Intermetallic compound spalling characteristics of Sn-3.5Ag solder over ternary electroless Ni under-bump metallurgy
- PDF / 415,826 Bytes
- 6 Pages / 584.957 x 782.986 pts Page_size
- 62 Downloads / 225 Views
Jin Yua) Electronic Packaging Laboratory, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Yuseong-gu, Daejeon 305-701, Korea (Received 19 June 2011; accepted 20 September 2011)
Ternary electroless nickel, NiXP, films were produced by adding salts of Mo, Re, Tl, Cu, W, Co, Fe, Zn, and Mn to conventional electroless Ni baths and subsequently reacted with Sn-3.5Ag solder. From the full width at the half maximum (FWHM) data, as-plated NiXP films can be categorized into two groups: one is close to the FWHM value of nanocrystalline Ni5P film and the other is close to amorphous Ni9P film. Alloying elements in the electrolessly plated under-bump metallurgy that effectively suppressed intermetallic compound (IMC) spalling were Mn, Zn, Re, Fe, and W, whereas Tl exacerbated spalling. The roles of Cu, Mo, and Co were less clear due to a lack of data. Based on scanning electron microscopy observations, a spalling map was presented, which showed elemental demarcation lines of IMC spalling in the X-P coordinates.
I. INTRODUCTION
The interfacial reaction between solder and underbump metallurgy (UBM) during reflow and ageing produces intermetallic compounds (IMCs), which play an important role in the solder joint reliability. Formation of IMCs is an essential part of the soldering, however, being inherently brittle per se, IMC thickening often deteriorates the joint reliability.1–8 When Sn-based Pbfree solder is reflowed and aged over Cu UBM, Cu rapidly reacts with Sn and Cu6Sn5 spalls off from the UBM upon complete consumption of the underlying Cu layer. This is related to the poor wetting property of the solder over an adhesion layer such as Ti and Cr film9,10 and to the nonreactivity of Sn to the adhesion material. However, when electroless nickel immersion gold (ENIG) is used as UBM, IMC spalling depends on the P content of the UBM. For ENIG UBM with 5 wt%P, which has a nanocrystalline structure, there was no spalling of IMC after the reflow. However, Ni3Sn4 spalled off completely from the amorphous UBM, which contained 9 wt%P.7 The IMC spalling subsequently led to brittle fracture of the solder joint.8 In contrast to the Cu UBM, which was completely consumed before the IMC spalling, spalling occurred before complete consumption of the ENIG UBM. To date, many efforts were made to suppress IMC spalling from the ENIG UBM by changing the solder composition2,11 or electroplating a thin layer of Sn or Cu on the UBM,12 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.371 3032
J. Mater. Res., Vol. 26, No. 24, Dec 28, 2011
http://journals.cambridge.org
Downloaded: 15 Mar 2015
but relatively little effort has been made to modify the composition of UBM. Ternary electroless NiXP films (X 5 Mo, Re, Tl, Cu, W, Co, Fe, Zn, Mn) have been explored as passivation layers for steels and magnetic materials due to their excellent wear/corrosion resistances and magnetic properties.13–20 However, few attempts have been made to use NiXP films as the UBM for
Data Loading...
