阅读说明：本技术 用于极端环境中的电子应用的高可靠性无铅焊料合金 (High reliability lead-free solder alloys for electronic applications in extreme environments ) 是由 穆德·哈斯宁 立克·韦·霍 于 2018-10-31 设计创作，主要内容包括：本发明公开了无铅焊料合金,其基于锡并且包含银、铜、铋、钴和钛。该合金还可包含锑、镍或两者。银以按焊料的重量计3.1％至3.8％的量存在。铜以按焊料的重量计0.5％至0.8％的量存在。铋可以按焊料的重量计0.0％(或1.5％)至3.2％的量存在。钴以按焊料的重量计0.03％至约1.0％(或0.05％)的量存在。钛以按焊料的重量计0.005％至0.02％的量存在。锑可以按焊料的重量计1.0％至3.0％的量存在。焊料的余量为锡。(The invention discloses a lead-free solder alloy, which is based on tin and contains silver, copper, bismuth, cobalt and titanium. The alloy may also contain antimony, nickel or both. Silver is present in an amount of 3.1% to 3.8% by weight of the solder. Copper is present in an amount of 0.5% to 0.8% by weight of the solder. Bismuth may be present in an amount of 0.0% (or 1.5%) to 3.2% by weight of the solder. Cobalt is present in an amount of 0.03% to about 1.0% (or 0.05%) by weight of the solder. The titanium is present in an amount of 0.005% to 0.02% by weight of the solder. Antimony may be present in an amount of 1.0% to 3.0% by weight of the solder. The balance of the solder is tin.)

1. A lead-free solder alloy comprising:

3.1 to 3.8 wt% silver;

0.5 to 0.8 wt.% copper;

0.0 to 3.2 wt% bismuth;

0.03 to 1.0 wt% cobalt;

0.005 to 0.02 wt% titanium; and

the balance tin, and any unavoidable impurities.

2. The lead-free solder alloy of claim 1, further comprising 0.01 to 0.1 wt.% nickel.

3. The lead-free solder alloy of claim 2, comprising 0.05 wt.% nickel.

4. The lead-free solder alloy of claim 1, comprising 3.8 wt% silver.

5. The lead-free solder alloy of claim 1, comprising 0.7 wt.% copper.

6. The lead-free solder alloy of claim 1, comprising 1.5 to 3.2 wt.% bismuth.

7. The lead-free solder alloy of claim 6, comprising 1.5 wt.% bismuth.

8. The lead-free solder alloy of claim 6, comprising 3.0 wt.% bismuth.

9. The lead-free solder alloy of claim 1, comprising 0.03 to 0.05 wt.% cobalt.

10. The lead-free solder alloy of claim 9, comprising 0.05 wt.% cobalt.

11. The lead-free solder alloy of claim 1, comprising 0.008 wt.% titanium.

12. A lead-free solder alloy comprising:

3.1 to 3.8 wt% silver;

0.5 to 0.8 wt.% copper;

0.0 to 3.2 wt% bismuth;

0.05 to 1.0 wt% cobalt;

1.0 to 3.0 wt.% antimony;

0.005 to 0.02 wt% titanium; and

the balance tin, and any unavoidable impurities.

13. The lead-free solder alloy of claim 12, further comprising 0.01 to 0.1 wt.% nickel.

14. The lead-free solder alloy of claim 13, comprising 0.05 wt.% nickel.

15. The lead-free solder alloy of claim 12, comprising 3.8 wt% silver.

16. The lead-free solder alloy of claim 12, comprising 0.8 wt.% copper.

17. The lead-free solder alloy of claim 12, comprising 1.5 to 3.2 wt.% bismuth.

18. The lead-free solder alloy of claim 17, comprising 1.5 wt.% bismuth.

19. The lead-free solder alloy of claim 17, comprising 3.0 wt.% bismuth.

20. The lead-free solder alloy of claim 12, comprising 0.05 wt.% cobalt.

21. The lead-free solder alloy of claim 12, comprising 1.0 wt.% antimony.

22. The lead-free solder alloy of claim 12, comprising 1.5 wt.% antimony.

23. The lead-free solder alloy of claim 12, comprising 0.008 wt.% titanium.

Technical Field

The present disclosure generally relates to lead-free solder alloys for electronic applications.

