Technical Field The present invention generally relates to a lead free solder alloy and to a composition for making the lead free solder alloy.

Background of the invention Lead-based solder materials have been used for interconnections of electronic components on printed circuit boards (PCBs) for many decades. However, lead toxicity has become an increasingly important occupational and environmental health issue as awareness of the environmental impact of this metal has increased amongst the general public. Accordingly, there has been increasing public pressure to eliminate or reduce the industrial use of lead within the electronic component industry.

Legislation and policies have been proposed in Europe and the USA to ban or limit the use of lead in solders. In the United States the electronic manufacturing industry has come to the consensus view that lead will be abandoned as a solder material in view of the Lead Exposure Act (s2.729) and the Lead Tax Act (H.R. 2479) . In Europe and Japan, it is proposed that legislation be introduced to force electronic component manufacturers to adopt the use of lead-free solder alloys in all electronic assemblies.

Efforts have been made in the electronic manufacturing industry to develop lead-free and environmentally "friendly" or non-toxic soldering materials to replace lead-based solders. Research has focussed on a direct substitute for Sn-/37Pb solder alloy lor surrace mount technology (SMT) manufacturing.

A solder with high melting temperature will have a major impact on the other polymeric materials used in microelectronic assembly and encapsulation. An acceptable 63Sn-/37Pb solder alloy substitute should desirably offer a melting point below 200 C. The desired features of a lead-free alternative to Pb/Sn alloys include:

• Low melting temperature • Minimal freezing range • Ease of manufacture • Ease of recycling • Minimum material cost

The majority of Pb-free solder alloys that have been proposed are based on Sn, In and Bi, with Sn as the matrix metal. These alloy compositions have eutectic melting temperatures close to that of Sn-Pb solder. However, as the major additive components of these alloys are Bi and In, these alloys are not considered to be a real alternative to Pb solders for one or more of the following reasons: a) the price of indium is high; b) large amounts of bismuth and indium are presently required to lower melting temperature, which leads to low melting phases formed in the system, which reduces the reliability of the solder due to thermal fatigue at higher temperatures; and c) it is difficult to recover usably purified materials from the solder alloy for recycling use when bismuth or indium is used as an additive element of the solder. On the other hand, lead-free alloys based on Sn-Ag, Sn- Cu and Sn-Ag-Cu eutectic systems have melting points in the 217 to 227 0C range, which is significantly higher than that of 63Sn37Pb (which is 183 C) . These alloys are thus not a suitable direct substitute of conventional Sn- Pb solder (e.g., Sn-37Pb) .

Another problem that may be associated with lead free solder alloys, is that the solder alloy has a propensity to oxidize upon exposure to air over a period of time.

In view of the foregoing, there is a need to provide a lead free solder alloy composition that may provide a substitute for conventional Sn-Pb solders used in electronic assemblies.

There is a need to provide a lead free solder alloy that overcomes or at least ameliorates one or more of the disadvantages described above.

Summary of the invention According to a first aspect, the present invention provides a lead free solder alloy comprising: from about 0.02% to about 1% by weight copper; from about 0.5% to about 3% by weight magnesium; from about 1.3% to about 5% by weight silver; and the remainder being tin and any incidental impurities.

In an embodiment of the first aspect, the present invention provides a lead free solder alloy comprising: from about 0.02% to about 1% by weight copper; from about 0.5% to about 3% by weight magnesium; from about 1.3% to about 5% by weignt silver; ana the remainder being tin.

According to a second aspect, the present invention provides a lead free solder alloy consisting essentially of copper, magnesium and silver in a tin matrix, wherein the alloy is capable of at least partially melting at a temperature of about 215°C or less. In one embodiment, the alloy is capable of at least partially melting at a temperature of about 200°C or less.

According to a third aspect, the present invention provides a lead free solder alloy comprising copper, magnesium and silver in a tin matrix, wherein the alloy is capable of at least partially melting at a temperature of about 215 C or less. In one embodiment, the alloy is capable of at least partially melting at a temperature of about 2000C or less.

According to a fourth aspect, the present invention provides a composition for use in the preparation of a lead free solder alloy comprising: from about 0.02% to about 1% by weight copper; from about 0.5% to about 3% by weight magnesium; from about 1.3% to about 5% by weight silver; and the remainder being tin and any incidental impurities.

