Plating electroless nickel

Many electroless coppers also have extended process Hves. Bailout, the process solution that is removed and periodically replaced by Hquid replenishment solution, must still be treated. Better waste treatment processes mean that removal of the copper from electroless copper complexes is easier. Methods have been developed to eliminate formaldehyde in wastewater, using hydrogen peroxide (qv) or other chemicals, or by electrochemical methods. Ion exchange (qv) and electro dialysis methods are available for bath life extension and waste minimi2ation of electroless nickel plating baths (see... 

G. G. Gawrilov, Chemical (Electroless) Nickel-Plating, PortcuUis Press, RedhiU, U.K., 1979. 

Approximately 4500 tons of sodium hypophosphite [7681-53-0] NaH2P02, was produced in 1990. This material is used principally in electroless nickel plating of plastic objects. Of the secondary products made from primary phosphoms compounds, phosphoms oxychloride is manufactured in the largest volume. Phosphoms pentachloride and phosphoms sulfochloride are made from phosphoms trichloride. 

Selenium and selenium compounds are also used in electroless nickel-plating baths, delayed-action blasting caps, lithium batteries, xeroradiography, cyanine- and noncyanine-type dyes, thin-film field effect transistors (FET), thin-film lasers, and fire-resistant functional fluids in aeronautics (see... 

Electrodeposition of Metals. Citric acid and its salts are used as sequestrants to control deposition rates in both electroplating and electroless plating of metals (153—171). The addition of citric acid to an electroless nickel plating bath results in a smooth, hard, nonporous metal finish. 

Commercial processes Commercial electroless nickel plating stems from an accidental discovery by Brenner and Riddell made in 1944 during the electroplating of a tube, with sodium hypophosphite added to the solution to reduce anodic oxidation of other bath constituents. This led to a process available under licence from the National Bureau of Standards in the USA. Their solutions contain a nickel salt, sodium hypophosphite, a buffer and sometimes accelerators, inhibitors to limit random deposition and brighteners. The solutions are used as acid baths (pH 4-6) or, less commonly, as alkaline baths (pH 8-10). Some compositions and operating conditions are given in Table 13.17 . 

Tanaka, M. Kobayashi, M. Seki, T. Recovery of nickel from spent electroless nickel plating baths by solvent extraction. International Solvent Extraction Conference, Cape Town, South Africa, Mar. 17-21, 2002, 787-792. 

Electroless Nickel Plating, W. Reidel, ASM International, Metals Park, Ohio, (1991). 

After the sintering stage, electrodes are applied, usually either by electroless nickel plating or by painting or screening on specially adapted silver paint. Leads are then soldered to the electrodes when, for many applications, the device is complete in other cases it may be encapsulated in epoxy or silicone resins. Examples are illustrated in Fig. 4.15. 

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. 

Gyliene, O., Aikaite,)., Tarozaite, R., Dolgov, and I.A. (2004) Regeneration and decontamination of a nickel citrate complex in spent electroless nickel plating solutions. Trans. Inst. Met. Finish., 82 (1-2), 33-37. 

Figure 4. Nickel (o ) and sodium hypophosphite (0 ) concentration in an electroless nickel plating solution at pH 5 as a function of the volume fraction suspended SiC (o ) and A1j03 (0 ) particles.107...

An electrochemical method of evaluating the substrate surface activity in electroless nickel plating has been proposed by Osaka et al., who used mixed potential measurements [6-8]. After activating a copper wire substrate with a mixed PdCl2/SnCl2 catalyst, the mixed potential of the Cu wire in the plating bath is... 

Fig. 5. Functionality test for electroless nickel plating, (a) Time dependence of mixed potential after activation, (b) time dependence of mixed potential after acceleration A-F indicate various catalyst solutions (T. Osaka et al., 1980 [6, 7]).

M. V. Sullivan and J. H. Eigler, Electroless nickel plating for making ohmic contacts to silicon,... 

Applications Hypophosphites are mainly used in electroless nickel plating (e.g. deposition of nickel phosphorus layers with 8 to 10% P in the Kanigan process). 

Selective electroless nickel plating of particle arrays on polyelectrolyte multilayer was investigated for the potential applications in sensors, optoelectronics, and biochips.96 This process is based on the preparation of functional colloidal arrays on surfaces. In the next step metal deposition is carried out on the surfaces of the patterned particles secured on the substrate. Samples of colloidal arrays on patterned polyelectrolyte templates are first pretreated with a Pd(II)-based catalyst. After rinsing with deionized water and drying, samples were plated with nickel using dimethylamine borane (DMAB) as a reducing agent. Based on the results of this work,96 it was shown that the selective electroless nickel deposition on 3D patterned surfaces can be successful. 

Organic acids are usually separated by means of ion-exclusion chromatography and detected via their electrical conductivity. Applications are mainly in the field of copper and electroless nickel plating baths. 

Fig. 8-45. Determination of 2-imidazolidinthione in an electroless nickel plating bath. - Separator column IonPac NS1 eluent acetic acid/methanol/ water (1 5 94 v/v/v) flow rate 0.8 mL/min detection UV (254 nm) injection 50 pL sample with 3 ppm of the relevant substance.

Gawrilov GG (1979) Chemical (electroless) nickel plating, 1st edn. Portculhs Press Limited, RedhiU... 

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. 

A commercial zincation bath is used. Single zincation time is varied between 0-30 s, and a second zincation time of 5-30 s. CMOS wafer chip samples are retained after each designed stage. Process steps like degreasing, soak clean and rinsing is the same for all experiments. The following outlines the typical zincation process for electroless nickel plating ... 

Step 7 Electroless nickel plating at 90°C for 1 h (only for CMOS chips)... 

Solutions 1-5 are used (Table 2). Samples at 30 s single zincation and 30/30 s double zincation are retained [4], SEM-EDX is done on single zincation whereas XPS done only for double zincation. CMOS wafer chip and sputtered A1 silicon wafer are zincated but only CMOS wafer chips are electroless nickel plated for 1 hour. 

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