P-rich Layer Research Articles

Enhanced mechanical properties and in vitro bioactivity of silicon nitride ceramics with SiO2, Y2O3, and Al2O3 as sintering aids.

Silicon nitride (Si₃N₄) ceramics exhibit excellent mechanical properties and biocompatibility, making them highly suitable for biomedical applications, particularly in implants. In this study, the mechanical properties and bioactivity of Si₃N₄ ceramics with varying amounts of Y₂O₃-Al₂O₃-SiO₂ sintering aids were investigated. Increasing the sintering additive content from 4wt% to 8wt% substantially improved the bulk density of the ceramics, leading to notable enhancements in mechanical properties. These included a Vickers hardness increase to 10.07GPa, a flexural strength increase to 605MPa, and a fracture toughness increase to 2.43MPam1/2. The optimal combination of mechanical properties was achieved with 8wt% sintering additives due to the higher aspect ratio and lower porosity. After immersion in simulated body fluid (SBF), the surface of the Si₃N₄ ceramics was coated with a Ca and P-rich layer, morphologically similar to hydroxyapatite. The layer formation was facilitated by the presence of SiO₂, which promoted hydroxyapatite nucleation and growth, as well as the rapid release of Ca2⁺ ions and the sustained stability of the apatite layer.

The Intermediate Barrier Performance of Electroless Co-W-B / Ni-P Stacked Deposits Between Cu and Solder Joint

Nickel (Ni) is one of the most common surface finishing materials for solder joint and wire bonding because it can behave as the diffusion barrier for Copper (Cu) and bring excellent reliability. Electroless Ni plating has many advantages such as high productivity, good thickness uniformity, and the deposition ability for isolated patterns of printed circuit boards without supplying electrolytic power. Electroless Ni plating is widely used as the jointing material for Tin (Sn) or Sn alloy solder in printed circuit boards, lead frames, and so on. The amorphous deposits of electroless Nickel-Phosphorus (Ni-P) generate the intermetallic compounds (IMC) with solder after the reflow and the remaining Ni behaves as the barrier between Cu and solder. In this time, the P amount of Ni-P deposits generally have the impact to the growth of IMC. Electroless Ni-P with high P (high P Ni) such as 10-12 wt% has been selected to achieve both corrosion resistance and solder joint reliability. Because the growth of Sn-Ni IMC between high P Ni is faster than deposits with lower P, the target thickness of high P Ni has been set to approximately 10 µm to sustain the Ni-P layer as the barrier layer between Cu and solder during reflow. However, if the Ni-Sn IMC is repeatedly formed and dissolved by the diffusion after solder jointing, the Ni-P layer reduces and finally disappears. As a result, an additional barrier layer is desirable for higher reliability. In this study, we investigated adding electroless Cobalt-Tungsten-Boron (Co-W-B) as a new intermediate barrier between Cu and solder jointing. We evaluated the bonding strength and IMC analysis after mounting Sn-Cu-Ni-P type solder on Cu/Co-W-B/Ni-P by using different reflow profiles. Results showed that Co-W-B 0.1-0.2 µm/Ni-P 1-2 µm stacked deposits had excellent bonding strength even though the Ni-P thickness is thinner such as 1 µm. After mounting solder, a P-rich layer was generated on the Co-W-B layer in cross-sectional Transmission Electron Microscope (TEM) observation. Scanning Transmission Electron Microscope (STEM) –Energy Dispersive X-ray Spectroscopy (EDS, STEMEDS) analysis showed the P-rich layer and Co-W-B layer prevented diffusion between solder and Cu. Furthermore, even if after the thermal loading of high temperature, the bonding strength was excellent. Additionally, the cross-section analysis of STEM-EDS revealed that a thin layer composed of Ni, Co and P was formed between Co-W-B and the P-rich layer. This thin layer also might behave as the barrier for solder. In conclusion, Co-W-B / Ni-P stacked deposits exhibited excellent reliability as the additional intermediate barrier layer between Cu and solder.

