TW202225420A - Composite solder and method for manufacturing the same - Google Patents

Abstract

The present disclosure provides a composite solder and a method for manufacturing the same. The method form manufacturing the composite solder includes following steps. A first solder containing a binary alloy of Ag and Bi is provided. With respective to 100 parts by weight of the binary alloy, the content of Ag is about 2.5 parts by weight, and the content of Bi is about 97.5 parts by weight. A second solder containing a ternary alloy of Sn, Ag and Cu is provided. With respective to 100 parts by weight of the ternary alloy, the content of Sn is about 96.5 parts by weight, the content of Ag is about 3 parts by weight, and the content of Cu is about 0.5 parts by weight. A composite solder is formed by mixing the first solder and the second solder in a mixing temperature.

Description

Composite solder and method of making the same

The present invention relates to a solder and a method of making the same, and more particularly, to a composite solder and a method of making the same.

With the advancement of science and technology, electronic components are constantly developing towards "light, thin, short, and small", and electronic packaging technology with high density and high precision has gradually received attention. Electronic packaging technology can be divided into five different levels according to the process. The zeroth level is the wiring process for integrated circuit chips. The first level is the process of adhering several integrated circuit chips on the package substrate and completing the electrical connection and sealing protection, which can also be called the chip-to-module process. The second level is a process of mounting several components completed by the first level of packaging on a circuit board, also known as a module to PCB process. The third level is the process of mounting several printed circuit boards completed by the second level packaging on the motherboard, also known as the process of PCB to mother board. The fourth level is to combine several motherboards to form a complete electronic product.

However, in the packaging process at each level or between different levels, multiple reflow processes are performed, so the combined components may fall off due to the re-melting of the solder joints, resulting in problems such as electronic components falling or solder joint displacement. , which may cause two adjacent solder joints to contact each other and cause a short circuit.

The present invention provides a composite solder and a manufacturing method thereof. A binary alloy containing Ag and Bi is mixed with a ternary alloy containing Sn, Ag and Cu to form a composite solder with a low liquefaction temperature, so that the accumulation of thermal stress can be avoided. And ensure the reliability of solder joints in other packaging processes.

The present invention provides a method for manufacturing composite solder, which includes the following steps. Provide the first solder. The first solder contains a binary alloy of Ag and Bi. With respect to 100 parts by weight of the binary alloy, the content of Ag is about 2.5 parts by weight, and the content of Bi is about 97.5 parts by weight. A second solder is provided. The second solder contains a ternary alloy of Sn, Ag and Cu. With respect to 100 parts by weight of the ternary alloy, the content of Sn is about 96.5 parts by weight, the content of Ag is about 3 parts by weight, and the content of Cu is about 0.5 parts by weight. The first solder and the second solder are mixed at a mixing temperature to form a composite solder.

In an embodiment of the present invention, the weight ratio of the first solder and the second solder is 25:75 to 75:25.

In an embodiment of the present invention, the eutectic temperature of the first solder is greater than the eutectic temperature of the second solder.

In an embodiment of the present invention, during the process of mixing the first solder and the second solder at the mixing temperature, the second solder coats the first solder and diffuses Sn of the second solder to form a common bond with Bi of the first solder crystal phase.

In one embodiment of the present invention, the liquefaction temperature of the composite solder is between 130°C and 136°C.

In one embodiment of the present invention, the step of mixing the first solder and the second solder includes the use of a flux.

In an embodiment of the present invention, after the composite solder undergoes a reflow process, the solidified precipitate has the following intermetallic phases: acicular Ag ₃ Sn phase, Cu ₆ Sn ₅ phase, and eutectic phase of Bi and β-Sn .

In an embodiment of the present invention, the step of preparing the first solder includes mixing Ag metal and Bi metal in a weight ratio of 2.5:97.5 and performing homogenization treatment at 800°C.

The present invention provides a composite solder, which is prepared by the above-mentioned method for manufacturing the composite solder.

Based on the above, in the composite solder and its manufacturing method of the present invention, the binary alloy containing Ag and Bi is mixed with the ternary alloy containing Sn, Ag, and Cu, so that the liquefaction temperature of the composite solder can be greatly reduced to avoid Thermal stress builds up on the solder joints and ensures the reliability of the solder joints.

