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Chromium plating has excellent corrosion resistance and is widely used in industry. However, it also has a high environmental load. As an alternative, electric Ni-W plating is attracting attention. However, it is not widely used because the stress is high and the film is prone to cracks. Furthermore, although it is necessary to thicken the film to improve the corrosion resistance, there are also problems that the current efficiency is low and the plating time is long. Therefore, we investigate a film with high corrosion resistance by using the jet-flow plating method that enables plating at a high current density. Our results show that the jet-flow plating enables plating of 50 µm, and high corrosion resistance is obtained by randomly generating fine cracks in the film at 20 A·dm−2. We also found that the stress changed depending on the current density and shape of the crack also changed.

Plating stress in nickel plating increases with high current density. A remedy for this has been demonstrated by using a step control method through combining plating at 20 A dm−2 (low current density) and 40 A dm−2 (high current density). Internal stress could be reduced in comparison to plating at a fixed current density by the initial formation of crystals at a 20 A dm−2 low current density, such that a state of low stress was maintained by epitaxial growth.

In order to induce adhesion of electroless CuNiP deposition to polyimide (PI) film substrate, surface modification of PI film with an aqueous dispersion of ozone micro–nano bubbles was investigated. The treatment resulted in maximum adhesion strength of 1·14 kN m−1 for a treatment time of 5 min. Structure of the modified PI surface, the PI/plating interface, mechanism for adhesion and laminate properties were analysed. Despite increased adhesion, surface roughness of PI was not notably changed by the ozone induced surface modification. Contact of PI surface with high ozone concentration micro–nano bubbles with sufficient frequency was found to modify the surface with a low total ozone concentration of the aqueous dispersion. Cross-sectional observation of the interface suggested that formation of a thin nanoporous anchor layer on the PI surface was responsible for plating adhesion. This method provides an environment friendly and improved process for plating on PI using low concentration ozone treatment.

Watt’s nickel bath and nickel sulfamate bath are commonly applied for plating of micro-fabrication parts. In particular, the nickel sulfamate bath produces nickel plating with low residual stress and high tensile strength. Nickel sulfamate baths are therefore used extensively for electroforming and Micro Electro Mechanical Systems (MEMS). Boric acid is usually used as a pH buffering agent in the plating bath. However, boron-containing effluents are increasingly regulated because of environmental concerns. To solve these problems, organic acids such as acetic acid and citric acid were investigated as alternatives to boric acid. The pH buffering action of the organic acid baths was higher than that of the boric acid bath. Furthermore, the mechanical properties of nickel films obtained from a low-concentration nickel plating bath using an organic acid buffer were superior to those obtained from a bath buffered with boric acid. Nickel films with good mechanical properties were obtained from high-concentration nickel baths, which showed good pH stability even without a buffering agent in the formulation. Subsequent SEM and XRD analyses of these plating films revealed a defect free cantilever structure prepared with MEMS.

Deposition of a heavier coating requires more careful attention to process control to prevent nodules and pitting. Electroless nickel plating is sensitive to deficiencies such as pit, pinhole and nodules. These defects are generally caused by the bath ingredients and operating conditions. This study specifically examined that the defects free electroless Ni-P deposits for heavy coating. Results of our investigation show that selection of complexing agent, elimination of insoluble particles from the plating solution using fine filtration, selection of pH adjustor and operating conditions are critical factors to avoid these defects.

近年の電子機器の高機能化に伴い, 実装部品の内部接続の高密度化が求められている。それゆえ, 無電解ニッケルめっきおよび置換金めっきは高い信頼性を有するプリント配線板を作製するための重要な工程となっている。信頼性を低下させる要因の1つは, パラジウム触媒が銅配線間の樹脂上に吸着して発生するニッケルの異常析出である。そのため, パラジゥム触媒フリーでの銅配線上への無電解ニッケルめっき法の開発が望まれている。そこで, 本研究ではパラジウム触媒フリーで銅配線上に無電解ニッケルめっきを施す手法を検討し, 銅上で触媒活性を有するヒドラジンを次亜リン酸を含む無電解ニッケルめっき浴に混合する手法を考案した。本法の適用により, パラジウム触媒フリーで銅上に無電解ニッケルめっきが可能となり, 異常析出の発生も抑制された。

Boric acid is generally added to buffer the pH and improve the life expectancy of a nickel plating bath. The plating industry has requested alternatives to boric acid because its use will be restricted in the future. In this study, the hull cell, pH buffer correlation and cathode current efficiency tests were conducted using 21 different substitute buffering agents. From these 21 agents, acetic acid, propionic acid, nickel acetate and citric acid showed the same appearance and buffering ability as boric acid. Physical properties, such as Vickers hardness, tensile strength and internal stress test were measured on nickel samples made using these four buffering agents, as well as boric acid. When using these four organic compounds, the internal stress somewhat higher compared with a standard boric acid bath, but the other physical properties were almost all the same, except in the case of citric acid. It was found that citric acid produced samples with higher Vickers hardness. For all the buffers, as current density increased, Vickers hardness decreased and tensile strength increased. The physical properties of samples made with these buffers show the same trends vs. current density as those made with boric acid bath.

