Low-temperature soldering paste for reflow soldering and preparation method and application thereof

Abstract

The application discloses a low-temperature soldering paste for reflow soldering and a preparation method and application thereof, and comprises, in percentage by mass, 10-15% of a soldering paste and 85-90% of a metal alloy powder; wherein the soldering paste comprises 10-15% of rosin resin, 1-3% of a curing agent and 82-89% of an active agent with instant wetting burst force. The application provides a low-temperature soldering paste for reflow soldering which can provide instant burst force at different temperatures, aiming at the welding defects such as open circuit, virtual welding (ball pocket) and continuous soldering which are prone to occur in the existing reflow soldering. The soldering paste can provide instant wetting burst force at different temperatures, and through the instant wetting burst force, wetting can be effectively carried out, so that welding is completed, and finally the problem of HIP (pillow effect, also known as ball pocket defect) is solved.

Description

Technical Field

[0001] This invention relates to the field of brazing materials technology, and in particular to a low-temperature solder paste for reflow soldering, its preparation method, and its application. Background Technology

[0002] To date, only a handful of manufacturers are capable of producing chipsets, including VIA (Via Technologies, Taiwan), SiS (Silicon Integrated Systems, Taiwan), ULI (Universal Technology, Taiwan), ALi (ALi Technology, Taiwan), AMD (Advanced Micro Devices, USA), NVIDIA (NVIDIA Corporation, USA), ATI (Asia Technologies, Canada, which has been acquired by AMD), ServerWorks (USA), IBM (USA), and HP (USA). Among them, Intel and AMD chipsets are the most common.

[0003] Chip warpage is a common phenomenon in semiconductor packaging during surface mount technology (SMT) assembly. The root cause of chip warpage lies in the difference in thermal expansion coefficients between the chip and the substrate. When chips, especially large or even giant chips, are soldered to printed circuit boards or directly to electronic products, the warpage morphology and deformation in the soldering area directly determine soldering defects such as open circuits, cold solder joints (ball sockets), and solder bridges. The solder paste industry has been dedicated to researching and addressing this issue.

[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a low-temperature solder paste for reflow soldering, its preparation method and application, in order to solve the problem that soldering defects are prone to occur during soldering with existing solder pastes.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A low-temperature solder paste for reflow soldering, comprising, by mass percentage: 10%–15% flux and 85%–90% metal alloy powder; wherein the flux comprises: 10%–15% rosin resin, 1%–3% curing agent and 82%–89% activator with instantaneous wetting burst.

[0008] The low-temperature solder paste for reflow soldering, wherein the metal alloy powder is a low-temperature lead-free alloy powder.

[0009] The low-temperature solder paste for reflow soldering, wherein the low-temperature lead-free alloy powder is one of Sn42Bi55, Sn64.7Bi35Ag0.3, Sn42Bi57Ag1.0, and Sn64Bi35Ag1.0.

[0010] The low-temperature solder paste for reflow soldering, wherein the activator with instantaneous wetting burst is selected from one or two of n-hexylamine, 2-phenylimidazole, and N,N-dimethylhexylamine.

[0011] The low-temperature solder paste for reflow soldering, wherein the curing agent is selected from one or more of 590 curing agent, 593 curing agent, and dicyandiamide.

[0012] A method for preparing low-temperature solder paste for reflow soldering as described above in this invention, comprising the steps of:

[0013] The flux and metal alloy powder are mixed and stirred to obtain the low-temperature solder paste for reflow soldering.

[0014] The method for preparing low-temperature solder paste for reflow soldering includes the following steps:

[0015] Provides rosin resin;

[0016] 2-Phenylidene imidazole was mixed with hydrobromic acid and stirred to obtain 2-phenylimidazolium hydrobromide.

[0017] Hexane and hydrobromic acid were mixed and stirred to obtain hexylamine hydrobromide.

