Composite solder paste and preparation method and application thereof

Abstract

The invention discloses composite solder paste which comprises the following components in percentage by weight: 65%-75% of tin-lead alloy powder, 10%-15% of copper powder and the balance of organic soldering flux, the weight percentage of lead in the tin-lead alloy powder is 37%, and the weight percentage of tin is 63%. According to the composite solder paste, the probability of plug plugging can be reduced, the jet printing performance is improved, under the condition that the average jet printing dot diameter is not changed, the dot diameter fluctuation range is reduced, and the stable printing effect is obtained; the preparation process is simple and easy to operate; the hot-melt adhesive is suitable for jet printing, can strengthen welding spots, improves the shearing strength of the welding spots, delays generation and expansion of cracks of the welding spots under the action of hot and cold cycle impact, and meets the requirement for thermal impact performance.

Description

Technical Field

[0001] The present invention relates to welding materials, and specifically to a composite solder paste and its preparation method and application. Background Art

[0002] During the packaging process of high-power devices, it is often necessary to perform local solder paste printing on parts with pits, protrusions, etc., or to perform step-by-step printing and welding on multi-layer 3D integrated circuits, and to ball BGA devices, etc. These electronic packaging application fields require both precise printing processes and local welding, controlling the influence of heat on other parts of the device and deformation, and more importantly, obtaining highly reliable solder joints. Therefore, the inkjet printing process combined with laser reflow soldering technology can better meet these requirements.

[0003] Existing single solder pastes are difficult to simultaneously meet the requirements of the above processes and performances. For example, ordinary SnPb solder paste is prone to plastic deformation due to the extrusion and impact of solder particles during printing, which affects the ejection of the solder paste and leads to plugging, and often has poor inkjet printing performance; at the same time, ordinary SnPb solder has poor thermal shock resistance and often needs to be strengthened by adding high-melting-point elements such as Ag and Ni. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a composite solder paste that can reduce the probability of plugging, adapt to inkjet printing and laser reflow, and meet the requirements of high solder joints and strong service reliability. Another object of the present invention is to provide a simple and easy-to-operate preparation method of the composite solder paste. The present invention also provides an application of the composite solder paste in non-contact inkjet printing.

[0005] Technical Solution: A composite solder paste according to the present invention includes the following components by weight percentage: 65% - 75% of tin-lead alloy powder, 10% - 15% of copper powder, and the balance is an organic flux; the weight percentage of lead in the tin-lead alloy powder is 37%, and the weight percentage of tin is 63%.

[0006] Further, the particle size of the tin-lead alloy powder is 15 - 25 μm, and the particle size of the copper powder is 5 - 10 μm.

[0007] Further, the organic flux includes the following components by weight percentage: 48% - 50% of rosin, 40% - 42% of ethylene glycol monohexyl ether, 3% - 5% of oxalic acid, and the balance is hydrogenated castor oil.

[0008] Further, the tin-lead alloy powder is 65% - 70%, the copper powder is 10% - 15%, and the balance is the organic solder flux; the particle size of the tin-lead alloy powder is 15 - 20 μm, and the particle size of the copper powder is 5 - 10 μm. By further optimizing the particle size and ratio, the average particle size is reduced, and the proportion of the mixed particles of lead and tin is decreased, which can reduce the viscosity of the composite solder paste and improve the jet printing performance. When the average dot diameter of the jet-printed dots remains unchanged, the dot diameter fluctuation range is reduced from 17% to 9%, and at the same time, the probability of clogging the nozzle is decreased. The jet-printed dots are more uniform while achieving a stable jet printing of ≥50 million dots.

[0009] The preparation method of the composite solder paste of the present invention includes the following steps:

[0010] (1) Pretreat the raw materials, weigh the tin-lead alloy powder and the copper powder and mix them evenly to obtain the composite tin powder;

[0011] (2) Prepare the organic solder flux;

[0012] (3) Mix and stir the composite tin powder in step (1) with the organic solder flux in step (2) evenly to obtain the composite solder paste.

[0013] Further, the heating temperature of the organic solder flux in step (2) is 130 - 150 °C.

[0014] Further, the whole process of stirring in step (3) is kept under vacuum and stirred in stages; in the first stage, low-speed premixing is carried out at 10 - 15 rpm for 5 - 8 min, and in the second stage, stirring is carried out at 30 - 35 rpm for 20 - 25 min.

[0015] The application of the composite solder paste of the present invention in non-contact jet printing.

[0016] Further, during the non-contact jet printing process of the composite solder paste, reflow occurs at 200 °C - 220 °C.

