Lead-free solder composition

Abstract

Lead-free solder composition, consisting of, based on 100% of the total weight of the lead-free solder composition, 0.3 to 3.0 wt.% silver (Ag), 0.5 to 3.0 wt.% antimony (Sb), 0.3 to 3.0 wt.% indium (In), at least one of the elements scandium (Sc), nickel (Ni), chromium (Cr) and cobalt (Co) and as the remaining proportion of tin (Sn), wherein, after soldering with the lead-free solder composition, the thickness increase ratio of an intermetallic compound layer after 2000 cycle repetitions in a thermal fatigue test is 40% or less, wherein one cycle comprises 125°C / 30 min to -40°C / 30 min.

Description

GENERAL STATE OF THE ART(A) Area

[0001] The present invention relates to a high-strength, lead-free solder composition. In particular, the present invention relates to a high-strength, lead-free solder composition comprising a four-element material consisting of tin (Sn), silver (Ag), antimony (Sb), and indium (In). (b) Description of the state of the art

[0002] Previously, lead was primarily used as soldering material. However, due to environmental regulations, its use in electronic products has recently been prohibited, and its use in vehicles is strictly forbidden. Therefore, conventional lead-based soldering materials are currently being replaced by various types of metal alloys. Lead-free soldering materials, however, have lower strength and corrosion resistance than conventional lead-based alloys and are more susceptible to ion migration. Depending on the application and purpose, common lead-free soldering compositions include Sn-Ag-Cu, Sn-Bi, and Sn-Ag.A Sn-Zn-Bi-based composition is used, and in particular, a Sn-Ag-Cu-based composition is used for the broadest range of applications and diverse purposes. The Sn-Ag-Cu-based lead-free solder composition is used in general electronic products, while for vehicles and products of comparable quality requiring high reliability, i.e., excellent thermal fatigue properties, other elements are added to the Sn-Ag-Cu-based lead-free solder composition. After soldering with an Sn-Ag-Cu-based lead-free solder composition, cracks are formed if the temperature repeatedly changes in an extreme manner, as a result of stresses caused by the difference in the coefficients of thermal expansion of the base components.When cracks develop, the adhesive strength decreases, and this can impair the reliability of the product.

[0003] A lead-free, low-melting-point solder alloy is known from US patent 2007 / 0071634 A1. One possible composition contains 0.001–3.5 wt.% Ag, 2.001–4 wt.% In, 0.0–1.0 wt.% Cu, and 91.5–97.998 wt.% Sn. Furthermore, patent D1 advises against implementing copper contents of 0.2 wt.% or less. The solder alloy disclosed in JP S57-30598 B2 has the following composition: Ag: 0.1–2 wt.%, In: 0.05–1 wt.%, Sb: 0.05–0.5 wt.%, Sn: 96.5–99.8 wt.%. Furthermore, the use of antimony concentrations of 0.5 wt.% or more is discouraged. Finally, DE 1 080 838 B describes a solder composition of Ag: 1-4 wt.%, In: 0.5-5 wt.%, Sb: 2-6 wt.%, Sn: >85 wt.%. BRIEF SUMMARY OF THE INVENTION

[0004] The present invention has been made in an effort to provide a lead-free solder composition with excellent wettability and processability and excellent thermal fatigue properties.

[0005] Furthermore, the present invention has been made in an effort to provide a lead-free solder composition that is harmless to humans and environmentally friendly.

[0006] Furthermore, the present invention arose in the endeavor to provide a lead-free solder composition that can be used in electronic products and vehicles. The present invention provides a lead-free solder composition with the features of claim 1. Further developments of the invention are described in the dependent claims.

[0007] According to the present invention, it is possible to provide a lead-free solder composition with excellent wettability and processability and excellent thermal fatigue properties. It is also possible to simultaneously reduce the silver (Ag) content.

[0008] Furthermore, the lead-free solder composition according to the present invention can be used in vehicles, electronic products and especially in microelectronics. DETAILED DESCRIPTION

[0009] The advantages and features of the present invention, as well as the methods for obtaining it, will become apparent from the exemplary embodiments described below with reference to the accompanying drawing. Throughout this description, the same reference numerals denote the same components.

