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SEM images of the a Cu, b Fe–73Ni and c Fe–45Ni solder joints after aging at 150 °C for 1000 h; and their enlargement of etched interfacial microstructures for d Cu, e Fe–73Ni and f Fe–45Ni solder joints; unetched interfacial microstructures for g Cu, h Fe–73Ni and i Fe–45Ni solder joints
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Ball shear test was conducted on the SnAgCu/Fe–Ni solder joints, as well as SnAgCu/Cu for comparison after reflow and 150 °C high temperature storage following the industrial JEDEC standards. According to microstructural observation, Fe–Ni UBMs show better diffusion barrier effect than Cu UBM, which form very thin FeSn2 or FeSn2+(Cu,Ni)6Sn5 layers...
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A new multilayer metallization, electroless-nickel electroless-palladium immersion gold (ENEPIG) with a thin 0.1-μm-thick Ni(P) layer (thin-ENEPIG), was plated onto a Cu printed circuit board substrate for fine-pitch package applications. We evaluated the interfacial reactions and mechanical strengths of Sn–3.0Ag–0.5Cu (SAC305) solder on thin ENEPI...
Citations
... At the same time, FeSn2 partially substitutes Cu6Sn5 in the solder joint [58]. Fe can dissolve into Cu6Sn5 [59], and its substitution for Cu introduces a lattice misfit of 0.31%. This results in an increase in lattice strain in Cu6Sn5, reducing the vacancy diffusion rate and slowing down grain coarsening in the solder joint [60]. ...
Due to the continuous miniaturization and high current-carrying demands in the field of integrated circuits, as well as the desire to save space and improve computational capabilities, there is a constant drive to reduce the size of integrated circuits. However, highly integrated circuits also bring about challenges such as high current density and excessive Joule heating, leading to a series of reliability issues caused by electromigration. Therefore, the service reliability of integrated circuits has always been a concern. Sn-based solders are widely recognized in the industry due to their availability, minimal technical issues during operation, and good compatibility with traditional solders. However, solders that are mostly Sn-based, such as SAC305 and SnZn, have a high melting point for sophisticated electronic circuits. When Bi is added, the melting point of the solder decreases but may also lead to problems related to electromigration reliability. This article reviews the general principles of electromigration in SnBi solder joints on Cu substrates with current flow, as well as the phenomena of whisker formation, voids/cracks, phase separation, and resistance increase caused by atomic migration due to electromigration. Furthermore, it explores methods to enhance the reliability of solder joint by additives including Fe, Ni, Ag, Zn, Co, RA (rare earth element), GNSs (graphene nanosheets), FNS (Fullerene) and Al2O3. Additionally, modifying the crystal orientation within the solder joint or introducing stress to the joint can also improve its reliability to some extent without changing the composition conditions. The corresponding mechanisms of reliability enhancement are also compared and discussed among the literature.
... However, there are still many problems with SAC305 solder compared to Sn-Pb solders, such as the poor wettability of SAC305 solder. In addition, the formation and growth of interfacial intermetallic compounds (IMCs) between the SAC305 solder and Cu substrate are detrimental to the reliability of the solder joints [11][12][13][14][15]. Numerous studies have confirmed that the thickness and shape of the IMCs between the SAC305 solder and Cu substrate have important effects on the thermal fatigue life, isothermal shear fatigue life, tensile strength and fracture toughness of the solder joints [16][17][18][19]. ...
