research, 2002, 17(2): 291-301.

DOI: 10.1557/jmr.2002.0042

[5] FREAR D R, JANG J W, LIN J K, ZHANG C. Pb-free solders for flip-chip interconnects [J]. Journal of Metals, 2001, 53(6): 28-32.

DOI: 10.1007/s11837-001-0099-3

[6] LEE Y G, DUH J G Interfacial morphology and concentration profile in the unleaded solder0 joint assembly [J]. Journal of Materials Science: Materials in Electronics, 2000, 11: 33-43.

[7] KARIYA Y, OTSUKA M. Mechanical fatigue characteristics of Sn-SAg-X (X= Bi, Cu, Zn, and In) solder alloys [J]. Journal of Electronic Materials, 1998, 27(11): 1229-35.

DOI: 10.1007/s11664-998-0074-7

[8] WADE N, WU K P, KLJNII J, YAMADA S, MIYAHARA K. Effect of Cu, Ag and Sb on the creep-rupture strength of lead-free solder alloys [J]. Journal of Electronic Materials, 2001, 30(9): 1228-1231.

DOI: 10.1007/s11664-001-0154-4

[9] LI C Y, CHEN B L, SHI S Q, WONG S C K, Effects of Sb addition on mechanical properties of Sn-3.5Ag-0.7Cu solder alloy and joints [J]. Thin Solid Films, 2006, 504: 421-425.

DOI: 10.1016/j.tsf.2005.09.060

[10] LI G Y, CHEN B L, TEY J N. Reaction of Sn-3.5Ag-0.7Cu-xSb solder with Cu metallization during reflow soldering [J]. IEEE Trans on EPM, 2004,27(1): 77-85.

DOI: 10.1109/tepm.2004.830507

[11] CHEN B L, LI G Y. An Investigation of effects of Sb on the intermetallic formation in Sn-3.5Ag-0.7Cu solder joints [J]. IEEE Trans on Comp & Pack Tech, 2005,28(3): 534-541.

DOI: 10.1109/tcapt.2005.848573

[12] Tseng, C. F., Jill Lee, C., & Duh, J. G. (2013). Roles of Cu in Pb-free solders jointed with electroless Ni(P) plating. Materials Science and Engineering A, 574, 60–67.

DOI: 10.1016/j.msea.2013.03.015

[13] Hsu, Y. C., Huang, Y. M., Chen, C., & Wang, H. (2006). Interfacial reaction and shear strength of Pb-free SnAg2.5Cu0.8Sb0.5 and SnAg3.0Cu0.5Sb0.2 solder bumps on Au/Ni(P) metallization. Journal of Alloys and Compounds, 417(1–2), 180–186.

DOI: 10.1016/j.jallcom.2005.06.087

[14] Huang, T. S., Tseng, H. W., Lu, C. T., Hsiao, Y. H., Chuang, Y. C., & Liu, C. Y. (2010). Growth Mechanism of a Ternary (Cu,Ni)6Sn5 Compound at the Sn(Cu)/Ni(P) Interface. Journal of Electronic Materials, 39(11), 2382–2386.

DOI: 10.1007/s11664-010-1339-5

[15] Huang, M. L., & Yang, F. (2015). Solder Size Effect on Early Stage Interfacial Intermetallic Compound Evolution in Wetting Reaction of Sn3.0Ag0.5Cu/ ENEPIG Joints. Journal of Materials Science & Technology, 31(2015), 252–256.

DOI: 10.1016/j.jmst.2015.01.003

[16] Siti Rabiatul Aisha, I., Ourdjini, A., & Saliza Azlina, O. (2016). The Effectiveness of Bismuth Addition to Retard the Intermetallic Compound Formation. International Journal of Chemical, Molecular, Nuclear, Material and Metallurgical Engineering, 10(1), 107–111.

[17] Mahdavifard, M. H, Sabri, M. F. M., Shnawah, D. A, Said, S. M, Badruddin I A, and Rozali, S., The effect of iron and bismuth addition on the microstructural, mechanical, and thermal properties of Sn-1Ag- 0.5Cu solder alloy., Microelectronics Reliability, vol. 55, pp.1886-1890. 8// (2015).

DOI: 10.1016/j.microrel.2015.06.134

[18] Hu, X., Li, Y., Liu, Y., and Min, Z., Developments of high strength Bi- containing Sn0.7Cu lead-free solder alloys prepared by directional solidification., Journal of Alloys and Compounds, vol. 625, pp.241-250, 1 3/15/ (2015).

DOI: 10.1016/j.jallcom.2014.10.205

[19] Yao, P., Liu, P., & Liu, J. (2009). Interfacial reaction and shear strength of SnAgCu-xNi/Ni solder joints during aging at 150 C. Microelectronic Engineering, 86(10), 1969–(1974).

DOI: 10.1016/j.mee.2008.12.013

[20] L. Zhanga, S.B. Xuea, G. Zenga, L.L. Gaoa, H. Yea. Interface reaction between SnAgCu/SnAgCuCe solders and Cu substrate subjected to thermal cycling and isothermal aging. Journal of Alloys and Compounds. 2012. 510(1): 38-45.

DOI: 10.1016/j.jallcom.2011.08.044