[0010] In some exemplary embodiments, a detailed description of well-known technologies is omitted to avoid any ambiguity in the interpretation of the present invention. Unless otherwise specified, all terms (including technical and scientific terms) used herein have the same meanings as they would normally be understood by a person skilled in the art. Furthermore, it is understood that the expression "comprise" and variations thereof, such as "includes" or "comprehensive," throughout this description are to be understood as including the specified elements but not excluding other elements. Furthermore, the singular forms "a," "an," "a," and "the," "a," "the," as used herein, are also to include the plural forms unless the context clearly indicates otherwise.

[0011] In exemplary embodiments of the present invention, a weight percent (wt%) is represented as a percentage of the weight of a corresponding composition relative to the weight of the total composition. Furthermore, in exemplary embodiments of the present invention, "inclusion" of an additional element means replacing the remaining tin (Sn) with an additional amount of the additional element.

[0012] A lead-free solder composition according to an exemplary embodiment of the present invention is an environmentally friendly and non-toxic solder composition without lead (Pb). According to the exemplary embodiment of the present invention, excellent thermal fatigue properties are ensured by using a four-element material based on tin (Sn), silver (Ag), antimony (Sb), and indium (In) during a thermal fatigue test (under thermal shock or temperature cycling).

[0013] The lead-free solder composition according to the exemplary embodiment of the present invention is designed taking into account the wettability and processability during soldering and the reliability during a test for thermal fatigue (under thermal shock or temperature cycling) and exhibits excellent quality compared to a conventional lead-free solder composition.

[0014] The lead-free solder composition according to the exemplary embodiment of the present invention contains silver (Ag), antimony (Sb), indium (In), and tin (Sn). Each component is described in detail below.

[0015] The lead-free solder composition according to the exemplary embodiment of the present invention contains 0.3 to 3.0 wt.% silver (Ag) by weight. In particular, it can comprise 0.5 to 2.0 wt.% silver (Ag), and more specifically, it can comprise 1.0 to 1.5 wt.% silver (Ag). An intermetallic Sn-Ag compound with a dense, needle-like structure, which forms during soldering within the aforementioned range, increases the strength of a solder alloy. Furthermore, the elongation is improved, thus enhancing the thermal fatigue properties and the resistance to dripping.

[0016] The lead-free solder composition according to the exemplary embodiment of the present invention contains 0.5 to 3.0 wt.% antimony (Sb) by weight. In particular, it can comprise 0.7 to 2.5 wt.% antimony (Sb), and more specifically, it can comprise 1.5 to 2.0 wt.% antimony (Sb). With an antimony content in the aforementioned range, it is possible to ensure the thermal fatigue properties by resisting shear stresses during thermal fatigue testing (under thermal shock or temperature cycling) and reducing crack initiation rate and extent, with this effect being maximized by a uniform distribution of the antimony (Sb) material.

[0017] The lead-free solder composition according to the exemplary embodiment of the present invention contains 0.3 to 3.0 wt.% indium (In) by weight. In particular, it can comprise 0.4 to 1.5 wt.% indium (In), and even more specifically, it can comprise 0.5 to 1.0 wt.% indium. With an indium content in the aforementioned range, it is possible to control the melting point to ensure excellent adhesion and wettability and to maintain strength by mitigating thermal fatigue.

[0018] In the lead-free solder composition according to the exemplary embodiment of the present invention, tin (Sn) is included as a residual component to reach 100% of its total weight. Tin (Sn) is non-toxic in itself and has excellent solubility in other metals; this allows for the trouble-free production of various alloys.

[0019] The lead-free solder composition according to the exemplary embodiment of the present invention can additionally comprise at least one of the elements scandium (Sc), nickel (Ni), chromium (Cr) and cobalt (Co).

[0020] If scandium (Sc) is also included, it may be present in amounts from 0.001 to 0.5 wt.% of the total weight of the composition. At concentrations within this range, the strength and spreading properties of the solder may be further improved. However, if scandium (Sc) is included in too large an amount, the workability may be impaired due to the formation of an insoluble compound. If scandium (Sc) is included in too small an amount, the improvement in strength and spreading properties may be limited to exemplary embodiments.

[0021] If nickel (Ni) is also included, it may be present in amounts of 0.001 to 0.05 wt.%, based on the total weight of the composition. At a content within the aforementioned range, it is possible to effectively ensure strength by reducing the thickness of an intermetallic compound. If nickel (Ni) is included in too large an amount, wettability may be impaired. If nickel (Ni) is included in too small an amount, the improvement in strength may be limited. Exemplary embodiments show that...