[0018] The 2-phenylimidazolium hydrobromide, the n-hexylamine hydrobromide, and the rosin resin are mixed, and then a curing agent, an activator, and a solvent are added and stirred to obtain the flux.

[0019] In the method for preparing low-temperature solder paste for reflow soldering, the molar ratio of n-hexane to hydrobromic acid is 1:1.

[0020] In the method for preparing low-temperature solder paste for reflow soldering, the molar ratio of 2-phenylimidazole to hydrobromic acid is 1:1.

[0021] An application of the low-temperature solder paste for reflow soldering as described above in the SMT (Surface Mount Technology) assembly process.

[0022] Beneficial effects: This invention discloses a low-temperature solder paste for reflow soldering, its preparation method, and its application. Addressing common soldering defects in existing reflow soldering methods such as open circuits, cold solder joints (ball and socket), and bridging, this invention provides a low-temperature solder paste for reflow soldering that can provide instantaneous burst force at different temperatures. This solder paste can provide instantaneous wetting burst force at different temperatures, effectively wetting the solder and achieving an ideal soldering state, ultimately solving the problem of HIP (pillow effect, also known as ball and socket defect). Attached Figure Description

[0023] Figure 1 This is a thermal deformation test image of an existing AMD chip.

[0024] Figure 2 This is a schematic diagram showing that the solder balls and solder paste are not in sufficient contact.

[0025] Figure 3 This diagram illustrates the full contact between the solder ball and the solder paste.

[0026] Figure 4 Diagrams showing the instantaneous explosive force of nickel plate welding at different temperatures.

[0027] Figure 5 This is a diagram of the wettability test process.

[0028] Figure 6 This is a diagram of the solder ball testing process.

[0029] Figure 7 This is a diagram of the thermal collapse test process.

[0030] Figure 8 This is a diagram illustrating the testing process for a bronze mirror.

[0031] Figure 9 This is a representative photograph of the appearance of the comb-type electrode after the SIR test.

[0032] Figure 10 This is a diagram of the SC-side pads for the formal trial production of SPI. Detailed Implementation

[0033] This invention provides a low-temperature solder paste for reflow soldering, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Taking AMD chips as an example, in the thermal deformation test diagram of the chip ( Figure 1 The results showed that the chip deformed most significantly between 100℃-140℃ and 120℃-155℃. During reflow soldering, the increased temperature can cause the chip to warp, resulting in insufficient contact between the solder paste and the solder balls. Figure 2 This leads to HIP (Hardware Injection) problems and a significant increase in the defect rate. The low-temperature solder paste for reflow soldering of this invention utilizes the wetting burst force of the solder paste's activity during the reflow soldering process at temperature points with stable warpage, namely 170°C, 165°C, 155°C, and 145°C, to ensure sufficient contact between the solder paste and the solder balls, achieving good soldering, reducing HIP problems, and thus greatly solving the problem of high defect rates. A schematic diagram of sufficient contact between the solder paste and the solder balls is shown below. Figure 3 .

[0035] Based on this, the present invention provides a low-temperature solder paste for reflow soldering, wherein, by mass percentage, it comprises: 10% to 15% flux and 85% to 90% metal alloy powder; wherein the flux comprises: 10% to 15% rosin resin, 1% to 3% curing agent and 82% to 89% activator with instantaneous wetting burst power.

[0036] Specifically, this invention addresses common soldering defects in existing reflow soldering processes, such as open circuits, cold solder joints (ball-and-socket defects), and bridging. It provides a low-temperature solder paste for reflow soldering that offers instantaneous bursts of power at different temperatures. The activator in the solder paste provides instantaneous wetting bursts of power at various temperatures. This instantaneous wetting bursts of power effectively wet the solder, allowing the solder paste to instantly "hold" the solder balls when the chip warps at its normal warp point. This ensures full contact between the solder paste and the solder balls, achieving an ideal soldering state and ultimately solving the problem of HIP (pillow effect, also known as ball-and-socket defects).