Microstructural Optimization of Sn-58Bi Low-Temperature Solder Fabricated by Intense Pulsed Light (IPL) Irradiation

In this study, intense pulsed light (IPL) soldering was employed on Sn-58Bi solder pastes with two distinct particle sizes (T3: 25–45 μm and T9: 1–8 μm) to investigate the correlation between the solder microstructure and mechanical properties as a function of IPL irradiation times. During IPL soldering, a gradual transition from an immature to a refined to a coarsened microstructure was observed in the solder, impacting its mechanical strength (hardness), which initially exhibited a slight increase followed by a subsequent decrease. It is noted that hardness measurements taken during the immature stage may exhibit slight deviations from the Hall–Petch relationship. Experimental findings revealed that as the number of IPL irradiation sessions increased, solder particles progressively coalesced, forming a unified mass after 30 sessions. Subsequently, after 30–40 IPL sessions, notable voids were observed within the T3 solder, while fewer voids were detected at the T9-ENIG interface. Following IPL soldering, a thin layered structure of Ni3Sn4 intermetallic compound (IMC) was observed at the Sn-58Bi/ENIG interface. In contrast, reflow soldering resulted in the abundant formation of rod-shaped Ni3Sn4 IMCs not only at the reaction interface but also within the solder bulk, accompanied by the notable presence of a P-rich layer beneath the IMC.

Electrolyte Role in SEI Evolution at Si in the Pre-lithiation Stage vs the Post-lithiation Stage

The formation and evolution of the dynamic solid electrolyte interphase (SEI) at the Si anode/electrolyte interface are yet to be completely understood to solve irreversible capacity loss and increase battery cycle life. Herein, the evolution of SEI and its dynamic properties at the Si anode/electrolyte interface are investigated in two electrolyte systems, a 1.2 M LiPF6 in EC: EMC 3:7 (wt%) electrolyte (referred to as Gen2) and a 1.2 M LiTFSI in EC: EMC 3:7 (wt%) electrolyte (referred to as LiTFSI). Two lithiation stages are studied: the pre-lithiation (pre-Li) SEI stage and the post-lithiation (post-Li) stage. Findings reveal at the pre-Li, SEI formation starts at an early potential and contributes to the greater mass gain in the Si/Gen2, and it is dominated by the formation of a non-uniform F- and P-rich layer in Si/Gen2, in contrast to a homogeneous F- and C-containing layer at the Si/LiTFSI interphase. The initially formed SEI in LiTFSI further benefits the charge transfer kinetics. At the post-Li stage, a more substantial SEI evolution is observed at Si/LiTFSI. This study offers a foundational understanding of the SEI dynamic evolution with electrolyte dependence. Findings from this report offer important insights into solving the complex SEI stability issues on Si.

Reconstruction of a surficial P-rich layer on Ni-P electrocatalysts for efficient hydrogen evolution applicable in acidic and alkaline media

Ni-P is a promising catalytic material for the hydrogen evolution reaction (HER) due to its high catalytic activity, highly competitive cost, and practical usefulness. To achieve the best catalytic performance with the Ni-P-based material, it is necessary to control the P ratio in Ni-P because the catalytic kinetics of Ni-P depend on the number of reaction sites of the positively and negatively charged Ni and negatively charged P to adsorb the hydride/hydroxide and proton in acidic and alkaline media. Here, we introduce a facile surface-treatment based on dealloying to control the surficial P ratio with multiple CV cycles. As a result, the 20 and 10 times cycled Ni-P/CFPs show improved catalytic activities of 30.8% and 23.5% along with higher stabilities of 99.8 and 97.9% retention in acid and alkaline media, respectively. In particular, the different kinetics according to P ratio in both acid and alkaline media can be elucidated by DFT calculations of the free energy changes related to each RDS.

