Vesa Vuorinen

Thermodynamics, diffusion and the Kirkendall effect in solids

Thermodynamics, phases and phase diagrams.- Structure of Materials.- Ficks laws of diffusion.- Development of interdiffusion zone in different systems.- Atomic mechanism of diffusion.- Interdiffusion and the Kirkendall effect in binary systems.- Growth of phases with narrow homogeneity range and line compounds by interdiffusion.- Microstructural evolution of the diffusion zone.- Interdiffusion in multicomponent systems.- Short circuit diffusion.- Reactive phase formation in thin film systems.

Effect of dissolution and intermetallic formation on the reliability of FC joints

The dissolution processes and subsequent intermetallic reactions between high tin solder bump alloys and Cu‐ or Ni‐based UBM‐metallisations were investigated both theoretically and experimentally. The results showed that when the Cu UBM layer is used together with eutectic or higher Sn‐based solder alloys the dissolution of Cu and the rate of the Cu6Sn5 formation is too high for reliable interconnections. On the contrary, Ni provides feasible solution for UBM/high tin solder applications. Although there is strong chemical interaction between nickel and high Sn solder bump alloys, the dissolution and subsequent Ni3Sn4 layer growth rates are very low. Thus, a thin Ni layer can sustain interactions with high Sn liquid as well as solid solders during high temperature use. On the basis of the results obtained flip chip bonding with Ni‐based UBM structures provides a viable interconnection solution for reliable fine‐pitch applications.

Combined Thermodynamic-Kinetic Analysis of the Interfacial Reactions between Ni Metallization and Various Lead-Free Solders

In this paper we will demonstrate how a thermodynamic-kinetic method can be utilized to rationalize a wide range of interfacial phenomena between Sn-based lead-free solders and Ni metallizations. First, the effect of P on the interfacial reactions, and thus on the reliability, between Sn-based solders and electroless Ni/immersion Au (ENIG) metallizations, will be discussed. Next, the effect of small amounts of Cu in Sn-based solders on the intermetallic compound (IMC), which forms first on top of Ni metallization, will be covered. With the help of thermodynamic arguments a so called critical Cu concentration for the formation of (Cu,Ni)6Sn5 can be determined as a function of temperature. Then the important phenomenon of redeposition of (Au,Ni)Sn4 layer on top of Ni3Sn4 IMC will be discussed in detail. The reasons leading to this behaviour will be rationalized with the help of thermodynamic information and an explanation of why this phenomenon does not occur when an appropriate amount of Cu is present in the soldering system will be given. Finally, interfacial reaction issues related to low temperature Sn-Zn and Sn-Bi based solders and Ni metallization will be discussed.

Migration From PLC to IEC 61499 Using Semantic Web Technologies

This paper proposes a new methodology of migration from IEC 61131-3 PLCs to IEC 61499 function blocks. The aim of this migration process is to recreate IEC 61131-3 applications in IEC 61499 implementations with equivalent execution behavior. The formal model of the IEC 61131-3 standard for migration and cyclical execution model is defined. This method also creates a foundation for correct-by-design development tools and automatic migration between the IEC 61131-3 and IEC 61499 standard. Formal migration rules based on ontology mappings, restoring execution model including tasks and programs scheduling and variables mapping with different access levels, are provided. A transformation engine for importing PLC code, mapping from PLC ontology model to function block model and code generation is implemented based on the ontological knowledge base and semantic query-enhanced web rule language. The migration approach is demonstrated on a simple airport baggage handling system.This paper proposes a new methodology of migration from IEC 61131-3 PLCs to IEC 61499 function blocks. The aim of this migration process is to recreate IEC 61131-3 applications in IEC 61499 implementations with equivalent execution behavior. The formal model of the IEC 61131-3 standard for migration and cyclical execution model is defined. This method also creates a foundation for correct-by-design development tools and automatic migration between the IEC 61131-3 and IEC 61499 standard. Formal migration rules based on ontology mappings, restoring execution model including tasks and programs scheduling and variables mapping with different access levels, are provided. A transformation engine for importing PLC code, mapping from PLC ontology model to function block model and code generation is implemented based on the ontological knowledge base and semantic query-enhanced web rule language. The migration approach is demonstrated on a simple airport baggage handling system.

Effect of Ni content on the diffusion-controlled growth of the product phases in the Cu(Ni)-Sn system

Abstract A strong influence of Ni content on the diffusion-controlled growth of the (Cu,Ni)3Sn and (Cu,Ni)6Sn5 phases by coupling different Cu(Ni) alloys with Sn in the solid state is reported. The continuous increase in the thickness ratio of (Cu,Ni)6Sn5 to (Cu,Ni)3Sn with the Ni content is explained by combined kinetic and thermodynamic arguments as follows: (i) The integrated interdiffusion coefficient does not change for the (Cu,Ni)3Sn phase up to 2.5 at.% Ni and decreases drastically for 5 at.% Ni. On the other hand, there is a continuous increase in the integrated interdiffusion coefficient for (Cu,Ni)6Sn5 as a function of increasing Ni content. (ii) With the increase in Ni content, driving forces for the diffusion of components increase for both components in both phases but at different rates. However, the magnitude of these changes alone is not large enough to explain the high difference in the observed growth rate of the product phases because of Ni addition. (iv) Kirkendall marker experiments indicate that the Cu6Sn5 phase grows by diffusion of both Cu and Sn in the binary case. However, when Ni is added, the growth is by diffusion of Sn only. (v) Also, the observed grain refinement in the Cu6Sn5 phase with the addition of Ni suggests that the grain boundary diffusion of Sn may have an important role in the observed changes in the growth rate.

