Suppression of Cu 6 Sn 5 in TiO 2 reinforced solder joints after multiple reflow cycles

Abstract

In the current generation of 3D electronic packaging, multiple reflows are often required during soldering. In addition, electronic packages may be subjected to additional solder rework or other heating processes. This paper investigates the effects of multiple reflow cycles on TiO2 reinforced Sn-0.7Cu solder fabricated by a powder metallurgy microwave sintering technique.Compared to TiO2-free equivalents, a relative suppression of the Cu6Sn5 phase, both as primary crystals and as an interfacial layer was observed. The likely mechanism relates to the TiO2 nanoparticles promoting nucleation and decreasing the amount of time that liquid is in contact with the interfacial layer. The TiO2 particles appear to stabilise the interfacial Cu6Sn5 layer and result in a more planar morphology. The suppression of Cu6Sn5 results in TiO2 reinforced solder joints having a higher shear strength after multiple reflow cycles compared to Sn-0.7Cu solder joints. IntroductionSolder alloys play a crucial role in determining performance and reliability in the assembly and interconnection of electronic products and have electrical, thermal and mechanical functions [1,2]. The relative importance of solder alloy properties has increased due to continued miniaturization of microelectronic circuitry and the use of finer pitch interconnects. Higher functional densities in printed circuit boards (PCB) have been made possible by surface mount technology (SMT) using reflow soldering, often with multiple reflow cycles. Other heating cycles can be present in manufacturing such as additional solder rework [3]. One challenge associated with current generation Pb-free solder alloys is that during multiple thermal cycles, the joint strength may degrade due to the rapid growth of the interfacial layer of intermetallic compounds [4][5][6][7][8][9][10][11][12]. In a typical Pb-free solder joint, Cu6Sn5, which may form either as primary crystals or an interfacial layer during soldering can play a determining role in solder joint strength. There is evidence that by suppressing the Cu6Sn5 interfacial layer, solder joint properties could be improved [13][14][15][16][17] and as such there are benefits associated with controlling the growth of this layer during multiple reflows.It has recently been reported that additions of reinforcement to a variety of solder matrices, with compounds including silicon carbide (SiC) [18][19][20], nickel oxide (NiO) [21], alumina (Al2O3) [22][23][24], zirconia (ZrO2) [25][26][27][28], titanium oxide (TiO2) [29][30][31][32][33][34] and silicon nitride (Si3N4) [35,36] result in suppression of the growth of the interfacial layer during soldering [37]. In our recent study [38], we developed a method of fabricating a reinforced solder using a powder metallurgy microwave sintering method that results in a homogeneous distribution of TiO2 in the solder material and an improvement in the bulk solder material thermal and mechanical properties. However, properties related to the solder joint strength after multiple reflows of t...

Effects of Ni and TiO2 additions in as-reflowed and annealed Sn0.7Cu solders on Cu substrates

“…As in Figure 2a However, the interfacial Cu3Sn layer of the reinforced Sn0.7Cu was slightly thicker compared to the non-reinforced Sn0.7Cu. As reported by Mohd Salleh et al (2016b), the grooves between the Cu6Sn5 scallops play a critical role in the growth of Cu-Sn interfacial layer and during annealing, the grooves serves as diffusion paths of Cu into the solder. It is also reported that during soldering, the TiO2 particles come into intimate contact with the Cu6Sn5 interfacial layer modifying the Cu diffusion and dissolution path into the molten solder and preventing individual Cu6Sn5 grains from growing further and reducing the Cu6Sn5 channels.…”

Time-resolved and <i>in-situ</i> Observation of Semisolid Deformation in Al–Cu Alloys with Equiaxed and Columnar Grain Structures by Using a Combination Technique of 4D-CT and 3DXRD

“…X-ray imaging using synchrotron radiation has allowed observation of the solidification behavior in various metallic alloys such as Sn alloys, [7][8][9][10][11][12][13][14][15][16] Al alloys, 9,10,17,18) cast iron, [19][20][21][22][23] Fe-C steels, 11,[24][25][26][27][28] and stainless steels. 29) Installing a deformation device in the observation apparatus, in-situ observation of semisolid deformation by X-ray transmission imaging (referred to as 2D observation hereinafter) was achieved with a high spatial resolution with respect to grain size.…”

Research Status of Evolution of Microstructure and Properties of Sn-Based Lead-Free Composite Solder Alloys

“…[50] demonstrated that the doping of TiO 2 could have resulted in the refinement of microstructure of Sn-0.7wt%Cu-0.05 wt%Ni solder by the fabricate process of microwave sintered and the homogeneous (Cu, Ni) 6 Sn 5 intermetallics appear in the grains of particles. Moreover, they also investigated the evolution of Cu 6 Sn 5 IMC of TiO 2 additive Sn-0.7Cu composite solder after different reflow cycles [110]. It was confirmed that the incorporation of TiO 2 nanometer particles could suppress the growth of Cu 6 Sn 5 , which was associated with the inhibiting effect as shown in Figures 26 and 27, respectively.…”