Electroless Ni-P Deposits Research Articles

Electrochemical analysis of zincate treatments for Al and Al alloy films

Electrochemical behavior of Al and Al alloy films in zincate solution was investigated to elucidate the effect of the zincate pretreatment for electroless NiP deposition, which is used for under bump metallization for LSI interconnects. The immersion potential for AlCu and AlSiCu, immediately reached to constant, which was almost equal potential to zinc reference electrode. The corrosion current for the AlCu and AlSiCu films was larger than that of the Al and AlSi films in the zincate solution. It was also confirmed that the deposited Zn at the surface of AlCu and AlSiCu films possessed smaller grain size and larger amount of nucleation, resulted in the formation of flat NiP films.

Corrosion Resistance of Electroless Ni-P Deposits and Its Relation to P Contents

Corrosion Resistance of Electroless Ni-P Deposits and Its Relation to P Contents

The growth morphology and crystallinity of electroless NiP deposition on silicon

The growth morphology and crystallinity of the electroless NiP deposited on Si substrate pretreated by SnCl 2/HCl and PdCl 2/HCl solutions is studied using transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), and energy dispersive X-ray spectrum (EDS). Combining cross-sectional and surface observations show that the reaction mechanism of electroless NiP on Si is an electrochemical mechanism and the deposits are composed of a columnar structure grown along the vertical direction of the substrate surface. The phosphorus content does not have influence on the growth morphology but affects the crystallinity of the deposits. The crystallinity of the deposits is directly observed by the lattice image using high-resolution transmission electron microscope (HRTEM). The as-deposited NiP with 10.7 at.% P possesses good crystallinity and consists of Ni nanocrystal about 4–8 nm distributed randomly in the deposits. The size of nanocrystal in the deposits with 15.2 at.% P is about 2–5 nm. The deposits with 20.3 at.% P have a smaller order range and the size of nanocrystal is under 1.5 nm. The grain size decreases as the phosphorus content increases.

The interfacial reaction between Sn-Zn-Ag-Ga-Al solders and metallized Cu substrates

The interfacial interaction between the Sn-8.55Zn-0.5Ag-0.5Ga-0.1Al solder and three kinds of metallized substrates (Cu, Cu/Au, and Cu/Ni-P/Au) does not form the Cu-Sn intermetallic compound (IMC). Continuous Cu-Zn and discontinuous Ag-Zn interfacial IMC layers formed between the Cu and Sn-Zn-Ag-Ga-Al solder, while Cu-Zn and Au-Al-Zn IMCs formed on the Cu/Au substrate. Only the Au-Al-Zn IMC formed at the interface when the electroless Ni-P deposit was the diffusion barrier between Cu and the Au surface layer.

Effects of Thickness of Electroless Ni-P Deposit on Corrosion Fatigue Damage of 7075-T6 under Salt Spray Atmosphere

Fatigue tests under reversed flexure have been conducted on samples of 7075-T6 Al-alloy with the application of electroless Ni-P deposits of thickness ranging from 5 to 50 μm after salt spray corrosion (100, 500 and 1000 hours). The corrosion damage of the coated and uncoated samples was determined through the measurement of the mass loss and surface corroded morphology. The mean microhardness of the high phosphorous (Hi-P) deposits in 5, 25 and 50 μm thickness were found to be 334, 457 and 606 Hv 5 0 , and the mean surface roughness (Ra) were measured at 0.197, 0.217 and 0.223 μm for 5, 25 and 50 μm thickness, respectively. The salt spray tests revealed that the corrosion damage increases as the exposure time increases for the 5 pm coating. The corrosion damage literally stopped when the coating thickness was increased to 25 μm. The fatigue strength of the coated samples was found decrease slightly as the deposit thickness increases to 25 μm, whereas the reduction on the fatigue strength for the 50 μm deposit is significant. It has been observed that the reduction in the fatigue strength is less or to none for the thicker coating system. For the 5 pm Hi-P deposit sample, the fatigue crack initiation started at the surface corrosion pitting then extending to the substrate and onto failure, this phenomenon reduced the fatigue strength as compared to the uncoated samples. The fatigue strength is decreased slightly as the thickness increases to 25 μm and 50 μm. With or without corrosion damage, the fatigue crack initiation all started from the coating and extended to the substrate through the bonding between the coating and the substrate. Balancing between the need for the corrosion resistance and the fact on the fatigue strength reduction, the optimum coating thickness seems to be greater than 5 μm but less than 25 μm for the aerospace alloy 7075-T6 Al-alloy.