Background

Solder alloys are widely used in the manufacture and assembly of various electronic devices. Traditionally, the solder alloy is a tin-lead based alloy. Tin-lead based alloys are used to prepare solders with desirable material properties, including suitable melting point and paste temperature ranges, wetting properties, ductility, and thermal conductivity. However, lead is a highly toxic, environmentally hazardous material that can lead to a wide range of deleterious effects. Accordingly, research has been directed to preparing lead-free solder alloys having desirable material properties.

The present disclosure relates to a high reliability lead-free solder alloy that provides lower undercooling temperatures, improved thermo-mechanical reliability, and high temperature creep resistance in extreme hot and cold weather, as compared to certain prior art alloys.

Disclosure of Invention

According to one aspect of the present disclosure, a lead-free alloy includes: 3.1 to 3.8% by weight of silver, 0.5 to 0.8% by weight of copper; 0.0 to 3.2 wt% bismuth; 0.03 to 1.0 wt% cobalt; 0.005 to 0.02 wt% titanium; and the balance tin, and any unavoidable impurities. Optionally, the alloy may further comprise 0.01 to 0.1 wt% nickel.

According to another aspect of the present disclosure, a lead-free alloy includes: 3.8% by weight of silver, 0.7% by weight of copper; 1.5 wt% bismuth; 0.05 wt% cobalt; 0.008 wt% titanium; and the balance tin, and any unavoidable impurities. Optionally, the alloy may also include 0.05 wt% nickel.

According to another aspect of the present disclosure, a lead-free alloy includes: 3.1 to 3.8% by weight of silver, 0.5 to 0.8% by weight of copper; 0.0 to 3.2 wt% bismuth; 0.05 to 1.0 wt% cobalt; 1.0 to 3.0 wt.% antimony; 0.005 to 0.02 wt% titanium; and the balance tin, and any unavoidable impurities. Optionally, the alloy may further comprise 0.01 to 0.1 wt% nickel.

According to another aspect of the present disclosure, a lead-free alloy includes: 3.8% by weight of silver, 0.8% by weight of copper; 1.5 wt% bismuth; 0.05 wt% cobalt; 1.0% by weight of antimony; 0.008 wt% titanium; and the balance tin, and any unavoidable impurities. Optionally, the alloy may also include 0.05 wt% nickel.

It is to be understood that both the foregoing general description and the following detailed description describe various embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments described herein and together with the description serve to explain the principles and operations of the claimed subject matter.

Drawings

This patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the office upon request and payment of the necessary fee.

The following is a description of the embodiments depicted in the accompanying drawings. The figures are not necessarily to scale and certain features and certain views of the figures may be shown exaggerated in scale or in schematic for clarity or conciseness.

FIG. 1A is an SEM micrograph of a prior art SAC305 alloy in the as-cast condition.

FIG. 1B is an SEM micrograph of a prior art SAC305 alloy that has been aged at 125 ℃ for 24 hours.

Fig. 2A is an SEM micrograph of an alloy according to the present disclosure in the as-cast condition.

FIG. 2B is an SEM micrograph of an alloy according to the present disclosure that has been aged at 125 ℃ for 24 hours.

FIG. 3 is a Differential Scanning Calorimetry (DSC) profile of a prior art SAC305 alloy.

FIG. 4 is a Differential Scanning Calorimetry (DSC) profile of an alloy according to the present disclosure.

FIG. 5 is a Differential Scanning Calorimetry (DSC) profile of an alloy according to the present disclosure.

FIG. 6 is a Differential Scanning Calorimetry (DSC) profile of an alloy according to the present disclosure.

FIG. 7 is a Differential Scanning Calorimetry (DSC) profile of an alloy according to the present disclosure.

FIG. 8 is a Differential Scanning Calorimetry (DSC) profile of an alloy according to the present disclosure.

FIG. 9A is a bar graph showing a comparison between the wetting times of two alloys according to the present disclosure and a prior art SAC305 alloy.