ABS樹脂は, 家電部品や自動車などに応用され, プラスチックへのめっき材料として広汎に使用されている。一般的に, ABS樹脂は, 素材および析出金属問の密着性を得るために, H2SO4およびCrO3から成る強力な酸化剤によってエッチングする。近年, 環境汚染の規制は, WEEEやRoHS指令の文書に見られるように, 世界的に重要な関心事となっている。したがって, 有害物質を使用しない環境調和型エッチング技術が必要である。そこで, われわれは, クロム酸代替として光触媒である酸化チタンの使用に着目し, TiO2存在下で, UV照射を行うことにより, 有効な表面改質が可能であることを見いだした。本報ではABS樹脂中のブタジェン含有率を変化することにより, 密着強度の改善を検討した。その結果, ブタジェン含有率15～30%の範囲のABS樹脂で, 1.0kNm-1の密着強度が得られることがわかった。われわれはSEMおよびFE-TEM観察より, その密着性は粗れた樹脂表面なしで, ナノレベルのアンカー効果により得られることを確認した。

ABS resin has been widely applied as a plating substrate for plastics in applications such as the parts of vehicles and electrical devices. Hexavalent chromium has been applied as an etchant of plating on ABS resin. However, it is required to eliminate hexavalent chromium from the pretreatment process, since the prohibition of these treatments was determined by the EU directive on the End of Life Vehicles (ELV) from July, 2007. Therefore, alternative etching without hexavalent chromium has been investigated by using ultra violet irradiation (UV) and titanium oxide (TiO2) as a photocatalyst. We already achieved adhesion with the strength of about 1.0kNm−1 between ABS resin and deposited metal without hexavalent chromic acid etching. In this study, the mechanism of adhesion strength improvement with photocatalysts has been investigated using ABS specimens and rubber related ABS resin. As the results, the 1,2-polybutadiene distributed in the AS matrix was preferentially reformed and induced hydrophilicity on the reformed surface with the remaining network structure by cross-linking. In addition, we found that the reformed layer was composed a few μm thick and the catalyst penetrated into 30-40nm from the surface. It was concluded that the good adhesion strength between the deposited metal and resin was derived from the nano-anchor effect by the deposition of metal from the inside of 30-40nm of reformed resin.

ABS樹脂は, 最も身近な素材であり, 自動車や家電部品に幅広く使われている。一般的に, ABS樹脂および析出金属間の密着強度を改善するために, H2SO4およびCrO3を含有するエッチング溶液を使用する。また, その手法は工業的に40年以上行われている。近年, 環境汚染の問題はWEEE/RoHS指令に代表されるように, 世界的に重要なテーマとなっている。特に, 自動車における防錆表面処理技術は, EUのELV指令の環: 境負荷物質削減の大きな課題となっている。これらの規制により関係する部品は, 2007年7月以降, EU域内に6価クロムの使用が禁止となる。したがって, 有害物質を使用しない代替技術に変更が迫られている。われわれは, 光触媒である酸化チタンを利用したクロム酸を含まないエッチング代替処理に着目した。TiO2共存下において紫外線照射を行うことで, ABS樹脂表面が改質されることを見出した。この表面改質により, 無電解NiPめっき膜とABS樹脂との密着性が改善されることを確認した。さらに, 最適な条件下で, 約1kgf/cmの密着強度が得られた。

Electroless nickel initial deposition and subsequent steady state deposition process on a nonconductor and conductor were investigated.It is indicated that phosphorus contents in the deposited films during the initial nickel deposition reaction were higher than the subsequent steady state deposited films. The plating baths containing acetic acid, propionic acid, succinic acid, malic acid, citric acid, glycine and aspartic acid as a complexing agent showed higher phosphorus in the deposited films.On the conductor, lactic acid and glycolic acid added bath showed the shortest induction time and deposited films readily changed to continuous films at the initial deposition steps. Also, it is confirmed that a bath exhibiting a higher deposition rate compared with a basic bath leads to extraneous particles during the initial deposition period.On the nonconductor, the morphology of initially deposited nickel was not a layer-by-layer structure on nonconductor, it is confirmed that deposited films are composed of fine particles. Also, particle sizes of nickel-phosphorus deposits ranged from 10 to 40nm.