[0017] Further, after the solder joints formed by non-contact jet printing reflow undergo 1000 times of -55 °C - 125 °C thermal cycling, the shear strength retention rate is greater than 90%.

[0018] Principle of the present invention: Compared with general SnPb solder pastes, the present invention uses composite solder powders with a gradient particle size distribution, combined with organic additives to form a composite solder paste system. The main feature is the addition of copper powder particles with graded particle sizes, which are heterogeneous particles present in the solder paste. The density of copper is relatively smaller than that of the SnPb alloy, and the particle size of copper particles is relatively smaller than that of SnPb particles, while the melting point of copper is higher and it will not melt and dissolve during reflow at 200 - 220 °C. It remains in the solder joint after reflow and is dispersed, dispersing the stress of the solder joint. The solder paste thus formed has an optimal solid particle content, so it is easier to maintain a dispersed suspension state in a relatively low mixed organic additive, which is beneficial to maintaining the stability of the microstructure of the solder paste during high-speed movement, thereby improving the stability of printing; it is beneficial to improving the stress conditions of SnPb particles during the inkjet printing process and reducing the probability of plugging of SnPb particles due to plastic deformation.

[0019] Advantages: Compared with the prior art, the present invention has the following significant features: The composite solder paste has the probability of reducing plugging, improving the inkjet printing performance. When the average dot diameter of the inkjet printing remains unchanged, the fluctuation range of the dot diameter is reduced, and a stable printing effect is obtained; the preparation process is simple and easy to operate; it is suitable for inkjet printing, can strengthen the solder joint, and increase the shear strength of the solder joint to more than 55 MPa. The formed solder joint can delay the generation and propagation of cracks under the action of 1000 times of thermal cycling shock at -55 °C to 125 °C, meeting the requirements of thermal shock performance. Description of the Drawings

[0020] Figure 1 is the SEM image of the composite solder powder of the present invention;

[0021] Figure 2 is the SEM of the solder joint of the composite solder paste prepared in Example 10 of the present invention;

[0022] Figure 3 is the SEM image of the solder joint of the composite solder paste prepared in Example 10 of the present invention after thermal shock;

[0023] Figure 4 is the reflow curve graph of the composite solder paste prepared in Example 10 of the present invention;

[0024] Figure 5 is the inkjet printing effect diagram of the application of the composite solder paste prepared in Example 10 of the present invention. Detailed Embodiments

[0025] The following further describes the content of the present invention in combination with specific embodiments.

[0026] The purchased metal ingots, including tin ingots and lead ingots, are placed in a heating furnace according to the designed alloy composition and heated at 400 °C for 5 h. During the heating process, a mechanical stirrer is used to stir every 30 min to homogenize the melt, while removing the oxide impurities on the surface. Then, after the composition is completely uniform, tin-lead alloy powder is prepared by an ultrasonic atomization process. The prepared tin-lead alloy powder and the purchased copper powder are selected for tin powder with the target particle size through a sonic vibration type fully automatic screening particle size analyzer, obtaining tin-lead alloy powder with a particle size of 15 - 25 μm and copper powder with a particle size of 5 - 10 μm.

[0027] Example 1

[0028] A preparation method of a composite solder paste, comprising the following steps:

[0029] (1) After the raw materials are pretreated, 300 g of tin-lead alloy powder and 40 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0030] (2) 28.8 g of rosin, 24 g of ethylene glycol monohexyl ether, 1.8 g of oxalic acid, and 5.4 g of hydrogenated castor oil are weighed and mixed evenly and heated at a temperature of 130 °C to obtain an organic flux.

[0031] (3) The composite tin powder in step (1) is mixed with the organic flux in step (2), placed in a vacuum mixer for staged stirring. In the first stage, low-speed premixing is carried out at 10 rpm for 5 min, and in the second stage, stirring is carried out at 30 rpm for 20 min to obtain a uniform composite solder paste.

[0032] As Figure 1 shown, the surrounding of the intermediate copper particles in the composite tin powder is coated with tin-lead alloy particles.

[0033] Example 2

[0034] A preparation method of a composite solder paste, comprising the following steps:

[0035] (1) After the raw materials are pretreated, 300 g of tin-lead alloy powder and 50 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0036] (2) 25 g of rosin, 21 g of ethylene glycol monohexyl ether, 2.5 g of oxalic acid, and 1.5 g of hydrogenated castor oil are weighed and mixed evenly and heated at a temperature of 135 °C to obtain an organic flux.