[0022] If chromium (Cr) is also included, it may be present in amounts of 0.001 to 0.05 wt.%, based on the total weight of the composition. At a content within the aforementioned range, it is advantageous for improvements in corrosion protection, droplet impact, and strength. If chromium (Cr) is included in too large an amount, processability may be impaired. If chromium (Cr) is included in too small an amount, the improvements in corrosion protection, droplet impact, and strength may be limited to exemplary embodiments.

[0023] If cobalt (Co) is also included, it may be present in amounts of 0.001 to 0.05 wt.%, based on the total weight of the composition. At a content within the aforementioned range, metal diffusion occurring during thermal fatigue is suppressed, thus improving strength retention, and the growth of the intermetallic compound (IMC) layer may also be suppressed. If cobalt (Co) is included in an excessive amount, processability may be impaired. If cobalt (Co) is included in an excessive amount, the aforementioned effect may be observed in exemplary embodiments.

[0024] According to an exemplary embodiment of the present invention, by using a four-element material based on tin (Sn), silver (Ag), antimony (Sb), and indium (In), it is possible to obtain a lead-free solder composition that exhibits excellent strength. In particular, its tensile strength can reach 55 MPa or more when evaluated according to ASTM A370. Since ASTM A370 is well-known, a detailed description of it is omitted.

[0025] Since the four-element material consisting of tin (Sn), silver (Ag), antimony (Sb), and indium (In) is applied to the lead-free solder composition according to the exemplary embodiment of the present invention, its thermal fatigue properties are excellent. This is because it is possible to suppress the formation of a densely packed intermetallic compound layer (IMC layer) and thickness increase. The Ag3Sn intermetallic compound layer has a densely packed needle-like structure and can ensure excellent initial strength.Furthermore, the addition of Sb reduces shear stress, while the addition of In increases deformability and consequently the resistance of a joint section to environmental influence testing, thus maintaining strength and suppressing intermetallic compound (IMC) growth, makes it advantageous to retain initial strength regardless of service life.

[0026] Since the growth of the intermetallic compound layer is maximally suppressed in the lead-free solder composition according to the exemplary embodiment of the present invention, the thermal fatigue properties are improved. In particular, with regard to the thickness of the intermetallic compound layer after soldering with the lead-free solder composition, after 2000 cycles of thermal fatigue testing for 30 minutes (one cycle corresponds to 125 °C to -40 °C), the thickness increase ratio of the intermetallic compound layer can be 40% or less. In particular, it can be 35% or less.

[0027] The lead-free solder composition according to the exemplary embodiment of the present invention can be applied to at least one solder product consisting of a solder paste, a solder ball, a solder rod, a solder wire, a solder bead, a solder plate, a solder powder, a solder band and a solder ring.

[0028] The lead-free solder composition according to the exemplary embodiment of the present invention can be produced from a lead-free solder alloy, and the lead-free solder alloy can advantageously be used in electronic components and vehicles.

[0029] Examples of the present invention and comparative examples are described in detail below. However, the following examples serve only for illustration, and the scope of protection of the present invention is not limited to them. Examples 1 to 8 and comparative examples 1 to 14: Production of lead-free solder compositions

[0030] Lead-free solder compositions according to examples 1 to 8 or comparative examples 1 to 14 were produced using the compositions shown in Table 1. (Table 1) Classification Silver (wt%) Antimony (wt%) Indium (wt%) Other (wt%) Tin (wt%) Comparative example 1 - - - - 100 Comparative example 2 3,0 - 0,5 - Remaining amount Comparative example 3 0,3 - 0,7 - Remaining amount Comparative example 4 - - - Ni: 0.01 Remaining amount Comparative example 5 - - - Cr: 0,01 Remaining amount Comparative example 6 - - - Co: 0.01 Remaining amount Comparative example 7 - - - Sc: 0.01 Remaining amount Comparative example 8 - - - Sc: 0.005 Remaining amount Comparative example 9 0,5 - - Sc: 0.005 Remaining amount Comparative example 10 1,5 - - Sc: 0.005 Remaining amount Comparative example 11 1,5 - 0,5 Sc: 0.005 Remaining amount Comparative example 12 1,5 - 1,0 Sc: 0.005 Remaining amount Comparative example 13 - 1 1,0 Sc: 0.005 Remaining amount Comparative example 14 - 2 1,0 Sc: 0.005 Remaining amount Example 1 1,5 2 1,0 Sc: 0.005 Remaining amount Example 2 1,5 1 1,0 Sc: 0.005 Remaining amount Example 3 1,5 2 0,5 Sc: 0.005 Remaining amount Example 4 1,0 2 1,0 Sc: 0.005 Remaining amount Example 5 1,0 1 0,5 Sc: 0.005 Remaining amount Example 6 1,5 1 1,0 Ni: 0.005 Remaining amount Example 7 1,5 1 1,0 Cr: 0,005 Remaining amount Example 8 1,5 1 1,0 Co: 0.005 Remaining amount

