Wetting behaviour and reactivity of lead free Au–In–Sn and Bi–In–Sn on Cu substrate.pdf

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International Journal of Adhesion & Adhesives 27 (2007) 409–416

Wetting behaviour and reactivity of lead free Au–In–Sn and Bi–In–Sn

alloys on copper substrates

F. Gneccoa, E. Riccia, S. Amorea,b, D. Giurannoa, G. Borzoneb, G. Zanicchib,R. Novakovica,

aNational Research Council (CNR)—Institute for Energetics and Interphases (IENI), Via De Marini, 6–16149-Genoa, ItalybDCCI-University of Genoa, Via Dodecaneso, 31–16146-Genoa (Italy) and Genoa Research Unit of National Consortium of Materials Science & Technology

(INSTM), Italy

Available online 23 October 2006

Abstract

The main objective of this work is to determine the wetting behaviour of lead-free solders on copper substrates in view of their

applications in electronic industry. The wetting behaviour of X–In–Sn (X ¼ Au, Bi) ternary molten alloys in contact with copper has

been studied and compared with the corresponding behaviour of their binary subsystems with a particular attention to the In–Sn/Cu

system. The contact angle measurements on Cu-plates were performed by using a sessile drop apparatus. The solder/copper interface was

characterised by the SEM-EDS analysis.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Interfaces; Metals; Contact angles; Lead-free solder alloys

1. Introduction

The solder process is determined by the physico-chemical

properties of the liquid solder/solid substrate system and

by the environmental conditions over which the solder

process is carried out. For this reason, a complete

characterisation of the surface properties (surface tension,

surface segregation) [1] as well as of the wetting behaviour

has to be done. The wetting properties of a solder/substrate

system are usually characterised by the contact angle, y, of

the liquid metal drop formed on the solid substrate.

Another important parameter of a liquid metal/solid

substrate system is the adhesion strength, generallyrepresented by the work of adhesion, W A [2]. The joint

reliability is related to the wettability of the surfaces to be

joined and subsequently, the ability of the joint to retain its

performance. However, in practice the wettability of filler

alloys is often overlooked or ignored by the producers. The

formation of a thin intermetallic compound layer is

desirable to achieve a good metallurgical bond [3–5].

Soft soldering has been adapted to microchip packingand high-level system assembly [4]. Up to now, the tin–lead

solders have a combination of properties superior to those

attained with any other alloy system, and their unique

physical, mechanical and electrical properties have made

these solders attractive for joining at low temperatures [4].

The Pb–Sn phase diagram shows the existence of a simple

eutectic indicating a tendency towards phase separation.

The melting temperature of the eutectic composition

Pb–73.9 at%Sn is 456 K [6]. Due to a shallow eutectic,

small variations in the solder composition change the

liquidus temperature slightly. The interface reactions

between the solder and the substrate (Cu, Ni, Fe) aredominated by the Sn-component. During soldering, the

Pb–Sn solder alloys react with the substrate to form

intermetallic compounds at the interface. An excessively

thick intermetallic layer can be a source of mechanical

weakness in the soldered joints due to the thermal

expansion coefficient and elastic modulus mismatch as

well as the brittle nature of intermetallic compounds [3,7].

It has been experimentally determined and subsequently

theoretically confirmed that at the interface between Sn-

based solders (Sn–Pb, Sn–Bi, Sn–Ag) and Cu-substrate the

ARTICLE IN PRESS

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E-mail address: [email protected] (R. Novakovic).

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two intermetallic compounds, Z-Cu6Sn5 (adjacent to

solder) and e-Cu3Sn (adjacent to Cu), are formed [4,8,9].

Lee et al. [9] calculated the nucleation activation energies of

these two compounds at soldering temperatures. When

compared, the Z-Cu6Sn5 resulted energetically favoured.

Depending on the kinetics of growth for a particular solder

alloy/substrate system as well as on the operative condi-tions, both intermetallic phases grow in the solid state

during ageing at lower temperatures up to a significant

thickness (420mm).

The presence of Pb in the Pb–Sn solders affects neither

the formation of the Cu–Sn intermetallic compounds nor

the solid-state growth kinetics of these intermetallics.

