Reliability analysis of Au–Sn flip-chip solder bump fabricated by co-electroplating

Abstract

In this study, we fabricated eutectic Au–Sn (Au–20 wt% Sn) flip-chip solder bumps from a single electroplating bath. After reflowing, the average diameter of the solder bump was approximately 80 μm. The (Ni,Au)3Sn2 phase was initially formed when the liquid Au–Sn solder reacted with the Ni UBM (under bump metallization). After aging at 150 °C, the (Ni,Au)3Sn2 intermetallic compound (IMC), which formed at the interface during reflow, was fully transformed into the (Au,Ni)Sn IMC due to the restricted supply of Ni atoms from the UBM to the interface. On the other hand, after aging at 250 °C for 1000 h, two IMC layers, (Au,Ni)Sn and (Ni,Au)3Sn2, were formed at the interface. The lower (Ni,Au)3Sn2 phase was formed when the (Au,Ni)Sn phase reacted with the Ni UBM. The interfacial (Au,Ni)Sn IMC grew with the preferential consumption of the available δ-phase in the solder matrix. Eventually, the ζ-phase covered most of the interfacial layer. In the bump shear tests, the Au–Sn/Ni joint aged at 150 °C fractured through the bulk of the solder, confirming the mechanical reliability of the interface. In contrast, the Au–Sn/Ni joint aged at 250 °C fractured along the interface, thereby demonstrating brittle failure, possibly a result of the brittle IMC layer at the interface.

Liquid-state and solid-state interfacial reactions of fluxless-bonded Au–20Sn/ENIG solder joint

“…6(a)) was consumed and -phase covered the (Au,Ni)Sn IMC layer, indicating that the Ni(P) substrate reacted primarily with the ␦-phase rather than the -phase in the solder. A similar result was also reported in the literature [6,21]. On the other hand, we recently studied the interfacial reactions of Au-20Sn/Cu solder joint [22], and reported that the Cu substrate reacted primarily with the -phase in the solder.…”

“…Eutectic Au-20Sn (in wt.%) solder has been widely used for bonding applications in microelectronic and optoelectronic packages because it can provide relatively low melting point, high strength, low elastic modulus and high thermal conductivity [1][2][3][4][5][6][7][8][9][10][11]. The Au-Sn binary system has a complicated equilibrium phase diagram, as shown in Fig.…”

Development of a 3-D Process Technology for Wafer-Level Packaging of MEMS Devices

“…It is known that the diffusion and reaction of metallic atoms are accelerated under the combined loading of high temperature, moisture, and pressure. Therefore the fractures are formed along the interface or through the bulk of the solder with the growth of the brittle inter-metallic compound layers, such as (Au, Ni)Sn and (Ni, Au) 3 Sn 2 [25]. However, the average shear strength after the combination test was still satisfied the MIL-STD-883F specification.…”

Design for reliability of solid state lighting systems

“…The material stress-strain properties and material lifetime S-N dependence (i.e. cyclic stress vs. cycles to failure) corresponding to the metallic materials have been taken from [5][6][7]. The initial stress has been determined, as in Section 4.1, according to the temperature profiles imposed during soldering and moulding processes.…”