[0031] The tensile strengths of the solder alloys produced with the lead-free solder compositions of Examples 1 to 8 and Comparative Examples 1 to 14 were evaluated. The tensile strength of the metal was assessed according to ASTM A370. The evaluated results are shown in Table 2. (Table 2) Classification Tensile strength of the metal (MPa) Comparative example 1 24 Comparative example 2 49 Comparative example 3 34 Comparative example 4 37 Comparative example 5 35 Comparative example 6 38 Comparative example 7 41 Comparative example 8 42 Comparative example 9 44 Comparative example 10 51 Comparative example 11 50 Comparative example 12 52 Comparative example 13 54 Comparative example 14 58 Example 1 61 Example 2 57 Example 3 60 Example 4 56 Example 5 55 Example 6 58 Example 7 60 Example 8 57

[0032] Table 2 shows that the intensity of the examples containing silver (Ag), antimony (Sb) and indium (In) is significantly improved compared to the comparison examples. Experimental example: Feature evaluation of lead-free solder compositions

[0033] The characteristics of the solder alloys produced with the lead-free solder compositions of Examples 1 to 8 and Comparative Examples 1 to 14 were evaluated according to the following test procedures. After a solder wire had been produced using a halogen-free flux of class ROL1, it was evaluated, and the evaluation results are shown in Table 3.

[0034] Table 3 lists numerical values ​​for spreading capacity, for thermal fatigue testing (under thermal shock or temperature cycling) the presence or absence of cracks after corresponding cycles as OK or NIO, and numerical values ​​for the thickness of the intermetallic compound layer (IMC layer). Numerical values ​​are also given for the strength reduction ratio. (Table 3) Classification Spreadability Cracking due to thermal fatigue (thermal shock, temperature cycling) 2000 cycles 0 cycles 500 cycles 1000 cycles 1500 cycles 2000 cycles IMC layer change ratio Strength reduction ratio Comparison 82,6 % OK NIO NIO NIO NIO +52 % -51 % game 1 Comparative example 2 81,7 % OK OK OK NIO NIO +41 % -43 % Comparative example 3 80,2 % OK OK NIO NIO NIO +42 % -45 % Comparative example 4 80,1 % OK OK NIO NIO NIO +45 % -48 % Comparative example 5 80,3 % OK OK NIO NIO NIO +44 % -49 % Comparative example 6 80,1 % OK OK NIO NIO NIO +44 % -49 % Comparative example 7 82,7 % OK OK NIO NIO NIO +46 % -48 % Comparative example 8 82,3 % OK OK NIO NIO NIO +45 % -48 % Comparative example 9 82,9 % OK OK OK NIO NIO +42 % -42 % Comparative example 10 83,2 % OK OK OK NIO NIO +41 % -34 % Comparative example 11 82,7 % OK OK OK OK NIO +33 % -26 % Comparative example 12 82,2 % OK OK OK OK NIO +31 % -23 % Comparative example 13 80,6 % OK OK OK NIO NIO +44 % -20 % Comparative example 14 80,3 % OK OK OK NIO NIO +41 % -19 % Example 1 82,1 % OK OK OK OK OK +26 % -14 % Example 2 81,4 % OK OK OK OK NIO +30 % -17 % Example 3 81,1 % OK OK OK OK NIO +30 % -16 % Example 4 81,5 % OK OK OK OK NIO +32 % -19 % Example 5 81,8 % OK OK OK OK NIO +32 % -22 % Example 6 82,2 % OK OK OK OK OK +30 % -20 % Example 7 83,1 % OK OK OK OK OK +28 % -15 % Example 8 82,1 % OK OK OK OK NIO +35 % -25 % (1) Comparison of spreading ability

[0035] For each composition, the spreading ability was measured with a micrometer by heating for 30 seconds to a temperature of +50 °C, based on a melting point (liquid phase).