Diffusion Barrier Properties of the Intermetallic Compound Layers Formed in the Pt Nanoparticles Alloyed Sn-58Bi Solder Joints Reacted with ENIG and ENEPIG Surface Finishes

Pt-nanoparticle (NP)-alloyed Sn-58Bi solders were reacted with electroless nickel-immersion gold (ENIG) and electroless nickel-electroless palladium-immersion gold (ENEPIG) surface finishes. We investigated formation of intermetallic compounds (IMCs) and their diffusion barrier properties at reaction interfaces as functions of Pt NP content in the composite solders and duration of solid-state aging at 100 °C. At Sn-58Bi-xPt/ENIG interfaces, typical Ni3Sn4/Ni3P(P-rich layer) microstructure was formed. With the large consumption of the Ni-P layer, the Ni-P and Cu layers were intermixed and Cu atoms spread over the composite solder after 500 h of aging. By contrast, a (Pd,Ni)Sn4/thin Ni3Sn4 microstructure was observed at the Sn-58Bi-xPt/ENEPIG interfaces. The (Pd,Ni)Sn4 IMC effectively suppressed the consumption of the Ni-P layer and Ni3Sn4 growth, functioning as a good diffusion barrier. Therefore, the Sn-58Bi-xPt/ENEPIG joint survived 500 h of aging without microstructural degradation. Based on the experimental results and analysis of this study, Sn-58Bi-0.05Pt/ENEPIG is suggested as the optimum combination for future low-temperature soldering systems.

Microstructural evolution of intermetallic compounds between crystalline/amorphous Cobalt-Phosphorous coatings and lead-free solders

In the advanced microelectronic packaging, Cu/Sn joints require high-quality diffusion barriers to inhibit Cu–Sn intermetallic compounds (IMCs) growth and improve the interface brittleness. Cobalt-Phosphorous (Co–P) alloy coatings are ideal candidates due to their good wettability, promising diffusion resistance and low interfacial brittleness. In this work, the microstructural evolution of IMCs between crystalline/amorphous Co–P coatings and lead-free solders during the solid-state diffusion were systemically investigated. The microstructure, phase distribution, and grain characteristics of coatings and IMCs were carefully characterized by SEM, EPMA, EBSD, and TEM. It was found that the consumption rate of crystalline Co–P, 21.2 nm/h, was significantly slower than that of amorphous Co–P, 96.4 nm/h, and exhibited an excellent diffusion resistance, which was attributed to the nanocrystalline structure and the P-rich layer which performed the diffusion barriers for Sn and Cu atoms. Compared with Ni, amorphous Co–P coatings could better improve the interfacial brittleness with soft and ductile Co–Sn compounds (hardness of 3.0 GPa) growing with the rapid diffusion of Co, and the toughened Co–Sn–P attributing to the diffusion of Sn. Kinetic analysis showed that the growth rate-controlling process of Co–Sn IMCs was jointly controlled by interfacial reaction and volume diffusion, and the effect of the interfacial reaction is more pronounced in the amorphous system, which leads to coarse Co–Sn grains that are beneficial to the softness and ductility of IMCs. Crystalline and amorphous Co–P coatings can be applied to the surface treatment for die pads and print-circuit-board pads according to their own characteristics, respectively.

Influencing mechanism of phosphorous on intragranular M23C6 of a Ni-base superalloy studied by atom probe tomography

Moderate addition of phosphorous (P) could remarkably improve the stress rupture properties of some superalloys by optimizing M23C6 carbide at grain boundary, but the influencing mechanism of P on M23C6 carbide is still unclear. Using atom probe tomography, the distribution of P across M23C6/γ interface and grain boundary were determined quantitatively. P segregation at γ/M23C6 interface was observed for the first time. A P-rich layer enveloped M23C6 carbide forms. It is expected to inhibit the coarsening and coalescence of M23C6 carbide. The improvement of intragranular M23C6 carbide should be attributed to the formation of P-rich layer around M23C6 carbide and P segregation at grain boundary.

