Effect of Au-Coating on the Laser Spot Cutting on Spring Contact Probe (SCP) for Semi-Conductor Inspection

Spring contact probes (SCPs) are used to make contact with various test points on printed circuit boards (PCBs), wire harnesses, and connectors. Moreover, they can consist of the test interface between the PCBs and the semiconductor devices. For mass production of SCPs, ultra-small precision components have been manufactured by conventional cutting methods. However, these cutting methods adversely affect the performance of components due to tool wear and extreme shear stress at the contact point. To solve this problem, laser spot cutting is applied to Au-coated SCP specimens as an alternative technique. A 20 W nano-second pulsed Ytterbium fiber laser is used, and the experimental variables are different laser parameters including the pulse duration and repetition rate. After the spot cutting experiments, the heat-affected zone (HAZ) and material removal zone (MRZ) formed by different total irradiated energy (Etotal) was observed by using a scanning electron microscope (SEM). Then, the size of HAZ, top and bottom parts of MRZ, and roundness were measured. Furthermore, the change rate of HAZ and MRZ on Au-coated and non-coated specimens was analyzed with regard to different pulse durations. Based on these results, the effect of Au-coating on the SCP was evaluated through the comparison with the non-coated specimen. Consequently, in the Au-coated specimen, hole penetration was observed at a low pulse duration and low total energy due to the higher thermal conductivity of Au. From this study, the applicability of laser spot cutting to Au-coated SCP is investigated.

Effect of micro-arc oxidation coating on stress corrosion behavior of AA7050

Purpose This paper aims to study the effect of Micro-arc oxidation (MAO) coating on stress corrosion and electrochemical behavior of aluminum alloy. Design/methodology/approach The stress corrosion cracking behavior of 7050 aluminum alloy (AA7050) after MAO treatment was investigated in 3.5 Wt.% NaCl solution using the constant load ring. Electrochemical impedance spectroscopy (EIS) was used to evaluate the change of corrosion resistance of MAO specimens in 3.5 Wt.% NaCl solution, and appropriate equivalent circuits were established. Findings The results demonstrated that the MAO coating can improve the corrosion resistance of the AA7050 and avoid the reduction of mechanical properties caused by corrosion. In the initial stage of corrosion, the corrosion resistance of coated specimen decreased at first and then increased. In the middle and final stage of corrosion, the corrosion resistance of coated specimen decreased at first and then stabilized. Originality/value The long-term corrosion behavior of MAO specimens under stress was studied by constant load experiment and EIS. It has guiding significance for the application of MAO technology on aluminum alloy.

Wet Coated Thin Barrier Films to Prevent Hydrogen Embrittlement on SUS304 Stainless Steel

Hydrogen barrier coating is a promising technology for preventing hydrogen embrittlement in metals. In this study, characterizations of hydrogen barrier films coated on surfaces of austenitic stainless steel, SUS304 of the Japanese Industrial Standard (JIS), by wet coating processes applied electro-polishing and chemical oxidation method are carried out using cross-sectional transmission electron microscopy (TEM) analyses, and then slow strain rate tensile (SSRT) tests are performed in 1.1MPa hydrogen and nitrogen gases at room temperature. The hydrogen barrier films show 200–300nm total thickness of compositionally modulated Chromium oxide dense layer. The SSRT results reveal that both the elongation and reduction of area are decreased in hydrogen gas compared with those in nitrogen gas for the non barrier-coated specimens but no significant differences appear for the barrier-coated specimens. The fracture surface of the non barrier-coated specimen shows quasi-cleavagy cracking in hydrogen gas while that of the barrier-coated specimen shows only ductile dimple fracture in hydrogen gas, indicating that the coated films effectively prevent the hydrogen embrittlement of SUS304 stainless steel in hydrogen.

Characterization and exploration of polyurethane nanofiber webs coated with graphene as a strain gauge

The objectives of this study were as follows: (a) to compare two coating methods (i.e., brush painting and doctor blade coating) for applying graphene onto polyurethane nanofiber webs (PU NWs) for developing e-textiles; (b) to investigate the surface characteristics and chemical and mechanical properties of the specimens based on the coating conditions; (c) to find the relationship between the electrical resistances of the specimen and the amounts of graphene in the PU NWs; and (d) to evaluate electrical resistance changes when specimens are physically strained to calculate the gauge factors. The linear resistances of the graphene-coated PU NWs were less than 600 Ω/cm on all specimens. The PU NW linear resistances are about 1–500 Ω/cm when coated with silver nanowires and about 1000–7000 Ω/cm when coated with polypyrrole. The graphene-coated specimen linear resistances are lower than those of the polypyrrole-coated specimens and higher than those of the silver nanowire-coated specimens. As has been demonstrated in other studies, brush painting is a simple fabrication process, but the field emission scanning electron microscopy image showed that it did not produce uniform coatings compared to the doctor blade method. However, it was found that it is possible to fabricate e-textiles with linear resistances of less than 100 Ω/cm by merely using repetitive brush painting. Fourier transform infrared spectroscopy analysis confirmed the peak bands of urethane and the -NH- bending peak to investigate the graphene coating conditions. The tensile strength of the graphene-coated specimen was much lower than that of the untreated, but the elongation/strain at rupture was higher than that of the untreated specimen. This result shows that the graphene-coated specimens are strained to a smaller force than the untreated one. Furthermore, this indicates that graphene coating induced the changes of the tensile properties of the specimens. The electrical resistances are varied depending on the graphene coating uniformity. Using the doctor blade method, the electrical resistance values of the specimens were slightly lower than those for the brush painted specimens. The gauge factor values of the specimens were examined by the stretch and release test. The highest gauge factor was 97.24 (D2.6) and the lowest was 20.54 (D2.2).