[0037] In some embodiments, the metal alloy powder is a low-temperature lead-free alloy powder.

[0038] In some embodiments, the low-temperature lead-free alloy powder is one of Sn42Bi55, Sn64.7Bi35Ag0.3, Sn42Bi57Ag1.0, and Sn64Bi35Ag1.0.

[0039] Specifically, the solder paste provided by this invention contains 85% to 90% by mass of metal alloy powder. The metal alloy powder is categorized into high-temperature and low-temperature types. Due to the heat-induced warpage of chips, low-temperature lead-free alloy powder is preferred. Low-temperature lead-free alloy powders include Sn42Bi55, Sn64.7Bi35Ag0.3, Sn42Bi57Ag1.0, and Sn64Bi35Ag1.0, etc. (High temperatures cause chip warpage, hence the choice of low temperatures). Considering the soldering temperature profile, chip deformation, and the instantaneous wetting burst force of the solder paste, Sn42Bi57Ag1.0 is preferred in this embodiment. This alloy powder is directly purchased from manufacturers such as Yunnan Tin, Epus, Heraeus, and Complutense.

[0040] In some embodiments, the active agent with instantaneous wetting burst is selected from one or two of n-hexylamine, 2-phenylimidazole, and N,N-dimethylhexylamine.

[0041] Specifically, in electronic manufacturing, imidazole derivatives have been widely used in large-scale integrated electronic packaging materials. This invention focuses on providing an surfactant with instantaneous wetting burst activity. Through extensive experimentation, this invention aims to provide two surfactants that form corresponding salts with acids. These salts, synthesized through chemical reactions, exhibit excellent instantaneous burst activity, thereby solving the HIP (Hybridization Injection) problem. The surfactant is one or two of n-hexylamine, 2-phenylimidazole, and N,N-dimethylhexylamine. These surfactants were chosen because nitrogen molecules form a trigonal pyramidal shape during bonding, with SP (specified structure) as the base. 3 Hybrid orbital bonding, in which lone pairs of electrons occupy one sp orbital position. 3 Hybrid orbitals, which result in salts with excellent activity, enable the instantaneous wetting burst force of this invention.

[0042] In some embodiments, the curing agent is selected from one or more of curing agents 590, 593, and dicyandiamide.

[0043] The present invention also provides a method for preparing low-temperature solder paste for reflow soldering as described above, comprising the steps of:

[0044] The flux and metal alloy powder are mixed and stirred to obtain the low-temperature solder paste for reflow soldering.

[0045] In some embodiments, the method for preparing the flux paste includes the steps of:

[0046] S10, provides rosin resin;

[0047] S20. Mix 2-phenylimidazolium with hydrobromic acid and stir to obtain 2-phenylimidazolium hydrobromide.

[0048] S30. Mix n-hexane with hydrobromic acid and stir to obtain n-hexylamine hydrobromide;

[0049] S40. Mix the 2-phenylimidazolium hydrobromide, the n-hexylamine hydrobromide and the rosin resin, then add the curing agent, activator and solvent, and stir to obtain the flux paste.

[0050] In some embodiments, the molar ratio of n-hexane to hydrobromic acid is 1:1.

[0051] In some embodiments, the molar ratio of the 2-phenylimidazole to the hydrobromic acid is 1:1.

[0052] The present invention also provides an application of the low-temperature solder paste for reflow soldering as described above in the SMT chip mounting process.

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are intended only to illustrate the present invention and not to limit it. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0054] Example 1

[0055] A method for preparing low-temperature solder paste for reflow soldering, comprising the following steps:

[0056] The flux paste and metal alloy powder are mixed and stirred to obtain the low-temperature solder paste for reflow soldering; wherein, the preparation method of the flux paste includes the following steps:

[0057] S10, provides rosin resin;

[0058] S20. Mix 2-phenylimidazolium and hydrobromic acid in a 1:1 molar ratio and stir to obtain 2-phenylimidazolium hydrobromide.