According to a fifth aspect, the present invention provides a method of preparing lead free solder alloy comprising the steps of: (i) heating a lead free solder alloy comprising: from about 0.02% to about 1% by weight copper; from about 0.5% to about 3% by weight magnesium; from about 1.3% to about 5% by wexy∏t O-L-LVCL., cm^ the remainder being tin and any incidental impurities at a temperature to melt the copper, magnesium, silver and tin; and (ii) cooling the composition to form a lead free solder alloy.

According to a sixth aspect, the present invention provides an electronic structure comprising a first electronic component that is electrically bonded to a second electronic component by a lead free solder alloy according to the first aspect, the second aspect, the third aspect or the fourth aspect.

According to a seventh aspect, the present invention provides a method of joining two electronic components comprising the steps of: (a) providing a first electronic component and a second electronic component to be joined; and (b) electrically connecting the components together by soldering the components with a lead free solder comprising: from about 0.02% to about 1% by weight copper; from about 0.5% to about 3% by weight magnesium; from about 1.3% to about 5% by weight silver; and the remainder being tin and any incidental impurities.

According to a eighth aspect, the present invention provides a lead free solder alloy comprising copper, magnesium, silver, and tin and having at least a partial melting temperature of at least 180°C. According to an ninth aspect the present invention provides a lead free solder alloy produced by the method of the fifth aspect.

Definitions The following words and terms used herein shall have the meanings indicated:

The term "melting temperature" generally refers to the temperature at which a solid transforms into a liquid.

The terms "partially melting" or "partial melting" and grammatical variations thereof are to be interpreted broadly to be the point at which the alloy is not completely solid but has at least begun to melt.

The term "eutectic temperature" generally refers to the lowest temperature at which an alloy solid will melt to form a liquid phase.

The terms "mushy range" and "pasty range" generally refer to the range of temperatures between the "solidus" temperature, which is the highest temperature at which an alloy is completely solid (i.e., the point where melting starts when the alloy is heated) and the "liquidus" temperature, which is the lowest temperature at which the alloy is completely liquid (i.e., the point where solidifying starts as the alloy is cooled) .

The term Λincidental impurities' refers to any material that may be present in the raw materials used to produce the lead free solder alloy. Incidental impurities include unavoidable impurities as well as avoidable impurities.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. Disclosure of embodiments A disclosed embodiment provides a novel lead free solder alloy. Advantageously, the lead free solder alloy may advantageously have a melting temperature of less than 215°C and more preferably 2000C. The novel lead free solder alloy may advantageously provide a direct substitute for conventional Sn-Pb solder alloys used in electronic assemblies.

In one embodiment, the novel lead free solder alloy comprises no more than about 1% by weight copper. The amount of copper by weight in the lead free solder alloy may be selected from the group consisting of: 0.02% to 0.99%; 0.05% to 0.98%; 0.1% to 0.97%; 0.15% to 0.96%; 0.2% to 0.95%; 0.25% to 0.94%; 0.3% to 0.9%; 0.35% to 0.85%; 0.4% to 0.6%; 0.45% to 0.5%; 0.1% to 0.795%; 0.1% to 0.846%; and 0.1% to 0.9%.

In one embodiment, the novel lead free solder alloy comprises about 0.9% to about 3% by weight magnesium. The amount of magnesium by weight in the lead free solder alloy may be selected from the group consisting of: 0.95% to 2.9%; 1% to 2.9%; 1.5% to 2.9%; 1.8% to 2.9%; 1.9% to 2.9%; 2% to 2.8%; 2.2% to 2.8%; 2.4 to 2.8%; 2.5% to 2.8%; and 2.6% to 2.8%.

In one embodiment, the novel lead free solder alloy comprises about 1.3% to about 5% by weight silver. The amount of silver by weight in the lead free solder alloy may be selected from the group consisting of: 1.4% to 5%; 1.8% to 5%; 2% to 4.9%; 2.4% to 4.9%; 2.8% to 4.9%; 3% to 4.9%; 3.5% to 4.9%; and 4.5% to 4.9%. The lead free solder alloy may comprise at: ieasi y±^s by weight tin. The amount of tin in the lead free solder alloy may be in the range between 91% to 98% or 94% to 98% by weight. In one embodiment, the amount of tin by weight in the lead free solder alloy may be selected from the group consisting of: 91.7% to 97.77%; 91.7% to 92.6%; 93.84% to 97.78%; 94% to 97%; 94% to 96.5%; and 95% to 96%.

