Snbinitete alloy solder suitable for high-density packaging and preparation method and application thereof

Abstract

The application discloses a SnBiInTe alloy solder suitable for high-density packaging and a preparation method and application thereof, and belongs to the technical field of low-temperature brazing filler metal and preparation thereof. The application solves the problems of low tensile elongation and poor plasticity of the existing Sn-Bi eutectic solder. The application effectively improves the mechanical properties of the solder by adding 2.5% of In element in the Sn-Bi solder, so that the tensile strength of the solder and the shear strength of the joint are improved, and the application range of the Sn-Bi solder in the electronic packaging field is widened. Meanwhile, the mechanical properties of the solder are effectively improved by adding 1%-3% of Te element in the solder through the solid solution strengthening and second phase strengthening mechanism, and the reliability of the welded joint is greatly improved.

Description

Technical Field

[0001] This invention relates to a SnBiInTe alloy solder suitable for high-density packaging, its preparation method and application, belonging to the field of low-temperature solder and its preparation technology. Background Technology

[0002] The application of 5G is increasingly penetrating daily life, and technologies such as the Internet of Things (IoT), virtual and augmented reality (VR), and artificial intelligence are booming, placing higher demands on microelectronic devices. Currently, the mainstream development direction for electronic devices is towards smaller size, multifunctionality, high integration, high reliability, and low cost. However, in the semiconductor manufacturing field, Moore's Law is nearing its limit, making it extremely difficult to further increase transistor density on a single silicon wafer. Therefore, advanced packaging technology has become a focus of current electronic device development. High-density interconnect technologies such as chiplet technology, 2.5D interposer technology, and 3D stacking technology provide new development directions for the semiconductor industry. However, the complex packaging structure and large number of components in high-density interconnect technologies make welding process problems and solder joint mechanical reliability issues particularly prominent. Multiple high-temperature thermal shocks during welding can cause thermal stress accumulation in structural components, inducing welding defects such as board warping. Furthermore, the poor heat dissipation performance of high-density packaging results in high operating temperatures for devices, easily inducing solder joint creep and other failures. Therefore, developing high-reliability low-temperature solder suitable for high-density packaging is an important research direction in the field of electronic packaging.

[0003] Solder used in electronic packaging typically uses Sn as the base element or main alloying element. Sn has a melting point of 231.9℃, which decreases significantly when combined with other metallic elements to form eutectic alloys. Sn-Bi eutectic solder is considered a promising solder system, with a melting point of 138℃ and a peak reflow soldering temperature of approximately 160℃. It exhibits excellent creep resistance and tensile strength and is inexpensive. However, pure Sn-Bi eutectic solder has low elongation and poor plasticity, increasing the risk of brittle failure in electronic products during mechanical impact and significantly affecting the stability of the solder joint. Summary of the Invention

[0004] This invention addresses the shortcomings of existing Sn-Bi eutectic solders, such as low tensile elongation and poor plasticity, by providing a SnBiInTe alloy solder suitable for high-density packaging, its preparation method, and its application.

[0005] The technical solution of the present invention:

[0006] One objective of this invention is to provide a method for preparing SnBiInTe alloy solder, the method comprising the following steps:

[0007] S1, place high-purity Sn, Bi, In and Te metal particles in a quartz crucible according to the formula ratio;

[0008] S2, KCl and LiCl are placed in a graphite crucible and stirred thoroughly at 750°C;

[0009] S3, pour the molten mixed salt obtained in S2 into a quartz crucible containing metal particles, cover the metal particles, and then place the whole mixture into a melting furnace for melting.

[0010] S4. After melting, the obtained liquid metal brazing filler metal is poured into a graphite mold to cool and demold, thus obtaining the brazing filler metal alloy.

[0011] S5. The surface oxide layer of the solder alloy is removed by sanding with sandpaper, and then it is rolled into a foil with a thickness of 200μm by cold rolling. Finally, the foil is cut into a size suitable for welding by wire cutting to obtain SnBiInTe alloy solder.

[0012] Further specified, the Sn element content is 42%, the In element content is 2.5%, the Te element content is 1% to 3%, and the balance is Bi element.

[0013] Further specified, the content of Te element is 1%, 1.5%, 2% or 3%.