This paper aims to study the effect of soldering time and ultrasonic-assisted time to microstructures, chemical compositions and thickness of intermetallic compounds (IMCs) of three types solder joints after soldering at 290 °C. The Sn3.0Ag0.5Cu (SAC305) solder and three types substrate (pure Cu, Cu–50Co and Cu–50Fe) were selected. The results showed that the compounds formed at the SAC305/Cu solder joint were Cu3Sn and spherical Cu6Sn5, the stick-like (Co,Cu)Sn3 and finely needle-like (Cu,Co)6Sn5 were generated in SAC305/Cu–50Co, while the prismatic (Cu,Fe)6Sn5 and finely granular FeSn2 were produced in SAC305/Cu–50Fe. With the soldering time increased, the IMC overall thickness of all three types solder joints gradually increased. While ultrasound was used, the morphology of Cu6Sn5, (Co,Cu)Sn3 and (Cu,Fe)6Sn5 transformed into prismatic shapes, blocky and slender stick due to cavitation and acoustic flow effects. Moreover, with the application of ultrasound, the IMC thickness of SAC305/Cu and SAC305/Cu–50Co solder joints decreased first then started to up, while that of SAC305/Cu–50Fe solder joints decreased and then remained unchanged.
... The FeSn 2 phase is a kind of interfacial intermetallic compound (IMC) formed within Sn-based solder joint when Fe element is added into substrate [7][8][9][10] or solder material [11]. In recent years, with the trend of miniaturization of electronic packaging, novel under bump metallization (UBM) materials with superior performance are urgently needed. ...
... In recent years, with the trend of miniaturization of electronic packaging, novel under bump metallization (UBM) materials with superior performance are urgently needed. Fe-Ni alloy was indicated as a superior UBM material within Sn-Ag-Cu/Fe-Ni solder joint for their excellent wettability [12], superior diffusion barrier effect [9,13,14] and excellent electro-migration resistance [15] compared to the conventional Cu and Ni UBM. As a result, two IMCs, i.e. (Fe,Ni)Sn 2 and (Cu,Ni) 6 Sn 5 were formed. ...
The effect of Ni element on mechanical properties of FeSn2 phase was investigated by means of nano-indentation measurements and first-principles calculations. The Ni content within (Fe,Ni)Sn2 interfacial intermetallic compounds (IMCs) were controlled by using different FeNi under bump metallizations (UBMs) within SnAgCu(SAC)/Fe-Ni solder joints. For SAC/Fe-45Ni (45 wt% Ni) solder joint, (Fe,Ni)Sn2 phase has coarser grains with an average amount of 1.5 at.% Ni as confirmed by scanning electron microscopy (SEM) observation and energy disperse spectroscopy (EDS). Its average Young's modulus and hardness are 134.1 GPa and 6.0 GPa respectively as measured by nano-indentation test. While for SAC/Fe-73Ni solder joints, (Fe,Ni)Sn2 phase has smaller grain size with 4.2 at.% Ni solid solution. The corresponding Young's modulus and hardness are 143.2 GPa and 6.1 GPa respectively. As further confirmed by transmission electron microscopy (TEM) and selected area electron diffraction (SAED), the (Fe,Ni)Sn2 phase possesses a crystalline of I4/mcm space group. The mechanical properties of pure FeSn2, Fe23NiSn48(about 1.5 at. % Ni) and Fe7NiSn16(about 4.2 at. % Ni) are also calculated using first principle calculation. The calculated results showed that Young's modulus increased from 134.8GPa to 139.9GPa as the Ni concentrations increased from 0 at.% to 4.2 at.%. Combining theoretical and experimental methods, we can safely conclude that the introduction of Ni element improves the Young's modulus of FeSn2 phase. However, ductility of FeSn2-based phase was the worst among the common IMCs deducing from the B/G value. And the brittleness was also confirmed by the fracture surface according to SEM observation. The brittleness of (Fe,Ni)Sn2 phase might be a risk of the reliability of SAC/Fe-Ni solder joints.
... The (Cu,Ni) 6 Sn 5 at the SAC/Fe-Ni interface possessed a hexagonal structure. At the same time, our previous work [16] demonstrated the scalloped Cu 6 Sn 5 formed at the SAC/Cu solder joint under the same conditions having a monoclinic structure. The hexagonal Cu 6 Sn 5 occurred at a high temperature and transformed into a monoclinic structure below 189 C, as depicted in the phase diagram [17]. ...
