Electroless Ni Film Research Articles

Black Pad Susceptibility of the Electroless Ni Films on the Cu UBM

The occurrence of black pad in the electroless Ni film during the immersion gold process is related to the surface morphology of the Ni(P) film. A nonuniform distribution of the nodule size and curvature is the crucial factor. Large nodules with small surface curvatures had higher P concentration and did not corrode, while small nodules with large surface curvatures had lower P concentration and corroded. Experiments using different types of Cu substrates suggest that the Ni(P) film black pad susceptibility increased with the defect density and/or the residual stress in the underlying substrate. Annealing the Cu substrate before the electroless Ni plating greatly reduced the black pad formation.

シクロオレフィンポリマーの酸素増感VUV表面改質によるパラジウム吸着表面層の形成

A photochemical process was applied to form an active surface layer on cyclo-olefine polymer (COP) for improved immobilization of palladium. A Xe excimer lamp irradiating vacuum ultraviolet (VUV) light of 172 nm wavelength was used as a light source for surface modification. COP samples placed in dry air with atmospheric pressure were irradiated with VUV light. Because of the dissociative excitation of oxygen molecules, atomic oxygen species were generated along with ozone molecules formed through the following chemical reactions of the oxygen atoms. These active oxygen species served as oxidants for COP surface modification. Based on VUV photochemistry assisted with oxygen, known as the oxygen-amplified VUV process, an oxidized COP layer with thickness of several tens of nanometers was formed on each COP sample. The layer, which contained highly concentrated hydrophilic functional groups such as -OH, -CHO, and -COOH, functioned as an adsorbing site for palladium catalysts. Consequently, this technique has been found to be effective as a pre-treatment of Ni-P electroless plating. Electroless Ni films with sufficient adhesion to pass the cross-cut tape test were deposited on the VUV-modified COP substrates. Direct patterning without photolithography has been demonstrated for fabricated Ni micropatterns.

Structures and Magnetic Properties of Electroless Ni Multilayers on Fe/Si Substrate

Nanosized single and multiple layers of electroless Ni films were deposited on Fe film. The multilayer films consisting of a Fe/(Ni1 Ni2)n structure, where Ni1 and Ni2 denote various electroless Ni films deposited in plating baths with different pH values, and n denotes layer numbers and equals to 2, 4, 8, and 16, were formed by alternately changing the pH value of plating baths under controlled deposition time during the deposition process. The ensuing results showed that the boundaries between films are almost even. The deposition of various electroless Ni films on Fe film can increase the coercivity and squareness ratio of Fe film.

Deposition of electroless Ni on micro-sized acrylic spheres

In this work a thin film of electroless Ni was deposited on the surface of commercial acrylic spheres about 4 μm in size. After the acrylic spheres were cleaned, sensitized and activated successively, they were put into an acid plating bath containing sodium hypophosphite as reducing agent for the electroless Ni deposition. The acrylic spheres with a film of Ni deposit were molded into a cold set resin and ground and polished to form a cross section for observation. The thickness of the Ni film was measured and the state of the adhesion of Ni film to the surface of the acrylic sphere was observed by a scanning electron microscope. The results showed that the Ni film deposited in a plating bath with pH 4.2 can tightly adhere on the surface of the acrylic sphere due to the compressive stress of the Ni film. The thickness of the Ni film on the acrylic sphere can reach about 0.35 μm in 3 min of deposition time at 50–70 °C of plating temperature. The activation energy of electroless Ni deposition in plating bath with pH 4.2 is about 28.50 kJ/mole. The acrylic spheres with a layer of electroless Ni film deposited by the method proposed in this work can be further applied to anisotropic conductive adhesives in flip chip package.