[0014] Further specifying, the mass ratio of KCl to LiCl in S2 is 10:13.

[0015] Further specified, the melting temperature in S3 is 450℃, the melting time is 4h, and the stirring is performed once every 15min during the melting process.

[0016] The second objective of this invention is to provide a SnBiInTe alloy solder obtained by the above preparation method, wherein the melting point of the alloy solder is 131℃~136℃.

[0017] The third objective of this invention is to provide an application of the aforementioned SnBiInTe alloy solder, specifically for high-density electronic packaging.

[0018] The fourth objective of this invention is to provide a welding method for the above-mentioned SnBiInTe alloy solder, the method comprising the following steps:

[0019] (1) The low-temperature lead-free solder is sandwiched between two base materials, and a layer of flux is applied between the base materials and the solder foil to form the workpiece to be soldered;

[0020] (2) Place the workpiece to be welded into the groove of the graphite fixture and fix it, and then place it in the reflow oven to achieve welding of the two base materials.

[0021] Further specified, during the welding process, the reflow oven heating rate is 10℃ / min, the reflow peak temperature is 160℃, the holding time is 6min, and the cooling time to room temperature is 300s.

[0022] Further specifying, the flux is rosin, and the base material is copper sheet.

[0023] Beneficial effects:

[0024] This invention effectively improves the mechanical properties of Sn-Bi solder by adding 1%–3% Te by mass through solid solution strengthening and second-phase strengthening mechanisms, thereby enhancing the joint's resistance to mechanical impact. Simultaneously, the addition of 2.5% In by mass further improves the solder's mechanical properties, increasing both its tensile strength and the joint's shear strength, thus broadening the application range of Sn-Bi solder in electronic packaging. The resulting composite solder exhibits a single melting peak with a melting point of 131℃–134℃, meeting the requirements for low-temperature solders in electronic packaging. Furthermore, the solder alloy achieves a maximum tensile strength of 62 MPa and a maximum joint shear strength of 58 MPa. After isothermal aging at 110℃ for 700 hours, the joint strength remains at 50 MPa, demonstrating high welding reliability.

[0025] Furthermore, this invention employs molten salt covering during the alloy preparation process, effectively preventing the oxidation of metal elements during high-temperature melting. Comparative experiments were conducted on the welding process parameters, ultimately yielding the optimal parameters: a heating rate of 10℃ / min, a reflow peak temperature of 160℃, a holding time of 6min, and a cooling time of 300s. Attached Figure Description

[0026] Figure 1 The tensile stress-strain curve of the SnBiInTe alloy solder prepared in Example 1 of this invention;

[0027] Figure 2 A comparison of the shear strength of welded joints obtained by welding using SnBiInTe alloy solders prepared in different embodiments and comparative examples;

[0028] Figure 3 The shear strength of the welded joint after isothermal aging obtained by welding using the SnBiInTe alloy solder prepared in Example 1;

[0029] Figure 4 The interfacial microstructure of the SnBiIn alloy solder prepared in Comparative Example 1;

[0030] Figure 5 The interfacial microstructure of the SnBiInTe alloy solder prepared in Example 1;

[0031] Figure 6The interfacial microstructure of the SnBiInTe alloy solder prepared in Example 2;

[0032] Figure 7 The interfacial microstructure of the SnBiInTe alloy solder prepared in Example 3;

[0033] Figure 8 The interfacial microstructure of the SnBiInTe alloy solder prepared in Example 4;

[0034] Figure 9 for Figure 8 A magnified view of a portion of the image. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0039] Example 1

[0040] Step 1: According to the weight percentage, place high-purity (99.9% purity) Sn, Bi, In and Te metal particles in a quartz crucible with Sn metal particles content of 42%, In metal particles content of 2.5%, Te metal particles content of 1%, and Bi metal particles as the balance.

[0041] Step 2: KCl and LiCl in a mass ratio of 10:13 are fully melted and stirred evenly in a graphite crucible at a temperature of 750°C.

[0042] Step 3: Pour the molten mixed salt into a quartz crucible containing metal particles, covering the metal particles, and then place the whole thing into a melting furnace and melt it at 450°C for 4 hours. During the melting process, stir it every 15 minutes.

[0043] Step four: After melting, the liquid metal solder is poured into a graphite mold to cool and demold, yielding a solder alloy.

