MATERIAL SCIENCE.docx

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COPPER-TIN ALLOYS

The important alloys of copper and tin from an industrial point of view are the

bronzes comprised within certain limits of tin content. As in the case of the brasses, the

addition of tin to copper results in the formation of a series of solid solutions.

The addition of tin to copper results in the formation of a series of solid solutions

which, in accordance with usual practice, are referred to in order of diminishing copper

content as the α, β, γ, etc., constituents.

PHASE DIAGRAM Sn-Cu

Figure show the phase diagram for Sn-Cu



PHYSICAL PROPERTIES

(Atomic arrangement sn-cu)

Figure: Projection of the structure of Yb3.63Cu23.13Sn10.83 along the c axis. Open, full

and double circles represent atoms at heights 0, 1/2 and ±1/4∼, respectively. The Yb1

atoms are inside the highlighted polyhedra, while Yb2 (open large circles) and Cu4

(small full circles) are at the vertices of the unit cell.

(Defects)

The concept of a defect phase diagram is introduced which quantifies the effects

of Cu and Pb additions to electrodeposited Sn films on surface defect formation,

including but not limited to the formation of Sn whiskers. Transitions were observed in

both the defect densities and the morphologies of hillocks and whiskers as Cu and Pb

film compositions were systematically varied. Changes in crystallographic texture were

also reported for a subset of the Sn-Cu-Pb alloys examined. The transitions between

different defect types and the coexistence of certain defect types help to interpret the

role of grain boundary pinning in hillock and whisker formation.



(Density)

High-density area-array 3-D interconnects are a key enabling technology for 3-D

integrated circuits. This paper presents results of the fabrication and testing of large 640

by 512 area arrays of Cu/Sn-Cu interconnects positioned on 10-μ centers. Theprocesses used to create the interconnects are designed to be compatible with CMOS

wafer requirements. Through testing of the electrical continuity of long chains of

interconnects, bond yield is estimated to be greater than 99.99% in the large arrays. The

properties of Cu/Sn-Cu interconnects remain stable through exposure to thermal cycling

and high-humidity testing

SOLIDIFICATION FOR Sn-Cu

The important alloys of copper and tin from an industrial point of view are the

bronzes comprised within certain limits of tin content. As in the case of the brasses, the

addition of tin to cooper results in the formation of a series of solid solutions. The

constitutional diagram of copper-tin alloys is very complex, but that part of it which deals

with alloys of industrial importance is reproduced in Fig. 1.

Figure 1: Constitutional Diagram of the Copper-Tin Alloys



The addition of tin to copper results in the formation of a series of solid solutions

which, in accordance with usual practice, are referred to in order of diminishing copper

content as the α, β, γ, etc., constituents. The diagram may be summarized as follows:

Percentage composition Constituent just

below the freezing

point

Constituent after

slow cooling to 400°CCopper Tin

100 to 87 0 to 13 α Α

87 to 86 13 to 14 α + β Α

86 to 78 14 to 22 α + β α + δ

78 to 74 22 to 26 β–>(α + β) α + δ

Further changes on cooling from 400°C to room temperature are so sluggish that

they only occur in conditions very far removed from actual practice.

The α solution is the softest of the constituents; it may be rolled or stamped cold,

but it hardens under this treatment much more rapidly decreases than α -brass.

The β and a constituents do not exist in the alloy slowly cooled to room

temperature: this is due to successive changes occurring at 586°C and 520°C whereby

β is resolved into α +γ and γ into α + δ.

The δ constituent has the crystal structure of γ-brass. It has a narrow range of

composition corresponding approximately to the formula Cu3lSn8 and, like all

intermetallic compounds, is extremely hard and brittle. The δ -> (α + ε) change at 350°Cdoes not occur in commercial practice, though alloys richer in tin may contain the a

constituent, which corresponds to Cu3Sn, and the η solid solution, which approximates

to the composition CuSn.



SOLID SOLUBILITY Sn-Cu (hume-rothery rule)

On cooling from the liquid condition, the solid solution which first forms contains

only about 2 percent of tin. Thus the cast metal has a cored structure and the coring is

very marked because of the long range between liquidus and solidus; but it may be

eliminated by diffusion on cooling more slowly or by annealing.