FIG. 9B is a bar graph showing a comparison between the maximum wetting force of two alloys according to the present disclosure and a prior art SAC305 alloy.

FIG. 10A is a bar graph showing a comparison between the spreading rates of an alloy according to the present disclosure and a prior art SAC305 alloy.

FIG. 10B is a bar graph showing a comparison between the spreadability of an alloy according to the present disclosure and a prior art SAC305 alloy.

Fig. 11A is a bar graph showing the spreading rate of alloys according to the present disclosure on three different substrates.

Fig. 11B is a bar graph showing the spreadability of alloys according to the present disclosure on three different substrates.

FIG. 12A is a line graph showing a comparison between the dissolution rate of copper wire at 260 ℃ for an alloy according to the present disclosure and a prior art SAC305 alloy.

FIG. 12B is a line graph showing a comparison between the dissolution rate of copper wire at 280 ℃ for an alloy according to the present disclosure and a prior art SAC305 alloy.

FIG. 13A shows a series of comparative optical micrographs comparing the dissolution rate of copper wire at 260 ℃ for an alloy according to the present disclosure and a prior art SAC305 alloy.

FIG. 13B shows a series of comparative optical micrographs comparing the dissolution rate of copper wire at 280 ℃ for alloys according to the present disclosure and prior art SAC305 alloy.

FIG. 14A is a bar graph showing a comparison between the hardness of an alloy according to the present disclosure and a prior art SAC305 alloy.

FIG. 14B is a bar graph showing a comparison between the hardness of an alloy according to the present disclosure and a prior art SAC305 alloy, where both alloys have been isothermally aged at 150 ℃.

FIG. 15 is a line graph showing stress-strain curves for an alloy according to the present disclosure and a prior art SAC305 alloy.

FIG. 16 is a bar graph showing a comparison of the ultimate tensile strength of an alloy according to the present disclosure and a prior art SAC305 alloy.

FIG. 17 is a line graph showing creep strain as a function of time for an alloy according to the present disclosure and a prior art SAC305 alloy in the as-cast state and after aging at 150 ℃ for 144 hours.

Fig. 18A shows a series of photomicrographs of the interface between an alloy according to the present disclosure and an underlying copper substrate after aging at 150 ℃ for 240 hours, 720 hours, and 1440 hours.

Figure 18B shows a series of photomicrographs of the interface between the prior art SAC305 alloy and the underlying copper substrate after aging at 150 ℃ for 240 hours, 720 hours, and 1440 hours.

FIG. 19 is a line graph showing the total IMC thickness of an alloy according to the present disclosure and a prior art SAC305 alloy as a function of aging time at 150 ℃.

FIG. 20 is a drawing showing an alloy according to the present disclosure and a prior art SAC305 alloyCu₃Line graph of Sn IMC thickness as a function of aging time at 150 ℃.

The foregoing summary, as well as the following detailed description of embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the claims are not limited to the arrangements and instrumentality shown in the drawings. Further, the appearance shown in the drawings is one of many decorative appearances that can be used to achieve a specified function of the device.

Detailed Description

In the following detailed description, specific details may be set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, to one skilled in the art, that the disclosed embodiments may be practiced without some or all of these specific details. Well-known features or methods may not be described in detail for the sake of brevity. Further, like or identical reference numerals can be used to identify common or similar elements.

Novel lead-free solder alloy compositions suitable for various electronic applications, particularly in extreme environments, are described below. These solder alloy compositions may be used in various forms. For example, the solder alloy composition may be used in the form of a rod, wire, solder powder, solder paste, or another predetermined preform. These solder alloy compositions are tin-based, particularly tin-silver-copper (sometimes referred to as "SAC").

With the start of the internet of things (IoT), electronic devices are looking for applications in increasingly challenging operating environments, resulting in higher power densities. Thus, there is a pressing need in the electronic assembly industry for solders that can operate at higher temperatures. The operating temperatures of power electronics applications such as automobiles, trains, aerospace, oil drilling, downhole natural gas exploration and power stations typically vary between 100 ℃ and 200 ℃. Solder joints exposed to elevated temperatures for extended periods of time often lose their mechanical strength and structural integrity.