However, it has been established that Pb affects many of

the desired properties in the Pb–Sn solders. Indeed Pb

improves the corrosion resistance by the formation of a

tenacious oxide skin on the Pb-rich phase of the Pb–Sn

eutectic, prevents the ‘‘tin-pest’’ phenomenon, i.e., the b-Sn

to a-Sn transition upon cooling at T ¼ 286K, and lowers

the surface tension of solders with respect to the pure Sn

increasing consequently the wettability of the substrate

[3,4].

In view of environmental and health concerns, the lead-

free solders have only recently become a common subject

for fundamental research. Alternative solder alloys do not

meet completely environmental regulations and require-

ments for the reliability of corresponding properties. The

candidate alloys involve Sn as the base element, Ag, Bi, Cu

and Zn as the major alloying elements and some minor

additions such as In and Sb [4,8–14]. In the framework of

the Action COST 531 project some alloys of the Bi–In–Sn

and Au–In–Sn systems have been proposed as candidatesfor a lead-free solder in modern electronic. There are many

literature data on the thermodynamic properties [16], few

data on the surface properties of the Bi–In–Sn system and

its subsystems [17], while on the wetting properties as well

as the joining of both, the Bi–In–Sn and Au–In–Sn systems

on Cu-substrate a complete lack of data was observed.

Joining studies have been done for different compositions

and temperatures, so that it is difficult to find experimental

data obtained under comparable conditions [12,15,18]. In

the present work, the sessile drop method was used to

determine the contact angle of some binary and ternary

liquid alloys of X–In–Sn (X ¼ Au, Bi) in contact with Cu-

substrate.

2. Experimental

The contact angle measurements were performed on

some binary and ternary systems (Table 1) from the

melting point up to 768 K. The alloy specimens were

prepared by mixing high purity metals (99.9999% Marz-

grade) for each nominal composition, pre-melted in a

vitreous carbon crucible under a vacuum of P ¼ 102 Pa at

a temperature about 100 K above the melting point. The

final alloy composition was controlled by the SEM-EDS

analysis. The measurements were performed in a horizontal

furnace heated by an 800 kHz high-frequency generator

coupled to a graphite heater and thermal shields. Metallic

drops of about 1.0 g were mechanically cleaned by

scratching, and then chemically rinsed with pure ethanol

in an ultrasonic bath. The sample was introduced at the

centre of the chamber, placed on a high purity copper

(99.9999%) substrate (plate + ¼ 10 mm), metallographi-

cally mirror polished. Before the test, the furnace was

heated and degassed under vacuum (P ¼ 104 Pa), then

pure Argon (ArN60) was introduced. The resulting oxygen

pressure, P O2, was around an average value 106 Pa. The

temperature, monitored by a K-thermocouple placed just

below the specimen, was kept constant within 72 K.

Resting on a perfectly levelled substrate, the sample was

illuminated by an aligned light source and its image wascaptured by a CCD camera connected to a PC. A specific

image analysis software, ASTRAviews [19,20] with fast

automatic acquisition (0.5 s) was applied which allows the

contact angle values to be calculated in real time with an

accuracy of about 1%. Contact angles have been measured

in a temperature range from above the liquidus tempera-

ture up to a final value, defined for each specific system, at

which the isothermal conditions were reached. DSC

measurements have been done on the ternary alloys. A

differential scanning calorimeter designed as a Calvet

calorimeter (DSC 111, Setaram), has been used for the

determination of the solid–liquid transition temperatures.

The specimens (about 700 mg) were enclosed in a tight-

sealed tantalum crucible. The calibration of the apparatus

was performed with measurements of the temperature of

pure metallic In, Sn, Pb and Zn elements. Temperatures

were measured at 70.5 K. The DSC analyses were

performed in continuous heating mode at a rate of 1, 3

and 5 K/min. Generally, a series of different runs in various

temperature ranges were made and, in order to verify

consistency, each run was repeated three times. More

details on the working conditions may be found in [21].

The metallographic examinations of the alloy–substrate

interface were accomplished by optical microscopy, SEM

and EDS.