In one embodiment, the incidental impurities present in the alloy by weight may be up to 0.1%, preferably up to 0.05% and more preferably up to 0.01%. The incidental impurities that may be present in the alloy may be from the group consisting of: Al, Ca, Mn, Si, Zn, As, fluoride, bromide, chloride, alkali metal and S and oxides thereof, for example.

The melting temperature of the lead free solder alloy is 215°C or less and more preferably 200°C or less. The lead free solder alloy may have a melting temperature in the range selected from the group consisting of: 180°C to 199°C; 182°C to 198°C; 184°C to 198°C; 196 °C to 198°C; 186°C to 197°C; 188°C to 196°C; 190°C to 196°C; 192°C to 196°C; and 194°C to 196°C. In one embodiment, the lead free solder alloy may have a eutectic temperature of about 197.3°C.

In one embodiment, there is provided a lead free solder alloy comprising: 0.4% to 0.8 by weight copper; 2.5% to 2.8% by weight magnesium; 4.5% to 4.9% by weight silver; and the remainder being tin and any incidental impurities.

Preparation of the lead free solder alloy The lead free solder alloy is prepared by first preparing a lead free solder alloy composition. The composition may be prepared by mixing Cu, Mg, Ag and Sn powders. The median particle size of the powdered metal may be between about 20 to about 50 Mesh or about 20 to about 40 Mesh or about 20 to about 30 Mesh or about 30 to about 40 Mesh or about 25 to about 35 Mesh. The powdered material may be mixed to form a substantially homogenous material.

In one embodiment, the composition for preparing the lead free solder alloy may comprise: 0.4% to 0.8 by weight copper; 2.5% to 2.8% by weight magnesium; 4.5% to 4.9% by weight silver; and the remainder being tin and any incidental impurities.

The lead free solder alloy may be prepared from the composition by heating at a temperature to melt the Cu, Mg, Ag and Sn. The surface of the composition may be covered with a salt. The salt may be a metal salt such as an alkali metal salt. The alkali metal salt may be an alkali metal fluoride, alkali metal bromide, alkali metal chloride or alkali metal chlorate. The alkali metal chloride may be selected from the group consisting of: lithium chloride; sodium chloride; potassium chloride; and rubidium chloride. The composition may form a molten composition by heating to a temperature in the range selected from the group consisting of: 600°C to 1000°C; 650°C to 9500C; 700°C to 9000C; and 750°C to 850°C. The heating may occur for 1 to 2 hours.

After heating, the molten composition may be cooled to a temperature in the range selected from the group consisting of: 3500C to 5500C; 3000C to 5000C; and 3500C to 4500C.

The cooled molten composition may then be homogenized, such as by shaking or rotating the composition. After homogenisation, the molten composition may be allowed to cool to a solid phase and thereby form a lead free solder alloy.

A flux may optionally be added to the composition to assist in the prevention of the formation oxides, particularly while the composition is being heated. The amount of flux in the composition, in weight percent, present in the composition may be within the range selected from the group consisting of: 0% to 95%; 0% to 90%; 0% to 85%; 0% to 80%; 5% to 75%; 10% to 70%; 15% to 65%; 20% to 60%; 25% to 55%; 30% to 50%; and 35% to 45%. Suitably fluxes are known to those skilled in the art. Exemplary fluxes that may be able to be used are disclosed in US Patent nos. 4,298,407 and 4,168,996.

It has been found by the inventors that a relatively low amount of Cu may be added to a Sn-Ag-Mg ternary eutectic Pb-free solder alloy to thereby increase the oxidation resistance of the alloy. Advantageously, Cu is relatively low in cost and therefore Cu provides an inexpensive alternative to known additives ror prouucmy lead free solder alloys that have low melting temperatures. The addition of Cu also enhances the oxidation resistance of the solder composition without significantly increasing the eutectic temperature and microstructure stability of the solder alloy. Accordingly, the combination of the Cu, Mg, Ag and Sn produces a lead free solder alloy that has a melting temperature of less than 200°C and which has oxidation resistant properties.