Initial deposition rate and appearance of deposited nickel on glass are measured to realize the role of a complexing agent in the electroless plating bath.We evaluated carboxylic acids, hydro carboxylic acids and amino acids as complexing agent.Among these complexing agents, carboxylic acids and hydro carboxylic acids indicated an acceleration effect and amino acids showed a retardation effect on the plating rate.Deposited nickel particles are agglomerated ranging from 10 to 30nm in the early deposition stages.Glycine among the complexing agents showed the smallest particle sizes in the initial deposition stages and nickel was uniformly deposited and distributed on glass.Therefore, this may lead the improvement of the adhesion strength of deposited nickel on glass.

An electroless nickel plating bath with a hydrazine reducing agent has been investigated. An electroless nickel plating bath with a deposition rate of about 3μm/hr and superior bath stability as compared to previously reported bath has been developed. The new bath is a simple system consisting of glycine and boric acid in addition to nickel and hydrazine. The optimum plating conditions for the bath are in the range of 85-90°C at a pH of 12. The deposits obtained from the developed bath are black with a surface morphology that has a dendrite structure. Characteristics of deposits such as specific resistance and solderability were superior to those of conventional nickel-phosphorus deposits. Results confirmed that nickel was directly deposited on a copper substrate from an electroless nickel plating bath with a hydrazine reducing agent without an activation step in pretreatment.

A double zincate pretreatment of Al for plating was investigated in a LiOH-based zincate solution. The zinc deposition rate from the LiOH-based zincate solution was lower than that from NaOH or KOH-based solutions, resulting in decreased deposition of Zn and dissolution of the Al substrate. This phenomenon was interpreted as a large coordination number for water molecules to bond with Li+ ions compared to Na+ and K+ in the zincate solutions. For a LiOH-based zincate solution at a concentration near the solubility limit of water, the concentration of free water molecules decreases due to a strong restriction around Li+ ions. This situation results in a decrease of the activity coefficient of OH- which leads to dissolution of the Al substrate, and decreases the coordination number for water molecules to in relation to Zn(OH)42- ions to accelerate the electron transfer from and Zn deposition on the Al substrate. Addition of Fe(III) ions to the LiOH-based zincate solution increased the rate of Zn deposition, suggesting that the co-deposition of Fe obstruct the growth of Zn deposition and results in imperfect insulation of the Al substrate by Zn deposition.

Surface pretreatment effects of Al and Al-Mg alloy on Zn deposition in the zincate process were evaluated using SEM and XPS. Al surface dissolution in a concentrated NaOH solution followed by zincate treatment produced rapid Zn particles nucleation with uniform size due to Al surface oxide film thinning. The anodic oxidation pretreatment of Al used jointly with electropolishing followed by zincate treatment also resulted in deposition of uniform Zn particles. Anodic oxidation pretreatment without electropolishing, however, resulted in nonuniform Zn deposition indicating that defects in the oxide film could be active sites for Zn nucleation. Al-Mg alloys require both alkaline and acid cleaning in surface pretreatment because Al dissolves in concentrated alkaline solution, and Mg dissolves in acid solution. Magnesium or its enriched compounds on the surface during zincate process in an alkaline zincate solution inhibits Al dissolution and Zn deposition. XPS showed that Zn2+ remains in the Al oxide layer, which partially charged after Zn stripping in a HNO3 solution. The role of the first zincate process in double zincate treatment is discussed based on these results.

The double-zincate processing of aluminum in three different zincate solutions was examined to evaluate the effect of solution composition. Higher concentrations of NaOH and ZnO in zincate solution dissolve both the Al oxide layer and Al substrate more rapidly. This leads to faster Zn deposition. In a solution containing Fe3+ions, Fe codeposition resulted in the growth of rather small, nonhexagonal Zn particles during the first zincate process. In the second zincate process, a stratiform Zn layer grows to cover the Al substrate in a zincate solution without Fe3+ions. Granular Zn is deposited due to Zn growth suppressed laterally by the codeposition of Fe in a solution containing Fe3+ions. Such granular Zn deposition provides a sufficient anchor effect for subsequent electroless Ni plating.

Studies were conducted using the double zincate method on the surface morphologies of aluminum substrates at each stage from pretreatment to electroless nickel plating, on the structure of immersion zinc-iron deposits and on the initial deposition process of electroless nickel plating on aluminum. A large number of zinc crystals about 1μm in diameter were deposited by displacement plating after the first zincate stage, and island-like protuberances were observed on the aluminum surface after stripping of the zinc crystals. It was confirmed that zinc crystals were formed on the tops of the protuberances prior to the flat aluminum surface during the second zincate displacement reaction.The zinc crystal formed in both the first and second zincate processes contained about 1wt% of iron.The structure of the initial electroless nickel deposition layer was studied by TEM of cross sections prepared by ultramicrotomy. The presence on the zinc crystal surface of a layer that appeared to be pure nickel, acting as a center of autocatalytic reaction was confirmed.