[0036] Referring to the measurement results shown in Table 3, it was confirmed that the degree of spreading ability varied depending on the type and content of the added components, and that the spreading ability of the examples was equal to or much better than that of comparison examples 2 and 3, which correspond to the conventional composition based on three elements. (2) Crack comparison during testing for thermal fatigue (under thermal shock or temperature cycling)

[0037] After the solder alloy had been soldered onto an epoxy perforated circuit board, crack formation was investigated using a heat shock test device at 125 °C or -40 °C and 500, 1000, 1500 or 2000 cycles (cycle / 30 minutes).

[0038] Referring to the observation results shown in Table 3, it was confirmed that the starting point of crack generation was better in the four-element-based alloys of the examples than in the comparison examples. (3) Change ratio of the intermetallic compound layer (IMC layer)

[0039] After repeating 2000 cycles in the same manner as the thermal shock test for crack formation, the thickness change of the intermetallic compound layers (IMC layers) was confirmed by comparison with those before the thermal shock test for crack formation. Change in thickness of an intermetallic compound layer (%) = ([Thickness after thermal shock testing for cracking] − [Thickness before thermal shock testing for cracking]) / [Thickness before thermal shock testing for cracking]

[0040] Referring to the results shown in Table 3, it was confirmed that the thickness changes of the intermetallic compound layers (IMC layers) in the four-element-based alloys of the examples were less than in the comparison examples. (4) Strength reduction ratio

[0041] The strength change ratios of the test specimens were confirmed in the same manner as in the IMC layer change ratio test. The strength change varies depending on the coarsening of the internal metal structure and the occurrence of cracking, and the difference in strength change between examples and comparison examples was clearly confirmed. A low strength reduction ratio indicates that there are few internal cracks, which means that the change in electrical resistance is small. Therefore, the strength reduction ratio is an absolute criterion for classifying high-strength lead-free solder compositions and lead-free solders in general.

[0042] It has been confirmed that the strength reduction ratios of the alloys in the examples are remarkably low compared to the reference examples. Therefore, it was concluded that the composition of the examples corresponds to the characteristics of the high-strength lead-free solder composition.

[0043] As shown in Table 3, it has been confirmed that the solder made from tin-silver-antimony-indium exhibits better spreading behavior and better reliability in the thermal fatigue test (under thermal shock or temperature cycling) than the solder corresponding to the comparison example, and that sufficient adhesion strength is ensured.

Claims

[1] Lead-free solder composition, consisting of, based on 100% of the total weight of the lead-free solder composition, 0.3 to 3.0 wt.% silver (Ag), 0.5 to 3.0 wt.% antimony (Sb), 0.3 to 3.0 wt.% indium (In), at least one of the elements scandium (Sc), nickel (Ni), chromium (Cr) and cobalt (Co) and as the remaining proportion of tin (Sn), wherein, after soldering with the lead-free solder composition, the thickness increase ratio of an intermetallic compound layer after 2000 cycle repetitions in a thermal fatigue test is 40% or less, wherein one cycle comprises 125°C / 30 min to -40°C / 30 min. [2] Lead-free solder composition according to claim 1, wherein scandium (Sc) is included in 0.001 to 0.5 wt.%. [3] Lead-free solder composition according to claim 1 or 2, wherein nickel (Ni) is included in 0.001 to 0.05 wt.%. [4] Lead-free solder composition according to claim 1, 2, or 3, wherein chromium (Cr) is included in 0.001 to 0.05 wt.%. [5] Lead-free solder composition according to claim 1, 2, 3 or 4, wherein cobalt (Co) is included in 0.001 to 0.05 wt.%. [6] Lead-free solder composition according to any of the preceding claims, wherein silver (Ag) constitutes 0.5 to 2.0 wt.%, preferably 1.0 to 1.5 wt.%. [7] Lead-free solder composition according to any of the preceding claims, wherein antimony (Sb) constitutes 0.7 to 2.5 wt.%, preferably 1.5 to 2.0 wt.%. [8] Lead-free solder composition according to any of the preceding claims, wherein indium (In) constitutes 0.4 to 1.5 wt.%, preferably 0.5 to 1.0 wt.%. [9] Lead-free solder composition according to any of the preceding claims, wherein the lead-free solder composition has a tensile strength of 55 MPa or more, as assessed according to ASTM A370. [10] Electronic component comprising the lead-free solder composition according to any one of claims 1 to 9. [11] Vehicle comprising the lead-free solder composition according to any one of claims 1 to 9.