The present invention is more fully described with reference to the drawings of this embodiment. However, the present invention may be embodied in various forms and should not be limited to the embodiments described herein. The thicknesses of layers and regions in the drawings are exaggerated for clarity. The same or similar reference numerals denote the same or similar elements, and the repeated descriptions will not be repeated in the following paragraphs.

It will be understood that when an element such as that is referred to as being "on" or "connected to" another element, it can be directly on or connected to the other element or intervening elements may also be present. When an element is referred to as being "directly on" or "directly connected to" another element, there are no intervening elements present. As used herein, "connected" may refer to a physical and/or electrical connection, and "electrically connected" or "coupled" may refer to the presence of other elements between two elements.

"About," "approximately," or "substantially" as used herein includes the recited value and the average within an acceptable deviation of the particular value that can be determined by one of ordinary skill in the art, taking into account all The measurement in question and the specific amount of error associated with the measurement (ie, the limitations of the measurement system). For example, "about" can mean within one or more standard deviations of the stated value, or within ±30%, ±20%, ±10%, ±5%. Furthermore, as used herein, "about", "approximately" or "substantially" may be used to select a more acceptable range of deviation or standard deviation depending on optical properties, etching properties or other properties, and not one standard deviation may apply to all properties. .

The terminology used herein is used to illustrate exemplary embodiments only, and not to limit the disclosure. In this case, the singular includes the plural unless the context clearly dictates otherwise.

FIG. 1 is a flowchart of a method for manufacturing a composite solder according to an embodiment of the present invention.

Referring to FIG. 1 , step S1 is performed to provide a first solder including a binary alloy of Ag and Bi. With respect to 100 parts by weight of the binary alloy, the content of Ag may be about 2.5 parts by weight, and the content of Bi may be about 97.5 parts by weight. The eutectic temperature of the first solder (ie, the Ag-Bi alloy) may be about 262.5°C. In some embodiments, the first solder is lead-free solder. No intermetallic compound is formed between Ag and Bi, and the Ag-Bi alloy formed by Ag and Bi in the proportions of 2.5 wt.% and 97.5 wt.% has the lowest eutectic temperature of the alloy and the proportion of Ag is very small. , which can effectively reduce costs.

In some embodiments, the method of manufacturing the first solder may include the following steps. First, Ag metal and Bi metal with a purity of 99.9% were used. Next, 2.5 wt. % and 97.5 wt. % of Ag metal and Bi metal were weighed with respect to the total weight of Ag metal and Bi metal, respectively. Then, a cleaning process is performed on the weighed Ag and Bi metals. Then, the cleaned Ag metal and Bi metal are placed in a container (such as a quartz glass tube) and sealed (to avoid oxidation). After that, the container in which the Ag metal and the Bi metal are placed is subjected to a homogenization process. Finally, the homogenized container was immediately quenched in ice water and brought to room temperature.

In some embodiments, the following steps can be used to perform the above cleaning process. First, the surface oil stains of Ag metal and Bi metal are removed with an organic solution such as acetone. Next, the surface oxides of Ag metal and Bi metal are removed with an acidic solution such as dilute hydrochloric acid. Then, surface impurities of Ag metal and Bi metal are removed with an organic solution such as alcohol.

In some embodiments, the following parameters can be used for the homogenization process. The temperature of the homogenization treatment may be 800°C. The time for the homogenization treatment can be 24 hours. The pressure of the homogenization treatment may be 2.0×10 ⁻³ torr.

Please continue to refer to FIG. 1 , step S2 is performed to provide a second solder including a ternary alloy of Sn, Ag and Cu. With respect to 100 parts by weight of the ternary alloy, the content of Sn may be about 96.5 parts by weight, the content of Ag may be about 3 parts by weight, and the content of Cu may be about 0.5 parts by weight. In addition to the Sn matrix phase, the phases generated by the mutual reaction of Sn, Ag and Cu atoms will also generate Ag ₃ Sn, Cu ₆ Sn ₅ and Cu ₃ Sn eutectic phases. The Ag ₃ Sn and Cu ₆ Sn ₅ eutectic phases can reduce the Sn matrix region and can help hinder the sliding of grain boundaries to improve the mechanical properties of the material and prolong the fatigue life of the material at high temperatures.