無電解めっきの活性化前処理に用いられるセンシタイジング液の経時変化

SnCl2 aqueous solution including HCl is used as a sensitizer of two-step catalyzation (sensitization-activation) pretreatment for electroless metal plating onto non-conducting substrates. The sensitizer is inactivated by aging. In this study, the relationships among the Sn2+ concentration of sensitizer, amount of adsorbates formed on the substrates, induction period of electroless Ni-P deposition and aging time have been investigated quantitatively. As the aging proceeded, the Sn2+ concentration decreased, while the amount of adsorbates, including Sn species formed by sensitization, increased. With the decrease of Sn2+ concentration, the amount of Pd adsorbates formed during activation decreased, and the induction period was extended. An independent investigation using mixture solutions of SnCl2 and SnCl4 gave similar results for aging. These results show that the aging of sensitizer induces the decrease of divalent Sn species and the rise of tetravalent Sn species, which is inactive for the formation of Pd adsorbates. Thus, the aging decreases the Pd adsorbates and extends the induction period.

二液法活性化により非導電性基板上に形成される吸着物と無電解Ｎｉ‐Ｐめっき初期析出物の微視的形態

二液法活性化により非導電性基板上に形成される吸着物と無電解Ｎｉ‐Ｐめっき初期析出物の微視的形態

Growth of an intermetallic compound layer with Sn-3.5Ag-5Bi on Cu and Ni-P/Cu during aging treatment

Growth kinetics of intermetallic compound (IMC) layers formed between the Sn-3.5Ag-5Bi solder and the Cu and electroless Ni-P substrates were investigated at temperatures ranging from 70°C to 200°C for 0–60 days. With the solder joints between the Sn-Ag-Bi solder and Cu substrates, the IMC layer consisted of two phases: the Cu6Sn5 (η phase) adjacent to the solder and the Cu3Sn (e phase) adjacent to the Cu substrate. In the case of the electroless Ni-P substrate, the IMC formed at the interface was mainly Ni3Sn4, and a P-rich Ni (Ni3P) layer was also observed as a by-product of the Ni-Sn reaction, which was between the Ni3Sn4 IMC and the electroless Ni-P deposit layer. With all the intermetallic layers, time exponent (n) was approximately 0.5, suggesting a diffusion-controlled mechanism over the temperature range studied. The interface between electroless Ni-P and Ni3P was planar, and the time exponent for the Ni3P layer growth was also 0.5. The Ni3P layer thickness reached about 2.5 µm after 60 days of aging at 170°C. The activation energies for the growth of the total Cu-Sn compound layer (Cu6Sn5 + Cu3Sn) and the Ni3Sn4 IMC were 88.6 kJ/mol and 52.85 kJ/mol, respectively.

Electroless Ni-P Deposition through Imperfections in Anodic Oxide Films on Aluminum and Al5052 Alloy

Electroless Ni-P Deposition through Imperfections in Anodic Oxide Films on Aluminum and Al5052 Alloy

Interfacial reaction of Pb-Sn solder and Sn-Ag solder with electroless Ni deposit during reflow

The interfaces between electroless Ni-P deposit and Pb-Sn solder and Sn-Ag solder were formed by reflowing for different time periods to examine their microstructures and microchemistry. It was found that the Pb-Sn solder interface is more stable than the Sn-Ag solder interface. Sn-Ag solder reacts quickly with the electroless Ni-P deposit and forms nonadherent Ni-Sn intermetallic compounds (IMCs). Pb-Sn solder reacts slowly and forms adherent Ni-Sn IMC. A P-rich Ni layer, revealed as a dark layer under scanning electron microscopy (SEM), is formed on the electroless Ni-P deposit due to the solder reaction. For short reflow times, this P-rich Ni layer consists of only Ni3P compound, but during prolonged reflow, new crystals of Ni2P, Ni5P4, and NiP2 are also found to be formed from the amorphous electroless Ni-P layer.