[0044] Step 5: Remove the surface oxide layer of the obtained solder alloy by sanding with sandpaper, and then cold roll the solder alloy block into a foil with a thickness of 200μm.

[0045] Step 6: Cut the foil according to the welding requirements to obtain the brazing foil for welding.

[0046] Example 2

[0047] The difference between this embodiment and Embodiment 1 is that in step one, Sn, Bi, In and Te metal particles are placed in a quartz crucible with Sn metal particles accounting for 42%, In metal particles accounting for 2.5%, Te metal particles accounting for 1.5%, and Bi metal particles accounting for the remainder. The other parameter settings and process steps are the same as in Embodiment 1.

[0048] Example 3

[0049] The difference between this embodiment and Embodiment 1 is that in step one, Sn, Bi, In and Te metal particles are placed in a quartz crucible with Sn metal particles accounting for 42%, In metal particles accounting for 2.5%, Te metal particles accounting for 2%, and Bi metal particles accounting for the remainder. The other parameter settings and process steps are the same as in Embodiment 1.

[0050] Example 4

[0051] The difference between this embodiment and Embodiment 1 is that in step one, Sn, Bi, In and Te metal particles are placed in a quartz crucible with Sn metal particles accounting for 42%, In metal particles accounting for 2.5%, Te metal particles accounting for 3%, and Bi metal particles accounting for the remainder. The other parameter settings and process steps are the same as in Embodiment 1.

[0052] Comparative Example 1

[0053] The difference between this embodiment and Embodiment 1 is that in step one, Sn, Bi, In and Te metal particles are placed in a quartz crucible with Sn metal particles content of 42%, In metal particles content of 2.5%, Te metal particles content of 0%, and Bi metal particles as the balance. The other parameter settings and process steps are the same as in Embodiment 1.

[0054] Example of effect

[0055] (1) The melting points of the solder alloys prepared in Examples 1-4 and Comparative Example 1 were tested. A cast solder block was taken and cut into 0.5mm × 0.5mm × 0.5mm pieces using a diamond wire cutter. The solder blocks were placed in a nitrogen atmosphere and heated at 5℃ / min. The melting point of the solder was tested using a differential scanning calorimeter (STA449F3) manufactured by Netzsch GmbH, Germany. The test results showed that, in the order of Examples 1-4 and Comparative Example 1, the melting points of the solder alloys were 134℃, 132℃, 131.5℃, 131.3℃, and 136℃, respectively.

[0056] (2) The brazing foils prepared in Examples 1 to 4 and Comparative Example 1 are sandwiched between two base materials, specifically copper sheets. A layer of flux rosin is applied between the base materials and the brazing foils. The assembled brazing foils and base materials are then placed in the groove of a graphite fixture for fixation. Subsequently, they are placed in a reflow oven for welding connection. The reflow oven heating rate is 10℃ / min, the reflow peak temperature is set to 160℃, the holding time is 6min, and the cooling time to room temperature is 300s.

[0057] The mechanical properties of the obtained welded joints were tested. The joints were clamped using a special fixture, and room temperature shear tests were performed using an electronic universal testing machine with a range of 20 kN. The shear rate was set to 0.5 mm / min. Five samples were tested per group, and the average value was taken. The shear strength was as follows: Figure 2 As shown, by Figure 2 As can be seen, according to Examples 1-4 and Comparative Example 1, the shear strengths of the welded joints are 56 MPa, 54 MPa, 54 MPa, 50 MPa, and 45 MPa, respectively. This is because the Te element added to the solder partially dissolves in the Sn phase lattice, forming a Sn-based solid solution, which enhances its mechanical properties. During the welding process, the Te element that has not dissolved into the Sn phase will also react with the Sn element to generate SnTe IMC dispersed in the solder matrix. The SnTe second phase present in the matrix effectively hinders the movement of dislocations during shearing, thus enhancing the shear resistance of the welded joint.