The eutectic temperature of the second solder may be less than the eutectic temperature of the first solder. The eutectic temperature of the second solder (ie, Sn-Ag-Cu alloy, also known as SAC alloy) may be about 217°C. In some embodiments, the second solder is lead-free solder.

Please continue to refer to FIG. 1 , step S3 is performed, and the first solder and the second solder are mixed at a mixing temperature to form a composite solder. The liquefaction temperature of the composite solder may be between 130°C and 136°C. In some embodiments, the step of mixing the first solder and the second solder may include using a flux such as rosin mildly activated (RMA) flux. The flux is a rosin-like organic substance, with the addition of a slightly acidic organic acid, which has high volatility. The purpose of adding flux is that during the soldering process, the flux will clean the metal surface, increase the wettability between the solders, and volatilize after the soldering process, and will not remain between the solders. The general addition amount is about 0.03mL. In some embodiments, the weight ratio of the first solder to the second solder may be 25:75 to 75:25. In some embodiments, the mixing temperature is between the eutectic temperature of the first solder and the eutectic temperature of the second solder. In some embodiments, the mixing temperature may be 230°C.

In some embodiments, the following steps may be used to mix the first solder and the second solder to form a composite solder. First, the first solder and the second solder are placed in a container (eg, a quartz glass tube) at a preset weight ratio. Next, add flux to the container. Then, the container was placed in a melting furnace at 230° C. for complete dissolution and constant temperature for 5 minutes to form a composite solder. Finally, the composite solder is removed and cooled in air.

In some embodiments, since the eutectic temperature of the first solder is greater than the eutectic temperature of the second solder, and the mixing temperature is between the eutectic temperature of the first solder and the eutectic temperature of the second solder, in this During the process of mixing the first solder and the second solder at the mixing temperature, the second solder will melt first to cover the first solder and diffuse Sn of the second solder to form an eutectic phase with Bi of the first solder. In this way, even if the mixing temperature is lower than the eutectic temperature of the first solder, a more stable eutectic phase composition is formed with Bi along with the diffusion of Sn, so that the liquefaction temperature of the first solder is gradually lowered, and the mixing temperature can be improved. completely melted.

Based on the above, in the composite solder and its manufacturing method of the embodiment, the binary alloy containing Ag and Bi is mixed with the ternary alloy containing Sn, Ag, and Cu, so that the liquefaction temperature of the composite solder can be greatly reduced to avoid Thermal stress builds up on the solder joints and ensures the reliability of the solder joints.

Hereinafter, the features of the present invention will be described more specifically with reference to Examples 1-3 and Comparative Example 1. FIG. Although the following examples are described, the materials used, their amounts and ratios, processing details, processing flow, and the like may be appropriately changed without departing from the scope of the present invention. Therefore, the present invention should not be construed restrictively by the embodiments described below. first solder

First, Ag metal and Bi metal (purchased from Yuwa Trading Co., Ltd.) with a purity of 99.9% were used. Next, 2.5 wt. % and 97.5 wt. % of Ag metal and Bi metal were weighed with respect to the total weight of Ag metal and Bi metal, respectively. Then, Ag metal and Bi metal were washed sequentially with acetone, dilute hydrochloric acid and alcohol. Then, the cleaned Ag metal and Bi metal were placed in a quartz glass tube and sealed. After that, the quartz glass tube containing Ag metal and Bi metal was put into a high-temperature furnace, and the homogenization treatment was performed at a temperature of 800° C. and a time of 24 hours. Then, after the homogenization treatment is completed, the quartz glass tube is taken out and immediately put into ice water for quenching so that the temperature reaches room temperature. Finally, the quartz glass tube was broken to remove the Ag-Bi alloy rod. second solder

The SAC alloy was obtained from Daihui Electronics, wherein the SAC alloy contained 3 wt.% Ag, 0.5 wt.% Cu and 96.5 wt.% Sn. Examples 1-3