Interfacial reactions of electroless nickel thin films on silicon

Interfacial reactions of electroless nickel thin films on blank silicon annealed at 300–900 °C have been studied by both cross-sectional and planview TEM as well as by sheet resistance measurement. Samples were prepared by depositing Ni on (0 0 1)Si substrate by electroless plating deposition followed by annealing to form a silicide. An amorphous interlayer was found in interface between electroless nickel thin films and silicon. The amorphous interlayer blocks the reaction between Ni and Si and change the silicide formation sequence. The epitaxial NiSi 2 was found on electroless plating nickel thin films on silicon at the temperature as low as 300 and 400 °C. The presence of phosphorus in the electroless Ni films and/or amorphous interlayer between electroless Ni films and Si were found to promote the formation of the epitaxial NiSi 2 at low temperature. The dominant phase was NiSi in samples annealed at 500–700 °C. The results have shown that NiSi film formed by electroless plating process has the same resistance property as the NiSi film formed by vacuum plating process. The electroless plating technique can provide a cheap and easy process for forming nickel silicide, and has potentiality of application for the electronic device industries.

Studies of electroless nickel under bump metallurgy—Solder interfacial reactions and their effects on flip chip solder joint reliability

The electroless-deposited Ni-P under bump metallurgy (UBM) layer was fabricated on Al pads for Sn containing solder bumps. The amount of P in the electroless Ni film was optimized by controlling co...

Stresses in electroless Ni-P films for electronic packaging applications

Electroless-plated nickel films for electronic packaging applications such as under bump metallurgy (UBM) and flip chip bumps are investigated in this study. Quantitative stress of an electroless-plated Ni-P film on an Al coated Si wafer has been measured using a laser scanning profiler and the Stoney equation. A tensile intrinsic stress was developed due to plating defects, and also a tensile extrinsic thermo-mechanical stress due to temperature change and the CTE mismatch of Ni film and Si substrate was observed. It was found that the extrinsic stress became more tensile as the phosphorus content of the electroless Ni film decreased. Therefore, it is necessary to reduce the amount of stresses developed at the electroless Ni film by controlling phosphorous content of the electroless Ni film for reliable electronic packaging applications.

The Influence of Phosphorus Concentration of Electroless Plated Ni-P Film on Interfacial Structures in the Joints between Sn-Ag Solder and Ni-P Alloy Film

The interface structure between Sn-3Ag solder and electroless plated Ni film and the structure near that interface were examined. Plated electroless Ni films contained 3.7 mass% phosphorus or 8.5 mass% phosphorus. A P-enriched layer is formed at the joining interface between plated electroless Ni film and Sn-3Ag solder, in each sample with 3.7 mass%P and 8.5 mass%P. P-enriched layers of both P concentration samples contained double the P concentration than the original plated Ni films. Also, the P-enriched layer of the Ni-8.5 mass%P sample was much thicker than that of the Ni-3.7 mass%P sample. Both P-enriched layers have been composed of Ni-Sn-P layer and P enriched Ni-P layer. Kirkendall voids were formed between the 1st Ni-Sn-P layer and 2nd Ni-P layer. The number of voids observed in Ni-8.5 mass%P sample was much greater than those in the Ni-3.7 mass%P sample. Intermetallic compounds, mixtures of Ni 3 Sn 2 and Ni 3 Sn 4 , were formed by the interfacial reaction. In the case of the Ni-3.7 mass%P sample, Ni-Sn intermetallic compounds continuously crystallized on the P-enriched layer, while in the case of the Ni-8.5 mass%P sample, Ni-Sn intermetallic compound crystallized dispersively in the solder.

Bonding mechanism of electroless Ni-P film with AlN substrate and Cu foil

Electroless Ni (EN) plating method is employed to metallize Y2O3-doped AlN ceramic substrates with different surface morphologies, including the as-received, polished, and etched AlN. The EN-plated AlN substrate is bonded with the Cu foil to form a sandwich-like AlN-EN/Cu/EN-AlN assembly by hot pressing in vacuum with a pressure of 6.5 MPa for 30 min. The bonding strength of the joint is determined by the adhesive abilities of EN/AlN and EN/Cu interfaces. Bonding between the Cu foil and the EN film is achieved by the interdiffusion of Cu and Ni atoms to form a solid solution interlayer, while the EN film is adhered on the AlN substrate mainly by the mechanical interlocking through the rough interface, etched holes, and open pores. At the bonding temperatures lower than 400/spl deg/C, no reaction occurs between the Cu foil and the EN film. Increasing bonding temperature enhances the interdiffusion of Cu and Ni to form a strong bonded solid solution interlayer. However, the depletion of the element Ni in EN film results in the formation and enlargement of the pores at EN/AlN interface, which makes a poor adhesion between EN film and AlN substrate. An optimum bonding temperature is observed around 600 and 700/spl deg/C for various surface conditions of AM substrates. Theoretical calculations of the residual thermal stresses in AlN, EN, and Cu layers with respect to the bonding temperatures are related to the variation of the bonding strengths. The relations of the adhesion strengths, interfacial morphologies, elemental distribution, and calculated residual stresses is proposed.

