Mechanical properties electroless deposits

A major advantage of the electroless nickel process is that deposition takes place at an almost uniform rate over surfaces of complex shape. Thus, electroless nickel can readily be applied to internal plating of tubes, valves, containers and other parts having deeply undercut surfaces where nickel coating by electrodeposition would be very difficult and costly. The resistance to corrosion of the coatings and their special mechanical properties also offer advantages in many instances where electrodeposited nickel could be applied without difficulty. 

The coevolution of H2 gas in electroless deposition processes is a phenomenon that needs to be understood not only to elucidate the mechanism of deposition, but also since it impacts the properties of deposits by H inclusion. Van den Meerakker [51] first proposed a correlation between simultaneous hydrogen evolution in electroless deposition and the heat of adsorption of hydrogen. In this useful endeavor, however, he has been criticized for erroneously calculating the heats of adsorption of H at Cu by Gottesfeld et al. [52], and Group I (or SP type) metals in general by Bindra and Tweedie [53]. 

The incorporation of a third element, e.g. Cu, in electroless Ni-P coatings has been shown to improve thermal stability and other properties of these coatings [99]. Chassaing et al. [100] carried out an electrochemical study of electroless deposition of Ni-Cu-P alloys (55-65 wt% Ni, 25-35 wt% Cu, 7-10 wt% P). As mentioned earlier, pure Cu surfaces do not catalyze the oxidation of hypophosphite. They observed interactions between the anodic and cathodic processes both reactions exhibited faster kinetics in the full electroless solutions than their respective half cell environments (mixed potential theory model is apparently inapplicable). The mechanism responsible for this enhancement has not been established, however. It is possible that an adsorbed species related to hypophosphite mediates electron transfer between the surface and Ni2+ and Cu2+, rather in the manner that halide ions facilitate electron transfer in other systems, e.g., as has been recently demonstrated in the case of In electrodeposition from solutions containing Cl [101]. 

Finally, as in electrodeposition, additives are often employed to obtain deposits with decreased internal stress and improved mechanical properties. This is an important area, but one that is not well documented in the technical literature. Since it is not in their best interest, information about such additives is usually not disclosed by vendors of plating solutions, yet additives are often the key ingredient in a plating solution that makes it more suitable than others for a particular application. A discussion of additives used in electrodeposition is available in [124], A brief discussion of additive selection for a new electroless Cu solution is also available [96],... 

In this chapter we discuss the electrochemical model of electroless deposition (Sections 8.2 and 8.3), kinetics and mechanism of partial reactions (Sections 8.4 and 8.5), activation of noncatalytic surfaces (Section 8.6), kinetics of electroless deposition (Section 8.7), the mechanism of electroless crystallization (Section 8.8), and unique properties of some deposits (Section 8.9). 

In this section we show that some electroless deposits have unique properties compared to electrodeposited, evaporated, or sputtered metal deposits. Our discussion is limited to mechanical and diffusion barrier properties. 

There are four types of fundamental subjects involved in the process represented by Eq. (1.1) (1) metal-solution interface as the locus of the deposition process, (2) kinetics and mechanism of the deposition process, (3) nucleation and growth processes of the metal lattice (M a[tice), and (4) structure and properties of the deposits. The material in this book is arranged according to these four fundamental issues. We start by considering the basic components of an electrochemical cell for deposition in the first three chapters. Chapter 2 treats water and ionic solutions Chapter 3, metal and metal surfaces and Chapter 4, the metal-solution interface. In Chapter 5 we discuss the potential difference across an interface. Chapter 6 contains presentation of the kinetics and mechanisms of electrodeposition. Nucleation and growth of thin films and formation of the bulk phase are treated in Chapter 7. Electroless deposition and deposition by displacement are the subject of Chapters 8 and 9, respectively. Chapter 10 contains discussion on the effects of additives in the deposition and nucleation and growth processes. Simultaneous deposition of two or more metals, alloy deposition, is discussed in Chapter 11. The manner in which... 

Electroless deposition, as a very important area of the modern technology, needs further developmental studies to ensure the successful operation of the process and desirable properties of the finally obtained material. Significant further work is definitely required to learn more about the kinetics and mechanisms of the reactions involved in these sophisticated processes. 

Copper is rapidly emerging as the interconnect metal of choice for the next generation of sub-0.25pm devices. It has superior mechanical properties, lower resistivity and higher electromigration resistance when compared to aluminum. Electrochemical deposition (electroless/electroplating) of copper is a versatile, inexpensive and reliable way of filling... 

Industrial treatments are made to materials surfaces for various reasons. One is to improve the appearance of a finished product to attract potential buyers. Other purposes for surface treatments are to improve corrosion resistance, wear resistance, mechanical properties, electrical properties, etc. Surface finishing processes include electroplating, electroless plating, painting, physical vapor deposition, chemical vapor deposition, and more. 

Hsu J and Lin K, (2005) The effect of saccharin addition on the mechanical properties and fracture behavior of electroless Ni-Cu-P deposit on AI. Thin Solid Eilms 471 186-193. 

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