The first solder and the second solder were placed in a quartz glass tube in the proportions shown in Table 1 below. Next, add about 0.03 mL of rosin-neutral activated flux (RMA) into the quartz glass tube. Then, it was put into a melting furnace at 230° C. to be completely melted and kept at a constant temperature for 5 minutes to form a composite solder. After that, it was taken out and cooled in air. [Table 1] First Solder (wt.%) Second Solder (wt. %) Example 1 (25AgBi-75SAC) 25 75 Example 2 (50AgBi-50SAC) 50 50 Example 3 (75AgBi-25SAC) 75 20 Comparative Example 1

The SAC alloy was obtained from Daihui Electronics, wherein the SAC alloy contained 3 wt.% Ag, 0.5 wt.% Cu and 96.5 wt.% Sn. Experiment 1

The curing curves of Examples 1-3 were calculated using Pandat software to obtain the Schell curing paths of Examples 1-3, and the experimental results are shown in FIG. 2A , FIG. 3A and FIG. 4A , respectively. FIG. 2A is a Shere curing curve diagram of the composite solder of Example 1. FIG. FIG. 3A is a Shere curing curve diagram of the composite solder of Example 2. FIG. FIG. 4A is a Schell curing curve diagram of the composite solder of Example 3. FIG.

From the results shown in FIGS. 2A , 3A and 4A, it can be seen that Ag ₃ Sn will be precipitated in Examples 1-3 at the beginning, but as the temperature decreases, Ag ₃ Sn+Cu ₆ Sn will be precipitated in Examples 1 and 2 ₅ phase (see Figure 2A and Figure 3A), while Example 3 (see Figure 4A) will precipitate Ag ₃ Sn+Bi phase. Then, as the temperature continues to drop, the Ag ₃ Sn+Cu ₆ Sn ₅ +Sn phase will be precipitated in Examples 1 and 2 (see Figure 2A and Figure 3A), while Example 3 (see Figure 4A) still does not have The intermetallic Cu ₆ Sn ₅ phase is formed. After the final curing temperature was lowered by 142.6°C, the eutectic Bi+β-Sn phase was precipitated in Examples 1 and 2, and there was no more brittle pure Bi phase, but in Example 3, the eutectic Bi+β-Sn phase was precipitated In addition, a relatively brittle pure Bi phase is also precipitated. Experiment 2

The alloy microstructures of Examples 1-3 after being reflowed once at 230° C. were analyzed by SEM, and the experimental results are shown in FIG. 2B , FIG. 3B and FIG. 4B , respectively. FIG. 2B is an SEM image of the composite solder of Example 1 after being reflowed once. 3B is an SEM image of the composite solder of Example 2 after being reflowed once. FIG. 4B is an SEM image of the composite solder of Example 3 after being reflowed once. Fig. 5 is the SEM image of the composite solder of Example 1-3 after reflowing once, wherein (a), (d), (g) of Fig. 5 are the SEM images of Example 1 under different magnifications; Fig. 5 (b), (e), (h) are the SEM images of Example 2 under different magnifications; Figure 5 (c), (f), (i) are the SEM images of Example 3 under different magnifications. SEM image.

Referring to FIGS. 2B and 5 , a needle-shaped Ag ₃ Sn phase and a smaller dot-shaped Cu ₆ Sn ₅ phase can be observed from FIG. 2B , which are consistent with the Schell solidification path shown in FIG. 2A . From this, it can be seen that Example 1 has an Ag ₃ Sn phase that can increase the mechanical strength, and does not generate a relatively brittle Bi phase. In addition, the Bi+β-Sn phase of the eutectic can be observed from Fig. 5, which conforms to the Schell solidification path shown in Fig. 2A.

Referring to FIGS. 3B and 5 , a needle-shaped Ag ₃ Sn phase and a smaller dot-shaped Cu ₆ Sn ₅ phase can be observed from FIG. 3B , which are consistent with the Schell solidification path shown in FIG. 3A . From this, it can be seen that Example 2 has an Ag ₃ Sn phase that can increase the mechanical strength, and does not generate a relatively brittle Bi phase. Comparing the results shown in FIG. 2B and FIG. 3B , due to the high Sn content in Example 1, Ag ₃ Sn+Cu ₆ Sn ₅ +Sn phase was precipitated at 185.5°C, while in Example 2, the phase was precipitated at 147.5°C ( The Ag ₃ Sn+Cu ₆ Sn ₅ +Sn phase is precipitated when it is close to the eutectic temperature. In addition, the Bi+β-Sn phase of the eutectic can be observed from Fig. 5, which conforms to the Schell solidification path shown in Fig. 3A.