[0037] (3) The composite tin powder in step (1) is mixed with the organic flux in step (2), placed in a vacuum mixer for staged stirring. In the first stage, low-speed premixing is carried out at 15 rpm for 8 min, and in the second stage, stirring is carried out at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0038] Example 3

[0039] A preparation method of a composite solder paste, comprising the following steps:

[0040] (1) After pretreatment of the raw materials, 300 g of tin-lead alloy powder and 60 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0041] (2) 19.6 g of rosin, 16.4 g of ethylene glycol monohexyl ether, 1.6 g of oxalic acid and 2.4 g of hydrogenated castor oil are weighed and mixed evenly, and heated at a temperature of 140 °C to obtain an organic flux.

[0042] (3) The composite tin powder in step (1) is mixed with the organic flux in step (2), and placed in a vacuum mixer for staged stirring. In the first stage, low-speed premixing is carried out at 15 rpm for 8 min, and in the second stage, stirring is carried out at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0043] Example 4

[0044] A preparation method of a composite solder paste, comprising the following steps:

[0045] (1) After pretreatment of the raw materials, 290 g of tin-lead alloy powder and 40 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0046] (2) 33.6 g of rosin, 28 g of ethylene glycol monohexyl ether, 2.1 g of oxalic acid and 6.3 g of hydrogenated castor oil are weighed and mixed evenly, and heated at a temperature of 145 °C to obtain an organic flux.

[0047] (3) The composite tin powder in step (1) is mixed with the organic flux in step (2), and placed in a vacuum mixer for staged stirring. In the first stage, low-speed premixing is carried out at 15 rpm for 8 min, and in the second stage, stirring is carried out at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0048] Example 5

[0049] A preparation method of a composite solder paste, comprising the following steps:

[0050] (1) After pretreatment of the raw materials, 290 g of tin-lead alloy powder and 50 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0051] (2) 30 g of rosin, 25.2 g of ethylene glycol monohexyl ether, 3 g of oxalic acid and 1.8 g of hydrogenated castor oil are weighed and mixed evenly, and heated at a temperature of 150 °C to obtain an organic flux.

[0052] (3) The composite tin powder in step (1) is mixed with the organic flux in step (2), and placed in a vacuum mixer for staged stirring. In the first stage, low-speed premixing is carried out at 15 rpm for 8 min, and in the second stage, stirring is carried out at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0053] Example 6

[0054] A preparation method of a composite solder paste, comprising the following steps:

[0055] (1) After pretreatment of the raw materials, 290 g of tin-lead alloy powder and 60 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0056] (2) 24.5 g of rosin, 20.5 g of ethylene glycol monohexyl ether, 2 g of oxalic acid and 3 g of hydrogenated castor oil are weighed and mixed evenly, and heated at a temperature of 140 °C to obtain an organic flux.

[0057] (3) The composite tin powder in step (1) is mixed with the organic flux in step (2), and placed in a vacuum mixer for staged stirring. In the first stage, low-speed premixing is carried out at 15 rpm for 8 min, and in the second stage, stirring is carried out at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0058] Example 7

[0059] A preparation method of a composite solder paste, comprising the following steps:

[0060] (1) After pretreatment of the raw materials, 280 g of tin-lead alloy powder and 40 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0061] (2) 38.4 g of rosin, 32 g of ethylene glycol monohexyl ether, 2.4 g of oxalic acid and 7.2 g of hydrogenated castor oil are weighed and mixed evenly, and heated at a temperature of 150 °C to obtain an organic flux.

[0062] (3) The composite tin powder in step (1) is mixed with the organic flux in step (2), and placed in a vacuum mixer for staged stirring. In the first stage, low-speed premixing is carried out at 15 rpm for 8 min, and in the second stage, stirring is carried out at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0063] Example 8

[0064] A preparation method of a composite solder paste, comprising the following steps:

[0065] (1) After pretreatment of the raw materials, 280 g of tin-lead alloy powder and 50 g of copper powder are weighed and mixed evenly to obtain composite tin powder.

[0066] (2) 35 g of rosin, 29.4 g of ethylene glycol monohexyl ether, 3.5 g of oxalic acid and 2.1 g of hydrogenated castor oil are weighed and mixed evenly, and heated at a temperature of 130 °C to obtain an organic flux.

[0067] (3) Mix the composite tin powder from step (1) with the organic flux from step (2), place it in a vacuum mixer for staged stirring. In the first stage, pre-mix at a low speed of 15 rpm for 8 minutes, and in the second stage, stir at 35 rpm for 25 minutes to obtain a uniform composite solder paste.