ARTICLE IN PRESS

Table 1

Selected alloys as candidates for lead-free solders

Alloy composition (at%) T l (K) y0 (1) T f (K) yf (1) tf (s)

In–70Sn 450 142 708 41 680

In–85Sn 485 165 690 23 400

Au–55In 768 162 852 50 640

Au–97In 588 160 760 21 550

Au–82Sn 582 143 695 34 300

Au–5In–81Sn 538 128 645 33 600

Au–11In–84Sn 493 117 600 52 600

Au–8In–88Sn 503 127 602 39 550

Bi–52In 383 160 623 51 550

Bi–80In 355 122 648 44 700

Bi–5In–81Sn 483 92 608 39 620

Bi–8In–88Sn 430 66 608 30 600

F. Gnecco et al. / International Journal of Adhesion & Adhesives 27 (2007) 409–416 410



3. Results and discussion

The selected binary and ternary compositions of the

X–In–Sn (X ¼ Au, Bi) alloys are shown in Fig. 1(a) and

(b), respectively. The alloy compositions, the initial contact

angles (y0), the final temperatures (T f ), times (tf ) and the

contact angles (yf ) are reported in Table 1. The liquidus

temperatures (T l) refer to the corresponding binary phase

diagrams [6] or, in the case of ternary systems, the values

obtained by DSC [21].

The wetting behaviour of ternary molten alloys in

contact with Cu-substrate has been studied together with

the corresponding behaviour of their binary subsystems

with a particular attention to the In–Sn/Cu system and the

effect of a third component, Au or Bi, on it. Once the

wetting experiments were completed and characteristic

parameters mentioned above (Table 1) were determined,the samples were cooled for about 600 s, and then prepared

for the microstructural characterisation with the aim to

study the reactivity of the systems investigated. A summary

of the results of the characterisation of each alloy tested is

reported in Table 2.

3.1. In–Sn system

In the In–Sn system, the eutectic is formed at inter-

mediate composition, In–48.3 at%Sn at 393 K. Some

information on the In–50Sn solder in contact with copper

substrate is reported in [4,10,18]. The effect of solder-bath

temperature on the performance of In–50Sn alloy has been

studied by [4] at temperatures well above the alloy’s

liquidus. Poor wettability was observed at temperatures

close to T ¼ 488 K, while at higher temperatures an

improvement was observed. Therefore, according to these

tests an increase in the solder temperature is a first

promising approach to improve the solderability. Accord-

ing to [10], the In–Sn solders wet Cu by forming Sn–In–Cu

intermetallics. The interfacial microstructure is affected by

the high solubility of Cu in In–50Sn liquid alloy and by the

participation of In in the intermetallic layer at the solder/

Cu interface, exhibiting two layers consisted of Cu2(Sn,In)

and Cu2In3Sn intermetallics, with the In-rich Cu2In3Snphase on the solder side of the interface.

In this work, two In–Sn alloys were investigated:

In–70Sn: The variations of contact angle and tempera-

ture as function of time for the In–70Sn are shown in Fig.

2. The initial contact angle (the mean value of the left and

right contact angles which differo4%) is close to 1401 at

T ¼ 573 K. y starts to decrease after 2 s, and reaches a

constant value yf ¼ 411 at T f ¼ 708 K in 680 s. After

cooling the sample was metallografically prepared in order

to characterise the interface cross section obtained by the

SEM and EDS analyses. Close to Cu-substrate a thick

interface layer (60mm) of the Cu–7In–19Sn composition

was identified (Table 2, Fig. 3). In many points adjacent to

the solder alloy the phase Cu–13In–31Sn (light grey spots)

was detected. It is interesting to notice that Cu-contents of

these phases are very close to the well known intermetallics,

e-Cu3Sn and Z-Cu6Sn5, respectively, formed in the case of

the eutectic Pb–Sn/Cu-substrate [4,9]. The remaining

composition, identified as In–74Sn is close to the initial

alloy composition. The changes in composition can be

attributed to the loss of In due to its volatility, as proved by

the spots of In found on the substrate surface near the

drop.

In–85Sn: The initial contact angle was close to 1651 at

T ¼ 523 K. The spreading was observed starting from

ARTICLE IN PRESS

Fig. 1. Selected alloy compositions (a) the Au–In–Sn system and (b) the

Bi–In–Sn system.




590 K and y reached a constant value yf ¼ 231 at

T f ¼ 690 K after 400 s. The EDS analysis has shown the

presence of a thin layer (3 mm) close to Cu-substrate

containing the Cu–11In–12Sn phase.