Referring to FIGS. 4B and 5 , the Ag ₃ Sn phase and the bulk pure Bi phase can be observed from FIG. 4B , and the Cu ₆ Sn ₅ phase is not observed, which is consistent with the Schell solidification shown in FIG. 4A . path. From this, it can be seen that Example 3 has an Ag ₃ Sn phase that can increase the mechanical strength, but generates a bulky and relatively brittle Bi phase. In addition, the Bi+β-Sn phase of the eutectic can be observed from Fig. 5, which conforms to the Schell solidification path shown in Fig. 3A. Experiment 3

Thermal analysis of Examples 1-3 and Comparative Example 1 after different reflow times was performed with DSC. In the DSC analysis, the temperature was raised from room temperature to 250°C at a heating rate of 5°C/min, and after 3 minutes of constant temperature, the temperature was lowered to room temperature at a rate of 5°C/min. The experimental results are shown in FIGS. 6A to 6D and FIGS. 7A to 7D , respectively.

FIGS. 6A to 6D are DSC curves of the composite solders of Examples 1-3 and Comparative Example 1 after different reflow times and a heating rate of 5° C./min, respectively. 7A to 7D are respectively DSC curves of the composite solders of Examples 1-3 and Comparative Example 1 after different reflow times with a cooling rate of 5°C/min. In FIGS. 6A to 6D and FIGS. 7A to 7D , the numerical values before Comparative Example 1 and Example 1 to 3 represent the number of reflows. For example, 1-Comparative Example 1 shown in Figures 6A and 7A represents the DSC curve of Comparative Example 1 after 1 reflow; 2-Example 1 shown in Figures 6B and 7B represents Example 1 DSC curve of 2 reflows.

From the results shown in FIGS. 6A to 6D , it can be seen that the initial liquefaction temperature (T _onset ) of Comparative Example 1 after 1-5 times of reflow was all 215.5°C. Whereas, the initial liquefaction temperature of Examples 1-3 after 1-5 reflows was in the range of 130 to 136°C. In addition, it can be seen from FIG. 6B that there is a small peak near the temperature of 180°C. Since the Sn content in Example 1 is relatively large, the peak should be caused by the melting factor of the β-Sn phase, which is consistent with the results shown in FIG. 2A . The Schell solidification path shown, the β-Sn phase begins to precipitate at about 185°C.

From the results shown in FIGS. 6A to 6D , the pasty range (ΔT) of Examples 1-3 and Comparative Example 1 can be calculated. The mushy region is determined by subtracting the initial liquefaction temperature from the _end liquefaction temperature in the DSC ramp (Tend- _Tonset ). If the mushy area is too high, it means that the solder exists in a partially liquid state for a long time during the solidification process, so a reliable solder joint cannot be formed. The results for the initial liquefaction temperature (T _onset ) and the mushy region (ΔT) shown in Figures 6A-6D are collated in Table 2. [Table 2] Reflow times Composite solder T _onset (℃) ΔT (°C) 1 Comparative Example 1 215.5 13.8 Example 1 133.8 10.0 Example 2 132.9 13.7 Example 3 133.0 12.0 2 Comparative Example 1 215.6 13.9 Example 1 133.9 8.7 Example 2 133.9 13.3 Example 3 132.7 9.1 3 Comparative Example 1 215.6 13.6 Example 1 134.8 8.7 Example 2 135.9 14.6 Example 3 133.6 10.0 4 Comparative Example 1 215.7 14.1 Example 1 133.2 8.2 Example 2 133.8 15.1 Example 3 133.8 10.2 5 Comparative Example 1 215.5 13.6 Example 1 133.4 7.8 Example 2 133.4 14.2 Example 3 133.7 11.5