Electrochemical and X-ray photoelectron spectroscopy investigation into anodic behaviour of electroless Ni–9·5 wt-%P in acidic chloride environment

AbstractThis paper reports on the anodic behaviour of as plated (X-ray amorphous) and heat treated (crystalline) high P electroless Ni-P deposits investigated by potentiodynamic and potentiostatic methods in acidic aqueous chloride solutions. Potentiodynamic measurements show an active-passive behaviour for both structures. The valence of P dissolution was assessed by the weight loss v. charge technique; dissolution valences do not correlate clearly with potentiodynamic behaviour. This can nevertheless be clearly interpreted in terms of ex situ X-ray photoelectron spectroscopy analyses of attacked layer composition; the layers formed at lower anodic potential within the passive range consist of NiO, the ones obtained at high anodic polarisation contain phosphate. Differences in anodic behaviour of as plated and heat treated specimens can be explained in terms of the defectiveness of protective NiO layers as a function of grain boundaries emerging at the surface.

無電解ＮｉＰめっき膜中におけるリンの分布状態

無電解ＮｉＰめっき膜中におけるリンの分布状態

Fatigue behavior of a 4340 steel coated with an electroless Ni-P deposit

The fatigue properties of a quenched and tempered (Q&T) 4340 (NiCrMo) steel coated with a commercial electroless Ni-P (EN) deposit, has been investigated. Such an EN deposit had a P content of approximately 10 wt.% and a thickness of approximately 18 μm. The evaluation of the fatigue properties of the coated material was conducted in two different conditions: (a) as-deposited and (b) deposited and post-heat treated (PHT) at 698 K for 1 h, a condition in which the maximum hardness of the deposit was observed. It has been determined that both the fatigue life and fatigue limit of the coated substrate are substantially reduced, in comparison with the uncoated material, and that such a reduction is significantly higher if the deposit is in the PHT condition. The Basquin parameters of the materials tested under different conditions have been determined and used to compute the reduction in fatigue life. Thus, it has been shown that the fatigue life of the steel substrate can be reduced up to 94% in the as-deposited condition and up to 99.1% in the as-deposited and PHT condition. Also, the fatigue limit can be reduced between 28.3–50.5% depending upon the condition of the coating. From the microscopic point of view, it has been observed that the fatigue fracture of the substrate-coating composite initiates in the deposit and that it remains well adhered to the substrate during fatigue testing since interfacial cracks have been very rarely observed. Such adhesion characteristics enhance the transference of the early cracks nucleated towards the substrate steel, a belief that is supported by the analysis of the fracture surfaces of the samples tested at different stress levels.

Evaluation of the corrosion resistance of electroless Ni-P and Ni-P composite coatings by electrochemical impedance spectroscopy

Electroless Ni-P composite coatings have gained a good deal of popularity and acceptance in recent years as they provide considerable improvement of desirable qualities such as hardness, wear, abrasion resistance, etc. The disagreement among researchers on the corrosion behaviour of these coatings warrants a thorough investigation. Among the various techniques available for the determination of corrosion resistance, electrochemical impedance spectroscopy (EIS) is considered to be superior as it provides not only an assessment of the corrosion resistance of different deposits but also enables the mechanistic pathway by which the deposits become corroded to be determined. The present investigation focuses on the evaluation of the corrosion resistance of electroless Ni-P and Ni-P-Si3N4, Ni-P-CeO2 and Ni-P-TiO2 composite coatings produced using an acidic hypophosphite-reduced electroless nickel bath, using EIS. The study makes evident that the same fundamental reaction is occurring on all the coatings of the present study but over a different effective area in each case. The charge transfer resistance of electroless Ni-P and Ni-P composite deposits are in the range 32,253–90,700 Ω cm2, whereas the capacitances of these coatings are in the range 11–17 µF/cm2. The improved corrosion resistance obtained for electroless Ni-P and Ni-P composite coatings is due to the enrichment of phosphorus on the electrode surface, which enables the preferential hydrolysis of phosphorus over that of nickel. The better corrosion resistance obtained for electroless Ni-P composite coatings can be ascribed to the decrease in the effective metallic area prone to corrosion. Among the three electroless Ni-P composite coatings, the corrosion resistance is in the following order: Ni-P-CeO2=Ni-P-Si3N4>Ni-P-TiO2.