Reconstruction of a Surficial P-Rich Layer on Ni-P Electrocatalysts for Efficient Hydrogen Evolution Applicable Over Wide Ph Ranges

Reconstruction of a Surficial P-Rich Layer on Ni-P Electrocatalysts for Efficient Hydrogen Evolution Applicable Over Wide Ph Ranges

Preparation of corrosion-resistant MgAl-LDH/Ni composite coating on Mg alloy AZ31B

Compared to single coatings, multiple-layer coatings or composite coatings could provide better and more durable corrosion protection to magnesium alloys. In this paper, a MgAl-LDH/Ni composite coating was successfully prepared on magnesium alloy AZ31B via preparation of a LDH primer, an electroless-deposited Ni-B (ENB) intermediate layer, and an electroless-deposited Ni-P(ENP) top layer. The surface morphologies, chemical compositions, and corrosion resistance of the composite coating were characterized and discussed. The results showed that nano-scale Ag particles acting as the activation sites were introduced onto the surface of the LDH layer after the activation process. Ni particles were deposited in the areas where Ag particles exist, and an intact Ni-B layer formed after 15 min of ENB plating. The total thickness of the composite coating is about 38 µm, in which the LDH layer is ~13 µm, and the EN coating is ~25 µm. The composite coating does not show any perforation after exposure to a 3.5 wt% NaCl solution for 210 h or 0.1 mol·dm−3 HCl solution for 30 h, attributed to the amorphous structure of the electroless-deposited nickel layer and the P-rich layer formed at the surface to hamper nickel oxidation. In comparison, obvious corrosion holes appeared on the LDH coating after immersion in a 3.5 wt% NaCl solution for 20 h or in a 0.1 mol·dm−3 HCl solution for 30 min. Furthermore, the EIS test results confirmed the durable corrosion protection of the composite coating to the magnesium alloy substrate.

Effects of Ni(P) layer thickness and Pd layer type in thin-Au/Pd/Ni(P) surface finishes on interfacial reactions and mechanical strength of Sn–58Bi solder joints during aging

To analyze the effects of Ni(P) layer thickness and Pd layer composition on interfacial reactions and the mechanical reliabilities of Sn–58Bi solder joints, we evaluated a phosphorous-contained Ni (Ni(P)) layer thicknesses ranging from 0.3 to 1.0 μm with Au/Pd/Ni(P) or a phosphorous-contained Pd [Au/Pd(P)/Ni(P)] layer in thin-electroless-nickel electroless-palladium immersion gold (ENEPIG) with Sn–58Bi solder joint after aging test. (Pd, Au)Sn4 and Ni3Sn4 intermetallic compounds (IMCs) were dominantly formed at the interfaces of the 0.3 µm to 1.0 μm Ni(P) layers in the thin-Au/Pd/Ni(P) or thin-Au/Pd(P)/Ni(P) joints after aging at 85 °C and 95 °C for 100 h. However, the Ni3Sn4 IMC layer changed to the (Cu, Ni)6Sn5 IMC layer in the 0.3 μm Ni(P) layer contained the Au/Pd/Ni(P) joint after aging at 85 °C for 300 h, because the Cu elements in a Cu pad penetrated through the P-rich Ni layer. Otherwise, the Ni3Sn4 IMC of the 0.3 μm Ni(P) layer in the Au/Pd(P)/Ni(P) joint changed to (Ni, Cu)3Sn4 IMC after aging at 105 °C and 115 °C for 1000 h, due to the P in the Pd layer, which affects the IMC growth rate. The 0.7 µm and 1.0 μm Ni(P) layers in the Au/Pd/Ni(P) or Au/Pd(P)/Ni(P) joints were attributed to the Ni3Sn4 IMC layer for whole aging conditions because the thick P-rich Ni layer suppress Sn and Cu diffusion during aging. In a high-speed shear tests, the shear strength of the 0.3 μm Ni(P) layer in the Au/Pd/Ni(P) joints was relatively low than that of the Au/Pd(P)/Ni(P) joints after aging at 105 °C and 115 °C for 100 h. Ni3Sn4 IMC was observed at the fracture surfaces of the 0.3 μm Ni(P) layer in the Au/Pd(P)/Ni(P) joints after aging at 115 °C for 1000 h, whereas the fracture surface of the Au/Pd/Ni(P) joint was Cu substrate. Therefore, Ni(P) layer thicknesses in excess of 0.7 μm and the P-contain Pd layer in the thin-ENEPIG surface finish with Sn–58Bi solder joints are expected to be highly reliable after long-term aging treatment.