Electronic structure The novel lead free solder alloy may be used to connect electronic components together. Two electronic components may be connected together by first melting the lead free solder alloy with a soldering iron. A flux may optionally be added to the melted solder to assist in flowability of the solder andi to assist in the prevention of the formation oxides during soldering. The amount of flux present with the melted alloy, in weight percent, may be within the range selected from the group consisting of: 0% to 95%; 0% to 90%; 0% to 85%; 0% to 80%; 5% to 75%; 10% to 70%; 15% to 65%; 20% to 60%; 25% to 55%; 30% to 50%; and 35% to 45%. Suitable fluxes are those known to those skilled in the art. Exemplary fluxes that may be able to be used are disclosed in US Patent nos. 4,298,407 and 4,168,996.

The molten lead free solder alloy and the flux may then be used to connect the two electronic components together once the alloy has cooled to the solid phase. This provides an electrical connection between the two electronic components. The electronic components may be mounted on a substrate, such as a printed circuit board. Brief description of drawings Non-limiting modes known to the applicants for practicing the invention will be further described with reference to the accompanying drawings in which:-

Fig. 1 shows a crystal structure of Mg2Sn showing the occupation site of Cu and Mg in the sublattice of Mg2Sn.

Fig.2 shows a composition map of the microstucture of a quaternary alloy sample Sn91.99Ag4.79Mg2.7Cuo.5, analyzed by Energy Dispersive X-Ray (EDX) Spectroscopy.

Fig. 3A shows a magnification of a portion of the microstructure of Fig. 2 with a line-scan shown applied to a section of the mapped microstructure.

Fig.3B shows an expanded view of the line scan of Fig. 3A.

Detailed description of modes of performing the invention Referring to Fig. 1, there is shown a body-centered tetragonal structure (BCT) of Mg2Sn showing the occupation site of Cu and Mg in the sublattice of Mg2Sn. For reference, the body centered tetragonal structure (BCT) is an example of a unit cell. The unit cell is the smallest structure that repeats itself by translation throughout the crystal. "BCT_A5" is the respective Strukturbericht designation accorded to the structure of Fig. 1.

Without being bound by theory it is thought that the Cu may be dissolved in the Mg2Sn phases of the alloy microstructure. Advantageously, this is thought to reduce the overall amount of Mg in the alloy, which is a contributor to alloy metal brittleness.

In one example, the eutectic microstructure of these elements is formed by the Sn-rich phase of the body- centered tetragonal structure (BCT_A5), Ag3Sn and Mg2Sn.

Accordingly, the quaternary lead free solder alloys of the disclosed embodiments advantageously possess eutectic temperatures which are less than 200°C.

Another advantage of the disclosed quaternary lead free solder alloys of the disclosed embodiments is that they avoid the need to utilize In or Bi to reduce the formation of a low-melting phase in a Sn-rich Pb free solder.

Another advantage is that that the addition of up to 1% by weight Cu may allow a reduction in the amount of Ag content that is required in the composition compared to ternary eutectic alloys (Sn-Ag-Mg), which reduces the material cost.

Without being bound by theory, it is thought that the addition of Cu may also suppress or retard the diffusion of Cu between the solder and a Cu-based substrate to which the solder is applied.

The disclosed lead free solder may also advantageously exhibit favorable mechanical properties such as a small "mushy range" or "pasty range". Without being bound by theory it is thought that the small mushy range and compounds in the alloy systems stabilize the microstructure by refining grain size and reducing composition macro-segregation, which nave an impoxLCUIL impact on the mechanical properties of the solder alloy.

Properties of compositions for use in the manufacture of lead free solder alloys may be estimated by the application of computational thermodynamics. Computational thermodynamics involves the use of phase diagrams and associated data to analyze thermodynamic properties. Computational thermodynamics enables the prediction of some features of an alloy system, such as melting temperature, which are not easily measured or predicted for complex multicomponent systems.