The addition of a small amount of cobalt to tin-silver-copper solder significantly reduced the undercooling temperature and reduced the larger Ag₃Sn flakes form (which otherwise could lead to poor mechanical properties). In addition, cobalt andthe synergistic effect of titanium results in a refined, uniform and stable microstructure. Such a microstructure can significantly extend the fatigue life of the solder joint. As an additive to tin-silver-copper alloys, both bismuth and antimony are dissolved in the tin matrix and act as solid solution strengtheners, which improve the mechanical properties and thermo-mechanical reliability of the solder, especially in harsh environments.

It has been found that the compositions shown in tables 1 to 5 exhibit desirable properties over certain prior art alloys. For example, the lead-free solder compositions described in tables 1-5 provide lower undercooling temperatures, reasonable wetting and spreading properties, improved thermo-mechanical reliability, and high temperature creep resistance in extreme hot and cold weather, as compared to certain prior art alloys.

Table 1 provides several compositions according to the present disclosure that include tin, silver, copper, bismuth, cobalt, and titanium. Optionally, these compositions may also comprise nickel.

TABLE 1

Table 2 provides several further compositions according to the present disclosure shown as specific examples.

TABLE 2

Table 3 provides several compositions according to the present disclosure that include tin, silver, copper, bismuth, cobalt, titanium, and antimony. Optionally, these compositions may also comprise nickel.

TABLE 3

Table 4 provides several further compositions according to the present disclosure shown as specific examples.

TABLE 4

Table 5 provides several more components according to the present disclosure shown as specific examples.

TABLE 5

The controlled addition of bismuth (Bi), antimony (Sb), cobalt (Co) and/or titanium (Ti) in the tin-silver-copper (Sn-Ag-Cu) system serves to refine the grain structure of the alloy and increase the mechanical strength of the alloy. More specifically, cobalt may be added to the alloy to refine the grain structure and reduce the undercooling temperature. Furthermore, the synergistic effect of the addition of cobalt and titanium results in a refined, uniform and stable microstructure. Such microstructures significantly enhance the fatigue life of the solder joint. As an additive to the tin-silver-copper system, both bismuth and antimony are dissolved in tin and can be added to the alloy to provide solid solution strengthening and thus improve the mechanical properties of the alloy and the thermal cycling reliability of any resulting solder joint, especially in harsh environments. Also, bismuth lowers the solidus temperature of the alloy and lowers its surface tension, thereby improving wettability. Antimony increases the mechanical strength of the alloy. Optionally, nickel may be added to further improve the mechanical properties of the alloy. In addition, elements such as germanium or phosphorus may be added to improve the oxidation resistance of the alloy. The proper synergy between the above mechanisms, achieved by the specific compositional ranges claimed in this patent application, optimizes the mechanical properties of the alloy as well as the thermal cycling resistance of any resulting weld spot, especially in harsh environments.

The disclosed compositional ranges have been found to exhibit superior resistance to thermal fatigue and creep over certain prior art alloys. The high reliability lead-free solder compositions described herein provide significant reduction in supercooling temperature, reasonable wetting and spreading performance, improved thermo-mechanical reliability, and resistance to high temperatures in extreme hot and cold weatherCreep at warm temperatures. The disclosed solder compositions have been found to exhibit significantly reduced supercooling temperatures and improved thermo-mechanical reliability and creep resistance. Prevention of formation of large Ag₃Sn flakes. The disclosed solder compositions are suitable for use in electronic device applications in high temperature or harsh environments, including but not limited to automotive, train, aerospace, oil drilling, down hole natural gas exploration, and power station applications.