The results obtained show that with an increase of Sn in

the solder the contact angle decreases together with the

thickness of the interface layer between solder and Cu-

substrate. Accordingly, the wetting behaviour changed

from a dissolutive wetting, characterised by a thick

interface layer to a macroscopically planar, thin layer

formed of Sn-rich alloys. Indeed, in the case of the

In–70Sn, the final contact angle should be considered as

an apparent one due to the evident high reactivity of this

system. The reactivity decreases strongly with an increase

in Sn-content. The value yf ¼ 231 obtained for the alloy

with higher Sn-content can be taken as the real equilibrium

value.

3.2. Au–In and Au–Sn systems

Reactions and characteristics of Au–In microjoints need

to be investigated in detail to establish the suitability of this

system as candidate material for engineering applications

such as microelectronic packing [22]. In order to avoid

ARTICLE IN PRESS

Table 2

Summary of the results obtained by SEM-EDS characterization of the microstructure of each alloy tested

Initial composition (at%) Interface composition (at%) Layer thickness (mm) T f (K) Bulk-phase compositions (at%)

In–70Sn Cu–7In–19Sn 60 708 Cu–13In–31Sn

In–74Sn

In–85Sn Cu–11In–12Sn 3 690 Cu–21In–23Sn

Au–55In Cu–20In–14Au 40 852 Cu–33In–45Au

Au–97In Cu–22In 40 760 Cu–39In–1Au

Cu–38In 30

Au–82Sn Cu–26Sn–2Au o2 695 Cu–50Sn–23Au

Au–5In–81Sn Cu–2In–22Sn–1Au 6 645 Cu–4In–44Sn–15Au (near interface)

Cu–3In–59Sn–12Au

Au–11 In–84 Sn Cu–4In–20Sn–1Au 22 600 Cu–7In–39Sn–8Au (near interface)

In–17Sn–33Au

Au–8In–88Sn Cu–51In–42Sn–8Au 20 602 Cu–33In–41Sn–23Au (near interface)

Cu–6In–42Sn–8Au

Bi–52In Cu–32In o1 623 In–48Bi (near interface)

In–36Bi

Bi–80In Cu–46In 7 648 Bi–37In

Bi–5In–81Sn Cu–20Sn 5 608 Cu–40Sn (near interface)

In–2Sn–39Bi

Bi–8In–88Sn Cu–9In–38Sn o1 608 Sn–6Bi (near interface)

Cu–8In–38Sn

140

120

100

80

60

40

C o n t a c t A n g l e [ ° ]

7006005004003002001000

Time [s]

700

680

660

640

620

600

580

T e m p e r a

t u r e [ K ]

Fig. 2. Variations of contact angle (o) and temperature (D) as function of time for the In–70Sn (at%) alloy on pure Cu-substrate.




open circuits during reflow soldering of all components, a

high melting soldering process is required for the bonding

of integrated circuits (IC). A flip-chip bonding with an

Au–Sn metallization system has been successfully intro-

duced for the mounting of IC [23]. Binary gold containing

alloys investigated in this work were:

Au–55In: The variations of contact angle and tempera-ture as function of time for the Au–55SIn are shown in Fig.

4. The initial contact angle is close to 1621 at T ¼ 773 K. y

starts to decrease after 1 s, and reaches a constant value

yf ¼ 501 at T f ¼ 852 K in 640 s. The analyses of the cross

section of this alloy sample showed the formation close to

Cu-substrate of a thick interface layer (40mm) of the

Cu–20In–14Au composition (Table 2, Fig. 5). Cu-content

of this phase is very close to that of the Z-Cu2In

intermetallic compound [6]. The reaction between the

Au–55In alloy and Cu-substrate led to an increase in the

total volume of the liquid phase. According to [2] the

observed wetting behaviour can be classified as dissolutive

wetting as observed in the case of In–70Sn alloy. So, the

contact angle value of 501 observed (Table 1) at the final

temperature T f ¼ 852 K can also be considered as anapparent angle.

Au–97In: In this case, the presence of higher In-content

justifies a decrease in the final contact angle value, yf ¼ 211

at T f ¼ 760 K. A thick interface composed of two layers of

40 and 30 mm was found by EDS. The composition of these

layers was Cu–22In and Cu–38In, respectively.

ARTICLE IN PRESS

Fig. 3. SEM micrograph of a cross section of the In–70.3Sn (at%) alloy

on pure Cu-substrate.

160

140

120

100

80

60

C o n t a c t A n g l e [ ° ]

7006005004003002001000

Time [s]

800

780

760

740

720

700

T e m p e r a t u r e

[ K ]

Fig. 4. Variations of contact angle (o) and temperature (D) as function of time for the Au–55In (at%) alloy on pure Cu-substrate.