The effect of Cu addition to Sn-Ag-Mg ternary eutectic alloys has been studied by the CALPHAD (Computer Calculation of Phase Diagrams) technique. In the CALPHAD technique, thermodynamic models consistent with experimental binary data are first obtained, then a standard thermodynamic extrapolation method is used to calculate the quaternary system, i.e., measured values from binary mixtures are used to estimate the thermodynamic properties of multicomponent systems.

A number of commercially available software packages are available on the market that use the CALPHAD technique to predict theoretical multi-component alloy system behavior. Commercially available software packages include CHEMSAGE™ and FACTSAGE™ from GTT Technologies of Aachen, Germany; MTDATA™ from the National Physical Laboratory of Teddington, Middlesex, United Kingdom; and THERMO-CALC™ from Thermo-Calc Software, Bjornnasvagen , Stockholm, Sweden. FACTSAGE™ was initially used to estimate the theoretical melting points of a Cu-Ag-Mg-Sn quaternary system. Compositions A, B, C and D are exemplary ranges (in weight percent) that have been calculated by FACTSAGE™ as having melting temperatures less than 2000C:

Alloy Composition A 0.02% to 0.8% by weight Cu; 0.5% to 3% by weight Mg; 1% to 4.8% by weight Ag; and 91.4% to 98.48% by weight Sn

Alloy Composition B 0.02% to 0.795% by weight Cu; 1.362% to 1.568% by weight Mg; 2.43% to 3.283% by weight Ag, and 94.5% to 96.178% by weight Sn.

Alloy Composition C 0.02% to 0.846% by weight Cu; 1.14% to 1.56% by weight Mg; 1.36% to 3.256% by weight Ag, and 94.84% to 97.47% by weight Sn.

Alloy Composition D 0.02% to 0.9% by weight Cu; 0.92% to 1.43% by weight Mg; 1.34% to 3.23% by weight Ag, and 95.1% to 97.71% by weight Sn.

The theoretical melting points were then confirmed in the following experiments. Example 1 Step 1: lOOOg of Composition 1 was prepared by placing the following into a mixing vessel: 5g of 99.95% pure Cu powder having a mean particle size of 1.25 mm; 27g of 99.99% pure Mg powder having a mean particle size of 1.25 mm; 47.9g of 99.99% pure Ag powder having a mean particle size of 1.25 mm; and 910.9g of 99.99% pure Cu powder having a mean particle size of 1.25 mm.

The powders were obtained from CERAC Inc., of Milwaukee, Wisconsin.

Step 2: The powder composition of step 1 was mixed to form a homogenous mixture.

Step 3: The homogenous mixture of step 2 was subjected to compression in a press to form 13mm diameter pellets.

Step 4: The pellets of step 3 were covered by an upper and a lower salt layer compositions in an alumina crucible. The lower layer composition was 45.3% LiCl and 54.7% KCl by weight. The upper layer composition was 41% NaCl and 59% KCl by weight.

Step 5 The Alumina crucible of step 4 was placed in a chamber furnace and heated to 800 C for 40 minutes. Step 6 The Alumina crucible was removed from the chamber furnace and allowed to cool under ambient conditions until the temperature of reached 400 C.

Step 7 The Alumina crucible was shaken for another 10 minutes.

Step 8 The crucible was allowed to cooled under ambient conditions.

Step 9 An ingot of the Pb-free solder alloy was obtained by washing out the salts from the crucible with water.

Results and discussion -Example 1 A sample of the ingot was found to have a eutectic temperature of 197.46°C. The composition of the sample was as follows: 0.5% by weight Cu; 2.7% by weight Mg; 4.79% by weight Ag; and 92% by weight Sn. (ie Sn92Ag4.79Mg2.7Cu0.5)

The eutectic temperature of the alloy was 197.46°C, which was in good agreement with the theoretical models calculated from FACTSAGE™. Hardness Test The alloy of example 1 was found to have a Rockwell B Hardness of 71.2. The hardness of a comparative ternary alloy having a composition of Sn92.419-7Ag4.907498Mg2.6728 and not forming part of the invention was 74.0. This indicates that alloys of the present invention have reduced brittleness compared to ternary alloys.