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films

Plasma-enhanced atomic layer deposition was utilized to grow aluminum nitride (AlN) films on Si from trimethylaluminum and N2:H2 plasma at 200 °C. Thermal treatments were then applied on the films which caused changes in their chemical composition and nanostructure. These changes were observed to manifest in the refractive indices and densities of the films. The AlN films were identified to contain light element impurities, namely, H, C, and excess N due to nonideal precursor reactions. Oxygen contamination was also identified in the films. Many of the embedded impurities became volatile in the elevated annealing temperatures. Most notably, high amounts of H were observed to desorb from the AlN films. Furthermore, dinitrogen triple bonds were identified with infrared spectroscopy in the films. The triple bonds broke after annealing at 1000 °C for 1 h which likely caused enhanced hydrolysis of the films. The nanostructure of the films was identified to be amorphous in the as-deposited state and to become n...

Microstructural Evolution and Mechanical Properties of Au-20wt.%Sn|Ni Interconnection

In this paper, the microstructural evolution and properties of Au-20wt.%Sn|Ni reaction couples were investigated from two perspectives: (1) by analyzing the microstructure of the as-soldered and aged samples, as well as (2) by measuring the mechanical properties of the intermetallic compounds formed within the reaction zone. The evolution of interfacial reaction products for both the as-soldered and aged interconnections was rationalized by using the experimental results in combination with assessed thermodynamic data from the Au-Ni-Sn system. Moreover, nanoindentation tests were implemented to measure the indentation modulus and hardness of the compounds formed at the interface. It was found that aging had a negligible influence on the elastic modulus and hardness of AuSn and Au5Sn, while the solubility of the third element significantly changed the indentation modulus and hardness of the intermetallic compounds.

Interconnections based on Bi-coated SnAg solder balls

To decrease the bonding temperature required for eutectic SnAg solder, SnAg solder bumps were chemically coated with a pure Bi layer. During heating, a low melting eutectic forms between the Bi coating and the SnAg, enabling bonding at temperatures below the melting points of either pure Bi or SnAg solder. As the composition of the molten solder changes toward more dilute Bi concentrations, the melting point in the joint region increases and the joint solidifies. After solidification the joints will no longer melt at the original bonding temperature. Bi-coated SnAg solder balls were joined to metallized substrates at temperatures ranging from 180/spl deg/C to 250/spl deg/C. The microstructure at the joint interface was characterized by the SEM/EDS technique. As expected, at 180/spl deg/C the Bi-coated SnAg solder balls melted only locally at the interfacial regions between the ball and the substrate and so retained their spherical shape during bonding. After solidification there were a lot of small Bi precipitates in the joint region. At higher temperatures, the wetting was evidently better, and there were less Bi precipitates, because the melt was more dilute in bismuth. In all cases, Bi formed relatively small, equi-axed precipitates instead of the eutectic structure found in eutectic Sn-Bi solder joints.

Microstructural Evolution and Mechanical Properties in (AuSn)eut-Cu Interconnections

The interfacial reactions between the widely employed solder Au-20wt.%Sn and the common contact metallizations (e.g. Ni, Cu and Pt) are normally complex and not well determined. In order to identify the proper contactor for Au-20wt.%Sn solder, the present study focuses on (1) rationalizing the interfacial reaction mechanisms of Au-20wt.%Sn|Cu as well as (2) measuring the mechanical properties of individual intermetallics formed at the interface. The evolution of interfacial reaction products were rationalized by using the experimental results in combination with the calculated Au-Cu-Sn phase diagram information. It was found that the growth of the AuCu interfacial intermetallic layer was diffusion-controlled. The diffusion path of Au-20wt.%Sn|Cu at 150°C was proposed. The hardness and indentation modulus of the interfacial reaction products were measured using nanoindentation tests. The results revealed a significant influence of the Cu solubility on the mechanical properties of (Au,Cu)Sn and (Au,Cu)5Sn, i.e. their hardness and contact modulus increased with the increase in the amount of Cu. Furthermore, results obtained here for the Au-20wt.%Sn|Cu joints were compared to those from Au-20wt.%Sn|Ni in order to assess the similarities and differences between these widely used interconnection metallization systems.

Effect of Ti on the interfacial reaction between Sn and Cu

The effect of Ti on the solid state reactions between Sn and Cu has been investigated in this work. Based on the experimental results the following statements about the effect of Ti can be made: Firstly, the presence of Ti does not have measurable effect on the thickness of either Cu6Sn5 or Cu3Sn during solid state annealing. However, the unevenness of both Cu6Sn5 and Cu3Sn layers is increased by the addition of Ti. Secondly, there is no marked solubility of Ti to either Cu6Sn5 or Cu3Sn. Rather Ti reacts with Sn to form large Ti2Sn3 platelets inside the solder matrix. These findings were subsequently rationalized with the help of the assessed Cu–Sn–Ti phase diagram. By utilizing this phase diagram information, the absence of any marked effects of Ti on the growth of Cu–Sn intermetallic compound (IMC) formation was rationalized. As there is a very low solubility of Ti to SnAg solder and to Cu–Sn IMC’s, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Cu–Sn IMC layer thickness or quality by Ti alloying.