Electroless Ni plating

Figure 3.52 Electroless Ni plated carbon fiber. Source Kind permission of Acordis Ltd (formerly Courtaulds PLC).

Unfortunately, Ni catalyzes the crystallization of carbon fibers when heated and the high modulus carbon fibers are more resistant to recrystallization than the high strength types [41,42]. The effect of 1 h of heat treatment in the range 800-1300°C in Ar on the tensile strength, modulus and recrystallization of electroless Ni plated carbon fibers was determined by Warren [105], who showed that the high modulus PAN type carbon fibers were less affected. 

Dhar S, Chakrabarti S (1996) Electroless Ni plating on n- and p-type porous Si for ohmic and rectifying contacts. Semicond Sci Technol 11 1231... 

Electroless Electrolytic Plating. In electroless or autocatalytic plating, no external voltage/current source is required (21). The voltage/current is suppHed by the chemical reduction of an agent at the deposit surface. The reduction reaction must be catalyzed, and often boron or phosphoms is used as the catalyst. Materials that are commonly deposited by electroless plating (qv) are Ni, Cu, Au, Pd, Pt, Ag, Co, and Ni—Fe (permalloy). In order to initiate the electroless deposition process, a catalyst must be present on the surface. A common catalyst for electroless nickel is tin. Often an accelerator is needed to remove the protective coat on the catalysis and start the reaction. 

In the case of a solution such as electroless Ni-P, Ni2+ is usually complexed by citrate, and the stability constants are ca. 104 and 2 x 108 (overall value) for the ML and ML2 complexes [67], Thus, pM will change relatively slowly with pH. On the other hand, the stability constant for the Pd-EDTA complex system (ML type only) is reported to be 1024 [67], i.e. Pd2+ is strongly complexed by EDTA. The Pd2+ pM value changes drastically, in a practical electroless deposition sense, over a rather narrow pH range. Consequently, in the case of an electroless Pd solution with EDTA as complexant, the solution may go from a condition of near spontaneous plating out to one where deposition virtually ceases. 

After fixing Pd catalyst on modified nylon 12 surfaces by various methods, they were coated by electroless Ni-P alloy plating. Alumina- or silica-modified nylon 12 was well wet by electroless plating liquid, and modified nylon 12 situations in a liquid were good dispersed. Nickel metal was deposited on silica or alumina surface. Finally, it was confirmed that the formation of metal layer was depended mainly on the method of Pd catalyst fixing. 

In the case of dissolved metal as major additive compounds, a combination of precipitation and redissolution can be applied for recovery from spent solutions. Gyliene et al. [94] found, for recovery of the main additive in nickel electroless plating, that the Ni(II)-citrate complex could be precipitated with alkali followed by redissolution in citric acid for reuse in electroless nickel plating after separation of the precipitate. Additionally, for decontamination of spent electroless nickel plating solutions Fe(III) can be used to precipitate the pollutant. 

This paper describes a process for activating polyimide surfaces for electroless metal plating. A thin surface region of a polyimide film can be electro-chemically reduced when contacted with certain reducing agent solutions. The electroactivity of polyimides is used to mediate electron transfer for depositing catalytic metal (e.g., Pd, Pt, Ni, Cu) seeds onto the polymer surface. The proposed metal deposition mechanism presented is based on results obtained from cyclic voltammetric, UV-visible, and Rutherford backscattering analysis of reduced and metallized polyimide films. This process allows blanket and full-additive metallization of polymeric materials for electronic device fabrication. 

The deposition of metals such as Pd, Pt, Ni, and Cu renders the surface active towards further metal deposition from conventional electroless metal plating baths. Well-adhering metal films can be formed on polyimides by this method. The main process steps for blanket metallization of a polyimide film, illustrated in Scheme I, involve polymer reduction, metal seeding, and electroless metal plating. Specific details of each process step are provided in the discussion below. 

Table 6. Bath compositions and operating conditions for electroless Ni alloy plating (T. Osaka et al., 1992 [38]).

To find the conditions in which the electroless deposition of gold at Ni-P surfaces with an acceptable appearance and adhesion would be possible, the activation of Ni-P substrates with 10% HC1 solution or a mixture of 0.1 M NH4F and sodium sulfamate was investigated. The results showed that only low phosphorus alloys (P content less than 5 wt%) pretreated with ammonium fluoride/sodium sulfamate mixture can be used for a successful electroless gold plating from cyanide solution and hydrazine as a reducing agent.31... 

Kim DH et al (1996) Electroless Ni-Fe-B alloy plating solution using DMAB as a reducing agent. Plat Surf Finish 83 78-80... 

Kim DH (1994) Preparation of soft magnetic films by electroless Ni-Fe-P plating. J Surf Finish Soc Jpn 45 203-206... 

Electroless Ni-P Plating under Open-Circuit Conditions.456... 

According to the electrochemical mechanism of electroless Ni-P plating, the electrons generated in the anodic half-reaction of hypophosphite oxidation (19.11) are involved in simultaneous cathodic reactions, that is, proton discharge from water (19.12), Ni(II) reduction... 

It should be noted that such a stoichiometry of the phosphorus formation reaction during electroless Ni-P deposition was confirmed by using analytical methods to determine the amounts of Ni and P deposited, the overall amount of hypophosphite used, and the isotopic composition of the evolved gas, which allows to quantify the contribution of reaction (19.12) under these conditions [78,79]. Therefore, anodic partial current is equal to the sum of cathodic currents during electroless Ni-P plating under open-circuit conditions ... 

Typically, before Ni coating on Al, a zincation pretreatment of the A1 is essential to enhance the Al-Ni interfacial contact, acting as a sacrificial layer during the autocatalytic electroless nickel plating process [3], This paper focuses on the zincation treatments for electroless nickel plating by analyzing the surface morphology and the deposited Ni properties. 

Solution 1 (100g/l of ZnO) is used (Table 1). Samples are retained at each individual step. Run 1 sample is just after NaOH etch. Run 2 is just after nitric acid etch, but without any zincation. All 3 types of substrates are used. Only CMOS wafer chips are plated with electroless Ni for 1 h after each run. 

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