**5. Conclusions**

Tribocorrosion is the degradation of material surfaces by the combined action of corrosion, electrochemical passivation, and external mechanical interactions. It is essentially a surface related process, but some events like hydrogen evolution and absorption by the material, can modify the mechanical properties of the sub-surfaces on materials. Under conditions where tribocorrosion is active, the material loss depends in a complex way on many parameters like the tribological conditions in the contact, the composition of the environment, the temperature, the flow rate, the pH and eventually the applied potential. By analogy it is possible to extend this concept when, in the process previously described, a chemical or physical adsorption of inhibiting species strengthens or replaces the electrochemical passivation process. The successive repetition of some of these processes can lead to a possible synergism between mechanical stress and the effect of the environment what results in a damage of surfaces and systems through an accelerated loss of functionality.

Electrochemical methods used for corrosion studies are of interest in tribocorrosion since they allow the *in situ* monitoring and analysis of the interactions between surfaces and their

Tribocorrosion: Material Behavior Under

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environment as well as changes induced by a mechanical action like sliding or impact. In combination with conventional tribological measurements, they allow to understand the evolution of the surface state in a time space. The choice of methods to be used depends on the type of mechanical action. The data interpretations must be adapted to the heterogeneous state of surfaces undergoing a mechanical interaction, and also to the contact conditions.

Taking into account the surface state heterogeneity that results from successive mechanical and corrosive interactions, the development of an analysis of local phenomena on surfaces is needed to predict the impact of varying environmental conditions, tribological, and even geometrical ones on the operating behavior of a tribological system. Besides the methods already mentioned above, *ex situ* techniques to characterize surfaces, like the determination of residual stresses, micro-and nano-hardness, topography by 3D profilometry, chemical and structural micro-analysis of surfaces, microscopy at different length scales, must be implemented to acquire the spatial response of materials subjected to combined corrosion and mechanical loadings.

#### **6. References**


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**6. References** 


**5** 

L.C. Tsao

*Taiwan* 

**Corrosion Resistance of Pb-Free and** 

*National Pingtung University of Science & Technology, Neipu, Pingtung,* 

Tin-lead (Sn-Pb) alloys for metal interconnections were first used about 2000 years ago. Recently, the use of alloys has become essential for the interconnection and packaging of virtually all electronic products and circuits. Sn-Pb solder alloys have been widely used in the modern electronics industry because of their low melting points, good wettability, good corrosion resistance, low cost, reasonable electrical conductivity, and satisfactory mechanical properties. However, due to health concerns, recent legislation, and market pressures [1], the electronic industry is moving toward green manufacturing as a global trend. In the area of packaging, mainly driven by European RoHS (Reduction of Hazardous Substances), lead was banned effective July 1, 2006, except in some exempt items. In addition, Pb and Pb-containing compounds, as cited by the Environmental Protection Agency (EPA) of the US, are listed among the top 17 chemicals posing the greatest threat to human life and the environment [2] because of lead's toxicity [3]. In the electronics industry, the lead generated by the disposal of electronic assemblies is considered hazardous to the environment. Therefore, developing viable alternative Pb-free solders for electronic

Although several commercial and experimental Pb-free solder alloys are available as replacements for Sn-Pb solders, the following families of solders are of particular interest and are the prevailing choices of industry [4]: eutectic Sn-Ag, eutectic Sn-Cu, eutectic Sn-Zn, eutectic Bi-Sn, and Sn–In, as shown in Table 1. Since the properties of the binary Pb-free solders cannot fully meet the requirements for applications in electronic packaging, additional alloying elements are added to improve the performance of these alloys. Thus, ternary and even quaternary Pb-free solders have been developed [5-7], such as Sn-Ag-Cu, Sn-Ag-Bi, and Sn-Zn-Bi solder. However, the knowledge base on Sn-Pb solders gained by experience is not directly applicable to lead-free solders. In other words, the reliability of Pbfree solder joints in consumer products is attracting more interest and concern from both

**1. Introduction** 

assemblies is of principal importance.

**2. Lead-free solder systems** 

academia and technologists[8-10].

**Novel Nano-Composite Solders** 

**in Electronic Packaging** 

*Department of Materials Engineering,* 