Laser deposition of bioactive coatings by in situ synthesis of pseudowollastonite on Ti6Al4V alloy

The feasibility of obtaining bioactive coatings on Ti6Al4V alloy by laser deposition was studied. A Nd:YAG source was used under the following parameters: 65 or 70% of average power, 8 ms of pulse duration, 8 Hz of frequency and 0.7 mm/s of travel speed. A CaO-SiO2 powder mixture, with a molar ratio of 1:1, was projected to the metallic surface during the laser treatment. Due to the heat supplied by the laser, pseudowollastonite was the main compound formed in situ on the Ti6Al4V alloy samples as a result of the chemical interaction among calcium and silicon oxides and titanium from the alloy. A higher quantity of pseudowollastonite was formed on the sample treated at the highest average power used (70%). In vitro bioactivity assessment was performed by immersing pulsed laser-treated samples in a simulated body fluid (SBF) for 21 days. A dense Ca, P-rich layer was formed on the samples. The spherical morphology of the agglomerates formed is similar to the apatite formed on the existing bioactive systems.

Study of Three-Dimensional Small Chip Stacking Using Low Cost Wafer-Level Micro-bump/B-Stage Adhesive Film Hybrid Bonding and Via-Last TSVs

Three-dimensional (3-D) small chip stacking using low cost wafer-level insert-bump hybrid bonding and via-last TSVs is proposed and investigated. The proposed hybrid bonding method realized by micro Cu pillar solder bumps and photo-patternable B-stage adhesive film has been successfully applied to an 8 inch wafer with 86 255 gross dies and a bump pitch of 150 μm. The complete process flow is successfully validated and a well electrical connectivity for the whole wafer is obtained. Two hybrid bonding approaches, i.e., “adhesive-first” hybrid bonding and “Cu pillar bump-first” hybrid bonding, are studied. A void-free hybrid bonding interface with a final gap between top chip and bottom chip lower than 30 μm is achieved using the “Cu pillar bump-first” hybrid bonding approach. The interaction of SnAg solder with electroless Ni-P/immersion Au and electro Ni are investigated. Two types of interfacial compounds, i.e., Ni3Sn4 and P-rich Ni layer containing Sn atoms, are found. The via-last through silicon vias (TSVs) have a diameter of 40 μm and a depth of 95 μm. The results indicate that it is a promising method for 3-D integrated circuits stacking technology using hybrid bonding and via-last TSVs.

Bioactivity and biomineralization ability of calcium silicate-based pulp-capping materials after subcutaneous implantation.