From the results shown in FIG. 7A , it can be seen that Comparative Example 1 has only one peak during the curing process, mainly because the composition of Comparative Example 1 is close to the eutectic point, so the solidified phase is directly precipitated from the eutectic point during the curing process. Comparing the results shown in FIG. 7B to FIG. 7D , it can be seen that only one peak appears in Example 2 during the curing process. According to the results of the curing path shown in FIG. 3A , it can be explained that Example 2 is in the curing process. Ag ₃ Sn+Cu ₆ Sn ₅ is precipitated, and the last eutectic phase is precipitated at a temperature close to the lowest eutectic temperature of 142.6°C after only one breaking point. Different from Example 1 and Example 3, it can be explained according to the results of the curing path shown in Figure 2A and Figure 4A, Example 1 and Example 3 experienced two inflection points during the curing process (Ag ₃ Sn+Cu ₆ Sn ₅ and Ag ₃ Sn + Cu ₆ Sn ₅ +Sn) before the final eutectic phase is precipitated. The data of the first peak and the second peak shown in FIGS. 7A to 7D are collated in Table 3. [table 3] Reflow times Composite solder The first peak (℃) Second peak (°C) 1 Comparative Example 1 199.5 - Example 1 146.1 116.9 Example 2 - 114.7 Example 3 163.6 119.8 2 Comparative Example 1 200.9 - Example 1 146.9 139.5 Example 2 - 115.0 Example 3 155.8 118.8 3 Comparative Example 1 200.1 - Example 1 148.6 116.6 Example 2 - 115.4 Example 3 179.3 120.0 4 Comparative Example 1 193.8 - Example 1 148.8 118.5 Example 2 122.6 116.4 Example 3 174.3 119.2 5 Comparative Example 1 193.0 - Example 1 144.9 117.8 Example 2 124.1 117.5 Example 3 179.7 119.5

The supercooling degrees of Examples 1-3 and Comparative Example 1 were calculated from the results shown in FIGS. 6A to 6D and FIGS. 7A to 7D . The degree of subcooling is defined as the initial liquefaction temperature of the _heating process (represented by T _onset in the table ₎ minus the initial liquefaction temperature of the _cooling process (represented by T _onset in the table ₎ . The results are summarized in Table 4. [Table 4] Reflow times Composite solder T _{onset ( temperature rise )} (℃) T _{onset ( cooling )} (℃) Subcooling degree (℃) 1 Comparative Example 1 215.5 199.5 16.0 Example 1 133.8 116.9 16.9 Example 2 132.9 114.7 18.2 Example 3 133.0 119.8 13.2 2 Comparative Example 1 215.6 200.9 14.7 Example 1 133.9 139.5 - Example 2 133.9 115.0 18.9 Example 3 132.7 118.8 13.9 3 Comparative Example 1 215.6 200.1 15.5 Example 1 134.8 116.6 18.2 Example 2 135.9 115.4 20.5 Example 3 133.6 120.0 13.6 4 Comparative Example 1 215.7 193.8 21.9 Example 1 133.2 118.5 14.7 Example 2 133.8 116.4 17.4 Example 3 133.8 119.2 14.6 5 Comparative Example 1 215.5 193.0 22.5 Example 1 133.4 117.8 15.6 Example 2 133.4 117.5 15.9 Example 3 133.7 119.5 14.2

It can be seen from Table 4 that, compared with Example 1 and Example 2, Example 3 has a lower degree of undercooling, which is because the Bi precipitated in Example 3 can effectively reduce the degree of undercooling, because it can inhibit the The growth rate of β-Sn and the refined microstructure can also slow down the growth of the metallic phase. In addition, the precipitation of Bi particles can provide sites for heterogeneous nucleation, promote the solidification process and reduce the degree of supercooling. Experiment 4

The wettability of Examples 1-3 and Comparative Example 1 was measured by a wetting balance (solder checker, SAT-5100, Rhesca Co. Ltd., Japan). The maximum wetting force ( _Fmax ) and the 2/3 maximum wetting force (2/ _3Fmax ) are summarized in Table 5, while the average wetting times for Examples 1-3 and Comparative Example 1 are summarized in Table 6. [table 5] _Fmax (mN) 2/3F _max (mN) Comparative Example 1 0.28±0.04 0.18±0.02 Example 1 0.25±0.04 0.17±0.03 Example 2 0.18±0.03 0.12±0.02 Example 3 0.13±0.06 0.08±0.04 [Table 6] Average wetting time (s) Comparative Example 1 0.65±0.3 Example 1 1.00±04 Example 2 0.91±0.4 Example 3 1.39±0.2