The control reference in the test was an alloy of Ag3Sn+Sn:69.8. The Rockwell B hardness test was carried out using a hardness tester with a ball indenter under 100Kg for 15s. It can be seen from the above Rockwell B hardness measurements of quaternary and ternary alloys (similar composition), that the quaternary solder alloy has reduced brittleness compared to the ternary solder alloy.

Fig.2 shows the composition mapping of the microstucture of the quaternary alloy sample SnS2Ag4.79Mg2-7CUo.5, which was analyzed by Energy Dispersive X-Ray (EDX) Spectroscopy. The EDX Spectroscopy technique is described in B. Williams, J.I. Goldstein, D.E. Newbury, "X-ray Spectrometry in Electron Beam Instruments", Plenum, New York, 1995 and D.B. Williams, CB. Carter. "Transmission Electron Microscopy, a Textbook for Materials Science", Plenum, New York, 1996, which are incorporated herein for reference. Fig. 2, shows that the Cu, Mg, Ag, and Sn were homogeneously distributed in the microstructure, except for a small size Mg2Sn phase.

Fig. 3A shows a magnification of a portion of the microstructure of Fig. 2. A line-scan shown by arrow (10) has been applied to a section or tne mappeα microstructure. The line-scan plots the abundance of an element with distance along a line rather than as a measure of intensity over a two-dimensional image.

Fig.3B shows an expanded view of the line scan (10) . The line scan (10) can be used to show the location of Cu in the microstructure. It can be seen from Fig. 3B that some Cu appears at the same site as Mg and Sn (see the oval circle part 12) . This would appear to support the theory that Cu is soluble in Mg2Sn: (Cu,Mg) (Mg,Sn) .

Example 2 A second ingot was prepared according to the method of example 1 but having a different composition. The composition of the second quaternary alloy was as follows: 0.57% by weight Mg; 0.15% by weight Cu; 3.29% by weight Ag; and 95.99% by weight Sn.

The eutectic temperature of the Sng5.9gAg3.29Mgo.57Cuo.i5 alloy was 197°C.

Example 3 A third ingot was prepared according to the method of example 1 but having a different composition. The composition of the third quaternary alloy was as follows: 0.59% by weight Mg; 0.22% by weight Cu; 3.47% by weight Ag; and 95.72% by weight Sn. The eutectic temperature of the Sn95 -71AgS - 47Mg0 - SgUUo.22 alloy was 197°C .

Example 4 A fourth ingot was prepared according to the method of example 1 but having a different composition. The composition of the fourth quaternary alloy was as follows: 0.55% by weight Mg; 1.00% by weight Cu; 3.39% by weight Ag; and 95.06% by weight Sn.

The eutectic temperature of the Sn95 - OsAgS - 39Mg0.55CU1.00 alloy was 215°C .

Application(s)

As a relatively low amount of Cu is present in the lead free solder alloy of the disclosed embodiments, the cost of the solder alloy is lower compared to lead free solder alloys that use In and Bi as additives. Advantageously, the disclosed lead free solder alloys meet the need of providing a low cost alternative to lead free solder compositions.

The disclosed lead free solder alloys have a eutectic temperature less than 215°C, and advantageously less than 2000C, and therefore at least partially reduce, or eliminate completely, thermal damage to polymeric materials to which they might be applied during the assembly of electronic components. The addition of Cu also enhances tne oxidation resistance of the solder composition without significantly increasing the eutectic temperature and microstructure stability of the solder alloy. Furthermore, as it is also thought that Cu is soluble in Mg2Sn, it is thought that a lower amount of Mg needs to be used due to the addition of Cu. As the addition of Mg contributes to the brittleness of the solder alloy, it is thought that a reduction in Mg by replacement with Cu may lead to increased mechanical strength.

The disclosed lead free solder compositions are also easy to manufacture and recycle. The compositions advantageously overcome the recycling difficulties associated with solders that utilize bismuth or indium as an additive elements.

As Cu is added in the disclosed lead free solder compositions, the compositions also fulfill the need of providing a lead free solder that has reduced propensity to oxidize upon exposure to air over a period of time.

Advantageously, the disclosed lead free solder compositions provide a lead free solder alloy composition that may provide a direct substitute for conventional Sn- Pb solders.

The disclosed lead free solder compositions have reduced brittleness compared to ternary solder compositions.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit ana scope or the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.