To evaluate the abilities of three calcium silicate-based pulp-capping materials (ProRoot MTA, TheraCal LC and a prototype tricalcium silicate cement) to produce apatite-like precipitates after being subcutaneously implanted into rats. Polytetrafluoroethylene tubes containing each material were subcutaneously implanted into the backs of Wistar rats. At 7, 14 and 28days post-implantation, the implants were removed together with the surrounding connective tissue, and fixed in 2.5% glutaraldehyde in cacodylate buffer. The chemical compositions of the surface precipitates formed on the implants were analysed with scanning electron microscopy-electron probe microanalysis (SEM-EPMA). The distributions of calcium (Ca) and phosphorus (P) at the material-tissue interface were also analysed with SEM-EPMA. Comparisons of the thicknesses of the Ca- and P-rich areas were performed using the Friedman test followed by Scheffe's test at a significant level of 5%. All three materials produced apatite-like surface precipitates containing Ca and P. For each material, elemental mapping detected a region of connective tissue in which the concentrations of Ca and P were higher than those in the surrounding connective tissue. The thickness of this Ca- and P-rich region exhibited the following pattern: ProRoot MTA > prototype tricalcium silicate cement≥TheraCal LC. ProRoot MTA had a significantly thicker layer of Ca and P than the other materials at all time-points (P<0.05), and a significant difference was detected between the prototype cement and TheraCal LC at 28days (P<0.05). After being subcutaneously implanted, all of the materials produced Ca- and P-containing surface precipitates and a Ca- and P-rich layer within the surrounding tissue. The thickness of the Ca- and P-rich layer of ProRoot MTA was significantly thicker than that of the other materials.

Solder Volume Effect on Interfacial Reaction between Sn-Ag-Cu/ENImAg Substrate

The purpose of this study is to investigate the effect of solder volume on interfacial reaction during reflow soldering between Sn-3.0Ag-0.5Cu (SAC305) and Sn-4.0Ag-0.5Cu (SAC405), and electroless nickel/immersion silver (ENImAg) surface finish. Different solder balls with sizes of 300μm, 500μm and 700μm diameters were used. The characteristics of intermetallic compound (IMC) were analysed by using field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), optical microscope and energy dispersive x-ray (EDX). After the plating process, the result showed that ENImAg surface finish was free from black line nickel. After reflow soldering, a thin layer Ni3P or P-rich layer was formed. The result also revealed that an IMC layer was formed at the interface of (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 as well as Ag3Sn platelet. In term of morphologies, the grains type of IMC layer appeared as chuck, needles, rode, plate, diamond and bar shape. The result also indicated that, the solder volume can influence the IMC thickness, where the smaller size of solder balls produced a thinner IMC layer compared with a larger solder ball during the reflow soldering process. Meanwhile, a total of the IMC thickness for SAC305 was thinner than SAC405 solder ball.

TEM observation of interfacial compounds of SnAgCu/ENIG solder bump after laser soldering and subsequent hot air reflows

In three-dimensional (3D) packaging and assembly technology, Lead-free SnAgCu solder joints inevitably experience multiple reflows. The interfacial compounds of Sn3.0Ag0.5Cu (SAC305)/ Electroless Ni–P/Immersion Au (ENIG) solder bump after laser soldering and subsequent hot air reflows were observed by transmission electron microscopy (TEM), respectively. The initial laser soldering played a key role in interfacial compound evolution during the subsequent multiple reflows. After laser soldering, a thin P-rich layer and an ultrafine scallop-type (Ni, Cu)3Sn4 layer formed at the interface of SAC305/ENIG. The valleys of ultrafine (Ni, Cu)3Sn4 grains served as rapid channels for Ni diffusion, which contributed to the formation of dendritic η-(Cu, Ni)6Sn5+(Ni, Cu)3Sn2 intermetallic compounds after the first hot air reflow. However, with the number of reflow times increasing, the η-(Cu, Ni)6Sn5 totally transformed to noodle-like (Ni, Cu)3Sn2 owing to their similarly hexagonal lattice structure and the limited Cu supply in solder.

Electromigration behavior in Cu/Ni–P/Sn–Cu based joint system with low current density

Although electromigration in solder joints has great influence on reliability, few study has been reported on the Cu/Ni–P/Sn–Cu based joint system electromigration with realistic current density range lower than 10kA/cm2. We investigated a Cu/Ni–P/Sn–0.7Cu/Ni–P/Cu joint with current densities of 5.0 and 7.5kA/cm2 at 423K. Solder joint breakdown at the cathode side was detected for both stress conditions. Ni–P plating disappeared completely at the cathode side and a Cu–Sn intermetallic compound (IMC) formed at the interface. Cu–P IMC formed on the solder breakdown interface. Ni diffusion in Ni–P plating at the cathode was accelerated and the P-rich layer grew thicker than at the anode side before breaking down under electromigration stress. The P-rich layer reached the Cu electrode resulting in cracking along the interface between solder layer and Cu. Sn was diffused from the Ni3SnP IMC to the P-rich layer cracks and formed Cu3Sn IMC with the Cu electrode. Thus, the electromigration mechanism in an electroless Ni–P plating/Sn–Cu based joint system with low current density was clarified.