Thermal stability of electroless-nickel/solder interface: Part A. interfacial chemistry and microstructure

The thermal stability of the interface between the Sn-Pb eutectic alloy and an electroless Ni-P coating was examined by cross-sectional transmission electron microscopy (TEM). The interface was formed by reflowing the eutectic Sn-Pb solder alloy between electroless Ni-P deposits. The microchemistry and microstructure of the interface were analyzed in the as-reflowed, mild-aged, and overaged conditions, by energy-dispersive spectroscopy (EDS), selected-area electron diffraction (SAD) convergentbeam electron diffraction (CBED), and bright- and dark-field imaging. In the as-reflowed condition, the interfacial microstructure consisted of a thin Ni3Sn4 intermetallic layer and a thin P-rich layer. The P-rich layer was composed of two phases, face-centered cubic (fcc) Ni and Ni3P, and the excess P was primarily due to the ejection of P from the electroless Ni-P when it reacted with Sn in the reflow process. Following the mild aging, a trilayer interfacial microstructure was found, including a coarsened Ni3Sn4 layer, a P-rich layer with increased P concentration, and a P-deficient layer. With overaging, a multilayer interfacial microstructure was developed, which consisted of two Ni-Sn intermetallic layers, Ni3Sn4 and Ni3Sn2, and three distinct P-rich layers, Ni12P5, Ni12P5 + Ni3P, and Ni3P + Ni.

Fatigue behavior of a quenched and tempered AISI 4340 steel coated with an electroless Ni-P deposit

The fatigue life of a quenched and tempered AISI 4340 steel has been evaluated in three different conditions: (a) uncoated, (b) coated with an electroless Ni-P (EN) deposit of a P content of approximately 12–14wt.%, as-deposited and (c) as-deposited, followed by a two-step post-heat treatment (PHT): 473 K for 1 h plus 673 K for 1 h. The results indicate that plating the base steel with this kind of deposit leads to a significant reduction of the fatigue life of the material, particularly if the deposit is subjected to a subsequent PHT. Such a reduction has been quantified by determining the Basquin parameters from the fatigue life curves obtained for the uncoated, coated, coated and PHT substrates. It has been shown that the fatigue life of the base steel can be reduced by 78% in the as-deposited condition and a 92% after a subsequent PHT. The microscopic observation of the fracture surfaces of the samples indicate that the fatigue process is initiated at the surface of the deposit and, subsequently, transferred to the substrate, with the assistance of the metallic bonding established at the deposit-substrate interface. This belief is supported by the observation of some continuity of the fracture features between the coating and the substrate under low alternating stresses. In the present study, the bonding between the EN deposit and the base steel was observed to be rather poor. Extensive secondary cracking along the coating-substrate interface after fatigue testing as well as the complete separation of the deposit from the substrate during tensile testing support this view. Such a behavior is believed to be related to the significant difference that exists between the elastic and plastic properties of the EN deposit and the base steel. Nonetheless, the slight degree of metallic bonding that remains after the first stage of fatigue testing seems to be enough to allow the passage of the fatigue cracks, prior nucleated in the deposit, into the substrate. It is therefore concluded that, in the present case, the EN deposit acts as a surface crack source or surface notch which decreases the fatigue life of the coated material by reducing the crack nucleation stage.