Fig. 1A and 1B show scanning electron microscope ("SEM") micrographs of a surface region of a prior art alloy ("SAC 305") containing 96.5 wt% tin, 3.0% silver, and 0.5 wt% copper. Fig. 2A and 2B show SEM micrographs of surface areas of alloys according to the composition of example 4.5 shown in table 4. FIGS. 1A and 2A illustrate an as-cast alloy; while figures 1B and 2B show the alloy after aging at a temperature of 125 c for 24 hours. As can be seen from the SEM micrographs, the grain structure of the SAC305 alloy (shown in FIGS. 1A and 1B) coarsens during aging at elevated temperatures. In contrast, the example 4.5 alloy maintained its finer, more uniform grain structure during aging at 125 ℃ (compare fig. 2A with fig. 2B). The microstructure comprises Ag₃Sn and Cu₆Sn₅The precipitates, and bismuth and antimony each dissolve in the tin matrix, which provides solid solution strengthening. Cobalt and titanium were used as micro-alloying elements to refine the microstructure. Finely distributed Ag during aging at elevated temperatures₃Sn and Cu₆Sn₅The precipitates and solid solution strengthening stabilize the microstructure.

TABLE 6

As shown in fig. 3 to 8, the melting characteristics of the solder alloy were measured by Differential Scanning Calorimetry (DSC). The degree of supercooling (i.e., the temperature difference between the heating start temperature and the cooling start temperature) of the solder alloy was measured. Supercooling occurs because precipitation of crystals is not spontaneous, but requires activation energy. FIG. 3 shows the DSC curve of a prior art SAC305 alloy containing 96.5 wt% tin, 3.0% silver, and 0.5 wt% copper. Fig. 4, 5, 6, 7, and 8 show DSC curves for alloys according to the compositions of examples 4.1, 4.2, 4.3, 4.4, and 4.5 shown in table 4, respectively. In addition, data of DSC analysis are shown in table 6.

The deep undercooling behavior of tin-silver-copper (Sn-Ag-Cu) solder indicates that molten tin solder is difficult to solidify. Deep undercooling is attributed to the difficulty in nucleating the solid phase from the liquid phase. Deep undercooling can affect microstructural features such as tin dendrites, eutectic microstructures, primary intermetallics (Ag)₃Sn，Cu₆Sn₅) This in turn affects the mechanical properties of the solder. Such undercooling can have a severe impact on the reliability of the solder joint and create the disadvantage that the joint solidifies at different times. This can lead to stress concentrations in the cured joint and mechanical failure. For example, the SAC305 alloy has a supercooling temperature of 20 ℃. In contrast, alloys according to the present disclosure exhibit less undercooling, e.g., as low as 4.5 ℃, as shown in example 4.3 alloy.

As can be seen by comparing fig. 3 with fig. 4-8 and by examining table 6, several exemplary alloys exhibit a significant reduction in supercooling as compared to the prior art SAC305 alloy. For example, for the prior art SAC305 alloy, heating begins (T)₁) 217 ℃ and cooling started (T)₂) Is 197 ℃ to provide a supercooling degree (Δ Τ) of 20 ℃. For the alloy of example 4.3, T₁Is about 217.5 ℃ and T₂Is about 213 ℃, thereby providing a degree of supercooling (Δ Τ) of about 4.5 ℃.

FIGS. 9A and 9B show a comparison between the wetting time (FIG. 9A) and the maximum wetting force (FIG. 9B) for a prior art SAC305 alloy, an example 4.3 alloy, and an example 4.5 alloy. The wetting experiments were carried out according to the IPC (International Association Connecting Electronics Industries) standard IPC-TM-650. This standard relates to the wetting balance test, which involves determining the total wetting time and maximum wetting force. Shorter wetting times correspond to higher wettability. Shorter wetting times and higher wetting forces reflect better wetting performance and are associated with spreading and fillet formation for a given welding process. FIGS. 9A and 9B show that the wetting characteristics of the example 4.3 alloy and the example 4.5 alloy are superior to (or minimally equivalent to) the prior art SAC305 alloy.