[0059] S30. Mix n-hexane and hydrobromic acid in a 1:1 molar ratio and stir to obtain n-hexylamine hydrobromide.

[0060] S40. Mix the 2-phenylimidazolium hydrobromide, the n-hexylamine hydrobromide and the rosin resin, then add the curing agent, activator and solvent, and stir for 30 minutes in three batches to obtain the flux paste.

[0061] The low-temperature solder paste for reflow soldering obtained in Example 1 was well verified through nickel plate soldering tests, wettability tests, solder ball tests, thermal collapse tests, copper mirror tests, and SIR tests. It not only enables instant soldering but also ensures product reliability.

[0062] 1) Soldering test of nickel plate: Nickel plate is one of the most difficult substrates to solder in the SMT industry. This experiment is to verify whether the anti-HIP low-temperature solder paste of the present invention can be instantly soldered under different temperatures with instantaneous burst force.

[0063] Test method: Print solder paste onto a nickel plate, adjust the oven temperature to the corresponding test temperature, heat quickly for 1-3 seconds and then cool, and check the soldering effect.

[0064] Test result: Test passed Figure 4 It can be concluded that the solder paste's active wetting burst force at 170℃, 165℃, 155℃, and 145℃ can effectively wet the nickel plate and result in good soldering.

[0065] 2) Wettability test

[0066] Test materials: copper sheet / brass sheet / nickel sheet, IPC-defined standard steel sheet

[0067] Test method: IPC-TM-650 2.4.45:1995 Solder Paste—Wetting Test

[0068] Evaluation standard: SJ / T11186-209 "General Specification for Solder Paste"

[0069] Test result: Pass Figure 5 It was found that the copper plate and nickel plate were well wetted.

[0070] 3) Tin ball test

[0071] Test material: standard ceramic sheet

[0072] Test method:

[0073] IPC-TM-650 2.4.43:1995Solder Paste–Solder Ball Test

[0074] Evaluation standard: JIS Z 3284-4(2014)

[0075] Test result: Pass Figure 6 Therefore, the tin ball is classified as level 2.

[0076] 4) Thermal collapse test

[0077] Test material: standard ceramic sheet

[0078] Printing conditions: 0.2mm thick screen printing template, such as... Figure 7

[0079] Pad A (0.63x2.03mm), printing time 0min.

[0080] B pad (0.33x2.03mm), printed at 120℃ for 15 minutes.

[0081] Test results: 0.63×2.03mm pads: No bridging.

[0082] 0.33×2.03mm pads: No bridging when the spacing is greater than 0.10mm (standard requirement: no bridging when the spacing is greater than 0.3mm).

[0083] 5) Bronze mirror test

[0084] Test method: IPC-TM-650 2.3.32

[0085] Evaluation criteria: IPC J-STD-005A

[0086] Test environment: Placed in an environment of 23±2℃ and 50±5%RH for 24 hours.

[0087] Test results: such as Figure 8 The sample was placed in an environment of 23±2℃ and 50±5%RH for 24 hours and no copper mirror corrosion was observed. The sample is classified as L grade.

[0088] 6) SIR test

[0089] Test method: IPC, 7 days, @85℃ / 85%RH

[0090] Test standard: IPC J-STD-004B

[0091] Test results: Insulation resistance is greater than 1×10⁻⁶. 8 Ω (L type: not cleaned after soldering). Representative appearance photos of the comb electrode after SIR testing are shown below. Figure 9 No metal dendrites grew on the comb-shaped electrode. The test results are shown in Table 1.

[0092] Table 1 SIR Test Results

[0093]

[0094]

[0095] This invention provides an application of low-temperature solder paste for resisting instantaneous bursts of force at different temperatures. In the mass production process of PCBA (Printed Circuit Board Assembly), due to various possible factors related to equipment and operators, it is impossible to guarantee that all produced PCBAs are perfect. This necessitates the addition of various testing equipment and tools at the end of the production process to ensure that all finished circuit boards are completely consistent with the design specifications and parameters. Therefore, products need to undergo various testing methods such as ATE (Automatic Optical Inspection), AOI (Automated Optical Inspection), and FCT (Functional Testing).