Any absorption of oxygen occurring during manufacture results in the presence of

SnO2 in the alloy, tending to make it brittle. A deoxidizer such as zinc is therefore

frequently added. The addition of zinc, as in coinage bronze, causes no change in the

microscopical appearance of the homogeneous α constituent. The zinc, however, exerts

its deoxidizing effect in the liquid, and slight hardening effect on the solid solution. The

structure of a bronze coin shows marked deformation of the crystals. On annealing,

recrystallization takes place with subsequent crystal growth. Twinning is a characteristic

feature of the cold-worked and annealed alloy.

PHASES

(Occurance)

The selection and evaluation of Pb-free solders requires information that is best

determined through a knowledge of ternary and higher order phase diagrams. As part of

an ongoing program on Pb-free solder phase diagrams at the National Institute of

Standards and Technology, a thermodynamic model is formulated for the Sn-Bi-Agphase diagram. Thermodynamic functions for the various phases obtained by fitting

measured data for the three constituent binary systems are extrapolated to the ternary

system using the method of Muggianu. Modeling results are compared to preliminary

experimental data for the ternary system and are applied in the calculation of the

solidification path.



(Stability)

A method of limiting cracking in the Cu6Sn5 intermetallic compounds (IMCs) at

the interface between lead-free solders and copper substrates has been developed. To

explore the mechanism of crack inhibition in the nickel-containing IMC reaction layers,detailed synchrotron x-ray powder diffraction with Rietveld analysis and differential

scanning calorimetry have been used. The results show that nickel stabilizes the high-

temperature hexagonal allotrope of Cu6Sn5, avoiding stresses induced by a volumetric

change that would otherwise occur on transformation to the monoclinic phase.

PHASE TRANSFORMATION

Copper tin alloys or tin bronzes are known for their corrosion resistance. Tin

bronzes are stronger and more ductile than red and semi red brasses. They have high

wear resistance and low friction coefficient against steel. Tin bronzes, with up 15.8% tin,

retain the structure of alpha copper. The tin is a solid solution strengthener in copper,

even though tin has a low solubility in copper at room temperature. The room

temperature phase transformations are slow and usually do not occur, therefore thesealloys are single phase alloys. The tin bronzes are used in bearings, gears, piston rings,

valves and fittings. The cast tin bronzes are designated by UNS C90200 through

C91700. Lead is added to tin bronzes in order to improve machinability and pressure

tightness. Lead decreases the tensile strength and ductility of the tin bronzes, but the

composition can be adjusted to balance machinability and strength requirements. High

leaded tin bronzes are primarily used for sleeve bearings. These alloys have a slow fail

mechanism that temporarily prevents galling and seizing. The slow fail mechanism

works by lead seeping out of the alloy and smearing over the surface of the journal. The

cast leaded tin bronzes are designated as UNS C92200 through C94500.



The microstructure of the cast tin bronzes consists of cored dendrites, they have

a composition gradient of increasing tin as they grow. The last liquid to solidify is

enriched with tin upon cooling, and forms alpha and delta phases. The alpha and delta

phases fill in the areas between the dendrite arms. the microstructure of the leaded tin

bronzes are similar to the nonleaded materials with the addition of lead particles in the

inter-dendritic boundaries. The lead is practically insoluble in solid copper and it

solidifies last as almost pure lead in the grain boundaries.

THREE PHASE REACTION

Eutectic transformation



Eutectoid transformation

Peritectic reaction transformation



Peritectoid reaction transformation

Copper tin phase diagram showing a peritectic point



The peritectic reaction (see diagram above) is an important example of a

microstructural transformation. Sn – 21wt.%Cu exhibits this transformation from a solid

phase and a liquid phase to a different, solid phase.

Before the transformation begins the system is comprised of the ε phase andliquid. Below 415°C the equilibrium solid phase is η The peritectic transformation begins

to take place at 415°C; the new phase prec ipitates heterogeneously on the surface of ε

precipitates. The growing layer of η on the surface of the epsilon precipitates prevents

the copper diffusing out to remove inhomogeneities, so some of the copper is trapped

within the ε precipitates and the liquid has a lower Cu concentration than the bulk

composition. This means the peritectic reaction never goes to completion (i.e. all liquid

and solid going to the second solid). In this example the liquid continues to cool until it

reaches the eutectic temperature, 227°C, when it transforms.