[0058] Further mechanical property tests were performed on the solder alloy obtained in Example 1. Tensile tests were conducted on the solder alloy according to the national standard GB / T 228.1-2021 using a PicoFemto HS-5KN, 2KN, 100N in-situ tensile testing machine. The measured tensile stress-strain curves are shown below. Figure 1 As shown, by Figure 1It can be seen that the elastic deformation stage during tension is very small, and it quickly enters the plastic strain hardening stage. The maximum stress is reached at a strain of 3.4%, with a tensile strength of 62 MPa. It fractures instantaneously when the strain rate reaches 4.2%. The solder exhibits minimal plastic deformation during tension, with no necking observed, and the fracture surface is smooth. The addition of Te contributes to the high tensile strength of 62 MPa.

[0059] The welded joints obtained by welding the solder prepared in Example 1 were further subjected to isothermal aging treatment at 110°C, and shear strength tests were conducted on the welded joints with different treatment durations. The results are as follows: Figure 3 As shown, by Figure 3 It can be seen that the shear strength is 50 MPa after isothermal aging for 720 hours.

[0060] (3) The microstructure of the alloy brazing filler metals prepared in Comparative Example 1 and Examples 1, 2, 3 and 4 was characterized, and the results are as follows: Figures 4-9 As shown, comparison Figure 4 and Figure 5 , 6 As shown in points 7, 8, and 9, SnTe IMC exists in the matrix with added Te. When the Te content reaches 2 wt%, in addition to the regularly shaped SnTe IMC, the solder matrix also contains a large number of triangular star-shaped SnTe IMC. These SnTe IMC are randomly distributed in the solder matrix, with Bi-rich and Sn-rich phases randomly distributed around the SnTe. When the Te content reaches 3 wt%, SnTe IMC exists in the matrix in the form of regular large blocks, such as... Figure 9 Furthermore, irregularly distributed IMCs alternating with the Bi phase appeared. With the increase of Te, the number of SnTeIMCs in the solder matrix increased and became more concentrated, tending to exist in large aggregates within the matrix. In summary, the addition of Te introduces a second phase, which is dispersed in the solder matrix and interacts with dislocations, effectively hindering dislocation movement and improving the mechanical properties of the solder.

[0061] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing SnBiInTe alloy solder, characterized in that, include: S1, place high-purity Sn, Bi, In and Te metal particles in a quartz crucible according to the formula ratio; By weight percentage, the Sn element content is 42%, the In element content is 2.5%, the Te element content is 1%~3%, and the balance is Bi element; S2, KCl and LiCl are placed in a graphite crucible and stirred thoroughly at 750°C; S3, pour the molten mixed salt obtained in S2 into a quartz crucible containing metal particles, cover the metal particles, and then place the whole mixture into a melting furnace for melting. S4. After melting, the obtained liquid metal brazing filler metal is poured into a graphite mold to cool and demold, thus obtaining the brazing filler metal alloy. S5. The surface oxide layer of the solder alloy is removed by sanding with sandpaper, and then it is rolled into a foil with a thickness of 200μm by cold rolling. Finally, the foil is cut into a size suitable for welding by wire cutting to obtain SnBiInTe alloy solder.

2. The preparation method according to claim 1, characterized in that, The Te element content is 1%, 1.5%, 2% or 3%.

3. The preparation method according to claim 1, characterized in that, The mass ratio of KCl to LiCl in S2 is 10:

13.

4. The preparation method according to claim 1, characterized in that, The melting temperature in S3 is 450℃, and the melting time is 4 hours. During the melting process, the mixture is stirred once every 15 minutes.

5. A SnBiInTe alloy solder obtained by the preparation method according to any one of claims 1 to 4, characterized in that, The melting point of this alloy solder is 131℃~136℃.

6. The application of the SnBiInTe alloy solder according to claim 5, characterized in that, Used for electronic packaging.

7. A welding method using the SnBiInTe alloy solder according to claim 5, characterized in that, include: (1) The low-temperature lead-free solder is sandwiched between two base materials, and a layer of flux is applied between the base materials and the solder foil to form the workpiece to be soldered; (2) Place the workpiece to be welded into the groove of the graphite fixture and fix it, and then place it in the reflow oven to achieve welding of the two base materials.

8. The welding method according to claim 7, characterized in that, During the welding process, the reflow oven heating rate is 10℃ / min, the reflow peak temperature is 160℃, the holding time is 6min, and the cooling time to room temperature is 300s.

9. The welding method according to claim 7, characterized in that, The flux is rosin, and the base material is copper sheet.

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