Fatigue properties of an AISI 1045 steel coated with an electroless Ni-P deposit

The fatigue behavior of samples of an AISI 1045 steel plated with electroless Ni-P (EN) deposits, both on an industrial and laboratory scale, has been evaluated under completed reverse bending or rotating bending conditions. The fatigue experiments were conducted in air at a frequency of 50 Hz, in the stress range of 292–346 MPa. On the laboratory scale, the deposition was carried out in a alkaline solution and the coatings were 17 μm thick, had a P content in the range of 8.4–9.4 wt.% and were post-heat treated in two different ways: at 473 K for 1 h and at 473 K for 1 h followed by 673 K for 1 h. On an industrial scale, the deposition was conducted in an acid bath, the deposits were 25 μm thick, had a P content in the range of 10.4–11.3 wt.% and were post-heat treated at 673 K for 1 h. Both deposits are observed to reduce the fatigue life of the coated components in relation to the uncoated substrate. The reduction in fatigue life is more severe for the samples coated at the laboratory scale, post-heat treated at 673 K. In general, the reduction in fatigue life is associated with the passage of fatigue cracks nucleated in the deposit to the substrate material rather than the nucleation of cracks at the deposit-substrate interface. The nucleation and propagation of such cracks from the surface of the EN coating is enhanced by the microstructural characteristics at the surface of the deposits, by residual stresses present in the coatings and by degradation of the fatigue properties of the coating from the interface to surface. An increase by approximately 2 wt.% in the P content of the deposit, compensates for the reduction in fatigue life induced by an increase in the coating thickness of 8 μm. The parameters involved in the relationship put forward earlier by Basquin, to describe the change in the number of cycles to failure in terms of the alternating stress, are reported for all the conditions investigated.

The evolution of texture during annealing of electroless Ni-Co-P deposits

The Ni-Co-P alloy deposits can be obtained from alkaline solutions over the entire range of Co compositions. The deposits with higher Co concentrations are applied to magnetic recording media and vertical magnetic recording media by adding Mn and Re. An increase in Co concentration causes a decrease in P content and increase in grain size. No study has been made of texture changes during annealing of the Ni-Co-P alloy deposits. Microstructures and crystallization of the electroless Ni-P deposits and magnetic properties and microstructures of electroless Ni-Cu-P deposits were studied by the present authors. In this paper, the evolution of texture and phase transformation behavior during annealing of the Ni-Co-P deposits have been discussed.

Preparation and Characterization of Electroless Ni-P and Ni-P-Si3N4 Composite Coatings

SUMMARYThe present work pertains to the study of electroless Ni-P and Ni-P-Si3N4 composite coatings. The deposits are obtained from a proprietary high phosphorus electroless nickel plating bath, comprising nickel sulphate, sodium hypophosphite, complexing agents and stabilizers. The maximum weight percent of Si3N4 incorporated in the electroless deposit is obtained at a concentration of 10 g/l in the bath. The electroless Ni-P deposits having 0%, 2.01%, 5.81% and 8.10% of Si3N4, respectively, obtained from baths containing 0, 2, 5 and 10 g/l of Si3N4, are characterized by optical microscopy, XRD and TEM. Hardness is found to increase with the incorporation of Si3N4 at all heat treatment temperatures studied. Also hardness increases with an increase in weight percent of Si3N4 incorporated in the deposit. The analyses of the composite coatings by XRD and TEM reveal that the inclusion of Si3N4 particles does not change the amorphous nature of the Ni-P matrix.

Tensile behaviour of as deposited and heat-treated electroless Ni-P deposits

Electroless Ni-P coatings were deposited on mild steel substrates and the effect of heat-treatment on their structure and tensile behaviour was studied, with the following conclusions. The as-deposited electroless Ni-P coating is amorphous and it remains amorphous up to 300 °C. At 400 °C the coating becomes crystalline and consists of a Ni3P matrix containing areas of metallic nickel. For the selected coating/substrate thickness ratio, the contribution of the coating in the tensile properties of the coating-substrate system is negligible as expressed by the values of yield strength, ultimate tensile strength and fracture strain in mild steel substrates and coated as-deposited and heat-treated specimens. Extensive cracking of the coating accompanied by spalling was occurred during the tensile tests. The density of cracks was found to increase close to the fracture surface of the tensile specimen and with increasing heat-treatment temperature. The cracks observed on the surface of the coatings are believed to form due to the inability of the brittle coating to accommodate the strain generated in the ductile substrate. Their orientation to the tensile axis is in close relation to the structure of the coating and the failure mechanism that is dictated by this structure. The first cracks on the surface of the coatings were found to form after the yield strength of the tensile specimen has been reached and plastic deformation of the substrate takes place. Their density increases with the accumulation of strain up to fracture.