MECHANICAL PROPERTIES

Tin (Sn)

TIN coatings were deposited on hot working steel substrates by ion beam

assisted deposition technique. The deposition process was conducted at two different

temperatures 50 and 400 C. the influence of applied deposition temperature on the

mechanical properties, adhesion strength and surface morphology of TIN coatings was

studied. The mechanical Properties. i.e. hardness, modulus of elasticity and coating

strength was evaluated by generally accepted scraptch test testnique. In addition, HRC

adhesion test was utilized to compare adhesion of different coatings qualitatively.Surface morphology was analyzed by atomic force microscopy before and after the film

deposition. The coating deposited at higher temperature displayed higher hardness, and

also higher critical loads were obtained during the deposition process enhances the

adatom mobility allowing the deposition of coatings with high hardness and adhesion

strength even at low temperatures.



Copper (Cu)

The mechanical properties and microstructures of copper and brass soldered with

eutectic tin-bismuth solder have been determined and the joints examined usingmetallographic techniques. Joints made with copper were stronger than those made with

brass. At the copper/solder interface a uniform layer 2μm thick of Cu5.2Sn5 was formed

and at the brass/solder interface a uniform layer 2 μm thick of (Cu, Zn)2.9Sn and an

irregular layer 2 to 5μm thick of (Cu, Zn)5.7Sn5 were formed. Copper joints fractured

etthocopper/solder interface and brass joints fractured in the internmetalic layer. Copper

joints soldered with eutectic Sn-Bi were stronger than copper joints soldered with

eutectic Sn-Pb and the reverse was true for brass joints. Results are also given for the

effect of thermal shock on copper and brass joints soldered with Sn-Bi and Sn-Pb

solders, and also for We fatigue and creep behaviour of joints soldered with eutectic Sn -

Bi solder.

APPLICATION FOR Sn-Cu

(Electric motors)

Main article: Copper in energy efficient motors

Copper’s greater conductivity versus other metallic materials enhances the

electrical energy efficiency of motors. This is important because motors and motor-

driven systems account for 43%-46% of all global electricity consumption and 69% of all

electricity used by industry.[73] Increasing the mass and cross section of copper in a coil

increases the electrical energy efficiency of the motor. Copper motor rotors, a new

technology designed for motor applications where energy savings are prime design

objectives, are enabling general-purpose induction motors to meet and exceed National

Electrical Manufacturers Association (NEMA) premium efficiency standards.



(Wire and cable)

Main article: Copper wire and cable

Despite competition from other materials, copper remains the preferred electricalconductor in nearly all categories of electrical wiring with the major exception being

overhead electric power transmission where aluminium is often preferred. Copper wire is

used in power generation, power transmission, power distribution, telecommunications,

electronics circuitry, and countless types of electrical equipment. Electrical wiring is the

most important market for the copper industry. This includes building wire,

communications cable, power distribution cable, appliance wire, automotive wire and

cable, and magnet wire. Roughly half of all copper mined is used to manufacture

electrical wire and cable conductors. Many electrical devices rely on copper wiring

because of its multitude of inherent beneficial properties, such as its high electrical

conductivity, tensile strength, ductility,creep (deformation) resistance, corrosion

resistance, low thermal expansion, high thermal conductivity, solderability, and ease of

installation.



REFERENCES

http://link.springer.com/article/10.1007%2FBF03029299?LI=true#page- 1

http://www.chemguide.co.uk/physical/phaseeqia/snpb.html

http://www.copper.org/resources/properties/microstructure/cu_tin.html

http://www.keytometals.com/Article70.htm

http://en.wikipedia.org/wiki/Tin

http://en.wikipedia.org/wiki/Copper

http://www.mas.bg.ac.rs/istrazivanje/biblioteka/publikacije/Transactions_FME/Volume40/1/06_PTerek.pdf )

http://link.springer.com/article/10.1007%2FBF03029299?LI=true#page-











http://www.mas.bg.ac.rs/istrazivanje/biblioteka/publikacije/Transactions_FME/Volume40/1/06_PTerek.pdf










http://link.springer.com/article/10.1007%2FBF03029299?LI=true#page-

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