High temperature storage was conducted on SnAgCu/Fe-Ni (73 wt% Ni and 45 wt% Ni) as well as SnAgCu/Cu solder joints at 125 °C, 150 °C, and 175 °C to evaluate the diffusion barrier effect of Fe-Ni under bump metallization (UBM). For Fe-73Ni solder joints, rod-like (Cu,Ni)6Sn5 finally accumulated in the form of a continuous outer layer on the FeSn2 layer, as the aging time increased. Compared to Cu UBM, the Fe-73Ni UBM showed a better diffusion barrier effect at 125 °C and 150 °C. However, when the temperature increased to 175 °C, the inter-diffusion between FeSn2 and (Cu,Ni)6Sn5 generated a mixed IMC layer, which further transformed into the (Ni,Cu)3Sn4 phase which was accompanied with an abrupt increase of IMC thickness and rapid dissolution of UBM. In terms of the SAC/Fe-45Ni solder joints, the growth rate of (Cu,Ni)6Sn5 and the transformation of (Ni,Cu)3Sn4 were both suppressed, resulting in a compact FeSn2 layer and a higher Fe content after the UBM. As a result, the Fe-45Ni UBM showed an excellent diffusion barrier effect from 125 °C to 175 °C, as compared to the Cu and Fe-73Ni UBM. Using the statistical thicknesses of the interfacial intermetallic compounds (IMCs), the activation energies of the diffusion controlled growth of FeSn2 and (Cu,Ni)6Sn5 in Fe-45Ni solder joints were calculated as 106 kJ/mol and 122 kJ/mol, which were higher than that for the Cu3Sn (97 kJ/mol) and Cu6Sn5 (86 kJ/mol) in the Cu solder joints.
... In the case of electroless deposition methods, FeNiP amorphous ternary alloy particles can be reduced from the solutions of their salts by chemical reduction method [17]. As for electrodeposition glass FeNiP films, its morphology, composition control, annealing, phase separation of crystallization process and magnetic properties have been reported [17][18][19]. Winkler et al. [15] have synthesized FeNiP amorphous nanowires with AAO templates and investigated the phase stability and transformation from amorphous nanowires into crystalline nanowires using in-situ transmission electron microscopy (TEM) technique, which provides important views into the evolution of complex magnetic structures in confinement. It was found that crystallization of amorphous FeNiP nanowires can lead to coupling exchange between spins and the multilayer structure of two different alternating magnetic phases. ...
Amorphous FeNiP nanoparticles with homogeneous composition are synthesized by reduction of aqueous Fe2 + and Ni2 + with sodium borohydride (NaBH4) and hypophosphite at room temperature. These amorphous nanoparticles can be crystallized by heating up to 300 °C to form FeNi3 and Ni3P crystals. Ni phase appeared at the sintering temperature of 500 °C, and a special net structure was formed at 700 °C due to the joining and diffusion among different nanoparticles. At a higher temperature of 800 °C, phase transformation happened and only pure Ni nanospheres and monoclinic ((Ni, Fe)3[PO4]2) nanorods can be observed, which should be governed by the long-range diffusion in the net structure. The amorphous FeNiP nanoparticles have excellent soft magnetic property with Ms of 13.2 emu/g and Hc of 0.7 Oe. However, the sintered mixing nanoparticles show varied magnetic properties due to the phase transformation and proportion change among different phases involved in.
... Less IMC was also detected for the solder joints on Fe-45Ni compared with Fe-73Ni, which can be attributed to the diffusion barrier effect of the FeSn 2 layer. In our previous work, 29 the grain size of FeSn 2 within solder joints on Fe-45Ni was demonstrated to be larger than for those on Fe-73Ni. Meanwhile, small grain size is reported to be beneficial for rapid grain-boundary diffusion. ...
... Although Fe-Ni UBM exhibited inferior thermal cycling reliability compared with commercial Cu UBM in this study, its reliability for high-temperature storage and electromigration are better than the Cu UBM according to our systematic investigations. 29,42 To overcome the deficiency in thermal cycling reliability for use in applications, proper design of the soldering pad is needed to reduce thermal stress at the neck belt area. Also, thermal stress can be further reduced by choosing a proper composition for the Fe-Ni UBM, such as the Fe-73Ni composition in this study. ...