[0068] Example 9

[0069] A method for preparing a composite solder paste, comprising the following steps:

[0070] (1) After the raw materials are pretreated, weigh 280 g of tin-lead alloy powder and 60 g of copper powder, mix them evenly to obtain composite tin powder.

[0071] (2) Weigh 29.4 g of rosin, 24.6 g of ethylene glycol monohexyl ether, 2.4 g of oxalic acid and 3.6 g of hydrogenated castor oil, mix them evenly and heat at a temperature of 135 °C to obtain an organic flux.

[0072] (3) Mix the composite tin powder from step (1) with the organic flux from step (2), place it in a vacuum mixer for staged stirring. In the first stage, pre-mix at a low speed of 15 rpm for 8 minutes, and in the second stage, stir at 35 rpm for 25 minutes to obtain a uniform composite solder paste.

[0073] Example 10

[0074] A method for preparing a composite solder paste, comprising the following steps:

[0075] (1) After the raw materials are pretreated, weigh 260 g of tin-lead alloy powder and 40 g of copper powder, mix them evenly to obtain composite tin powder.

[0076] (2) Weigh 48 g of rosin, 40 g of ethylene glycol monohexyl ether, 3 g of oxalic acid and 9 g of hydrogenated castor oil, mix them evenly and heat at a temperature of 140 °C to obtain an organic flux.

[0077] (3) Mix the composite tin powder from step (1) with the organic flux from step (2), place it in a vacuum mixer for staged stirring. In the first stage, pre-mix at a low speed of 15 rpm for 8 minutes, and in the second stage, stir at 35 rpm for 25 minutes to obtain a uniform composite solder paste.

[0078] Example 11

[0079] A method for preparing a composite solder paste, comprising the following steps:

[0080] (1) After the raw materials are pretreated, weigh 260 g of tin-lead alloy powder and 50 g of copper powder, mix them evenly to obtain composite tin powder.

[0081] (2) Weigh 45 g of rosin, 37.8 g of ethylene glycol monohexyl ether, 4.5 g of oxalic acid and 2.7 g of hydrogenated castor oil, mix them evenly and heat at 145 °C to obtain an organic soldering flux.

[0082] (3) Mix the composite tin powder from step (1) with the organic soldering flux from step (2), place it in a vacuum mixer and stir in stages. In the first stage, premix at a low speed of 15 rpm for 8 min, and in the second stage, stir at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0083] Example 12

[0084] A method for preparing a composite solder paste, comprising the following steps:

[0085] (1) After pretreatment of the raw materials, weigh 260 g of tin-lead alloy powder and 60 g of copper powder, mix them evenly to obtain composite tin powder.

[0086] (2) Weigh 39.2 g of rosin, 32.8 g of ethylene glycol monohexyl ether, 3.2 g of oxalic acid and 4.8 g of hydrogenated castor oil, mix them evenly and heat at 150 °C to obtain an organic soldering flux.

[0087] (3) Mix the composite tin powder from step (1) with the organic soldering flux from step (2), place it in a vacuum mixer and stir in stages. In the first stage, premix at a low speed of 15 rpm for 8 min, and in the second stage, stir at 35 rpm for 25 min to obtain a uniform composite solder paste.

[0088] In the above examples, Example 10 is the best example.

[0089] Comparative Example 1

[0090] A method for preparing a composite solder paste, comprising the following steps:

[0091] (1) After pretreatment of the raw materials, weigh 260 g of tin-lead alloy powder. Different from Example 10, no copper powder is mixed in.

[0092] (2) Weigh 67.2 g of rosin, 56 g of ethylene glycol monohexyl ether, 4.2 g of oxalic acid and 12.6 g of hydrogenated castor oil, mix them evenly to obtain an organic soldering flux.

[0093] (3) The remaining preparation method is the same as that of Example 10.

[0094] Comparative Example 2

[0095] A method for preparing a composite solder paste, comprising the following steps:

[0096] (1) After pretreatment of the raw materials, different from Example 10, weigh 240 g of tin-lead alloy powder and 80 g of copper powder, mix them evenly to obtain composite tin powder.

[0097] (2) Weigh 38.4 g of rosin, 32 g of ethylene glycol hexyl ether, 2.4 g of oxalic acid and 7.2 g of hydrogenated castor oil, and mix them evenly to obtain an organic soldering flux.

[0098] (3) The remaining preparation methods are the same as those in Example 10.

[0099] Comparative Example 3

[0100] A preparation method of a composite solder paste, comprising the following steps:

[0101] (1) After the raw materials are pretreated, different from Example 10, weigh 320 g of tin-lead alloy powder and 20 g of copper powder, and mix them evenly to obtain composite solder powder.