Improving anti-oxidation performance of 430 SS by fabricating co-contained spinel coating as solid oxide fuel cells interconnect

PurposeThe purpose of this study is to improve the performance of AISI 430 stainless steel (430 SS) in increasing its oxidation resistance, suppressing coating spalling and cracking, sustaining appropriate conductivity and blocking Cr evaporation as an interconnect material for intermediate temperature solid oxide fuel cells; a protective co-contained coating is formed onto stainless steel via the surface alloying process and followed by thermal oxidation.Design/methodology/approachIn this work, oxidation behavior of coated specimen is studied during isothermal and cyclic oxidation measurements. Moreover, the conductivity is also investigated by area specific resistance (ASR) measurement.FindingsCo-contained spinel layer shows an outstanding performance in preventing oxidation and improving conductivity compared with uncoated specimens. The protective spinel coating also reduces the ASR for coated specimen (0.0576O cm2) as compared to the uncoated specimen (1.87296O cm2) after isothermal oxidation.Originality/valueThe probable mechanism of co-contained alloy converting into spinel and the spinel transfer electron is presented.

Improvement of Corrosion Resistance of Hastelloy-N Alloy in LiF-NaF-KF Molten Salt by Laser Cladding Pure Metallic Coatings

The corrosion protection of Hastelloy-N alloy in LiF-NaF-KF (commonly referred to as FLiNaK) molten salt has been developed by pure Ni and Co coatings using the laser cladding technique. An immersion experiment with samples was performed in molten FLiNaK salt at 900 °C for 100 h. It was found that the corrosion rates of the pure Ni-coated specimen and the pure Co-coated specimen are 39.9% and 35.7% of that of Hastelloy-N alloy, respectively. A careful microstructural characterization indicates that a selective dissolution of the elemental Cr occurred in the surface of bare Hastelloy-N alloy, showing a severe intergranular corrosion. For pure metal-coated specimens, in contrast, only metal oxide formed during the laser cladding process dissolved into the molten fluoride salt. The dense pure metal (Ni or Co) coatings exhibit a slightly general corrosion and protect the Hastelloy-N substrate effectively. The possible corrosion mechanism for both coated and uncoated Hastelloy-N under the current experimental condition are discussed in this work.

Flaking Initiation Life under Rolling Contact Fatigue of Ceramic Coated Steels Quenched after Coating Process

In our previous studies, a new surface modification method by combination of ceramic coating and heat treatment, named “substrate quenching after coating” was developed. The thrust type rolling contact fatigue tests were carried out for TiN coated steels and CrAlN coated steels processed by substrate quenching after coating, and the effects of the type of ceramic coating (TiN or CrAlN) and the quenching methods (by furnace quenching or by laser quenching) on the flaking initiation life were investigated. For the specimens quenched by furnace, the flaking life of CrAlN coated specimen was longer than that of TiN coated specimen. This reason could be explained by the difference of the oxidization of CrAlN and TiN in their furnace quenching process. For CrAlN coated specimens, the flaking life of the specimens quenched by laser was longer than that of the specimens quenched by furnace. This reason could be explained by the difference of the process time of the furnace quenching and the laser quenching. It is considered that laser quenching after coating could be an effective way to improve the flaking initiation life under rolling contact fatigue.

High Temperature Oxidation Behaviour of Detonation-Gun-Sprayed Cr3C2-NiCr-CeO2 Coatings on Inconel-718 at 900°C

The high temperature oxidation behavior of detonation-gun sprayed Cr3C2-NiCr coatings with and without 0.4 wt. % CeO2 additive on Ni-based superalloy inconel-718 is comparatively discussed in the present study. Oxidation studies were carried out at 900°C for 100 cycles in air under cyclic heating and cooling conditions on bare and coated superalloys. The thermo-gravimetric technique was used to establish kinetics of oxidation. X-ray diffraction, SEM/EDAX and X-ray mapping techniques were used to analyze the oxidation products of bare and coated samples. The results indicate that Cr3C2-NiCr-CeO2 coated specimen showed better oxidation resistance. The overall weight gain and parabolic rate constant of Cr3C2-NiCr-CeO2 coated specimen was found to be lowest in the present study signifying that the addition of CeO2 in Cr3C2-NiCr powder has contributed to the development of adherent and dense oxide scale on the coating at elevated temperature.