Thermal cycling tests have been conducted on Sn-Ag-Cu/Fe-xNi (x = 73 wt.% or 45 wt.%) and Sn-Ag-Cu/Cu solder joints according to the Joint Electron Device Engineering Council industrial standard to study their interfacial reliability under thermal stress. The interfacial intermetallic compounds formed for solder joints on Cu, Fe-73Ni, and Fe-45Ni were 4.5 μm, 1.7 μm, and 1.4 μm thick, respectively, after 3000 cycles, demonstrating excellent diffusion barrier effect of Fe-Ni under bump metallization (UBM). Also, two deformation modes, viz. solder extrusion and fatigue crack formation, were observed by scanning electron microscopy and three-dimensional x-ray microscopy. Solder extrusion dominated for solder joints on Cu, while fatigue cracks dominated for solder joints on Fe-45Ni and both modes were detected for those on Fe-73Ni. Solder joints on Fe-Ni presented inferior reliability during thermal cycling compared with those on Cu, with characteristic lifetime of 3441 h, 3190 h, and 1247 h for Cu, Fe-73Ni, and Fe-45Ni UBM, respectively. This degradation of the interfacial reliability for solder joints on Fe-Ni is attributed to the mismatch in coefficient of thermal expansion (CTE) at interconnection level. The CTE mismatch at microstructure level was also analyzed by electron backscatter diffraction for clearer identification of recrystallization-related deformation mechanisms.
... For example, novel UBM materials such as Co-P [6], Cu-Zn [7,8] and Ni-P doped with ZrO2 particles [9] were reported. Notably in the recent years, related studies show that both the addition of W [10] and Fe [11][12][13] within the Ni-based UBM materials can achieved remarkable performance in diffusion barrier for lead-free solders. It is also reported that the electroless Ni-W-P and electroplated Ni-Fe UBMs are promising to replace the conventional Ni(P) in the future [14,15]. ...
The interfacial reliability of Au-Si bonding between Cu/MoCu/Cu (named as CPC) substrate and silicon chip is analyzed. The results of optical microscopy (OM) and conformal laser scanning microscopy (CLSM) revealed that the Au layer of the cracked sample has small roughness without any patterns on it. Furthermore, the results of scanning electron microscopy (SEM), electron back-scattered diffraction (EBSD) and electron probe micro-analysis (EPMA) demonstrated that the void or crack initiated at the interface between a thin intermetallic compound (IMC) layer and the NiCo layer. It showed that the cracked sample had higher Ni content within NiCo layer and smaller size of Au layer. Moreover, the IMCs were characterized using transmission electron microscopy (TEM), which were identified as bulk-like dispersed NiSi2 and a thin continuous (Ni,Co)2Si layer. Based on the experimental results, the failure mechanism of Au-Si bonding is concluded coming from the unbalanced diffusion rate between Ni and Si during interfacial reaction. Higher Ni content of NiCo layer and small grain size of Au and (Ni,Co)2Si layer accelerate the diffusion of Ni, which also promotes the growth of interfacial Ni-contained IMC. As a result, the vacancy flows diffuse inversely towards the interface and form voids along the interface, which leads to the final crack failure.
Uniaxial magnetic anisotropy has been induced in multi-element soft magnetic amorphous FeNiPGd thin films, which were fabricated by electroplating with an external magnetic field applied parallel to the plane of the electrode. After the application of the magnetic field, surface morphology of the FeNiPGd layer is improved. The crystal grains are refined, and the number of pores generated on the surface is remarkably reduced. The introduction of external magnetic field can significantly improve the deposition rate and dynamic permeability. And the cutoff frequency can achieve 500 MHz when the applied magnetic field is 40 mT during the deposition process. Specifically, the in-plane anisotropy field of the film was calculated by the area integral method to be approximately 116Oe while the magnetic field is 10 mT, which is obviously higher than that of the binary FeNi material.