[0102] (2) Weigh 28.8 g of rosin, 24 g of ethylene glycol hexyl ether, 1.8 g of oxalic acid and 5.4 g of hydrogenated castor oil, and mix them evenly to obtain an organic soldering flux.

[0103] (3) The remaining preparation methods are the same as those in Example 10.

[0104] Performance test

[0105] Use a Malcom viscometer (PCU-205) to measure the viscosity of the composite solder pastes prepared in Examples 1 to 12 and Comparative Examples 1 to 3, and the viscosities are shown in Table 1 below.

[0106] Table 1 Performance test results of the composite solder paste

[0107]

[0108]

[0109] Apply the composite solder pastes prepared in Examples 1 to 12 and Comparative Examples 1 to 3 to pneumatic spraying controlled by air pressure and conduct a shear test on the strength of the solder joints; Figure 2 It is the microscopic structure diagram of the solder joints formed by welding; the reliability of the solder joints is verified by thermal cycling shock. After the reflow soldered samples are placed in a high and low temperature cycling shock test chamber, the set test conditions are -55 to 125 °C, the residence time is 30 min, and the cycle is 1000 times. As Figure 3 shown, it can be found that the Cu particles are evenly distributed inside the solder joints and strengthen the performance of the solder joints in the form of the second phase. In Comparative Example 1, the absence of Cu particles cannot achieve the effect of particle strengthening. In Comparative Example 2, due to the excessive content of Cu particles, segregation will occur during melting, so they cannot be dispersed in the solder joints to play a strengthening role. As Figure 4As shown, the composite solder welding method adopts the reflow soldering process, where the reflow peak temperature is 200 - 220 °C and the peak time is 60 - 90 s. After the reflow soldering is completed, the solder joints are horizontally sheared by a push-pull tester to measure the strength, and the solder joint strength is shown in Table 1 below. Combining the performance test results of the composite solder paste in Table 1 with Figure 5 the spray printing effect diagram, the composite solder paste of the present invention is applied to pneumatic spray printing controlled by air pressure, which can achieve precise filling of micro-holes and avoid stencil clogging. For multi-variety and small-batch production, the spray printing position can be quickly switched through digital control, reducing the stencil cost.

Claims

1. A composite solder paste, characterized in that, It includes the following components by weight percentage: 65% - 75% of tin-lead alloy powder, 10% - 15% of copper powder, and the balance is organic solder flux; the weight percentage of lead in the tin-lead alloy powder is 37%, and the weight percentage of tin is 63%.

2. The composite solder paste according to claim 1, wherein: The particle size of the tin-lead alloy powder is 15 - 25 μm, and the particle size of the copper powder is 5 - 10 μm.

3. The composite solder paste according to claim 1, characterized in that: The organic solder flux includes the following components by weight percentage: 48% - 50% of rosin, 40% - 42% of ethylene glycol monohexyl ether, 3% - 5% of oxalic acid, and the balance is hydrogenated castor oil.

4. The composite solder paste according to claim 1, wherein: The tin-lead alloy powder is 65% - 70%, the copper powder is 10% - 15%, and the balance is organic solder flux; the particle size of the tin-lead alloy powder is 15 - 20 μm, and the particle size of the copper powder is 5 - 10 μm.

5. A method for preparing the composite solder paste according to claim 1, characterized in that, It includes the following steps: (1) Pretreat the raw materials, weigh the tin-lead alloy powder and copper powder and mix them evenly to obtain composite tin powder; (2) Prepare the organic solder flux; (3) Mix and stir the composite tin powder in step (1) with the organic solder flux in step (2) evenly to obtain composite solder paste.

6. The preparation method of the composite solder paste according to claim 6, wherein: The heating temperature of the organic solder flux in step (2) is 130°C - 150°C.

7. The preparation method of the composite solder paste according to claim 6, wherein: The stirring in step (3) is carried out in stages; in the first stage, low-speed premixing is carried out at 10 - 15 rpm for 5 - 8 min, and in the second stage, stirring is carried out at 30 - 35 rpm for 20 - 25 min; the whole stirring process is kept under vacuum.

8. Application of the composite solder paste according to claim 1 in non-contact spraying.

9. The application of the composite solder paste according to claim 8 in non-contact spraying, characterized in that: During the non-contact spraying process of the composite solder paste, it has a reflow at 200°C - 220°C.

10. The application of the composite solder paste according to claim 8 in non-contact spraying, characterized in that: After the solder joints formed by the non-contact spraying reflow undergo 1000 times of -55°C - 125°C thermal cycling, the shear strength retention rate is greater than 90%.

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