Solder electromigration behavior in Cu/electroless Ni–P plating/Sn–Cu based joint system at low current densities

Electromigration (EM) in solder joints has great influence on their reliability. Nevertheless, few reports have been published on the EM in solder joints with Ni–P barrier layers at lower current densities less than 10 kA/cm2. In the present study, EM in Cu/Ni–P/Sn–0.7Cu/Ni–P/Cu joints was investigated at 150 °C with current densities of 5.0 and 7.5 kA/cm2. The breakdown mode was open failure of the solder joint on the cathode. It was found that Ni in the Ni–P barrier layer diffused toward the anode, resulting in a thicker P-rich layer, which caused the cracks and the delamination of the P-rich layer. Additionally, the diffusion of Sn detached the solder from the Ni3SnP intermetallic compound on the cathode.

Investigation of micro-arc oxidation coating growth patterns of aluminum alloy by two-step oxidation method

The micro-arc oxidation (MAO) process of 2A70 aluminum alloy in different electrolytes containing silicate or phosphate by two-step oxidation was investigated. The growth rate, surface roughness and element distributions of the micro-arc oxidation coatings were characterized. The results show that the coating growth patterns are different in Si and P electrolytes although they both grow inward. The discharge channels formed in Si-electrolyte and P-electrolyte are trumpet-shaped and dumbbell-shaped, respectively. The trumpet-shaped channel is conducive to gather heat and extend the reaction area inward, which leads to a layer growth pattern in P-electrolyte. The dumbbell-shaped channel limits the reactive area but introduces more electrolytes during the cooling process, which results in an island growth pattern in Si-electrolyte. Therefore, a newly formed P-rich layer can be observed between substrate and initially formed Si-rich layer after the second-step oxidation in P-electrolyte, but only localized Si-rich areas could be found when the second-step oxidation was performed in Si-electrolyte.

Effect of Bath Life of Ni(P) on the Brittle-Fracture Behavior of Sn-3.0Ag-0.5Cu/ENIG

The effect of bath life of Ni(P) on the brittle-fracture behavior of Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC)/electroless nickel immersion gold (ENIG) was evaluated in this study. The bath lives of Ni(P) for the ENIG surface finish in this study were varied from 0 to 3 metal turnover (MTO), which were indirectly indicative of Ni(P) bath life, with “0 MTO” denoting the as-make-up state and “3 MTO” denoting almost waste plating solution. The SAC/ENIG sample when Ni(P) was plated in the 3 MTO bath (3 MTO sample) had thicker (Cu,Ni)6Sn5 and P-rich layers than when Ni(P) was plated in the 0 MTO bath (0 MTO sample). The brittle-fracture behavior of the 0 and 3 MTO samples was evaluated by use of a igh-speed shear (HSS) test with a strain rate of 0.1–2.0 m/s. The shear strength of the 0 MTO sample was higher than that of the 3 MTO sample. The incidence of brittle fracture increased as the bath life of Ni(P) of ENIG (= MTO of Ni(P)) increased. Observation by transmission electron microscopy (TEM) revealed nano-sized voids (or particles) in the Ni-Sn-P layer. As the MTO of the Ni(P) increased, the number of nano-sized voids in the Ni-Sn-P layer of the SAC/ENIG interface increased. The poor brittle-fracture behavior of the 3 MTO sample originated from the weak interface at the thick P-rich layer and from the large nano-sized voids.