The wetting properties of solder can also be expressed in terms of spreading rate and spreadability. The spread area indicates how much solder is on the pad substrate and can be expressed as a spread rate. The spreading test was carried out according to IPC (IPC J-STD-004B, TM 2.4.46) and JIS Z3197 standards. The spreading rate and spreadability of three different substrates were studied: bare copper (Cu), Organic Solderability Preservative (OSP) coated copper, and Electroless Nickel Immersion Gold (ENIG) copper plating. A solder alloy (circular preform) is melted onto the substrate to be tested using a flux. The wetted area was measured using an optical microscope before and after the test. The spread rate was calculated by dividing the wetted area after reflow soldering/melting by the wetted area before reflow soldering/melting. The solder height was measured to calculate the spreadability (or spreading factor). The spreadability was calculated using the formula, where S_RSpreadability, D-solder diameter (assumed to be spherical), H-height of spread solder, and V-solder volume (g/cm)³) (estimated from the quality and density of the solder tested):

wherein D-1248 × V^1/3

Fig. 10A shows a comparison between the spreading rates of the example 4.6 alloy compared to the prior art SAC alloy on bare copper substrates at two different temperatures (260 ℃ and 300 ℃). FIG. 10B shows a comparison between the spreadability of the example 4.6 alloy compared to a SAC alloy of the prior art at two different temperatures (260 ℃ and 300 ℃).

Fig. 11A shows a comparison between the spreading rates of the example 4.6 alloy on three different copper substrates (OSP, bare copper and ENIG) at 255 ℃. Fig. 11B shows a comparison between the spreadability of the example 4.6 alloy on three different copper substrates (OSP, bare copper and ENIG) at 255 ℃.

Fig. 12A, 12B, 13A and 13B show a comparison between the copper dissolution rates of the prior art SAC305 alloy and the example 4.3 alloy (alloy-M) at 260 ℃ (fig. 12A and 13A) and at 280 ℃ (fig. 12B and 13B). From these figures, it can be seen that the copper dissolution rate of the example 4.3 alloy is slower compared to the prior art SAC305 alloy. Copper dissolution testing was performed using pure copper wire that was washed with acid solution, degreased, cleaned, rinsed and dried. The test was performed at two temperatures: 260 ℃ and 280 ℃. The copper wire was exposed to the molten solder for 5 seconds, 10 seconds, and 20 seconds. The cross-section of the copper wire was analyzed by optical microscopy, including for area measurement and analysis.

FIG. 14A shows the hardness values of the example 4.5 alloy compared to the prior art SAC305 alloy. As can be seen from the bar graph, the hardness of the example 4.5 alloy is about twice that of the prior art SAC305 alloy. FIG. 14B shows the hardness values of the example 4.6 alloy compared to the prior art SAC305 alloy. The example 4.6 alloy retained its hardness after aging, which is in contrast to the prior art SAC305 alloy, as shown in FIG. 14B, which shows the hardness test results in the as-cast state, after aging at 150 ℃ for 144 hours, and after aging at 150 ℃ for 720 hours.

The Coefficient of Thermal Expansion (CTE) of the alloys according to the present disclosure was also measured. A mismatch between the CTE of the solder and the underlying substrate can lead to fatigue failure during cyclic loading. As the CTE mismatch increases, the shear strain also increases, which reduces the thermal cycle life of the component. Cracks can initiate and propagate at stress concentration sites due to CTE mismatch. Cracks in the solder joint can be reduced by reducing the difference between the CTE of the solder and the underlying substrate. Table 7 shows the CTE of the alloy according to the present disclosure compared to the prior art SAC305 alloy, and with reference to the CTE of the exemplary underlying substrate.

TABLE 7

A tensile stress-strain plot of an exemplary alloy according to the present disclosure (example 4.6 alloy) compared to a prior art SAC305 alloy is shown in FIG. 15. cast solder is processed and cut into rectangular pieces with dimensions 100mm × 6mm × 3 mm. the samples are isostatically aged at 150 ℃ for up to 720 hours. 10 at room temperature^-2s^-1Tensile testing was performed. Ultimate tensile strength of alloyThe degrees and yield strengths are shown in table 8. The significant improvement in tensile strength shown by the example 4.6 alloy can be attributed to the addition of bismuth and the solid solution strengthening effect. The example 4.6 alloy also shows to be more ductile than the prior art SAC305 alloy. The tensile strength properties of the example 4.6 alloy and the prior art SAC305 alloy after aging at 150 ℃ are shown in FIG. 16. Both the example 4.6 alloy and the prior art SAC305 alloy showed a decrease in ultimate tensile strength after aging at elevated temperatures, but such a decrease was significantly more pronounced for the prior art SAC305 alloy, which showed a decrease in tensile strength of about 42%.