Fig. 5. SEM micrographs of a cross section of the Au–54.9In (at%) alloy





Au–82Sn: Due to a slight dissolution of Cu, the interface

of this alloy remained macroscopically planar and as a

consequence an equilibrium contact angle value yf ¼ 341

was reached at the temperature of 695 K (Table 1). In

addition, close to Cu-substrate a thin interface layer

(o2mm) of the Cu–26Sn–2Au composition was identified

(Table 2, Fig. 6). In this layer, Cu-content is slightlydifferent from that in the e-Cu3Sn intermetallic compound,

formed in the case of the eutectic Pb–Sn/Cu-substrate [4,9].

Adjacent to the solder the Cu–50Sn–23Au phase was

detected.

3.3. Au–In–Sn system

Three ternary alloys that belong to this system have been

investigated:

Au–5In–81Sn: The mean value of the contact angle of

this ternary alloy at T f ¼ 645 K is yf ¼ 331 (Table 1). As in

the case of the Au–82Sn alloy, the interface examined bySEM seems to be macroscopically planar. Close to Cu-

substrate a thin interface layer (o10mm) of the

Cu–2In–22Sn–1Au composition was identified (Table 2,

Fig. 7). It is interesting to note that, also in this case, the

Cu-content of this phase is close to that of the e-Cu3Sn

intermetallic compound [4,8,9]. In many points near the

interface the Cu–4In–44Sn–15Au, Cu–3In–59Sn–12Au and

Sn–2In phases were found.

Au–11In–84Sn: A constant contact angle value yf ¼ 521

reached after 600 s and at the temperature T f ¼ 600 K was

observed (Table 1). The SEM and EDS analyses revealed

an interface layer

22mm thick of composition75Cu–4In–20Sn–1Au (Table 2).

Au–8In–88Sn: For this alloy, a contact angle value

y ¼ 391 was reached at T f ¼ 602K (Table 1) and a layer

20 mm thick of composition Cu–51In–42Sn–8Au was

identified by EDS (Table 2). The reduction of In and Sn-

content from Au–11In–84Sn and Au–8In–88Sn to

Au–5In–81Sn leads to a sharp reduction in reactivity

despite an increase in T (from 600 to 645 K). Indeed,

among the three alloys considered, the Au–5In–81Sn alloy

having the highest Au-content is characterised by the

formation of 3–4 times thinner interface layer (6mm) in

respect to the Au–11In–84Sn and Au–8In–88Sn alloys.

3.4. Bi–Sn system

In the Bi–Sn system, the constituent phases of the

eutectic are terminal solid solutions, as they are in the

Pb–Sn system. The Bi–Sn solder forms a well-definedeutectic microstructure at all solidification rates. According

to the literature these solders wet Cu by forming Sn-

containing intermetallics that resemble the intermetallics

formed by eutectic Pb–Sn [9]. The microstructure of the

Bi–Sn/Cu interface is similar to that formed at Pb–Sn/Cu

interface. The principal intermetallic compound is the

Cu6Sn5. During ageing in the solid state, the Cu3Sn

intermetallic compound is formed and its growth at the

Cu-interface can be observed [4,10,15].

3.5. Bi–In–Sn system

Two binary and two ternary Bi-containing alloys have

been investigated in this work:

Bi–52In: A contact angle yf ¼ 511 was reached at

T f ¼ 623 K in 550s (Table 1). By EDS analysis a very thin

interface layer (o1mm) with composition of Cu–32In close

to the d-Cu7In3 [6] was identified (Fig. 8). No dissolution of

Cu was observed. This can be explained by a tendency of

the Bi–Cu system to phase separation [6]. Two intermetallic

compounds, the BiIn and BiIn2 were identified in the bulk

alloy indicating the same alloy composition before and

after experiment. The presence of some spots of the Z-

Cu2In phase was also detected by EDS analysis (Table 2).

ARTICLE IN PRESS

Fig. 6. SEM micrographs of a cross section of the Au–81.8Sn (at%) alloy


Fig. 7. SEM micrograph of a cross section of the 14.3Au–5.2In–80.5Sn

(at%) alloy on pure Cu-substrate.