Ion implantation for nucleation of electroless Ni films on Si

Our previous work has recently established ion implantation as a viable technique to seed electroless Cu films on several substrates. In this work we employ this technique for selective nucleation of electroless Ni films on Si substrates. Pd ions are implanted into <100> Si using a metal vapour vacuum arc (MEVVA) ion implanter. The implantation dose is varied between 7E14 and 3.6E16 ions cm -2. The substrates and plated films are studied with Rutherford backscattering spectroscopy and channelling (RBS-C), SEM, EDX, profilometery and the scotch tape test (STT). A threshold dose required for nucleation of electroless Ni plating has been determined. Plated films, several microns thick, with good adhesion have been made using this technique. The effect of implantation parameters such as ion energy, ion dose and of plating conditions on the growth kinetics and morphology of the plated films has been investigated. A test structure in the shape of a coil has been fabricated using this technique.

Adhesion strength and microstructural evaluation in electroless Ni-P metallized AlN substrate

The adhesion strength of the electroless Ni (EN)-plated AlN substrates is studied through investigation of the microstructural morphologies at the AlN-EN interfaces. Etching sites around the Al-Y-O compounds on the etched AlN substrate provide the anchor acceptors for interlocking the EN film to achieve a high adhesion strength. Separation of the EN film from the AlN substrate under the action of force leaves the fracture cracks propagating along the AlN/EN interface, cutting through the anchors and making the fragmental EN films around the etching sites reside on the AlN fracture surface. However, the polished AlN substrate lacks the interlocking sites and fails to obstruct the cracks propagating along the AlN/EN interface, and thus results in a poor adhesion strength. An appropriate adhesion strength of 13.7 MPa with a small standard deviation (/spl plusmn/2.3 MPa) can be obtained for the previously etched and 10 /spl mu/m thick EN-plated AlN substrate.

Indirect bonding of Ni-electroless plated AlN and Cu by hot pressing method

The electroless Ni (EN) plating method was employed to metallize the AlN ceramic substrates. The EN-plated AlN substrate was bonded with the Cu foil to form a sandwich-like AlN-EN/Cu/EN-AlN assembly by hot pressing in vacuum with a pressure of 6.5 MPa for 30 min. For the bonding temperature below the Ni-P eutectic temperature of EN at 880/spl deg/C, the samples were bonded through solid state diffusion. On the other hand, the samples were bonded via a liquid phase media through both wetting and diffusion if the bonding temperature was above 880/spl deg/C. An optimum adhesion strength around 10 MPa occurred within bonding temperature range 600-700/spl deg/C. The fracture took place in the EN/Cu interface for samples bonded below 600/spl deg/C, while fracture took place in the AlN/EN interface above 700/spl deg/C, The increasing temperature enhanced interdiffusion of Cu and EN to form a strong bond, yet resulted in a large residual thermal stress in the AlN/EN interface. The bonded samples with as-received AM exhibited higher adhesion strength than those with polished AlN because there existed a residual compression perpendicular to the AlN/EN interface at surface irregularities in the as-received AlN, which resulted in an additional shear strength offset in the adhesion test. The adhesion strength of samples with etched AlN was the highest as compared to those of as-received and polished AlN, although the surface roughness of the etched AlN was the same as that of the as-received one. It is argued that the etched surface of AlN with micro-etched holes provides the anchor sites for interlocking with the EN film, which results in a good mechanical bonding in the joint. However, a mechanical trimming on the edges of bonded samples would damage the joint, and a low adhesion strength is instead observed. >