TABLE 8

Packaging is due to the high homologous temperatures involved. Due to the different Coefficients of Thermal Expansion (CTE) between the chip and other layers within the package, the solder experiences thermo-mechanical stress. These stresses can lead to plastic deformation over long-term use. The solder alloy may creep even at room temperature. In real life applications, the electronic module may operate in a temperature range of-40 ℃ to +125 ℃, which is 0.48 to 0.87T_mThus, creep deformation in lead-free solder is well understood to be an important concern in the electronics packaging industry. cast solder is processed and cut into rectangular pieces with dimensions of 120mm × 6mm × 3 mm. the sample is isostatically aged at 150 ℃ for up to 144 hours. creep testing is performed at room temperature and stress levels of 10 MPa. as shown in FIG. 17, the example 4.6 alloy exhibits superior creep resistance compared to the prior art SAC305 alloy.the creep resistance exhibited by the example alloy may be due to the addition of micro-alloys to refine the microstructure, as well as strengthening mechanisms such as solid solution and precipitation hardening.

During the soldering operation, material from the solid substrate melts and mixes with the solder, allowing the formation of intermetallic compounds (IMCs). A thin, continuous and uniform layer of IMC tends to be important for good soldering. Without IMC, the solder/conductor joint tends to be weak because no metallurgical interaction occurs in the solder. However, a thicker IMC layer at the interface may reduce the reliability of the solder joint, as a thicker IMC layer may be brittle. The IMC layer formed between the solder and the OSP substrate was examined as a function of exposure time and temperature. The solder alloy was melted on the OSP substrate and reflow soldered in an Electrovert OmniExcel 7 zone reflow oven using solder flux. The solder alloy samples were then exposed to an elevated temperature of 150 ℃ for up to 1440 hours. The IMC layer was evaluated at different aging periods.

Fig. 18A and 18B show a comparison between IMC layer growth for the example 4.6 alloy and the SAC305 alloy after aging at 150 ℃ for up to 1440 hours. As can be seen from these figures, both the example 4.6 alloy and the SAC305 alloy exhibit IMC layer growth. However, the SAC305 alloy showed signs of brittleness as indicated by the presence of Kirkendall voids (Kirkendall void) (e.g., after 720 hours of aging). Both alloys show Cu formation at the interface between the solder and the copper substrate₆Sn₅And Cu₃And a Sn layer. Figure 19 shows the total IMC thickness as a function of aging time. As shown in fig. 19, the IMC layer of the SAC305 alloy is much thicker than the IMC layer of the example 4.6 alloy. Refining the microstructure with the addition of micro-alloys can limit diffusion and therefore also limit the overall IMC growth. The lower IMC thickness in the example 4.6 alloy may make the example 4.6 alloy suitable for longer life applications at elevated temperatures. FIG. 20 shows Total Cu as a function of aging time₃And Sn thickness. In Cu₆Sn₅At the interface with the Cu substrate, Cu is formed for both alloys₃A new IMC layer of Sn. In the alloy of example 4.6, the addition of the microalloy inhibited Cu₃Growth of Sn, which may limit the formation of Kirkendall voids (Kirkendall void).

Some elements described herein are explicitly identified as optional, while other elements are not identified in this manner. Even if not so identified, it should be noted that in some embodiments, some of these other elements are not intended to be construed as essential, and will be understood by those skilled in the art as optional.

While the disclosure has been described with reference to certain implementations, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the inventive method and/or system. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. For example, the systems, blocks, and/or other components of the disclosed embodiments may be combined, divided, rearranged, and/or otherwise modified. Therefore, the present disclosure is not limited to the particular implementations disclosed. On the contrary, this disclosure is to cover all embodiments falling within the scope of the appended claims, both literally and under the doctrine of equivalents.