It can be seen from Table 5 and Table 6 that the wetting properties of Examples 1-3 and Comparative Example 1 both meet the industry standard, that is, the wetting effect is achieved within 2 seconds in the wetting time. In addition, the maximum wetting force (F _max ) and the 2/3 maximum wetting force (2/3 F _max ) of Example 1 are similar to those of Comparative Example 1, so it can be proved that Example 1 not only has a low liquefaction temperature, but also has a low liquefaction temperature. Wetting properties are similar to Comparative Example 1 in performance.

To sum up, in the above-mentioned composite solder and its manufacturing method, the binary alloy containing Ag and Bi is mixed with the ternary alloy containing Sn, Ag, and Cu, so that the liquefaction temperature of the composite solder can be greatly reduced, so that the Avoid thermal stress buildup on solder joints and ensure solder joint reliability.

Although the present invention has been disclosed as above with examples, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present invention. The protection scope of the present invention shall be determined by the scope of the appended patent application.

S1, S2, S3: Steps

FIG. 1 is a flowchart of a method for manufacturing a composite solder according to an embodiment of the present invention. 2A is a Scheil curing graph of the composite solder of Example 1. FIG. FIG. 2B is a scanning electron microscope (SEM) image of the composite solder of Example 1 after one reflow. FIG. 3A is a Shere curing curve diagram of the composite solder of Example 2. FIG. 3B is an SEM image of the composite solder of Example 2 after being reflowed once. FIG. 4A is a Schell curing curve diagram of the composite solder of Example 3. FIG. FIG. 4B is an SEM image of the composite solder of Example 3 after being reflowed once. FIG. 5 is an SEM image of the composite solders of Examples 1-3 after being reflowed once. 6A to 6D are differential scanning calorimetry (DSC) curves of the composite solders of Examples 1-3 and Comparative Example 1 after different reflow times and a heating rate of 5°C/min. 7A to 7D are respectively DSC curves of the composite solders of Examples 1-3 and Comparative Example 1 after different reflow times with a cooling rate of 5°C/min.

S1, S2, S3: Steps

Claims (10)

A method of making composite solder comprising: providing a first solder, comprising a binary alloy of Ag and Bi, wherein relative to 100 parts by weight of the binary alloy, the content of Ag is about 2.5 parts by weight, and the content of Bi is about 97.5 parts by weight; A second solder is provided, comprising a ternary alloy of Sn, Ag and Cu, wherein with respect to 100 parts by weight of the ternary alloy, the content of Sn is about 96.5 parts by weight, the content of Ag is about 3 parts by weight, and the content of Cu is about 3 parts by weight. The content is about 0.5 parts by weight; and The first solder and the second solder are mixed at a mixing temperature to form a composite solder. The method of claim 1, wherein the weight ratio of the first solder and the second solder is 25:75 to 75:25. The method of claim 1, wherein the eutectic temperature of the first solder is greater than the eutectic temperature of the second solder. The method of claim 3, wherein the mixing temperature is between the eutectic temperature of the first solder and the eutectic temperature of the second solder. The method of claim 4, wherein during mixing of the first solder and the second solder at the mixing temperature, the second solder encapsulates the first solder and causes the second solder Sn of the solder diffuses to form an eutectic phase with Bi of the first solder. The method of claim 1, wherein the liquefaction temperature of the composite solder is between 130°C and 136°C. The method of claim 1, wherein the step of mixing the first solder and the second solder includes using a flux. The method according to claim 1, wherein after the composite solder is subjected to a reflow process, the solidified precipitate has the following intermetallic phases: acicular Ag ₃ Sn phase, Cu ₆ Sn ₅ phase, and between Bi and β-Sn Eutectic phase. The method of claim 1, wherein the step of preparing the first solder comprises mixing Ag metal and Bi metal in a weight ratio of 2.5:97.5 and performing a homogenization treatment at 800°C. A composite solder, prepared by the method for manufacturing a composite solder according to any one of claim 1 to claim 9.

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