Bi–80In: For this In-rich alloy, the mean value of the

equilibrium contact angle reached at T f ¼ 648 K was

yf ¼ 441 (Table 1). A thin interface layer of about 7 mm

having the composition Cu–46In was identified by EDS

(Table 2).

Bi–5In–81Sn: The mean value of the contact angle of this

ternary alloy at T f ¼ 608K is yf ¼ 391 (Table 1). At the

interface the Cu4Sn phase with a thickness of about 5 mm

was formed (Table 2, Fig. 9). It is interesting to notice that

close to this phase some spots of the Cu–40Sn compound

(similar to Zphase) [8,9] were observed. The same

composition was detected in a few points of the solidified

alloy drop.

Bi–8In–88Sn: The mean value of the contact angle of this

ternary alloy at T f ¼ 608 K is yf ¼ 301 (Table 1). Close to

Cu-substrate, a very thin interface layer of the

Cu–9In–38Sn composition was identified by EDS analysis

(Table 2).

Bi-containing alloys in contact with copper substrate

exhibit low reactivity. Generally, the wetting of these alloys

increases and the corresponding contact angle values

decrease with a decrease in Bi, exhibiting the minimum

value, yf ¼ 301

in the case of the Bi–8In–88Sn alloy havingonly 4 at%Bi.

The high melting point of lead-free solders with respect

to the traditional Pb–Sn alloys is usually a weak point in

electronic package. The addition of Au to the In–Sn system

increases the melting point of these binary solders, but

might be useful for some applications at higher tempera-

tures. Gold is widely used in electronic industry as contact

and conductor material. At the interface between Au–Sn

solders and Cu-containing substrates, the brittle AuSn4

phase can be observed [24]. Indium has a much lower

affinity for Au and dissolves Au at a rate 13–14 times

slower than Sn. The addition of In into Sn-based solders

facilitates the AuIn2 formation at the interface and inhibits

the AuSn4 formation. Accordingly, the solubility of Au in

the In–Sn system can be reduced, and an optimised ternary

composition could give a solder with required character-

istics. On the contrary, the addition of Bi to Sn-based

solders can reduce melting temperatures, promotes the

wetting, but according to the present results, only a limited

quantity of Bi (o4 at%) is suggested.

4. Conclusions

The wetting behaviour of a certain number of solder

alloys pertaining to the systems of In–Sn, Au–Sn, Au–In,

Bi–In, Au–In–Sn, and Bi–In–Sn in contact with a Cu-

substrate has been analysed. Their wetting behaviour

changed from a dissolutive wetting, characterised by the

formation of a thick interface layer (In–Sn, Au–In),

through a macroscopically planar, thin layer formation

(In–Sn, Au–Sn, Au–In–Sn) to the formation of an

extremely thin interface layer (Bi–In, Bi–In–Sn) or isolated

spots (Bi–In) as in the case of Bi-containing solders.

Among these systems, the In–Sn solders with high Sn-

content exhibit wetting characteristics very similar to those

of the Pb–Sn system. In the case of Au–In–Sn alloys, an

increase in In-content increases the interface layer thick-

ness, as it is also observed in the In–Sn and Au–In alloys.

On the contrary, the behaviour of Bi–In–Sn alloys in

contact with Cu-substrate is opposite with respect to that

of the In–Sn system. Namely, the higher is the In-content

the thinner the interface layer observed. Accordingly, the

Bi–In–Sn system exhibits the same behaviour as the Bi–In.

In order to improve their wetting characteristics and

consequently the mechanical properties, it is very impor-

tant to optimise the composition and the joining process

parameters to avoid an excessive growth of the interface

reaction layer.

ARTICLE IN PRESS

Fig. 8. SEM micrograph of a cross section of the Bi–51.5In (at%) alloy on

pure Cu-substrate.

Fig. 9. SEM micrograph of a cross section of the 14.3Bi–5.2In–80.5Sn

(at%) alloy on pure Cu-substrate.




Acknowledgement

This work was performed in the framework of the E.C.

Action COST 531 project: ‘‘Lead-free solder materials’’.

The authors would like to thank the National Consortium

of Materials Science and Technology (INSTM) for

financial support (PRISMA project). The authors wouldlike to thank Mr. C. Bottino, IENI-CNR, Genoa, for

performing the EDS and SEM analyses.

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Wetting behaviour and reactivity of lead free Au–In–Sn and Bi–In–Sn on Cu substrate.pdf

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