[0096] Figure 10 For on-site trial production, the solder paste printing on the SC side pads was all straight through. The defect / pass was due to insufficient glue application. The alarm was due to the solder paste area in the fixed area being too small. The manual review was then passed.

[0097] Test results:

[0098] 1) AOI test: No open circuits, cold solder joints, or component displacement.

[0099] 2) ATE test: NTF above 95%.

[0100] 3) FCT test: 166pcs total, 2 were defective, 1 was damaged, 1 had a dead CPU, no HIP issues.

[0101] In summary, this invention discloses a low-temperature solder paste for reflow soldering, its preparation method, and its application. By mass percentage, it comprises: 10%–15% flux and 85%–90% metal alloy powder; wherein the flux comprises: 10%–15% rosin resin, 1%–3% curing agent, and 82%–89% activator with instantaneous wetting burst force. This invention addresses common soldering defects in existing reflow soldering, such as open circuits, cold solder joints (ball and socket), and bridging, by providing a low-temperature solder paste for reflow soldering that can provide instantaneous burst force at different temperatures. This solder paste can provide instantaneous wetting burst force at different temperatures, effectively wetting the solder and thus completing the soldering process, ultimately solving the problem of HIP (pillow effect, also known as ball and socket defect).

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-temperature solder paste for reflow soldering, characterized by, By weight percentage, it includes: 10%~15% flux and 85%~90% metal alloy powder; wherein, the flux includes: 10%~15% rosin resin, 1%~3% curing agent and 82%~89% activator with instant wetting burst power. The active agent with instantaneous wetting burst power is 2-phenylimidazolium hydrobromide obtained by mixing 2-phenylimidazolium with hydrobromic acid and n-hexane hydrobromide obtained by mixing n-hexane with hydrobromic acid.

2. The low-temperature solder paste for reflow soldering according to claim 1, characterized by, The metal alloy powder is a low-temperature lead-free alloy powder.

3. The low-temperature solder paste for reflow soldering according to claim 2, characterized by, The low-temperature lead-free alloy powder is one of Sn42Bi55, Sn64.7Bi35Ag0.3, Sn42Bi57Ag1.0, and Sn64Bi35Ag1.

0.

4. The low-temperature solder paste for reflow soldering according to claim 1, characterized by, The curing agent is selected from one or more of 590 curing agent, 593 curing agent, and dicyandiamide.

5. A process for producing a low-temperature solder paste for reflow soldering according to any one of claims 1 to 4, characterized by, Including the following steps: The flux and metal alloy powder are mixed and stirred to obtain the low-temperature solder paste for reflow soldering.

6. The method of producing a low-temperature solder paste for reflow soldering according to claim 5, characterized by, The method for preparing the flux paste includes the following steps: Provides rosin resin; 2-Phenylidene imidazole was mixed with hydrobromic acid and stirred to obtain 2-phenylimidazolium hydrobromide. Hexane and hydrobromic acid were mixed and stirred to obtain hexylamine hydrobromide. The 2-phenylimidazolium hydrobromide, the n-hexylamine hydrobromide, and the rosin resin are mixed, and then a curing agent, an activator, and a solvent are added and stirred to obtain the flux.

7. The method of producing a low-temperature solder paste for reflow soldering according to claim 6, characterized by, The molar ratio of hexane to hydrobromic acid is 1:

1.

8. The method of claim 6, wherein the low temperature solder paste for reflow soldering is prepared by adding the fluxing agent to the solder powder and the solvent. The molar ratio of 2-phenylimidazole to hydrobromic acid is 1:

1.

9. The application of the low-temperature solder paste for reflow soldering as described in any one of claims 1 to 4 in the SMT surface mount technology (SMT) process.

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